Textbook of Nanoscience and Nanotechnology

Materials have been of great interest to human beings since time immemorial. A few million years ago, it was found that rocks could be used to break things that were impossible to break with bare hands. Stones were the first tools and even today they are still in use in kitchens and laboratories to pound and grind, or as mortars and pestles. Around 5000–6000 years ago, it was accidentally discovered that when a rock containing copper was placed on a fire, molten copper could be collected. This discovery led to the reduction of metal ores to produce metals for the fabrication of items from ploughshares to swords. New materials with greater hardness and longer use than stone became available for making tools. Our growth and progress have paralleled the development of metals and metallurgy.

As we approach nanoscale dimensions, we move closer to the atomic or molecular scales. Atoms are the building blocks of all matter. They can be assembled in many ways to obtain the desired product. Both the chemistry and the geometric arrangement of atoms can influence the properties of the material. Hence, if we have the ability to construct matter, atom by atom, we would be able to perform wonders. For example, we know that both graphite and diamond are made of pure carbon. Thus, in principle, if we are able to rearrange the atoms (carbon) in graphite at our discretion, it would be possible to make diamond! Or, if we could rearrange the atoms (silicon and oxygen) in sand (and add a few other trace elements), it should be possible to make a computer chip! Engineering at the nano-level can bring about large changes in the properties of the products. In Chapter 1, we saw how the high defect concentration in nanomaterials results in novel and unique physical, chemical, elastic and mechanical properties of this class of materials. A few of these are highlighted in this chapter.

There are different ways of classifying the synthesis routes for nanostructured materials. One of them is based on the starting state of material, namely, gas, liquid and solid. Techniques such as vapour condensation [physical vapour deposition (PVD) and chemical vapour deposition (CVD) and variants of these techniques] use the gaseous state of matter as the starting material for synthesizing nanoparticles. Techniques such as sol-gel, chemical and electrochemical (electrolytic) deposition and rapid solidification processing use liquids as the starting material. Severe plastic deformation processes such as high-energy ball milling, equichannel angular extrusion, etc., and nano-lithography, start with solids for synthesizing nanocrystalline materials.

Historically, there are several recorded instances of technologies that have revolutionized human civilization. From the invention of automobile wheels to the printing press, technological revolutions have resulted in remarkable improvement in the quality of life and have eventually led to societal transformations. With nanotechnology promising to impact almost every sector (Fig. 4.1), it is popularly believed that this could be the next revolution.

The characterization of small structures or small-sized materials in the nanometric-scale usually calls for sophisticated characterization tools. Characterization of nanomaterials and nanostructures has been largely based on certain critical advancement of conventional characterization methods developed for bulk materials. For example, X-ray diffraction (XRD) has been widely used for the determination of crystalline character, crystallite size, crystal structures and lattice constants of nanoparticles, nanowires and thin films. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM), together with electron diffraction, have been commonly used in the characterization of nanoparticles to get an idea of the size, shape and defects present in these materials.

Materials development has remained the backbone of human civilization and will continue to be the anchor for all future developments. The development of new materials and advanced material technologies has served as the cradle for most engineering developments. Revolutions in the communication, computing, energy, chemical, transport and engineering industries have been possible only due to credible advances in materials technology and the development of new classes of materials. As discussed in earlier chapters, nanomaterials are slowly beginning to make their presence felt in science and technology. The potential engineering applications of nanomaterials are vast. This chapter will describe only a few typical nanostructured materials of current interest. One extreme end of nanostructures is single electron transistors. Figure 6.1 shows an example of a single electron transistor with niobium leads and aluminium islands.

One of the most oft quoted but extremely important sayings can be traced to the late physicist Richard A Feynmann. The expression “There is plenty of room at the bottom”, captured the minds of generations of scientists and triggered a whole new science and revolutionary technology. Nearly five decades after Feynman's lecture, nanotechnology enhanced products are increasingly used in routine as well as high-end cutting-edge technology applications. More exciting possibilities exist in biomedical, energy and environmental related applications. Nanoengineered materials have witnessed extensive application in pollution control, purification and desalination of water and in effective waste management of hazardous by-products. It is a popular belief that the nano-revolution is set to have a far larger global econo-techno-political impact than the industrial revolution of the nineteenth century or the information technology revolution of the twentieth century.