Electromigration-Fabricated Molecular Junctions and the Instrumentation for Inelastic Electron Tunneling Spectroscopy
Date Issued
2014
Date
2014
Author(s)
Chen, Ting-Yun
Abstract
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.
Subjects
分子電性
電遷徙
非彈性電子穿隧能譜
硫醇
Type
thesis
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