Atomic Layer Deposition of MoS2 Decorated TiO2 Nanotubes for Photoelectrochemical Water Splitting

A thermal atomic layer deposition (ALD) process to fabricate MoS2 thin films is successfully demonstrated by using cycloheptatriene molybdenum tricarbonyl (C7H8Mo(CO)(3)) and H2S as precursors at an ALD temperature below 300 degrees C. The process is systematically investigated, showing a typical self-limiting characteristic within an ALD temperature window of 225-285 degrees C and a high growth-per-cycle of 0.11 nm. The as-deposited films are amorphous while they can be crystallized in situ by sulfurization with H2S at a low temperature of 300 degrees C. A prototypical application of the developed ALD process is demonstrated by constructing a MoS2/TiO2 heterostructure through depositing MoS2 onto anodized TiO2 nanotubes for photoelectrochemical water splitting. The MoS2/TiO2 heterostructures exhibit approximately three times superior photoelectrochemical performance than the pristine TiO2 nanotubes. This is attributed to an enhanced visible light-harvesting ability of MoS2 and an improved separation of the photo-generated charge carriers at the heterostructure interface, which is affirmed by a staggering gap (type II) between MoS2 and TiO2 as probed by ultraviolet photoelectron spectroscopy.