以角解析光電子能譜及低能量電子繞射儀研究鉛薄膜成長在鍺(111)之介面效應

Study of the interfacial effects on the growth of Pb thin films on Ge(111) by ARPES and LEED

陳韋全(Wei-Chuan Chen)

指導教授 ： 唐述中

國立清華大學/原子科學院/先進光源科技學位學程/碩士(2012年)

https://doi.org/10.6843/NTHU.2012.00095

摘要

本論文以低能量電子繞射(LEED)與角解析光電子能譜(ARPES)來探討鉛薄膜成長在鉛/鍺(111)-(√3×√3)R30˚-β phase與金/鍺(111)-(√3×√3)R30˚的介面現象與電子結構。
晶格匹配對於外延成長薄膜是一個重要的因素，鉛與鍺的晶格常數分別為4.95 Å與5.658 Å相差約13%，過大的晶格不匹配會產生應力使薄膜無法層狀成長(layer-by-layer)，但我們成功的分別在鉛/鍺(111)-(√3×√3)R30˚-β phase與金/鍺(111)-(√3×√3)R30˚上成長出大面積均勻且平整的鉛薄膜。鉛原子與金原子的潤濕層在鍺(111)面上都形成(√3×√3)R30˚的結構。然而，我們發現鉛薄膜在成長在這兩個潤濕層上的晶格結構是不同的。
對於鉛薄膜成長在鉛/鍺(111)-(√3×√3)R30˚-β phase上，我們發現1 ML的鉛薄膜會沿著鍺基底的晶面方向成長，且從LEED繞射圖觀察到鉛薄膜與鍺基底形成莫爾結構(Moiré superstructures)，經由低能電子繞射圖計算得到莫爾條紋的週期為25 Å和由鉛與鍺原子結構模型預測28 Å，相差約10%的形變量。 而鉛薄膜成長在金/鍺(111)-(√3×√3)R30˚系統中，觀察不同厚度鉛薄膜的低能量電子繞射圖只有顯現單一領域的鉛(1×1)結構。不同於鉛薄膜成長在鉛/鍺(111)上當鉛薄膜厚度超過2 ML時，除了鉛(1×1)結構外還產生鉛(1×1)旋轉三十度的結構。
此外，我們還發現鉛薄膜從低溫升溫至室溫後，鉛薄膜與潤濕層會互相擴散形成鉛金合金，經由角解析光電子能譜測量ΓK與ΓM方向的能帶結構，在布里淵區中心(Brillouin Zone Center) Γ 觀察到兩個Dirac-cone-like state。在表面布里淵區的邊緣M點，有兩個拋物線能帶相互交叉，這意味著一個巨大的Rashba分裂。

關鍵字

鉛薄膜 ； 角解析光電子能譜 ； 低能量電子繞射 ； 量子井態 ； 莫爾條紋

並列摘要

In this thesis, low energy electron diffraction (LEED) and angle-resolved photoemission (ARPES) were used to study the interfacial phenomena and electronic structure of Pb film grown on the reconstructed surfaces, Pb/Ge(111)-β phase and Au/Ge(111)-(√3×√3)R30˚.
Lattice match is an important factor for epitaxial growth. The lattice mismatch between the Pb (a = 4.95 Å) and Ge (a = 5.65 Å), is 13%. Such large lattice mismatch between Pb and Ge causes a strong strain on the Pb adlayer, which should hinder the layer-by-layer growth of Pb films. On the contrary, we succeeded to produce atomically uniform Pb films on Pb/Ge(111)-β phase and Au/Ge(111)-(√3×√3)R30˚, respectively. However, we found that the lattice structures grown on these two wetting layers are different.

For Pb films on Pb/Ge(111)-β phase, initially at 1 ML, Pb films grow in the same direction as the Ge(111) substrate, forming a Moiré superstructures as revealed by LEED pattern. The periodicity of the Moiré structure determined from LEED pattern is 25 Å, differed from the value 28 Å derived from the bulk lattices of Pb and Ge, indicating a 10% strain.

For Pb films grown on Au/Ge(111)-(√3×√3) R30˚, the corresponding LEED patterns showed the one-domain Pb (1×1) structure, being independent of Pb films thickness. This is different from Pb films on Pb/Ge(111)-β phase which has one more different lattice structure, Pb(1×1)- R30˚, as the thickness increases above 2 ML. In addition, we found that Pb films would interdiffuse with Au to form a unique alloy phase after being annealed to room temperature from 140 K, as revealed by the distinct LEED pattern and ARPES spectrums. The band dispersions were measured along two symmetry directions, ΓK and ΓM. At the surface zone center,Γ, we observed two Dirac-cone-like bands. And unusually, two parabolic bands cross each other at the surface zone boundary of Ge(111),M, implying a giant Rashba splitting

並列關鍵字

Pb film ； ARPES ； LEED ； Quantum well state ； Moiré pattern

參考文獻

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