Reaction of trimethylphosphate with TiC and VC(1 0 0) surfaces

We have investigated trimethylphosphate [(CH3O)3PO] (TMP) chemistry on the TiC(1 0 0) and VC(1 0 0) surfaces as a function of temperature to understand the adsorption and reaction of this model lubricant additive on hard ceramic materials. High resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), and temperature programmed desorption (TPD) have been used to determine that TMP adsorbs molecularly on both surfaces at low temperature. At room temperature and above, the molecule decomposes on TiC, forming strong Ti–O–P chemical bonds while breaking C–O bonds in the process. The reaction products that persist on the surface after heating up to 873 K are determined to be phosphate-like (POx) and carbonaceous species. This reaction, however, has been determined to be influenced by the initial coverage of molecular TMP at the cryogenic dosing temperature; when the monolayer coverage was substantially lower, phosphate-like species were chemically reduced at high temperature. Identical experiments on VC(1 0 0) indicated much less decomposition of TMP, even with large exposures, and the presence of a chemically reduced form of phosphorous and –O–C species on the surface at high temperatures.