Physical Chemistry:  Chemical interactions of plasmas with solid surfaces.

Research in the Blumenthal Group is focused on the chemical interactions of plasmas with solid surfaces. Over the years, our interests have ranged from problems of concern to the semiconductor industry (the etching of silicon and magnetic metals), thin film deposition (the deposition of diamond thin films), and the military (the ignition of propellants).

Method Development (Supersonic Pulse, Plasma Sampling Mass Spectrometry): Our first efforts were dedicated to the development of a new mass spectrometric method, Supersonic Pulse, Plasma Sampling Mass Spectrometry. In this technique, we release a short pulse of argon into the low-pressure plasma environment. The gas pulse expands and cools as it traverses the plasma region, ultimately resulting in supercooling of the gas. Species originally in the plasma become the nucleation centers for the formation of argon clusters, which then transport the species to the mass spectrometer. This technique allows us to obtain a mass spectrum of a nearly intact sample of the chemical composition of the plasma.

Thin Film Deposition (Applications include tools and multi-blade razors): The first problem that we tackled with this new technique was the mechanism of diamond deposition in high-density plasmas. We were able to show that the primary chemistry of the feed gases is the stripping of hydrogen from the carbon backbone. Based on our observations, we were also able to make a convincing argument that the “growth species” of diamond is •C₂H₃, not •CH₃ as is commonly believed.

Semiconductor Processing (Transistor and non-volatile RAM Fabrication): In the semiconductor etching field, we were the first group to measure the fraction of chlorine that is dissociated in these plasmas. We have determined the mechanism responsible for the 250% etch rate enhancement in the etch rates of magnetic metals, observed when CO is added to NH3 plasmas. That mechanism is the first one reported that includes a species responsible for the etching that is synthesized in the plasma environment. We are currently exploring a number of other gas chemistries to determine both their etch rates and their mechanisms.

Military Effectiveness (Ignition of Propellants for Artillery Applications): We are investigating the mechanism of the plasma ignition of propellants. Plasma ignition has been demonstrated to have several advantages over conventional ignition, including a reduced and highly reproducible ignition delay, important in targeting moving objects. By investigating the interactions of a propellant with the individual components and combinations of the components of an igniter pulse, we have developed a mechanism for the plasma ignition process that also explains the reproducible ignition delay. We are actively working on a number of other issues related to propellant ignition.

Selected Publications: