Transition Voltage Spectroscopy of Porphyrin Molecular Wires

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 6; no. 22; pp. 2604 - 2611
• Main Authors: Bennett, Neil, Xu, Gengzhao, Esdaile, Louisa J., Anderson, Harry L., Macdonald, J. Emyr, Elliott, Martin
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 22.11.2010; WILEY‐VCH Verlag
• Subjects: Contact; contact asymmetry; Dimerization; Displays; Electric potential; Microscopy, Scanning Tunneling; Porphyrins; Porphyrins - chemistry; scanning tunneling microscopytransition voltage spectroscopy; Self-assembled monolayers; single molecules; Transport; Voltage; Wire
• ISSN: 1613-6810; 1613-6829; 1613-6829
• DOI: 10.1002/smll.201001046

Measurements are presented of the current‐voltage (I–V) characteristics of individual thiol‐tethered porphyrin molecules (isolated in an alkanethiol matrix) and of self‐assembled monolayers. In both cases, it is found that I/V2 displays a minimum at a characteristic “transition voltage” Vm. Repeated measurements of the transition voltage enable both its time development and statistical behavior to be determined. For isolated molecules, the transition voltage shows a multipeaked distribution of values, indicating the presence of a small number of distinct molecular/contact configurations, each having different transport characteristics. For self‐assembled monolayers, in contrast, a single‐peaked distribution was observed, which is consistent with parallel conduction through many molecules. I–V characteristics of isolated porphyrin molecules display a minimum in I/V2 at a characteristic “transition voltage” Vm. Fluctuations at the molecular contact effect changes in Vm and from repeated measurements both its time development and statistical behavior is determined. This contrasts with the more stable contact over a self‐assembled monolayer with parallel conduction through many molecules.