The effect of complexing agent on crystal growth, structure and properties of nanostructured Cu_（2-x）S thin films

Thin films of Cu2 x S（x = 0, 1） were deposited on self-assembled, monolayer modified substrates in the copper–thiosulfate system with various concentrations of ethylene diamine tetraacetic acid（EDTA） at a low temperature of 70 8C. The thin films were characterized by means of X-ray diffraction（XRD）, X-ray photoelectron spectroscope（XPS）, field emission scanning electron microscopy（FESEM）, transmission electron microscopy（TEM）. The optical and photoelectrochemical（PEC） properties of the Cu2 x S semiconductor films were investigated by ultraviolet–visible（UV–vis） absorption spectroscopy and a three-electrode system. It is found that EDTA plays a key role in the process of Cu2 x S nanocrystals formation and growth. The compositions of the Cu2 x S nanocrystals varied from Cu2S（chalcocide） to Cu S（covellite） through adjusting the concentration of EDTA, which is used as a complexing agent to yield high-quality Cu2 x S films. The growth mechanisms of Cu2 x S nanocrystals with different EDTA concentrations are proposed and discussed in detail.