We have investigated the electrical transports of double-walled carbon nanotube field effect transistors (DWNT-FETs) with modified contacts. The CNT/Au metal contacts of DWNT-FETs were modified with a self-assembled monolayer of 2-aminoethanethiol molecules. In ambient air, the contact-modified DWNT-FETs showed a decreased conductance in the p-channel (negative gate voltages) and an increased conductance in the n-channel (positive gate voltages), while the original device showed p-type transport. In a vacuum, the n-channel current in the contact-modified DWNT-FET started to rise. We observed a clear n-type transport in the high vacuum. Almost no changes in the gate threshold voltages were observed by means of the contact-modification with a self-assembled monolayer. While the semiconducting DWNT-FET showed a clear transition from a p-type to n-type transistor with contact modification, no apparent changes were observed in semi-metallic DWNT devices.
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