XPS study of copper sulphides inserted into a Langmuir-Blodgett matrix

Abstract

X-ray photoelectron spectroscopy (XPS) is used to characterize copper sulphides inserted into Langmuir-Blodgett (LB) films of behenic acid. Comparisons are made between samples exhibiting very different electrical conductivity but synthesized by the same method. Sulphur atoms with two different environments are found: divalent sulphur S2- and dimer sulphur (S2)2-, higher concentrations of dimer sulphur (S2)2- being present in insulating samples. Chemical bonding of copper in LB films is compared with CuS and Cu2S powders. The copper to sulphur ratio and the divalent to dimer sulphur ratio are obtained from various samples and lead to the formula: Cu2S, xS2 with x ranging from 0.5 to 0.8. © 1993.