Optical properties and X-ray diffraction of amorphous systems

By appealing to the persistence of short range order in amorphous materials a simple estimate of the form of the static structure factor can be obtained. It is also possible to derive an expression for the optical absorption of amorphous materials involving a convolution of the corresponding crystalline expression and a simple function.     

An X-ray diffraction study of the amorphous structure of chemically vapor-deposited silicon nitride

X-ray diffraction measurements have been carried out for two kinds of samples of CVD-amorphous silicon nitride with different values of the density. From radial distribution analysis, it became clear that the short range structure in these samples resembles that of the crystalline β-phase. Coloring in CVD-amorphous Si₃N₄ was found to be induced by X-ray irradiation. Based on the deficient numbers of the first nearest neighbours in SiN bondings, it was proposed that CVD-amorphous Si₃N₄ consists of small clusters including vacancies in their matrix.     

X-ray diffraction study of thiocarbamide hydrochloride

Thiocarbamide hydrochloride single crystals forming a salt with the composition [(NH₂)₂CSH]⁺Cl^? are studied by the X-ray diffraction method. The tetragonal crystals have the unit-cell parameters a = 7.556(1) Å and c = 18.329(3) Å, V = 1046.5 ų, Z = 8, ρ_calcd = 1.436 g/cm³, sp. gr. P4₁2₁2, and R = 0.050. Each chloride anion in the crystal forms five hydrogen bonds with thee different cations.     

X-ray diffraction study of some indolinones

X-ray diffraction studies are reported for six indolinones. The results show that two different types of associates are present in the crystal state of the compounds having an NH group. The indolinone molecules without any substituents form cyclic dimers while those with one or two methyl groups attached to the C3 atom of the lactam ring form infinite hydrogen bonded chains. It is confirmed that the lactam moiety forms a typical planar amide structure with no sign of the enol form present.     

X-ray powder diffraction study of polytetrafluoroethylene

Samples of polytetrafluoroethylene were studied by X-ray diffraction. A quantitative X-ray powder diffraction analysis of three components of the polymer was performed for the first time. All samples of polytetrafluoroethylene were found to be three-phase and consist of one crystalline and two amorphous phases. One of the amorphous phases is composed of low-molecular-weight products. The structure of the latter phase was established for the first time by X-ray diffraction methods and computer simulation.     

X-ray diffraction study of mesophase bitemplate-containing silicas

The effect of the composition of a bitemplate (solubilization) mixture on the formation of a spatially organized structure of mesophase siliceous systems has been investigated by X-ray diffraction. Alkylpyridinium halides (C _n PyHal with n = 8?16 (counterion Cl) and 18 (counterion Br)) were used a solubilizator, and monoethanolamides (EAC _m ) of saturated n-aliphatic acids (m = 10?16) and trialkylphosphine oxides (H_{2e + 1}C _e )₃PO, where e = 8, 10, or 12, were used as solubilizates. Differences in the mesophase structure of template-containing silicas synthesized in aqueous and aqueous salt (NaCl) solutions have been revealed. It is shown that the type and degree of ordering of the silica mesophase structure depends on the nature, spatial organization, and the solubilizator and solubilizate concentrations.     

An electron diffraction study of amorphous silicon oxide films

Amorphous silicon oxide films have been examined by high energy electron diffraction using the sector-microphotometer method of data collection common to gas phase electron diffraction. This data was analyzed with a least-squares procedure that is designed to minimize extraneous detail in the radial distribution function obtained by the Fourier sine transform of the interference function. The results of this analysis for thin film SiO₂ show that the overall bonding topology of the thin film agress well with that of bulk (vitreous) SiO₂ examined by X-ray diffraction. The experimental short distance parameters for the films whose composition was determined to be ～SiO_1.3, SiO, and SiO_0.8 are found to be consistent with those expected for a mixture of tetrahedrally bonded amorphous Si and SiO₂ phases in which the scale of the Si-like and SiO₂-like regions is of the order of a few basic tetrahedral units. This result is in agreement with previous examinations of SiO powder by X-rays and a previous examination of thin silicon oxide films by electron diffraction.     

