ABSTRACT
Nanomaterials have been an emerging œeld of research due to the novel properties exhibited when the size of building blocks is reduced below 100 nm. Several size-dependent phenomena make nanomaterials attractive in terms of potential applicability compared to their larger-sized counterparts, justifying the importance and attention of this research.1-3 For thermoelectric research, nanomaterials are of great interest due to the possibility of decoupling electrical and thermal transport properties which may help attain higher ZT values for the currently available materials.4,5
še commonly accepted nomenclature of nanomaterials is based on the number of degrees of freedom of charge carriers for the description of their dimensionalities. šus, a thin œlm or superlattice is conœned in one dimension, but is a 2D nanomaterial. Similarly, a nanowire is conœned in two dimensions, hence is a 1D nanomaterial, and œnally a nanoparticle is conœned in three dimensions and is therefore a 0D nanomaterial. In the case of larger nanocrystals (not quantum conœned), the size and shape of the nanocrystals also a¤ect their properties due to di¤erences in surface-to-volume ratio. Bulk nanostructured (NS) TE materials are fabricated using a bulk process rather than a nanofabrication process, which has the important advantage of being produced in large quantities and in a form that is compatible with commercially available devices.6 šey are di¤erent from the advanced low-dimensional TE materials as they are consolidated under high T and P, resulting in larger-sized (40-200 nm) grains. še advanced low-dimensional TE materials are usually in quantum size and have well-deœned shapes such as rod-like or tube-like structures. še nanoe¤ects of bulk NS TE materials will not be as strong as in the case of advanced low-dimensional TE materials, but since the material is closer to bulk material, it can be easily handled the same way as bulk TE materials using conventional TE module/device technology for further steps toward direct applications. So far, of all the NS materials, only bulk NS materials have been produced in enough quantity to be used in this manner.
