Single-crystal impurity removal

Clean substrate surfaces for nonoptical experiments were prepared by a series of Ar+-sputtering/thermal annealing cycles to remove surface impurities and restore atomic smoothness, respectively, using AES and/or XPS to determine cleanliness and LEED to assess surface ordering for single crystal specimens. Most of the work so far reported has involved nominally unreactive substrates, namely Ag and Au. 

Very pure single crystals have defects that can effect corrosion, but impurities and alloying elements, grain boundaries, second phases, and inclusions often have serious effects. Welded structures invariably corrode first at the welds because of metallurgical heterogeneities that exist in and near welds. The most susceptible site or defect in a metal will be the first to be attacked on exposure to a corrosive environment. Sometimes such attack simply results in innocuous removal of the susceptible material, leaving a surface with improved corrosion resistance. (Frankel)5... 

Another attempt to make feed rods for FZ crystal growth from cheap starting material is to melt solar (or lower) grade raw silicon in a quartz crucible and pull a rod of the desired diameter after the CZ method, not necessarily a single crystal. A lot of impurities can be removed by segregation and in the subsequent FZ step, almost all oxygen and most of the other impurities can be removed, too. However, the actual costs of such an approach must be carefully considered, but it is still an option to overcome the diameter limitations of the Siemens process. 

Once again, Pt will be used as a sample system to illustrate the effect of one adspecies on the desorption of another. Single crystals of Pt often contain large surface impurities of S, P, Ca, C, Cl and O and these adatoms are often very difficult to remove. The influence of S at the surface on the desorption of CO from Pt is shown in Fig. 40 from the work of Bonzel and Ku [325]. Clearly, S substantially affects the desorption, decreasing both the desorption energy of the adsorbate and the amount adsorbed. Oxygen adsorbs on platinum to form an oxide and McCabe and... 

Sample preparation is always an important part of surface studies. Single crystals are oriented by X-ray back-diffraction, cut, and polished. They are then ion-bombarded or chemically treated to remove undesirable impurities from their surfaces. 

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