chapter{one}
nano technology (sometimes shortened to "nanotech") is the study of manipulating matter on an atomic and molecular scale. Generally, nanotechnology deals with structures sized between 1 to 100 nanometer in at least one dimension, and involves developing materials or devices within that size. Quantum mechanical effects are very important at this scale, which is in the quantum realm.
Nanotechnology is very diverse, ranging from extensions of conventional device physics to completely new approaches based upon molecular self-assembly, from developing new materials with dimensions on the nanoscale to investigating whether we can directly control matter on the atomic scale.
There is much debate on the future implications of nanotechnology. Nanotechnology may be able to create many new materials and devices with a vast range of applications, such as in medicine, electronics, biomaterials and energy production. On the other hand, nanotechnology raises many of the same issues as any new technology, including concerns about the toxicity and environmental impact of nanomaterials(1) and their potential effects on global economics, as well as speculation about various doomsday scenarios. These concerns have led to a debate among advocacy groups and governments on whether special regulation of nanotechnology is warranted.
Buckminsterfullerene C60, also known as the buckyball, is a representative member of the carbon structures known as fullerenes. Members of the fullerene family are a major subject of research falling under the nanotechnology umbrella.
The first use of the concepts found in 'nano-technology' (but pre-dating use of that name) was in "There's Plenty of Room at the Bottom", a talk given by physicist Richard Feynman at an American Physical Society meeting at California Institute of Technology (Caltech) on December 29, 1959. Feynman described a process by which the ability to manipulate individual atoms and molecules might be developed, using one set of precise tools to build and operate another proportionally smaller set, and so on down to the needed scale. In the course of this, he noted, scaling issues would arise from the changing magnitude of various physical phenomena: gravity would become less important, surface tension and van der Waals attraction would become increasingly more significant, etc. This basic idea appeared plausible, and exponential assembly enhances it with parallelism to produce a useful quantity of end products. The term "nanotechnology" was defined by Tokyo Science University Professor Norio Taniguchi in a 1974 paper (2)as follows: "'Nano-technology' mainly consists of the processing of, separation, consolidation, and deformation of materials by one atom or by one molecule." In the 1980s the basic idea of this definition was explored in much more depth by Dr. K. Eric Drexler, who promoted the technological significance of nano-scale phenomena and devices through speeches and the books Engines of Creation: The Coming Era of Nanotechnology (1986) and Nanosystems: Molecular Machinery, Manufacturing, and Computation, (3) and so the term acquired its current sense. Engines of Creation is considered the first book on the topic of nanotechnology. Nanotechnology and nanoscience got started in the early 1980s with two major developments; the birth of cluster science and the invention of the scanning tunneling microscope (STM). This development led to the discovery of fullerenes in 1985 and carbon nanotubes a few years later. In another development, the synthesis and properties of semiconductor nanocrystals was studied; this led to a fast increasing number of metal and metal oxide nanoparticles and quantum dots.. In 2000, the United States National Nanotechnology Initiative was founded to coordinate Federal nanotechnology research and development and is evaluated by the President's Council of Advisors on Science and Technology.
Fundamental concepts
One nanometer (nm) is one billionth, or 10−9, of a meter. By comparison, typical carbon-carbon bond lengths, or the spacing between these atoms in a molecule, are in the range 0.12–0.15 nm, and a DNA double-helix has a diameter around 2 nm. On the other hand, the smallest cellular life-forms, the bacteria of the genus Mycoplasma, are around 200 nm in length.
To put that scale in another context, the comparative size of a nanometer to a meter is the same as that of a marble to the size of the earth. Or another way of putting it: a nanometer is the amount an average man's beard grows in the time it takes him to raise the razor to his face. (4)
Two main approaches are used in nanotechnology. In the "bottom-up" approach, materials and devices are built from molecular components which assemble themselves chemically by principles of molecular recognition. In the "top-down" approach, nano-objects are constructed from larger entities without atomic-level control. (5)
Areas of physics such as nanoelectronics, nanomechanics, nanophotonics and nanoionics have evolved during the last few decades to provide a basic scientific foundation of nanotechnology.
Larger to smaller: a materials perspective
Image of reconstruction on a clean Gold(100) surface, as visualized using scanning tunneling microscopy. The positions of the individual atoms composing the surface are visible.
A number of physical phenomena become pronounced as the size of the system decreases. These include statistical mechanical effects, as well as quantum mechanical effects, for example the “quantum size effect” where the electronic properties of solids are altered with great reductions in particle size. This effect does not come into play by going from macro to micro dimensions. However, quantum effects become dominant when the nanometer size range is reached, typically at distances of 100 nanometers or less, the so called quantum realm. Additionally, a number of physical (mechanical, electrical, optical, etc.) properties change when compared to macroscopic systems. One example is the increase in surface area to volume ratio altering mechanical, thermal and catalytic properties of materials. Diffusion and reactions at nanoscale, nanostructures materials and nanodevices with fast ion transport are generally referred to nanoionics. Mechanical properties of nanosystems are of interest in the nanomechanics research. The catalytic activity of nanomaterials also opens potential risks in their interaction with biomaterials. (6)
Materials reduced to the nanoscale can show different properties compared to what they exhibit on a macroscale, enabling unique applications. For instance, opaque substances become transparent (copper); stable materials turn combustible (aluminum); insoluble materials become soluble (gold). A material such as gold, which is chemically inert at normal scales, can serve as a potent chemical catalyst at nanoscales. Much of the fascination with nanotechnology stems from these quantum and surface phenomena that matter exhibits at the nanoscale. (7)
Simple to complex: a molecular perspective
Modern synthetic chemistry has reached the point where it is possible to prepare small molecules to almost any structure. These methods are used today to manufacture a wide variety of useful chemicals such as pharmaceuticals or commercial polymers. This ability raises the question of extending this kind of control to the next-larger level, seeking methods to assemble these single molecules into supramolecular assemblies consisting of many molecules arranged in a well defined manner.
These approaches utilize the concepts of molecular self-assembly and/or supramolecular chemistry to automatically arrange themselves into some useful conformation through a bottom-up approach. The concept of molecular recognition is especially important: molecules can be designed so that a specific configuration or arrangement is favored due to non-covalent intermolecular forces. The Watson–Crick basepairing rules are a direct result of this, as is the specificity of an enzyme being targeted to a single substrate, or the specific folding of the protein itself. Thus, two or more components can be designed to be complementary and mutually attractive so that they make a more complex and useful whole.
Such bottom-up approaches should be capable of producing devices in parallel and be much cheaper than top-down methods, but could potentially be overwhelmed as the size and complexity of the desired assembly increases. Most useful structures require complex and thermodynamically unlikely arrangements of atoms. Nevertheless, there are many examples of self-assembly based on molecular recognition in biology, most notably Watson–Crick basepairing and enzyme-substrate interactions. The challenge for nanotechnology is whether these principles can be used to engineer new constructs in addition to natural ones.
Molecular nanotechnology: a long-term view
Molecular nanotechnology, sometimes called molecular manufacturing, describes engineered nanosystems (nanoscale machines) operating on the molecular scale. Molecular nanotechnology is especially associated with the molecular assembler, a machine that can produce a desired structure or device atom-by-atom using the principles of mechanosynthesis. Manufacturing in the context of productive nanosystems is not related to, and should be clearly distinguished from, the conventional technologies used to manufacture nanomaterials such as carbon nanotubes and nanoparticles.
When the term "nanotechnology" was independently coined and popularized by Eric Drexler (who at the time was unaware of an earlier usage by Norio Taniguchi) it referred to a future manufacturing technology based on molecular machine systems. The premise was that molecular scale biological analogies of traditional machine components demonstrated molecular machines were possible: by the countless examples found in biology, it is known that sophisticated, stochastically optimised biological machines can be produced.
It is hoped that developments in nanotechnology will make possible their construction by some other means, perhaps using biomimetic principles. However, Drexler and other researchers (8) have proposed that advanced nanotechnology, although perhaps initially implemented by biomimetic means, ultimately could be based on mechanical engineering principles, namely, a manufacturing technology based on the mechanical functionality of these components (such as gears, bearings, motors, and structural members) that would enable programmable, positional assembly to atomic specification. (9) The physics and engineering performance of exemplar designs were analyzed in Drexler's book Nanosystems.
In general it is very difficult to assemble devices on the atomic scale, as all one has to position atoms on other atoms of comparable size and stickiness. Another view, put forth by Carlo Montemagno, (10) is that future nanosystems will be hybrids of silicon technology and biological molecular machines. Yet another view, put forward by the late Richard Smalley, is that mechanosynthesis is impossible due to the difficulties in mechanically manipulating individual molecules.
This led to an exchange of letters in the ACS publication Chemical & Engineering News in 2003. (11) Though biology clearly demonstrates that molecular machine systems are possible, non-biological molecular machines are today only in their infancy. Leaders in research on non-biological molecular machines are Dr. Alex Zettl and his colleagues at Lawrence Berkeley Laboratories and UC Berkeley. They have constructed at least three distinct molecular devices whose motion is controlled from the desktop with changing voltage: a nanotube nanomotor, a molecular actuator, (12) and a nanoelectromechanical relaxation oscillator. (13)
An experiment indicating that positional molecular assembly is possible was performed by Ho and Lee at Cornell University in 1999. They used a scanning tunneling microscope to move an individual carbon monoxide molecule (CO) to an individual iron atom (Fe) sitting on a flat silver crystal, and chemically bound the CO to the Fe by applying a voltage.
Current research
This device transfers energy from nano-thin layers of quantum wells to nanocrystals above them, causing the nanocrystals to emit visible light. (14)
Nanomaterials
The nanomaterials field includes subfields which develop or study materials having unique properties arising from their nanoscale dimensions. (15)
- Interface and colloid science has given rise to many materials which may be useful in nanotechnology, such as carbon nanotubes and other fullerenes, and various nanoparticles and nanorods. Nanomaterials with fast ion transport are related also to nanoionics and nanoelectronics.
- Nanoscale materials can also be used for bulk applications; most present commercial applications of nanotechnology are of this flavor.
- Progress has been made in using these materials for medical applications; see Nanomedicine.
- Nanoscale materials are sometimes used in solar cells which combats the cost of traditional Silicon solar cells
- Development of applications incorporating semiconductor nanoparticles to be used in the next generation of products, such as display technology, lighting, solar cells and biological imaging; see quantum dots.
Bottom-up approaches
These seek to arrange smaller components into more complex assemblies.
- DNA nanotechnology utilizes the specificity of Watson–Crick basepairing to construct well-defined structures out of DNA and other nucleic acids.
- Approaches from the field of "classical" chemical synthesis also aim at designing molecules with well-defined shape (e.g. bis-peptides (16)).
- More generally, molecular self-assembly seeks to use concepts of supramolecular chemistry, and molecular recognition in particular, to cause single-molecule components to automatically arrange themselves into some useful conformation.
- Atomic force microscope tips can be used as a nanoscale "write head" to deposit a chemical upon a surface in a desired pattern in a process called dip pen nanolithography. This technique fits into the larger subfield of nanolithography.
Top-down approaches
These seek to create smaller devices by using larger ones to direct their assembly.
- Many technologies that descended from conventional solid-state silicon methods for fabricating microprocessors are now capable of creating features smaller than 100 nm, falling under the definition of nanotechnology. Giant magnetoresistance-based hard drives already on the market fit this description, (17) as do atomic layer deposition (ALD) techniques. Peter Grünberg and Albert Fert received the Nobel Prize in Physics in 2007 for their discovery of Giant magnetoresistance and contributions to the field of spintronics. (18)
- Solid-state techniques can also be used to create devices known as nanoelectromechanical systems or NEMS, which are related to microelectromechanical systems or MEMS.
- Focused ion beams can directly remove material, or even deposit material when suitable pre-cursor gasses are applied at the same time. For example, this technique is used routinely to create sub-100 nm sections of material for analysis in Transmission electron microscopy.
- Atomic force microscope tips can be used as a nanoscale "write head" to deposit a resist, which is then followed by a etching process to remove material in a top-down method.
Functional approaches
These seek to develop components of a desired functionality without regard to how they might be assembled.
- Molecular electronics seeks to develop molecules with useful electronic properties. These could then be used as single-molecule components in a nanoelectronic device. (19) For an example see rotaxane.
- Synthetic chemical methods can also be used to create synthetic molecular motors, such as in a so-called nanocar.
Biomimetic approaches
- Bionics or biomimicry seeks to apply biological methods and systems found in nature, to the study and design of engineering systems and modern technology. Biomineralization is one example of the systems studied.
Bionanotechnology the use of biomolecules for applications in nanotechnology, including use of viruses.
nano_chemistry
nano_chemistry
1. Chemistry as nanochemistry
Is chemistry all along in the business of nanotechnology? Some might argue that it is, but on a
practical level, it is not—not until about 20 years ago. For sure, it is contributing a lot to this new wave
of technology.
