Potassium adsorption on hydrogen- and oxygen-terminated diamond(100) surfaces

The adsorption of K at 298 K is a route for the titration of surface groups like O and OH. The experiments were performed on a semi-conducting natural diamond (100) surface cleaned by a 480-W microwave hydrogen plasma at 750 degreesC and a hydrogen pressure of 20 mbar, resulting in a very clean, ordered (2 x 1) surface. A second type of C(100) surface was prepared by ex situ oxidation, using a mixture of hydrochloric and nitric acids. The adsorption experiments were carried out in a UHV system equipped with facilities for photoelectron spectroscopy (XPS and UPS). K deposition was achieved using a dispenser source from the SAES Getters Company. The K uptake of H-terminated C(100) at room temperature is marginal, with a sticking coefficient of < 0.03. The acid-treated C(100) surface shows the presence of a broad O Is spectrum with different oxygen states (different binding energies) in the XPS region. The sticking coefficient for R adsorption at 298 K on this surface is nearly 1. The amount of K accommodated on the surface correlates with the oxygen coverage and a stoichiometry of nearly K/O = 1 is reached for the saturated K coverage. In the O Is spectrum, the high-energy state (534.2 eV) disappears, whereas the overall O Is intensity is constant. Due to the K adsorption, the C Is peak shifts by 0.5 eV to a higher binding energy. UPS He I spectra demonstrate a lowering of the work function by -1.9 eV. (C) 2001 Elsevier Science B.V. Ah rights reserved.