Optical Properties of Thin Films of Haycockite

Thin films of haycockite Cu4Fe 5 S 8 on glass substrates were deposited by flash evaporation technique from powders of this compound. The composition of thin films correspond to the atomic content of Cu, Fe, and S of 24.13, 27.90, and 47.97 at.% with the Cu/Fe and S/(Cu + Fe) atomic ratios of 0.87 and 0.92 respectively, whereas the corresponding theoretical values for this material amount to 0.80 and 0.89. The as-prepared thin films of haycockite consist of a set of separate fractions of approximately identical areas of about 400 - 600 µm 2 . It can be assumed that this structure evolved during cooling down of thin films since it completely covers the surface of thin films. A small inclusion of a second phase with the chemical composition close to talnakhite Cu 9 Fe 8 S 16 is also observed. Haycockite Cu 4 Fe 5 S 8 is found to be a direct gap semiconductor with the energy band gap E g equal to 1.26 eV as determined using both transmission and surface photovoltage methods.