Anisotropy effects in superconductors with magnetic impurities

The influence of Fermi surface anisotropy on the specific heat jumps,C, at the phase transition for superconductors containing magnetic and nonmagnetic impurities is discussed. In the framework of a simple two-band or two-zone model we find for small interband electron-phonon coupling constants characteristic maxima in theC(T _c )-curve.These departures from the correspondingC-curve of a single-band isotropic superconductor are mostly pronounced forweak andstrong interband Coulomb scattering of conduction electrons on nonmagnetic ions. There is only a small range of intermediate scattering rates for which the maxima are smeared out.Work performed within the research program of the Sonderforschungsbereich 125 — Aachen/Jülich/Köln     

Metal adsorption on monolayer blue phosphorene: A first principles study

We investigated the electronic structure, adsorption energies, magnetic properties, dipole moment and work function of metal adatoms (Mg, Cr, Mo, Pd, Pt, and Au) adsorption on a blue phosphorene monolayer. For Mg, Pt and Au metals, the most stable state was found in hollow site while for Cr, Mo and Pd metals we found an adsorption in valley site. We suggest that the Pd and Pt atoms prefer 2D growth mode while the Mg, Cr, Mo and Au atoms prefer 3D island growth mode on monolayer phosphorene. The electronic band structures and magnetic properties were dependent on the doping site and dopant materials. For instance, the semiconducting features were preserved in Mg, Pd, Pt, and Au doped systems. However, the Cr and Mo doped systems displayed half-metallic band structures. The total magnetic moment of 4.05, 2.0 and $0.77{\text{μ}}_B/\text{impurity}$ atom were obtained in Cr, Mo and Au doped systems whereas the Mg, Pd and Pt doped systems remained nonmagnetic. We also investigated the magnetic interaction between two transition metal impurities. We observed ferromagnetic coupling between two transition metal impurities in Cr and Mo doped systems while the Au doped system displayed almost degenerated magnetic state. For Mg, Cr, and Mo adsorptions, we found relatively large values of dipole moments compared to those in the Pd, Pt and Au adsorptions. This resulted in a significant suppression of the work function in Mg, Cr and Mo adsorptions. Overall, adsorption can tune the physical and magnetic properties of phosphorene monolayer.     

Laser-induced reactions of NO2 in the visible region

The reaction of NO₂ with isobutane, induced by 488 nm laser radiation, to form 2-nitro-2-methylpropane has been investigated and the results computer-modeled according to two possible reaction mechanisms. The first scheme involves the direct abstraction of H from isobutane by vibronically excited NO₂ (NO ₂ ^* ), and the second, abstraction by an intermediate NO₃ radial produced by NO ₂ ^* +NO₂. The modeling results strongly support the NO ₂ ^* scheme as the dominant reaction mechanism.     

Temperature dependence of SSW linewidth in metallic thin films

Measurements of the standing spin wave linewidth H _n at 17·6 GHz from 6 °K to 400 °K are presented for two permalloy films whose structure is either polycrystalline or epitaxial. It is shown that in both films, H _n is proportional ton ² (n is the mode number). Although H _n is little modified by temperature (20% variation maximum over the entire temperature range), we experimentally state that the slopep of H _n (n ²) is a linear function of the saturation magnetizationM which agrees with a planar inhomogeneity model.The authors wish to thank H. Pascard and F. Hoffmann who have prepared and selected the films as also E. Villain and A. Gatineau for invaluable technical assistance.     

Au-197 Mössbauer isomer shift in Au-Cu and Au-Ag alloys: The role of the Au 5d electrons

The Au-197 Mössbauer isomer shift (IS) for a series of Au-Cu and Au-Ag alloys is correlated with the change in the 5d electron population (5d hole count) at the Au site upon alloying. The Au 5d hole counts have been derived from the area under the whiteline of the Au L_3,2 edge X-ray absorption near edge structures (XANES) of the alloys. It is found that there exists a linear corelation betweenIS and Au 5d hole counts, indicating that the redistribution of 5d electrons has a significant effect on the isomer shift. From theIS-5d hole correlation, the ratio of 5d loss to 6s gain ( n _d / n _s ) is determined to be –0.62.     

