Surface Preparations

Surface preparations or predeposited matrix crystal layers are also often called thin-layer or two-layer preparations, and were introduced to enhance sensitivity, homogeneity of the preparation, automation, and liquid chromatography (LC)-spotting. 

Surface Preparation. Before passivation, various surface preparations may be used to remove surface damage induced by mechanical polishing which would otherwise significantly reduce carrier lifetime (26). Chemical etching or chemical-mechanical polishing with various concentrations of Br in methanol (or other solvents) have been used, and have been shown to leave the surface depleted of Cd, and to a lesser extent, Hg (27-31). Electropolishing techniques (32) as well as oxidation and etchback (27)(28) have been used to address this problem, and seem to leave the surface closer to its original stoichiometry. 

Such wide variances in material and surface preparation can be expected to have a significant effect on a surface process such as anodic oxidation. However, the literature Is full of studies of anodic oxidation, with each study using the researchers favorite material and surface preparation, often with conflicting results. In the following pages, an attempt will be made to summarize these studies and find a common ground where one exists. Also, an attempt will be made to note material and surface preparation differences when they have been reported, so that conflicting results can be better understood. 

With all of the problems associated with anodic oxidation, it is inevitable that an attempt be made to develop alternative passivation methods. Some, such as suifidization, are electrochemical, others are 

Summary of Hgt Cd Te Electrical and Ofitcal Properties (All Values Shown are Highly Approximate) 

Source Reprinted from Reine, M.B., et al, Semiconductors and Semimetals Vol. 18, Academic Press, 1981, with permission of Publisher. 

Good wetting of the substrate surface is essential for developing reliable bonds. Adhesives that do not wet the surface will not spread out and fill substrate surface irregularities. Wetting occurs when the surface tension of the liquid adhesive is lower than the critical surface tension of the substrates being bonded (see Section 6.1). 

Solvent cleaning with solvents such as isopropyl alcohol is generally a very acceptable cleaning method although it should be noted that sometimes these solvents can stress crack or craze some amorphous thermoplastics [7]. They can also remove all traces of moisture from the surface and this can slow down or even inhibit the cure of cyanoacrylates. 

Correct surface preparation also results in improved durability [8] (see Section 9.1.1). 

No single adhesive will satisfy all needs. Designers and engineers must balance a variety of adhesive properties to obtain the required bond strength and ease of use in production. 

Shields, Adhesives Handbook, Edition, Butterworths Co, London, UK, 1984, p.l3. 

Surface engineering means both surface preparation and sterilization of the modified surface. A recent review of surface engineering [2] indicates that plasma surface preparation is well adapted to the preparation of biomaterials because it is easy to reproduce and clean the treated sample, and good for the environment (no pollution) as weU. This type of treatment can also be appHed in a clean room. Several plasma processes are possible for surface engineering. 

The resolution of atomic-scale defects in STM images requires surfaces as flat as possible to start with. Scanning probe microscopy has improved our knowledge concern- 

Flat surfaces are easy to prepare with layered materials. There have yet been only few in-situ studies, the resolution has been not as good as expected, with the exception of InSe [22]. Steps and pit formation have been reported on M0S2 [45]. Cleaved pyrite and related material such as RUS2 also give nice flat and stable surfaces [145, 146]. 

After cleaning, the next step in the process is designed to establish a sound surface on which to bond. For steel there exists a number of processes, which may be used 

The essential property of paint is adhesion, and good adhesion requires proper surface preparation. Although correct surface preparation varies somewhat with the type of paint being applied, the following five factors affect all paint classes. 

The surface must be knit together tightly enough to resist shrinkage of the curing paint film. If the surface is loose or crumbly, fire paint system will lose adhesion and peel off. 

The surface must be free of any foreign material that will prevent the paint from flowing onto the surface and covering it. If the paint cannot flow, it will lack film continuity, and if it does not cover the surface, it will lack adhesion. 

The surface must be filled, sanded, etc., to produce the required smoothness of the finished paint system (combined eoats of paint applied). The paint system will faithfirlly reproduce the contours of the substrate unless a rough-textured paint has deliberately been chosen to hide surface imperfections. This reproduction of substrate contours by the paint system is termed photographing. 

