Degree Of Crystalline Order Research Articles

Characterization of Microcrystalline Si Films by MeV Ion Scattering Techniques

AbstractRutherford Backscattering Spectroscopy (RBS) and channeling studies with 1.4 MeV−4He ions as well as Heavy-Ion Elastic Recoil Detection Analysis (HI-ERDA) with 230 MeV 129Xe ions have been applied to characterize structural properties and the impurity content of thin Si films. The analytical potential of these ion-beam techniques is demonstrated for two types of samples: (1) μc-Si films prepared by dc magnetron sputtering in a pure Ar plasma and (2) homoepitaxial Si films deposited by low-temperature electron-cyclotron resonance PECVD at the transition from oriented to disordered growth. For μc-Si the atomic area density N.d obtained by RBS was compared with the optical thickness n.d (n=refractive index) derived from the interference structure of IR reflection spectra. It is shown that the ratio R=n.d/N.d of these quantities can serve as a figure of merit for the degree of crystalline order. An apparent similarity was found in the case of the epitaxially grown films between the Si disorder profiles evaluated from the RBS channeling spectra and the hydrogen and oxygen profiles determined by HI-ERDA. This suggests that hydrogen and oxygen are preferentially incorporated in the disordered parts of the films.

Structural Characterization of Electrooptically Active Poly(nonylbithiazole)

We have examined the microstructure, solution processing, thermal transitions, and mechanical properties of regioregular poly(nonylbithiazole) (PNBT). PNBT can adopt three distinct colors in the solid stateyellow, red, and metallic greendepending on processing conditions such as polymer concentration, solvent evaporation rate, temperature, and pressure. Microstructural variations were observed between samples of different colors, including the intensification of optical absorption with the degree of crystalline order and/or crystal size. Yellow samples lacked well-developed three-dimensional order, whereas red and green samples were semicrystalline. The development of a lyotropic mesophase was observed at intermediate concentrations in a “diffusion couple” geometry. A crystal model with two planar, π-stacked chains per unit cell was shown to be consistent with the experimental diffraction data. The simulated orthorhombic unit cell parameters are a = 2.38 nm, b = 0.72 nm, and c = 0.79 nm.

Residual disorder in low pressure, low thermal gradient liquid encapsulated Czochralski gallium arsenide observed in high resolution synchrotron diffraction imaging

High resolution synchrotron X-radiation diffraction images of low thermal gradient, low pressure, liquid encapsulated Czochralski (LEC) silicon-doped gallium arsenide display a degree of crystalline order that is far higher than that found in undoped conventional LEC material. No distinct volume irregularity is observed in one crystal where it is unstrained. Only a set of surface-treatment-related dislocations is prominent in a second. A third crystal exhibits two distinct sets of quasi periodic dislocations, which have been analyzed in detail. The results support a model previously proposed for the evolution of disorder in gallium arsenide and suggest the role that silicon plays in its control.

Crystals of HIV-1 Reverse Transcriptase Diffracting to 2·2 Å Resolution

Reverse transcriptase (RT) from the human immunodeficiency virus type 1 has been crystallized in four closely related forms, the best of which diffract X-rays to 2·2 Å resolution. The RT was crystallized as a complex with a non-nucleoside inhibitor, either nevirapine or a nevirapine analogue. Crystals grew from 6% PEG 3400 buffered at pH 5. These were of space group P 212121 with unit cell parameters a = 147 Å, b = 112 Å, c = 79 Å (form A), with one RT heterodimer in the asymmetric unit. Changes in unit cell parameters and degree of crystalline order were observe on soaking pregrown crystals in various solutions, giving three further sets of unit cells. These were a = 143 Å, b = 117 Å, c = 79 Å (form B), a = 141 Å, b = 111 Å, c = 73 Å. (form C), a = 143 Å, b = 117 Å, c = 66·5 Å (form D). The last two forms diffract X-rays to 2·2 Å resolution. Structure determinations of these latter crystal forms of RT should give a detailed atomic model for this therapeutically important drug target.