In retrospect, chemistry is sometimes referred to as the central science, because one cannot escape
the fact that to study nature one has to deal with the basic building blocks of matter, the atoms and
molecules. In this author's opinion, the best definition for chemistry nowadays would be the answer to
the question “what do chemists do?” Since the beginning, chemists (or alchemists) had been attempting
to transform matter, but these attempts could not have progressed without a proper theory or model, at
least in part, to help in the design of the method of transformation. The Greek Philosophers Leucippus
and Democritus had proposed (450 B. C.) the idea that matter must be made of smaller building blocks,
'the atomos', a proposition which could have just been a rational extrapolation of the observation that the
beach looks solid when viewed from afar, but is in fact granular on closer inspection. The atomic theory
was developed by Dalton in his opus A New System of Chemical Philosophy (1808)(20) which explained
very well those different transformations observed then for some of the known substances. Chemists,
since then, have been involved in 'playing' with these atoms and molecules, transfiguring matter by
combining atoms into various possibilities of atomic bonding combinations, permutations, configurations,
and molecular arrangements. Nearly every general textbook in chemistry begins with the atomic concept
—that all matter is made up of atoms. Learning more and more about the atoms and how to deal or 'play'
with them is generally what chemists do.
Chemistry succeeded as a science because it was able to develop techniques for 'handling' atoms
and molecules. The typical size of the atom? Order of magnitude, it is about 1 Angstrom (Å) in
diameter or 0.0000001 of a millimeter. Clearly, too small to touch or handle individually. But how did
chemists manage to do it? Well, the 'handling' is really a logical manipulation of the atomic model. By
knowing the reactivities of the elements and compounds, chemists had a way of peering into the
properties of the individual atoms or the molecules that they are made of. Chemistry owes a lot to
thermodynamics (1800s) for providing a framework for accounting of all the energetics involved—and
so, even before quantum theory, knowing relative bond strengths between carbon atoms and a bit of
imagination such as Kekulé's dream, an accurate molecular model for the benzene was conjured (1872).
It also owes a lot to quantum theory (early 1900s) for improving the model for the atom, which explained
in further detail the observed chemical and physical properties of matter in terms of the electronic
structure of the atom. Thus now, we have a clearer understanding of the chemical reactivities of atoms or
molecules, are able to predict the molecular shape and electronic properties, or predict how they will
interact with light, electricity, magnetism or with other atoms, assess their stabilities and reactivities, and
all of these with fairly good accuracy. These molecular properties are, in turn, related to the observed
property of bulk matter. Bulk matter here is made of at least 10 16 atoms or molecules in an assemblage
that has a size that can be manipulated and handled in glass vessels or crucibles typically found in a
chemical laboratory; a typical lab specimen size being of micro- or milligrams, grams or even kilograms
in quantity, which is readily weighed using a laboratory balance.
It is also no wonder why chemists often engage in discussions of structure-property relationships
or in other words, in explaining an observed behavior of bulk matter in terms of the properties of the
molecules that it is made of. For instance: this author overheard an auto-mechanic trying to explain why
battery acid spills on polyester pants do not readily burn into holes—so he explained: “it is because the
acid did not easily absorb into the polyester fabric, unlike in cotton.” A fine observation and a good
So what makes chemistry nanochemistry? Whereas before, bulk behavior was routinely
measured, nowadays, the observation data on properties of matter are not only limited to bulk behavior
but also include those of matter made up of only a cluster of atoms—in the hundreds, thousands, or just a
few million atoms bonded together in assembled structures whose final dimensions are only in the tens or
hundreds of Angstroms. In other words, in the nanometer size regime. These structures—which we may
refer to as nanostructures—are not like the molecules of old, but are materials yielding behavior unlike
their bulk counterparts. And as more of them are cropping up these days, new phenomena are being
observed, and in turn, there is more impetus to create new ones and innovate methodologies for making
them into various morphologies or modes of molecular organization. The motivation is both fundamental
and practical. Fundamental: to discover and understand new phenomena exhibited by matter at these
newly accessible dimensions, and practical: to form them into useful somethings: as novel electronic
devices, as efficient drug delivery systems, as ultrasensitive sensors, as ultra-lightweight structural
materials, as highly efficient alternative energy sources, as environmentally benign materials, or as new
materials for an entirely new application.
2. The Tipping Point for Nanotechnology
Many years before, there had been nanostructures formed, such as Faraday's gold colloids
prepared in 1857, which remained stable for over a century until it was destroyed during World War II (21,22) .
There was also the ultrathin films formed by Langmuir (1920) in his water trough, with thicknesses that
span only one molecular length (~30 Å) or several layers of them (~100 Å).(23) In 1959, the Physics Nobel
Laureate Richard Feynman made bold predictions for nanotechnology in his talk “There's Plenty of Room
at the Bottom.”(24) He even offered a US$1,000 reward for the first one to fabricate an operating electric
motor not exceeding 1/64 th inch cube in volume (not counting the lead-in wires)—which was promptly
answered by a young engineer in the following year.(25) Therefore, many of the tools or incentives for
nanotechnology are not really new, but the immediate spread and rapidity of its development in the past
20 years must have been brought about by a 'tipping point,' (borrowing Gladwell's idea that a confluence
of events must produce a tipping point that allows for fashion, fads, or trends to spread). (26)Nanotechnology
probably hit its tipping point just before 1990: due to breakthroughs such as the invention of the scanning
probe microscope, the successful synthesis and isolation of the fullerenes and carbon nanotubes, and at
the same time, the rapid progress in the personal computing industry and its drive towards further
miniaturization of the microchip (now it's a nanochip). The semiconductor industry is fervently
conforming with Moore's Law—which states that the size of the computer chip decreases by half every
one-and-a-half years. (27)
The scanning tunneling microscope and atomic force microscope, (28,29)which are also generically
referred to as scanning probe microscopies (SPM), are relatively new imaging tools then that allowed
visualization of solid surfaces at atomic-level or Angstrom resolutions. Similar resolutions were already
possible by high resolution electron microscopy even long before, but the SPM provided chemists and
other researchers with a more readily accessible instrumentation for viewing surfaces and ultrathin
molecular films. The instrument is relatively easy to operate and the interpretation of its images is almost
straightforward—the image produced is what you have (well, there were some problems with
interpretation of some artifacts produced, but this was resolved early on, and researchers now knew
better). SPM works much like how a phonograph works, by 'feeling' the atomic or molecular bumps on a
solid surface by moving a probe tip (a metal or inorganic wire) in a raster pattern on a flat solid surface.
The moving probe's minute deflections are then translated into a 3-D, topographic image of the surface.
Key to the SPM's invention were the ability to move the probe in tiny nanometer steps by attaching it to a
piezoelectric crystal whose X-Y-Z expansion, upon application of a voltage, is readily calculable; and
also the stabilization of the base on which the sample is placed, which eliminates possible blurring of the
image due to ground or surrounding vibrations. An analogy can also be made with a blind person reading
a Braille book—by scanning by touch the bumps on the pages of the book.
SPM provided a rapid and new way of 'looking' at properties exhibited by materials with
dimensions that are in the nanometer range. It provided a tool with which scientists could probe
properties observable or manifested in nanometer dimensions. When IBM spelled its company name by
picking up and laying down single atoms of Xe on a surface using an SPM probe tip—it demonstrated to
the world that indeed, there is a tool that can literally handle individual atoms!(30) What makes this tool
especially more powerful, aside from using it to image or to pick-up and deposit atoms from one location
to another, is that it can change its mode of action by changing the probe tip or the type of forces that it
measures. For example, one can measure the stretching of a single strand of a polysaccharide molecule
tethered between the probe tip and a surface, in a new technique called single-molecule force
spectroscopy;(31) or measure thermal, magnetic, or frictional forces on a surface; or replace the tip with an
optic fiber to allow optical imaging at very close spaces eliminating diffraction effects, in a technique
called near-field scanning optical microscopy (NSOM).(32) Each technique is an avenue for investigating
phenomena at the nanometer scale that was not available before.
The fullerenes and carbon nanotubes are a class in itself—these are new allotropes of carbon and
they present many interesting properties and possibilities for nanotechnology. Whereas Kekulé dreamt of
the ring structure of the benzene molecule, Richard Smalley (1996 co-winner of the Nobel Prize in
Chemistry) pasted pieces of paper cut outs, hexagons and pentagons, to form the buckyball shape of a C 60
molecule. Who would have taught that by burning carbon rods (or graphite) in an arc discharge in a glass
chamber with argon gas, one would form a black soot composed of these interestingly shaped molecules?
In 1991, Iijima reported that in the same soot, one would find rolled up sheets of carbon that are now
called carbon nanotubes (CNTs)—there were earlier reports of the discovery of these carbon fibrils, as
early as 1952 which went largely unnoticed. The CNTs are like molecular fibrils of about 1 nm diameter,
with tensile strength that is 60 times that of steel, the electronic property can vary from semiconducting to
conducting just like a metal, and its periphery amenable to functionalization with molecular moieties. 4
Thus, there is also an explosive growth in research on these forms of carbon, because of the exciting
properties and its potential applications in electronics, structural materials, and many others.
Around the same period of time, the silicon industry is keeping up with Moore's Law, which in
turn produced cheaper and faster computing hardware. The newest computer silicon chip processors
today are built using less than 100-nm manufacturing technology. Some say that as this pace continues,
the device on the silicon chip will hit its physical size limit soon enough (~2016). Therefore, there is also
increasing trend in finding alternative electronic device structures, designs and materials, and perhaps a
new paradigm for computing that is based on quantum theory.(33) These future nano-scaled electronics
could be composed of molecules or clusters of atoms that are able to function just like its silicon-based
counterparts or that may work using new quantum computing algorithms.
In summary, the drive towards electronic device miniaturization, the invention of a new tool for
studying nanostructures, and the discovery of a new class of carbon materials provided a tipping point for
the hype and frenzy, widespread research interest, and worldwide investment in nanotechnology today.
In the U. S. alone, a total of about US$ 4 billion investment comes from government, small business and
industry to support efforts towards nanotechnology. (34)
3. Approaches to Nanochemistry
And so, what do nanochemists do? The answer would depend on whether the goal is
fundamental or practical. We can start with the fundamental, such as the question of fabrication or
synthesis, and discuss possible applications. Or alternatively, we can target the application, and concern
ourselves with how to do it, nano-wise. Generally, the former is the approach to science, because the
more that we understand the system (first), and then it is easier for us to predict where and what they may
be good for. We shall use this approach in our discussion.
If one is to study properties of nanostructured systems, then one must find ways to synthesize or
fabricate them. The problem can be posed this way: if given 1 million atoms, each with a radius of about
1 Å, what type of nanomaterial can be made out of these and how would one do it? (A million sounds a
lot, but actually, this is too small to weigh in a laboratory balance—but there are ways to prepare this
number, of course. Anyway, we can just think hypothetically to illustrate some of the approaches to
nanochemistry or nanotechnology.) The type of nanomaterial that can be formed will depend on its
dimensionality.
Ultrathin films (Two-Dimensional Nanostructures)
We can try to spread the atoms on a flat surface to form a single layer, and thus we would have
constructed an ultrathin film (or coating, if you will) which is only 1 Å thick and can cover roughly a
square area of 1000 Å 2 or 1 µm 2 when compacted. The covered area is not nanometer-sized, but the film
thickness is sub-nanometer, and thus, this film is within the realm of nanotechnology. This may be done
in the lab by vaporizing the 10 6 atoms and allow them to adhere onto a solid substrate. In the lab, this
technique is called atomic layer deposition.(35) It is important to note, however, that to form a single layer
of atoms on a flat substrate is not trivial, because it may not be stable. Atoms at a surface or interface
experience an imbalance of forces. Below and beside them, they have other atoms that pull them inward
due to bonding interactions, and above them it is just air or vacuum. Nature abhors this imbalance—it is
unstable, and thus, ordinarily, the surface atoms would seek ways to minimize this imbalance, to lower
the surface energy. Clustering is one way to minimize surface energy. In fact, the growth of our film
formed by vapor deposition would most likely start with clustering of atoms (nucleation) and this growing
cluster may begin to coalesce with the other clusters to eventually form a continuous film. In this case,
our film may not be mono-atomic in thickness but would turn out to be several atomic layers thick.
Nonetheless, it may still be nanometer-thin and so we have a nanostructured system. The preparation of
ultrathin films poses experimental and theoretical challenges, and thus many scientists are busying
themselves with these concerns.
Another way would be for us to disperse the atoms into a solvent to form a solution, and from
there, allow the atoms to spontaneously organize onto a solid substrate. Obviously, gravity would not do
it—because they are too small to be settling down; there are other forces in solution that will keep them
dissolved. The formation of our thin film will happen if there is a strong preferential attraction of our
atoms to the substrate. What we hope to do here is to spontaneously crystallize our atoms onto a surface
or interface: a self-assembling technique. Self-assembly is a generic term for forming nanostructures
from a disordered state. This is a major technique, actually, that is widely used because it offers a
generally straightforward manner of building nanostructures, and is amenable to mass production of the
nano-material for commercial purposes. This is a bottom-up approach to nano-synthesis, because the
structure is built in a manner that is one atom-at-a-time. If self-assembly were not possible, a bottom-up
approach is not going to be efficient, if one is to build atom-by-atom mechanically. This methodology is
opposed to the top-down approach, wherein one first makes a bulk material, and then its size is decreased
by mechanical or some other means until the material is divided or fabricated into the nanometer size
range.
One example of self-assembly is Langmuir's technique—here, one spreads a very dilute solution
of amphiphilic molecules (e.g., surfactants) on a water surface. The amphiphilic molecules will not quite
dissolve into the water, and once its solvent evaporated, they are left floating at the water-air interface.