Diffusion of Al in ion-implanted Pd and Pt

The diffusion coefficients of aluminium have been measured in polycrystalline fcc Pd and Pt. The Al-implanted palladium and platinum samples were annealed at 400°–800 °C and 450°–900 °C, respectively. The aluminium profiles were probed using the nuclear resonance broadening (NRB) technique. Values of (1.41±0.09) and (1.38±0.09) eV for the activation energy and (1.5 _–1.0 ⁺⁵ )×10^–6 and (4 _–3 ⁺¹⁰ )×10^–7cm²/s for the frequency factor were obtained for Al in Pd and Pt, respectively. These anomalous results, compared to the normal impurity diffusion, were checked using also Al-evaporated samples.     

Calibration of the isomer shift of83Kr

Radioactive⁸³Rb was implanted in 6 different cubic metals (Al, W, Au, Ir, Pt, Pb) and both internal conversion electron spectra and Mössbauer spectra of the daughter nucleus⁸³Kr were measured. A value (r ²)=+5.1(9)×10^–3 fm² (corresponding to R/R=+1.6(3)×10^–4) was derived for the change of the mean square charge radius during the 9.40 keV transition in⁸³Kr. The systematics of the isomer shifts of krypton and other sp-elements substitutionally dissolved in metals are discussed.     

Combined effects of donor and acceptor impurities on the thermoelectric properties of cadmium antimonide

A study was made of the effect of the simultaneous doping with donor (Te) and acceptor (Cu, Ag, Au) elements on the thermoelectric properties of CdSb. Doping with tellurium changes the p-type conductivity of the CdSb crystals to an n-type conductivity with an impurity (Te) activation energy of E_d = (0. 11 ± 0. 01) eV. Doping with an acceptor impurity changes the energy of the donor level, by E_d = 0. 14 eV for doping with silver, by E_d = 0. 10 eV for doping with gold and by E_d = 0. 095 eV for doping with copper. It is shown that the type of conductivity and the thermoelectric properties of CdSb can be adjusted in the desired direction through simultaneous doping with two impurities.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 90–94, June, 1970.     

Ab initio calculations of generalized-stacking-fault energy surfaces and surface energies for FCC metals

The ab initio calculations have been used to study the generalized-stacking-fault energy (GSFE) surfaces and surface energies for the closed-packed (1 1 1) plane in FCC metals Cu, Ag, Au, Ni, Al, Rh, Ir, Pd, Pt, and Pb. The GSFE curves along (1 1 1) direction and (1 1 1) direction, and surface energies have been calculated from first principles. Based on the translational symmetry of the GSFE surfaces, the fitted expressions have been obtained from the Fourier series. Our results of the GSFEs and surface energies agree better with experimental results. The metals Al, Pd, and Pt have low γ_us/γ_I value, so full dislocation will be observed easily; while Cu, Ag, Au, and Ni have large γ_us/γ_I value, so it is preferred to create partial dislocation. From the calculations of surface energies, it is confirmed that the VIII column elements Ni, Rh, Ir, Pd, and Pt have higher surface energies than other metals.     

Calibration of the isomer shift of125Te from internal conversion and mössbauer measurement

Radioactive¹²⁵I was ion-implanted into 7 different metal matrices. Al, Au, In, Pt, Sn, Te and Zn, and internal conversion and Mössbauer spectra associated with the 35.46 keV M1 transition of¹²⁵Te were measured for the same samples. A value R/R=(0.853±0.115)×10^–4 was derived for the relative difference of the nuclear charge radius for the 35.46 keV M1 transition of¹²⁵Te.     

Calibration methods and avoidance of errors in measurement of intracellular pH (pHcyt) using the indicator bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) in human platelets

