Effects of oxygen on multiwall carbon nanotubes growth by PECVD

Abstract

Multiwall carbon nanotubes (MWCNTs) were grown by dielectric barrier discharge (DBD)-type plasma enhanced chemical vapor deposition (PECVD) method in downstream. The temperature was 973 K and the compositions of gases were methane, hydrogen and oxygen in the total pressure of 0.05 MPa. The effect of O2 concentration in the mixture on the configuration of carbon nanotubes (CNTs) was investigated in detail. Results from scanning electron microscope (SEM) and transmission electron microscope (TEM) showed that CNTs grown in CH4/H2 (38.6%/61.4%, volume) mixture have many defects and contained disordered graphitic materials. With the addition of appropriate amount of O2 (∼0.67%), high-purity CNTs could be obtained. However, no CNT, even no carbon matrix existed under the condition of an excessive oxygen concentration (>1.0%, volume) in the mixture. In order to understand the role of O2 during CNTs growth, optical emission spectroscopy (OES) was in-situ employed and the results predicted that the improvement of CNTs quality in O2 addition was attributed to the effect of OH oxidation from the reaction of atomic oxygen with hydrogen in the plasma.