Mössbauer and XRD study of pulse plated Fe–P and Fe–Ni thin layers

⁵⁷Fe conversion electron Mössbauer spectroscopy, X-ray diffraction, electrochemical and magnetic measurements were used to study pulse electroplated Fe–P and Ni–Fe coatings. XRD and ⁵⁷Fe CEMS measurements revealed the amorphous character of the novel pulse plated Fe–P alloys. CEM spectra indicated significant differences in the short range order and in the magnetic anisotropy between the Fe–P deposits pulse plated at medium long deposition time (t _on?=?2 ms), with short relaxation time (t _off?=?9 ms) and low current density (I _p?=?0.05 Acm^?2) or at short deposition time (t _on?=?1 ms) with long relaxation time (t _off?=?250 ms) and high current density (I _p?=?1.0 Acm^?2). The broad peaks centred around the fcc reflections in XRD of the pulse plated Ni-22 wt.% Fe deposit reflected a microcrystalline Ni–Fe alloy with a very fine, 5–8 nm, grain size. The CEM spectrum of the pulse plated Ni-22 wt.% Fe coating corresponded to a highly disordered solid solution alloy containing a minute amount of ferrihydrite. Extreme favourable soft magnetic properties were observed with these Ni–Fe and Fe–P pulse plated thin layers.     

Specific features of the electronic structure and spectral properties of NdNi5 − x Cu x compounds

The spectral properties of the intermetallic compounds NdNi_{5 ? x} Cu _x (x = 0, 1, 2) have been studied using optical ellipsometry in the wavelength range 0.22–16 μm. It has been established that substitution of copper atoms for nickel leads to noticeable changes in the optical absorption spectra, plasma frequencies, and relaxation frequencies of conduction electrons. Spin-polarized calculations of the electronic structure of these compounds have been performed in the local spin density approximation allowing for strong electron correlations (LSDA + U method) in the 4f shell of the rare-earth ion. The calculated electron densities of states have been used to interpret the experimental dispersion curves of optical conductivity in the interband light absorption region.     

Computation of effective electron–phonon relaxation times in a high-Tc superconductor using the measured track radii

Energy relaxation processes after fast heavy ions passage through YBa₂Cu₃O_7−δ single crystal have been calculated. Effective times τ of electron–atom energy relaxation have been determined as fitting parameters for each pair of the measured track radius and the value of dE/dx. The latter quantity has been chosen over the interval of 20–40 keV/nm. The calculated results are compared with short pulse laser experiments and with Allen's theory, which predicts almost a linear dependence of τ on electron temperature.     

EPR Study of Sc<Subscript>2</Subscript>SiO<Subscript>5</Subscript>:Nd<Superscript>143</Superscript> Isotopically Pure Impurity Crystals

The Sc₂SiO₅ single crystals doped with 0.001 at.% of the ¹⁴³Nd³⁺ ion were studied by continuous-wave and pulse electron paramagnetic resonance methods. The g-tensors and hyperfine structure tensors for two magnetically non-equivalent Nd ions were obtained. The spin–spin and spin–lattice relaxation times were measured at 9.82 GHz in the temperature range from 4 to 10 K. It was established that three relaxation processes contribute to the spin–lattice relaxation processes. There are one-phonon spin–phonon interaction, two-phonon Raman interaction and two-phonon Orbach–Aminov relaxation processes. It was established that spin–spin relaxation time is of the same magnitude for neodymium ion doped in Sc₂SiO₅ and in Y₂SiO₅.     

Transient optical absorption induced by an electron pulse in KPb<Subscript>2</Subscript>Cl<Subscript>5</Subscript> crystals

The efficiency of formation and time evolution of radiation-induced structural defects and pulsed luminescence in KPb₂Cl₅ crystals under the action of a single electron pulse (E = 250 keV, τ = 20 ns) have been investigated. The spectra (1.1–3.8 eV) and relaxation kinetics (time interval 5 × 10^?8?5 s) of transient optical absorption and the pulsed cathodoluminescence spectra and decay kinetics (1.4–3.1 eV) have been measured in the temperature range 80–300 K. It is revealed that the induced optical density and its time evolution depend strongly on temperature, and the absorption relaxation time contains several components and reaches several seconds at T = 300 K. The decay kinetics of transient absorption and pulsed cathodoluminescence kinetics have different orders and are controlled by different relaxation processes.     