Emulsion polymerization of aniline

In this communication, we report that aniline can be conveniently polymerized directly into conducting material using an emulsion polymerization technique. The polymerization is carried out in non-polar or weakly polar solvents in the presence of a functionalized protonic acid that acts simultaneously as a surfactant (emulsifier) and as a protonating agent (dopant) for the resulting electrically conducting polyaniline. It was found that the present direct, one-step preparation of polyaniline-protonic acid complexes in organic solvents may lead to polyaniline with significantly higher molecular weight than that prepared in acidic aqueous solutions. In addition, the present polyaniline-functionalized acid complexes displayed higher solubilities in non-polar or weakly polar organic solvents than corresponding complexes obtained by mechanically mixing the emeraldine base form of polyaniline with the protonic acid. Films cast from concentrated solutions routinely exhibit conductivities in excess of 100 S cm −1. Additionally, it was found that, using the emulsion polymerization route, polyaniline-functionalized protonic acid complexes of fibrillar morphology can be produced, which have an exceptional degree of crystalline order and orientation.

Effect of heat-moisture treatment on the structure and physicochemical properties of cereal, legume, and tuber starches

Native wheat, oat, lentil, yam, and potato starches were heat treated at 100°C for 16 h at moisture contents between 10 and 30%. The heat treatment did not change granule size and shape. In oat starch, granules were less compactly packed after heat treatment. The X-ray diffraction intensities increased in wheat, oat, and lentil starches, but decreased in potato and yam. The X-ray patterns of wheat and oat starches remained unchanged, while those of lentil, potato, and yam starches became more cereal-like. In all starches, the swelling factor and amylose leaching decreased, being more pronounced in potato. Heat treatment induced complex formation between amylose and native lipids. Differential scanning calorimetry of the heat-treated samples showed a broadening of the gelatinization-temperature range and a shifting of the endothermal transition towards higher temperatures. These changes were more pronounced in potato starch. The gelatinization enthalpy of wheat, oat, and lentil starches remained unchanged, but those of potato and yam starches decreased on heat treatment. Heat treatment increased the 95°C viscosity of wheat starch, but decreased those of oat, lentil, potato, and yam starches. In all starches, thermal and shear stability increased after heat treatment. Acid hydrolysis decreased on heat treatment of wheat and lentil starches, but increased in oat, potato, and yam starches. However, in potato and yam starches, the foregoing trend was evident only during the first seven days of hydrolysis. Thereafter, acid hydrolysis was more pronounced in native than in heat-treated starches. The susceptibility towards hydrolysis by porcine pancreatic alpha amylase decreased on heat treatment of wheat and lentil starches, whereas increases were observed for oat, potato, and yam starches. The results indicated that the extent of starch-chain associations within the amorphous regions and the degree of crystalline order are altered during heat-moisture treatment. The magnitude of these changes were found to be dependent upon the moisture content during heat treatment and on the starch source.

Defects in III–V materials and the accommodation of strain in layered semiconductors

High resolution monochromatic synchrotron-radiation diffraction images of five, high quality epitaxial heterojunctions on silicon, gallium arsenide, and indium phosphide substrates display several forms of accommodation to lattice mismatch. From the images, we deduce a coherent set of factors for the loss of crystalline order in layered semiconducting crystals. Lattice mismatch is demonstrated in each of the systems by warping after layer deposition. Nevertheless, local lattice orientation is maintained across each layer interface. In two of the systems, one severely mismatched while the other is not, no arrays of dislocations appear. Sets of mixed linear lattice mismatch dislocations, consistent with identification as 60° dislocations, are found in two of the other systems with intermediate degrees of mismatch. A set of pure edge dislocations penetrating all layers is found in a system with a grid structure. These observations indicate that the formation of extensive arrays of dislocations during uniform one micrometer layer deposition depends not only on the extent of lattice mismatch and layer thickness but also on the degree of crystalline order of the substrate. Establishment of a nonpseudomorphic layer mismatched with the substrate by several tenths of a percent is an important factor, as previously determined. However, localized absence of crystalline order, e.g. in the form of scratches or dislocations in the substrate, appears also to be required for the formation of arrays of interface mismatch dislocations. Where these criteria are not fulfilled, the formation of dislocations in uniform layered systems is inhibited. Localized residual stress can initiate dislocation formation even where it would not appear in uniform layers. The images show also that crystalline disorder in state-of-the-art indium phosphide differs markedly from that in comparable gallium arsenide. Understanding of crystalline order in both monolithic materials is extended by this work.

Emulsion polymerization of aniline

High quality polyaniline, PANI, has been made by polymerization of aniline using a direct one-step emulsion polymerization technique. The polymerization is carried out in an emulsion comprising water and a non-polar or weakly polar organic solvent in the presence of the functionalized protonic acid dodecylbenzene sulphonic acid (DBSA). We found that using the emulsion polymerization technique, conducting PANI-DBSA complexes can be produced that exhibit high molecular weight, high conductivity and high solubility in organic solvents in the electrically conducting state. We found, furthermore, that using this technique, in-situ production of PANI-DBSA fibrils can be produced that exhibit a high aspect ratio and an exceptional degree of crystalline order and orientation.

