Tunneling Spectroscopy of Organic Monolayers and Single Molecules
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- 作者：K. W. Hipps (1) hipps@wsu.edu
- 关键词：Inelastic – ; Elastic – ; Tunneling – ; Spectroscopy – ; Orbital mediated – ; Vibrational – ; Electronic – ; Ionization levels – ; Affinity levels
- 刊名：Topics in Current Chemistry
- 出版时间：2012
- 出版年：2012
- 期刊代码：129_0340-1022
- 类别：ch
- 卷：313
- 期：1
- 页码：189-215
- 数据来源：sp
摘要
Basic concepts in tunneling spectroscopy applied to molecular systems are presented. Junctions of the form M-A-M, M-I-A-M, and M-I-A-I′-M, where A is an active molecular layer, are considered. Inelastic electron tunneling spectroscopy (IETS) is found to be readily applied to all the above device types. It can provide both vibrational and electron spectroscopic data about the molecules comprising the A layer. In IETS there are no strong selection rules (although there are preferences) so that transitions that are normally IR, Raman, or even photon-forbidden can be observed. In the electronic transition domain, spin and Laporte forbidden transitions may be observed. Both vibrational and electronic IETS can be acquired from single molecules. The negative aspect of this seemingly ideal spectroscopic method is the thermal line width of about 5 kBT. This limits the useful measurement of vibrational IETS to temperatures below about 10 K. In the case of most electronic transitions where the intrinsic linewidth is much broader, useful experiments above 100 K are possible. One further limitation of electronic IETS is that it is generally limited to transitions with energy less than about 20,000 cm−1. IETS can be identified by peaks in d2 I/dV 2 vs bias voltage plots that occur at the same position (but not necessarily same intensity) in either bias polarity.