Surface Cleaning by Glow Discharge in High-Volume Gas Flow

Abstract

Abstract : Surfaces of solids and the surfaces of domains within the solids are generally coated with contaminants which determine many of the mechanical properties of those surfaces (such as the ability to cold weld). This report describes a technique of cleaning the solid surface by continually purging a glow-discharge chamber with ultra clean, dry, and chemically inert gas during the flow-discharge phase. A large vacuum chamber is used which is 81 centimeters in diameter and 3 meters long. The purging gas is allowed to flow through the chamber, past the sample holder, at a rate of about 3 chamber volumes per minute. Such a large chamber is used instead of standard commercial glow- discharge devices to allow for many mean free paths for the contaminants to expand into and thus increase the time required to contact the chamber walls. This allows the sweeping action of the gas flow to move the contaminants downstream and thus reduce the probability of recontaminating either the chamber walls or the test surfaces. The cleaning effectiveness is compared by measuring the contact angles that high-surface-energy liquid drops make with the cleaned surface. The liquids used are triply distilled water for detecting by hydrophobic contamination and methylene iodide for detecting water contamination. The surfaces used to demonstrate the cleaning technique were stainless steel and aluminum oxide. Some of the contact angles were too flat to observe but were estimated to be less than 1 degree. The small contact angles are interpreted to mean that there is less than 1 monomolecular layer of contaminant on the cleaned surface.