Potassium adsorption on NiO(100)

Room temperature (RT) adsorption of potassium (K) on NiO(100) was studied with LEED, AES, TDS and WF measurements. The LEED pattern showed a background increase and no extra spots. The WF of NiO upon potassium adsorption decreased from 4.4 eV to a saturation value near 1.3 eV without a minimum. The TD spectra were not broadened towards RT at saturation. Thermal desorption revealed two states. The appearance of the second state is correlated with a sudden decrease of the sticking coefficient as evidenced by AES. The O(520 eV) Auger peak of NiO was shifted upon adsorption, indicating ionic bonding between alkali adatoms and substrate oxygen. A correlation of the experimental results suggests that K on NiO forms clusters and not uniform adlayers as on metals and most semiconductors.