33 research outputs found
Ab initio computation of d-d excitation energies in low-dimensional Ti and V oxychlorides
Using a quantum chemical cluster-in-solid computational scheme, we calculate
the local d-d excitation energies for two strongly correlated Mott insulators,
the oxychlorides TiOCl and VOCl. TiOCl harbors quasi-one-dimensional spin
chains made out of S = 1/2 Ti3+ ions while the electronic structure of VOCl
displays a more two-dimensional character. We find in both cases that the
lowest-energy d-d excitations are within the t2g subshell, starting at 0.34 eV
and indicating that orbital degeneracies are significantly lifted. In the
vanadium oxychloride, spin triplet to singlet excitations are calculated to be
1 eV higher in energy. For TiOCl, the computed d-level electronic structure and
the symmetries of the wavefunctions are in very good agreement with resonant
inelastic x-ray scattering results and optical absorption data. For VOCl,
future resonant inelastic x-ray scattering experiments will constitute a direct
test of the symmetry and energy of about a dozen of different d-d excitations
that we predict here
High efficiency and low absorption Fresnel compound zone plates for hard X-ray focusing
Circular and linear zone plates have been fabricated on the surface of
silicon crystals for the energy of 8 keV by electron beam lithography and deep
ion plasma etching methods. Various variants of compound zone plates with
first, second, third diffraction orders have been made. The zone relief height
is about 10 mkm, the outermost zone width of the zone plate is 0.4 mkm. The
experimental testing of the zone plates has been conducted on SPring-8 and ESRF
synchrotron radiation sources. A focused spot size and diffraction efficiency
measured by knife-edge scanning are accordingly 0.5 mkm and 39% for the first
order circular zone plate.Comment: 5 pages, 7 figure
ОПТИМИЗАЦИЯ ТЕХНОЛОГИИ ВОЛОЧЕНИЯ ТРИМЕТАЛЛИЧЕСКИХ СВЕРХПРОВОДНИКОВЫХ КОМПОЗИТОВ
A procedure of determining the optimal angles of the drawing tool for a three-component billet, which takes into account the presence of the finishing die cylinder and provides a minimal drawing stress, is proposed. The influence of manufacturing parameters on the magnitude of optimal conicity angles of the manufacturing tool is shown. The relationship for the calculation of the optimal drawing, which provides minimal drawing stress, is found for standard dies with a fixed conicity angle.Предложена методика определения оптимальных углов волочильного инструмента для трехкомпонентной заготовки, учитывающая наличие калибрующего пояска волоки и обеспечивающая минимальное значение напряжения волочения. Показано влияние технологических параметров на величину оптимальных углов конусности технологического инструмента. Для стандартных волок с фиксированным углом конусности получено соотношение для расчета оптимальной вытяжки, обуславливающей минимальные значения напряжения волочения
Optical study of orbital excitations in transition-metal oxides
The orbital excitations of a series of transition-metal compounds are studied
by means of optical spectroscopy. Our aim was to identify signatures of
collective orbital excitations by comparison with experimental and theoretical
results for predominantly local crystal-field excitations. To this end, we have
studied TiOCl, RTiO3 (R=La, Sm, Y), LaMnO3, Y2BaNiO5, CaCu2O3, and K4Cu4OCl10,
ranging from early to late transition-metal ions, from t_2g to e_g systems, and
including systems in which the exchange coupling is predominantly
three-dimensional, one-dimensional or zero-dimensional. With the exception of
LaMnO3, we find orbital excitations in all compounds. We discuss the
competition between orbital fluctuations (for dominant exchange coupling) and
crystal-field splitting (for dominant coupling to the lattice). Comparison of
our experimental results with configuration-interaction cluster calculations in
general yield good agreement, demonstrating that the coupling to the lattice is
important for a quantitative description of the orbital excitations in these
compounds. However, detailed theoretical predictions for the contribution of
collective orbital modes to the optical conductivity (e.g., the line shape or
the polarization dependence) are required to decide on a possible contribution
of orbital fluctuations at low energies, in particular in case of the orbital
excitations at about 0.25 eV in RTiO3. Further calculations are called for
which take into account the exchange interactions between the orbitals and the
coupling to the lattice on an equal footing.Comment: published version, discussion of TiOCl extended to low T, improved
calculation of orbital excitation energies in TiOCl, figure 16 improved,
references updated, 33 pages, 20 figure
X-ray Nanodiffraction on a Single SiGe Quantum Dot inside a Functioning Field-Effect Transistor
For advanced electronic, optoelectronic, or mechanical nanoscale devices a detailed understanding of their structural properties and in particular the strain state within their active region is of utmost importance. We demonstrate that X-ray nanodiffraction represents an excellent tool to investigate the internal structure of such devices in a nondestructive way by using a focused synchotron X-ray beam with a diameter of 400 nm. We show results on the strain fields in and around a single SiGe island, which serves as stressor for the Si-channel in a fully functioning Si-metal-oxide semiconductor field-effect transistor
Phasecontrast X-ray imaging with synchrotron radiation for materials science applications
Abstract Since R€ o ontgenÕs discovery of X-rays just over a century ago the vast majority of radiographs have been collected and interpreted on the basis of absorption contrast and geometrical (ray) optics. Recently the possibility of obtaining new and complementary information in X-ray images by utilizing phase-contrast effects has received considerable attention, both in the laboratory context and at synchrotron sources (where much of this activity is a consequence of the highly coherent X-ray beams which can be produced). Phase-contrast X-ray imaging is capable of providing improved information from weakly absorbing features in a sample, together with improved edge definition. Four different experimental arrangements for achieving phase contrast in the hard X-ray regime, for the purpose of non-destructive characterization of materials, will be described. Two of these, demonstrated at ESRF in France and AR in Japan, are based on parallel-beam geometry; the other two, demonstrated at PLS in Korea and APS in USA, are based on spherical-beam geometry. In each case quite different X-ray optical arrangements were used. Some image simulations will be employed to demonstrate salient features of hard X-ray phase-contrast imaging and examples of results from each of the experiments will be shown
Extracellular Hsp90 and TGFP regulate adhesion, migration and anchorage independent growth in a paired colon cancer cell line model
Tumour metastasis remains the major cause of death in cancer patients and, to date, the mechanism and signalling pathways governing this process are not completely understood. The TGF-ß pathway is the most commonly mutated pathway in cancer, however its role in cancer progression is controversial as it can function as both a promoter and a suppressor of metastasis. Although previous studies have suggested a role for the molecular chaperone Hsp90 in regulating the TGF-ß pathway, the level at which this occurs as well as the consequences in terms of colon cancer metastasis are unknown