Determinations of pH_cyt in suspensions of human platelets using BCECF [bis(carboxyethyl)-5(6)-carboxyfluorescein] can be seriously biased by leakage of the fluorescent indicator. Two methods (pH jump and Mn²⁺) are presented for determining the fraction of external indicator (B _ext) and eliminating this error. Both methods rely on rapid perturbations (pH jump or Mn²⁺ addition), which affect the fluorescence of the external dye immediately and the intracellular dye more slowly. Identical values ofB _ext are reported. Failure to correct for dye leakage can result in overestimation of pH_cyt by as much as 0.4 unit at physiological external pH (pH_ext). Two methods of calibration of the cytoplasmic signal were compared after correcting forB _ext: the digitonin lysis method and the nigericin calibration method. In the digitonin method the dye is released at the end of the experiment and the dependence of its fluorescence is determined as a function of pH. The method assumes that the fluorescence and titration characteristics of the dye in the cytoplasm are not different from those in solution. It gives pH_cyt=6.75±0.07 for pH_ext=7.3. In the nigericin method, 150 mM external K⁺ and 10 M nigericin are used for the purpose of setting pH_cyt=pH_ext to accomplish anin situ calibration. The method was complicated by extra leakage induced by nigericin. Assuming that the ionophore could equilibrate pH in the alkaline range, the fluorescence of the anionic form of BCECF in the cytoplasm would be 15% lower than in solution and pH_cyt would be 0.3 unit higher than presented above. A number of observations favor the digitonin lysis method of calibration. The fluorescence polarization of BCECF in platelets is small and indistinguishable from that in solution (0.000±0.022). The spectrofluorimetric characteristics of the intracellular dye are identical to those in solution (150 mM NaCl or KCl). There was no evidence for self-quenching or binding to cellular elements for cytoplasmic BCECF concentrations up to 1.8 mM. The following agents are capable of introducing error: (1) the Na⁺ substituteN-methyl-d-glucamine doubles theK _d and decreases by 13% the F _max of BCECF; (2) the Na⁺/H⁺ exchange inhibitor amiloride quenches BCECF fluorescence and is intrinsically fluorescent; and (3) bovine serum albumin (used to remove nigericin) quenches external BCECF with kinetics mimicking acidification of the cytoplasm.     

Temperature dependence and input optical power tolerance of an InGaAsP electroabsorption modulator module

We report the temperature dependence and input optical power tolerance of an InGaAsP electroabsorption (EA) modulator module. Thermal stability of the module was found to be very high. The optimum E _g at 20°C has been estimated to be 48–55 meV. At E _g of 53 meV, the insertion loss was almost independent of the temperature, while the driving voltage was strongly dependent on the temperature. The breakdown phenomena were investigated in detail; these occurred under conditions of very high input power and/or high bias voltage. Input power for breakdown was smaller for higher bias voltage or smaller E _g. Allowable maximum input optical power has a large margin (>5 dB) for the conventional input level in practical systems.     

Calibration of the isomer shift of129I

Radioactive^129mTe was implanted in 6 different transition metals (V, Fe, W, Au, Pt, Pb) and internal conversion electron spectra as well as Mössbauer spectra of the daughter nucleus¹²⁹I were measured. A value (r ²)=+1.8(4)×10^–2 fm² (corresponding to R/R=+4.1(10)×10^–4) was derived for the change of the mean square charge radius during the 27.8 keV transition in¹²⁹I. The consequences of this measurement on the calibration constants of the Mössbauer isomer shifts of other isotopes of the 5sp elements are discussed.     

Ordering processes and activation energy in Ni3Fe-based ternary alloys

The measurement of electrical resistance () has been used, to study the kinetics of isothermal ordering in the range 200 °–545 ° C in Ni₃(FeMn) alloy quenched from 970 ° C, and the kinetics of ordering at 390 ° C in the alloy quenched from various temperatures in the 600 °–800 ° C range. The sections method and the gradient of the (t) curves were used to find the activation energy for migration and vacancy formation in this alloy on the assumption that the excess vacancies frozen in the alloy by quenching at temperatures above T_c are responsible for ordering. The activation energies for vacancy formation and migration were respectively U₀ = 33 ± 3 kilocal/mole and U_m = 39 ± 4 kilocal/mole, which in total give the activation energy for diffusion Q = 72 ± 7 kilocal/mole in the alloy studied; this approximates to the activation energy for diffusion in pure nickel.     

Use of infrared absorption spectra for studying the conformational equilibrium of cis-1-methyl-2-ethylcyclohexane

The equilibrium of the three most stable conformations of cis-1-methyl-2-ethylcyclohexane has been examined on the basis of changes in intensity of the triplet at 585–610 cm^–1 in its infrared absorption spectrum on changing the temperature from 30° to –140° C. H and S have been determined.     

