Characterization of acetylene in a microwave plasma chemical vapor deposition reactor

Alfredo D Tuesta, Purdue University

Abstract

Since its recent discovery as a standalone material, research on single to multi layer graphene has surged with studies ranging from growing techniques to applications that promise to revolutionize nanotechnology and bring to fruition many awaited technological advances. While several techniques for growth exist, microwave plasma chemical vapor deposition of graphene over a catalyst-free substrate provides excellent control over the reacting species involved and lower growth temperatures which allow for the use of a variety of materials. This thesis investigates the plasma environment of a microwave plasma chemical vapor deposition reactor through absorption spectroscopy of acetylene and aims to elucidate the chemical composition and physical processes involved at the site of graphene growth. Experiments which allowed for the production of acetylene to reached steady state within the reactor reveal translational temperatures between 300 and 350 K and rotational temperatures slightly higher, reaching almost 400 K. These results provide evidence for an abundance of cooler acetylene outside the plasma which limits the sensitivity of the signal from acetylene within. It is believed that the signal originating from acetylene within the plasma is overwhelmed by the signal from the cooler acetylene near the periphery of the reactor. Monitoring of the rotational temperature as a function of time from the instance in which methane is introduced into the reactor reveal much higher rotational temperatures of acetylene reaching values of up to 500 K for approximately the first minute and half. It is speculated that these higher rotational temperatures originate from acetylene within the plasma where most of the acetylene might be concentrated. This in turn provides an indication of the disparity between acetylene properties within the plasma and outside. Furthermore, the results indicate that adequate measurements of acetylene can be made which should enable other spectroscopic techniques to be applied.

Degree

M.S.M.E.

Advisors

Lucht, Purdue University.

Subject Area

Nanotechnology|Optics

COinS