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X-ray and XPS studies of evaporated cuxs thin-films
The structural changes in Cu x S films have been monitored by x_ray diffraction and correlated to the chemical changes taking place on the Cu x S surface, the latter monitored by XPS. The results show: evaporated Cu x S films contained chalcocite, free copper phases, and probably a third phase (of sulfur); resistivity is related to the amounts of free Cu and S in the film; air heat treatments converted chalcocite to Cu deficient phases and resulted in the disappearance of the sulfide and predominance of CuSO4_nH2O and CuO; argon heat treatment tended to react Cu and S to form Cu x S; Cd is detected on the surface of Cu x S deposited onto CdS and is significantly increased in amount by heat treatments. These results can be related to chemical processes occurring on Cu x S/CdS and Cu x S/(Zn,Cd)S solar cells. For the CdS cell, oxides and sulfates of Cu and Cd are found on the Cu x S surface and the sulfates are enhanced by the heat treatment in moist air. CuO and CuSO4 are formed in the absence of Cd, and dominate the Cu x S surface.