RHEED Investigations on Low-temperature Thermal SiO2 Films

The structural changes in thermal SiO₂ films grown at 1123–1173 K in a double walled furnace tube with chlorine between the inner and the outer tube are studied. The layers have a higher degree of crystallinity in comparison with the layers grown by standard high temperature dry oxidation (1273 K). A difference between the crystalline type structures of SiO₂ films on p- and n-Si is observed. The increase of the growth temperature from 1123 to 1273 K increases the variety of crystalline structures in the layers but decreases strongly their quantity and makes the films predominantly amorphous.     

Structural Investigations of Novel Indoloacridines

Abstract  5,6-Dihydro-9-chloro-7-phenylindolo[3,2-c]acridinium sulfates (3a-c) were formed from 2,3,4,9-tetrahydro-1H-carbazol-1-ones (1a-c) on reaction with 2-amino-5-chlorobenzophenone. 3b and 3c are isostructural and all three sulfates crystallize in the triclinic system with the space group P each with two crystallographically independent organic cations and one sulfate anion in the asymmetric unit. 3a exhibits the parameters a = 9.8896(17), b = 14.165(2) and c = 14.583(2) ?, α = 83.184(3)°, β = 78.985(3)° and γ = 75.903(3)°; 3b a = 10.5713(9), b = 14.5667(12) and c = 14.9947(13) ?, α = 90.916(1)°, β = 97.153(1)° and γ = 97.208(1)°; and 3c a = 10.5505(10), b = 14.6090(13) and c = 15.2960(14) ?, and α = 91.4310(10)°, β = 98.8630(10)° and γ = 98.9100(10)°. The structure of 3c exhibits voids of 286 ?³ of ill defined and disordered solvate molecules. The structure of 3a is both non-merohedrally twinned and also exhibits an interesting type of pseudosymmetry. All but the sulfate ion and the ethylene moieties also fit with a unit cell half the size with only one independent cation, and disordered ethylene moieties and sulfate anions. The choice of unit cell was made based on the diffraction pattern and the absence of disorder in the larger cell, pointing towards alternating ordered ethylene and sulfate units rather than randomly disordered ones. Index Abstract  [The structures of three indoloacridines 3a, 3b, and 3c with similar packing motifs are described. The structure of 3a is both non-merohedrally twinned and also exhibits an interesting type of pseudosymmetry by being a double volume ordered supercell of an alternative cell with disordered ethylene and sulfate anion moieties.]      

High-temperature Raman Investigations of Arsenic Vapour

Raman spectra of arsenic vapour were measured at temperatures up to 1210 K. The intensity ratio of the vibrational modes was used to determine the partial pressure ratio of As₂ and As₄. The data obtained exhibit discrepancies to existing theoretically predicted values. The reason for these differences is yet unclear.     

Investigations of positron-annihilation rate in semimetals

The annihilation rates of thermalized positrons in the semimetals bismuth and antimony were measured. We found that the different rates were not based on the various conduction-electron densities. However, excellent agreement with experimental results was achieved by taking into consideration many-body effects in a random phase approximation.     

X-ray Investigations of Shape Memory Alloys

The investigation aims to analyse the influence of different kinds of thermal treating on the structure of martensite. Maxima of the X-value are observed at 60–70 minutes for the sample aged at 200°C and 90 minutes for that aged at 375 °C and minima for Y after almost the same time. We consider that with these results the discussion on the processes occurring during short ageing times will be activated, because in the literature there is lack of such a results.     

Investigations of Dissolving Mechanically Processed Quartz Grains

The dissolution of polycrystalline quartz strained by compression and shear or by impact crushing in 1-N NaOH lead to different results. The defects of the impact crushed quartz grains, measured as crystallinity by X-ray methods, are not preferentially concentrated in regions near the surface. It is assumed that in this case the corners and edges of the quartz grains are preferred centers of defects.     

单壁碳纳米管的稳定性研究

采用化学气相沉积法(CVD),以正己烷为碳源制备单壁碳纳米管(SWNTs),研究了纯化后的单壁碳纳米管在空气中的稳定性,分别对刚纯化后和在空气中放置5d、10d和15d后的样品进行了SEM、HRTEM和TG表征,结果发现单壁碳纳米管的氧化程度随在空气中放置时间的延长而增加,15d后几乎完全转化为无定形碳.表明单壁碳管在空气中不稳定,很容易氧化,需要密闭保存.     

