We report here a practical application of known local Joule heating processes to reduce the contact resistance between carbon nanotubes and metallic electrical contacts. The results presented in this study were obtained from a series of systematic Joule heating experiments on 289 single-walled carbon nanotubes (SWCNTs) and 107 multiwalled carbon nanotubes (MWCNTs). Our experimental results demonstrate that the Joule heating process decreases the contact resistances of SWCNTs and MWCNTs to 70.4% and 77.9% of their initial resistances, respectively. The I-V characteristics of metallic nanotubes become more linear and eventually become independent of the gate voltages (Vgs). For semiconducting nanotubes, the contact resistance has a similar decreasing tendency but the dependency of source-drain current (Ids) on Vgs does not change with the Joule heating process. This suggests that the reduction of the contact resistance and the decrease of the transport potential barrier are largely attributed to the thermal-energy-induced desorption of adsorbates such as water and oxygen molecules from the nanotube surface and the interface region, as well as thermal-energy-enhanced bonding between the nanotubes and electrode surfaces. In comparison to several other methods including rapid thermal annealing, e-beam lithography patterning of the top metal layer, and focused ion beam induced metal deposition of the top layer, the Joule heating process not only effectively reduces the contact resistance but also simultaneously measures the resistance and monitors the change in the transport potential barrier at the interface region.

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Large channel length field effect transistors (FETs) based on Pt contacts to ferromagnetic BiMn-codoped ZnO bicrystal nanobelts have been fabricated using dielectrophoresis and a focused ion beam. Electrical transport studies show n-type behavior of the ferromagnetic ZnO nanobelts. The current-voltage characteristics of the FETs exhibit Schottky barrier behavior. The contact resistances and the Pt diffusion are responsible for the reduction of the conductance and the threshold shift. The reduction of the mobility can be attributed to the enhanced interface scattering at Pt electrodes/nanobelt contact regions after Pt deposition. The devices are also found to be strongly dependent on the channel length.

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We recently developed a novel floating-potential dielectrophoretic method to selectively position individual single-walled carbon nanotubes between two floating electrodes while the bundles of nanotubes and impurities were attracted into the region between two control electrodes. In this study, we investigated effects of several process parameters including electric field distribution, electric field frequency, and solution media in order to understand the physical mechanisms of this dielectrophoretic process and to improve its efficiency. Results showed that both the magnitude and the direction of electrical force applied onto the nanotubes can be tailored by changing these process parameters. It was found that a 1 wt% sodium dodecyl sulfate in deionized water is an efficient solution for separating bundles of nanotubes into individual nanotubes and aligning individual nanotubes with a clean surface between two electrical contacts in comparison to N,N-dimethylformamide, 1,2-dichloroethane, 1,2-dichlorobenzene, 1,1-dichloromethane, ethanol, and isopropanol solutions. The fabricated carbon nanotube devices exhibit electronic properties comparable to nanotube transistors and interconnects fabricated by other methods.