Effects of photoacoustic measurements on a nanostructured ZnSe mechanically alloyed

Zinc-blende ZnSe powder, with particles containing nanometric grains, was prepared using the mechanical alloying technique, from an equiatomic mixture of elemental Zn and Se powders. An important interfacial component was observed in the as-milled powder, which affects its thermal and optical properties. In order to obtain a high-quality zinc-blende ZnSe powder an annealing process was applied. The structural properties of both as-milled and annealed powders were characterized by an x-ray diffraction technique. The effects of defect centers on the optical band gap of both as-milled and annealed zinc-blende ZnSe powders were studied through optical absorbance measurements. The results showed a substantial broadening and a shift of the band gap energy to lower values in the as-milled powder, while for the annealed sample no effects were observed. For the annealed sample, the measured band gap energy value is in good agreement with those reported in the literature. A sequence of photoacoustic absorption measurements of the as-milled ZnSe sample showed that the absorbed energy promotes a structural relaxation. This relaxation causes a change in the heat transfer mechanism from thermal diffusion to thermoelastic bending and a reduction in the thermal diffusivity values. Similar measurements of the annealed nanostructured ZnSe sample showed the thermal diffusivity value to have a high degree of stability, and to be in good agreement with values reported in the literature.