ABSTRACT
38The conventional experimental techniques leave a number of lacunae in their limited success while trying to explore the fascinating properties of the nanomaterials and nanosystems. The defects are an area that is often untouched for discussion as if their role in governing the structure and properties of nanomaterials is inconsequential and it is the ultimate outcome which is of sole importance. Here positron annihilation spectroscopy is being introduced as a versatile nuclear experimental spectroscopic probe that can reflect about the properties of the defects in nanomaterials and it is shown that the technique can offer solutions to a number of issues related to the exotic features nanomaterials exhibit compared to their bulk counterparts. For example, the negative vacancies in wide band gap semiconductor nanomaterials can be precisely sensed by the positrons and, by monitoring their transformation in terms of size and concentration, can provide information on their structure, phase, and composition. Positrons can also sensitively probe the structural and phase transformations in spinel nanomaterials and their success is established through a number of experimental data illustrating the smooth and qualitative variation of the positron lifetime or its intensity. Apart from these, the success of coincidence Doppler broadening measurements in the identification of the momentum distribution of electrons in a complex nanomaterial system is also briefly discussed. The aim of this chapter is to highlight the sensitivity and success of a non-conventional defect-investigative probe for understanding nanomaterials and following their evolution under varying experimental conditions such as crystallite size variation, heat treatment and doping.