Investigations of crystal defects with reflection-section topography

A simple topographic technique is presented that allows an exact determination of the depth of kinematically reflecting regions below the crystal surface. A kinematical reflection full of contrast can be achieved by a spatial separation of the images from perfect and disturbed parts of the crystal. Possible applications of reflection-section topography are e.g. demonstrated by lattice deformations caused by laser irradiation and ion implantation as well as by growth bands and dislocations. In weakly deformed crystals a new kind of interference fringes can be observed.     

Investigations of impurity striations in potassium bichromate crystals

Impurity striations in potassium bichromate crystals (KBC, lopezite) formed during crystal growth from aqueous solution were revealed by chemical etching and analyzed. Striations were revealed as etch grooves, as rows of dislocation etch pits and as rows of flat‐bottomed etch pits. Various types and groups of striations have been visualized. Some striations were due to lateral segregation of impurities caused by convection flow of the mother solution, other were formed during growth stoppages whereas induced striations were generated by changes in hydrodynamical conditions. Growth rates changes resulted in zonal distribution of impurities, formation of planar lattice strain, rows of clusters of point defects and rows of dislocations. Generation of striations with different intensities in various sectors is a proof of the selective capture of impurities. Ratios of growth rates of various faces of KBC crystals growing in forced and free convection regimes were determined by induced striations. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigations on Flux Grown Cadmium Sulphide Crystals

Observations on surface microtopography of flux grown CdS crystals are reported. Crystals resulting with cooling rate above 30 °C/hr are reported to be dendritic crystals, while those with cooling rate below 30 °C/hr are reported to be normal crystals like mineral greenockite as reported in standard books on mineralogy. Reasoning for dendritic growth is briefly discussed. Growth patterns and etch pits formation on them are interpreted. It is established that these crystals grow by two-dimensional nucleation mechanism and by spreading and piling of growth layers.     

Crystallographic and Computational Investigations of Triphenylamine/Anthraquinone Hybrids

Journal of Chemical Crystallography - Understanding of relationship between structure and property of thermally activated delayed fluorescence (TADF) materials is essential for developing efficient...     

In-situ HVEM Investigations under the Influence of Ion Beams

A 200 kV ion accelerator was coupled to a 500 kV TEM for in-situ studies of the 80 keV He⁺ irradiation of 316 stainless steel. Dynamic and static observations of bubble growth, exfoliation and blistering show that slip bands, incoherent twin boundaries and grain boundaries are preferred sites for helium bubble formation. Bubble growth is enhanced by plastic deformation during irradiation. Exfoliation and blistering occur in samples thinner than the projected range of 80 keV He⁺ ions. Crack propagation during tensile tests proceeds through the bubbles enlarging them in diameter by a factor of two. Bubble enlargement also accompanies the formation of a blister cap. Brittle intergranular failure, even in samples with a large bubble population on the grain boundaries, occurred only when tensile tests were performed at elevated temperatures.     

Structural Investigations of Polyacetylene and Polyphenylene by Neutron Scattering

Wide angle neutron scattring patterns of deuterated cis- and trans-polyacetylene (PA) and deuterated polyphenylene (PPh) doped with AsF₅ have been measured. For undoped trans-PA a refined crystal structure is proposed to reproduce the neurtron scattering data. Doping of PA with AsF₅ is explained on the basis of an intercalation model. Deuterated PPh has been prepared by different polyerisation procedures, variing the crystallinity of the undoped material in a wide range. Strong extra peaks are observed during doping with AsF₅, wheres the crystallinity of the samples remains essentially unchanged. An intercalation model similar to AsF₅.-doped graphite is proposed.     

Investigations of the energy flow of X-ray wavefields in crystals

The energy flow of the X-ray wavefields in the Laue case of diffraction and its importance for X-ray topography and interferometry are discussed.     

Reflection Splitting in RHEED Investigations of Vacuum Evaporated GaAs Layers

RHEED-diagrams of vacuum deposited GaAs-films with high density of structural defects often show splitting of matrix reflections into satellites. It can be shown by simple models, for example of {111}-oriented films, that this phenomenon is originated by formation of stacking faults perpendicular to 〈ĪĪĪ〉-B growth directions of the films. The conditions for 〈110〉 and 〈211〉 azimuths are discussed.     

Investigations on the nucleation kinetics of bis glycine sodium nitrate

The nucleation parameters such as, energy per unit volume, radius of critical nucleus, critical free energy barrier, number of molecules in the critical nucleus and nucleation rate have been evaluated for bis glycine sodium nitrate single crystals. The interfacial energy of the solution at various temperatures has been estimated from existing solubility data. The metastable zone width and induction period measurements have been carried out experimentally.