Abstract
A new approach for electrical and thermal improvement of contacts
between carbon nanostructures (multi-wall carbon nanotubes - MWCNTs and
multi-layer graphene - MLG) and metal electrodes by localized laser
heating is presented. The nanostructures were deposited over electrodes
using the dielectrophoresis (DEP) technique. A focused laser beam was
used for direct heating the samples in ambient atmosphere. The Raman
spectroscopy was used to determine the process temperature by
observations of the graphitic C-line downshift. In the laser annealing
experiments, the C-line position was found first to downshift linearly
with laser power indicating gradual heating of the sample proportional
to the absorbed power. However, with increasing power the shift was
found to saturate at levels that depend on the metal and the contact
area. This saturation was attributed to gradual increase of the contact
area and improvement of the thermal contacts between the nanostructures
and metal electrode that can occur during sample heating. The maximum
sample temperature in the beginning of the annealing process was always
higher for MW samples, due to smaller area of contact established
between rigid multi-layer graphene and initially rough metal surface.
The final result is the increased heat losses to the electrodes and,
subsequently, the reduction of the samples temperature. The main
advantage of this method, when compared with traditional and rapid
thermal annealing, is that the thermal treatment is localized in a small
pre-determined region, allowing individually controlled annealing
process. (C) 2014 Elsevier B.V. All rights reserved.
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