Monolayer Structure and Electronic Properties of Fe-Perylenetetracarboxylic-dianhydride (Fe-PTCDA) on Cu(111)

本論文研究 Cu(111)單晶表面的苝四甲酸二酐(PTCDA)與鐵-苝四甲酸二酐 (Fe-PTCDA)兩種單層分子膜的排列與電子結構。Fe-PTCDA 錯合物的排列結構由 掃描穿隧顯微術(STM)加以分析；PTCDA 和Fe-PTCDA 的電子結構以掃描穿隧能 譜(STS)進行量測。 在研究初期，儀器並未順利運作，無法在標準試片(HOPG)表面上得到原子級 解析度，也未能進行掃描穿隧能譜實驗。藉由最佳化濺射探針的參數以改善探針的 品質、改善腔體的真空度、改善儀器接地和微調防震桌水平度等方式，方得以經常 地獲得HOPG 原子級解析度之影像，並以此為標準校正STM 的壓電驅動器。在安 裝並設定鎖相放大器之後，先後以HOPG、Cu(111)和Ag(111)表面測試，可成功地 獲得dI/dV 能譜和駐波的dI/dV 圖。 實驗方法為先準備Cu(111)單晶表面；經由熱阻式蒸鍍獲得PTCDA/Cu(111)樣 品；或是同時蒸鍍鐵和PTCDA 分子，再經最後加熱而得Fe-PTCDA/Cu(111)樣品。 dI/dV 能譜顯示PTCDA 的最低未占軌域(LUMO)與Cu(111)形成混成態，STM 影像 亦確認此結果。STM 影像顯示Fe-PTCDA 在Cu(111)表面係由兩種位向分子(鏈型 和桄型)構成梯狀排列，且兩種分子的占有態能階相同；從dI/dV 能譜進一步獲知 此占有態能階是由Fe-PTCDA 的LUMO 與Cu(111)所形成之混成態。dI/dV 能譜同 時顯示桄型分子在未占有態具有較鏈型分子高的能態密度，代表鏈型PTCDA 的 LUMO 被鐵原子提供的電子完全占有而桄型PTCDA 的LUMO 僅被部分占有。由 於鏈型分子與4 個鐵原子配位，而桄型分子僅配位2 個鐵原子，可知鐵與PTCDA 間的電荷轉移與配位數有關。This thesis presents the investigation of PTCDA (3,4,9,10-perylenetetracarboxylicdianhydride) and Fe-PTCDA complex on Cu(111). Monolayer structure of Fe-PTCDA was studied by scanning tunneling microscopy (STM); electronic properties of PTCDA and Fe-PTCDA were measured by scanning tunneling spectroscopy (STS). dI/dV spectra of PTCDA on Cu(111) revealed the formation of a hybrid state, indicative of a strong chemical interaction between the adsorbate and substrate. The molecular orbital involved in the hybridization was LUMO (lowest unoccupied molecular orbital), confirmed by topographic images. Topographic images of Fe-PTCDA/Cu(111) revealed a ladder-like structure, which is distinctly different from the herringbone structure of PTCDA/Cu(111). Two types of molecules were named according to their orientation in a ladder-like structure, that is, chain- and rung-PTCDA. Topographic features of chain- and rung-PTCDA resolved at the molecular level are unprecedented. The images unraveled that both types of molecules had the same occupied molecular state. However, dI/dV spectra showed that rung-PTCDA have higher density of unoccupied states compared with chain-PTCDA. This means that the LUMO of rung-PTCDA is only partially occupied with the electrons donated by Fe. Since chain-PTCDA binds to 4 Fe atoms while rung-PTCDA binds to only 2 Fe atoms, the result showed that the charge transfer from Fe to PTCDA is coordination number-related.口試委員會審定書 ........................................................................................................... # 謝辭 ................................................................................................................................... i 中文摘要 .......................................................................................................................... ii ABSTRACT .................................................................................................................... iii 目錄 ................................................................................................................................. iv 圖目錄 ............................................................................................................................. vi 表目錄 ........................................................................................................................... viii 第1 章 緒論 ............................................................................................................... 1 1.1. 研究動機 ...................................................................................................... 1 1.2. 掃描穿隧顯微術原理 .................................................................................. 2 1.2.1. 穿隧電流 .......................................................................................... 3 1.2.2. 定電流模式 ...................................................................................... 5 1.2.3. 雜訊 .................................................................................................. 7 1.3. 掃描穿隧能譜原理 ...................................................................................... 8 1.3.1. 鎖相技術 .......................................................................................... 9 1.3.2. dI/dV 圖 .......................................................................................... 10 1.4. 文獻回顧 ..................................................................................................... 11 1.4.1. PTCDA 與分子鍍膜 ....................................................................... 11 1.4.2. PTCDA 在金、銀、銅表面之比較 .............................................. 14 1.4.3. 有關Fe-PTCDA 的研究 ................................................................ 22 第2 章 儀器介紹 ..................................................................................................... 26 2.1. Load-lock 腔 ............................................................................................... 27 2.2. 準備腔 ........................................................................................................ 28 2.3. 觀察腔 ........................................................................................................ 30 2.4. 高溫烘烤 .................................................................................................... 30 2.5. STM ............................................................................................................ 34 2.6. 鎖相放大器 ................................................................................................ 34 第3 章 Cu(111)表面的PTCDA 與Fe-PTCDA ...................................................... 36 3.1. 儀器效能 .................................................................................................... 36 3.1.1. STM 掃描頭校正 ........................................................................... 37 3.1.2. 鎖相放大器測試 ............................................................................ 39 3.2. 探針與樣品製備 ........................................................................................ 40 3.2.1. 鎢探針 ............................................................................................ 40 3.2.2. Cu(111)單晶表面 ........................................................................... 41 3.2.3. 蒸鍍PTCDA 單層膜 ..................................................................... 42 3.2.4. 蒸鍍鐵原子 .................................................................................... 43 3.2.5. 製備Fe-PTCDA 單層膜 ................................................................ 43 3.3. 結果與討論 ................................................................................................ 45 3.3.1. PTCDA/Cu(111)混成態 ................................................................. 46 3.3.2. Fe-PTCDA 排列與電子結構 ......................................................... 48 3.3.3. PTCDA 與Fe-PTCDA 綜合比較 .................................................. 50 第4 章 結論 ............................................................................................................. 52 參考文獻 ......................................................................................................................... 5