Soft reverse current-voltage characteristics in V 2 O 5 nanofiber junctions
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Soft reverse current-voltage characteristics in V2O5 nanofiber junctions Gyu-Tae Kim, Jörg Muster, Marko Burghard, and Siegmar Roth Max-Planck Institut für Festkörperforschung, Heisenbergstr. 1, D-70569, Stuttgart, Germany ABSTRACT V2O5 nanofibers showed the rectifying current-voltage characteristics under an asymmetric contact configuration at room temperature, indicating the formation of a Schottky diode. The ideality factors as a Schottky diode were estimated to be 6.1 at the forward bias and 1.4 at the reverse bias. The larger current at the reverse bias defined by the negative voltage at the metal electrode may originate from the contribution of the tunneling via field emission or thermionic field emission. The ultimate geometric size of nanofibers enhances the influence of the tunneling mechanism and modifies the nano-scale Schottky diode, requiring more understanding in designing the nano-scale electronic devices with the metal contacts.
INTRODUCTION Synthetic nanofibers such as carbon nanotubes are invoking the scientific interest nowadays [1-3]. With the development of the synthesis techniques for the synthetic nanofibers, the molecular electronics based on synthetic nanofibers become more plausible by making the nanoscale electronic devices [2-7]. To achieve the realistic electronic chips, all practical issues such as electrical connection, the assembling technique and the integration processes should be considered for the new functional nano-scale devices [4,7]. Till now the electrical properties of nanofibers were investigated from the point of a field effect transistor, a rectifying diode and optoelectronic devices [3-7]. As the carbon nanotube is under the highlight because of its noble structure and outstanding electrical properties, other synthetic nanofibers are also attracting from the basic research and the application [2,3,6,7]. V2O5 nanofiber was found a century ago, and identified to have the ultimate geometric dimension with a good uniformity in the fibrous structure [8]. Recently a field effect transistor made of V2O5 nanofibers was demonstrated with a small electrical mobility of 10-2 cm2/V s owing to the hopping conduction [6]. Most of the electrical contacts defined on the V2O5 nanofibers showed the ohmic behaviors, indicating the symmetric contact in the two-probe configuration [9]. In the present study, a significant asymmetric current-voltage characteristics in a V2O5 nanofiber junction is shown and discussed by considering the influence of the tunneling mechanism through the nanofiber Schottky barrier. EXPERIMENT V2O5 sols were prepared from 0.2 g ammonium(meta)vanadate (NH4VO3) and 2 g acid ion exchange resin (DOWEX 10×80) in 40 ml water. With aging for a few days, the average length of floating individual V2O5 nanofibers in the orange color solution increases up to a few µm. For the better deposition of individual V2O5 nanofibers on bare substrates, a Si substrate silanized by 3-amminopropyltriethoxysilane (3-APS) solution was dipped into a mixture of V2O5 sol/water (1:10) for 2 ∼ 3
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