Sometimes good adhesion is difficult or impossible to obtain without minute surface roughness, which need not be pronounced enough to affect the surface smoothness of the completed paint system. Mechanical anchorage due to the tooth, or anchor pattern of the substrate is required for paint systems subject to vibration, impact, andbending, particularly when the paint is subject to weathering the automobile s paint system, for example, is subject to weathering. 

The inhibition of nisting can be achieved by passivating the iron. This can be accomplished by including chromates, nitrites, or red lead in the paint. Proper surface preparation is an important aspect of effective protection against corrosion. 

Metal surface treatment is usually divided into three classes (1) the metal surface is not altered, (2) the metal surface is etched either chemically or mechanically, and (3) metallic salts are produced at the metal surface. 

Vapor degreasing is another form of surface cleaning which is superior to solvent dipping because the tendency to leave an oil film on the surface is greatly reduced. 

When phosphoric acid is used for surface cleaning, it can leave an inert metallic phosphate coat on the surface which can then act as a corrosion inhibitor. Chromic acid either by itself or with phosphoric acid will form insoluble metallic chromates which remain on the metal surface and inhibit corrosion while binding the coat film. This treatment is used for Al, Mg, Zn, Sn, and alloys of these metals. 

The treatment of nonmetaUic surfaces is generally determined by the porosity of the material, its moisture content, and roughness. Such surfaces are often treated with a primer or undercoat to seal the surface and act as an intermediate bond between substrate and coating. 

Quite contrary to popular belief - a belief founded on the use of traditional adhesives - reliable joints can be obtained from unprepared surfaces. Of course, there is no denying that the better the preparation the better the overall performance. But, providing contamination is not gross, perfectly adequate levels of performance can normally be obtained from Anaerobic Cyanoacrylate Plastisol Toughened acrylic and Toughened, heat-cured, epoxide-based adhesives. 

The accommodation of surface contamination shown by some adhesives depends upon two distinct factors. First, as the anaerobic adhesives rely almost exclusively on their jamming action, any further reduction in their levels of true adhesion is unimportant provided that the contamination is not so gross that the hardened film of adhesive slides on the oil film. Situations as bad as this are rare and, when likely, must be either prevented or countered by cleaning. 

By contrast, the other adhesives are either excellent solvents, or become so with the aid of added scavengers when the temperature is raised. This is the main reason why heat-cured epoxies cope so much better with contamination than cold-cured variants. At room temperature the solubility of oil in all epoxy resins is low. 

While both cyanoacrylate and toughened acrylic adhesives contain no solvents - all the liquid present is converted to solid - their common base material is an excellent solvent in its own right and so both function well on unprepared surfaces. Toughened acrylics are noteworthy in this respect, though the tolerance of the cyanoacrylates is partially limited because contamination may inhibit hardening. Nonetheless, the cyanoacrylates generally cope well with the unprepared surfaces of the small plastics, rubber and metal parts that they are usually used on. 

Plastisol adhesives differ because the plasticising oils they contain become very powerful solvents as the curing temperature is approached. During curing these specialised oils and the contamination they pick up are incorporated in the hardening adhesive mass. 

In some cases it is impossible to provide the best prepared surface because there is insufficient money or time to do the job and/or it is not permitted because of possible product contamination, fire hazard, or some other reason. It must however be recognized that when there is a lesser surface preparation, the longevity of a coating system will likely be compromised. 

The surface properties of the substrate to which a coating is applied will influence its performance. Surfaces in compression often increase coating performance because they tend to be attacked less than surfaces that are less stressed on the other hand, surfaces in tension may cause coatings to fail earlier than they would otherwise. Differences in expansion rates between a coating and a substrate impose stresses on the coating which may lead to cracking and failure. Additionally, both inadequate and excessive coating thickness may lead to failure. 

When designing an electrochemical experiment, there are several factors that need to be decided. It is common that the design of the experiment and the preparation of samples comprise the hardest and most time-consuming part of electrochemical experimentation. Decisions need to be made regarding sample selection, surface preparation, masking to expose a certain area, specifics of the experimental 

The microstructure of a metal often plays a critical role in the corrosion process. Therefore, it is critical to choose the material stock for testing carefully. Microstructure can change depending on the form of the material, that is, plate, rod, sheet, or thin film. End grains of a worked structure are often more susceptible to attack. Temper can play a very important role in the corrosion of A1 alloys. Ideally, the material used in experiments should be identical to that used in the real application. If the form of the material is unknown, it might be of interest to investigate the role of processing and microstructure on the corrosion process. 

