Preparation of clean surfaces

To prepare crystalline surfaces, usually the starting material is a suitable, pure, three-dimensional single crystal. From this crystal, a slice of the desired orientation is cut. Therefore the crystal must be oriented. Orientation is measured by X-ray diffraction. Hard materials are then grounded and polished. Soft materials are cleaned chemically or electrochemically. The surfaces are still mechanically stressed, contaminated, or chemically changed, e.g. oxidized. In principle, electrochemical processes in liquid can be used to generate clean crystalline surfaces. The problem is that an electrochemical setup is not compatible with an UHV 

Thermal treatment. Heating of the material may cause desorption of weakly bound species from the surface and can therefore be used to clean surfaces. A positive side effect is that annealing reduces the number of surface defects since it increases the diffusion rates of surface and bulk atoms. There can also be some unwanted side effects surface melting and other types of phase transitions may occur well below the bulk melting point, leading to other than the desired surface structure. 

Cleavage of bulk crystals to expose clean, defined lattice planes is possible for brittle substances. Some materials, like mica or highly oriented pyrolytic graphite (HOPG) that exhibit a layered structure, are readily cleaved by just peeling off some layers or using a razor blade. For other materials the so-called double-wedge technique can be used (Fig. 8.8). 

Sputtering. A universal method for cleaning surfaces is sputtering. In sputtering the surface is bombarded with noble gas ions. Thereby contaminants — and in most cases the first few layers of the substrate as well — are removed. In sputtering, an inert gas (usually 

Evaporation is a simple and well understood vacuum technique for thin film deposition. The material to be deposited is heated until it starts to evaporate. Mainly two methods are used for evaporation  

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More than with continuous improvement in the preparation of clean surfaces in electrochemistry, the measurement of 0 is rather casual in surface science at present. In particular, work functions are mostly measured for d-metals rather than for sp-metals, which are more common in electrochemical double-layer studies. As a consequence, compilations of work function values report data for sp-metals that are 20 to 30 years old.63,856,857 This does not imply that the data are unreliable, but imparts to the situation a sense of frustration related to the immobility in one of the variables. 

The preparation of clean surfaces in uhv has become by now a standard procedure. Several texts deal with this problem [see for example Refs. (21) and (22)]. Single crystal surfaces are generally cleaned by chemical means (e.g. oxidation and subsequent flashing in the case of tungsten) or by argon ion sputtering (23) or by a combination of both (24). 

Preparing a clean surface is often a prerequisite for surface-science studies. UHV-based methods of sample preparation and characterization are established, and these may be exploited for studies of surfaces immersed in solution by interfacing an electrochemical cell with an UHV chamber. Samples can then be transferred from UHV and immersed into electrolyte solution under a purified-Ar atmosphere. However, even under these clean conditions, some metals oxidize or get contaminated prior to immersion. Other techniques for the preparation of clean surfaces that do not require UHV techniques are available for some metals. For example, flame annealing and quenching have been successfully used, but this procedure is probably limited to Au, Pt, Rh, Pd, Ir, and Ag substrates. In this technique, substrates are annealed in an oxygen flame and quenched in pure water. 

Preparation of clean surfaces for contact angle measurements... 

Defence Standard 03-2/Issue 3. Cleaning and preparation of metal surfaces, British Ministry of Defence, March 1995. 

One of the biggest challenges in this industry is the wide variety of substrates that can be encountered for any given application. Not only can the materials be substantially different in their chemical make up, but they may also be quite different in surface roughness, surface curvature and thermal expansion behavior. To help adhesion to these substrates, preparation of the surface to be bonded may be critical. This preparation may be as simple as a cleaning step, but may also include chemical priming and sanding of the surface. 

The Cleaning and Preparation of Melal Surfaces, Defence Standard 03-2/1 (1970), obtainable from the Ministry of Defence, First Avenue House, High Holborn, London, W.C.I. 

CP30I2 1972, Cleaning and preparation of metal surfaces , B.S.I., London Wernick, S. and Pinner, R., The Surface Treatment and Finishing of Aluminium and Its Alloys, Robert Draper, London, 3rd edn (1964)... 

To implement this program of measurements on well-defined electrodes, the method of preparation of clean and well-ordered single crystal surfaces is essential. Such surfaces can be obtained either by the use of ultra-high vacuum or "atmospheric" procedures, the latter methods will briefly be described below. 

Hovis, J. S., Hamers, R. J. and Greenlief, . M. Preparation of clean and atomically flat germanium(OOl) surfaces. Surface Science 440, L815-19 (1999). 

Preparation of Metal Surfaces for Soldering. Prior to soldering, thoroughly clean the surface of the metal with a file or emery paper. Such surface cleaning is not needed when soldering tinplate. Large metallic surfaces to be soldered should first be tinned. To do this, heat the metal article on the flame of a burner (300-350 °C), spread ammonium chloride over the surface to be soldered (for what purpose ), put a piece of tin on it, and spread the tin over the metal surface with an asbestos wad. 

LEED studies of clean surfaces have revealed that most of these surfaces, if prepared under proper conditions, are ordered on an atomic scale and exhibit sharp diffraction beams and high diffraction beam intensities. Metal, semiconductor, alkali halide, inert gas, and organic crystal surfaces have been studied this way, and all exhibit ordered surface structures. 

We can define pretreatment as the initial conditioning period whereby a corrosion inhibitor is applied to the metal surfaces of the cooling system. Pretreatment conditions must be conducive to the rapid formation of the protective barrier. The conditioning procedure should involve (1) the cleaning and preparation of metal surfaces, and (2) the actual application of higher than normal inhibitor concentrations. 

For the study of crystalline surfaces, ultrahigh vacuum (UHV) is required. The preparation of clean crystalline surfaces is usually carried out within the UHV system by cleavage, sputtering, evaporation, thermal treatment, or molecular beam epitaxy. 

In this context we might mention that surface preparation is a major factor in obtaining good, adherent coatings of any type. Degreasing, chemical cleaning and, in some cases, mechanical treatment are essential steps in the preparation of the surface for coating, which often consists of several layers, for optimum protection. 

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