The molecules at the surface may be compressed to occupy a smaller area using a non-sticky barrier such
as a Teflon TM sheet. Compression will form a two-dimensional condensed, monomolecular layer at the
water-air interface. The use of the dilute solution allows one to limit and calculate the number of
dissolved molecules that will be covering a given area of the water interface. The stability and integrity of
the film depends also on the interaction between molecules. The formed films at the interface may
subsequently be transferred onto a solid substrate by dipping the latter through the film/interface. These
are called Langmuir-Boldgett films, (36,37)and one can make single- or muti-molecular layers on glass and
others substrates. This procedure was developed way back in the 1920s and is still being used today
using other types of molecules to prepare various films of different properties. At least nowadays, the
film structure and morphology can be routinely imaged by SPM and other advanced characterization
tools.
Another similar-type film is the so-called self-assembled monolayer (SAM), which is formed by
allowing molecules with a dangling sulfur atom at one end (these molecules are called thiols) to stick onto
a flat gold surface. This procedure is much easier than Langmuir-Blodgett's technique. The formed film
is stable because of the chemical bond between the sulfur and gold, and the attraction between the alkyl
chains of the thiol molecules allows the formation of a pseudo-two-dimensional crystal at the gold
surface. One of the very first papers published by Whitesides et al. of Harvard University on SAMs is
one of the most cited research papers in Chemistry today. (38,39)Because of the ability of chemists to modify
molecular structures, various SAMs have been formed with all sorts of molecular groups attached onto
gold.(40) It also paved way for such new techniques for creating patterned nanostructures (called soft-
lithography), wherein nanosized SAMs features are 'imprinted' on a gold surface by micro-stamping a
solution of thiols on gold.(41) A recent review of the uses of SAMs for nanofabrication is given in reference
22. SAMs were also used as 'ink' for writing on gold in what is called dip-pen nanolithography (DPN)—
here the probe of the SPM is wet with thiols and the SPM probe is programmed to 'write' patterns across
the gold surface, depositing a layer of SAMs on the gold as it moves. The DPN technique proved useful
for other molecules as well.(42) This approach promises to be a way to build nanostructures on a surface,
and by using a multi-probe writing device (e.g., one with 55,000 pen tips) it was demonstrated that one
can write massively on a surface, which makes it feasible for mass production of the nanostructured
system. (43)
Nanoparticles (Zero-Dimensional Nanostructures)
If the 10 6 atoms that we have are all in one solid mass, and are closed-packed in a particle, it will
occupy a volume of about 6000 nm 3 with a width or diameter of only about 18 nm. A million atoms
make a nanoparticle! Many everyday-life particles that we encounter are already nanometer in
dimensions, such as the micelles formed by soap molecules in water, smoke particulates, or clay particles.
In fact, nanoparticles were used hundreds of years ago as colorants in Chinese vases or pigments in the
stained glass windows of cathedrals in Europe. There is much renewed interests in nanoparticles because
chemists and other researchers are able to characterize their behavior at higher precision using the
advanced tools that are now available. There are also various ways to synthesize and stabilize them, and
new possible applications are discovered.
Because of its small size, the number of surface atoms becomes significant. The smaller the
radius of the particle, the bigger the fraction of surface atoms. For a spherical particle, the surface area A s
= 4πr 2 , whereas the volume of the particle is V = (4/3)πr 3 . Thus, the surface area-to-volume ratio is A s /V
= 3/r, and since the number of surface atoms is proportional to the area exposed, then this ratio is
proportional to the fraction of surface atoms in the particle. The smallest closed-packed cluster of
spherical atoms is a 13-atom cluster wherein one atom is surrounded by 12 surface atoms (its
coordination number). Here, the surface-to-volume ratio of atoms is very large at 92.3% ( or 12/13). A
100-particle cluster will have a surface-to-volume ratio of 68.0%; a thousand, 38.4 %; and a million,
4.4%. For a micron-sized particle composed of 10 11 atoms, the surface-to-volume ratio is 0.10%. Indeed,
the nanometer-sized cluster will have significant surface energy. Recall that our surface atoms
experience an imbalance of forces around them creating a surface energy that seeks to be minimized.
Therefore, the surface energy and surface curvature become dominant factors that affect the overall shape,
stability, and property of the nanoparticle. Generally, the particle will be stable at or above a critical
radius wherein the effects of surface energy is compensated by the overall free energy of the entire
particle. Any smaller size, means the surface atoms will have to reconstruct, melt away, or seek other
ways to minimize surface energy. For example, the melting point for gold crystals was shown to have a
dramatic decrease with decreasing radius of the crystal, especially right around 3-4 nm radius. (44)
This discussion of stability of a cluster generally applies to metal or semiconductor nanoparticles
which form tiny crystallites or nanocrystals. (A review of nanocrystal chemistry is published by El-Sayed
et al. 26 ) In general, the synthesis goal is to produce stable nanoparticles of uniform size, shape, and
properties. The nanocrystals may be synthesized from the vapor phase by crystallization onto a substrate
through heterogeneous nucleation, or by controlled homogeneous nucleation in a liquid phase that is
usually a supersaturated solution. 4 In solution crystallization, stabilization of the nanoparticles is
generally achieved by lowering the surface free energy through bonding with organic molecules that
passivate the surface atoms. For example, nanocrystalline or colloidal gold is typically formed by
reduction of gold ions in solution by citrate ions producing typically ~20 nm particles. The
agglomeration of the colloidal gold is prevented by electrostatic repulsion between the Au particles that
are flanked by negatively charged citrate ions. The size of gold particles can also be controlled to be 1.5
nm to 20.0 nm radius by 'capping' it with thiol molecules to thermodynamically stabilize and stop further
growth of the nanocrystals. (45) Stabilization of the nanoparticles is also done using polymers, which was
found to also influence the resulting size and shape of the nanocrystals that are formed. In our lab, for
example, we were able to grow CdS nanoparticles in situ a carrageenan polymer which was previously
impregnated with cadmium ions. Here, the growth of the crystal occurred by slow precipitation upon
diffusion of hydrogen sulfide into the Cd 2+ -polysaccharide matrix. (46) Bawendi et al. (47) found a procedure
for synthesis of semiconductor nanoparticles of CdSe in a 'wet laboratory' technique, which involved
controlled precipitation and stabilization using small organic ligands. They can prepare CdSe particle
sizes between 1.5 nm to 11.5 nm with very narrow size distributions (monodisperse).
Semiconductor nanoparticles are also sometimes referred to as quantum dots or 'synthetic atoms'
because of quantum confinement effects. When a particle is energetically excited, an electron leaves a
hole creating an electron-hole pair that is called an exciton. Because of the small size of the particle, the
electron-hole pair may still be 'bound' to each other thus creating electronic energy levels that are
modeled after the electron-proton pair of a hydrogen atom. This is theoretically and experimentally
observable for cases when the size of the nanocrystal is less than the corresponding Bohr radius of the
bulk crystal. For nanocrystals, electronic properties become size-dependent, because the electronic
energy level structure is quantized or discrete as opposed to the electronic band structures exhibited by
bulk crystals. Therefore, nanocrystals are tunable opto-electronic elements. This is dramatically
exhibited by the varying colors of CdSe solutions (or colloidal dispersion), due to the sharp absorption
lines of the excitons in the visible region of light. Another very interesting property in this size regime is
the discreteness of electron conductivity, wherein the observed current-voltage characteristics produce a
staircase-like pattern due to individual tunneling of single electrons. 26 This is different from the
continuous curve predicted by Ohm's Law. Measurement of this effect may be done by connecting an
SPM probe tip (specifically STM) on top of a nanoparticle adsorbed on a metal. This behavior which is
also known as Coulomb blockade or 'Coulombic staircase' offers a possibility for single electron
transistors that may be part of future computing devices. Because of the availability of a method to
synthesize monodisperse CdSe nanocrystals, many researchers have incorporated them into other
nanostructured systems for various applications: nanoelectronics, optoelectronics, photonics, catalysis,
snesors, etc. (48) There are of course many other types of semiconducting systems: CdS, PbS, ZnS, TiO 2 ,
ZnO, etc., but to review them is beyond the scope of this paper, and the reader is referred to the review
given by reference 26.
Metallic nanoparticles exhibit strong surface plasmon absorption that give them the characteristic
deep red color, such as Faraday's colloidal gold dispersion. Surface plasmon resonance arises from the
coherent motion of electrons in the conduction band of the metal, which 'resonates' with light. 26 This is
another 'tunable' property, because the absorption band can shift in wavelength depending on the size of
the metallic nanoparticle. Because colloidal gold is easily synthesized, and they are amenable to self-
assembly interactions with molecules with thiol groups, they have been used a lot in various
functionalized forms. In fact, the test strip used in pregnancy or rapid drug screening comprise of a
dispersion of gold colloids that are bioconjugates with antibodies that can selectively bind with a target
compound—when a sufficient number of these gold clusters are concentrated (and not a lot is needed
because of the strong surface plasmon absorption of light) on a part of the strip, one sees the development
of a purple or reddish line which can indicate presence or absence of the compound; the level of detection
can be as low as 50 parts per billion (ppb) or even lower.(49) Thus, metallic nanoparticles have found use in
biomedical diagnostics. (50,51)Other applications reported are for medical purposes, using the catalytic
properties of these particles, that can have antimicrobial and possibly anti-HIV properties. (52)
Of course, atoms can also bond with other atoms covalently to make molecules, and in this way,
the bonding requirement by each atom is satisfied, that is, there is no dangling bond left at the surface.
Nonmetallic elements generally do these to form a molecular species—small molecules or very large ones
(polymers) which have extensive covalent bonding. Polymers are large molecules wherein each atom is
covalently bonded to each other in a particular way, such as to form a very long chain that can fold into a
random coil. The radius of the coil can go as high as several microns. Polymers are not new, but they
also figure in a lot in nanochemistry because they make interesting nanostructures, may be used as agents
to stabilize the system, as templates for nanostructure fabrication, and many other uses. The folded
helical DNA molecule, for example, is comprised of strands of a nature-designed polymer.
Nanowires (One-Dimensional Nanostructures)
Going back to our starting 1 million atoms, we know that to produce a one-dimensional structure,
we will need to align the atoms unidirectionally to make elongated structures. Based on the length of the
nanostructure, it could be a nanowire or a nanorod. Bonding the atoms to make a linear polymer chain is
not new, but this is possible only with elements that are amenable to extensive covalent linkages,
otherwise, the structure will be unstable. For semiconductor or metallic elements, nanowires are made
with nanometer-sized radii, such that the cross-section of the wire consists of hundreds or thousands of
atoms. They may be formed by controlling the growth process, usually along preferred directions of
crystallization or using a template to align the process. There are various techniques for making
nanowires, which may be from the vapor phase such as the nanobelts of the semiconducting ZnO
produced by Wang et al. (53): by evaporating the oxide under vacuum and condensing them on alumina
substrate (~30 nm diameter and several hundred nm long). Or from solution, such as the silver nanowires
(30-40 nm diameters, ~50 µm long) grown by reduction of silver nitrate with ethylene glycol and
allowing the metal to grow from Pt seed nanoparticles, and inducing unidirectional growth using a
polymer polyvinyl pyrrolidone as surfactant that adsorb on the growth surfaces.(54) Of course, present-day
photolithographic techniques (more of a top-down approach) allow 'printing' of lines that are less than
100 nm in width, and are used now in the manufacture of computer processors. The most recent
processors released by Intel TM are based on the so-called 65-nm production process which have transistor
gates about 35 nm in width; this is about a 100 times smaller in diameter than a red blood cell. (55,56)As
pointed out earlier, one of the most interesting nanowires nowadays are those of carbon nanotubes.
Supramolecular assemblies
What was discussed so far are nanostructures that can be formed based on the dimensionality of
the material that is produced. However, nanotechnology or nanochemistry is not limited to these types,
and more often than not, the nanostructured system or material is a composite of various types.
Ultimately, nanotechnology will approach molecular-level control of the device or material architecture.
What is uniquely nanotechnology today is that the design is molecular in approach to form materials that
are supramolecular assemblies. (57) Much of what is happening in biological cells, for example, is a
molecular machinery of sorts that is responsible for the spontaneous copying, transcription, and
reproduction of the DNA and proteins, for example. And some researchers have also begun to look at
nature to come up with biologically-inspired nanomaterials. One example is a nacre-like nanostructured
composite formed by layer-by-layer assembly of polymers and clay materials that are nanometer-spaced
—the resulting structure is brickwork in the nanometer scale. (58) Those engaged in nanocrystal research,
for example, also discovered that nanoparticles can form superlattices, and a group of researchers has
already begun forming various types based on binary nanoparticle superlattices. (59) Polymers also form
nanostructure assemblies such as those used in nano-patterning using block copolymers (or polymers with
two parts of the chain that are different in chemical composition) in a self-assembly approach. (60)
It is not necessary to just form nanostructures to be working in the realm of nanotechnology. An
effect that is manifested in nanometer dimensions is also considered part of this field. The semiconductor
properties of some inorganic materials, such as titania (TiO 2 ), for instance, had found applications as
nano-photocatalysts, and are now currently used as coatings in ceramic tiles which are 'self-cleaning' and
anti-microbial. UV light can produce an exciton in TiO 2 nanoparticles which are trapped as electrons
(which form radicals) and holes at the surface, in turn acting as reducing or oxidizing agents, respectively.
These catalyze the degradation of organics to carbon dioxide and water—the self-cleaning effect, and
they also find use in the remediation of pollutants such as dioxins. (61) In our lab, we have found, for
example, that a thin TiO 2 coating, when etched to nanoscale roughness will have increased anti-microbial
properties. (62) Nanostructured TiO 2 , after dye-sensitization, is also useful for solar cell devices.(63,64)
Another nano-sized manifestation is the wettability of a surface, which is usually attributed to its polarity,
but can be made super-hydrophobic or super-hydrophilic (or in other words, super non-stick or super-
wettable by water) by varying the surface nanostructures. (65) These surfaces improve the self-cleaning
properties because of lowered adhesion of surface impurities.
