Growth Mechanism of Single-Walled Carbon Nanotubes from Pt Catalysts by Alcohol Catalytic CVD
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Growth Mechanism of Single-Walled Carbon Nanotubes from Pt Catalysts by Alcohol Catalytic CVD Takahiro Maruyama1, Hiroki Kondo2, Akinari Kozawa2, Takahiro Saida1, Shigeya Naritsuka2, and Sumio Iijima3,4 1 Department of Applied Chemistry, Meijo University, Nagoya 468-8502, Japan 2 Department of Materials Science and Engineering, Meijo University, Nagoya 468-8502, Japan 3 Faculty of Science and Technology, Meijo University, Nagoya 468-8502, Japan 4 Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565 ABSTRACT Single-walled carbon nanotube (SWCNT) growth from Pt catalysts by an alcohol gas source method, a type of cold-wall chemical vapor deposition (CVD), was investigated. Raman results showed that the diameters of SWCNTs grown from Pt were below 1.2 nm, while transmission electron microscopy (TEM) showed that the diameters of most Pt catalyst particles were above 1.2 nm. This suggests that SWCNT diameters were smaller than Pt catalysts particles. X-ray photoelectron spectroscopy measurements showed that reduction of Pt particles occurred during the SWCNT growth. Based on these experimental data, growth mechanism of SWCNTs was discussed. INTRODUCTION Since the discovery of single-walled carbon nanotubes (SWCNTs) in 1991 [1], they have been anticipated for application to various electronics devices, such as a field effect transistor (FET) and a single electron transistor (SET). To fabricate SWCNT devices in a conventional LSI process, it is desirable to grow SWCNTs at low temperature under high vacuum. Thus far, we have reported SWCNT growth using Co catalysts in an alcohol gas source method, a type of cold-wall chemical vapor deposition (CVD) and succeeded in SWCNT growth at 400ºC by optimizing the growth condition [2]. Recently, by using Pt as catalysts, we attained SWCNT growth under an ethanol pressure of 10-3 Pa, while the SWCNT yield was larger than those grown from Co catalysts at the growth temperature of 700ºC [3]. In this study, we investigated SWCNT growth from Pt catalysts, especially the relationship between the SWCNT diameter and the catalyst particle size. In addition, the chemical states of Pt catalysts were investigated by X-ray photoelectron spectroscopy (XPS). EXPERIMENTAL PROCEDURE SiO2(100 nm)/Si substrates on which Pt catalysts were deposited were used for the SWCNT growth. The nominal thickness of Pt was fixed to be 0.2 nm, which was the optimal thickness to obtain the highest yield [4]. After deposition of catalysts in an ultra-high vacuum (UHV) chamber, the substrate temperature was increased to the growth temperature, 700ºC, under hydrogen gas flow at a pressure of 1×10-3 Pa to prevent oxidation of catalysts. After stopping the H2 supply, SWCNTs were grown by the alcohol gas source method in the UHV chamber, a type of cold-wall CVD equipment. Ethanol gas was supplied to the substrate
surface for 1 h through a stainless steel nozzle with a hole (diameter~0.5 mm) at the tip. The supply of ethanol gas was con
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