Surface cleavage

The immobility of the surface atoms of a refractory solid has the consequence that the surface energy and other physical properties depend greatly on the immediate history of the material. A clean cleavage surface of a crystal will have a different (and probably lower) surface energy than a ground, abraded, heat-treated or polished surface of the same material. 

Muscovite mica naturally contains ions on its cleavage surface. A fraction of these ions become solvated and mobile in humid enviromnents. Experiments were per-... 

Auger spectroscopy (q.v.) is usually employed in the study of cleavage surfaces, but an advantage of XPS in such studies is that the chemical nature of elements segregating on the surface can be investigated. 

Clean single-crystal surface, 15 31 Clean surfaces, alcohol reactions, 29 37-38 Clear Air Act of 1970, 24 59, 62 Cleavage surfaces, dislocations on, 19 331-333 ClOj, ESR of, 22 309... 

The most important FeSa surface is the (100) surface, which is the most common growth surface and is also the perfect cleavage surface. Research from Nesbitt et al. (1998) suggest that the (100) surface of pyrite exhibits good stability and only minimal relaxation fi om the truncated solid. Therefore, our adsorption calculation is based on FeSa (100) surface and the relaxation of surface is ignored. 

The most important ZnS surface is the (110), which is the most common growth surface and is also the perfect cleavage surface. Therefore, the calculation is based on the ZnS (110) surface. The surfaces are cleaved from the bulk ZnS with the optimtun tinit cell volume determined using the GGA with CASTER The Cu and Fe doped surfaces are built by the substitution of Cu or Fe for Zn atom on the cleaved surface. A vacuum spacing of 1.5 nm is inserted in the z-direction to form a slab and mimic a 2D surface. In order to eliminate the interactions between mirror images in the z-direction due to the periodic boimdary conditions, in test calculations, we have done some total energy calculation to find a proper thickness of slab. The result shows that 1.5 run is a desirable thickness. 

Although when examined using optical or even electron microscopy, crystal surfaces appear smooth, this is rarely the case. Techniques such as AFM and STM and optical interference methods (see Chap. 7) show that both growth and cleavage surfaces consist of terraces separated by steps which can be as little as one atomic layer... 

The same phenomenon is observed on other layered materials, for which the deformation perpendicular to the cleavage surface is relatively easy. When the large corrugation amplitudes are observed, the apparent barrier height becomes very low, indicating a nearly synchronous motion of the sample surface with the tip. 

Figure 7.3. (a) In situ X-ray reflectivity vs. time (measured at the anti-Bragg condition, shown in inset at top) during dissolution of orthoclase feldspar, KAlSi308, (001) cleavage surface at extreme pH values. The removal of successive monolayers (ML) is noted for each set of data, (after [100]) (b) in situ crystal truncation rod diffraction profiles for a freshly cleaved orthoclase (001) surface (circles) and after reaction at pH = 2.0 (1 and 15 ML dissolved) (diamond and square) and pH = 12.9 (2 ML dissolved) (triangle) (after [103]). (Figures provided by P. Fenter.)... 

These salts have been found to have the sodium chloride arrangement when deposited from the vapor onto cleavage surfaces of mica or certain other crystals L. G. Schulz, J. Chem. Phys. 18, 996 (1950). The observed interionic distances CV—Cl = 3.47, Cs+—Br = 3.62, Os+--T 3.83 A. 

Figure 1. Anthraxolite-bearing nodule in slate, seen on cleavage surface. ExplodedV anthraxolite fragments are engulfed in matrix of quartz and calcite intergroum in comb structure which parallels the tectonic z-lineation of the slate. Darker bands are distorted carbonaceous primary laminae. (Compare with Figure 3.)...

From specular reflection experiments with molecular beams of hydrogen or helium (4) it may be concluded that cleavage surfaces of LiF or NaCl are very smooth surfaces indeed, the inequalities being caused only by the temperature movement and amounting to the order of magnitude of 10 8 cm. Diffraction spectra obtained with helium beams (5), indicate moreover (6) that the distance between two fluorine ions in the outer layer of LiF is exactly the same as in the crystal. 

The method described above has been used by Avgul et al. (I) to calculate the dispersion interactions between a number of adsorbates and the cleavage surface of graphite. A prime disadvantage of the method of direct lattice sums, apart... 

Sphalerite (or zincblende ) has a lattice with zinc atoms at the corners and face centers of a unit cube and sulfur atoms at the centers of four out of the eight smaller cubes into which the large cube can be divided. Both zinc and sulfur are in regular tetrahedral coordination. The cleavage surface is the (110) surface, and this nonpolar face of ZnS (and other zinc-blende-structure binary compounds) is by far the best understood of all semiconductor surfaces (Kahn, 1983). 

Preferred orientation of metal films can be clearly achieved by depositing the metal on the smooth surface of a well-crystallized solid in vacuo. For example, Uyeda (94) and Kainuma (95) obtained (lll)-oriented films of nickel, copper, and platinum when these metals were deposited on a cleavage surface of molybdenite (0001) at temperatures ranging from 20° to 500°C. Miyake and Kubo (96) observed a temperature dependency of the orientation of deposited films of face-centered cubic metals when they were deposited on a cleavage surface of zinc blende (110). 

Fig. 44. Matched cleavage surfaces of a graphite crystal. Note correspondence both in positions of etch pits and the directions of the cleavage steps. 250 x. (62)...

---