Deposition of titanium-vanadium oxide thin films on organic self-assembled monolayers: Role of complexing agents

Titanium-vanadium oxide films were co-deposited from aqueous solutions on organic self-assembled monolayers (SAMs) with alkylammonium or amine surface functional groups. The chemical composition of the films was manipulated via the use of lactic acid and oxalic acid as complexing agents. From solutions with [oxalate]: [vanadium] < 1: 1, titanium-enriched films were formed. However, with [oxalate]: [vanadium] > 1:1, the Ti:V ratio dropped back to that of films deposited in the absence of complexing agents. Therefore, it is concluded that oxalic acid chelates both titanium and vanadium, but preferentially vanadium. At high concentrations of oxalic acid, no films formed, indicating that both titanium and vanadium were chelated strongly. Lactic acid, in contrast, was oxidized by pentavalent vanadium. When [lactate]: [vanadium] < 1:2, the resulting V4+ increased the deposition rate of vanadium, and vanadium-rich films were formed. For [lactate]: [vanadium] > 1:2, the remaining (i.e., unoxidized) lactic acid preferentially complexed vanadium and showed effects comparable to those seen with oxalic acid. The thickness of films formed on the alkylammoniurn SAMS increased with increasing vanadium content in the films, whereas film composition had little or no effect on the thickness of films formed on amine SAMS.