Effect of organic amine type on the structure and properties of the complex Zn(II) salts of ethylene–methacrylic acid copolymer with organic amines

AbstractThe complex Zn(II) salts of ethylene–methacrylic acid copolymer (EMAA) were synthesized by using various organic amines from monoamines to polyamines, from primary amines to tertiary amines, and from molecular amines to polymer amines. Thermal analyses by differential scanning calorimetry (DSC), and the measurement of stiffness, melt flow rate (MFR), and dielectric properties were employed for the complex salts. It was found that the valence, strength of base, rigidity and flexibility, and bulkiness of the organic amines affect the degree of crystalline order of the ionic crystallites, which governs the stiffness of the complex ion ionomers. The stiffness is higher for the complex salts which form the higher orderliness in the ionic aggregates. The organic amines with two or more primary aliphatic amino groups and higher boiling temperatures from more rigid ionic crystallites in the complex ion ionomers leading to the enhanced modulus. Monoamines or polyamines with amino groups attached to flexible chains such as polyether and polysiloxane scarcely develop ionic crystallites and preferentially solvate the amorphous region including ionic groups leading to the decreased modulus. These results provide us with the fundamental information to control the modulus of ionomers.

Fabric development in lime treated clay soils : Wild, S; Arabi, M; Ward, G L Ground EngngV22, N3, April 1989, P35–37

A regeneration of interest in the use of lime stabilised clay soils for subgrade capping material in highway construction has led to renewed consideration of the physical changes involved. It has generally been held that the long-term development in strength of lime stabilised soil is due to a gradual increase in the degree of crystalline order. The author describes work on illite and lime, kaolinite and lime and montmorillonite and lime carried out at high temperatures and for periods of up to two years. The formation of a calcium silicate aluminate hydrate gel is described which also occurs at lower temperatures but at a slower rate. TEM micrographs show the gel which is also seen in a sample taken from the lime-stabilised foundations of a 400 year old bridge in Iran. The author suggests that stability comes from the gradual formation of the gel product and development of the gel-clay particle microstructure rather than from crystallisation of the gel. The effect on permeability and how this increases or decreases with age are considered.

Growth-Packed PPT-A Fiber for the Replacement of Native Asbestos

AbstractA now type of crystal that can be defined as a “gel crystal” was first made with oligomeric poly-p-phenyleneterephthalainide (PPT-A), associating a large amount of dimethylacetamide (DMAc) liquid molecules, in which catalytic amount of heterocyclic tertiary amine, coupled with alkali metal cations or phosphoric triamidos are incorporated. Under mechanical orientation of the growing PPT-A, before gelation of the reaction “mixture, a hark agar-like gel crystal is formed. It shows a strong optical birefrin,- gence with four clear extinction positions under crossed polarizers when the gel was sectioned either along the direction of PPT-A orientation or perpendicular to it. When the gel formed without orientation it exhibitil speckled birefringence due to a large number of tiny spherulitic crystallites. The degree of crystalline order was similar to that of lyotropic, nematic liquid crystals when evaluated from X-ray diffractograins. The same type of gel crystals with extinction positions were observed in animal and vegetable tissues. It is assumed that the gel crystal has a threedimensionally ordered molecular network structure in which oligo-PPT-A's are arranged end-to-end in parallel lines. The lines are connected laterally, to form sheets, by DMAc bridges that are linear associations of DMAc molecules, which are connected to the oligo-PPT–A at the CONH groups. PPT-A molecular growth and self-ordering occurs within this gel crystal. A similar process gives rise to wool, cotton and ol.her fibrous biological materials.The high molecular weight PPT-A fiber thus grown in the gel crystal is constructed with numerous unit fibrils which connect themselves in a three-dimensional network, that resembles native flax or ranie fibers. The molecular growth of PPT-A in the gel crystal reaches ultra high molecular weight that can rarely be attained in ordinary solvent polyinerization. The gel state of PPT-A fibrils are initially formed spontaneously by selfsubdivision of the gel crystal after the molecular growth of PPT-A. Solid fibrils and fibers are finally fortoed by removing DMAc. The PPT-A gel fibrils thus formed resemble closely “the nascent fibril” of cellulose, and the microstructure and morphology of PPT-A fibrils are consequently very similar to those of native cellulose. The thickness of PPT-A fibrils can readily be controlled by the temperature in the gel crystal before fibril formation. The direction of the fibrils depends on the initial orientation of oligo-PPT-A's immediately before the formation of the gel crystal.This growth-packed PPT-A fibril, that can be produced by a one step chemical reaction, is considered as a good candidate for the replacemerit of native asbestos, because of the lower production cost, microfibrillation property, and inherently high heat-resistance.

