Anomalous Branch-structured Carbon Nanotubes on Silicon Substrates
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1057-II05-30
Anomalous Branch-structured Carbon Nanotubes on Silicon Substrates Yaser Abdi1,2, Shams Mohajerzadeh1, Kokab Baghbani1, Sara Paydavosi1, and Ebrahim Asl Soleimani1 1 School of Electrical and Computer Engineering, University of Tehran, Thin Film and NanoElectronics Lab, Tehran, 14395515, Iran 2 Department of Physics, University of Tehran, Tehran, 14395515, Iran ABSTRACT We have grown vertically aligned carbon nanotubes on (100) silicon substrates by means of a plasma enhanced chemical vapor deposition method. The growth of CNTs is achieved by a mixture of hydrogen and acetylene gases in a CVD reactor and a 5-10nm thick nickel is used as the seed for the growth. Following the growth of nanotubes on silicon substrates, they are covered by a titanium-oxide layer and then the substrate is placed back into the original chamber to be exposed to hydrogen plasma. Depending on the hydrogenation step the nickel seed layer, which is placed on the tip side of the original nanotube, is expanded. The subsequent process in the same reactor leads to the growth of carbon nanotubes in a branched manner. Scanning electron microscopy has been used to investigate the results of such tree-like nanostructures. INTRODUCTION Carbon nanotubes have emerged as a promising technology for the fabrication of fieldemission devices and sensors [1-3]. Over the past decade, several techniques have been used for the growth of single and multi-wall carbon nanotubes including thermal catalyst-based CVD, laser-vaporization deposition and arc-discharge growth. Vertical CNTs with sharp tips are desired for optimal field emission characteristics. Among various techniques, plasma enhanced chemical vapor deposition (PECVD) has been shown to yield CNTs with suitable morphological and emission properties [4-6]. Carbon nanotubes have been used in nano-lithography applications as well as in the fabrication of field-effect transistors operating on a ballistic transport mechanism. The application of CNTs in logic circuits has also been investigated. We have recently reported the vertical growth of carbon nanotubes using a PECVD technique where a mixture of acetylene and hydrogen was used for the deposition of CNTs [6-8]. In this paper, we report a novel growth method of carbon nanotubes with a branched tree-like structure on silicon substrates. The evolution of such nanostructures has been possible by controlling the hydrogenation as a post-growth step. The subsequent growth has been achieved using the same PECVD reactor under similar conditions. The growth of branched nanotubes on the original ones are repeated and tree-like structures can be achieved. Such branched structures can be used to improve the field emission properties of CNTs. EXPERIMENT Vertically aligned carbon nanotubes are grown using a PECVD technique with a mixture of C2H2 and H2. P-type (100) Si substrates are used for the growth of CNTs where 5-10nm-Ni is used as the seed for the growth [6-8]. By patterning the nickel layer prior to the CNT growth, desired features with micrometer a
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