Investigating and Engineering the Electronic Structure at Organic-Inorganic Interfaces

有機電子元件的特性主要受有機分子與無機電極或是基材的介 面影響，因此，設計有機分子元件的關鍵在於掌握策畫有機-無機混 成系統的能力。本篇論文中，高空間、能量解析的掃描穿隧電子顯微 鏡用於探討由可調控的製程完成的有機-無機混成系統的結構及電子 特性的連結。用於研究有機-無機混成系統為PTCDA 有機分子以及 與鐵原子鍵結的結構成長於Au(111), Cu(111)以及Bi2Se3 基材上。 PTCDA/Au(111)呈現物裡吸附，而Fe-PTCDA/Au(111)形成有序 的鏈狀以及網狀的金屬-有機奈米結構。這樣的奈米結構提供分子不 同的鍵結環境進而影響電子轉移的強度。由前緣分子軌域的位移量化 現象推論出在Fe-PTCDA 混成系統中的特定鍵結會影響電子轉移的 有趣現象。另一方面，化學吸附系統: PTCDA/Cu(111)呈現強的分子 與基材耦合，在PTCDA 與鐵原子鍵結之後，PTCDA 與Cu(111)之間 的作用力將被減弱。這些關於金屬與分子混成系統的研究成果提供了 一個獨特的方法去策畫分子的混成以及分子與基材間的耦合強度。 在拓墣絕緣體的元件發展中，為了保存自旋-動量鎖定的拓樸表 面態，製造與電極之間平整的介面以及阻絕層是一個關鍵議題。本篇 論文驗證了使用有機分子做為穿隧能障不僅有平整的介面還能阻絕 蒸鍍鐵原子對拓樸表面態的影響。因為弱的PTCDA-Bi2Se3 的作用 力，拓樸表面態在有序的PTCDA 自組裝層上仍可以被保存。鐵原子 對拓樸表面態的影響，例如，電子參雜以及庫倫散射，在鐵與PTCDA 混成之後，消除了這些來自鐵原子的影響。Organic/inorganic interfaces strongly a ect the functions of organic devices. Thus, skills of engineering the organic-inorganic hybrids hold the keys for designing molecular electronic devices. Organic-inorganic systems with controllable fabrications are studied by scanning tunneling microscopy (STM) which is a powerful tool to study the interplay between structural and electronics properties with high spatial and energy resolution. In this thesis, the prototype molecule PTCDA (perylene- 3,4,9,10-tetracarboxylic dianhydride) and the coordination with iron atoms on various substrates [Au(111), Cu(111) and Bi2Se3] are investigated. Physisorption of PTCDA/Au(111) is identi ed while well-ordered metal-organic nanostructures chains and networks form in Fe-PTCDA/Au(111). Such nanostructures provide di erent metal-organic coordination for molecules and disparities in the degree of charge transfer. Digitized frontier orbital shifts are addressed in the Fe-PTCDA hybridization system, which implies the speci c coordination a ects the magnitude of charge transfer onto each PTCDA. On the other hand, chemisorption is found with PTCDA/Cu(111), in which the molecule-substrate coupling is strong yet can be attenuated by incorporating Fe adatoms. These ndings show that the formation of the metal-organic complex o ers a unique way to engineer the degree of hybridization of involved molecules as well as tune the molecule-substrate coupling. Fabricating smooth interfaces and isolations between topological insulator (TI) surfaces and electrodes are key issues for conserving the spin-momentum locked metallic surface states in TI devices. An alternative using organic molecules as a tunneling barrier is demonstrated to possess a smooth interface and the ability to prevent disturbances in the topological surface state (TSS) upon metal deposition. Utilizing the weak interaction between PTCDA molecules and Bi2Se3 surfaces, the TSS of Bi2Se3 is conserved on top of the well-ordered PTCDA assembly layer. By forming Fe-PTCDA hybrids, in uences, such as doping e ect and Coulomb scattering, of Fe atoms on the Bi2Se3 surface state are eliminated