1.2 The Significance of the Nanoscale
The promise and essence of the nanoscale science and technology is based on the fact that materials at the nanoscale have properties (i.e. chemical, electrical, magnetic, mechanical and optical) quite different from the bulk materials. Some of such properties are intermediate between properties of the smallest elements from which they can be composed of and those of the macroscopic materials. Compared to bulk materials, nanoparticles possess enhanced performance properties when they are used in similar applications. Surface morphology, surface to volume ratio and electronic properties of materials could change appreciably due to particle size changes. Composites made from nanoparticles of ceramics or metals can suddenly become much stronger than that predicted by existing materials science models. For example, metals with a so called grain size of around 10 nanometers are as much as seven times harder and tougher than their ordinary counterparts with grain sizes in the hundreds of nanometers.
Fig. 1.1: Scale of things
Nanoscale is a magical point on the dimensional scale. Structures in nanoscale (called nanostructures) are considered as the borderline of the smallest of man made devices and the largest molecules of living systems. The ability to control and manipulate nanostructures will make it possible to exploit new physical, biological and chemical properties of systems. There are many specific reasons why nanoscale has become so important, some of which are as the following:
(i) The quantum mechanical effects come into play at very small dimensions. By designing materials at the nanoscale, it is possible to vary the fundamental properties of materials, such as electrical, optical, mechanical and magnetic without changing their chemical composition.
(ii) Nanodevices with bio-recognition properties provide tools at nanoscale, which offers a tremendous opportunity to study biochemical processes and to manipulate living cells at single molecule level. The synergetic future of nanotechnologies hold great promise for further advancement in tissue engineering, prostheses, pharmacogenomics, surgery and general medicine.
Nanoscale components have very high surface to volume ratio, making them ideal for use in composite materials, reacting systems, drug delivery and chemical energy storage. Since atom is very close to the surface or interface, behaviour of atoms at these higher-energy sites have a significant influence on the properties of the material. For example, the reactivity of a metal catalyst particle generally increases appreciably as its size is reduced. It is interesting that macroscopic gold is chemically inert, whereas at nanoscales gold becomes extremely reactive and catalytic, and even melts at a lower temperature. The larger surface area allows more chemicals to interact with the catalyst simultaneously, which makes the catalyst more effective.
Macroscopic systems made up of nanostructures can have much higher density than those made up of microstructures. They can also be better conductors of electricity. This can result in new electronic device concepts, smaller and faster circuits, more sophisticated functions and greatly reduced power consumption.
The new generations of scientific tools that operate in nanoscale enable to collect data and to manipulate atoms and molecules on a very small scale. With these tools, it is found that many familiar materials act differently and have different characteristics and properties when they are in nanoscale quantities. Moreover, materials at the nanoscale can exhibit surprising characteristics that are not seen at large scales. For instance:
Carbon in the form of graphite (like pencil lead) is soft and malleable; at the nano-scale, carbon can be stronger than steel and is six times lighter. Also, carbon atoms in the form of a nanotube exhibit tensile strength 100 times than that of steel.
Collections of gold particles can appear orange, purple, red or greenish, depending upon the specific size of the particles making up the sample.
Zinc oxide is usually white and opaque; however, at the nano-scale it becomes transparent.
Aluminum can spontaneously combust at the nano-scale and could be used in rocket fuel.
Nano-scale copper becomes a highly elastic metal at room temperature. It can be stretch up to 50 times its original length without breaking.
Researchers hope to imitate nature’s secrets of building from the nanoscale, to create processes and machinery. They have already copied the nanostructure of lotus leaves to create water repellent surfaces, being used to make stain free clothing and materials. Human bodies and those of all animals use natural nanoscale materials, such as proteins and other molecules, to control many systems and processes in it. A typical protein, haemoglobin, which carries oxygen through the bloodstream, is 5 nanometers in diameter. That is, many important functions of living organisms take place at the nanoscale.
1.3 History of Nanotechnology
Humans have unwittingly employed nanotechnology for thousands of years, but it is not clear when they first began to use the advantage of nanophase materials. In the fourth century Roman glass workers were fabricating glasses containing nano metals. A cup, called Lycurgus cup (depicts the death of King Lycurgus) made during this period is exhibited at the British Museum in London. This is made from soda lime glass containing silver and gold nanoparticles. The colour of the cup changes from green to red when a source of light is placed inside it. The beautiful colours of the windows of medieval churches are also due to the presence of metal nanoparticles in the glass. During the 10th century, nanoscale gold was used in stained glass and ceramics.
In 1661, Irish chemist Robert Boyle questioned Aristotle’s belief that matter is composed of earth, fire, water and air. He suggested that tiny particles of matter combine in various ways to form corpuscles. Michael Faraday published a paper in the Philosophical Transactions of the Royal Society in 1857, which explained how metal particles affect the colour of glass windows of churches. In German journal Annalen der Physik (1908), Gustav Mie reported an explanation of the dependence of the colour of the glasses on metal size. James Clerk Maxwell in 1867 mentioned some of the distinguishing concepts in nanotechnology and proposed a tiny entity known as “Maxwell’s Demon”. He also produced the first colour photograph that depends on production of silver nanoparticles sensitive to light in 1861.
