分子電性量測平台：微影製程與電遷徙之製作及其非彈性電子穿隧能譜

Abstract

分子接合點(molecular junctions)是由「電極-分子-電極」所構成，此為分子電性量測的基本架構。量測分子接合點所獲取的I-V曲線，其d2I/dV2-V曲線稱為非彈性電子穿隧能譜(inelastic electron tunneling spectra，IETS)，此能譜源自於分子接合點中的分子振動，可與分子振動光譜相互對應，因此IETS技術可檢驗分子是否存在於分子橋接系統中，用以研究分子導電性與非彈性電子穿隧現象。本論文以黃光及電子束微影技術製作具有奈米金線的元件，搭配電遷徙(electromigration)技術形成奈米等級的裂縫，作為可供分子架接之分子電性量測平台。本論文嘗試建構IETS電路系統，以鎖相放大器(lock-in amplifier)直接擷取dI/dV、d2I/dV2資訊，相較於數學微分所得的dI/dV、d2I/dV2，由鎖相放大器擷取的資訊具有較高的訊雜比，可提供解析度較好的IETS能譜。本實驗室先前的IETS電路系統之軟體無法整合系統所需之數部儀器，導致無法準確控制數據之取點速率，且鎖相放大器參數設定不佳，導致IETS能譜的解析度不足。目前的IETS電路系統改以整合性軟體控制所有儀器，得以準確控制數據之取點速率，提升d2I/dV2的訊雜比，取得具有明顯譜峰的IETS能譜。藉由目前的系統取得之單壁奈米碳管的IETS能譜具有明顯譜峰，且可與振動光譜指認，並藉由IETS譜峰變寬的現象證實能譜的確由IETS訊號所貢獻。然而，1,4-丁二硫醇的IETS能譜僅部分譜峰得以與文獻指認，仍有部分譜峰無法指認，推測是受雜訊或是分子接合點構型不同之影響，使得譜峰能量位置與分子振動光譜的振動模式比對仍有差異。

The study on charge transport through an MMM junction (metal-molecule-metal) is a fundamental method for investigation into molecular electronics. The second derivatives of the current-voltage curves yield inelastic electron tunneling spectroscopy (IETS). IETS originates from the excitation of the vibrational modes when electrons tunnel through a molecular junction. With vibrational modes consistent with Raman and infrared spectra, IETS provides spectroscopic evidence for the presence of molecules at the junctions. The devices are fabricated by photolithography and e-beam lithography, followed by electromigration technique. To obtain IETS of molecular junctions, the IETS circuit system is established with two lock-in amplifiers to acquire dI/dV and d2I/dV2 data directly from first and second harmonic signals. The signals obtained with lock-in amplifiers have better signal-to-noise ratios than those obtained numerically. The IETS circuit system is amended to improve the signal-to-noise ratio by integrating all required techniques in a customized program. The prominent peaks in the IETS of single-walled carbon nanotubes (SWNTs) obtained with the system can be assigned with the Raman spectra. However, not all of the peaks in the IETS of 1,4-butandithiol are consistent with reported IETS. It is presumed that the discrepancy comes from the noise and the geometry of the molecular junctions.