4. Concluding Remarks
Nanotechnology is here. Today, we are at the building-box age of nanotechnology moving on towards
integration of nanosystems to existing products (such as the computer processor). And it is just a matter of time
when we fully grow into the age of nanomanufacturing wherein researchers and engineers have come up with ways
to mass-produce functional nanostructured systems for specific applications. Here, nano-chemistry makes its
contribution as that science that investigates, designs, synthesizes, and fabricates matter that are in the
nanometer-size regime through molecular control of these systems.
Chapter{tow}
Experimental advances
Experimental advances
Nanotechnology and nanoscience got a boost in the early 1980s with two major developments: the birth of cluster science and the invention of the scanning tunneling microscope (STM). This development led to the discovery of fullerenes in 1985 and the structural assignment of carbon nanotubes a few years later. In another development, the synthesis and properties of semiconductor nanocrystals were studied. This led to a fast increasing number of semiconductor nanoparticles of quantum dots. IBM researcher Don Eigler was the first to manipulate atoms using a scanning tunneling microscope in 1989. He used 35 Xenon atoms to spell out the IBM logo(66)
In the early 1990s Huffman and Kraetschmer, of the University of Arizona, discovered how to synthesize and purify large quantities of fullerenes. This opened the door to their characterization and functionalization by hundreds of investigators in government and industrial laboratories. Shortly after, rubidium doped C60 was found to be a mid temperature (Tc = 32 K) superconductor. At a meeting of the Materials Research Society in 1992, Dr. T. Ebbesen (NEC) described to a spellbound audience his discovery and characterization of carbon nanotubes. This event sent those in attendance and others downwind of his presentation into their laboratories to reproduce and push those discoveries forward. Using the same or similar tools as those used by Huffman and Kratschmere, hundreds of researchers further developed the field of nanotube-based nanotechnology.
At present in 2007 the practice of nanotechnology embraces both stochastic approaches (in which, for example, supramolecular chemistry creates waterproof pants) and deterministic approaches wherein single molecules (created by stochastic chemistry) are manipulated on substrate surfaces (created by stochastic deposition methods) by deterministic methods comprising nudging them with STM or AFM probes and causing simple binding or cleavage reactions to occur. The dream of a complex, deterministic molecular nanotechnology remains elusive. Since the mid 1990s, thousands of surface scientists and thin film technocrats have latched on to the nanotechnology bandwagon and redefined their disciplines as nanotechnology. This has caused much confusion in the field and has spawned thousands of "nano"-papers on the peer reviewed literature. Most of these reports are extensions of the more ordinary research done in the parent fields.
For the future, some means has to be found for MNT design evolution at the nanoscale which mimics the process of biological evolution at the molecular scale. Biological evolution proceeds by random variation in ensemble averages of organisms combined with culling of the less-successful variants and reproduction of the more-successful variants, and macroscale engineering design also proceeds by a process of design evolution from simplicity to complexity as set forth somewhat satirically by John Gall: "A complex system that works is invariably found to have evolved from a simple system that worked. . . . A complex system designed from scratch never works and can not be patched up to make it work. You have to start over, beginning with a system that works." (67)A breakthrough in MNT is needed which proceeds from the simple atomic ensembles which can be built with, e.g., an STM to complex MNT systems via a process of design evolution. A handicap in this process is the difficulty of seeing) and manipulation at the nanoscale compared to the macroscale which makes deterministic selection of successful trials difficult; in contrast biological evolution proceeds via action of what Richard Dawkins has called the "blind watchmaker"(68) comprising random molecular variation and deterministic reproduction/exti
Tools and techniques
Tools and techniques
Typical AFM setup. A microfabricated cantilever with a sharp tip is deflected by features on a sample surface, much like in a phonograph but on a much smaller scale. A laser beam reflects off the backside of the cantilever into a set of photodetectors, allowing the deflection to be measured and assembled into an image of the surface.
There are several important modern developments. The atomic force microscope (AFM) and the Scanning Tunneling Microscope (STM) are two early versions of scanning probes that launched nanotechnology. There are other types of scanning probe microscopy, all flowing from the ideas of the scanning confocal microscope developed by Marvin Minsky in 1961 and the scanning acoustic microscope (SAM) developed by Calvin Quate and coworkers in the 1970s, that made it possible to see structures at the nanoscale. The tip of a scanning probe can also be used to manipulate nanostructures (a process called positional assembly). Feature-oriented scanning-positioning methodology suggested by Rostislav Lapshin appears to be a promising way to implement these nanomanipulations in automatic mode. However, this is still a slow process because of low scanning velocity of the microscope. Various techniques of nanolithography such as optical lithography, X-ray lithography dip pen nanolithography, electron beam lithography or nanoimprint lithography were also developed. Lithography is a top-down fabrication technique where a bulk material is reduced in size to nanoscale pattern.
Another group of nanotechnological techniques include those used for fabrication of nanowires, those used in semiconductor fabrication such as deep ultraviolet lithography, electron beam lithography, focused ion beam machining, nanoimprint lithography, atomic layer deposition, and molecular vapor deposition, and further including molecular self-assembly techniques such as those employing di-block copolymers. However, all of these techniques preceded the nanotech era, and are extensions in the development of scientific advancements rather than techniques which were devised with the sole purpose of creating nanotechnology and which were results of nanotechnology research.
The top-down approach anticipates nanodevices that must be built piece by piece in stages, much as manufactured items are made. Scanning probe microscopy is an important technique both for characterization and synthesis of nanomaterials. Atomic force microscopes and scanning tunneling microscopes can be used to look at surfaces and to move atoms around. By designing different tips for these microscopes, they can be used for carving out structures on surfaces and to help guide self-assembling structures. By using, for example, feature-oriented scanning-positioning approach, atoms can be moved around on a surface with scanning probe microscopy techniques. At present, it is expensive and time-consuming for mass production but very suitable for laboratory experimentation.
In contrast, bottom-up techniques build or grow larger structures atom by atom or molecule by molecule. These techniques include chemical synthesis, self-assembly and positional assembly. Dual polarisation interferometry is one tool suitable for characterisation of self assembled thin films. Another variation of the bottom-up approach is molecular beam epitaxy or MBE. Researchers at Bell Telephone Laboratories like John R. Arthur. Alfred Y. Cho, and Art C. Gossard developed and implemented MBE as a research tool in the late 1960s and 1970s. Samples made by MBE were key to the discovery of the fractional quantum Hall effect for which the 1998 Nobel Prize in Physics was awarded. MBE allows scientists to lay down atomically precise layers of atoms and, in the process, build up complex structures. Important for research on semiconductors, MBE is also widely used to make samples and devices for the newly emerging field of spintronics.
However, new therapeutic products, based on responsive nanomaterials, such as the ultradeformable, stress-sensitive Transfersome vesicles, are under development and already approved for human use in some countries.[citation needed]
Types of carbon nanotubes and related structures
Single-walled
| Armchair (n,n) | The chiral vector is bent, while the translation vector stays straight | Graphene nanoribbon | The chiral vector is bent, while the translation vector stays straight |
| Zigzag (n,0) | Chiral (n,m) | n and m can be counted at the end of the tube | Graphene nanoribbon |
The (n,m) nanotube naming scheme can be thought of as a vector (Ch) in an infinite graphene sheet that describes how to "roll up" the graphene sheet to make the nanotube. T denotes the tube axis, and a1 and a2 are the unit vectors of graphene in real space.
Transmission electron microscopy image showing a single-walled carbon nanotube
Most single-walled nanotubes (SWNT) have a diameter of close to 1 nanometer, with a tube length that can be many millions of times longer. The structure of a SWNT can be conceptualized by wrapping a one-atom-thick layer of graphite called graphene into a seamless cylinder. The way the graphene sheet is wrapped is represented by a pair of indices (n,m) called the chiral vector. The integers n and m denote the number of unit vectors along two directions in the honeycomb crystal lattice of graphene. If m = 0, the nanotubes are called "zigzag". If n = m, the nanotubes are called "armchair". Otherwise, they are called "chiral". The diameter of a nanotube can be calculated from its (n,m) indices as follows
where a = 0.246 nm.
Single-walled nanotubes are an important variety of carbon nanotube because they exhibit electric properties that are not shared by the multi-walled carbon nanotube (MWNT) variants. In particular, their band gap can vary from zero to about 2 eV and their electrical conductivity can show metallic or semiconducting behavior, whereas MWNTs are zero-gap metals. Single-walled nanotubes are the most likely candidate for miniaturizing electronics beyond the micro electromechanical scale currently used in electronics. The most basic building block of these systems is the electric wire, and SWNTs can be excellent conductors.(69,70) One useful application of SWNTs is in the development of the first intramolecular field effect transistors (FET). Production of the first intramolecular logic gate using SWNT FETs has recently become possible as well.(71) To create a logic gate you must have both a p-FET and an n-FET. Because SWNTs are p-FETs when exposed to oxygen and n-FETs otherwise, it is possible to protect half of an SWNT from oxygen exposure, while exposing the other half to oxygen. This results in a single SWNT that acts as a NOT logic gate with both p and n-type FETs within the same molecule.
Single-walled nanotubes are dropping precipitously in price, from around $1500 per gram as of 2000 to retail prices of around $50 per gram of as-produced 40–60% by weight SWNTs as of March 2010.(72,73)
Multi-walled
SEM image of carbon nanotubes bundles.
Triple-walled armchair carbon nanotube
Multi-walled nanotubes (MWNT) consist of multiple rolled layers (concentric tubes) of graphite. There are two models which can be used to describe the structures of multi-walled nanotubes. In the Russian Doll model, sheets of graphite are arranged in concentric cylinders, e.g. a (0,8) single-walled nanotube (SWNT) within a larger (0,17) single-walled nanotube. In the Parchment model, a single sheet of graphite is rolled in around itself, resembling a scroll of parchment or a rolled newspaper. The interlayer distance in multi-walled nanotubes is close to the distance between graphene layers in graphite, approximately 3.4 Å.
The special place of double-walled carbon nanotubes (DWNT) must be emphasized here because their morphology and properties are similar to SWNT but their resistance to chemicals is significantly improved. This is especially important when functionalization is required (this means grafting of chemical functions at the surface of the nanotubes) to add new properties to the CNT. In the case of SWNT, covalent functionalization will break some C=C double bonds, leaving "holes" in the structure on the nanotube and thus modifying both its mechanical and electrical properties. In the case of DWNT, only the outer wall is modified. DWNT synthesis on the gram-scale was first proposed in 2003[74] by the CCVD technique, from the selective reduction of oxide solutions in methane and hydrogen.
Torus
In theory, a nanotorus is a carbon nanotube bent into a torus (doughnut shape). Nanotori are predicted to have many unique properties, such as magnetic moments 1000 times larger than previously expected for certain specific radii.[75] Properties such as magnetic moment, thermal stability, etc. vary widely depending on radius of the torus and radius of the tube.[76]
Nanobud
Carbon nanobuds are a newly created material combining two previously discovered allotropes of carbon: carbon nanotubes and fullerenes. In this new material, fullerene-like "buds" are covalently bonded to the outer sidewalls of the underlying carbon nanotube. This hybrid material has useful properties of both fullerenes and carbon nanotubes. In particular, they have been found to be exceptionally good field emitters. In composite materials, the attached fullerene molecules may function as molecular anchors preventing slipping of the nanotubes, thus improving the composite’s mechanical properties.
Cup stacked carbon nanotubes
Cup-stacked carbon nanotubes (CSCNTs) differ from other quasi-1D carbon structures, which normally behave as quasi-metallic conductors of electrons. CSCNTs exhibit semiconducting behaviors due to the stacking microstructure of graphene layers.[77]
Extreme carbon nanotubes
Cycloparaphenylene
The observation of the longest carbon nanotubes (18.5 cm long) was reported in 2009. These nanotubes were grown on Si substrates using an improved chemical vapor deposition (CVD) method and represent electrically uniform arrays of single-walled carbon nanotubes.[1]
The shortest carbon nanotube is the organic compound cycloparaphenylene which was synthesized in early 2009.[78][79][80]
The thinnest carbon nanotube is armchair (2,2) CNT with a diameter of 3 Å. This nanotube was grown inside a multi-walled carbon nanotube. Assigning of carbon nanotube type was done by combination of high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy and density functional theory (DFT) calculations.[81]
The thinnest freestanding single-walled carbon nanotube is about 4.3 Å in diameter. Researchers suggested that it can be either (5,1) or (4,2) SWCNT, but exact type of carbon nanotube remains questionable.[82] (3,3), (4,3) and (5,1) carbon nanotubes (all about 4 Å in diameter) were unambiguously identified using more precise aberration-corrected high-resolution transmission electron microscopy. However, they were found inside of double-walled carbon nanotubes.[83]
Properties
*Strength
*Hardness
*Kinetic
*Electrical
*Optical
*Thermal
*Defects
*One-dimensional transport
Because of the nanoscale dimensions, electrons propagate only along the tube's axis and electron transport involves many quantum effects. Because of this, carbon nanotubes are frequently referred to as “one-dimensional”.