Epitaxial Films of High Tc Oxide Superconductors Y1Ba2Cu3O7 Grown on SrTiO3 by Molecular Beam Epitaxy

ABSTRACTOrientation ordered high-Tc oxide films of Y1Ba2Cu3O7 were prepared by molecular beam epitaxy on SrTiO3 substrates. A combination of effusion cells and e-beam evaporators was used with the addition of an oxygen jet. The superconducting phase is formed by further O2 anneal at temperatures ≥800° C. For SrTiO3 (100), the Y1Ba2Cu3O7 films grow in the orientation of either the c-axis or the a-axis perpendicular to the film plane. Films with predominant “c⊥” orientation exhibit a high degree of crystalline order with a rocking curve 0.3° wide. The Jc is about two times higher than those with the “a⊥” orientation of a comparable Tc (R=0). For a typical film of 9000Å thickness, a Tc (R=O) of 87K, and a Jc of 7 × 104 A/cm2 at 77K were reproducibly achieved. For SrTiO3 (110), X-ray showed twinning of (110) and (103) orientations in Y1Ba2Cu3O7, thus precluding the observation of anisotropy expected for the in-plane axes of [001] and [110].

Infrared absorption of surface hydroxyl groups and lattice vibrations in lepidocrocite (γ-FeOOH) and boehmite (γ-AIOOH)

AbstractBoehmite and lepidocrocite, in the form of thin plates with well-developed (010) faces parallel to the constituent layers, show one predominant absorption band due to OH stretching of two-coordinated surface hydroxyl groups, which are shown to be unreactive towards phosphate. In very fine grained preparations of lepidocrocite, two other species of surface hydroxyl are detected, presumably associated with (100) and (001) faces. Marked differences in the frequencies of bulk vibrations between platy and rod-shaped lepidocrocite preparations can be explained partly by their crystal morphology, and partly by degree of crystalline order.

The preparation of NiO thin films and their use in optical measurements in the visible and ultraviolet

Several methods for producing NiO films for use in optical experiments are discussed including an indication of the significant problems encountered with each method. Transmission spectra between 2000 and 6000 Å are presented for films grown by both electron beam evaporation of nickel in an oxygen atmosphere and by reactive sputtering. The spectra appear to be consistent with one another as well as with the spectra of films grown on MgO by vapor deposition. The transmission spectra indicate that in addition to the absorption edge near 3700 Å, structure is present near 2300 Å. Electron reflection diffraction measurements indicate that films grown by electron beam evaporation and reactive sputtering on CaF 2 and LiF have at least some degree of crystalline order. Two films have been used to provide information on the shift of the NiO absorption edge with temperature, the results being −2.9 and −4.2. 10 −4 eV/°C. A Kramers Kronig analysis of the reflectivity of bulk NiO has been made and shows that the absorption of the films is consistent with the absorption constant derived from the reflectivity data. The reflectivities of a bulk sample and a film on MgO support the film transmission measurements in indicating structure near 2300 Å.

30—THE CHEMISTRY OF SILK FIBROIN I. THE ACTION OF SOME PROTEOLYTIC ENZYMES ON FIBROIN IN AQUEOUS SOLUTION, AND ITS BEARING ON THE MOLECULAR STRUCTURE OF SILK

The precipitate formed from an aqueous solution of fibroin by the action of pancreatic enzymes has been analysed, and shown to consist almost entirely of the three simplest amino acid residues, of glycine (G), alanine (A), and serine (S). The corresponding liquor contains all the amino acids of silk that have bulky side-chains. The insoluble fraction has a composition 30 G. 20 A. 10 S., and an experimentally-determined molecular weight of about 4,000. It has a high degree of crystalline order, as shown by X-ray analysis. The action of chymotrypsin, and of trypsin, on an aqueous solution of fibroin has also been investigated and the precipitates formed have been examined. The results are discussed in relation to Bergmann's rules for the specificity of proteolytic enzymes, and in relation to the molecular architecture of the fibroin molecule.