Photoelectrochemical activities of ultrathin lead sulfide films prepared by electrochemical atomic layer epitaxy

PbS ultrathin films were prepared by sequential underpotential deposition of S and Pb on Au(111) substrates. Observations of the resulting films with high resolution electron microscopy and energy dispersive X-ray spectrometry revealed the deposition of PbS thin films having the cubic rock salt crystal structure, the (200) planes of which were parallel to the Au surface. The scanning tunneling microscope images showed that the surface of the prepared PbS film was flat on an atomic level and no large protrusions were present, while etch pits with the height of the monatomic step of Au(111) were seen through the deposited films irrespective of the number of PbS monolayers. The PbS film-deposited Au electrodes showed anodic photocurrents in an aqueous solution containing triethanolamine as a sacrificial electron donor. The onset wavelength of their action spectra was largely blue-shifted from that of the bulk PbS due to the size quantization effects. The energy gap of the PbS thin films determined from the action spectra of anodic photocurrents decreased with an increase in the film thickness.