Synthesis
Powder of carbon nanotubes
Techniques have been developed to produce nanotubes in sizeable quantities, including arc discharge, laser ablation, high pressure carbon monoxide (HiPco), and chemical vapor deposition (CVD). Most of these processes take place in vacuum or with process gases. CVD growth of CNTs can occur in vacuum or at atmospheric pressure. Large quantities of nanotubes can be synthesized by these methods; advances in catalysis and continuous growth processes are making CNTs more commercially viable.
Arc discharge
Nanotubes were observed in 1991 in the carbon soot of graphite electrodes during an arc discharge, by using a current of 100 amps, that was intended to produce fullerenes However the first macroscopic production of carbon nanotubes was made in 1992 by two researchers at NEC's Fundamental Research Laboratory. The method used was the same as in 1991. During this process, the carbon contained in the negative electrode sublimates because of the high discharge temperatures. Because nanotubes were initially discovered using this technique, it has been the most widely-used method of nanotube synthesis.
The yield for this method is up to 30 percent by weight and it produces both single- and multi-walled nanotubes with lengths of up to 50 micrometers with few structural defects.
Laser ablation
In the laser ablation process, a pulsed laser vaporizes a graphite target in a high-temperature reactor while an inert gas is bled into the chamber. Nanotubes develop on the cooler surfaces of the reactor as the vaporized carbon condenses. A water-cooled surface may be included in the system to collect the nanotubes.
This process was developed by Dr. Richard Smalley and co-workers at Rice University, who at the time of the discovery of carbon nanotubes, were blasting metals with a laser to produce various metal molecules. When they heard of the existence of nanotubes they replaced the metals with graphite to create multi-walled carbon nanotubes. Later that year the team used a composite of graphite and metal catalyst particles (the best yield was from a cobalt and nickel mixture) to synthesize single-walled carbon nanotubes.
The laser ablation method yields around 70% and produces primarily single-walled carbon nanotubes with a controllable diameter determined by the reaction temperature. However, it is more expensive than either arc discharge or chemical vapor deposition.
Chapter{three}
Medicine
The biological and medical research communities have exploited the unique properties of nanomaterials for various applications (e.g., contrast agents for cell imaging and therapeutics for treating cancer). Terms such as biomedical nanotechnology, nanobiotechnology, and nanomedicine are used to describe this hybrid field. Functionalities can be added to nanomaterials by interfacing them with biological molecules or structures. The size of nanomaterials is similar to that of most biological molecules and structures; therefore, nanomaterials can be useful for both in vivo and in vitro biomedical research and applications. Thus far, the integration of nanomaterials with biology has led to the development of diagnostic devices, contrast agents, analytical tools, physical therapy applications, and drug delivery vehicles.
Diagnostics
Nanotechnology-on-a-chip is one more dimension of lab chip -on-a- technology. Magnetic nanoparticles, bound to a suitable antibody, are used to label specific molecules, structures or microorganisms. Gold nanoparticles tagged with short segments of DNA can be used for detection of genetic sequence in a sample. Multicolor optical coding for biological assays has been achieved by embedding different-sized quantum dots into polymeric microbeads. Nanopore technology for analysis of nucleic acids converts strings of nucleotides directly into electronic signatures.
Drug delivery
Nanotechnology has been a boom in medical field by delivering drugs to specific cells using nanoparticles. The overall drug consumption and side-effects can be lowered significantly by depositing the active agent in the morbid region only and in no higher dose than needed. This highly selective approach reduces costs and human suffering. An example can be found in dendrimers and nanoporous materials. Another example is to use block co-polymers, which form micelles for drug encapsulation.[ 84] They could hold small drug molecules transporting them to the desired location. Another vision is based on small electromechanical systems; NEMS are being investigated for the active release of drugs. Some potentially important applications include cancer treatment with iron nanoparticles or gold shells. A targeted or personalized medicine reduces the drug consumption and treatment expenses resulting in an overall societal benefit by reducing the costs to the public health system. Nanotechnology is also opening up new opportunities in implantable delivery systems, which are often preferable to the use of injectable drugs, because the latter frequently display first-order kinetics (the blood concentration goes up rapidly, but drops exponentially over time). This rapid rise may cause difficulties with toxicity, and drug efficacy can diminish as the drug concentration falls below the targeted range.
Tissue engineering
Nanotechnology can help to reproduce or to repair damaged tissue. “Tissue engineering” makes use of artificially stimulated cell proliferation by using suitable nanomaterial-based scaffolds and growth factors. For example, bones can be regrown on carbon nanotube scaffolds. Tissue engineering might replace today's conventional treatments like organ transplants or artificial implants. Advanced forms of tissue engineering may lead to life extension.
Chemistry and environment
Chemistry and environment
Chemical catalysis and filtration techniques are two prominent examples where nanotechnology already plays a role. The synthesis provides novel materials with tailored features and chemical properties: for example, nanoparticles with a distinct chemical surrounding (ligands), or specific optical properties. In this sense, chemistry is indeed a basic nanoscience. In a short-term perspective, chemistry will provide novel “nanomaterials” and in the long run, superior processes such as “self-assembly” will enable energy and time preserving strategies. In a sense, all chemical synthesis can be understood in terms of nanotechnology, because of its ability to manufacture certain molecules. Thus, chemistry forms a base for nanotechnology providing tailor-made molecules, polymers, etcetera, as well as clusters and nanoparticles.
Catalysis
Chemical catalysis benefits especially from nanoparticles, due to the extremely large surface to volume ratio. The application potential of nanoparticles in catalysis ranges from fuel cell to catalytic converters and photocatalytic devices. Catalysis is also important for the production of chemicals.
Platinum nanoparticles are now being considered in the next generation of automotive catalytic converters because the very high surface area of nanoparticles could reduce the amount of platinum required.[ 85] However, some concerns have been raised due to experiments demonstrating that they will spontaneously combust if methane is mixed with the ambient air.[ 86] Ongoing research at the Centre National de la Recherche Scientifique (CNRS) in France may resolve their true usefulness for catalytic applications.[ 87] Nanofiltration may come to be an important application, although future research must be careful to investigate possible toxicity.[ 88]
Filtration
A strong influence of photochemistry on waste-water treatment, air purification and energy storage devices is to be expected. Mechanical or chemical methods can be used for effective filtration techniques. One class of filtration techniques is based on the use of membranes with suitable hole sizes, whereby the liquid is pressed through the membrane. Nanoporous membranes are suitable for a mechanical filtration with extremely small pores smaller than 10 nm (“nanofiltration”) and may be composed of nanotubes. Nanofiltration is mainly used for the removal of ions or the separation of different fluids. On a larger scale, the membrane filtration technique is named ultrafiltration, which works down to between 10 and 100 nm. One important field of application for ultrafiltration is medical purposes as can be found in renal dialysis. Magnetic nanoparticles offer an effective and reliable method to remove heavy metal contaminants from waste water by making use of magnetic separation techniques. Using nanoscale particles increases the efficiency to absorb the contaminants and is comparatively inexpensive compared to traditional precipitation and filtration methods.
Some water-treatment devices incorporating nanotechnology are already on the market, with more in development. Low-cost nanostructured separation membranes methods have been shown to be effective in producing potable water in a recent study.[ 89]
Energy
The most advanced nanotechnology projects related to energy are: storage, conversion, manufacturing improvements by reducing materials and process rates, energy saving (by better thermal insulation for example), and enhanced renewable energy sources.
Reduction of energy consumption
A reduction of energy consumption can be reached by better insulation systems, by the use of more efficient lighting or combustion systems, and by use of lighter and stronger materials in the transportation sector. Currently used light bulbs only convert approximately 5% of the electrical energy into light. Nanotechnological approaches like light-emitting diodes (LEDs) or quantum caged atoms (QCAs) could lead to a strong reduction of energy consumption for illumination.
Increasing the efficiency of energy production
Today's best solar cells have layers of several different semiconductors stacked together to absorb light at different energies but they still only manage to use 40 percent of the Sun's energy. Commercially available solar cells have much lower efficiencies (15-20%). Nanotechnology could help increase the efficiency of light conversion by using nanostructures with a continuum of bandgaps.
The degree of efficiency of the internal combustion engine is about 30-40% at the moment. Nanotechnology could improve combustion by designing specific catalysts with maximized surface area. In 2005, scientists at the University of Toronto developed a spray-on nanoparticle substance that, when applied to a surface, instantly transforms it into a solar collector.[1]
The use of more environmentally friendly energy systems
An example for an environmentally friendly form of energy is the use of fuel cells powered by hydrogen, which is ideally produced by renewable energies. Probably the most prominent nanostructured material in fuel cells is the catalyst consisting of carbon supported noble metal particles with diameters of 1-5 nm. Suitable materials for hydrogen storage contain a large number of small nanosized pores. Therefore many nanostructured materials like nanotubes, zeolites or alanates are under investigation. Nanotechnology can contribute to the further reduction of combustion engine pollutants by nanoporous filters, which can clean the exhaust mechanically, by catalytic converters based on nanoscale noble metal particles or by catalytic coatings on cylinder walls and catalytic nanoparticles as additive for fuels.
Recycling of batteries
Because of the relatively low energy density of batteries the operating time is limited and a replacement or recharging is needed. The huge number of spent batteries and accumulators represent a disposal problem. The use of batteries with higher energy content or the use of rechargeable batteries or itorssupercapac with higher rate of recharging using nanomaterials could be helpful for the battery disposal problem. Yield is an issue here.
Information and communication
Current high-technology production processes are based on traditional top down strategies, where nanotechnology has already been introduced silently. The critical length scale of integrated circuits is already at the nanoscale (50 nm and below) regarding the gate length of transistors in CPUs or DRAM devices.
Memory Storage
Electronic memory designs in the past have largely relied on the formation of transistors. However, research into crossbar switch based electronics have offered an alternative using reconfigurable interconnections between vertical and horizontal wiring arrays to create ultra high density memories. Two leaders in this area are Nantero which has developed a carbon nanotube based crossbar memory called Nano-RAM and Hewlett-Packard which has proposed the use of memristor material as a future replacement of Flash memory.
Novel semiconductor devices
An example of such novel devices is based on spintronics.The dependence of the resistance of a material (due to the spin of the electrons) on an external field is called magnetoresistance. This effect can be significantly amplified (GMR - Giant Magneto-Resistance) for nanosized objects, for example when two ferromagnetic layers are separated by a nonmagnetic layer, which is several nanometers thick (e.g. Co-Cu-Co). The GMR effect has led to a strong increase in the data storage density of hard disks and made the gigabyte range possible. The so called tunneling magnetoresistance (TMR) is very similar to GMR and based on the spin dependent tunneling of electrons through adjacent ferromagnetic layers. Both GMR and TMR effects can be used to create a non-volatile main memory for computers, such as the so called magnetic random access memory or MRAM.
In 1999, the ultimate CMOS transistor developed at the Laboratory for Electronics and Information Technology in Grenoble, France, tested the limits of the principles of the MOSFET transistor with a diameter of 18 nm (approximately 70 atoms placed side by side). This was almost one tenth the size of the smallest industrial transistor in 2003 (130 nm in 2003, 90 nm in 2004, 65 nm in 2005 and 45 nm in 2007). It enabled the theoretical integration of seven billion junctions on a €1 coin. However, the CMOS transistor, which was created in 1999, was not a simple research experiment to study how CMOS technology functions, but rather a demonstration of how this technology functions now that we ourselves are getting ever closer to working on a molecular scale. Today it would be impossible to master the coordinated assembly of a large number of these transistors on a circuit and it would also be impossible to create this on an industrial level.[ 90]
Novel optoelectronic devices
In the modern communication technology traditional analog electrical devices are increasingly replaced by optical or optoelectronic devices due to their enormous bandwidth and capacity, respectively. Two promising examples are photonic crystals and quantum dots. Photonic crystals are materials with a periodic variation in the refractive index with a lattice constant that is half the wavelength of the light used. They offer a selectable band gap for the propagation of a certain wavelength, thus they resemble a semiconductor, but for light or photons instead of electrons. Quantum dots are nanoscaled objects, which can be used, among many other things, for the construction of lasers. The advantage of a quantum dot laser over the traditional semiconductor laser is that their emitted wavelength depends on the diameter of the dot. Quantum dot lasers are cheaper and offer a higher beam quality than conventional laser diodes.
Displays
The production of displays with low energy consumption could be accomplished using carbon nanotubes (CNT). Carbon nanotubes are electrically conductive and due to their small diameter of several nanometers, they can be used as field emitters with extremely high efficiency for field emission displays (FED). The principle of operation resembles that of the cathode ray tube, but on a much smaller length scale.
Quantum computers
Entirely new approaches for computing exploit the laws of quantum mechanics for novel quantum computers, which enable the use of fast quantum algorithms. The Quantum computer has quantum bit memory space termed "Qubit" for several computations at the same time. This facility may improve the performance of the older systems.
Heavy Industry
An inevitable use of nanotechnology will be in heavy industry.
Aerospace
Lighter and stronger materials will be of immense use to aircraft manufacturers, leading to increased performance. Spacecraft will also benefit, where weight is a major factor. Nanotechnology would help to reduce the size of equipment and thereby decrease fuel-consumption required to get it airborne.
Hang gliders may be able to halve their weight while increasing their strength and toughness through the use of nanotech materials. Nanotech is lowering the mass of supercapacitors that will increasingly be used to give power to assistive electrical motors for launching hang gliders off flatland to thermal-chasing altitudes.
Construction
Nanotechnology has the potential to make construction faster, cheaper, safer, and more varied. Automation of nanotechnology construction can allow for the creation of structures from advanced homes to massive skyscrapers much more quickly and at much lower cost.
