A Comprehensive Study of the Single Molecule Conductance of ,-Di
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- 作者：Santiago Martí ; n ; Wolfgang Haiss ; Simon Higgins ; Pilar Cea ; M. Carmen Ló ; pez ; Richard J. Nichols
- 刊名：Journal of Physical Chemistry C
- 出版年：2008
- 出版时间：March 13, 2008
- 年：2008
- 卷：112
- 期：10
- 页码：3941 - 3948
- 全文大小：183K
- 年卷期：v.112,no.10(March 13, 2008)
- ISSN：1932-7455
文摘
We present here a comprehensive study of the single molecule conductance of alkanes with carboxylic-acidterminal groups, investigated with the I(s) and I(t) scanning tunneling microscopy (STM) methods. Thesemethods enable the formation of single molecular bridges between the gold substrate surface and gold STMtip without the need to first form a metallic break junction. The I(s) and I(t) methods have up until this studybeen used primarily with thiol head groups, and this current study shows that they can be extended to othercontact groups. The single molecule conductance of a series of dicarboxylic acids, HOOC-(CH2)n-COOH,has been investigated as a function of length of the alkane chain (N = 4-12), temperature, pH, electrochemicalpotential, and contact gap separation. The latter parameter, which has been often neglected in single moleculeconductance studies, is particularly noteworthy given the strong dependence of molecular conductance onthe separation between the STM tip and the surface. In this study, particular emphasis is put on determiningthe contact gap spacing corresponding to the measured conductance values. Both molecular conductance andthe temperature dependence of molecular conductance are shown to depend significantly on contact gapseparation for these dicarboxylic acid-terminated molecular wires. Possible origins for this behavior arediscussed. Values for the tunneling decay constant, 
N, and the contact resistance, A, have been determinedfor the 
,
-dicarboxylic acid-terminated alkanes fully stretched in the contact junction (all-trans configuration).N values determined for this stretched configuration agree well with literature expectations, and the highvalues for the contact resistance attest to a relatively poor coupling between the carboxylate end groups andthe Au contacts.
N, and the contact resistance, A, have been determinedfor the ,-dicarboxylic acid-terminated alkanes fully stretched in the contact junction (all-trans configuration).N values determined for this stretched configuration agree well with literature expectations, and the highvalues for the contact resistance attest to a relatively poor coupling between the carboxylate end groups andthe Au contacts.