Crystal cuts

In describing a particular surface, the first important parameter is the Miller index that corresponds to the orientation of the sample. Miller indices are used to describe directions with respect to the tluee-dimensional bulk unit cell [2]. The Miller index indicating a particular surface orientation is the one that points m the direction of the surface nonual. For example, a Ni crystal cut perpendicular to the [100] direction would be labelled Ni(lOO). 

In a subsequent work [182], it was shown that the photoelectrochemical performance of InSe can be considerably improved by means of selective (photo)electrochemical etching. Interestingly, whereas the cleavage vdW plane showed little improvement, the photocurrent in the face parallel to the c-axis was doubled. Note that, in contrast to InSe crystals cleaved in the plane perpendicular to the c-axis that are almost defect free, the crystals cut in the plane parallel to the c-axis contain a high density of defects on their surface which leads to a high rate of electron-hole recombinations and inferior quantum efficiency. The asymmetry in the role of electrons and holes, as manifested, e.g., in the fact that surface holes carry out the selective corrosion of the semiconductor surface in both cleavage orientations, was discussed. 

With crystalline membranes, the membrane material is most often an insoluble ionic crystal cut to a round, flat shape and having a thickness of 1 or 2 mm and a diameter of about 10 mm. This flat disk is... 

To model a tetragonal crystal, cut four straws in half. Cut four of the pieces in half again. Wire the eight shorter pieces to make four square ends. Use the longer pieces to connect the square ends. 

To model the orthorhombic crystal, cut four straws in half. Cut 1/3 off four of the halves. Connect the four long, four medium, and four short pieces so that each side is a rectangle. 

Using an experimentally-optimized focusing lens (/ = 15 mm spot radius, w = 4.3 pm) and a 3 mm KNbOj crystal (cut for NCPM at 22°C and 858 nm AR-coated), up to 11.8 mW of blue average power with a spectral width up to AIsh 1-4 nm at 429 nm was generated with only 44.6 mW of incident fundamental. The maximum observed SHG conversion efficiency was as high as 30 %. The overall efficiency of the electrical-to-blue process was over 1 %, and the blue pulses were measured by autocorrelation to be -500 fs in duration. ... 

Fig. 4.5 High resolution electron micrograph of synthetic goethite crystals cut perpendicular to the needle axis [010]. The crystals are bounded by 101 faces. The large crystal contains faults and some of the smaller, fault-free crystals show ca. 1 nm lattice fringes corresponding to the c -parameter of the unit cell (0.9956 nm) (Schwertmann, 1984, with permission, courtesy H. Vali, Schwertmann Cornell, 2000, with permission).

Single crystals, cut so that a certain crystal face is exposed to the solution, offer better definition and therefore reproducibility of results. By using electron diffraction measurements (which require a vacuum), one can determine the crystal face exposed to the solution before and after electrochemical measurements and hence ascertain if any change in crystal orientation has occurred as a result of contact with the solution. Such techniques, introduced by Hubbard in the 1970s, began a seminal change in electrode kinetics, the full fruits of which are still to be obtained. 

It is noted that commercial Ti02 (100), (110), and (001) surfaces, obtained by crystal cutting and appropriate polishing, have no truly atomically well-defined... 

First we study the surface structure and chemisorption characteristics of crystals cut along different crystallographic orientations. Then a well-chosen chemical reaction is studied at low pressure to establish correlations between reactivity and surface structure and composition. Below 10 4 Torr the surface can be monitored continuously during the reaction with various electron spectroscopy techniques. Then the same catalytic reaction is studied at high pressures (1-100 atm) and the pressure dependence of the reaction rate is determined using the same sample over the nine orders of magnitude range. Finally, the rates and product distributions that were determined at... 

Fig. 8 Glycyl-glycine crystals grown in the presence of DL-glycyl-leucine. a Photographs and morphology b Enantiomeric HPLC analyses of samples taken from single crystals cut at the + b and - b poles and sample from the whole crystal (left to right)...

The crystal cut determines the mode of oscillations. Shear vibrations are generated if one large crystal face moves parallel with respect to the underlying planes as in QCMs with AT-cut a-quartz crystals. This crystal wafer is prepared by cutting the quartz at approximately 35.17° from its Z-axis. A typical crystal plate is a cylindrical disk of a diameter 10 mm and thickness about 0.7 to 0.1 mm for resonant operation in the 2 to 15 MHz frequency range. This type of crystals shows weak dependence of the resonant frequency on the temperature and stress for room temperature operation. 

The thermal stability of any of the devices made from temperature-stable crystal cuts is degraded considerably when the device is coated with a polymeric film used for vapor sorption. Contact with a liquid may also introduce temperature variations that affect the short-term noise of the entire system. 

Quartz crystals have been used as thermometers in calorimetry relatively recently. Their use is based on the fact that the resonance frequency of the quartz crystal cut in a certain orientation to the axis of its crystal structure depends on temperature, whereby the temperature dependence is high and almost linear. 

The polychromatic beam produced by the X-ray source irradiates a plane crystal cut parallel to a family of crystal planes. This single crystal is oriented around a rotation axis parallel to the reference family of planes. For the chosen wavelength X, when the incidence angle of the X-ray beam is eqtral to the Bragg angle 0j, a diffracted beam with wavelength X is observed. 

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