Search results

1

Superdiffusion in Si Crystal Lattice Irradiated by Soft X-Rays

100%

Janavičius A., Balakauskas S., Kazlauskienė V., Mekys A., Purlys R., Storasta J.

Acta Physica Polonica A

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2008

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vol. 114

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issue 4

779-790

EN

We considered the reasons of superdiffusivity and measured profiles of boron and phosphorus in crystalline silicon at room temperature. The superdiffusivity or ultrafast diffusion of metastable vacancies at room temperature in Si crystal irradiated by soft X-rays was obtained experimentally. In this work, we presented experimentally obtained diffusion coefficients of singly and doubly negatively charged long-lived excited vacancies. These high concentration charged metastable vacancies (about 10^{13} cm^{-3}) at room temperature can very fast diffuse changing electrical conductivity and the Hall mobility of carriers. We measured the superdiffusivity of negatively charged vacancies, generated by the Auger effect in the regions of the sample, which were not affected by X-rays. In this paper, we presented the obtained superdiffusion profiles of boron and phosphorus in crystalline silicon measured with secondary-ion mass spectrometer.

2

Interference Effects in T-MOKE Spectra of Fe Thin Films at the 3p Edges - Theory and Experiment

80%

Legut D., Tesch M., Oppeneer P., Mertins H., Jansing C., Gilbert M., Gaupp A., Bürgler D., Schneider C.

Acta Physica Polonica A

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2015

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vol. 127

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issue 2

466-468

EN

We present combined first-principle calculations and experimental results of the transversal magneto-optical Kerr effect (T-MOKE) of thin Fe films across the 3p edges using linearly polarized synchrotron radiation. We show that the experimental T-MOKE spectra at the 3p edges of Fe exhibit clear signals that are strongly influenced by interference effects. Ab initio calculated T-MOKE asymmetry spectra confirm the importance of interference effects. The comparison of experimental with calculated spectra reveals some differences that we attribute to metal/metal interface roughness that is not taken into account in the calculations.

3

Axial Energy Distribution in Disc-Shaped Tantalum and Aluminium Bremsstrahlung Conversion Targets

80%

Williams T.

Acta Physica Polonica A

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2009

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vol. 115

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issue 6

1180-1182

EN

The axial distribution of energy deposited in bremsstrahlung conversion targets is modelled using the Monte Carlo N-Particle (MCNP™) code. Systems comprising a disc-shaped target, segmented axially, and a point source of paraxial, monoenergetic electrons (2, 7, 10, or 14 MeV) are considered. Thick tantalum and aluminium targets and also tantalum targets of optimum thickness are modelled. Energy density, as a function of depth within the target, is found to depend on overall target thickness and to exhibit a maximum value at a particular depth. The far-field radiation polar diagram is calculated for X-rays exiting the target through its output face.

4

X-Ray Resonant Magnetic Scattering: Application to Thin Films and Multilayers

80%

Raoux D., Jaouen N., Tonnerre J. M., Bontempi E.

Acta Physica Polonica A

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2000

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vol. 98

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issue 5

483-494

EN

This paper reports on the use of a new technique to investigate the magnetic properties of thin films, multilayers and artificial structures, the X-ray resonant magnetic scattering at small values of the scattering vector. It can be used either by registering the reflectivity pattern or in a diffraction mode. In comparison with magneto-optical Kerr effect or neutron scattering, it offers an atomic selectivity due to the resonant excitation of a core electron, and even an electronic shell one. Examples are presented mainly in the soft X-range allowing to probe the 3d band of transition metals. They demonstrate the promising possibilities of the method to measure the magnetic moments carried by each of the atomic components in complex systems, as well as their distribution through thin layers, with an atomic resolution.

5

Investigation of Electronic Density in C_{60} by Compton Scattering

80%

Bellin C., Marangolo M., Moscovici J., Loupias G., Rabii S., Erwin S.

Acta Physica Polonica A

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1997

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vol. 91

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issue 4

681-687

EN

High-resolution measurements of Compton profiles on C_{60} as well as K_{x} C_{60} have been carried out using 16 keV photons at LURE (Orsay, France) and at ESRF (Grenoble, France). Theoretical profiles are obtained using the plane wave expansion of wave functions from an ab-initio self-consistent field calculation of the energy band-structure. The linear combination of atomic orbitals method within the local-density-approximation has been employed for the calculation. In all cases, the agreement between theory and experiment is excellent. The C_{60} profiles indicate substantially greater delocalization of the ground-state charge density, compared to graphite. We have demonstrated, both by experiment and calculation, that the delocalization in C_{60} is mainly a molecular effect.