From the very first studies of SERS, it was clear that the morphology of the metal substrate has a significant influence on the SERS activity, much larger than one would expect from the changes in area available for adsorption. Various preparatory 

Another question one may ask in the present context is whether a roughening pretreatment is an absolute requirement for SERS. Alternatively, one may ask what is the magnitude of SERS from smooth surfaces (as far as these can be produced), and what is the added enhancement upon roughening We have already discussed this question and found that there is no unambiguous answer to it. The experimental evidence points to a small enhancement (below 100) on a smooth surface, but more work in this direction is required. 

In order to obtain high-quality SERS on silver (as well as on other metals exhibiting SERS) the electrodes have to be electro-chemically pretreated. As Schultz et and others have shown, this is not an absolute requirement, but it certainly helps in producing extremely large signals. 

The treatment generally begins with mechanical polishing with decreasing sizes of alumina (or equivalent). Then an etch with a mixture of ammonia and hydrogen peroxide or with a solution of sodium cyanide and hydrogen peroxide may be carried out. After a further wash with water, the electrode is immersed in the electrolyte solution, sometimes under cathodic potential control (-0.6 to -0.2 SCE). All the electric potentials in this review are referenced with respect to the standard calomel electrode (SCE), unless stated otherwise. 

In the next step, an electrochemical treatment is performed, which is basically composed of two distinct stages—an oxidation of the electrode and a reduction. The treatment is therefore often referred to as the ORC—oxidation-reduction cycle. The name remains even though the second step is not always performed, and the treatment can also consist of voltage steps or current pulses instead of cycling the potential. 

Aluminum can be cleaned in the same fashion as steel. Alternatively, it may be prepared for bonding by chemical etching. For instance, cyanoacrylates cure rapidly to give strong, durable bonds on aluminum etched by Forest Products Laboratory (FPL) chromic acid etching solution. 

Thermoplastics like polymethyl methacrylate (PMMA) or polystyrene should be thoroughly cleaned with a non-solvent such as isopropanol to remove surface contaminants. Abrasion is sometimes necessary to remove all traces of mold release agents. Cyanoacrylates form very strong bonds with many thermoplastics because the monomer swells into the adherend, and when cured, forms an intimate mixture of the plastic and the polycyanoacrylate. Thermosets such as filled phenolics should be treated in the same way as thermoplastics. Rubbers usually require abrasion as well as solvent cleaning to prepare them for bonding. 

With increased load, the adherends realign to a stable configuration - causing a rotational displacement of the bond region and peel loads along the bond edges 

Alignment of adherends to avoid offset load path, but kink may compromise strength. 

Doubled adherends balance the rotational force and radii reduce stress concentrations. 

In effect two single-lap joints with opposite rotation. Bending and peel may still arise. 

Similar principle to double-tap joint. Reduces the bending and oeet seen with single strap. 

Machining or application cost control Friction reduction Wear control Lubrication control Durability 

Resistance to initiation of corrosion Economic permanency of corrosion control Application of protective coatings Final appearance Consistency of operation Reduction of vibration. 

Surface finish control of such parts as gears may be necessary to secure quiet operation and to reduce vibration. 

The surface finish should be a compromise between sufficient roughness for proper wear-in and sufficient smoothness for expected service life. 

Incorrect clearances between two surfaces in relative motion may result in local hot spots and high oil consumption. 

---

E-1389 Rapid quality weld inspection without surface preparation Or. B. W. Shepherd BABCOCK Energy Ltd... 

For existing ships the only NDE method nominated by classification for the detection of fatigue cracks is close-up visual inspection - although all Surveyors have the option of requesting additional NDE when warranted. The sensitivity of visual inspection is influenced by the degree of surface preparation and the level of lighting at the inspected surface - which may not always meet the level of 500 lux nominated by some NDE specifications. 

An important newer use of fluorine is in the preparation of a polymer surface for adhesives (qv) or coatings (qv). In this apphcation the surfaces of a variety of polymers, eg, EPDM mbber, polyethylene—vinyl acetate foams, and mbber tine scrap, that are difficult or impossible to prepare by other methods are easily and quickly treated. Fluorine surface preparation, unlike wet-chemical surface treatment, does not generate large amounts of hazardous wastes and has been demonstrated to be much more effective than plasma or corona surface treatments. Figure 5 details the commercially available equipment for surface treating plastic components. Equipment to continuously treat fabrics, films, sheet foams, and other web materials is also available. 

