ABSTRACT
During the last few years nanostructured materials and devices have attracted a great deal of scientific and technological attention.1-3 The properties of nanostructures are strongly influenced by quantum effects. They exhibit novel optical, magnetic, and electronic properties, and present the perspective of designing and tuning materials properties with exceptional flexibility and control. Nanostructured materials are of enormous interest, from the point of view of discovering new physical phenomena as well as their exploitation possibilities in novel devices. As the size and dimensionality of a material decrease, its electronic structure and properties change tremendously due to the reduction in the density of states and the effective length scale of electronic motion. Now the energy levels of material are determined mostly by the material’s surface. This results in a transition from the bulk band structure to individual localized energy levels and hence the onset of quantum confinement effects. Because of the size-induced change in the electronic structure, optical properties of nanomaterials also change significantly. In the case of nanoparticles of noble metals, the surface plasmon resonance becomes very important and results in strong absorption of light in characteristic frequency range. Surface plasmon resonance occurs because of the coherent oscillations of the conduction band electrons induced by interaction with an electromagnetic field. The electric field of the incident light beam induces a polarization of the electrons with respect to the much heavier ionic core of the nanoparticles. A net charge difference is felt at the nanoparticle surface, which in turn acts as a restoring force. This creates a dipolar oscillation of all the electrons with the same phase. When the frequency of the electromagnetic field becomes resonant with the coherent electron motion, a strong absorption of incident radiation occurs. In the case of noble metals, particularly gold (Au) nanodots, a strong surface plasmon resonance occurs in the visible part of the electromagnetic radiation. Actual frequency and width of the surface plasmon resonance absorption depend on the size and shape of nanoparticles and the dielectric constant of metal and surrounding matrix. In this chapter we will show that how the phenomenon of surface plasmon resonance observed in gold nanodots can be utilized to enhance the optical and electrical characteristics of zinc oxide (ZnO).
