Search results for "Films"
showing 10 items of 2839 documents
Assessment of the out-plane and in-plane ordering of high quality ZnO nanorods by X-ray multiple diffraction
2013
Abstract ZnO nanorods grown on buffered and non buffered sapphire substrates have been investigated by X-ray multiple diffraction using Renninger scans of the ZnO(0001) and ZnO(0003) forbidden reflections. In this technique the diffracted X-ray beam is simultaneously diffracted by several sets of planes, providing information on the broadening in different directions, as well as from nanorods, and from the layer on which they grow. The intensities and angular widths of peaks obtained by azimuthal and omega scans have been analyzed, making a direct comparison with conventional measurements of the full width at half-maximum of symmetric and asymmetric reflections. The analysis leads to establ…
Chirality effects on 2D phase transitions
1996
Monolayers of the racemate and pure enantiomers of 1-hexadecyl-glycerol were investigated by grazing incidence X-ray diffraction (GID) at 5 and 20 °C on compression from 0 mN m−1 to pressures greater than 30 mN m−1. The racemate lattice is centred-rectangular for both temperatures at all investigated pressures. However, at both temperatures, there is a sharp phase transition from a low-pressure phase, in which the molecules are tilted towards nearest neighbours (NN) and the distortion azimuth also points towards NN, to a high-pressure phase, in which the molecules are tilted towards next-nearest neighbours (NNN) and an NNN-distorted lattice is observed. At 5 °C, the transition pressure is 1…
Pressure-Driven Symmetry-Preserving Phase Transitions in Co(IO3)2
2021
[EN] High-pressure synchrotron X-ray diffraction studies of cobalt iodate, Co(IO3)(2), reveal a counterintuitive pressure-induced expansion along certain crystallographic directions. High-pressure Raman and infrared spectroscopy, combined with density-functional theory calculations, reveal that with increasing pressure, it becomes energetically favorable for certain I-O bonds to increase in length over the full range of pressure studied up to 28 GPa. This phenomenon is driven by the high-pressure behavior of iodate ion lone electron pairs. Two pressure-induced isosymmetric monoclinic-monoclinic phase transitions are observed at around 3.0 and 9.0 GPa, which are characterized by increasing o…
Structural and vibrational properties of CdAl2S4 under high pressure: Experimental and theoretical approach
2014
The behavior of defect chalcopyrite CdAl2S4 at high pressures and ambient temperature has been investigated in a joint experimental and theoretical study. High-pressure X-ray diffraction and Raman scattering measurements were complemented with theoretical ab initio calculations. The equation of state and pressure dependences of the structural parameters of CdAl2S4 were determined and compared to those of other AB(2)X(4) ordered-vacancy compounds. The pressure dependence of the Raman-active mode frequencies is reported, as well as the theoretical phonon dispersion curves and phonon density of states at 1 atm. Our measurements suggest that defect chalcopyrite CdAl2S4 undergoes a phase transit…
Thickness and temperature dependent structure of Cd arachidate Langmuir-Blodgett films
1992
Abstract The structure of monolayers of Cd arachidate on water and on solid support, and the thickness dependent changes when building up a multilayer via the LB technique are studied by means of grazing incidence diffraction of X-ray. In monolayers the perpendicularly oriented amphiphilic molecules are arranged in a hexagonal lattice, whereas for thicker layers (even for three layers) they crystallize in an orthorhombic unit cell with a reduced molecular are ( A = 18.2 A 2 ) compared to that of the monolayer ( A = 19.7 A 2 ). In-plane diffraction measurements with wave vector transfer perpendicular to the surface (rod scans) could prove for multilayers a maximum tilt angle of 2°. The data …
First-Order Isostructural Phase Transition Induced by High Pressure in Fe(IO3)3
2020
The high-pressure (HP) behavior of Fe(IO3)3 was studied up to 35 GPa using powder X-ray diffraction, infrared micro-spectroscopy, and ab initio density-functional theory calculations. Fe(IO3)3 show...
IMAGING OF DICHROISM IN PHOTOEMISSION ELECTRON MICROSCOPY AT NONMAGNETIC MATERIALS USING CIRCULARLY POLARIZED SOFT X-RAYS
2002
A new approach for investigations of circular dichroism in the angular distribution of photoelectrons (CDAD) is presented. The image contrast using a photoemission line of a certain material is combined with imaging of the angular distribution pattern using a photoemission electron microscope (PEEM). CDAD can be used to investigate pure scattering information by means of the same instrument in microscopically selected regions on a surface. The experiment combines angle-resolved XPS imaging with the indirect mapping of the local environment of atoms by means of CDAD holography. In a conventional photoelectron diffraction or photoelectron holography experiment, it is necessary to move the sa…
Surface plasmon assisted thermal coupling of multiple photon energies
2006
A novel optical effect can be observed in a thin gold foil due to the excitation of surface plasmons which permits a form of all-optical modulation at low pulse rates. Modulated excitation of surface plasmons by infrared photons is shown to couple to several beams at visible-photon energies. The coupling is manifested by the observation of the visible photons being pulsed by the action of the infrared pulses, and by the far field diffraction of the visible beams into concentric rings. When each visible beam also excites surface plasmons, then a quadratic dependence of the visible photon power upon the infrared incident power is measured. The decay of surface plasmons is implicated as the pr…
Liquid Structure of Trihexyltetradecylphosphonium Chloride at Ambient Temperature: An X-ray Scattering and Simulation Study
2009
We report on an experimental and simulation study done on a representative room temperature ionic liquid, namely tetradecyltrihexylphosphonium chloride, at ambient conditions. The study was conducted using small and wide angle X-ray scattering and molecular dynamics simulations. Both approaches converge in indicating that this material is characterized by the existence of strong P-Cl interactions (with characteristic distances between 3.5 and 5.0 Å) and by the occurrence of nanoscale segregation, despite the symmetric nature of the cation and similarly to other room temperature ionic liquids. A good agreement is found between the structure factor and pair correlation functions obtained from…
Vapor growth of Hg1−xCdxI2 on glass using CdTe buffer
2001
Abstract Vapor phase epitaxy (VPE) of Hg1−xCdxI2 layers on glass substrates covered by a CdTe buffer layer has been studied. The buffer layers of 2–4 μm thickness were formed by VPE using polycrystalline CdTe and Cd metal sources. The Hg1−xCdxI2 layers were grown using a (Hg1−yCdy)1−z(I2)z polycrystalline source, with a composition in the range of y=0.1–0.5 and z=0.5–0.8. Scanning electron microscopy and X-ray diffraction studies have shown that the composition and structure of Hg1−xCdxI2 layers depend strongly on the VPE conditions. Varying the growth time and source composition, it has been possible to obtain Hg1−xCdxI2 layers with the composition x in the range from approximately 0 (HgI2…