Pentacene nanotransistor with carbon nanotube electrodes
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(a) SEM image of MWNT electrodes. Before disconnecting the MWNT, the source–drain characteristics of the MWNT through the leads were ohmic and exhibited no change in the gating effect within the applied voltage region. In the reference samples of the -diameter MWNTs with micrometer-order length, no Coulomb blockade effect was observed at . After the MWNT was disconnected by applying the electric degradation method to the nanotube (see Ref. 18), the current was found to be smaller than at . (b) An optical microscopy image of the pentacene nanotransistor. We used commercial pentacene powder provided by Aldrich Products as an evaporation source material. For the field-effect channel, a pentacene thin film of thickness detected on the crystal evaporation detector is thermally evaporated at an evaporation flux rate of at a substrate temperature of . The pentacene is selectively grown around the MWNT under these growth conditions (see the SEM image in the inset). Bird’s-eye view of schematic device structure of the pentacene nanotransistor with carbon nanotube electrodes (c), and cross-sectional view (d). The substrate used is a highly doped Si substrate with a thermally grown -thick layer. From the back of the substrate, the Al back-gate electrode was connected. We fabricated a total of 20 samples, and all of the devices were conductive at room temperature for the MWNT gaps filled by the pentacene film. The MWNT gaps without a continuous pentacene film exhibited no conduction. For the low-temperature characterization, we used two devices and similar electric characteristics were observed in them.
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FET characteristics of pentacene nanotransistor at room temperature. (a) Source–drain current with changing in source–drain voltage at various gate voltages applied to the back gate. (b) Source–drain current with changing in gate voltage at fixed source–drain voltage of . With changing from , changes from
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Low-temperature characteristics of pentacene nanotransistor with MWNT electrodes. A source–drain current while changing gate voltage with source–drain voltage fixed at (a), and 20, 10, and from top to bottom (b). Vertical bars show a regular period as visual guides. (c) Source–drain current while changing source–drain voltage . The characteristics were measured at various values from at steps of . Each trace was shifted for clarity. The current blocking region modulation near the zero source–drain voltage due to the Coulomb blockade effect through multiple tunneling junctions with a change in applied gate voltage is represented.
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