Page 205 - Science at the nanoscale

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8.4. Optical Tweezers
Laser Nanofabrication
Carbon nanotubes (CNTs) have been of great interest to
researchers due to their remarkable structural, electronic and
mechanical properties. As they have tunable electronic proper-
ties, they are being investigated as possible new materials for the
next generation of microelectronics and nanoelectronics devices.
They have also been identified as potentially useful materials for
a broad range of functions including actuators, fuel cells, flat panel
displays, biosensors and improved X-ray sources. Arrays of CNTs
have also been used as templates for a variety of materials to
achieve functions such as creating super-hydrophobic surfaces.
Many of these applications require a fabrication method capable
of producing extended areas of patterned and aligned CNTs with
uniform structures and periodic arrangements to meet device re-
quirements. There are a few conventional methods to fabricate
patterned aligned CNTs arrays. One such technique makes use
of electron beam lithography to define the patterns of catalytic
nanoparticles for the growth of CNTs.
In this section, we introduce a simple technique that makes use
of a tightly focused laser beam from a moderate power laser as a
precision cutting tool to create unique three dimensional 3D CNTs
9
Figure 8.33(a) shows a schematic of the
structures in ambient.
experimental set-up of an optical microscope-focused laser beam
system in the author’s lab. The system consists of an optical mi-
croscope and a medium power laser such as a He-Ne laser source
(∼20–40 mW). The role of microscope is to focus the laser beam
onto the sample and at the same time capture the image of the
sample. A parallel beam from the laser is directed into the micro-
scope via two reflecting mirrors (M). Inside the microscope, the 195 ch08
laser beam is directed towards an objective lens (L) via a beam
splitter (S). The laser beam is then focused by the objective lens
(L) onto the CNTs. Typically, an objective lens with high magnifi-
cation and long working distance is preferred. When the focused
laser beam is incident on the CNT sample, it readily trims away
the top layers of the CNTs. SEM analysis reveals that part of the
CNTs are removed cleanly without leaving behind any residue.
9 K. Y. Lim, C. H. Sow, J. Y. Lim, F. C. Cheong, Z. Y. Shen, J. T. L. Chin, K. C. Chin
and A. T. S. Wee, Advanced Materials, 15, 300–303 (2003).