Surface contaminants, cleaning

Instmmentation for tern is somewhat similar to that for sem however, because of the need to keep the sample surface as clean as possible throughout the analysis to avoid imaging surface contamination as opposed to the sample surface itself, ultrahigh vacuum conditions (ca 10 -10 Pa) are needed in the sample area of the microscope. Electron sources in tern are similar to those used in sem, although primary electron beam energies needed for effective tern are higher, typically on the order of ca 100 keV. 

Ingots of EGS are evaluated for resistivity, crystal perfection, and mechanical and physical properties, such as she and mass. The iagots are sHced iato wafers usiag at least 10 machining and polishing procedures. These wafers are sHced sequentially from the iugot, and evaluated for the correct surface orientation, thickness, taper, and bow. As a final procedure, the wafers are chemically cleaned to remove surface contaminants prior to use. 

Silica [7631-86-9 (colloidal)-, 112945-52-5 (fumed)]. Purification of silica for high technology applications uses isopiestic vapour distillation from cone volatile acids and is absorbed in high purity water. The impurities remain behind. Preliminary cleaning to remove surface contaminants uses dip etching in HF or a mixture of HCl, H2O2 and deionised water [Phelan and Powell Analyst 109 1299 1984],... 

Because of the extreme surface sensitivity of static SIMS, care should always be exercised not to handle the samples. Clean tools and gloves should be used always to avoid the possibility of contaminating the surface. While it is possible to remove surface contamination with solvents like hexane, it is always desirable not to clean the surface to be analyzed. 

Before 1950, it was impossible to examine the true structure of a solid surface, because, even if a surface is cleaned by flash-heating, the atmospheric molecules which constantly bombard a solid surface very quickly re-form an adsorbed monolayer, which is likely to alter the underlying structure. Assuming that all incident molecules of oxygen or nitrogen stick to the surface, a monolayer will be formed in 3 x 10 second at 1 Torr (=1 mm of mercury), that is, at 10 atmosphere a monolayer forms in 3 s at 10 Torr, or 10 atmosphere but a complete monolayer takes about an hour to form at 10 Torr. The problem was that in 1950, a vacuum of 10" Torr was not achievable lO Torr was the limit, and that only provided a few minutes grace before an experimental surface became wholly contaminated. 

Surface contaminant Any contaminant that adheres to a surface in a clean room. 

There are also occasions, particularly in hydrogen-containing atmospheres, when surface contamination of the titanium with iron can result in localised corrosion and embrittlement. This effect can be countered by avoidance of undue contamination with iron during fabrication, by postfabrication cleaning and by post-fabrication anodisingIt should be emphasized, however, that in general use in the marine and chemical industries discussed below, iron levels up to 0-2% do not adversely affect corrosion resistance. 

With materials like the stainless steels, which may be either active or passive in a test environment, it is common practice to produce a particular initial level of passivity or activity by some special chemical treatment prior to exposure. With stainless steels this objective may be subsidiary to eliminating surface contamination, such as iron from processing tools, by treatment in a nitric acid solution which might also be expected to achieve substantial passivity incidental to the cleaning action (ASTM A380 1988). 

Davies et al. (D9) have recently measured the rates of absorption of various gases into turbulently stirred water both with carefully cleaned surfaces and with surfaces covered with varying amounts of surfactants. That hydrodynamic resistances, rather than monolayer resistances, are predominant in their work is consistent with the high sensitivity of kL to very small amounts of surface contamination and also with the observation that a limit to the reduction in kL is found (D7, D9). This is in agreement with the results of Lindland and Terjesen (L9), who found that after a small concentration of surfactant had been used further additions caused but little change in terminal velocity (L9). 

The effect of surface contamination and the wettability between the tube wall and the fluids were also studied experimentally. It has been shown that a stable annular flow and gas slug formation with a stable thin liquid film formed between the tube wall and gas slugs, which appeared at high velocities under carefully treated, clean... 

To fulfil the background requirements typical of rare event physics, particular care was dedicated to the selection and treatment of the materials used for the construction of CUORICINO the crystals where grown with low contamination materials in China and sent by ship to Italy where they have been optically polished with specially selected low-contamination powders. The mechanical structure of the array was made exclusively in OFHC copper and PTFE both these materials have an extremely low radioactive content. All the copper and PTFE parts of the mounting structure underwent a chemical treatment to remove any possible surface contamination. Finally, the array was assembled in an underground clean room in a N2 atmosphere to avoid Radon contamination. 

Surface samples were collected in snow pits under ultra-clean conditions described elsewhere [13] with the exception that samples for anion analysis were collected in polystyrene cups precleaned without the use of acids. Ice core samples were cleaned to remove surface contamination using the "dry-core" procedure involving rinsing and melting of exterior surfaces with ultra-pure water [13]. Shallow-depth firn cores are permeable and the dry-core rinsing is unsuitable. Therefore an inner core of 2.5 cm diameter was taken from intervals of the 7.6 cm diameter South Pole firn core using a specially-built precleaned stainless steel corer within a -15 °C cold room. Prior to this coring, exposed ends of core sections were shaved away with precleaned stainless steel chisels. 

If the ITO-coated side of the electrode does not have a purple sheen, then the electrode is either dirty or damaged. The best way to clean an ITO electrode is with a low-molecular-weight alcohol such as isopropyl alcohol (IPA), which does not adsorb to the oxide layers. Some modem laboratories have advanced facilities for burning off the surface contaminants by using a low-pressure plasma. Few analysts would employ ITO-coated electrodes if they always required such stringent conditions prior to routine analyses. 

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