Growth, Nitrogen Doping and Characterization of Isolated Single-Wall Carbon Nanotubes using Liquid Precursors
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Growth, Nitrogen Doping and Characterization of Isolated Single-Wall Carbon Nanotubes using Liquid Precursors Gayatri Keskar1, Rahul Rao2, Jian Luo1, Joan Hudson3 and Apparao M. Rao2 1 School of Materials Science and Engineering, Clemson University, Clemson, South Carolina, 29634, USA. 2 Department of Physics and Astronomy, Clemson University, Clemson, South Carolina, 29634,USA. 3 Advanced Materials Research Laboratories, Clemson University, Clemson, South Carolina, 29634, USA.
ABSTRACT Isolated single wall carbon nanotubes (SWNTs) were prepared on bare quartz and SiO2 / Si substrates using chemical vapor deposition (CVD) in which a liquid precursor, such as xylene, was used as the carbon source. The coverage of isolated SWNTs on the substrates was controlled by adjusting the concentration of iron (III) nitrate nonahydrate/2-propanol solution which provided the Fe seed catalyst particles. Micro-Raman spectra were obtained using the 514.5 nm excitation which showed the typical tangential band around 1590 cm-1 for semiconducting nanotubes. The radial breathing mode (RBM) frequencies ranged between 150 to 240 cm-1 and the estimated tube diameters are in good agreement with those obtained from atomic force microscope (AFM) images. In our synthesis approach controlled doping of isolated SWNTs with nitrogen was achieved by mixing appropriate amount of acetonitrile with xylene. As the nitrogen concentration in the feed was increased from 0 – 33 at. %, the RBM intensity decreased dramatically while the intensity of the D-band increased gradually relative to that of the G-band. Interestingly, the D’ band was observed for the first time in the Raman spectrum of carbon nanotubes when the nitrogen concentration reached ~2-3 at. %. INTRODUCTION In the fast few decades, extraordinary advancements have been achieved in shrinking the size of silicon-based devices. This progress is primarily due to the development of the metal oxidesemiconductor field-effect transistor (MOSFET) with reduced dimensions and associated integrated electronic technology which enables both high speed performance and device density. However, the dimensions of these MOSFET devices are reaching a limit below which they cannot function properly and a search for alternate technologies based on nano-structured materials is on the rise. A promising future technology is based on molecular electronics in which the active part of the device is composed of a single, or few molecules [1]. One of the extensively studied molecules is the carbon nanotube (CNT) which exhibits unique physical, chemical, electrical and thermal properties [2-6]. SWNTs have been used as the “building blocks” in the fabrication of room temperature FETs [4-7], diodes [8] and inverters [9]. For developing nanotube-based complementary logic circuits, we need both type p-type as well as ntype of carbon nanotube field effect transistor (CNTFETs). Devices based on as-grown isolated SWNTs are invariably p- type behavior and degassing them leads to n-type characteristics [10]. The p- type c
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