Structure of amorphous LaNi5D3.3 studied by neutron and X-ray diffraction

In situ neutron and X-ray diffraction measurements in a D₂ gas atmosphere at a constant pressure of 1 MPa were performed on amorphous LaNi₅D_3.3, which was prepared by mechanical alloying in a D₂ gas atmosphere. Reverse Monte Carlo (RMC) simulation based on the neutron and X-ray diffraction data was applied to construct a three-dimensional atomic arrangement of this amorphous alloy. The RMC model shows that more than 90% of the deuterium atoms occupy tetrahedral sites consisting of La and/or Ni atoms. Furthermore, the local environments around the Ni and La atoms were investigated by Voronoi polyhedral analysis of the RMC configuration of the metal atoms. The results show the presence of a number of prismatic-like polyhedra around a Ni atom.     

X-ray diffraction study of amorphous alloys Al–Ni–Ce–Sc with using Ehrenfest’s formula

The effect of replacement of Ce by Sc in the amorphous Al₈₅Ni₁₀Ce₅ alloy on its structure has been studied. The replacement was shown to result in increasing the coordination number in the first coordination sphere, changing the type of short-range order. A splitting the first peak of the function of radial atom distribution into two subpeaks made it possible to determine separately the coordination number for the atom pair groups Ce–Al, Sc–Al, Al–Al and Ni–Al, Al–Al. The structure of the amorphous alloys Al₈₅Ni₁₀Ce_5−xSc_x (x = 0, 1, 5) was determined using X-ray diffractometry combined with application of Ehrenfest’s formula, which allowed us to directly determine the first coordination sphere radius from data on the structure factor and some cluster parameters obtained from the prepeak on the structure factor curve.     

X-ray diffraction study of gadolinium stearate Langmuir-Blodgett films

The comparative structural studies of gadolinium stearate Langmuir-Blodgett films prepared with the use of two different subphases (aqueous solutions of gadolinium chloride and gadolinium acetate) have been performed by the methods of X-ray diffractometry. The films were applied onto single-crystal silicon substrates coated with a native-oxide layer either with the use of buffer molecular stearic-acid layers or without such layers. It was established that the films obtained with the use of gadolinium acetate and the preliminarily formed buffer layers are, in fact, single-phase Y-type films with highly ordered molecular structure, and the thickness of the bimolecular layer d = (51.3 ± 0.5) Å.     

X-ray diffraction study of defects in zinc-diffusion-doped silicon

Samples of CZ n-Si〈Zn〉(111) are prepared by high-temperature zinc-diffusion annealing followed by quenching and are studied by X-ray diffraction. The silicon contains an initial phosphorus impurity and zinc-compensating admixture at concentrations N _P = 1.5 × 10¹⁴ cm^?3 and N _Zn = 1 × 10¹⁴ cm^?3; i.e., the relation N _P/2 < N _Zn < N _P is fulfilled. Microdefects are studied by double- and triple-crystal X-ray diffraction in the dispersion free modes (n, ?n) and (n, ?n, +n). The samples are found to contain microdefects with two characteristic sizes (average sizes of about 1 μm and 70 nm). The interplanar distance in the near-surface layer with a thickness of 0.1 μm is smaller than this parameter in the remaining matrix, the difference being equal to d ₀ Δd/d ₀ ≈ 2 × 10^?5. This layer contains mainly vacancy-type microdefects. The angle between the reflecting planes and the local surface relief is Δψ = (7 ± 1) arcmin.     

An X-ray diffraction study of sodium borate glasses

X-ray diffraction measurements have been performed on two pairs of sodium borate glasses of differing compositions. Glasses of given composition were obtained with two different thermal histories. The radial distribution functions of samples of the same composition appear similar. The short range order is not affected by the range of quenching rates explored.     

Structure of amorphous NaCl–glucose system studied by X-ray diffraction and IR methods

X-ray diffraction and diffuse reflection IR spectroscopic measurements have been carried out on amorphous NaCl–glucose mixtures, a-(NaCl)_x(glucose)_1−x, with x = 0, 0.05, 0.1 and 0.15, in order to obtain structural information on the intermolecular hydrogen-bonded interaction between glucose molecules affected by the presence of NaCl. The difference distribution function Δg^inter(r) was derived from the Fourier transform of the difference intermolecular interference term Δi^inter(Q) between X-ray intermolecular interference terms observed from amorphous NaCl-glucose and pure glucose samples. A negative peak appears at r ≈ 2.5 Å in the Δg^inter(r) observed for the 10 mol% NaCl sample, while, the Δg^inter(r) for the 15 mol% NaCl sample does not show pronounced negative peak. On the other hand, the IR spectra for the O–H stretching region (2300 ⩽ ν ⩽ 3800 cm⁻¹) indicate that hydrogen bonds between glucose molecules are significantly collapsed in the samples containing 5–15 mol% NaCl. These results imply that the contribution from the Na⁺⋯Cl⁻ contact ion pair is dominated in the 15 mol% NaCl sample.     