EPR Spectroscopy of Impurity Thulium Ions in Yttrium Orthosilicate Single Crystals

The frequency-field and orientation dependences of the electron paramagnetic resonance (EPR) spectra are measured for impurity Tm³⁺ ions in yttrium orthosilicate (Y₂SiO₅) single crystals by stationary EPR spectroscopy in the frequency range of 50–100 GHz at 4.2 K. The position of the impurity ion in the crystal lattice and its magnetic characteristics are determined. The temperature dependences of the spin–lattice and phase relaxation times are measured by pulse EPR methods in the temperature range of 5–15 K and the high efficiency of the direct single-phonon mechanism of spin–lattice relaxation is established. This greatly shortens the spin–lattice relaxation time at low temperatures and makes impurity Tm³⁺ ions in Y₂SiO₅ a promising basis for the implementation of high-speed quantum memory based on rare-earth ions in dielectric crystals.     

Relaxation phenomena in electronic and lattice subsystems on iron surface during its ablation by ultrashort laser pulses

Single-shot ablative spallation and fragmentation thresholds, as well as corresponding ablative crater depths, were measured on the surface of iron using optical interferometry, for different ultrashort laser pulse widths in the range τ_las = 0.3–3.6 ps. The nonmonotonic dependence of these thresholds on τlas with the minimum near 1.2 ps (the characteristic electron-phonon relaxation time τ _ep ) represents transport and emission relaxation phenomena for nonthermalized and thermalized carriers, generated by sub- and picosecond laser pulses, respectively. Compared to rather slow spallative ablation, much faster—picosecond—fragmentation ablation of the iron surface through hydrodynamic expansion of its supercritical fluid ceased for τ_las > τ _ep as a result of evaporative cooling.     

The ground state and EPR spectrum in monoclinic KY(WO4)2:Nd single crystal

The electron paramagnetic resonance (EPR) of Nd³⁺ ion in KY(WO₄)₂ single crystal was investigated at T=4.2 K using an X-band spectrometer. The observed resonance absorption represents the complex superposition of three spectra corresponding to neodymium isotopes with different nuclear momenta. The EPR spectrum is characterized by a strong g-factor anisotropy. The temperature dependences of the g-factor were caused by strong spin-orbit and orbit-lattice coupling. The resonance lines become broader as temperature increases due to the short spin-lattice relaxation time.     

Electrical properties of novel Li4.08Zn0.04Si0.96O4 ceramic electrolyte at high temperatures

Novel Li_4.08Zn_0.04Si_0.96O₄ electrolyte was synthesized by citric acid-assisted sol–gel method. The compound was studied by X-ray diffraction and complex impedance spectroscopy in the frequency range from 10 Hz to 10 MHz and temperature range from 573 to 773 K. The conductivity–frequency spectra exhibited two regions of conductivity dispersion related to Li⁺ ion transport in the bulk and grain boundaries. The activation energy of the bulk conductivity was found to be equal to the activation energy of relaxation frequency in the bulk. This indicated that the increase in conductivity with temperature was due to the increase in ion mobility while the number of charge carrier concentration was found to be constant with selected temperature range. The observation was in agreement with the calculated charge carrier concentration and ion mobility derived from conductance spectra, σ _ac(ω)?=?σ _o ?+?Aω ^α .     

Pulse EPR, ENDOR, and ELDOR Study of Anionic Flavin Radicals in Na+-Translocating NADH:Quinone Oxidoreductase

The Na⁺-translocating nicotinamide adenine dinucleotide (NADH):quinine oxidoreductase (Na⁺–NQR) is a component of respiratory chain of various bacteria and it generates a redox-driven transmembrane electrochemical Na⁺ potential. It contains four different flavin prosthetic groups, including two flavin mononucleotide (FMN) residues covalently bound to the subunits NqrB and NqrC. Na⁺–NQR from Vibrio harveyi was poised at different redox potentials to prepare two samples, containing either both FMN_NqrB and FMN_NqrC or only FMN_NqrB in a paramagnetic state. These two samples were comparatively studied using pulse electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR), and electron-electron double resonance (ELDOR) spectroscopy. The echo-detected EPR spectra and electron spin relaxation properties were very similar for flavin radicals in both samples. The splitting of the outer peaks in the proton ENDOR spectra, assigned to the C(8α) methyl protons, allows to identify both radicals as anionic flavosemiquinones. The mean interspin distance of 20.7 Å between these radicals was determined by pulse ELDOR experiment, which allows to estimate the edge-to-edge distance (r _e) between these flavin centers as: 11.7 Å < r _e < 20.7 Å. The direct electron transfer between FMN_NqrB and FMN_NqrC during the physiological turnover of the Na⁺–NQR complex is suggested.     

