A comparative study of PF 3, PH 3 AND P(CH 3) 3 on clean, k-covered, and Cl-covered Ag(111)

Abstract

The adsorption and desorption of PF 3, PH 3 and P(CH 3) 3 on clean, K-covered, and Cl-covered Ag(111) has been studied using temperature programmed desorption (TPD), work function change measurement (Δφ), ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). All three compounds adsorb molecularly at 105 K, adsorb through their P atoms, and desorb reversibly with no detectable decomposition. The adsorptions are accompanied by a maximum surface work function change of −0.15 eV (PF 3), −1.4 eV (PH 3) and −2.45 eV (P(CH 3) 3). The desorption energies increase in the order PF 3 < PH 3 < P(CH 3) 3. The desorption of PF 3 follows simple first-order kinetics with E d = 7.5 kcal mol . For PH 3 and P(CH 3) 3, there appear to be strong repulsive adsorbate-adsorbate interactions. The bonding modes of PH 3 and P(CH 3) 3 only involve σ-donation. For PF 3, σ-donation and π-back-donation are involved. TPD and Δφ measurements indicate that the σ-donation capability follows the order P(CH 3) 3 > PH 3 > PF 3. This order is directly related to the electronegativity of the group attached to the phosphorus. Δφ, UPS and XPS measurements indicate that there is some structural rearrangement taking place in the multilayer P(CH 3) 3 when the surface temperature is increased. Surface Cl stabilizes adsorbed PF 3, PH 3 and P(CH 3) 3. Surface K also stabilizes PF 3, but destabilizes PH 3 and P(CH 3) 3. We compare our results with the corresponding coordination chemistry.