Improvement of Electrical and Thermal Contacts Between Carbon Nanotubes and Metallic Electrodes by Laser Annealing

A new approach for improving electrical and thermal contacts between multi-wall carbon nanotubes (MWCNTs) and metal electrodes by localized laser heating is presented in this work. The nanotubes were suspended, using the dielectrophoresis technique, over a gap of 1 μm width and 5 μm depth connecting the ends of the patterned electrodes. Subsequently, the as deposited nanotubes were directly heated, in ambient atmosphere, by a focused laser beam, which was also used for exciting the Raman spectra of the nanotubes. The changes in the vibrational frequencies were used to estimate the local temperature that was controlled by the incident laser power density. The changes in the nanotubes due to laser heating were evaluated by using scanning electron microscopy, Raman spectroscopy and electrical measurements. The method was employed for improving the electrical contacts between suspended MWCNTs and different electrodes (W, Ti and Au). The reduction in the electrical resistance was up to three orders of magnitude, resulting in contact resistivity as low as ∼0.1–1 kΩ · μm², with the lowest values being obtained for Au electrodes. The main advantage of this method, when compared with traditional and rapid thermal annealing, is that the thermal treatment is localized in a small region, thus allowing the processing of circuits composed of different materials, whereby each process can be individually controlled.