X-ray diffraction study of highly purified human ceruloplasmin

The three-dimensional structure of ceruloplasmin (CP) with unoccupied labile metal-binding sites and the structure of CP containing Ni²⁺ in the labile sites were solved for the first time at 2.6 and 2.95 Å resolution, respectively. Crystallization was performed with the use of storage-stable CP, which was prepared in the presence of proteinase inhibitors and purified from (pre)proteinases. Ceruloplasmin with Ni²⁺ crystallized in the orthorhombic space group, which had been earlier unknown for CP. Ceruloplasmin with the unoccupied labile sites crystallized in the trigonal crystal form. The differences in intermolecular contacts observed in the trigonal and orthorhombic crystal structures of CP are considered. The conformational changes attendant upon Ni²⁺ binding are described. It was suggested that the labile sites are multifunctional and can both bind metal ions potentially toxic to organisms and be involved in electron transfer from substrates to the active site.     

X-ray diffraction and X-ray standing-wave study of the lead stearate film structure

A new approach to the study of the structural quality of crystals is proposed. It is based on the use of X-ray standing-wave method without measuring secondary processes and considers the multiwave interaction of diffraction reflections corresponding to different harmonics of the same crystallographic reflection. A theory of multiwave X-ray diffraction is developed to calculate the rocking curves in the X-ray diffraction scheme under consideration for a long-period quasi-one-dimensional crystal. This phase-sensitive method is used to study the structure of a multilayer lead stearate film on a silicon substrate. Some specific structural features are revealed for the surface layer of the thin film, which are most likely due to the tilt of the upper layer molecules with respect to the external normal to the film surface.     

X-ray diffraction study of short-period AlN/GaN superlattices

The structure of short-period hexagonal GaN/AlN superlattices (SLs) has been investigated by X-ray diffraction. The samples have been grown by metalorganic vapor-phase epitaxy (MOVPE) in a horizontal reactor at a temperature of 1050°C on (0001)Al₂O₃ substrates using GaN and AlN buffer layers. The SL period changes from 2 to 6 nm, and the thickness of the structure varies in a range from 0.3 to 1 μm. The complex of X-ray diffraction techniques includes a measurement of θ-2θ rocking curves of symmetric Bragg reflection, the construction of intensity maps for asymmetric reflections, a measurement and analysis of peak broadenings in different diffraction geometries, a precise measurement of lattice parameters, and the determination of radii of curvature. The thickness and strain of separate SL layers are determined by measuring the θ-2θ rocking curves subsequent simulation. It is shown that most SL samples are completely relaxed as a whole. At the same time, relaxation is absent between sublayers, which is why strains in the AlN and GaN sublayers (on the order of 1.2 × 10^?2) have different signs. An analysis of diffraction peak half-widths allows us to determine the densities of individual sets of dislocations and observe their change from buffer layers to SLs.     

X-ray diffraction and IR spectroscopy study of labuntsovite-group minerals

The distribution of cations over the positions in the structures of labuntsovite-group minerals was studied by X-ray diffraction analysis and IR spectroscopy. Several types of cation order over the five key positions are established depending on cation composition and their force characteristics.     

X-ray diffraction study of the structure of detonation nanodiamonds

The spatial structure of aggregates formed by detonation nanodiamonds is investigated using the wide-angle and small-angle X-ray scattering techniques. The effective sizes of crystallites and the crystallite size distribution function are determined. The shape of scattering aggregates is restored from the small-angle X-ray scattering data. An analysis of the results obtained allowed the conclusion that the nanodiamond aggregates have an extended spatial structure composed of nine to ten clusters, each involving four to five crystallites with a crystal lattice of the diamond type.     

Low temperature X-ray diffraction study of CdI2 crystals

Solid state structural transformations in polytypic crystals of cadmium iodide have been investigated at low temperatures using X-ray diffraction techniques. The crystals were cooled to liquid nitrogen and liquid helium temperatures employing three different methods. The results obtained are discussed on the basis of bond dissociation energies of interlayer and intralayer bonds and the possible mode of layer displacements in MX₂-type polytypic crystals.