Surface chemistry of TaCl5 on polycrystalline Ta

The surface chemistry of TaCl5 on polycrystalline Ta was studied by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) following adsorption at 130 K. XPS determined that no surface reactions occurred during adsorption at 130 K, and binding energy shifts in the Ta 4f and Cl 2p XP spectra suggested interactions between TaCl5 molecules in contact with the Ta substrate. TPD analysis from 130 to 900 K showed the desorption of two molecular states between 200 and 300 K, and the higher temperature state is more structurally ordered than the low temperature state. Chemical reaction between the TaCl5 interfacial layer and O absorbed in the Ta lattice was observed for the 250 K annealing of multilayers adsorbed at 130 K. Surface coverages estimated by XPS were less than coverages estimated by TPD, and the discrepancy is explained by the forward scattering of the substrate Ta 4f metallic photoelectrons through ordered TaCl5 adlayers.