Search results for "Diffraction"
showing 10 items of 1584 documents
RF magnetron-sputtered coatings deposited from biphasic calcium phosphate targets for biomedical implant applications
2017
Bioactive calcium phosphate coatings were deposited by radio-frequency magnetron sputtering from biphasic targets of hydroxyapatite and tricalcium phosphate, sintered at different mass % ratios. According to Raman scattering and X-ray diffraction data, the deposited hydroxyapatite coatings have a disordered structure. High-temperature treatment of the coatings in air leads to a transformation of the quasi-amorphous structure into a crystalline one. A correlation has been observed between the increase in the Ca content in the coatings and a subsequent decrease in Ca in the biphasic targets after a series of deposition processes. It was proposed that the addition of tricalcium phosphate to th…
Shaping graphene with optical forging: from a single blister to complex 3D structures
2020
Properties of graphene, such as electrical conduction and rigidity can be tuned by introducing local strain or defects into its lattice. We used optical forging, a direct laser writing method, under an inert gas atmosphere, to produce complex 3D patterns of single layer graphene. We observed bulging of graphene out of the plane due to defect induced lattice expansion. By applying low peak fluences, we obtained a 3D-shaped graphene surface without either ablating it or deforming the underlying Si/SiO2 substrate. We used micromachining theory to estimate the single-pulse modification threshold fluence of graphene, which was 8.3 mJ cm−2, being an order of magnitude lower than the threshold for…
Single-Crystal X-Ray Diffraction Study of Pressure and Temperature-Induced Spin Trapping in a Bistable Iron(II) Hofmann Framework.
2020
High-pressure single-crystal X-ray diffraction has been used to trap both the low-spin (LS) and high-spin (HS) states of the iron(II) Hofmann spin crossover framework, [FeII (pdm)(H2 O)[Ag(CN)2 ]2 ⋅H2 O, under identical experimental conditions, allowing the structural changes arising from the spin-transition to be deconvoluted from previously reported thermal effects.
Relative proportions of rutile and pseudo-brookite phases in the Fe(III)-TiO2 system at elevated temperature
1997
Abstract The Fe(III)-TiO2 system has been studied at T ≥ 1023 K in the range of concentration 2–10 at.% of iron by powder X-ray diffraction, transmission and scanning electron microscopy, and optical microscopy. The relationship between the relative proportions of the TiO2 rutile phase and the pseudo-brookite phase Fe2TiO5, has been investigated in powder samples. Single crystals of pure rutile and rutile doped with 0.5 at.% of iron have been examined to elucidate the microstructures found in the powders. The results suggest that a low degree of solid solubility exists and that doped crystals contain planar faults on 101 planes.
Zinc Chalcogenide Seed-Mediated Synthesis of CdSe Nanocrystals: Nails, Chesses and Tetrahedrons
2015
Systematically shape-controlled synthesis of colloidal semiconductor nanocrystals (NCs) has attracted increasing attention recently for both fundamental and technological interest. The study on the synthesis of colloidal CdSe NCs has given rise to well-developed methods for producing diverse shapes such as rods, wires, cubs and discs. In the current study, we demonstrate the shape evolution of CdSe NCs by using a seed-mediated approach by control reaction temperature and injection methods. The synthesis utilizes small (2.0–3.0 nm) zinc chalcogenide NCs with zincblende structure as seeds for subsequent growth, which results in distinct shapes of nail-shaped, tetrahedron-shaped, chess piece-s…
Holographic recording optimization in amorphous As-Se-S films
2003
The holographic recording parameters of amorphous chalcogenide semiconductor (AChS) thin films under optimization depend on hologram type. So, using self-enhancement effect during recording and wet etching after recording enable possibility to decrease recording energy and increase of signal/noise ratio for embossed holograms. Choosing the appropriate light exposure permit us to achieve equal values of diffraction efficiency (DE) for different diffraction orders during fabrication of light splitting holographic optical elements (HOE). Changing film thickness and recording wavelength it is possible to find optimal conditions for high DE holographic gratings readable at infrared region of lig…
Photodiffraction in InGaAs/InGaAsP multiple quantum wells enclosed in a microcavity
1997
Abstract We report new results on the diffraction properties of photoinduced gratings in InGaAs/InGaAsP MQW structures. The original feature of this device is that the QWs are enclosed in an asymmetric Fabry–Perot microcavity in order to increase the diffraction efficiency. We observe oscillations in the diffraction efficiency due to resonant effects in the microcavity. The experimental spectra are compared with theory. Diffraction efficiency at 1.55 μm attains a maximum value of 2.7% at a write beam fluence of 260 μ J cm −2 , and then decreases at higher fluences. We explain this phenomenon by an absorption saturation at high excitation.
FeMoO4 Revisited: Crosslike 90° Noncollinear Antiferromagnetic Structure Caused by Dzyaloshinskii–Moriya Interaction
2021
The ground state of Fe2+ (S = 2) in α- and β-FeMoO4 is investigated by experiments including X-ray diffraction, Raman scattering, and 57Fe–Mossbauer spectroscopy below 300 K and evaluated by theore...
The Poisson Ratio in CoFe2O4Spinel Thin Films
2012
The response of epitaxial CoFe2O4 thin films to biaxial compressive stress imposed by MgAl2O4 and SrTiO3 single crystalline substrates is studied using X-ray diffraction and Raman spectroscopy. It is found that the Poisson ratio ν signals a non-auxetic behavior and depends on the substrate used. The Raman modes show an increase in frequency when increasing compressive strain by reducing film thickness; this is due to the shrinking of the unit cell volume. Such behavior is in qualitative agreement with recent ab initio calculations, although the measured values are significantly smaller than predictions. In contrast, the measured Poisson ratio is found to be in good agreement with expectatio…
Ferroelectric domains in BaTiO3powders and ceramics evidenced by X-ray diffraction
1995
Abstract Through three different studies, using BaTiO3 samples, as a powder while heating over the Curie temperature, and as a ceramic while applying an electric field, it is shown how X-ray diffraction (XRD) is able to give information about the evolution of the ferroelectric domain microstructure. Firstly, the relative intensities of the 002 and 200 lines, as a function of the applied electric field, exhibit the motion of the 90[ddot] domain walls. However, XRD is unable to provide any distinction between two 180[ddot] domains. Secondly, the profile of those two lines and of the other double (hhl), (lhh) lines is particular: the unusual diffracted intensity between such double lines has t…