Electric Field Directed Growth of Molecular Wires of Charge Transfer Molecules on Prefabricated Metal Electrodes
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1058-JJ05-03
Electric Field Directed Growth of Molecular Wires of Charge Transfer Molecules on Prefabricated Metal Electrodes T Phanindra Sai1, and A K Raychaudhuri1,2 1 Department of Physics, Indian Institute of Science, Bangalore, 560012, India 2 Unit for Nanoscience, S.N.Bose National Center for Basic Sciences, Kolkata, 700 098, India ABSTRACT Molecular wires of charge transfer molecules were formed by co-evaporating the TCNQ (acceptor) and TTF (donor) molecules or by evaporating single complex of TTF:TCNQ across prefabricated metal electrodes The prefabricated metal electrodes were made using electron beam lithography on SiO2 and glass cover slip substrates. The temperature dependence of resistance shows that the formed molecular wires show semiconductor like behavior. INTRODUCTION There has been considerable interest in synthesis, design and characterization of organic charge transfer (CT) salts, a class of molecules in which metallic conductivity and even superconductivity has been observed1. Conducting organic micro and nanowires are useful for constructing efficient all organic electronic devices. Charge transfer molecules are for long considered as promising candidates for organic molecular conductors. Studies on charge transfer salts have been concentrated almost exclusively on single crystals. The single crystals even though providing clean systems for investigating the underlying physical processes are fragile and are difficult to process. This limits the prospects for practical application. Most well studied charge transfer molecules are complexes of TCNQ-TTF in single crystalline form and thin film form2,3,4,5,6,7. TCNQ-TTF belongs to quasi one-dimensional conductors having high electronic conduction along the ‘b axis’. Recent studies have shown that TTF-TCNQ charge transfer molecular electrodes can be used to replace the regular metal source-drain electrodes for organic thin film transistors with almost same contact resistance as the metal electrodes8,9. Organic nanochannel FETs has been recently fabricated using TTF-TCNQ molecular wires10. We are interested in growing single molecular wires of CT salts in a controlled way to study their electrical characteristics. There are different techniques of growing molecular wires one of which is Langmuir Blodgett, where a long amphiphilic chain is attached to either donor or acceptor molecules11. The other technique, which is used often, is co-evaporation technique to simultaneously evaporate the donor and acceptor charge transfer molecules form two different crucibles in a vacuum chamber12. We have used the co-evaporation technique to deposit the molecular wires on the prefabricated substrates. EXPERIMENT The SiO2 and glass cover slip substrates were thoroughly cleaned using RCA cleaning procedures. Ebeam lithography was used to pattern contact pads on PMMA coated SiO2 and cover substrates using FEI Quanta 200 SEM instrument with ebeam lithography attachment. The
substrates were developed and patterns were metalized with 5nm chromium and 30 nm gold in a v
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