Development of a Scanning Chemical Vapour Deposition Reactor for the realization of patterned and non-patterned depositions: a preliminary overview

The development of a prototype apparatus to perform patterned Chemical Vapour Deposition (CVD) on planar substrates is presented. The system consists of a fixed head which produces and drives a tiny spot of vapors of a suitable organometallic precursor over the substrate, which is mounted on a heatable and movable stage. WO deposition from W(CO) precursor was chosen as a model for a preliminary evaluation, to show how the main operational parameters affects the morphology and the photocatalytic performances of the deposited layer. As the result, due to the programmable movement of the holder, it is possible to perform any desired patterned deposition, finely controlling the X and Y movements, the head-substrate distance and the scan speed. The width of the deposited lines strongly depends on the morphology of the substrate (porous vs. flat): with porous substrates it ranges from 1 mm to 3.5 mm and can be tuned through the head-substrate distance. The minimum achievable thickness is about 10 nm and, starting from this minimum value, any desired thickness can be produced by means of the utilization of multiple scans. The capability of CVD to cover all the available surface even on structured substrates, is tested on a challenging surface made of hematite nanoplatelets vertically aligned over a Fluorine-doped tin oxide glass. The intimate contact between WO and hematite is assessed through photoelectrocatalytic and chronoamperometric measurements. Interestingly, texture analysis reveals that WO crystals, with domains of about 80-100 nm, are preferentially oriented with the (200) and (002) planes of the orthorhombic structure laying parallel to the substrate.