DOI: 10.1002/chem.201001181 Metal–Molecule–Metal Junctions in Langmuir–Blodgett Films Using a New Linker: Trimethylsilane Gorka Pera, [a, b] Santiago Martín, [a, b] Luz M. Ballesteros, [a, b] Adam J. Hope, [c] Paul J. Low, [c] Richard J. Nichols, [d] and Pilar Cea* [a, b] Introduction The development of ever smaller sized electronic devices has turned interest toward organic molecules as potential circuit components, such as conductors, rectifiers, transistors and logic gates. [1–3] To understand their electrical behaviour direct current-voltage (I–V) measurements are a require- ment for molecules arranged into metal-molecule-metal junctions. There are now a number of methods capable of achieving this feat and they include mechanical break junc- tions, [4, 5] nanopores, [6, 7] cross-wire junctions, [8] scanning tun- nelling microscopy (STM) [9–13] or conducting atomic force microscopy (c-AFM). [14–16] Molecular conductance values obtained from such devices, depend not only on the inherent molecular features, but also on other important parameters, such as the metal–molecule contact. Often, small variations in the nature or characteristics of the metal–molecule con- Abstract: Herein trimethylsilane (TMS) is demonstrated to be an effi- cient binding group suitable for con- struction of metal–molecule–metal (M– mol–M’) junctions, in which one of the metal contacts is an atomically flat gold surface and the other a scanning tunnelling microscopy (STM) tip. The molecular component of the M–mol– M’ devices is an oligomeric phenylene ethynylene (OPE) derivative Me 3 Si C CACHTUNGTRENNUNG{C 6 H 4 C C} 2 C 6 H 4 NH 2 , featuring both Me 3 SiC  C and NH 2 metal con- tacting groups. This compound can be assembled into Langmuir–Blodgett (LB) films on Au  substrates by surface binding through the amine groups. Al- ternatively, low coverage (sub-mono- layer) films are formed by adsorption from solution. In the case of condensed monolayers top electrical contacts are formed to STM tips through the TMS end group. In low coverage films, single molecular bridges can be formed between the gold surface and a gold STM tip. The similarity in the I–V re- sponse of a one-layer LB film and the single molecule conductance experi- ments reveals several points of critical importance to the design of molecular components for use in the construction of M–mol–M’ junctions. Firstly, the presence of neighbouring p systems does not have a significant effect on the conductance of the M–mol–M’ junction. Secondly, in the STM configu- ration, intermolecular electron hopping does not significantly enhance the junc- tion transport characteristics. Thirdly, the symmetric behaviour of the I–V curves obtained, despite the different metal–molecule contacts, indicates that the molecule is simply an amphiphilic electron-donating wire and not a mo- lecular diode with strong rectifying characteristics. Finally, the conductance values obtained from the amine/TMS- contacted OPE described here are of the same order of magnitude as thiol anchored OPEs, making them attrac- tive alternatives to the more conven- tionally used thiol-contacting chemistry for OPE molecular wires. Keywords: conducting materials · Langmuir–Blodgett films · molecu- lar wires · thin layers [a] G. Pera, Dr. S. Martín, L.M. Ballesteros, Dr. P. Cea Departamento de Química Orgµnica y Química Física Facultad de Ciencias Universidad de Zaragoza, 50009 (Spain) E-mail : pilarcea@unizar.es [b] G. Pera, Dr. S. Martín, L.M. Ballesteros, Dr. P. Cea Instituto de Nanociencia de Aragón (INA) edificio I + D + I, C/Mariano Esquilor s/n Campus Rio Ebro 50018, Zaragoza (Spain) [c] A. J. Hope, Prof. P. J. Low Department of Chemistry University of Durham Durham DH1 3 LE (UK) [d] Prof. R. J. Nichols Department of Chemistry University of Liverpool Crown Street, Liverpool, L69 7ZD (UK) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201001181.  2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Eur. J. 2010, 16, 13398 – 13405 13398