The Fabrication and Functionalisation of Schottky Barriers on Stainless Steel

Schottky barriers are a rectifying contact that can form between a semiconductor and a metal. The rectification is due to the formation of a depletion region in the semiconductor. This has been shown to be useful in the formation of a simple photovoltaic device on a stainless steel substrate, using silver nanowires to form the Schottky barrier. In this work, knowledge from crystal growth and rheology studies were used to inform a method of solvothermal synthesis of TiO2 in water and deposition on steel, avoiding the use of organic additives. TiN coated steel was used as a substrate, resulting in highly rectifying contacts. Although it was possible to model the current-voltage characteristics accurately, fits to thermionic emission theory were usually poor due to the impact of the changing surface at the range of temperatures used, the scan speed and environment. From the few accurate fits, estimates of dopant density and thus depletion region could be made and photocurrent efficiency in these regions estimated. As would be expected, the devices have a photocurrent in the UV region, where TiO2 absorbs light. However, the photocurrents observed on sol based devices are measured in both directions, the "reverse" direction is consistent with band gap excitation and the "forward" current is in the opposite direction. The other strongly absorbing species other than the TiO2 is the silver nanowires. The presence of the sol has a large impact on the UV-vis absorption profiles of silver nanowires and shows a peak at the same energy as the "forward" photocurrent. This is also present in the visible region in the presence of some dyes. This may suggest a plasmonic photocatalytic mechanism can be dominant under some conditions and this reaction may be sensitized by dyes such as Ru(dcbpy)2(NCS)2 or alizarin red