Nanotechnology and construction
Nanotechnology is one of the most active research areas that encompass a number of disciplines nstructions Such as electronics, bio-mechanics and coatings including civil engineering and construction materials.
The use of nanotechnology in construction involves the development of new concept and understanding of the hydration of cement particles and the use of nano-size ingredients such as alumina and silica and other nanoparticles. The manufactures also investigating the methods of manufacturing of nano-cement. If cement with nano-size particles can be manufactured and processed, it will open up a large number of opportunities in the fields of ceramics, high strength composites and electronic applications. Since at the nanoscale the properties of the material are different from that of their bulk counter parts. When materials becomes nano-sized, the proportion of atoms on the surface increases relative to those inside and this leads to novel properties. Some applications of nanotechnology in construction are describe below.
Nanoparticles and concrete
Concrete is most commonly used material in the construction. It is the current active area of research and development. Researchers are trying to develop nano-sized concrete (or nano-concrete) and to understand its structure using Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Focused Ion Beam (FIB) as these understanding leads to appropriate use of nanotechnology in construction.
The term nano-concrete is defined as a concrete made with portland cement particles that are less than 500 nano-meters. When Concrete is reduced to nano-level, strongly influenced by its nano-properties which causes an improvement in its strength and durability .The Silica (SiO2) is present in conventional concrete as part of the normal mix.When nano silica is added to concrete the particle packing can be improved which results in the densifying micro and nanostructures,which results in the improved mechanical properties.
The addition of nano-silica to cement based materials can also control the degradation of the fundamental C-S-H (calcium-silicatehydrate) reaction of concrete caused by calcium leaching in water as well as block water penetration and therefore lead to improvements in durability.
The strength of concrete can also be increase by adding haematite (Fe2O3) nanoparticles. The haematite (Fe2O3) nanoparticle can also monitors stress levels through the measurement of section electrical resistance.
The need for nano-concrete
- The micro-meter thick plates and other shapes such as cylinders can be manufactured using nano-cement for various applications including electronic components and high temperature sensors.
- Nano-cement using Carbon nano-tubes can be used for both strengthening and creating electric circuits.
- Nano-cement is very much useful in the area of coatings.
- Current portland cement-based coatings are thick and need polymer additions to improve adhesion. Nano-cement will create a new paradigm in this area of application.
- If portland cement can be formulated with nano-size cement particles, it will open up a large number of opportunities.For example, the cement can be used as an inorganic adhesive with carbon fibers.
- The nano-cement will not only be more economical than organic polymers but also will be fire resistant.
- It will not emit any volatile organic compounds (voc).
Challenges
Coatings are routinely used as protective barriers against abrasion, chemical attack,hydro-thermal variations and to improve aesthetics. As these coatings are in the micrometer range. So new materials and techniques have to be developed to develop nano-meter thick coatings that are durable and generate less heat due to reduced friction.Coatings should be self-cleaning and self-healing, durable under various exposure conditions. Coatings should have abrasion resistance, friction resistance, high temperature resistance and electrical characteristics. For the nano coatings, the properties of the coatings themselves need investigation.Brittle coatings usually fail by cracking. Coatings with a nano-scale of roughness that will repel water and dirt, modeled after the coating of the lotus leaf are being created.
The lotus leaf has extraordinary ability to keep itself clean and dry. Now nanotechnology is being used to mimic the lotus leaf surfaceand create new products such as hydrophobic or water-repellent surface, particles of dirt are removed by moving water.But on a Lotus simulated surface, dirt particles are collected by water drops and rinsedoff.
Nanoparticles and steel
Steel has been widely available material and has a major role in the construction industry. The use of nanotechnology in steel helps to improve the properties of steel. The fatigue ,which lead to the structural failure of steel due to cyclic loading, such as in bridges or towers.The current steel designs are based on the reduction in the allowable stress, service life or regular inspection regime. This has a significant impact on the life-cycle costs of structures and limits the effective use of resources.The Stress risers are responsible for initiating cracks from which fatigue failure results .The addition of copper nanoparticles reduces the surface un-evenness of steel which then limits the number of stress risers and hence fatigue cracking. Advancements in this technology using nanoparticles would lead to increased safety, less need for regular inspection regime and more efficient materials free from fatigue issues for construction.
The nano-size steel produce stronger steel cables which can be in bridge construction .Also these stronger cable material would reduce the costs and period of construction, especially in suspension bridges as the cables are run from end to end of the span.This would require high strength joints which leads to the need for high strength bolts. The capacity of high strength bolts is obtained through quenching and tempering .The microstructures of such products consist of tempered martensite. When the tensile strength of tempered martensite steel exceeds 1,200 MPa even a very small amount of hydrogen embrittles the grain boundaries and the steel material may fail during use. This phenomenon, which is known as delayed fracture, which hindered the strengthening of steel bolts and their highest strength is limited to only around 1,000 to 1,200 MPa.
The use of vanadium and molybdenum nanoparticles improves the delayed fracture problems associated with high strength bolts reducing the effects of hydrogen embrittlement and improving the steel micro-structure through reducing the effects of the inter-granular cementite phase.
Welds and the Heat Affected Zone (HAZ) adjacent to welds can be brittle and fail without warning when subjected to sudden dynamic loading.The addition of nanoparticles of magnesium and calcium makes the HAZ grains finer in plate steel and this leads to an increase in weld toughness. The increase in toughness at would result in a smaller resource requirement because less material is required in order to keep stresses within allowable limits.The carbon nanotubes are exciting material with tremendous properties of strength and stiffness, they have found little application as compared to steel,because it is difficult to bind them with bulk material and they pull out easily, Which make them ineffective in construction materials.
Nanoparticles in glass
The glass is also an important material in construction.There is a lot of research being carried out on the application of nanotechnology to glass.Titanium dioxide (TiO2) nanoparticles are used to coat glazing since it has sterilizing and anti-fouling properties. The particles catalyze powerful reactions which breakdown organic pollutants, volatile organic compounds and bacterial membranes.
The TiO2 is hydrophilic (attraction to water) which can attract rain drops which then wash off the dirt particles.Thus the introduction of nanotechnology in the Glass industry, incorporates the self cleaning property of glass. Fire-protective glass is another application of nanotechnology. This is achieved by using a clear intumescent layer sandwiched between glass panels (an interlayer) formed of silica nanoparticles (SiO2) which turns into a rigid and opaque fire shield when heated.Most of glass in construction is on the exterior surface of buildings .So the light and heat entering the building through glass has to be prevented. The nanotechnology can provide a better solution to block light and heat coming through windows.
Nanoparticles in coatings
Coatings is an important area in construction.coatings are extensively use to paint the walls ,doors and windows.Coatings should provides a protective layer which is bound to the base material to produce a surface of the desired protective or functional properties. The coatings should have self healing capabilities through a process of “self-assembly”.Nanotechnology is being applied to paints to obtained the coatings having self healing capabilities and corrosion protection under insulation.Since these coatings are hydrophobic and repels water from the metal pipe and can also protect metal from salt water attack. Nanoparticle based systems can provide better adhesion and transparency .The TiO2 coating captures and breaks down organic and inorganic air pollutants by a photocatalytic process ,which leads to putting roads to good environmental use.
Nanoparticles in Wear Resistant Plasma Transferred Wire Arc Coatings
The Intellectual Property Owner's Association's 2009 Invention of the Year[91] pertained to the use of nanotechnology coatings applied by the Plasma Transferred Wire Arc technology PTWA. The technology is used to apply a coating to the internal surface of engine cylinder bores to increase wear resistance. A supersonic plasma jet melts a wire, atomizes it into nanoparticles and propels it onto a substrate. The plasma jet is formed by a transferred arc between a non-consumable cathode and the wire. After atomization, forced air transports the stream of molten droplets onto the bore wall. The particles flatten when they impinge on the surface of the substrate, due to the high kinetic energy. The nano-particles rapidly solidify upon contact. The stacked particles make up a high wear resistant coating.
Nanoparticles in fire protection and detection
Fire resistance of steel structures is often provided by a coating produced by a spray-oncementitious process.The nano-cement has the potential to create a new paradigm in this area of application because the resulting material can be used as a tough, durable, high temperature coating. It provides a good method of increasing fire resistance and this is a cheaper option than conventional insulation.
Risks of using nanoparticles in construction
In building construction nanomaterials are widely used from self-cleaning windows to flexible solar panels to wi-fi blocking paint. The self-healing concrete, materials to block ultraviolet and infrared radiation, smog-eating coatings and light-emitting walls and ceilings are the new nanomaterials in construction. Nanotechnology is a promise for “smart home” a reality. Nanotech-enabled sensors can monitor temperature, humidity, and airborne toxins which needs nanotech based improved batteries.The building components will be intelligent and interactive since the sensor uses wireless components,it can collect the wide range of data.
If the nanosensors and nanomaterials becomes a every day part of the buildings to make them intelligent,what are the consequences of these materials on human beings?
1.Effect of nanoparticles on health and environment: Nanoparticles may also enter the body if building water supplies are filtered through commercially available nanofilters. Airborne and waterborne nanoparticles enter from building ventilation and wastewater systems. 2. Effect of nanoparticles on societal issues: As sensors become more common place,a loss of privacy may result from users interacting with increasingly intelligent building components.The technology at one side has the advantages of new building material. The otherside it has the fear of risk arises from these materials. However, the overall performance of nanomaterials to date, is that valuable opportunities to improve building performance, user health and
Vehicle manufacturers
Much like aerospace, lighter and stronger materials will be useful for creating vehicles that are both faster and safer. Combustion engines will also benefit from parts that are more hard-wearing and more heat-resistant.
Consumer goods
Nanotechnology is already impacting the field of consumer goods, providing products with novel functions ranging from easy-to-clean to scratch-resistant. Modern textiles are wrinkle-resistant and stain-repellent; in the mid-term clothes will become “smart”, through embedded “wearable electronics”. Already in use are different nanoparticle improved products. Especially in the field of cosmetics, such novel products have a promising potential.
Foods
Complex set of engineering and scientific challenges in the food and bioprocessing industry for manufacturing high quality and safe food through efficient and sustainable means can be solved through nanotechnology. Bacteria identification and food quality monitoring using biosensors; intelligent, active, and smart food packaging systems; nanoencapsulation of bioactive food compounds are few examples of emerging applications of nanotechnology for the food industry[92]. Nanotechnology can be applied in the production, processing, safety and packaging of food. A nanocomposite coating process could improve food packaging by placing anti-microbial agents directly on the surface of the coated film. Nanocomposites could increase or decrease gas permeability of different fillers as is needed for different products. They can also improve the mechanical and heat-resistance properties and lower the oxygen transmission rate. Research is being performed to apply nanotechnology to the detection of chemical and biological substances for sensanges in foods.
Nano-foods
New foods are among the nanotechnology-created consumer products coming onto the market at the rate of 3 to 4 per week, according to the Project on Emerging Nanotechnologies (PEN), based on an inventory it has drawn up of 609 known or claimed nano-products.
On PEN's list are three foods -- a brand of canola cooking oil called Canola Active Oil, a tea called Nanotea and a chocolate diet shake called Nanoceuticals Slim Shake Chocolate.
According to company information posted on PEN's Web site, the canola oil, by Shemen Industries of Israel, contains an additive called "nanodrops" designed to carry vitamins, minerals and phytochemicals through the digestive system and urea.[ 93]
The shake, according to U.S. manufacturer RBC Life Sciences Inc., uses cocoa infused "NanoClusters" to enhance the taste and health benefits of cocoa without the need for extra sugar.[ 94]
Household
The most prominent application of nanotechnology in the household is self-cleaning or “easy-to-clean” surfaces on ceramics or glasses. Nanoceramic particles have improved the smoothness and heat resistance of common household equipment such as the flat iron.
Optics
The first sunglasses using protective and anti-reflective ultrathin polymer coatings are on the market. For optics, nanotechnology also offers scratch resistant surface coatings based on nanocomposites. Nano-optics could allow for an increase inprecision of pupil repair and other types of laser eye surgery. Textiles
The use of engineered nanofibers already makes clothes water- and stain-repellent or wrinkle-free. Textiles with a nanotechnological finish can be washed less frequently and at lower temperatures. Nanotechnology has been used to integrate tiny carbon particles membrane and guarantee full-surface protection from electrostatic charges for the wearer. Many other applications have been developed by research institutions such as the Textiles Nanotechnology Laboratory at Cornell University, and the UK's Dstl and its spin out company P2i.
Cosmetics
One field of application is in sunscreens. The traditional chemical UV protection approach suffers from its poor long-term stability. A sunscreen based on mineral nanoparticles such as titanium dioxide offer several advantages. Titanium oxide nanoparticles have a comparable UV protection property as the bulk material, but lose the cosmetically undesirable whitening as the particle size is decreased.
Agriculture
Applications of nanotechnology have the potential to change the entire agriculture sector and food industry chain from production to conservation, processing, packaging, transportation, and even waste treatment. NanoScience concepts and Nanotechnology applications have the potential to redesign the production cycle, restructure the processing and conservation processes and redefine the food habits of the people.
