The Laser-only Single-event Effects Test Method for Spacecraft Electronics Based on Ultrashort-pulsed-laser Local Irradiation

The substantive laser method for studying the radiation hardness of semiconductor devices, not requiring calibration by ions, called ”local irradiation”, is described. The essence of the local approach is in irradiating the sample sensitive volume with the ultrashort-pulsed laser beam at some distance from its focus plane, where the beam becomes rather wide and divergent. Assuming the single-photon absorption, the relationship between the laser pulse energy and the excess charge actually generated in irradiated sensitive volume is obtained by accurate measurement of the electrical response, that makes possible to take into account non-uniform optical losses and avoid additional calibration by ions. Some results, obtained using both the front-side and the backside local irradiation of devices, are presented. Comparison with results obtained by traditional methods using focused laser radiation with subsequent calibration by ions showed that laser-only measurements, based on described local irradiation, give the correct estimates of radiation hardness parameters. Keywords: Ultrashort laser pulse, single-event effect, local laser irradiation, semiconductor device, integrated circuit

Double-spiral magnetic structure of the Fe/Cr multilayer revealed by nuclear resonance scattering

We have studied the magnetization depth profiles in a [57Fe(dFe)/Cr(dCr)]x30 multilayer with ultrathin Fe layers and nominal thickness of the chromium spacers dCr 2.0 nm using nuclear resonance scattering of synchrotron radiation. The presence of a broad pure-magnetic half-order (1/2) Bragg reflection has been detected at zero external field. The joint fit of the reflectivity curves and Mossbauer spectra of reflectivity measured near the critical angle and at the "magnetic" peak reveals that the magnetic structure of the multilayer is formed by two spirals, one in the odd and another one in the even iron layers, with the opposite signs of rotation. The double-spiral structure starts from the surface with the almost antiferromagnetic alignment of the adjacent Fe layers. The rotation of the two spirals leads to nearly ferromagnetic alignment of the two magnetic subsystems at some depth, where the sudden turn of the magnetic vectors by ~180 deg (spin-flop) appears, and both spirals start to rotate in opposite directions. The observation of this unusual double-spiral magnetic structure suggests that the unique properties of giant magneto-resistance devices can be further tailored using ultrathin magnetic layers.Comment: 9 pages, 3 figure

Density of Phonon States in Superconducting FeSe as a Function of Temperature and Pressure

The temperature and pressure dependence of the partial density of phonon states of iron atoms in superconducting Fe1.01Se was studied by 57Fe nuclear inelastic scattering (NIS). The high energy resolution allows for a detailed observation of spectral properties. A sharpening of the optical phonon modes and shift of all spectral features towards higher energies by ~4% with decreasing temperature from 296 K to 10 K was found. However, no detectable change at the tetragonal - orthorhombic phase transition around 100 K was observed. Application of a pressure of 6.7 GPa, connected with an increase of the superconducting temperature from 8 K to 34 K, results in an increase of the optical phonon mode energies at 296 K by ~12%, and an even more pronounced increase for the lowest-lying transversal acoustic mode. Despite these strong pressure-induced modifications of the phonon-DOS we conclude that the pronounced increase of Tc in Fe1.01Se with pressure cannot be described in the framework of classical electron-phonon coupling. This result suggests the importance of spin fluctuations to the observed superconductivity

Microscopic investigation of the Johari-Goldstein relaxation in cumene:Insights on the mosaic structure in a van der Waals liquid

The Johari-Goldstein (βJG) relaxation anticipates in time, and is closely connected to, the structural relaxation in deeply supercooled liquids. Probing its microscopic properties is a crucial step for a complete understanding of the glass-transition. We here report the investigation of the van der Waals glass-former cumene using time-domain interferometry, a technique able to probe microscopic density fluctuations at the spatial and temporal scales relevant for the βJG-relaxation. We find that the molecules participating in it undergo a restricted motion, though sufficient to induce local, cage-breaking events at the characteristic time-scale for molecular re-orientations. A detailed characterization of the relaxation strength, i.e. the fraction of molecules involved in the relaxation process, shows that such molecules are connected in a percolating cluster which, above the glass-transition temperature, Tg, is weakly dependent on temperature. Our results confirm thus previous observations of a mosaic structure associated to the βJG-relaxation in the supercooled state, and provide additional information on its temperature evolution above the glass-transition temperature. We conclude that the observed microscopic properties of the βJG-relaxation, and thus of the associated mosaic structure, are generic and independent of the molecular interaction potential. In addition, we show that, while the dynamics within the percolating cluster becomes progressively slower on approaching Tg, the fraction of the molecules involved in cage-breaking events within the βJG-relaxation is not affected by temperature.</p

Cavity Dynamical Casimir Effect in the presence of a three-level atom

We consider the scenario in which a damped three-level atom in the ladder or V configurations is coupled to a single cavity mode whose vacuum state is amplified by dint of the dynamical Casimir effect. We obtain approximate analytical expressions and exact numerical results for the time-dependent probabilities, demonstrating that the presence of the third level modifies the photon statistics and its population can serve as a witness of photon generation from vacuum.Comment: 7 pages, 4 figure

M\"ossbauer, nuclear inelastic scattering and density functional studies on the second metastable state of Na2[Fe(CN)5NO]⋅\cdot2H2O

The structure of the light-induced metastable state SII of Na2[Fe(CN)5NO]$\cdot$2H2O 14 was investigated by transmission M\"ossbauer spectroscopy (TMS) in the temperature range 15 between 85 and 135 K, nuclear inelastic scattering (NIS) at 98 K using synchrotron 16 radiation and density functional theory (DFT) calculations. The DFT and TMS results 17 strongly support the view that the NO group in SII takes a side-on molecular orientation 18 and, further, is dynamically displaced from one eclipsed, via a staggered, to a second 19 eclipsed orientation. The population conditions for generating SII are optimal for 20 measurements by TMS, yet they are modest for accumulating NIS spectra. Optimization 21 of population conditions for NIS measurements is discussed and new NIS experiments on 22 SII are proposed

Peculiarities of electronic structure and composition in ultrasound milled silicon nanowires

The combined X-ray absorption and emission spectroscopy approach was applied for the detailed electronic structure and composition studies of silicon nanoparticles produced by the ultrasound milling of heavily and lowly doped Si nanowires formed by metal-assisted wet chemical etching. The ultrasoft X-ray emission spectroscopy and synchrotron based X-ray absorption near edges structure spectroscopy techniques were utilize to study the valence and conduction bands electronic structure together with developed surface phase composition qualitative analysis. Our achieved results based on the implemented surface sensitive techniques strongly suggest that nanoparticles under studies show a significant presence of the silicon suboxides depending on the pre nature of initial Si wafers. The controlled variation of the Si nanoparticles surface composition and electronic structure, including band gap engineering, can open a new prospective for a wide range Si-based nanostructures application including the integration of such structures with organic or biological systems