Synthesis of Multiwalled Carbon Nanotubes on Stainless Steel by Atmospheric Pressure Microwave Plasma Chemical Vapor Deposition

Dashuai Li,Bo Gao,Ling Tong

doi:10.3390/app10134468

Abstract

In this paper, we synthesize carbon nanotubes (CNTs) by using atmospheric pressure microwave plasma chemical vapor deposition (AMPCVD). In AMPCVD, a coaxial plasma generator provides 200 W 2.45 GHz microwave plasma at atmospheric pressure to decompose the precursor. A high-temperature tube furnace provides a suitable growth temperature for the deposition of CNTs. Optical fiber spectroscopy was used to measure the compositions of the argon–ethanol–hydrogen plasma. A comparative experiment of ethanol precursor decomposition, with and without plasma, was carried out to measure the role of the microwave plasma, showing that the 200 W microwave plasma can decompose 99% of ethanol precursor at any furnace temperature. CNTs were prepared on a stainless steel substrate by using the technology to decompose ethanol with the plasma power of 200 W at the temperatures of 500, 600, 700, and 800 °C; CNT growth increases with the increase in temperature. Prepared CNTs, analyzed by SEM and HRTEM, were shown to be multiwalled and tangled with each other. The measurement of XPS and Raman spectroscopy indicates that many oxygenated functional groups have attached to the surface of the CNTs.

Highlights

Since Iijima synthesized carbon nanotubes (CNTs) by the arc discharge process in 1991 [1], many CNT synthesis processes have been developed
In order to improve the yield of CNTs, direct current plasma chemical vapor deposition (DC-PECVD) [6], radio-frequency plasma chemical vapor deposition (RF-PECVD) [7,8], and microwave plasma chemical vapor deposition (MPCVD) [9,10,11,12] were developed based on thermal
Compared with thermal CVD, the CNT growth rates of DC-PECVD, RF-PECVD, and MPCVD are increased by 2–5 times at the same temperatures and pressures

Summary

Introduction

Since Iijima synthesized carbon nanotubes (CNTs) by the arc discharge process in 1991 [1], many CNT synthesis processes have been developed. Compared with thermal CVD, the CNT growth rates of DC-PECVD, RF-PECVD, and MPCVD are increased by 2–5 times at the same temperatures and pressures. The combination of atmospheric pressure microwave plasma and a CVD tube furnace makes the technology have a strong precursor decomposition, a pure nanomaterial synthesis atmosphere, a large control range of particles density, and accurate temperature control, which overcomes the pressure limits of PECVD and achieves accurate control of the nanomaterials synthesis process. For this is the only study of nanomaterial synthesis by AMPCVD. Compared with the experiments in [13,14,15], the decomposition capacity of 200 W atmospheric pressure microwave plasma of the AMPCVD is high enough to decompose the precursors completely

AMPCVD

Experimental Setup

Characterizations

Plasma Parameters

Plasma

Exhaust