Surface finish requirements for the Vickers test vary with the test load. Heavy load tests can be made on a 120 grit ground surface. At low loads increasingly finer surface preparation is required, approaching that for metaHographic specimens, to permit accurate diamond indentation measurements. 

Application Methods and Surface Preparation. Eor good durabiHty and performance, proper surface preparation and correct appHcation of house paints are as important as the formulation of high quaHty paint. Proper surface preparation prior to painting involves several considerations. Eor new constmction, proper installation and protection of the substrate material are necessary. Eor previously painted surfaces, preparation involves mostly cleaning and removing any existing paint that is unstable. Once surface preparation is complete, the appHcation process can begin. 

Paring is the surface preparation in a processing faciUty which may be concrete, asphalt, gravel, cmshed shell, or brick. 

Surface preparation, always important in obtaining optimal coatings performance, is critical for marine coatings (see Metal surface treatments). Surface preparation usually comprises about half of the total coating costs, and if inadequate may be responsible for early coating failure. Proper surface preparation includes cleaning to remove contaminants and roughening the surface to faciUtate adhesion. 

Surface preparation of the dental implant prior to implantation wiH have an effect on corrosion behavior, initial metal ion release, and interface tissue response (316). The titanium and titanium aHoy dental implants in present use have many forms to assist bone ingrowth attachment including cylinders with holes, screw threaded surfaces, porous surfaces, and other types of roughened surfaces. Methods used to produce porous surfaces iaclude arc plasma... 

The painting procedure for other metal surfaces, although similar, the process of pre-treatment for cast iron components or non-ferrous metals, such as aluminium and copper, may need more care. The process of pre-treatment in such cases may vary slightly than for MS, as noted below. Such surfaces may require a change in the type of chemicals, their concentration and duration of treatment. The final surface preparation and painting procedure, however, will remain the same for all. 

K.S. Tunison and Y.M. Gupta, Effects of Surface Preparation on Elastic Precursor Decay in Shocked Pure Lithium Fluoride, Appl. Phys. Lett. 48, 1351-1353 (1986). 

Coatings for tanks have to be chosen so that they can withstand the particular conditions [10]. The high-grade modern systems demand very good surface preparation of Sa IVi, which cannot always be achieved in practice, because of their ribbed construction and confinement. The increased frequency of defects has to be reckoned with. 

Is surface preparation of the component required prior to processing (1 )(2)... 

Surface preparation, e.g. polishing, tumbling, blasting, etching or a machine process, may be required due to the nature of the process or due to surface contamination. This can be an added source of variability. 

Surface preparation may be required to remove oxides, moisture, grease, etc. Prior to welding they are removed by mechanical, pickl or degreasing processes, the application of which canbe an addedsouree of variability. 

The term direct TXRF refers to surface impurity analysis with no surface preparation, as described above, achieving detection Umits of 10 °—10 cm for heavy-metal atoms on the silicon surface. The increasit complexity of integrated circuits fabricated from silicon wafers will demand even greater surfrce purity in the future, with accordingly better detection limits in analytical techniques. Detection limits of less than 10 cm can be achieved, for example, for Fe, using a preconcentration technique known as Vapor Phase Decomposition (VPD). 

The obvious application of microfocus Raman spectroscopy is the measurement of individual grains, inclusions, and grain boundary regions in polycrystalline materials. No special surface preparation is needed. Data can be obtained from fresh fracture surfeces, cut and polished surfaces, or natural surfeces. It is also possible to investigate growth zones and phase separated regions if these occur at a scale larger than the 1-2 pm optical focus limitation. 

Since then, TXRE has become the standard tool for surface and subsurface microanalysis [4.7-4.11]. In 1983 Becker reported the angular dependence of X-ray fluorescence intensities in the range of total reflection [4.12]. Recent demands have set the pace of further development in the field of TXRE - improved detection limits [4.13] in combination with subtle surface preparation techniques [4.14, 4.15], analyte concentrations extended even to ultratraces (pg) of light elements, e. g. A1 [4.16], spe-dation of different chemical states [4.17], and novel optical arrangements [4.18] and X-ray sources [4.19, 4.20]. 

---