Our work has also sought to develop a reliable method for producing independently controlled intratube tunnel barriers. We have reported the realization and characterization of independently controllable tunnel barriers within a carbon nanotube. The nanotubes are mechanically bent or kinked using an atomic force microscope, and top gates are subsequently placed near each kink. Transport measurements indicate that the kinks form gate-controlled tunnel barriers, and that gates placed away from the kinks have little or no effect on conductance. The overall conductance of the nanotube can be controlled by tuning the transmissions of either the kinks or the metal-nanotube contacts. Scanned gate microscopy confirms that the kinks form locally depletable regions in the nanotube.
Fig. 1. Scanned Gate Microscopy: At right is a typical AFM height image, and at left is dc current measured in situ as a function of tip position. The tip electrostatically couples to the tube, differentially affecting transport based on its position. This image shows that mechanical deformations in nanotubes form locally gateable regions.
Fig. 2. SEM image of gated-kink device with arrow indicating the position of the nanotube under the SiO2 insulating layer. At far left and far right are the Ti/Au source and drain contacts.
Fig. 3. Gate response of single-kink device. Plot shows dc current as a function of three gate voltages, VG1, VG2 and VG3 over different sections of the nanotube, measured at T=135K (bottom, left axes) and of VBG at room temperature (top, right axes).
Fig. 4(a) Data for a double kink device producing AND logic. dc current as a function of VG4 and VG6, both over kinks in the nanotube, demonstrating the ability to inhibit transport through the device by appropriately tuning either kink. Fig. 4(b) dc current as a function of VG5 and VG4. VG5 , over an underformed section of the nanotube, has essentially no effect on transport.
For more information contact Michael Biercuk (biercuk@fas)