6

Application of Synchrotron Radiation to the Atomic and Electronic Structure of Semiconductors

80%

Altarelli M.

Acta Physica Polonica A

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1995

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vol. 87

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issue 1

17-24

EN

A brief review of the main experimental techniques exploiting synchrotron radiation in semiconductor physics is attempted. Topics emphasized include the study of surface and interface phenomena, such as surface structural properties (e.g. surface reconstruction) by X-ray diffraction, surface dynamical properties (e.g. adsorbate vibrational amplitudes) by the X-ray standing waves technique, etc. This review emphasizes brilliance (the phase-space density of photons) as the main figure of merit for many experimental techniques applicable to research in semiconductor physics. Examples of experiments made possible by the so-called "third generation", high-brilliance synchrotron sources are presented.

7

Comparison of Ultrafast Photodetectors Based on N^+GaAs and LT GaAs

80%

Białous M., Mogilinski R., Wierzbicki M., Świtkowski K., Pura B.

Acta Physica Polonica A

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2011

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vol. 119

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issue 3

382-386

EN

We present investigation of a photodetector based on nitrogen-ion-implanted GaAs. Device photoresponse signal shows 1.15 ps FWHM (400 GHz, 3 dB bandwidth) with the voltage amplitude ≈ 1 mV, measured using a constructed electro-optic sampling setup with 80 fs width, 795 nm wavelength and laser pulses repetition rate of 80 MHz. Changes in the shape of electrical signal for different beam powers excitation and voltage biases have been demonstrated, compared with LT GaAs photodetector based on the same finger geometry. Using technique of X-ray diffraction and diffuse scattering analyses we have observed the decrease of lattice constant, radius of nanoclusters after implantation, respectively, and linear density dislocations increased over twice.

8

X-Ray Magnetic Scattering

80%

Cooper M.

Acta Physica Polonica A

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1992

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vol. 82

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issue 1

137-146

EN

Magnetic X-ray diffraction with synchrotron radiation is now an established technique for studies of antiferromagnets. The problems associated with the small magnetic scattering cross-section being alleviated by the dramatic enhancements found near absorption edges through resonant exchange scattering. The technique is particularly useful for those materials that require high wavevector resolution to reveal the structural phase transitions that accompany the magnetic ordering process or those that are difficult to investigate with neutrons, (e.g. samarium, for which recent results are presented). In the actinides the work is also motivated by the objective of performing an empirical separation of the spin and orbital components of magnetisation. Diffraction studies of ferromagnets require circular polarised radiation and suffer from the superposition of the small magnetic signal and the charge scattering; to date Laue methods have proved more successful than monochromatic beam studies. Ferro- and ferrimagnets can also be studied by Compton (inelastic) scattering but the cross-section is less well established: considerable effort has been directed to determining whether orbital magnetisation can be measured in these experiments and results on HoFe2 now indicate this is not so. Magnetic Compton profiles provide information about the momentum distribution of electrons with unpaired spins, and this, together with magnetisation data can provide the basis for the separation of spin and orbital magnetisation.

9

Nonlinear Diffusion in Excited HgCdTe and Si Crystals

80%

Janavičius A., Norgėla Ž., Purlys R.

Acta Physica Polonica A

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2003

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vol. 104

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issue 5

459-467

EN

We discuss the properties of the nonlinear diffusion equation for the case of diffusion in excited systems. The diffusion coefficient is directly proportional to the concentration of impurities and depends on time in a special way. For the description of the excited systems, we used a special temperature function, which defined the time dependent diffusion coefficient and the Boltzmann distribution of the excited vacancies or impurity atoms in solids. This model was used for the approximation of indium concentration profiles in HgCdTe of a rapid diffusion component and very fast diffusion of metastable vacancies irradiated by soft X-rays in an excited Si crystal.

10

Fast Diffusion of Metastable Vacancies in Surface of Excited Si Crystals

80%

Janavičius A., Turskienė S.

|

EN

We considered the practically interesting, very fast nonlinear diffusion of metastable vacancies in the surface of Si crystal, excited by soft X-rays. Here we used experimentally defined diffusion coefficients of singly and doubly negatively charged very fast vacancies generated by soft X-rays. These high concentration (about 10^{13} cm^{-3}) metastable vacancies at room temperature can diffuse and exist in the crystal for a very long time (about 24 hours for not so fast neutral vacancies) changing electrical conductivity, the Hall mobility of carriers and generating some resonance phenomena in the lattice of Si crystal. We measured superdiffusivity of negatively charged vacancies, generated by the Auger effect in the regions of the sample, where X-rays did not acted. In the paper we modified the formerly obtained analytical solution of nonlinear diffusion equation for calculation of distribution of vacancies in two-dimensional surface.

