Noncrystalline Chromium, Molybdenum and Tungsten Phosphate Films Prepared by Metal Organic-Chemical Vapor-Deposition

Novel, glass-like transition metal phosphate films between 0.5 and 0.03-mu-m thick were prepared by metal organic chemical vapour deposition. The films were deposited at 250-262-degrees-C, using Cr(CO)5(PH3), Mo(CO)5(PH3) or W(CO)5(PH3) as the precursor compound. They were characterized by techniques including X-ray diffraction, secondary ion mass spectrometry, Rutherford backscattering, and X-ray photoelectron spectroscopy. The chromium phosphate films resemble crystalline beta-CrPO4 in terms of their composition and properties, but are not readily converted into crystalline material. The P:Mo ratio in the molybdenum phosphate films is approximately 0.83, and the average molybdenum oxidation state is near +5. Bulk molybdenum phosphate glasses with similar compositions and properties are known. The P:W ratio in the tungsten phosphate films is comparatively small, being approximately 0.12, and the average tungsten oxidation state is slightly lower than +6. Non-crystalline chromium phosphate films were also obtained in initial experiments investigating the effects of higher deposition temperatures. Molybdenum and tungsten phosphate films of the type described are potentially useful in solid state electrochemical devices.