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

我们构建了一种新的亚原子去激发光谱（MDS）装置，用于探测固体表面最外层原子层的局部电子态。在这个光谱学中，人们使用了在<He^*>亚介态和表面之间的俄歇型电荷交换所发射的电子。我们将其应用于清洁和金属吸附的Si（111）表面，以澄清吸附剂的局部功函数和局部电荷状态。亚稳态原子枪：我们新建的亚稳态原子枪具有<He^*>和HeI光子的飞行时间分离设施，从而可以同时测量MDS和UPS。<He^*>的速度分布与温度在1000K.2左右时的麦克斯韦分布相当。Si（111）表面<He^*>的去激发：通过对Si(111)7x7表面的MDS光谱分析，我们得到了亚稳原子通过共振电离和俄歇中和机制去激发的证据。Si(111)7x7上碱金属的局部电荷态：MDS光谱检测到吸附Li原子上剩余的价电荷，即使在吸附的最早阶段，这为Li共振的部分占用提供了明确的证据。

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.