Assessment Of Surface Damage Research Articles

Assessment of Surface Damage of Gallium Arsenide due to Reactive Ion Etching

Crystal damage of GaAs(100) caused by Reactive Ion Etching (RIE) using a mixture of Cl2 and Ar gas has been assessed using Surface Roughness (Ra), Resonant Raman Spectroscopy (RRS), Schottky diodes, and Spectroscopic Ellipsometry (SE). Plasma conditions for minimum induced damage have been determined and compared to optimised RIE processes using plasma gases SiCl4, CH4-H2, CCl2F2 and Ar. The SiCl4 plasma was found to produce the least crystal damage.

Qualitative and quantitative SEM of gastrointestinal tract

Introduction:The natural mucosal surfaces of the digestive tract provide an interface with the environment which undergoes structural changes in response to experimental procedures and naturally occurring disease. This paper describes the application of modern scanning electron microscopy (SEM) techniques to gastrointestinal research. Initially based on qualitative studies of mucosal responses to insult such as irradiation or hyperthermia, the interpretation of recent results has come to rely increasingly on the semi-quantitative assessment of surface damage and on the use of frozen hydrated specimens to eliminate processing artefact and to permit quantitative elemental analysis.Materials and Methods:Tissue has been collected from several sources. Irradiated mouse intestine has been compared with similar tissue exposed to hyperthermia or drug treatment. Biopsies of gastrointestinal tissue have been collected prospectively or retrospectively, the latter by dewaxing blocks of interest from hospital files. Routine scanning electron microscopy has often been followed by post-embedding the specimen for resin light microscopy and transmission electron microscopy (TEM). Alternatively, resin sections 1 μm thick mounted on coverslip fragments were surface etched by oxygen plasma, shadowed with platinum/palladium and gold coated prior to examination in the SEM. Etched surfaces of mouse duodenum and stomach have also been examined in the frozen hydrated state to record cell and tissue structure as well as data on ion concentrations through x-ray microanalysis.Results and Discussion:Qualitative studies of mucosal responses using secondary electron imaging, in use since the 1960s, are enhanced by the ability of the SEM to record extensive surface areas, if necessary through montage techniques. in this way, the problems of individual variation in an experimental series can be minimised. Mucosal responses to irradiation in small bowel have been documented. The collapse of the villous pattern from erect finger-like processes to irregular conical projections follows a time scale of several days after a single dose of irradiation, whereas equivalent structural changes are completed within 24 hours of an episode of heat injury. Correlative light microscopy and TEM studies show that the changes in shape of the villi after irradiation may be linked to alterations at the interface between surface epithelium and underlying connective tissue: focal irregularities of the basal lamina and detachment of epithelial cells may represent the earliest manifestation of subsequent damage to surface contours.

Anisotropy in the mechanical properties of lamellar solids and its effect on wear and transfer

Experiments have been made to determine the degree of anisotropy in mechanical properties of lamellar solids, such as graphite, MoS 2, mica, PbI 2, etc. Radioactive measurements of the wear of copper sliding against compacts of lamellar solids, together with qualitative assessment of surface damage on other metals, show that many of the solids are intrinsically abrasive. The amount of wear and surface damage depends on the relative maximum hardness of the solid and the metal and, in addition, on the extent to which the lamellar solid acquires a preferred orientation during sliding. The maximum hardness of MoS 2, for example, is 7–8 Mohs. It is suggested that embedding of suitably oriented crystallites of a lamellar solid into metal surfaces is a major factor in the formation of transferred films of the solids. Measurements of the endurance of transferred films of various solids deposited on metals of different hardnesses show that endurance increases as the hardness of the substrate metal decreases. In the particular experimental conditions used (relatively light loads and low speeds) there is no evidence that chemical interactions play a significant role in the bonding of a solid lubricant film to its substrate.

MODERN TECHNIQUES IN LUBRICATION RESEARCH

This paper provides a few examples of techniques that are being used at the Thornton Research Centre of “Shell” Research Limited in the development of lubricants. No attempt has been made to provide a detailed description of how the techniques were developed or how they are used. For some of them detailed information is already available in published articles or papers, and references are provided; others are still in the development stage and more information will probably be published at some later date. It will be obvious that to attempt to cover any one of these developments in detail would require much more time than is either at your disposal or mine, and I have therefore given only sufficient detail to perhaps whet your appetites for more. Typical of the sorts of information required for lubricant development are the following :— 1. Accurate temperature measurements of the moving and/or contacting and rubbing surfaces of the mechanism to be lubricated. 2. A qualitative or quantitative assessment of surface damage of contacting or rubbing parts. 3. An accurate measurement of wear rate. 4. An accurate measurement of the chemical change occurring on the surface of rubbing components in the presence of E.P. additives. This list could be extended almost indefinitely but it provides a fair cross‐section of the type of information likely to be required for the development of a lubricant. This sort of information must often be obtained from simulated mechanisms specially instrumented and designed, but we are designing lubricants for actual mechanism, gear trains, transmissions, bearings, clutch plates, etc., where it is extremely rare to find provision or access for the qualitative and/or quantitative examination so desired. As a result very elaborate and complicated methods have sometimes to be employed to obtain the necessary information. The following techniques represent only a few of those that have been used or are being used, but I hope they will demonstrate how some of our difficulties ware overcome.