A technique of measuring contact resistance between an individual nanotube and a deposited metallic film is described. Using laser ablation to sequentially shorten the contact length between a nanotube and the evaporated metallic film, the linear resistivity of the nanotube as well as the specific contact resistivity between the nanotube and metallic film can be determined. This technique can be generally used to measure the specific contact resistance that develops between a metallic film and a variety of different nanowires and nanotubes.
A focused ion beam (FIB) is used to sequentially reduce the contact length of an evaporated metal film to a multiwalled carbon nanotube (MWCNT). By using this FIB contact cutback technique, the contact resistance between an individual MWCNT and evaporated thin films of Au, Au∕Ti, and Ag are accurately determined. The data permit a rational way to specify the minimum contact length of a metallic thin film to a MWCNT.
The electrical resistance of individual multiwalled carbon nanotubes and the thermal interface resistance of nanotube arrays are investigated as functions of dc bias voltage used during growth. Nanotubes were grown from Fe 2 O 3 nanoparticles supported on Ti/SiO 2 /Si substrates by microwave plasma chemical vapor deposition (MPCVD) under dc bias voltages of -200, -100, 0, +100, and +200 V. Electrical resistances of individual nanotubes were obtained from I-V measurements of randomly selected nanotubes, while thermal interface resistances of nanotube arrays were measured using a photoacoustic technique. The study reveals that individual nanotubes and nanotube arrays grown under positive dc bias voltage (+200 V) show significant increases in their electrical and thermal interface conductance, respectively. The nanotubes have been further characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and electron microscopy in order to account for the marked differences in electrical and thermal interface conductance.
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