Studies of selenium and selenium dioxide isochromats

The allotropic forms of selenium, hexagonal and amorphous, and selenium dioxide have been studied by the isochromat method. A high vacuum spectrometer provided with bent crystal and water cooled targets was used. It is shown that a shift of the short wave-length limit of the continuous X-ray spectrum occurs for a semiconductor in comparison with a metal. The shift of hexagonal Se is found to be 1.7 ± 0.2 V, amorphous Se 1.5±0.3 V and SeO₂ 1.3 ± 0.2 V. The temperature was held at about 320 °K for the amorphous sample and at 400 °K for the others. The shifts of hexagonal and amorphous Se are in good agreement with the energy band gaps found by other methods. The fine structure near the short wave-length limit is discussed considering the Nijboer theory. Attempts have been made to explain the isochromat structure by comparison withL _I -absorption and characteristic energy loss spectra. The characteristic energy loss values found by the present method, which impliesreappearing intervals in the isochromats, have been compared with the theoretical values of? ω _p , given by the plasma oscillation theory.