Major Challenges related to agriculture like Low productivity in cultivable areas, Large uncultivable areas,Shrinkage of cultivable lands, Wastage of inputs like water, fertilizers, pesticides, Wastage of products and of course Food security for growing numbers can be addressed through various applications of nanotechnology.More informa **
Medical use of nanomaterials
Drug delivery
Nanomedical approaches to drug delivery center on developing nanoscale particles or molecules to improve drug bioavailability. Bioavailability refers to the presence of drug molecules where they are needed in the body and where they will do the most good. Drug delivery focuses on maximizing bioavailability both at specific places in the body and over a period of time. This can potentially be achieved by molecular targeting by nanoengineered devices.[ 95] 96] It is all about targeting the molecules and delivering drugs with cell precision. More than $65 billion are wasted each year due to poor bioavailability. In vivo imaging is another area where tools and devices are being developed. Using nanoparticle contrast agents, images such as ultrasound and MRI have a favorable distribution and improved contrast. The new methods of nanoengineered materials that are being developed might be effective in treating illnesses and diseases such as cancer. What nanoscientists will be able to achieve in the future is beyond current imagination. This might be accomplished by self assembled biocompatible nanodevices that will detect, evaluate, treat and report to the clinical doctor automatically.
Drug delivery systems, lipid- or polymer-based nanoparticles, [ 97] can be designed to improve the pharmacological and therapeutic properties of drugs.[ 98] The strength of drug delivery systems is their ability to alter the pharmacokinetics and biodistribution of the drug. Nanoparticles have unusual properties that can be used to improve drug delivery. Where larger particles would have been cleared from the body, cells take up these nanoparticles because of their size. Complex drug delivery mechanisms are being developed, including the ability to get drugs through cell membranes and into cell cytoplasm. Efficiency is important because many diseases depend upon processes within the cell and can only be impeded by drugs that make their way into the cell. Triggered response is one way for drug molecules to be used more efficiently. Drugs are placed in the body and only activate on encountering a particular signal. For example, a drug with poor solubility will be replaced by a drug delivery system where both hydrophilic and hydrophobic environments exist, improving the solubility. Also, a drug may cause tissue damage, but with drug delivery, regulated drug release can eliminate the problem. If a drug is cleared too quickly from the body, this could force a patient to use high doses, but with drug delivery systems clearance can be reduced by altering the pharmacokinetics of the drug. Poor biodistribution is a problem that can affect normal tissues through widespread distribution, but the particulates from drug delivery systems lower the volume of distribution and reduce the effect on non-target tissue. Potential nanodrugs will work by very specific and well-understood mechanisms; one of the major impacts of nanotechnology and nanoscience will be in leading development of completely new drugs with more useful behavior and less side effects.
Cancer
A schematic illustration showing how nanoparticles or other cancer drugs might be used to treat cancer.
The small size of nanoparticles endows them with properties that can be very useful in oncology, particularly in imaging. Quantum dots (nanoparticles with quantum confinement properties, such as size-tunable light emission), when used in conjunction with MRI (magnetic resonance imaging), can produce exceptional images of tumor sites. These nanoparticles are much brighter than organic dyes and only need one light source for excitation. This means that the use of fluorescent quantum dots could produce a higher contrast image and at a lower cost than today's organic dyes used as contrast media. The downside, however, is that quantum dots are usually made of quite toxic elements.
Another nanoproperty, high surface area to volume ratio, allows many functional groups to be attached to a nanoparticle, which can seek out and bind to certain tumor cells. Additionally, the small size of nanoparticles (10 to 100 nanometers), allows them to preferentially accumulate at tumor sites (because tumors lack an effective lymphatic drainage system). A very exciting research question is how to make these imaging nanoparticles do more things for cancer. For instance, is it possible to manufacture multifunctional nanoparticles that would detect, image, and then proceed to treat a tumor? This question is under vigorous investigation; the answer to which could shape the future of cancer treatment.[ 99] A promising new cancer treatment that may one day replace radiation and chemotherapy is edging closer to human trials. Kanzius RF therapy attaches microscopic nanoparticles to cancer cells and then "cooks" tumors inside the body with radio waves that heat only the nanoparticles and the adjacent (cancerous) cells.
Sensor test chips containing thousands of nanowires, able to detect proteins and other biomarkers left behind by cancer cells, could enable the detection and diagnosis of cancer in the early stages from a few drops of a patient's blood.[ 100]
The basic point to use drug delivery is based upon three facts: a) efficient encapsulation of the drugs, b) successful delivery of said drugs to the targeted region of the body, and c) successful release of that drug there.
Researchers at Rice University under Prof. Jennifer West, have demonstrated the use of 120 nm diameter nanoshells coated with gold to kill cancer tumors in mice. The nanoshells can be targeted to bond to cancerous cells by conjugating antibodies or peptides to the nanoshell surface. By irradiating the area of the tumor with an infrared laser, which passes through flesh without heating it, the gold is heated sufficiently to cause death to the cancer cells.[ 101]
Nanoparticles of cadmium selenide (quantum dots) glow when exposed to ultraviolet light. When injected, they seep into cancer tumors. The surgeon can see the glowing tumor, and use it as a guide for more accurate tumor removal.
One scientist, University of Michigan’s James Baker, believes he has discovered a highly efficient and successful way of delivering cancer-treatment drugs that is less harmful to the surrounding body. Baker has developed a nanotechnology that can locate and then eliminate cancerous cells. He looks at a molecule called a dendrimer. This molecule has over one hundred hooks on it that allow it to attach to cells in the body for a variety of purposes. Baker then attaches folic-acid to a few of the hooks (folic-acid, being a vitamin, is received by cells in the body). Cancer cells have more vitamin receptors than normal cells, so Baker's vitamin-laden dendrimer will be absorbed by the cancer cell. To the rest of the hooks on the dendrimer, Baker places anti-cancer drugs that will be absorbed with the dendrimer into the cancer cell, thereby delivering the cancer drug to the cancer cell and nowhere else (Bullis 2006).[editorializing?] [102]
Surgery
At Rice University, a flesh welder is used to fuse two pieces of chicken meat into a single piece. The two pieces of chicken are placed together touching. A greenish liquid containing gold-coated nanoshells is dribbled along the seam. An infrared laser is traced along the seam, causing the two sides to weld together. This could solve the difficulties and blood leaks caused when the surgeon tries to restitch the arteries that have been cut during a kidney or heart transplant. The flesh welder could weld the artery perfectly.[citation needed]
Visualization
Tracking movement can help determine how well drugs are being distributed or how substances are metabolized. It is difficult to track a small group of cells throughout the body, so scientists used to dye the cells. These dyes needed to be excited by light of a certain wavelength in order for them to light up. While different color dyes absorb different frequencies of light, there was a need for as many light sources as cells. A way around this problem is with luminescent tags. These tags are quantum dots attached to proteins that penetrate cell membranes. The dots can be random in size, can be made of bio-inert material, and they demonstrate the nanoscale property that color is size-dependent. As a result, sizes are selected so that the frequency of light used to make a group of quantum dots fluoresce is an even multiple of the frequency required to make another group incandesce. Then both groups can be lit with a single light source.
Medical applications of molecular nanotechnology
Molecular nanotechnology is a speculative subfield of nanotechnology regarding the possibility of engineering molecular assemblers, machines which could re-order matter at a molecular or atomic scale. Molecular nanotechnology is highly theoretical, seeking to anticipate what inventions nanotechnology might yield and to propose an agenda for future inquiry. The proposed elements of molecular nanotechnology, such as molecular assemblers and nanorobots are far beyond current capabilities.
Nanorobots
The somewhat speculative claims about the possibility of using nanorobots[103] in medicine, advocates say, would totally change the world of medicine once it is realized. Nanomedicine would make use of these nanorobots (e.g., Computational Genes), introduced into the body, to repair or detect damages and infections. According to Robert Freitas of the Institute for Molecular Manufacturing, a typical blood borne medical nanorobot would be between 0.5-3 micrometres in size, because that is the maximum size possible due to capillary passage requirement. Carbon could be the primary element used to build these nanorobots due to the inherent strength and other characteristics of some forms of carbon (diamond/fullerene composites), and nanorobots would be fabricated in desktop nanofactories specialized for this purpose.
Nanodevices could be observed at work inside the body using MRI, especially if their components were manufactured using mostly 13C atoms rather than the natural 12C isotope of carbon, since 13C has a nonzero nuclear magnetic moment. Medical nanodevices would first be injected into a human body, and would then go to work in a specific organ or tissue mass. The doctor will monitor the progress, and make certain that the nanodevices have gotten to the correct target treatment region. The doctor will also be able to scan a section of the body, and actually see the nanodevices congregated neatly around their target (a tumor mass, etc.) so that he or she can be sure that the procedure was successful.
DNA nanotechnology
DNA nanotechnology is a branch of nanotechnology which uses the molecular recognition properties of DNA and other nucleic acids to create designed, artificial structures out of DNA for technological purposes. In this field, DNA is used as a structural material rather than as a carrier of genetic information, making it an example of bionanotechnology. DNA nanotechnology has applications in molecular self-assembly and in DNA computing.
DNA nanotechnology
DNA nanotechnology is a branch of nanotechnology which uses the molecular recognition properties of DNA and other nucleic acids to create designed, artificial structures out of DNA for technological purposes. In this field, DNA is used as a structural material rather than as a carrier of genetic information, making it an example of bionanotechnology. DNA nanotechnology has applications in molecular self-assembly and in DNA computing.
Although DNA is usually considered in the context of molecular biology, as the carrier of genetic information in living cells, DNA nanotechnology considers DNA solely as a chemical and as a material, and is usually pursued outside of any biological context.. DNA nanotechnology makes use of the fact that, due to the specificity of Watson-Crick base pairing, only portions of the strands which are complementary to each other will bind to each other to form duplex DNA. DNA nanotechnology attempts to rationally design sets of DNA strands so that desired portions of each strand will assemble in the correct positions to for some desired target structure.
Although the field is usually called DNA nanotechnology, its principles apply equally well to other nucleic acids such as RNA and PNA, and structures incorporating these have been made. For this reason the field is occasionally referred to as nucleic acid nanotechnology.
References
1. Cristina Buzea, Ivan Pacheco, and Kevin Robbie (2007). "Nanomaterials and Nanoparticles: Sources and Toxicity". Biointerphases 2: MR17. http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=BJIOBN00000200000400MR17000001&idtype=cvips&gifs=Yes.
2. N. Taniguchi (1974). On the Basic Concept of 'Nano-Technology. Proc. Intl. Conf. Prod. London, Part II British Society of Precision Engineering.
3. Eric Drexler (1991). Nanosystems: Molecular Machinery, Manufacturing, and Computation. MIT PhD thesis. New York: Wiley. ISBN 0471575186. http://www.e-drexler.com/d/06/00/Nanosystems/toc.html.
5. Rodgers, P. (2006). "Nanoelectronics: Single file". Nature Nanotechnology. doi:10.1038/nnano.2006.5.
6. 22
7. Lubick, N. (2008). Silver socks have cloudy lining. Environ Sci Technol. 42(11):3910
12. Regan, BC; Aloni, S; Jensen, K; Ritchie, RO; Zettl, A (2005). "Nanocrystal-powered nanomotor.". Nano letters 5 (9): 1730–3. doi:10.1021/nl0510659. PMID 16159214. http://www.physics.berkeley.edu/research/zettl/pdf/312.NanoLett5regan.pdf.
13. Regan, B. C.; Aloni, S.; Jensen, K.; Zettl, A. (2005). "Surface-tension-driven nanoelectromechanical relaxation oscillator". Applied Physics Letters 86: 123119. ….doi:10.1063/1.1887827.http:/www.lbl.gov/science- .Articles/Archive/sabl/2005/May/Tiniest-Motor.pdf.
15. Clarkson, AJ; Buckingham, DA; Rogers, AJ; Blackman, AG; Clark, CR (2004). "Nanostructured Ceramics in Medical Devices: Applications and Prospects". JOM 56 (10): 38–43. doi:10.1007/s11837-004-0289-x. PMID 11196953.
16. _Levins, Christopher G.; Schafmeister, Christian E. (2006). "The Synthesis of Curved and Linear Structures from a Minimal Set of Monomers.". ChemInform 37. doi:10.1002/chin.200605222.
17. _"Applications/Products". National Nanotechnology Initiative. http://www.nano.gov/html/facts/appsprod.html. Retrieved 2007-10-19.
18. "The Nobel Prize in Physics 2007". Nobelprize.org. http://nobelprize.org/nobel_prizes/physics/laureates/2007/index.html. Retrieved 2007-10-19.
19. Das S, Gates AJ, Abdu HA, Rose GS, Picconatto CA, . ….Ellenbogen JC. (2007). "Designs for Ultra-Tiny, Special-….Purpose Nanoelectronic Circuits". IEEE Transactions on. ….Circuits and Systems I 54 (11): 2528–2540. doi: 20. Holton, G. and S. G. Brush. Introduction to Concepts and ……Theories in Physical Science, 2/e (Princeton University
……Press, 1985).
21. Turkevich, J., Gold Bull. 18 (1985) 86 as cited in reference 4.
22. Cao, G. Nanostructures & Nanomaterials: Synthesis, . …….Properties, & Applications (Imperial College Press, 2004).
23. Langmuir, I. J. Faraday Soc. 15 (1920) 6.
24. http://www.zyvex.com/nanotech/feynman.html (accessed ......12 October 2006)
25. Waterman, A. T. American Scientist, March 1961, 1-8.
26. Gladwell, M. The Tipping Point: How Little Things Can ……..Make a Difference (Back Bay Books, 2002).
27. http://www.intel.com/technology/silicon/mooreslaw/ ……(accessed 12 October 2006)
28. Binnig, G. and H. Rohrer. Rev. Mod. Phys. 59 (1987) 615-…….625.
29. Meyer, E., H. J. Hug, and R. Bennewitz. Scanning Probe …… …….Microscopy: The Lab on A Tip (Springer, 2003).
30. Eigler, D. M. and E. K. Schweizer. Nature 344 (1990) 524.
31. Rief, M., F. Oesterhelt, B. Heymann, and H. E. Gaub. …….Science 275 (1997) 1295-7.
32. Harris, C. Anal. Chem. 75 (2003) 223A-228A.
33. Schulz, M. Nature 399 (1999) 729-730.
34. http://www.nano.gov/ (accessed 12 October 2006)
35. , S. M., A. W. Ott, and J. W. Klaus. J. Phys. Chem. 100 ……(1996) 13121-13131.
