Design and Implementation of an In-Situ Microplasma Cell in an Environmental Scanning Electron Microscope for the Study of Plasma-Surface Interaction

Abstract

Microplasmas have a wide variety of applications, from synthesis of carbon nanostructures to the decomposition of greenhouse gases like carbon dioxide and methane. Past work done has been done at the Princeton Plasma Physics Laboratory (PPPL) with a carbon dioxide microplasma. The results of this work showed the necessity for performing in-situ analysis of the interaction between plasma and materials. Traditional methods of imaging materials after they have come in contact with plasma usually involve exposing the material to atmospheric conditions while transporting it to a microscope. This leads to potential contamination and results that are not very time dependent, which inspired the decision to design and implement an experiment that would not be faced with these issues. This thesis describes the design of an experiment for the in-situ analysis of plasma-material interactions within an environmental scanning electron microscope (ESEM). The ESEM, retrofitted to be able to house the plasma, provides flexibility in the gaseous enviornments it can accomodate and also in its pressure ranges. A microhollow cathode geometry, consisting of a stainless steel hollow cathode with a diameter of 1.75 mm and a nickel plate as the anode, is used to confine the DC-powered plasma. Operation pressures range from 2-5 Torr, making the pd value of the microplasma 0.35-0.875 cmTorr. The argon microplasma was successfully confined using the hollow cathode geometry, and plasma characteristics were obtained. Tests were done with the hollow cathode configuration, and polarity was reversed in order to additionally obtain results with a hollow anode configuration. A stable plasma was achieved, and reproducible results obtained both for the electrical characteristics of the plasma and the interaction between the plasma and the nickel substrate. Results validated the experimental methodology and design while showing the promise and potential of in-situ measurements in an ESEM.