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Crystallographic Directions (crystallographic + direction)

Distribution by Scientific Domains
Physics and Astronomy57%
Polymers and Materials Science28%

Selected Abstracts

Patterning Colloidal Metal Nanoparticles for Controlled Growth of Carbon Nanotubes,

ADVANCED MATERIALS, Issue 24 2008
Bing Li
Single-walled carbon-nanotube (SWCNT) arrays are generated on catalyst patterns with controlled location, orientation, and spacing using a straightforward approach. Dip-pen nanolithography is used to fabricate catalyst patterns with sub-70 nm resolution, and SWCNTs are successfully grown on these patterns through chemical vapor deposition. The growth direction of the SWCNTs on quartz is controlled, and along the [100] crystallographic direction. [source]

Micropore modification in InP

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2008
D. Nohavica
Abstract The structural features and optical properties of microporous InP substrates used for epitaxial overgrowth of thin films have been investigated. Both crystalographically oriented (CO) and current line oriented (CLO) pore networks were created by electrochemical dissolution. Heat treatment of the InP pores converted them into microcavities maintaining the same crystallographic direction. The effect of phosphorus vapour pressure was proved to be crucial for the microcavity formation, since it influences the mass transport during heat treatment. Electron microscopy and photoluminescence experiments revealed the absence of significant extended defects, both after the pore and cavities formation. The capability of improved structural quality homo- and hetero-epitaxial overgrown films on the porous InP, was also demonstrated. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Giant ultrasonic attenuation in ZnSe doped with Cr and its possible application in crystal characterization

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2010
V. V. Gudkov
Abstract Ultrasonic experiment was done at the frequency of 54,MHz on ZnSe:Cr2+ crystal with concentration of the dopand 3.8,×,1018,cm,3. Giant peak of attenuation of slow shear wave propagating along ,110, crystallographic direction was observed at low temperatures (about 13,K). The peak proved to be due to relaxation process in the Jahn,Teller system. Magnitude of the peak is proportional to the concentration of the dopand. This circumstance forms the basis for a new non-destructive method of characterization of the diluted crystals, which particularly could be useful for determining the low concentration of the Jahn,Teller ions. Estimation showed that the concentration of the dopand can be registered in ZnSe:Cr2+ crystal of the order of 1016,cm,3. Other Jahn,Teller ions prospective for such characterization are suggested. [source]

Optical properties of KGd(WO4)2 single crystals studied by Brillouin spectroscopy

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2006
D. Kasprowicz
Abstract The results of a study of KGd(WO4)2 single crystals by Brillouin scattering method are presented. The Brillouin spectra for the acoustic phonons propagating in the [100], [010], [001], [110] and [101] directions, taken in 90° and 180° scattering geometry at room temperature have been recorded. Using the Brillouin spectroscopy the refractive indices for some directions of KGd(WO4)2 crystals were determined. The refractive indices were also calculated for the same directions by the rotation transformation of the principal optical axes of the optical indicatrix to the crystallographic directions of KGd(WO4)2 crystals. Moreover, some anomalies of the acoustic phonons propagating connected with birefringence of KGd(WO4)2 crystals were discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Silicon-Doped LiFePO4 Single Crystals: Growth, Conductivity Behavior, and Diffusivity

ADVANCED FUNCTIONAL MATERIALS, Issue 11 2009
Ruhul Amin
Abstract Single crystals of silicon doped LiFePO4 with a silicon content of 1% are grown successfully by the floating zone technique and characterized by single-crystal and powder X-ray diffraction, secondary ion mass spectroscopy, and chemical analysis. Electron paramagnetic resonance demonstrates the presence of only Fe2+; no traces of Fe3+ are found. Impedance spectroscopy as well as step-function polarization/depolarization (DC) measurements are carried out using the cells Ti/LiFe(Si)PO4/Ti and LiAl/LiI/LiFe(Si)PO4/LiI/LiAl. The electronic and ionic conductivities as well as the Li-diffusivity of the sample in the major crystallographic directions ([h00], [0k0], and [00l]) are determined. Within experimental error the transport properties along the b- and c-axes are found to be the same but differ significantly from the a-axis, which exhibits lower values. Compared to undoped LiFePO4, Si-doping leads to an increase of the ionic conductivity while the electronic conductivity decreases, which is in agreement with a donor effect. The activation energies of conductivities and diffusivities are interpreted in terms of defect chemistry and relevant Brouwer diagrams are given. [source]

Selective area heteroepitaxy of low dimensional a -plane and c -plane InGaN nanostructures using pulsed MOCVD

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008
V. Jindal
Abstract High density a -plane and c -plane InGaN nanostructures have been developed by nanoscale selective area epitaxial growth using pulsed MOCVD. SiO2 was used as a mask with nanopatterning through an anodic aluminum oxide template. The lateral dimensions of the pattern were controlled and varied from 30 nm to 180 nm by changing the anodization voltage and the electrolyte. Different substrates such as a -plane GaN on r -plane sapphire, r -plane sapphire and c -plane sapphire were used to develop InGaN nanostructures in a - and c - crystallographic directions respectively. Under identical growth conditions, InGaN nanostructures of various shapes were obtained on different substrates with differences in emission wavelength. The shape of the nanostructures on different substrates is discussed with respect to the stability and growth rates of various planes. However, the difference in emission wavelength is attributed to the In incorporation in the nanostructures. The optical properties of the nanostructures were studied by photoluminescence (PL) spectroscopy. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Anisotropic crystal structure distortion of the monoclinic polymorph of acetaminophen at high hydrostatic pressures

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2000
E. V. Boldyreva
The anisotropy of structural distortion of the monoclinic polymorph of acetaminophen induced by hydrostatic pressure up to 4.0,GPa was studied by single-crystal X-ray diffraction in a Merrill,Bassett diamond anvil cell (DAC). The space group (P21/n) and the general structural pattern remained unchanged with pressure. Despite the overall decrease in the molar volume with pressure, the structure expanded in particular crystallographic directions. One of the linear cell parameters (c) passed through a minimum as the pressure increased. The intramolecular bond lengths changed only slightly with pressure, but the changes in the dihedral and torsion angles were very large. The compressibility of the intermolecular hydrogen bonds NH,O and OH,O was measured. NH,O bonds were shown to be slightly more compressible than OH,O bonds. The anisotropy of structural distortion was analysed in detail in relation to the pressure-induced changes in the molecular conformations, to the compression of the hydrogen-bond network, and to the changes in the orientation of molecules with respect to each other in the pleated sheets in the structure. Dirichlet domains were calculated in order to analyse the relative shifts of the centroids of the hydrogen-bonded cycles and of the centroids of the benzene rings with pressure. [source]