Self-aligned growth of single-walled carbon nanotubes using optical near-field effects
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Self-aligned growth of single-walled carbon nanotubes using optical near-field effects
Y. S. Zhou, W. Xiong, M. Mahjouri-Samani, W. Q. Yang, K. J. Yi, X. N. He and Y. F. Lu∗ Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0511
ABSTRACT By applying optical near-field effects in a laser-assisted chemical vapor deposition (LCVD) process, self-aligned growth of ultra-short single-walled carbon nanotubes (SWNTs) was realized in a well controlled manner at a relatively low substrate temperature due to the nanoscale heating enhancement induced by the optical near-field effects. Bridge structures containing single suspending SWNT channels were successfully fabricated. Ultra-sharp tip-shaped metallic electrodes were used as optical antennas in localizing and enhancing the optical fields. Numerical simulations using High Frequency Structure Simulator (HFSS) reveal significant enhancement of electrical fields at the metallic electrode tips under laser irradiation, which induces localized heating at the tips. Numerical simulations were carried out to optimize SWNT growth conditions, such as electrode tip sharpness and film thickness, for maximal enhancement of electrical near field and localized heating. INTRODUCTION Single-walled carbon nanotubes (SWNTs) are ideal platforms for fundamental study and promising candidates for technological applications due to their unique one-dimensional structures and superior properties [1]. SWNTs have been intensively investigated as an alternative material to replace current silicon-based devices [2]. Fabrication of SWNT-based devices requires integration of SWNTs. Chemical vapor deposition (CVD) process is presently the only economically viable process for integrating SWNTs into devices by yielding selective and aligned SWNT growth directly on various substrates [3]. Conventional CVD methods generally require high reaction temperatures up to 800 to 1200 ºC, and expose the substrate to the high temperature. However, high substrate temperature prevents integration of SWNTs into device fabrication. It is well known that ultra-sharp metallic tips can be used as optical antennas in localizing and enhancing optical fields due to the optical near-field effects [4]. Enhancement of the electric field at the tip results in an enhanced eddy current, which yields local heating enhancement and a significant temperature increase at the tip. In this study, optical near-field effects are integrated in the LCVD process to realize the self-aligned growth of SWNTs at a relatively low substrate temperature. The experimental results and numerical simulations demonstrate that the ∗
Correspondence should be addressed to Prof. Y. F. Lu, Tel: (402) 472-8323, Fax: (402) 472-4732, Email: [email protected].
laser-induced optical near-field effects produce nanoscale localized heating at electrode tips, which stimulates the selective growth of SWNTs at the tips. Influence of the tip sharpness and metallic film thickness were investigated via numerical simulation usin
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