Search results for "Optical"
showing 10 items of 7671 documents
Acyclic imidoselenium(ii) dihalides: synthesis and X-ray structures of ClSe[N(But)Se]nCl (n = 1, 2)
2000
The reaction of SeCl2 with tert-butylamine in THF yields the acyclic imidoselenium(II) dichlorides ClSeN(But)NSeCl and ClSeN(But)SeN(But)SeCl, in addition to the six-membered ring Se3(NBut)3.
Plastic deformation of selenium single crystals ina glide and X-ray observation of the induced substructure
1976
In the plastic deformation of trigonal selenium, a glide in the prismatic planes {1010} is found to be thermally activated, as in tellurium. The activation parameters are determined and a value for the maximum activation energy ΔGmax ≈ (0.6 ± 0.1) eV is obtained. The elastic limit increases up to σ ≈ 100 N mm−2 at low temperatures while it is only σ ≈ 1 N mm−2 at room temperature, i.e. in the athermal region. The deformation induced dislocation substructure is studied by X-ray reflection topography at different temperatures from 77 to 300 K in melt-grown single crystals. It is found that glide polygonization occurs forming rough tilt subgrain boundaries in the prismatic planes. In the ather…
Phase competition in (La1 − c,Src)CoO3solid solutions:ab initiothermodynamic study
2013
Statistical thermodynamics and density functional theory (DFT) formalisms are combined to analyze the phase competition of energetically preferable phases in (La1 − c,Src)CoO3 solid solutions upon LaCoO3 doping with Sr. La/Sr sublattice in ABO3 perovskite structure is considered as immersed in the field of CoO3 units and the superstructures that are stable with respect to the formation of antiphase domains are analyzed. The concentration-dependent energy parameters determining the relative stability of the cubic superstructures (phases) are extracted. This allows us calculations of concentration- and temperature dependences of the long-range order (LRO) parameters for different phases. The …
HgGa2 Se4 under high pressure: An optical absorption study
2015
High-pressure optical absorption measurements have been performed in defect chalcopyrite HgGa2Se4 to investigate the influence of pressure on the bandgap energy and its relation with the pressure-induced order–disorder processes that occur in this ordered-vacancy compound. Two different experiments have been carried out in which the sample undergoes either a partial or a total pressure-induced disorder process at 15.4 and 30.8 GPa, respectively. It has been found that the direct bandgap energies of the recovered samples at 1 GPa were around 0.15 and 0.23 eV smaller than that of the original sample, respectively, and that both recovered samples have different pressure coefficients of the dir…
Vacuum-ultraviolet absorption of hydrogenated and deuterated silanol groups and interstitial water molecules in amorphousSiO2
2005
Vacuum-ultraviolet (VUV) absorption cross sections of hydrogenated and deuterated silanol groups (SiOX, where $\mathrm{X}=\mathrm{H}$ or D) as well as interstitial water molecules $({\mathrm{X}}_{2}\mathrm{O})$ in amorphous $\mathrm{Si}{\mathrm{O}}_{2}$ $(a\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{2})$ were determined between photon energies of 7 and $8.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The absorption bands for the deuterated species are blueshifted compared to those for the hydrogenated ones by $\ensuremath{\sim}0.1\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}0.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ as a result of a decrease in the zero-point energy associat…
Relationship between microscopic and macroscopic structures of organic thin films for SHG
1993
The experiments described in this paper were undertaken in order to obtain information about the relationship between the structure and non-linear optical properties (second-harmonic generation) of organic thin films. For this purpose, two closely related dyes, diones and tetrones, were compared, both of which are shown to have large hyperpolarisabilities. Their microscopic properties are investigated by conformational analysis and electron diffraction. It could be shown that detailed knowledge about the structure and the adjacent neighbour packing can be obtained from conformational analysis and electron diffraction in order to understand the non-linear optical properties of the two dyes.
Crystallographic study of a family of Cs2BX4compounds
1990
Abstract Five compounds of the Cs2BX4 family with B = Zn, Co, Cu and X = Cl, Br were grown and studied. They belong to Pnma space group with 4 formula units per cell. From the full determination of the structure it appears that the ZnX4 tetrahedra are almost regular while the CuX4 tetrahedra are strongly distorted. This seems to be due to a strong Jahn-Teller effect induced by the Cu ions. This remark is extended to other compounds of the general family A2BX4.
Size-dependent alignment of Fe nanoparticles upon deposition onto W(110)
2010
Using in situ electron diffraction we study the orientation of mass-selected iron nanoparticles upon deposition onto single crystalline W(110) at room temperature. It is found that particles with a diameter below about 4 nm and a kinetic energy $\ensuremath{\le}0.1$ electron volt per atom spontaneously align with respect to the substrate. Larger particles preferentially rest with their (001) and (110) facets parallel to the surface, but do not show further alignment. The data may hint at thermally activated dislocation motions upon the impact on the substrate which are responsible for the observed orientation below 4 nm. By this uniformly oriented monodisperse nanostructures can be prepared…
Magnetic alignment of aliphatic lamellae
1993
Abstract Magnetic alignment of mesophases is normally only considered possible when the molecule contains an aromatic ring system. In this paper we report on the mesomorphous behaviour of a polyalkylacrylate resin with average sidechain length 22 and the alignment of its lamellae in cast films by annealing in a strong magnetic field.
Optical absorption of magnesia-supported gold clusters and nanoscale catalysts: Effects due to the support, clusters, and adsorbants
2005
Polarization-resolved optical spectra of magnesia-supported gold clusters ${\mathrm{Au}}_{N}∕\mathrm{Mg}\mathrm{O}$ $(N=1,2,4,8)$, bound at a surface color center ${F}_{s}$ of the MgO(100) face, are calculated from the time-dependent density functional theory. The optical lines for $N=1,2$ are dominated by transitions that involve strong hybridization between gold and ${F}_{s}$ states whereas for $N=4,8$ intracluster transitions dominate. The theoretical optical spectra are sensitive to cluster structure and adsorbants (here CO and ${\mathrm{O}}_{2}$ molecules on ${\mathrm{Au}}_{8}∕{F}_{s}@\mathrm{Mg}\mathrm{O}$) which suggests polarization-resolved optical spectroscopy as a powerful tool t…