Structure-Dependent Charge Transport and Storage in Self-Assembled Monolayers of Compounds of Interest in Molecular Electronics: Effects of Tip Material, Headgroup, and Surface Concentration
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- 作者：Fu-Ren F. Fan ; Yuxing Yao ; Lintao Cai ; Long Cheng ; James M. Tour ; and Allen J. Bard
- 刊名：Journal of the American Chemical Society
- 出版年：2004
- 出版时间：March 31, 2004
- 年：2004
- 卷：126
- 期：12
- 页码：4035 - 4042
- 全文大小：159K
- 年卷期：v.126,no.12(March 31, 2004)
- ISSN：1520-5126
文摘
The electrical properties of self-assembled monolayers (SAMs) on a gold surface have beenexplored to address the relation between the conductance of a molecule and its electronic structure. Weprobe interfacial electron transfer processes, particularly those involving electroactive groups, of SAMs ofthiolates on Au by using shear force-based scanning probe microscopy (SPM) combined with current-voltage (i-V) and current-distance (i-d) measurements. Peak-shaped i-V curves were obtained for thenitro- and amino-based SAMs studied here. Peak-shaped cathodic i-V curves for nitro-based SAMs wereobserved at negative potentials in both forward and reverse scans and were used to define the thresholdtip bias, VTH, for electric conduction. For a SAM of 2',5'-dinitro-4,4'-bis(phenylethynyl)-1-benzenethiolate,VII, VTH was nearly independent of the tip material [Ir, Pt, Ir-Pt (20-80%), Pd, Ni, Au, Ag, In]. For all of theSAMs studied, the current decreased exponentially with increasing distance, d, between tip and substrate.The exponential attenuation factors (
values) were lower for the nitro-based SAMs studied here, ascompared with alkylthiol-based SAMs. Both VTH and of the nitro-based SAMs also depended strongly onthe molecular headgroup on the end benzene ring addressed by the tip. Finally, we confirmed the "memory"effect observed for nitro-based SAMs. For mixed SAMs of VII and hexadecanethiol, I, the fraction of thecharge collected in the negative tip bias region that can be read out at a positive tip bias on reverse scan(up to 38%) depended on the film composition and decreased with an increasing fraction of I, suggestingthat lateral electron hopping among molecules of VII occurs in the vicinity of the tip.
values) were lower for the nitro-based SAMs studied here, ascompared with alkylthiol-based SAMs. Both VTH and of the nitro-based SAMs also depended strongly onthe molecular headgroup on the end benzene ring addressed by the tip. Finally, we confirmed the "memory"effect observed for nitro-based SAMs. For mixed SAMs of VII and hexadecanethiol, I, the fraction of thecharge collected in the negative tip bias region that can be read out at a positive tip bias on reverse scan(up to 38%) depended on the film composition and decreased with an increasing fraction of I, suggestingthat lateral electron hopping among molecules of VII occurs in the vicinity of the tip.