The extensive research, interdisciplinary efforts and public awareness has really made nanotechnology the most “sought after” field. In last decade or so nanotechnology has successfully emerged into an independent branch of study and there has been a constant rise in the expectations of people from the scientific community and general public alike. Scientists suggest that the recent achievements are just the tip of an iceberg and believe that there’s lot more to come. Infact, some science enthusiasts like to refer to it as the “technology of next century”.
Origins of Nanotechnology
This much hyped field of nanotechnology as many believe is not entirely new and unheard of. In fact, the importance of nanotechnology was first pointed out by Feynman as early as 1959, in his much cited lecture entitled “There’s plenty of room at the bottom”. Through this lecture he had put forward a vision which is recently coming to realization. With the recent advances in fabricating and characterization techniques, nanotechnology research as taken great strides. Throughout various fields of science and technology, a push towards the use of nano-scale technology is well underway. Moreover, nanotechnology is being hailed as the technology with the potential to revolutionize our industries and our daily lives. So, what is so unique about nanotechnology that gives it such great potentials?
Properties of Nanoscale Materials
The uniqueness of this field comes from the properties exhibited by nanoscale materials. It has been said that a nanometer is a magical point on the length scale, for this is the point where the properties of material significantly differ from those of atoms as well as bulk materials. And scientists have now found ways of exploiting the potential of this “size dependent change in properties” (nano-phenomenon). The effect of this size dependency is seen on properties including optical properties, magnetic properties, melting points, specific heats, electrical properties, surface reactivities, etc. and the reason behind this so called nano-phenomenon can be explained by studying the science behind it.
So How Do We Explain This Science?
Chemistry is the study of atoms and molecules, the dimensions of which are generally less than one nanometer, while condensed matter physics deals with solids of essentially an infinite array of bound atoms and molecules of dimensions greater than 100nm. Thus, leaving a big undefined gap between the two regimens, which deals with particles ranging from 1-100nm, or about 10 to106 atoms or molecules per particle. This nanoscale regime cannot be appropriately defined by either quantum chemistry or classical laws of physics.
Effects Observed in This Nanoscale Regime
Changes in The Total Energy Of The System
The energy of the system is imparted to it by the collective energies of electronic states of the matter and the energy levels of all the electronic states tend to lie in harmony. And as we all know the energies of electronic states depend on 1/L2, where L is the dimension of the system in that particular direction. Moreover, the spacing between successive energy levels also varies as 1/L2. Hence, the variation in the length scale of a system (numbers of atoms in a system) will result in significant variation in the energies and energy separations of the individual electronic states. Furthermore, as the system size decreases the allowed energy bands becomes substantially narrower than in bulk solid leading to distortion of normal collective (i.e. delocalized) electronic properties of the solid and the electron in the reduced dimensional system tend to behave more like the ‘particle in a box’ or what is referred to as “quantum confinement” affecting the electronic transitions and the properties associated with it. Furthermore, the energy levels are much more discrete in systems with nano dimensions.
In case of semiconductors such as Si, CdS etc. the band gaps (the energy required to promote an electron from the valence band to the conduction band) changes. In case where the band gap is in visible spectrum, this change in band gap results in difference in optical properties.
In case of magnetic materials such as Fe, Ni, Co etc, the change in the total energy of the system affects the coercive force (or magnetic memory) needed to reverse the internal magnetic field within the particle. Thus, this leads to variation in magnetic properties of materials.
Changes in The Structure Of The System
The structure of the systems depends on the arrangement of atoms or molecules. The dimensions of the material can influence the arrangement of atoms. When we go to nanometer scale length the number of atoms exposed at the surface changes significantly. Consider for example that a 3nm particle has 50% of its atoms on the surface, whereas a 10nm particle has just 20% and a 30nm only 5%. This change in the structure leads to relative increase in the defect states (i.e the difference in the behaviour of atoms at the surface which is due to the difference in the bonding on each side of the atom) of a material. Thus in case of nanomaterials, the defects states dominates due to increase in the fractions of surface atoms resulting in display of properties which are quite different from bulk.
The optical properties are generally influenced by the surface plasmons (i.e. collective excitation of surface electrons) and excitons (the equilibrium bond association of electron with its excited and ground levels governed by coulombs attraction). As we go down the size scale, a significant alteration in surface plasmon and excitons occurs, thus affecting the optical properties.
The reactivity of any material is determined by the surface morphologies and surface energies. At nanometer scale length the significant increase in the free energy of the surface and also the exposed surface area translates to enhanced intrinsic surface reactivities. The change in the structure of the system at nano level also results in changes in melting points and specific heat changes.
The recent studies in nanotechnology have resulted in greater promises for future and the potentials of this field are yet to be explored to the fullest. Scientific communities from not-so related fields are coming together to give shape to a brighter future of science with nanotechnology as the main theme. The potentials of nanotechnology are based upon the exciting science behind the nano-phenomenon. Much deeper insights and detailed studies can further improve our understating of this nano-phenomenon, which can then be applied to explore the field comprehensively.