A Dual-RF-Plasma Approach for Controlling the Graphitic Order and Diameters of Vertically-Aligned Multiwall Carbon Nanot
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A Dual-RF-Plasma Approach for Controlling the Graphitic Order and Diameters of Vertically-Aligned Multiwall Carbon Nanotubes Jitendra Menda, 1 Lakshman Kumar Vanga, 1 Benjamin Ulmen, 1 Yoke Khin Yap1,* Zhengwei Pan,2 Ilia N. Ivanov, 2 Alex A. Puretzky, 2 David B. Geohegan 3 1 Department of Physics, Michigan Technological University, Houghton, MI 49931, USA. 2 Department of Materials Science and Engineering, University of Tennessee 3 Condensed Matter Sciences Division, Oak Ridge National Laboratory * Email: [email protected]
ABSTRACT Plasma enhanced chemical vapor deposition (PECVD) is a unique technique for growing vertically-aligned multiwall carbon nanotubes (VA-MWNTs) at controllable tube densities. This technique is of considerable importance for low temperature growth of VA-MWNTs at desired locations. However, the graphitic order of these MWNTs is inferior to those grown by laser ablation, arc discharge, and thermal CVD techniques. Previously, these VA-MWNTs were grown by a one-plasma approach (DC, microwave etc), either for gas decomposition or substrate biasing. Here, we describe a dual-RF plasma enhanced CVD (dual-RF-PECVD) technique that offers unique capability for controlling the graphitic order and diameters of VA-MWNTs.
INTRODUCTION Carbon nanotubes (CNTs) are among the promising materials that are expected to play a major role in future nanoscience and nanotechnology. Their unique structural and electronic properties make them a potential candidate for many nano-electronic, mechanical, chemical, and biological applications. Some applications require CNTs to be grown with controllable dimensions and growth orientation. For example, electron field emission devices demand that the growth of CNTs be vertical-aligned to the substrate surface. Plasma enhanced chemical vapor deposition (PECVD) is of considerable importance for low temperature growth of VA-MWNTs at desired locations. However, the graphitic order of these MWNTs is inferior to those grown by laser ablation, arc discharge, and thermal CVD techniques. VA-MWNTs grown by PE-CVD are usually called carbon nanofibers (CNFs) and have highly distorted structures. Previously, these CNFs were grown by a one-plasma approach, either for gas decomposition or substrate biasing [1-4]. Here, we describe a dual-RF-plasma enhanced CVD (dual-RF-PECVD) technique that offers unique capability for controlling the graphitic order and diameters of VA-MWNTs. By the dual-RF-PECVD, we have demonstrated the growth of VA-MWNTs to an area as large as 25 cm2 at a substrate temperature as low as 540 °C [5]. The use of two RF-power sources in the technique allowed independent control of the potential and kinetic energies of the growth species. The potential energy refers to the excitation and ionization rates of the growth species. The kinetic energy depends on the speed of the ionic species accelerated toward the substrate by the substrate negative bias voltages. Here, we describe the function of these plasmas on the graphitic order and diameters of VA-MWNTs.
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