“…This behavior is typical of the formation of an electronic interface state (peak C). Because of the low temperatures of desorption of alkali metals, 550°C for Na [23,24,37], 600°C for K [35,38,39], 650°C for Rb [37,39] and Cs [23,24,37], the covalent bonding between alkali metal and silicon atoms is weak. The only two possible candidates in this energy range are the Si 3p and Na 3s valence electrons.…”