Crystal plane orientation

Three types of problems arise (a) dependence of 4> and MH bond energies on crystal-plane orientations at metal surfaces (b) dependence of In I o values on the same and (c) impurity adsorption effects which influence both Ini, and 0 values and which also depend on the nature of the metal and crystal surfaces studied. Most earlier data were for polycrystalline metals and for probably contaminated metal surfaces. 

The surface energy depends on a crystal plane orientation. The experimental measurement of the surface energy for solids is extremely difficult. There are few data about values of y in the literature. 

To observe the equilibrium shape of a crystal experimentally, it is necessary to confirm that the crystal one wants to observe exhibits such a shape. Since the equilibrium shape of a crystal in a matrix is the same as the equilibrium shape of the matrix entrapped within the crystal, the equilibrium crystal shape can be determined by observing the shape of the entrapped matrix. If a number of randomly oriented grains exhibit an equilibrium shape, the shape can also be determined stereographically from the crystal plane orientations of the grains and the directions of the grain interfaces on a planar section that can be obtained by the electron backscattered diffraction technique. For metals for which the anisotropy in interfacial energy is low at their processing... 

If the detection system is an electronic, area detector, the crystal may be mounted with a convenient crystal direction parallel to an axis about which it may be rotated under tlie control of a computer that also records the diffracted intensities. Because tlie orientation of the crystal is known at the time an x-ray photon or neutron is detected at a particular point on the detector, the indices of the crystal planes causing the diffraction are uniquely detemiined. If... 

Etch Profiles. The final profile of a wet etch can be strongly influenced by the crystalline orientation of the semiconductor sample. Many wet etches have different etch rates for various exposed crystal planes. In contrast, several etches are available for specific materials which show Httle dependence on the crystal plane, resulting in a nearly perfect isotropic profile. The different profiles that can be achieved in GaAs etching, as well as InP-based materials, have been discussed (130—132). Similar behavior can be expected for other crystalline semiconductors. It can be important to control the etch profile if a subsequent metallisation step has to pass over the etched step. For reflable metal step coverage it is desirable to have a sloped etched step or at worst a vertical profile. If the profile is re-entrant (concave) then it is possible to have a break in the metal film, causing an open defect. 

Fig. 2. Schematic representation of basal plane orientation in several types of carbon fibers. (A) Single crystal graphite. (B) ex-pitch carbon fiber. (C) ex-PAN carbon fiber, (D) VGCF.

Configurations of interest are those using disk-shaped samples cut from crystals in orientations that permit plane waves of uniaxial strain to propagate through their thickness when a uniform load is applied to their face. When the diameter of the disk is sufficiently large in comparison to its thick-... 

With powdered samples, an image of diffraction lines occurs because a small fraction of the powder particles will be oriented such that, by chance, a certain crystal plane is at the angle 6 to the incident beam for constructive interference (see Fig. 4.4). 

The information stored in the specimen database is sufficient to identify the particular specimen and the material from which it is made. Other parameters provide information on the orientation of the specimen and on its unit cell parameters. These latter parameters are used by the data collection tasks and the crystal geometry calculation function to determine diffraction angles, the angles between crystal planes, etc. The user can store information on several specimens in the specimen database, thus permitting him to easily remount and rerun a specimen after looking at the collected data. 

A sinusoidal plot of grf>2 vs.

crystal plane gives another set of Ks that depend on other combinations of the gy, eventually enough data are obtained to determine the six independent values of gy (g is a symmetric matrix so that gy = gy,). The g-matrix is then diagonalized to obtain the principal values and the transformation matrix, elements of which are the direction cosines of the g-matrix principal axes relative to the crystal axes. An analogous treatment of the effective hyperfine coupling constants leads to the principal values of the A2-matrix and the orientation of its principal axes in the crystal coordinate system. 

The XRD pattern of a powdered sample is measured with a stationary X-ray source (usually Cu Ka) and a movable detector, which scans the intensity of the diffracted radiation as a function of the angle 2 6 between the incoming and the diffracted beams. When working with powdered samples, an image of diffraction lines occurs because a small fraction of the powder particles will be oriented such that by chance a certain crystal plane is at the right angle 6 with the incident beam for constructive interference (see Fig. 6.1). 

The Ru single crystal was oriented by Laue x<-ray back-scattering to within 1° of the Ru(001) plane, cut by a diamond saw and mechanically polished. After being etched in hot aqua regia for about 15 min, the crystal was spot welded to two tantalum heating wires which were connected to two stainless steel electrodes on a sample manipulator. The temperature was monitored by a Pt/Pt-10% Rh thermocouple which was spot welded to the back of the crystal. 

To measure a powder pattern, a randomly oriented powdered sample is prepared so as to expose all possible planes of a crystalline powder. The scattering angle, 6, is measured for each family of crystal planes by slowly rotating the sample and measuring the angle of diffracted x-rays... 

The electrochemical oxidation of polyhydric alcohols, viz. ethylene glycol, glycerol, meso-erythritol, xilitol, on a platinum electrode show high reactivity in alkaline solutions of KOH and K2C03 [53]. This electro-oxidation shows structural effects, Pt(lll) being the most active orientation. This results from different adsorption interactions of glycerol with the crystal planes [59]. 

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