以掃描穿隧顯微術研究複合有機異質結構之表面形貌與電子組態

Abstract

隨著新穎科技與半導體產業的發展迅速，有機半導體材料近年因多元材料特性而受到廣泛關注。紅螢烯(Rubrene)在過去已有許多相關的物理、化學和材料科學等研究；除了以高載子遷移率著稱，用其製作之有機電子元件皆有相當出色的表現，顯現紅螢烯作為有機半導體的潛力。然而，紅螢烯沉積於表面的原子尺度形貌、能譜以及相關研究仍屬缺乏。本研究主要透過自組式熱蒸鍍槍沉積紅螢烯於矽(111)、HOPG基板上形成有機異質結構，再透過掃描穿隧顯微術(STM)和掃描穿隧能譜術(STS)進行量測。紅螢烯分子以Stranski–Krastanov模式首先形成小型島狀結構；再形成填滿表面區域的單、雙分子層高平台；最終形成交互堆疊的島狀結構，顯現出紅螢烯沉積時的複雜性。在鎳金屬沉積於紅螢烯有機異質結構表面後，我們觀察到表面形貌的清晰度顯著提升；若進行表面形貌分析則可觀察到符合紅螢烯分子尺寸的單塔亮點結構，也觀察到與紅螢烯側方苯取代基匹配的雙塔亮點結構，推測紅螢烯分子將以駢四苯骨幹平行於表面的方式吸附，或以不同的分子方向進行沉積。本研究STS量測發現鎳金屬沉積後的有機異質結構能譜更為明顯，能隙(E_g)與紅螢烯單晶的理論能隙相符，但是大於先前文獻以光學方法測得之能隙數據，且傳導帶(E_c)與價電帶(E_v)位置也不同，凸顯出紅螢烯分子能帶結構之複雜特性。總而言之，本研究對於紅螢烯有機異質結構進行一系列量測實驗，並發現與先前文獻有所異同的結果；同時，本研究再次驗證金屬蒸鍍於表面將有助於提升掃描穿隧顯微術與能譜術之解晰度。相信值得以此作為出發點更進一步延伸探討，也將開啟相關研究新的範疇與視野。With the rapid development of new technologies, organic semiconductors have gained widespread attention in recent years due to their special characteristics. Rubrene has been studied in domains of physics, chemistry, and materials science studies due to its high carrier mobility, and exhibits excellent performance while fabricated to electronic devices, which demonstrates its potential as an organic semiconductor material. However, there is still a lack of research on the atomic-resolution morphology and energy spectrum of rubrene heterostructures.In this study, we deposit rubrene onto silicon (111) and highly ordered pyrolytic graphite (HOPG) substrates to fabricate organic heterostructures through a self-assembled thermal evaporator, scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) are conducted to measure the surface. Firstly, we observed rubrene structures form through the Stranski–Krastanov mode on HOPG, followed by the small islands, molecular-high platforms, and finally stacked as interspersed island structures. After nickel (Ni) is deposited onto the surface of the rubrene heterostructures, significant enhancement in surface morphology is observed. Single-tower bright spot structures match the size of rubrene molecules, as well as double-tower bright spot structures corresponding to the distances of benzene substituent, suggesting that rubrene molecules adsorb in various molecular orientations. Finally, STS measurements also become more distinct after Ni deposition, revealing the energy spectrum of the organic heterostructures. The energy bandgap (E_g) is similar to the theoretical bandgap of rubrene single crystal but larger than the bandgap measured by optical methods in previous research. Different conduction bands (E_c) and valence bands (E_v) are observed, which presents the energy band structure of rubrene molecules.In conclusion, this study conducts a series of measurements on rubrene organic heterostructures, with numerous results that are both like and different from previous research. Additionally, this study reaffirms that metal deposition on the surface will enhance the resolution of scanning tunneling microscopy and spectroscopy. This is a starting point for further exploration, opening new perspectives for related research.