Surface chemistry of TiCl4 on W(100)

The interactions of titanium tetrachloride (TiCl4) with the W(100) surface are described. Reactions were studied using temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and low energy electron diffraction (LEED). From TPD measurements, it is concluded that TiCl4 is the sole desorption product below 700 K. Desorption occurs in three temperature regions, near 170 K, in a process assigned to multilayer sublimation, near 225 K, from two states designated alpha(1)- and alpha(2)-TiCl4, and near 455 K, from two states designated gamma(1)- and gamma(2)-TiCl4. The Ti(2p) and Cl(2p) photoelectron spectra imply that TiCl4 is molecularly adsorbed below 190 K. Between 190 and 275 K, alpha-TiCl4 desorption competes with dissociation to TiCl3(a) and Cl-(a). Adsorbed TiCl3, which has been spectroscopically identified by XPS, self-disproportionates between 300 and 500 K, yielding gamma-TiCl4, as well as adsorbed Ti and Cl. Adsorbed Cl eventually desorbs as a volatile tungsten chloride, and Ti probably evolves into the gas phase as Ti-(g).