以空間/角解析光電子能譜術研究二維電子系統之能帶結構

Spatially/Angle-resolved Photoemission Studies on the Electronic Structure of Two-dimensional Electron Systems

陳至瑋(Jhih-Wei Chen) ； 陳家浩(Chia-Hao Chen) ； 吳忠霖(Chung-Lin Wu)

《真空科技》 30卷3期 (2017/09) Pp. 62-68

摘要

二維電子系統已被應用於量子元件上。鋁酸鑭(LaAlO_3, LAO)與鈦酸鍶(SrTiO_3, STO)和石墨烯(Graphene)就是經典的例子。為了解導二維電子系統上的電性議題，如何直接探測電子結構變成相當重要的議題。因此本計畫首先將以異質接面LAO/STO接面上的二維電子氣為主體，透過傳統式光電子能譜量測，配合大面積控制PZT極化翻轉的技術，了解不同極性(極化)的電荷對LAO/STO，對接面能帶所造成的影響。再者，我們針對石墨烯graphene的二維自由載子，以掃描式光電子能譜量測具有空間解析度的影像，並配合其光電子能譜，可了解在數μm大小下的石墨烯的電子能帶中，在Au金屬影響下的摻雜效應。更進一步，針對單晶石墨烯graphene的自由載子，以角解析光電子能譜術量測具高能量解析度的Dirac cone，並了解在極少量的過渡金屬Ti的軌道耦合下，電子能帶將產生的高效能的摻雜效應。

關鍵字

異質氧化物接面－鋁酸鑭/鈦酸鍶 ； 石墨烯 ； 傳統式光電子能譜術 ； 掃描式光電子能譜術 ； 角解析光電子能譜術

並列摘要

Two-dimensional electron system has been wildly developed and applied into for advanced next-generation quantum electronic devices. The LAO/STO hetero-oxide interface and graphene are very classical examples. To understand conduction property of two-dimensional electron systems, it is quite essential to characterize and measure the electronic structure directly. In this study, the electronic structure of two-dimensional electron system has been systematically studied by photoemission techniques. Firstly, we present the electronic structures of LAO/STO measured by conventional XPS with respect to P_(up) and P_(down) polarization states. This enables us to understand polarization influence to electronic structures. Two distinct ferroelectric patterns are created and assisted by large-area scanning probe station. Then, the metal-contact induced doping in graphene electronic structure has been characterized by SPEM. The high-spatial resolution SPEM enables us to study the p-type doping effect inside exfoliated graphene and their core-level information. Finally, we measure the changes of electronic structures (Dirac cone) by small amount of Ti deposited onto graphene by ARPES. The dz^2 orbital of Ti is strongly hybridized with p_z orbital of C atom, which resulting in the high electron n-type doping efficiency.

並列關鍵字

LAO/STO hetero-oxide interface ； Graphene ； X-ray photoemission spectroscopy (XPS) ； Scanning photoelectron micro-spectroscopy (SPEM) ； Angle-resolved Photoemission spectroscopy (ARPES)