Amorphous materials experimental

Density, mechanical, and thermal properties are significantly affected by the degree of crystallinity. These properties can be used to experimentally estimate the percent crystallinity, although no measure is completely adequate (48). The crystalline density of PET can be calculated theoretically from the crystalline stmcture to be 1.455 g/cm. The density of amorphous PET is estimated to be 1.33 g/cm as determined experimentally using rapidly quenched polymer. Assuming the fiber is composed of only perfect crystals or amorphous material, the percent crystallinity can be estimated and correlated to other properties. 

In crystalline semiconductors, the most common technique for the measurement of carrier mobility involves the Hall effect. However, in noncrystalline materials, experimental data are both fragmentary and anomalous (see, for example. Ref. [5]). Measured HaU mobility is typically of the order of 10 - 10 cm A /s and is frequently found to exhibit an anomalous sign reversal with respect to other properties providing information concerning the dominant charge carrier. Thus, apart from some theoretical interest, the Hall effect measurements are of minimal value in the study of macroscopic transport in amorphous semiconductors. 

Figure 10.5 shows scanning electron micrographs of blend samples that were prepared as described in the Experimental Section . The etchant preferentially attacks polyethylene, producing a topography in which the polystyrene-rich domains are raised above the polyethylene domains. The interlamellar amorphous material provides a location for styrene to penetrate and polymerize. A considerable amount of polystyrene is present in the center of the spherulites. This is due either to amorphous polyethylene that is present in these locations or to voids that develop during crystallization... 

For amorphous materials, it is widely regarded that tunneling two-level system (TLS) is capable of explaining a wealth of experimental data for low-temperature... 

Gases interact with solids at high pressures, either by adsorption to crystal surfaces or by dissolution into amorphous materials, leading to volume changes. An experimental method to study the behavior of solids in the presence of dense gases has been developed. Sorption equilibria and solubilities are determined gravimetrically. Diffusion coefficients are derived with the help of suitable mass-transfer models. The swelling behavior of the solids is observed visually. 

The samples used in this study were both natural and synthetic varieties of mordenite and are listed in Table I. Each material contained more than 95% pure zeolite with the remainder being amorphous material as measured by x-ray diffractometry. Before being used in experimentation, each sample was exchanged to the sodium form. 

In summary, both amorphous and crystalline material is found in these vanadium phosphate catalysts, and it cannot be stated with any certainty whether or not the amorphous phase is the active phase. However, experimental observations have added weight to the postulate that amorphous material is the catalytically active material. 

The experimental techniques most commonly used to measure the phonon distributions are IR absorption, Raman scattering and neutron scattering. The IR and Raman spectra of crystalline silicon reflect the selection rules for optical transitions and are very different from the phonon density of states. The momentum selection rules are relaxed in the amorphous material so that all the phonons contribute to the spectrum. 

This book describes the material properties and physical phenomena of hydrogenated amorphous silicon (a-Si H). It covers the growth of material, the atomic structure, the electronic and optical properties, as well as devices and device applications. Since it focusses on the specific properties of one amorphous material, there is a considerable emphasis on describing and interpreting the experimental information. Familiarity with semiconductor physics is assumed, and the reader is also referred to the excellent books by Mott and Davis, Elliott, and Zallen for further information about the general properties of amorphous semiconductors and glasses.f... 

However, as mentioned in the introduction, the main advantage of XAS compared to other structural techniques is its element specificity, its potential operation under more or less any experimental conditions, its appUcabiUty for amorphous and X-ray amorphous materials and its straightforward sample preparation. In the following, some applications of XAS in catalytic systems will be discussed. 

Diffraction patterns from amorphous materials consist of a few vague halos. Accurate measurement of the intensity distributions of these halos in reciprocal space provides information about the distribution of atoms in real space. Reviews of the experimental methods and data handling techniques for X-ray-, electron-, and neutron-scattering is given in the literature The mathematical tool which is used to relate the... 

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