Jauch-Piron system of imprimitivities for phonons. I. Localizability in discrete space

This paper is devoted to a discussion of the notion of localizability for phonons, i.e., quasiparticles arising from the harmonic vibrations of a system ofn atoms bound to one another by elastic forces. The natural tools for the analysis of localizability are the projection operatorsÊ() acting on the Hilbert space of one-phonon states, where is an arbitrary subset of the set that consists ofn vectors specifying the equilibrium positions ofn atoms. The expectation value ofÊ() is the probability that the phonon belongs to the atoms whose equilibrium positions are characterized by the elements of . For a strongly localizable phonon all of the projection operatorsÊ() commute with one another, whereas in the case of a weakly localizable phonon the operatorsÊ(₁) andÊ(₂) do not commute when ₁ and ₂ overlap. With the aid of the Jauch-Piron quantum theory of localization in space, the present paper describes the method of obtainingÊ() and also shows that if in the system ofn atoms there exist normal modes of zero frequency, then the phonon is only weakly localizable. Given the explicit expression forÊ(), one can define the number-of-phonons operator as well as the quasiparticle analogue (given in a companion paper) of the Wigner distribution function.     

Energy band structure of CdSnAs2 and CdGeAs2

The energy band structure of CdSnA₂ and CdGeAs₂2 is calculated by the empirical-pseudopotential method, taking account of spin-orbital interaction. The calculated parameters – E_g = 0.25, _cr = 0.05, _s.o = 0.44 for CdSnAs₂ and E_g = 0.55, _cr = 0.20, and _s.o = 0.33 for CdGeAs₂ (all in eV) — are in good agreement with experiment. The conclusion drawn in a series of experimental works that there are additional minima close to the bottom of the CdSnAs₂ conduction band is not confirmed in the calculation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 78–82, December, 1981.     

The influence of the α′-precipitates on the electrical conductivity of Al-21·8 AT. % Zn alloy at higher temperatures

The applicability of the classical theoretical formulae for electrical conductivity of disperse metallic systems was experimentally verified on the Al-21·8 at. % Zn alloy. This alloy represents a two-phase system in the investigated temperature interval 276–302 °C. The conductivity values calculated for the system consisting of discrete spheres randomly distributed within the continuous matrix were compared with the measured isothermal deviationsR _f from the ideal resistivity, corresponding to the hypothetical continuous solid solution at the same temperature. The temperature 308 °C for the stable solvus was derived by extrapolation ofR _f s values.I would like to express my thanks to Doc. Dr. V.Syneek CSc., for stimulating author's interest in this problem and for providing helpful discussions. The author is indebted to Mrs.Mendlová for careful evaluation of experimental data.     

The theory of neutron scattering from mixed harmonic solids

In the intermediate valent cerium alloys Ce_1–xY_xPd₃, Ce(Pd_1–xRh_x)₃ and Ce(Pd_1–xAg_x)₃ the Gd³⁺-ESR shows a non-linear increase of the linewidth H(T) in the temperature range 4.2KT300K. The deviation from the linear Korringa law can be described by a reduced conduction electron density of states at the Gd site (which is a Ce lattice site) in the energy range E _4f (=width of the Ce 4f states). This supposition allows a determination of E _4f from the H(T)-data. For CePd₃:Gd³⁺ we find E _4f=(650±100) K. E _4f increases with Y- and Rh-concentration and decreases with Ag-concentration.     

Opto-thermal study of the melting transition of benzophenone

We report a series of opto-thermal transient emission radiometry (OTTER) measurements on benzophenone over the temperature range 20–80°C, which includes the melting transition at 48°C. At temperatures sufficiently close, but below the melting point, the form of the opto-thermal decay curves was found to change, when the laser pulse energy was sufficient to cause transient melting near the surface. Such measurements could be useful in the study of re-crystallation dynamics in pulsed laser annealing and similar surface treatments. In addition, the experiment gives a direct measure of ₀, the initial jump in surface temperature, and a comparison of solid and liquid thermal diffusivities. The values found in the present study are ₀, andD(solid)/D(liquid)=2.2±0.2.