Surface Modifications using Thiol Self-Assembled Monolayers on Au Electrodes in Organic Field Effect Transistors
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0965-S08-03
Surface Modifications using Thiol Self-Assembled Monolayers on Au Electrodes in Organic Field Effect Transistors Nobuya Hiroshiba1, Ryotaro Kumashiro1, Naoya Komatsu1, Yusuke Suto1, Hisao Ishii2, Shinya Takaishi3, Masahiro Yamashita3, Kazuhiro Tsukagoshi4, and Katsumi Tanigaki1 1 Department of Physics, Tohoku University, 6-3 Aoba, Aramaki, Aoba, Sendai, 980-8578, Japan 2 Chiba Univeristy, Chiba, 980-8578, Japan 3 Department of Chemistry, Tohoku University, Sendai, 980-8578, Japan 4 Riken, Wako, 351-0198, Japan
ABSTRACT The influences of self-assembled-monolayers (SAMs) modifications on the gold electrodes in organic field effect transistors are studied using benzen-thiols (BzTs) having amino (NH2), nitro (NO2) and methyl (CH3) substituents and pentacene as an organic semiconductor. The field effect transistor (FET) characteristics are found to be very sensitive to the preparation condition of the SAMs modified surfaces. This can be rationalized in terms of the barriers against carrier injections made by SAMs and this situation can be monitored using a surface contact-angle method. The enhancement in the field effect mobilities ยต s is observed when the SAMs modifications to the electrodes are applied, and this could be caused by the higher efficiency of carrier injection attained by the hole transfer from SAMs to pentacene molecules. INTRODUCTION Organic field effect transistors (OFETs) are important considering the future applications to electronic devices, and are currently being investigated with lots of enthusiasm [1,2]. In order to improve the properties of OFETs, however, methodologies have not still been established. Especially, one of the most important key issues will be the interfacial problems between organic thin-films and gate-insulators and/or electrodes [3]. This is now drawing much intense attention. The surface control using self-assembled-monolayers (SAMs) is a well-known good technique for such surface modifications and shall provide microscopically good interface regulations [4]. For applying the SAMs technique, two parts in the FET structure can be considered. One is the interface between gate insulators and organic semiconductors and the other is the one between electrodes and organic semiconductors. Extensive studies have so far been made for the former by many researchers [5,6] and better surface modifications have been reported to be achieved on SiO2 gate insulators when silane-type molecules are used as SAMs [7]. On the other hand for the latter, the SAMs treatments on the gold electrodes using thiol molecules are reported, but the effects are not clear at moment and moreover little influences are sometimes reported [8,9]. Therefore, it is very essential to clarify the real influences and establish a complete methodology of the SAMs modifications to the electrodes. In the present study, interfacial modifications of source and drain gold electrodes by thiol molecules have been studied in detail for pentacene-FETs, using three benzene thiol (BzT) molecules as SAMs with different
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