Titanium Phosphide Coatings from the Atmospheric Pressure Chemical Vapor Deposition of TiCl4 and RPH2 (R = t-Bu, Ph, CyHex)

Abstract

Atmospheric pressure chemical vapor deposition of titanium phosphide coatings was achieved on glass substrates from the reaction of TiCl4 and RPH2 (R = t-Bu, Ph, Cy-hex) at 450-550 degreesC. The coatings show good uniformity, surface coverage, and adherence; they passed the Scotch brand tape test and could not be scratched with a brass scalpel. The leading edge of the titanium phosphide films was a deep blue while the bulk of the film was reflective and silver. Growth rates were on the order of 1 mum min(-1) at 550 degreesC. The films were crystalline, single phase with a hexagonal cell of a = 3.49(1) Angstrom and c = 11.70(1) Angstrom. Scanning electron microscopy (SEM) revealed surface morphologies consistent with an island growth mechanism. X-ray photoelectron spectroscopy (XPS) binding energy shifts were at 454.6 eV for Ti-2p and at 128.6 eV for P-2p. Energy-dispersive X-ray analysis (EDXA) and electron probe studies gave elemental ratios that were in agreement indicating in most cases slightly P-rich films, TiP1.2, with negligible chlorine incorporation. Raman spectra exhibited bands at 245, 320, and 410 cm(-1). Sheet resistance measurements showed typically 10-120 mOmega cm, indicating good conductivity. Rutherford backscattering showed a bulk composition of TiP1.2. Optically, the films showed high reflectivity at 1000 nm and showed 5-25% total transmission from 300 to 800 nm. Contact angle measurements were in the range 40-50degrees for the as made films these showed little change after 30 min of irradiation at 254 nm. All of the films showed negligible photocatalytic activity in the destruction of an overlayer of stearic acid.