銀和鉛薄膜在鍺(111)基底上的電子結構的光電子能譜研究

Abstract

本論文中，我們利用光電子能譜研究銀和鉛薄膜在鍺(111)基板上的電子結構。在不同厚度時量測銀薄膜的表面電子態和量子井電子態，分析各量子數的量子井態在布里淵區中心的有效質量，我們發現隨著厚度的減少，布里淵區中心的有效質量會明顯變大。我們提出了一個模型來解釋所觀察到的現象，假設相位移與波向量的垂直和水平分量有關，從Bohr-Sommefeld量子化規則延伸，可得到量子井電子態在布里淵區中心的有效質量與薄膜厚度和相位移的公式，我們從銀薄膜在鍺(111)系統得到的實驗結果，可用來驗證我們所提出的模型。

鉛在鍺(111)基板上形成表面重構，觀察其電子結構，我們發現在低溫時，電子結構與室溫時大致相同，但是會出現一個新的表面電子態，能量靠近費米能階，電子結構的改變暗示著從室溫到低溫的過程可能伴隨著原子結構的改變。此外，我們所量測到的表面電子態，在布里淵區中心附近展現出鍺的價帶邊緣，包含自旋─軌道交互作用所形成的重電洞、輕電洞和裂帶電洞能帶和沒有自旋─軌道交互作用所形成的三重結構，我們推測當鉛原子在鍺表面形成重構時產生的表面電子態會造成鍺表面的能帶彎曲，造成表面電子態與晶體中的電子態交互作用，最後顯現出鍺的價帶邊緣結構。

The electronic structures of the ultrathin metal films on the semiconductor has been investigated by high resolution angle-resolved photoemission. In this thesis, the electronic structures of Ag/Ge(111) and of Pb/Ge(111) are studied. Ag/Ge(111) thin films are prepared at the thickness ranging 5-18 monolayers and the subband dispersions of quantum well states have been determined by angleresolved photoemission. The enhanced effective masses of the subbands for decreasing film thickness has been observed in some other systems. This behavior is also observed in Ag/Ge(111) system. An increased in-plane affective mass at the zone center at a small film thickness is observed; the trend follows closely a 1/N dependence. This can be attributed to a kinetic constraint for standing wave formation governed by a momentum-dependence phase shift function. Lead deposits on Ge(111) have received a large amount of attention and the electronic structure of the (rt3 × rt3)R30 reconstruction was reported. When the highly-doped n-type Ge(111) is used, the band structures are totally different from those in the previous reports. Near the zone center, the band dispersion reflects the valence band edges of Ge including the heavy-hole, light-hole, and split-off hole bands. Both spin-orbit splitting bands and non-spin-orbital splitting bands are observed. A new surface state band centered at k-bar emerges at T = 120 K while no phase transition is observed by LEED pattern.