Luminescence characteristics of cobalt doped TiO2 nanoparticles

TiO₂ nanoparticles doped with two different concentrations of Cobalt, 0.02 and 0.04 mol, are prepared by sol–gel method. The crystalline phase of the doped and undoped nanoparticles and particle sizes are observed with X-ray diffraction and transmission electron microscope. FTIR confirms the bonding interaction of Co²⁺ in TiO₂ lattice framework. The UV absorption spectra of the doped material shows two absorption peaks in the visible region related to d–d electronic transitions of Co²⁺ in TiO₂ lattice. Compared to undoped TiO₂ nanoparticles, the cobalt doped samples show a red shift in the band gap. Steady state photoluminescence spectra give emission peaks related to oxygen defects. The decrease in the intensity ratio of UV/visible emission peaks confirms distortion of structural regularity and formation of defects after doping. The intensity ratio of different visible emission peaks is nearly same for undoped and 0.02 Co²⁺. However, this ratio decreases profoundly at 0.04 Co²⁺, due to concentration quenching effect. Photoluminescence excitation spectra, recorded at 598 nm emission wavelength, give different excitation peaks associated with oxygen vacancies and Co²⁺. Time resolved photoluminescence spectra give longer decay time for doped samples, indicating longer relaxation of conduction band electrons on the defect and on dopant sites.     

Multichannel energy analysis of the ion flux from a theta pinch

The ion flux parallel to the axis of a linear theta pinch (p ₀=10–30 μ D₂) is analyzed by a new 10-channel energy spectrometer (E=1–10keV). Time resolved energy spectra were measured in each single discharge. It can be shown experimentally that neutral gas, electrons and magnetic fields considerably influence the flux distribution. The measured energy spectra (E≦15 keV) are broad and have no ion groups. At 10 μ D₂ dn/dE is proportional to exp {?E/ē} forE≧3 keV, whereē≈1 keV. For 10, 20 and 30 μ D₂ ē is about equal to thekT deduced from the neutron flux. The time developments of the neutron and ion fluxes (in the range 1–10 keV) are correlated. For the initial phase of the discharge the measuring results are incompatible with relaxation by Coulomb collisions. It seems rather, that there is anomalously fast relaxation due to a microinstability. After the anomalous relaxation the end losses, particularly of the slower ions, continue as a result of Coulomb collisions. This produces increasing distortion of theE-distribution with smallE, which leads to a second microinstability with loss of energetic ions in particular (probably a loss-cone type).     

MRICOM–MRI COntrast Modelling using 2D T1–T2 correlation spectra and relaxation signatures

Image contrast is calculated by inputting experimental 2D T₁–T₂ relaxation spectra into the ODIN software interface. The method involves characterising a magnetic resonance imaging pulse sequence with a “relaxation signature” which describes the sensitivity of the sequence to relaxation and is independent of sample parameters. Maximising (or minimising) the overlap between the experimental 2D T₁–T₂ relaxation spectra and the relaxation signature can then be used to maximise image contrast. The concept is illustrated using relaxation signatures for the echo planar imaging and Turbo spin-echo imaging sequences, together with in-vitro 2D T₁–T₂ spectra for liver and cartilage.     

Incomplete relaxation and plasmon formation in the K emission band of copper

A method of calculating the effect of self-absorption in X-ray emission spectra and which is suitable for non-adiabatic excitation processes is presented. The Fermi-level E_F and the “true” profile of the electron-excited (20–40keV) CuKβ_2,5 band are determined. A deviation from the calvulated one-electron spectrum in the energy interval [-12 eV, -7 eV] below E_F is interpreted as a result of plasmon formation and Auger broadening. A pronounced disagreement is found also in the range [-1 eV, + 10eV]. Above E_F, a part of the intensity may be due to incomplete electron relaxation.     

