Heat-capacity comparison among the nanocrystalline, amorphous, and coarse-grained polycrystalline states in element selenium

Nanocrystalline element selenium (nc-Se) samples were synthesized by completely crystallizing a melt-quenched amorphous selenium (a-Se). Heat capacities (C-p) of the nc-Se (with a mean crystallite size of 10 nm), a fully relaxed a-Se, and a coarse-grained polycrystalline Se were experimentally determined in a temperature range of 225-500 K. Measurement results show that there is no pronounced difference between the C-p values of the nc-Se and the a-Se below 250 K. Heat capacities of the nc-Se are found to be only about 2% higher than those of the coarse-grained polycrystalline selenium. The C-p enhancement for the nc-Se, which is much lower than those reported in other nanocrystalline elements, is discussed in terms of the grain-boundary configurations in the nanostructures.