An ion sputtering apparatus for thinning electron microscope specimens

Abstract

An apparatus for the controlled erosion of metal surfaces by ion beam sputtering has been designed and constructed. The apparatus was tested in the preparation of thinned specimens from ion - implanted metals so that the microstructure could be examined using transmission electron microscopy (TEM). Specimens corresponding to different depths below the implanted surface were prepared by the ion erosion of the implanted surface to different depths prior to chemical backthinning the specimens to perforation in a jet electropolishing bath. In a particular study, four high purity Cu foil targets were irradiated at normal incidence with 200 keV D+ ions at a temperature of 120 K, to a dose of 1.75 X 10 17 D+ / cm2 (a level corresponding to 10 % of the critical dose for radiation blistering, Cb7 ). Argon - ion milling was used to remove 0.1 μm from the surface of the first target. The depths removed from the other targets were 0.5 μm, 1.0 μm and 2.0 μm respectively. Scanning electron microscopy (SEM) was used to examine the eroded surfaces. Surface artifacts resulting from D+ irradiation were evident on all four targets. Argon - ion milling seemed to enhance the production of surface artifacts. An explanation in terms of heating effects is advanced. Microcrystallites were observed on eroded surfaces. Although the mechanisms leading to their formation are not yet clear it is thought that they result from a synergism between the implantation produced microstructure and sputtering processes. Examination of the backthinned targets using TEM revealed the presence of a high dislocation density 10 10 or 10 11 cm-2. No gas bubbles were found. Moire interference fringes were observed on all four targets. These fringes were attributed to the presence of cuprous oxide on specimen surfaces. It was found that at magnifications above 5 x 10 5 lattice images corresponding to some crystal planes in copper and in cuprous oxide could be observed directly.