Local effects in the interaction of potassium with Rh(111)

Abstract

As a model system for alkali promotor effects on catalysts we studied the potassium interaction with Rh(111) by UPS, AES, LEED, TDS and work-function (WF) measurements. For the first time also rare gas probe atoms other than Xe atoms have been applied to determine the local surface potential around the adsorbed potassium atoms. The photoemission of adsorbed Ar, Kr and Xe has been measured at 45 K on Rh(111) covered with about 3 at% potassium and on clean Rh(111). On the clean surface all three physisorbed gases show a single adsorption state below 1 ML, with the position of the Ar3p12, Kr4p12andXe5p12 photoemission peak at 8.7, 7.6 and 6.7 eV, respectively. For the potassium-covered surface all three rare gas atoms exist in three different adsorption states, being associated with rare gas atoms ontop of K, next to K and on bare Rh patches. The respective p12 signal from the Rh sites (located at lower binding energy (BE)) is shifted by 0.5 eV to higher BE with respect to clean Rh(111) independent of the nature of the probe rare gas atom. In turn, the state attributed to adsorption sites next to K atoms shows a probe-atom dependent shift by 0.74 (Ar), 0.63 (Kr) and 0.53 eV (Xe) to higher BE with respect to the Xe state on Rh sites.