Adsorption of Metals on Semiconductor Surfaces Studied by Penning Ionization of Metastable Atoms.

点击翻译按钮获取中文摘要

We constructed a new apparatus of metastable-atom deexcitation spectroscopy (MDS) for probing local electronic states of outermost atomic layers of solid surfaces. In this spectroscopy, one uses electrons emitted by the Auger-type charge exchange between <He^*> metastables and surfaces. We applied it to clean and metal-adsorbed Si(111) surfaces to clarify local workfunction and local charge states of adsorbates.1. Metastable-atom gun: Our newly-built metastable-atom gun has a facility of time-of-flight separation of <He^*> and HeI photons, thus enabling the simultaneous measurement of MDS and UPS. Velocity distribution of <He^*> was comparable to Maxwell's distribution characterized by the temperature around 1000K.2. Deexcitation of <He^*> at Si(111) surface: From an analysis of MDS spectra taken from a Si(111)7x7 surface, we obtained evidence of the fact that metastable atoms are deexcited by the mechanism of resonance ionization followed by Auger neutralization.3. Local charge states of alkali metals on Si(111)7x7: MDS spectra detected remaining valence charges on adsorbed Li atoms, even in the earliest stage of adsorption, which provides clear evidence of the partial occupancy of a Li resonance.