The effect of high iron-ion implantation doses on the X-ray emission spectra of silicon

X-ray emission spectroscopy (Si L _{2, 3} spectra, 3d3s → 2p electronic transition) was employed to study p-and n-type silicon samples implanted with Fe⁺ ions in a pulse mode (the implantation energy was 30 keV, the pulse current was varied up to 0.5 A, the pulse duration was 400 μs, and the ion irradiation doses ranged from 10¹⁴ to 10¹⁷ cm⁻²). The x-ray emission spectra were found to be dependent on the ion irradiation dose and the electron-accelerating voltage that was used in the x-ray studies. By comparing the Si L spectra with the spectra of reference materials and by modeling the former spectra, it was revealed that, as the ion-irradiation dose increases, there occur disordering of the structure, partial amorphization of the sample in a surface layer approximately 7200-? thick, and its subsequent recrystallization (under high irradiation doses). It was shown that this effect is most pronounced in a layer at a depth of ∼1000 ? and is not associated with the formation of iron silicide FeSi in the bulk of the sample but rather is due to the breakage of Si-Si bonds caused by ion implantation under the irradiation doses used. Original Russian Text ? D.A. Zatsepin, E.S. Yanenkova, é.Z. Kurmaev, V.M. Cherkashenko, S.N. Shamin, S.O. Cholakh, 2006, published in Fizika Tverdogo Tela, 2006, Vol. 48, No. 2, pp. 204–209.     

Influence of aluminum impurity on the electronic structure and optical properties of the TbNi5 intermetallic compound

The electronic structure of the TbNi_{5 ? x} Al _x intermetallic compounds (x = 0, 1, 2) is calculated in the local electron density approximation with the correction to strong electron correlations in 4f shell of terbium ions. Spectral properties of these compounds are measured by ellipsometry in a wavelength range of 0.22–16 μm. Frequency dependences of optical conductivity in the region of interband optical absorption are interpreted based on the results of calculations of electron densities of states. The relaxation and plasma frequencies of conduction electrons are determined.     

Relaxation mechanism in γ-ray-irradiated L-alanine studied by transfer saturation EPR and pulse EPR

Stable paramagnetic centers in γ-ray-irradiated L-alanine dosimeters exhibit a maximum in relaxation rate in the vicinity of 190 K. The mechanism of this relaxation rate has been investigated on the first stable alanine radical center, SARI, by employing continuous-wave transfer saturation electron paramagnetic resonance and pulse electron paramagnetic resonance techniques. The detected in-phase and out-of-phase spectra as well as phase memory times,T _M, indicate that besides the well-known τ_p of the CH₃ group of SAR1 an additional correlation time, τ_l (ΔElk=2689±50 K and 0 τ₁₀ = 0.15 ± 0.03 ps), is involved in the transverse relaxation process and effects the SAR1 center. For the SAR1 center this mechanism originates from the hindered motion of undamaged CH₃ and NH ₃ ⁺ groups in the lattice. The motion of these groups additionally effects the spectrum of the SAR1 center through averaging out of the anisotropic splitting.     

Electronic Raman scattering and the electron–phonon interaction in YB6

Electronic Raman scattering in YB₆ and in its structural and electronic analog LaB₆ has been studied in the temperature range of 10–730 K. The experimental spectra have been compared to those calculated on the basis of ab initio band structures with renormalization owing to the electron–phonon interaction. Good agreement between the calculation and experiment for LaB₆ has been obtained throughout the entire temperature range. This allows the determination of the coupling constant λ _ep = 0.25. To satisfactorily describe the spectra of electronic light scattering in YB₆, it is necessary to introduce an additional electron relaxation channel. In this case, the estimate of the electron–phonon coupling constant λ _ep is no more than 0.4; for this reason, a high superconducting transition temperature cannot be explained only by the phonon mechanism.     

Coherent optical pulse evolution in a CO2 amplifier

The coherent reshaping of short duration (2–5 nsec) CO₂ laser pulses in a low-pressure (∽ 5 torr), longitudinal discharge CO₂ amplifier is experimentally studied in the linear regime for a variable number of gain lengths (αL?7). Single pulses grow considerably in duration as well as amplitude in agreement with theoretical considerations. Analysis of the observed pulse evolution is used to obtain the transverse relaxation parameter T₂. Zero-degree pulses {∫^+∞_-∞E ( z, t) dt = 0} are observed to terminate much of the long tail which occurs in single-pulse amplification. Off-resonant amplification of short-duration pulses is shown to lead to dramatic changes in the zero-degree pulse evolution. Numerical calculations relating to pulse amplification in the nonlinear regime for high-pressure CO₂ amplifiers are also presented.