Chemical catalysis is an example of “old nanotechnology”. Today, catalysts speed up thousands of chemical transformations like those that convert crude oil into gasoline, small organic chemicals into life-saving drugs and polymers, and cheap graphite into synthetic diamond for making industrial cutting tools. Most catalysts were discovered by trial and error – by “shaking and baking” metals and ceramics, and then seeing how the result affects the reactions and their products.
Scientists have been studying and working with nanoparticles for centuries, but the effectiveness of their work has been hampered by their inability to see the structure of nanoparticles. The development of microscopes capable of displaying particles as small as atoms has allowed scientists to see what they are working with. The first observations and size measurements of nano-particles were made during first decade of 20th century by Richard Adolf Zsigmondy. He made detailed study of gold sols and other nanomaterials with sizes down to 10 nm and less. He used ultramicroscope that employs dark field method for seeing particles with sizes much less than wavelength of light. Zsigmondy was the first who used nanometer explicitly for characterizing particle size. He determined it as 1/1,000,000 of millimeter. He developed a first system classification based on particle size in nanometer range. There have been many significant developments during 20th century in characterizing nanomaterials and related phenomena, belonging to the field of interface and colloid science. In the 1920s, Irving Langmuir and Katharine B. Blodgett introduced the concept of a monolayer, a layer of material one molecule thick. Langmuir won Nobel Prize in chemistry for his work.
The concept of controlling matter at the atomic level-which is at the heart of nanotechnology’s promise-was first publicly articulated in 1959 by physicist Richard P. Feynman in his speech entitled, “There’s Plenty of Room at the Bottom – An Invitation to Enter a New Field of Physics.” He delivered this lecture at the annual meeting of the American Physical Society at the California Institute of Technology, Pasadena, CA, on 29th December, 1959. He envisioned the possibility and potential of nanotechnology. His lecture was published in the February (1960) issue of Engineering & Science quarterly magazine of California Institute of Technology.
“A biological system can be exceedingly small. Many of the cells are very tiny, but they are very active; they manufacture various substances; they walk around; they wiggle; and they do all kinds of marvelous things – all on a very small scale. Also, they store information. Consider the possibility that we too can make a thing very small which does what we want – that we can manufacture an object that maneuvers at that level.”
(Richard P. Feynman, 1959)
Feynman in his talk described how the laws of nature do not limit our ability to work at the molecular level, atom by atom. It is important to note that almost all of the ideas presented in Feynman’s lecture and even more, are now under intensive research by numerous nanotechnology investigators all over the world. In his lecture Feynman challenged the scientific community and set a monetary reward to demonstrate experiments in support of miniaturizations. Feynman proposed radical ideas about miniaturizing printed matter, circuits, and machines. “There’s no question that there is enough room on the head of a pin to put all of the Encyclopedia Britanica” he said. He also predicted that a library with all the world’s books would fit in a pamphlet in our hand. Many of Feynman’s speculations have become reality today. However, his thinking did not resonate with researchers at the time. Richard P. Feynman was awarded the Nobel Prize in physics in 1965 for his contributions to quantum electrodynamics.
The term “nanotechnology” was first coined by Japanese researcher Nario Taniguchi in 1974, to describe engineering at length scales less than a micrometer. The futurist K. Eric Drexler is widely credited with popularizing the term in the mainstream. In his books, “Engines of Creation” (1986), Drexler envisioned a world in which tiny machines or “assemblers” are able to build other structures with exquisite precision by physically manipulating individual atoms. If such control is technically achievable, atom-by-atom construction of larger objects can be a whole new way of making materials and will have the capacity to usher in a second industrial revolution with even more profound societal impacts than the first one.
Ralph Landauer (1957), a theoretical physicist working for IBM presented his ideas on nanoscale electronics and recognized the importance of quantum mechanical effects on such devices. Molecular beam epitaxy, invented by Alfred Cho and John Arthur at Bell Labs in 1968, enabled the controlled deposition of single atomic layers. In 1981Â Gerd BinnigÂ andÂ Heinrich RohrerÂ developed theÂ scanning tunneling microscopeÂ atÂ IBM’s laboratories in Switzerland. This tool enables scientists to image the position of individual atoms on surfaces. For this work Binnig and Rohrer were awarded Nobel PrizeÂ in 1986. In 1985, Robert F. Curl Jr., Harold W. Kroto and Richard E. Smalley discovered buckminsterfullerence (buckyballs) which are soccer ball shaped molecules made up of carbon. Buckyball is the third known form of pure carbon after diamond and graphite. These three scientists were awarded Nobel Prize in Chemistry (1996). Sumio Iijima working for NEC Corporation, Japan discovered carbon nanotubes in 1991, while researching buckyballs using an electron microscope.
Feynman’s challenge for miniaturization and his unerringly accurate forecast was met forty years later (1999) by a team of scientists using a nanotechnology tool called Atomic Force Microscope (AFM) to perform Dip Pen Nanolithography (DPN). Some of the important achievements which Feynman mentioned in his 1959 lecture included the manipulation of single atoms on a silicon surface, positioning single atoms with a Scanning Tunneling Microscope (STM) and the trapping of single, 3 nm in diameter, colloidal particles from solution using electrostatic methods. A few examples of nanomaterials are shown in figure 1.2.
Fig. 1.4: Examples of nanomaterials; (a) Buckyball, (b) SWNT, (c) MWNT,
(d) Diamondoid and (e) Nanoshell