11

Many-Body Effects Observed in the Positron Annihilation Experiment

80%

Kontrym-Sznajd G., Sormann H.

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EN

This paper is devoted to study many-body effects in the positron annihilation experiment, both electron-positron (e-p) and electron-electron (e-e) correlations. Various theories of the e-p interaction in real solids were used to verify them by comparing theoretical and experimental e-p momentum densities in Cu and Y. We show that the lattice potential has an essential influence on the e-p correlation effects, i.e. their proper description must be done via periodic lattice potential as e.g. in the Bloch modified ladder theory. Moreover, it is not true that the dynamic parts of the direct e-p and e-e interactions cancel each other because e-e correlations are observed not only in the Compton scattering but also in the positron annihilation experiments.

12

Surface-Coated CdS Nanocrystals

70%

Fernandez J., de Souza-Parise M., Morais P.

Acta Physica Polonica A

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2013

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vol. 124

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issue 1

108-111

EN

CdS nanocrystals were prepared using a standard colloidal route (co-precipitation chemical reaction) whereas modulation of the optical and structural properties was realized via surface coating the nanocrystals with ethylene glycol molecules using an in situ procedure. The as-produced nanocrystals were characterized by X-ray diffraction, Raman spectroscopy, UV-absorption measurements and photoluminescence. The nanocrystal quality was revealed by the spectroscopic data, though the final product presents a mixture of both zinc blende (cubic) and wurtzite (hexagonal) phases. The X-ray data indicated that the concentration of the ethylene glycol used during the synthesis process modulates the nanocrystal size and the crystal phase of the end material.

13

Phase Structure and Heat Generation in the Co-Precipitated Magnetite Nanoparticles

70%

Pawlik P., Pruba M., Pawlik K., Kotynia K.

Acta Physica Polonica A

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2017

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vol. 131

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issue 5

1217-1221

EN

In the present studies the phase structure and magnetic ordering of magnetite nanoparticles were investigated. The powder samples were obtained by co-precipitation from Fe(III) and Fe(II) salts. SiO₂ coating was performed using the modified Stöber process. X-ray diffraction studies revealed presence of the only one Fe₃O₄ crystalline phase both for the non-coated and SiO₂-coated samples. The Mössbauer studies have shown differences in shapes of measured spectral lines for Fe₃O₄ particles subjected to the Stöber process and non-coated particles. The heating efficiency was measured for glycerol dispersed nanoparticles. The analysis have shown changes in specific loss power depending on the concentration of the nanoparticles and amplitude of alternating magnetic field.

14

Effect of Pulsed Laser Power Annealing on Structural and Optical Characteristics of ZnSe Thin Films

61%

Aly S., Akl A., Howari H.

Acta Physica Polonica A

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2015

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vol. 128

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issue 3

414-418

EN

Samples of ZnSe of the same film thickness (320 nm) have been thermally evaporated on unheated quartz substrates using high purity powder. The prepared films were subjected to pulsed laser annealing of two different powers. X-ray diffraction studies revealed that the as-deposited samples were polycrystalline cubic (zinc-blende type) structure. As the annealing power increases, the crystallinity of ZnSe films was improved with preferential orientation along the (111) direction parallel to the substrate surface. Microstructural characterizations have been evaluated using the Debye-Scherrer formula. The absorption coefficient as well as the energy gap for the as-deposited and the annealed samples were also reported.

Refine search results

Superdiffusion in Si Crystal Lattice Irradiated by Soft X-Rays

Interference Effects in T-MOKE Spectra of Fe Thin Films at the 3p Edges - Theory and Experiment

Axial Energy Distribution in Disc-Shaped Tantalum and Aluminium Bremsstrahlung Conversion Targets

X-Ray Resonant Magnetic Scattering: Application to Thin Films and Multilayers

Investigation of Electronic Density in C_{60} by Compton Scattering

Application of Synchrotron Radiation to the Atomic and Electronic Structure of Semiconductors

Comparison of Ultrafast Photodetectors Based on N^+GaAs and LT GaAs

X-Ray Magnetic Scattering

Nonlinear Diffusion in Excited HgCdTe and Si Crystals

Fast Diffusion of Metastable Vacancies in Surface of Excited Si Crystals

Many-Body Effects Observed in the Positron Annihilation Experiment

Surface-Coated CdS Nanocrystals

Phase Structure and Heat Generation in the Co-Precipitated Magnetite Nanoparticles

Effect of Pulsed Laser Power Annealing on Structural and Optical Characteristics of ZnSe Thin Films