Layer resolved spectroscopy of potassium adsorbed on a Ru(001) surface: Photoemission and thermal desorption study

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Abstract
High‐resolution photoemission spectroscopy and thermal desorption were used to study the coverage dependence of the K 3p3/2,1/2 core levels of K overlayers on Ru(001). Three doublets were observed to evolve sequentially and to shift to higher binding energy with increasing coverage of potassium. The doublets were assigned to photoemission from the interface (first layer), ‘‘bulk’’ (second layer), and surface (third layer). Spin–orbit splitting was observed for the first time in the condensed potassium phase by photoemission. The results are discussed in terms of the equivalent core approximation using a Born–Haber cycle. In the thermal desorption data three coverage regimes can be distinguished: a first layer desorbing with first‐order kinetics and a strongly decreasing heat of adsorption (EA =2.80–0.87 eV); a second layer with zero‐order desorption kinetics and EA =0.78 eV; a third layer and multilayers with the same kinetic order but with EA increasing from 0.78 to 0.93 eV, which is close to the heat of sublimation of potassium.