36. Ulman, A. An Introduction to Ultrathin Organic Films: From ……Langmuir-Blodgett to Self-assembly (Academic
……Press, N. Y., 1991).
37. Enriquez, E. P. Kimika 14 (1998) 1-9.
38. Bain, C. D. , D. B. Troughton, Y. Tao, J. Evall, R. G. Nuzzo, …….and G. M. Whitesides. J. Am. Chem. Soc. 111 (1989)
…….321.
39. Borman, S. Chemical & Engineering News 81 (2003) 54.
40. Ulman, A. An Introduction to Ultrathin Organic Films: …….From Langmuir-Blodgett to Self-assembly (Academic
…….Press, N. Y., 1991).
41. Gates, B., Q. Xu, M. Stewart, D. Ryan, C. Grant Wilson, and …….G. M. Whitesides. Chem. Rev. 105 (2004) 1171-1196.
42. Ginger, D. S., H. Zhang, and C. A. Mirkin. Angewandte ……..Chemie Int'l Ed. 43 (2003) 30-45.
43. Salaita, K., Y. Huang, J. Fragala, R. A. Vega, C. Lui, and C. A. ……..Mirkin. Angewandte Chemie, 26Sep 2006 (on line).
44. Burda, C., X. Chen, R. Narayanan, and M. A. El-Sayed. ……..Chem. Rev. 105 (2005) 1025-1102.
45. Leff, D. V., P. C. Ohara, J. R. Heath, and W. M. Gelbart. J. ……..Phys. Chem. 99 (1995) 7036-7041.
46. Enriquez, E. P. and A. K. A. Aliganga, in Proceedings of the …….DOST-JSPS Workshop on Polymers and Materials
…….Chemistry (Ateneo Office of Research and Publications, …….(1998).
47. Murray, C. B., D. J. Norris, and M. G. Bawendi. J. Am. ……..Chem. Soc. 115 (1993) 8706-8715.
48. Murray, C. B., C. R. Kagan, M. G. Bawendi. Annu. Rev. …….Mater. Sci. 30 (2000) 545 as cited in reference 4.
49. http://www.homehealth-uk.com/index.html (accessed 12 ......October 2006). See for example: http://www.homehealth-
…….uk.com/medical/pregnancytest.htm.
50. Daniel, M-C., D. Astruc. Chem. Rev. 104 (2004) 293-346.
51. Han, M. S., A. K. R. Lytton-Jean, and C. A. Mirkin. J. Am. ……..Chem. Soc. 128 (2006) 4954-4955.
52. Elechiguerra, J. L., J. L. Burt, J. R. Morones, A. C-Bragado, X. ……..Gao, H. H. Lara, and M. J. Yacaman. J.
……..Nanobiotechnology\ 3:6 (2005).
53. Pan, Z. W., Z. R. Dai, and Z. L. Wang. Science 291 (2001) ……..1947-1948.
54. Sun, Y., B. Gates, B. Mayers, and Y. Xia. Nano Lett. 2 …….(2002) 165-168.
55. http://www.intel.com/technology/silicon/si08042.htm .......(accessed 12 October 2006).
56. Bjorkholm, J. E. “EUV Lithography—The Successor to ……..Optical Lithography? In
……..http://www.intel.com/technology/itj/q31998/pdf/euv.pdf …….(accessed 12 October 2006).
57. Schneider, H. J. and A. K. Yatsimirski. Principles and ……..Methods in Supramolecular Chemistry (Wiley, 2000).
58. Podsiadlo, P., S. Paternel, J. M. Rouillard, Z. Zhang, J. Lee, J. …….W. Lee, E. Gulari, and N. A. Kotov. Langmuir 21
…….(2005) 11915-11921.
59. Schevchengko, E. V., D. V. Talapin, C. B. Murray, and S. …….O.'Brien. J. Am. Chem. Soc. 128 (2006) 3627.
60. Krishnamoorthy, S., C. Hinderling, and H. Heinzelmann. …….Materials Today 9 (2006) 40-47.
61. Choi, W., S. J. Hong, Y-S. Chang, and Y. Cho. Environ. Sci. ……..Technol. 34 (2000) 4810-4815.
62. A. K. Aliganga and E. P. Enriquez, Proceedings of the16th ……..Philippine Chemistry Congress, 2000.
63. Bisquert, J., D. Cahen, G. Hodes, S. Rühle, and A. Zaban. J. ……..Phys. Chem. B 108 (2004) 8106-8118.
64. Mor, G. K., K. Shankar, M. Paulose, O. K. Varghese, and C. ……..A. Grimes. Nano Lett. 6 (2006) 215-218.
65. Martines, E., K. Suenarine, H. Morgan, N. Gadegaard, …….C.D.W. Wilkinson, and M. O. Riehle. Nano Lett 5 (2005)
67. Gall, John, (1986) Systemantics: How Systems Really ……Work and How They Fail, 2nd ed. Ann Arbor, MI : The ……General Systemantics Press.
68.^ Richard Dawkins, The Blind Watchmaker: Why the ……Evidence of Evolution Reveals a Universe Without Design, ……W. W. Norton; Reissue edition (September 19, 1996)
69. Mintmire, J.W.; Dunlap, BI; White, CT (3 February …...1992). "Are Fullerene Tubules Metallic?". Physical Review ……Letters 68 (5): 631–634. doi:10.1103/PhysRevLett.68.631. …...PMID 10045950. "Carbon nanotubes as molecular …..
70. Dekker, Cees (1999). quantum wires" (PDF). Physics Today …..52: 22–28. …..doi:10.1063/1.882658. …..http://www.physicstoday.org/vol-......56/iss-…..2/pdf/vol52no5p22-28.pdf.
71. Martel, R.; Derycke, V.; Lavoie, C.; Appenzeller, J.; Chan, …..K. K.; Tersoff, J.; Avouris, Ph. (2001). "Ambipolar ……Electrical Transport in Semiconducting Single-Wall ……Carbon Nanotubes". Physical Review Letters 87: 256805. ……..doi:10.1103/PhysRevLett.87.256805.
74. Flahaut, E.; Bacsa, R; Peigney, A; Laurent, C (2003). ….."Gram-Scale CCVD Synthesis of Double-Walled Carbon ……Nanotubes". Chemical Communications 12 (12): 1442–…..1443. doi:10.1039/b301514a. PMID 12841282.
75. ^ a b Liu, Lei; Guo, G. Y.; Jayanthi, C. S.; Wu, S. Y. (2002). …..."Colossal Paramagnetic Moments in Metallic Carbon … ……Nanotori". Physical Review Letters 88: 217206. …….doi:10.1103/PhysRevLett.88.217206.
76. Huhtala, Maria (2002). "Carbon nanotube structures: …...molecular dynamics simulation at realistic limit"76 …..(PDF). Computer Physics Communications 146: 30. ……doi:10.1016/S0010-4655(02)00432-0. …..http://www.princeton.edu/~msammalk/publications/cpc146_......02.pdf.
77. Liu, Q; Ren, W; Chen, Z; Yin, L; Li, F; Cong, H; Cheng, H …..(2009). "Semiconducting properties of cup-stacked carbon …..nanotubes". Carbon 47: 731. …..doi:10.1016/j.carbon.2008.11.005. …..http://carbon.imr.ac.cn/file/Journal/2009/1249016438117.pdf
78. ^ "A Better Way to Make Nanotubes". Berkeley Lab.. …..January 5, 2009. http://newscenter.lbl.gov/feature-.....stories/2009/01/05/better-way-to-make-nanotubes/.
79. ^ "Carbon Nanohoops: Shortest Segment of a Carbon …..Nanotube Synthesized". Berkeley Lab.. …...http://www.lbl.gov/msd/assets/docs/highlights/09-…..Bertozzi.pdf.
80. ^ "Synthetic organic chemistry". A centre of chemistry ……excellence. Nature. October 7, 2009. …….http://www.nature.com/naturejobs/2009/091008/full/nj0264…..html#a-centre-of-chemistry-excellence.
81. ^ Zhao, X.; Liu, Y.; Inoue, S.; Suzuki, T.; Jones, R. O.; …..Andol, Y. (2004). "Smallest Carbon Nanotube is 3 Å in …..Diameter". Physical Review Letters 92 (12): 125502. ……doi:10.1103/PhysRevLett.92.125502. PMID 15089683.
82. ^ Hayashi, Takuya; Kim, Yoong Ahm; Matoba, Toshiharu; …..Esaka, Masaya; Nishimura, Kunio; Tsukada, Takayuki; …..Endo, Morinobu; Dresselhaus, Mildred S. (2003). "Smallest …..Freestanding Single-Walled Carbon Nanotube". Nano …..Letters 3 (7): 887–889. doi:10.1021/nl034080r.
83. ^ Guan, Lunhui; Suenaga, Kazu; Iijima, Sumio (2008). ….."Smallest Carbon Nanotube Assigned with Atomic …..Resolution Accuracy". Nano Letters 8 (2): 459–462. ……doi:10.1021/nl072396j. PMID 18186659.
84. ^ University of Waterloo, Nanotechnology in Targeted …..Cancer Therapy, …….http://www.youtube.com/watch?v=RBjWwlnq3cA 15 …..January 2010
85. ^ Press Release: American Elements Announces P-Mite …..Line of Platinum Nanoparticles for Catalyst Applications, …..October 3, 2007
88. ^ Hillie, Thembela and Mbhuti according to sunil this …..method of catalysis will surely improve the performances of …..the old catalysis methodsHlophe. "Nanotechnology and the …..challenge of clean water." …..Nature.com/naturenanotechonolgy. November 2007: …..Volume 2.
89. ^ Hillie, Thembela; Hlophe, Mbhuti (2007). ….."Nanotechnology and the challenge of clean water". Nature …..Nanotechnology 2 (11): 663–664. ……doi:10.1038/nnano.2007.350. PMID 18654395.
90. ^ Waldner, Jean-Baptiste (2007). Nanocomputers and …...Swarm Intelligence. London: ISTE. p. 26. …….ISBN 1847040020.
92. ^ Suresh Neethirajan, Digvir Jayas. 2009. Nanotechnology …..for food and bioprocessing industries. 5th CIGR …..International Technical Symposium on Food Processing, …..Monitoring Technology in Bioprocesses and Food Quality …..Management, Postdam, Germany. 8 p.
93. ^ Canola Active Oil …….http://www.nanotechproject.org/inventories/consumer/brow…..se/products/canola_active_oil/
94. ^ Nano-foods: The Next Consumer Scare? …….http://www.islamonline.net/servlet/Satellite?c=Article_C&p…..agename=Zone-English-…..HealthScience%2FHSELayout&cid=1216208224637
95. ^ LaVan DA, McGuire T, Langer R. (2003). "Small-scale ……systems for in vivo drug delivery". Nat Biotechnol. 21 (10): ….1184–1191. doi:10.1038/nbt876. PMID 14520404.
96. ^ Cavalcanti A, Shirinzadeh B, Freitas RA Jr, Hogg T. …..(2008). "Nanorobot architecture for medical target …… …….identification". Nanotechnology 19 (1): 015103(15pp). …….doi:10.1088/0957-4484/19/01/015103.
97. ^ Nie, Shuming, Yun Xing, Gloria J. Kim, and Jonathan W. …...Simmons (2007). "Nanotechnology Applications in …...Cancer". Annual Review of Biomedical Engineering 9: 257. …….doi:10.1146/annurev.bioeng.9.060906.152025. …….PMID 17439359.
98. ^ Zheng G, Patolsky F, Cui Y, Wang WU, Lieber CM. …..(2005). "Multiplexed electrical detection of cancer markers ……with nanowire sensor arrays". Nat Biotechnol. 23 (10): ….1294–1301. doi:10.1038/nbt1138. PMID 16170313.
99. ^ Loo C, Lin A, Hirsch L, Lee MH, Barton J, Halas N, West …….J, Drezek R. (2004). "Nanoshell-enabled photonics-based ……..imaging and therapy of cancer". Technol Cancer Res Treat. ……3 (1): 33–40. PMID 14750891. 100. ^ Shi X, Wang S, Meshinchi S, Van Antwerp ME, Bi X, ……Lee I, Baker JR Jr. (2007). "Dendrimer-entrapped gold …...nanoparticles as a platform for cancer-cell targeting and …...imaging". Small 3 (7): 1245–1252. ……doi:10.1002/smll.200700054. PMID 17523182.
.
101. ^ a b Nanomedicine, Volume IIA: Biocompatibility, by ……Robert A. Freitas Jr. 2003, ISBN 1570597006
102. ^ Freitas, Robert A., Jr.; Havukkala, Ilkka (2005). ……"Current Status of Nanomedicine and Medical ……..Nanorobotics". Journal of Computational and Theoretical ……Nanoscience 2: 1–25. doi:10.1166/jctn.2005.001.
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