Poly crystallinity, crystallization

The next step is the hydrogen reduction of the trichlorosilane (Reaction 2 above). The end product is a poly crystalline silicon rod up to 200 mm in diameter and several meters in length. The resulting EGS material is extremely pure with less than 2 ppm of carbon and only a few ppb of boron and residual donors. The Czochralski pulling technique is used to prepare large single crystals of silicon, which are subsequently sliced into wafers for use in electronic devices.1 1... 

Many problems must be solved before practical, reliable, and cost-effective diamond semiconductor devices become available. Yet, the prospects are good, particularly if epitaxial single-crystal or highly oriented poly crystalline diamond can be effectively produced by CVD.P5]... 

In this section, we will investigate the surface structure of the electrode in the potential range before a surface or bulk oxide starts forming, and will restrict ourselves to the adsorption of atomic oxygen only (not OH ) [Jacob and Scheffler, 2007]. Furthermore, in our simulations, we assume a single-crystal Pt(lll) electrode, which will be compared with the experimental CV curve (Fig. 5.9) for poly crystalline Pt. This simplification is motivated by the fact that our interest here is to describe the general behavior of the system only. 

Distinct quadrupole shifts do occur as well in magnetically split spectra of single-crystals, poly crystalline powder or frozen solution samples. In all three cases, the line shifts obey the simple first-order expression at high-field condition. 

With h 6) - 1/sin 0)5(0 — Oq), one obtains the same result as given by (4.58), which implies that the anisotropy of the/factor cannot be derived from the intensity ratio of the two hyperfine components in the case of a single crystal. It can, however, be evaluated from the absolute/value of each hyperfine component. However, for a poly-crystalline absorber (0(0) = 1), (4.66) leads to an asymmetry in the quadrupole split Mossbauer spectrum. The ratio of l-Jh, as a function of the difference of the mean square amplitudes of the atomic vibration parallel and perpendicular to the y-ray propagation, is given in Fig. 4.19. 

As a function of the surface potential the electron work function for a given material depends on the state of the surface of that material (adsorption, the presence of surface compounds, etc.). For crystalline substances (see Table 3.1), various crystal faces have various electron work function values, which can be measured for single crystals. For poly crystalline substances, the final value of the electron work function depends on the contribution of the individual crystal faces to the entire area of the phase and the corresponding electron work functions the final value of the work function, however, is strongly dependent on the experimental method used for the measurement. 

Platinum electrodes are made usually from poly crystalline metal the crystal planes at the surface include both the (111) and (100) faces in approximately equal proportions. The electrochemical properties of Pt(lll) and Pt(100) faces are not identical. (Generally, the physical properties of individual metal crystal faces, such as work function, catalytic activity, etc., are different.)... 

Solvothermal growth of single crystals or poly crystalline aggregates from hydro-thermal or ammonothermal solution. 

It is noticed that the improvement of solar cells is remarkable, and the efficiencies of Si-single crystal cell and the poly crystalline cell reach 17 % and 12.5 %, respectively. The average cost of solar cell module is 3 per watt, which can be competitive with other conventional power sources [8],... 

CXRS entered the commercial market in the mid-to-late 1990s after a long development period. The basic principles have been known for many years, but practical development faced many hurdles. Most explosives have a crystalline structure. Because the crystals are small and randomly orientated, the structure is sometimes referred to as poly crystalline. These crystals exhibit a strong coherent scatter at certain angles that depend on the X-ray energy and the crystal lattice spacing. This coherent scatter (also called diffraction) is a property of the crystal lattice and is unrelated to... 

Since the electron work functions and the specific surface energies of different planes of the same crystal may have different values, it would be interesting to study the electronic interaction during adsorption of foreign molecules on monocrystals. Investigations of monocrystals, however, encounter many difficulties therefore, one has to restrict oneself in general to poly crystalline surfaces, which also give remarkable results because the force of interaction essentially depends on the nature of the metal and differs for the same metal from one species of adsorbed molecules to the other. 

A typical dc susceptibility-versus-temperature transition curve for polycrystalline LuNi2E>2C and YNi2E>2C with Tc 16.5 K and 15 K, respectively, is shown in Figure 1. The growth of very high-quality single crystals of nickel borocarbide superconductors (see, e.g., Xu et al., 1994) almost immediately after their discovery has had a profound impact on the quality of the work performed. Thus many of the pitfalls of the early research on other complex materials, such as high-Tc superconductors, carried out on poly crystalline samples of variable quality, have essentially been avoided (Cava, 2001). 

Another candidate for a useful material from very high pressure synthesis is the gem material, jadeite (NaAlSi206). The natural material of Imperial quality can cost as much as 2000 per carat. Jadeite can be synthesized at about 30 kb and above in equipment similar to that used for diamond growth, and it has been made into pieces of jewelry. Since jadeite is used as a poly-crystalline aggregate, synthesis is essentially hot pressing and sintering, much simpler than if single crystals were needed. However, it does not appear to be a commercial product in competition with the natural supply. 

Bias corrections determined from analysis of standards are applied to the samples under test. Use of such an average bias correction can be viewed only as an approximation to the truth so many factors contribute to bias that it is impossible to control them all. For example, as previously stated, the work function of a rhenium filament is determined by which crystal face is involved One way of loading samples on filaments is through use of single resin beads [56,57]. The beads are 100-200 xm in diameter, which is about the size of rhenium crystallites in a poly crystalline filament [17]. Clearly the work function applicable to the analysis in question may or may not be that operative when instrument calibration was carried out. Another parameter difficult to control in real-world conditions is sample purity, which also affects bias. It is impossible to purify all samples to the same degree, and contaminants adversely affect ionization efficiency low efficiency means higher filament temperatures, which in turn mean a different bias correction. These are only two of sundry variables that can affect ionization efficiency. 

Often, it is not possible to obtain single crystals that are large enough to be worked with in a convenient manner. In those cases, physical properties must be measured on poly crystalline samples. There is always discrepancy, or disagreement, between measured physical properties of single crystals and polycrystals due to microstructural effects. Hence, physical properties measured from polycrystalline samples are sometimes considered less reliable from a reproducibility standpoint. 

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