分子導電元件之製作與電性訊號之擷取

Silicon-based Devices for the Study of Molecular Conductance: Issues on Lithographic Fabrication and Data Acquisition

劉柏均(Po-Chun Liu)

指導教授 ： 陳俊顯

國立臺灣大學/理學院/化學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.11003

摘要

分子接合(molecular junctions)泛指「電極-分子-電極」的量測分子電性之基本架構。低溫條件下所獲得的I-V 曲線，若經兩次微分(d2I/dV2)，可轉換成非彈性穿隧能譜(IETS, inelastic tunneling spectroscopy)。此能譜所提供的資訊相當於分子振動光譜，可檢驗分子是否存在於電極間隙；IETS 也可用於釐清分子導電能力的增強是否受助於非彈性穿隧現象。為了獲得合適於於低溫實驗環境的分子電性量測平台，本論文工作以黃光及電子束微影製程，搭配電遷徙效應(electromigration effect)的方式去誘發一分子級的奈米裂縫的形成，藉此製作含分子接合的量測元件。此外，為了有效地提升訊號品質，本論文也嘗試以鎖相放大器為主的訊號擷取系統直接獲取分子的微分導電值(dI/dV)。和數學運算的結果相比，直接擷取所得的微分導電值，其訊雜比更高、訊號品質更好。儘管目前訊號的解析度仍不足以進行後續的光譜結果判定，但藉由比較不同擷取頻率的結果，可發現大部分擷取頻率的結果多呈雜訊貌，僅有特定頻率所得結果訊雜比較高，因此便可概略性推估以該特定頻率擷取出的結果，並非為一般雜訊的行為，可能是由待測分子所表現出的訊號。

關鍵字

分子導電值 ； 分子量測元件 ； 電子束微影 ； 黃光微影 ； 鎖相訊號擷取

並列摘要

The understanding of the electron-transporting mechanism through the MMM
junction (metal-molecule-metal) is important for the improvement of electric properties
via molecular design. The I-V curves acquired under low temperature can be
transformed into IETS spectra (inelastic tunneling spectroscopy) which are originated
from the absorption of electron energy and thus from the excitation of the corresponding
vibrational modes. Such an inelastic process is accompanied by an increase of
differential conductance (dI/dV) or the appearance of peaks in the derivative of
differential conductance (d2I/dV2). The latter offers information equivalent to those of
IR or Raman spectra. To prepare devices suitable for the measurements under low
temperature, great efforts in photolithography and e-beam lithography have been
involved. Lock-in amplification and AC modulation are devised to acquire IETS
spectra of our target compounds at 4 K. According to the results of, [Ni3(dpa)4(NCS)2]
(dpa‒: dipyridylamido anion), a unique class of molecular wires with features of
metal-metal chains distinct from carbon-based p-conjugated molecules, the S/N ratio of
differential conductance extracted by lock-in technique is better than the result of numerical derivative from I-V curve. Nevertheless, the resolution of signal still has to
be improved in the future, but the comparison with the results extracted by lock-in technique with different frequencies shows the quality of signal at specific frequency is superior to others. Therefore, we rudimentarily predict that the signal at specific frequency originates from the vibrational modes of molecule.

並列關鍵字

molecular conductance ； molecular devices ； e-beam lithography ； optical lithography ； lock-in technique

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