Search results for "FFR"

Polarized Fourier transform infrared microscopy as a tool for structural analysis of adsorbates in molecular sieves

1992

Using FTIR microscopy with polarized IR radiation on silicalite I single crystals fully loaded with p-xylene, the existence of an ordered adsorbate could be proven for the first time by IR spectroscopy. By analyzing the polarized absorption bands the orientation of the p-xylene molecules relative to the host structure could be determined. The results agree well with structural data obtained from X-ray diffraction experiments. These first results suggest that polarized IR microscopy could develop into a powerful tool for the analysis of adsorbate structures, assisting in complete structure resolution by diffraction techniques

Vibrational Properties of InSe under Pressure: Experiment and Theory

1996

The pressure dependence of the phonon modes in the layered semiconductor γ-InSe has been investigated experimentally and theoretically for pressures up to 11 GPa. The mode Gruneisen parameters of all Raman-active zone-center phonons have been determined by Raman scattering under pressure. In addition, features corresponding to second and third-order scattering processes are apparent in the Raman spectra under resonance conditions, from which information about zone-edge modes can be obtained. For the assignment of the observed Raman features to vibrational modes we have calculated the phonon dispersion curves using a rigid-ion model including couplings to first-nearest neighbors and long-ran…

1985

Nonlinear optical self diffraction effects for a light beam in a liquid crystalline polymer in its isotropic fluid state was observed. This effect is characterized by the absence of a threshold intensity, a diffraction pattern that does not depend on the polarization of the reading beam relative to that of the writing beam and which cannot be disturbed by transversally applied static electrical fields. This effect is attributed to a thermally induced spatial refractive index modulation. The time constants of the response are of the order of ms.

Water Sorption on Mesoporous Aluminosilicate MCM-41

1995

Characterization of the interaction of water with the highly ordered mesoporous solid MCM-41 (pore diameter ∼2.5 nm) is undertaken with the aid of several techniques (adsorption gravimetry, X-ray diffraction, Fourier transform infrared spectroscopy, and controlled rate-evolved gas analysis). The relatively complex water-MCM-41 interactions are characterized by a type V isotherm indicating an initial repulsive character followed by a capillary condensation step of the adsorbate. This highlights both hydrophobic and hydrophilic properties of this potential model mesoporous adsorbent.

DICHROISM IN ANGLE-RESOLVED PHOTOEMISSION FROM Pt(111)

2002

The angular dependence of the circular dichroism in photoemission from Pt(111) was investigated for excitation with VUV and soft X-ray radiation. VUV excitation was used to probe band structure and the circular dichroism for valence band emission. The measurements are compared to full relativistic single step photoemission calculations. XPS was used to investigate the circular dichroism in emission from the 4f core level. In this case, the dichroism is induced by photoelectron diffraction. First results from single step core level calculations are compared to the experimental observations.

In situ and time resolved study of the - transition in nanometric particles

2007

In situ and real-time study of the {gamma} to {alpha}-Fe{sub 2}O{sub 3} transition is carried out on the H10 beamline at LURE (France). {gamma}-Fe{sub 2}O{sub 3} particles are synthesized by soft chemistry. These particles have an average diameter evaluated by X-ray diffraction of 9{+-}1nm and a specific surface area of 116m{sup 2}g{sup -1}. The size of produced {alpha}-Fe{sub 2}O{sub 3} particles is determined by in situ and time resolved X-ray diffraction measurements at different temperatures. An amazing evolution of size with time is revealed: an abrupt doubling of the {alpha}-Fe{sub 2}O{sub 3} particle size is observed whatever the heating temperature. Some assumptions are given in ord…

Fast algorithms for free-space diffraction patterns calculation

1999

Here we present a fast algorithm for Fresnel integral calculation. Some fast algorithms using the fast Fourier transform are analysed and their performance has been checked. These methods are of easy implementation, but are only valid for a specific range of distances. Fast algorithms based on the Fractional Fourier transform allow accurate evaluation of the Fresnel integral from object to Fraunhofer domain in a single step.

Time multiplexing super-resolved imaging without a priori knowledge of the spatial distribution of the encoding structured illumination

2021

Time multiplexing is a super-resolution technique that sacrifices time to overcome the resolution reduction obtained because of diffraction. There are many super resolution methods based on time multiplexing, but all of them require a priori knowledge of the time changing encoding mask, which is projected on the object and used to encode and decode the high-resolution information. In this paper, we present a time multiplexing technique that does not require the a priori knowledge on the projected encoding mask. First, the theoretical concept of the technique is demonstrated; then, numerical simulations and experimental results are presented.

Investigation of Co$_2$FeSi: The Heusler compound with Highest Curie Temperature and Magnetic Moment

2006

This work reports on structural and magnetic investigations of the Heusler compound Co$_2$FeSi. X-Ray diffraction and M\"o\ss bauer spectrometry indicate an ordered $L2_1$ structure. Magnetic measurements by means of X-ray magnetic circular dichroism and magnetometry revealed that this compound is, currently, the material with the highest magnetic moment ($6 \mu_B$) and Curie-temperature (1100K) in the classes of Heusler compounds as well as half-metallic ferromagnets.

Elektrónová a pásová štruktúra CuMnAs študovaná optickou a fotoemissinou spektroskopiou

2017

Tetragonal phase of CuMnAs progressively appears as one of the key materials for antiferromagnetic spintronics due to efficient current-induced spin-orbit torques whose existence can be directly inferred from crystal symmetry. Theoretical understanding of spintronic phenomena in this material, however, relies on the detailed knowledge of electronic structure (band structure and corresponding wave functions) which has so far been tested only to a limited extent. We show that AC permittivity (obtained from ellipsometry) and UV photoelectron spectra agree with density functional calculations. Together with the x-ray diffraction and precession electron diffraction tomography, our analysis confi…