A study of electromigration of nickel in lead

The steady state method was used to study the electromigration of ⁶³Ni in Pb. For the temperature range 180–290°C, and Ni concentration range 0.1–1000 ppm, Ni migrates toward the anode. For dilute samples (0.1 ppm Ni) the effective charge varies linearly with the inverse resistivity from ?6.75 at 188°C to ?4.97 at 289°C. The 1/ρ dependence is given by $\text{Z1 = (1.4 ± 0.3)?(288 ± 13)× 10}{}^{\mathrm{?6}}\text{/ρ}$. The effective charge is a function of the Ni concentration, increasing in magnitude with increasing concentration. For 1000 ppm Ni, |Z1| exhibits a sharp maximum around 260°C; below 230°C electromigration takes place at a much slower rate, probably due to precipitation.     

Electromigration of gold (high concentration) in lead

The steady state method was used to study the electromigration of ¹⁹⁵Au in lead doped with 680 ppm Au. In the temperature range 165–270°C Au migrates toward the anode, as in the case of more dilute solutions; but the effective charge increases in magnitude with decreasing temperature at a faster rate than that observed for dilute Pb(Au) samples, so that the difference between the effective charge for the 680 ppm samples and that for dilute samples becomes larger as the solubility limit is approached. A simple model, which allows for formation of Au doublets in equilibrium with the singlets, predicts an apparent increase of Z¹ with concentration of impurity at lower temperatures somewhat greater than the observed effect.     

Electromigration and permeation of hydrogen and deuterium in silver

A steady state flow technique was used to measure the effective charge number (Z*) and permeability (N) of hydrogen and deuterium in silver. Over the range of temperature (485–720°C) and pressure (220–750 torr) the effective charge number is a constant. The interstitial impurity migrates in the direction of the electron wind with Z_H* = ?6·8 and Z_D* = ? 18. The values of Z* are of the same order as self-electromigration but the size of the isotope effect is surprising. The quantum theories used to explain the isotope effect for hydrogen electromigration in Fe and Ni appear to fail here. In order to determine the effective charge number is was necessary to measure the permeability. For both H₂ and D₂, the permeability in silver follows the equation N = N_O exp(? Q/RT) where N_0D = 2·39 ± 0·40, Q_D = 14400 ± 300, N_OH = 2·86 ± 0·70 and Q_H = 14200 ± 500. Here Q is in units of cal/mol and N is in units of cc(ntp)/(sec - atm² - cm) The isotope effect ratio N_H/N_D = 1·25 was smaller than the classically expected value of (2)^1/2, but could be explained by the theory of Ebisuzaki, Kass and O'Keeffe.     

Electromigration of cadmiun in lead

The electromigration of cadmium in lead up to a concentration of 510 at ppm Cd was measured at constant temperatures between 250 and 290°C by the steady state method and also by a somewhat novel transient technique; the latter required shorter running time and also gave additional information, namely the chemical diffusion coefficient, D_ch. From the steady state runs the observed effective charge number was Z¹_ss = + 2.5 ± 0.3 for the lowest concentration. The positive value was apparently the result of the counterflowing of the lead in a vacancy-interstitial pair mechanism. The temperature dependence of Z¹ is described by $\text{Z}{}^1\text{= (0.5 ± 2.4) + (0.9 ± 1.1)}$$\text{10}{}^{\mathrm{?4}}\text{ρ}$ and both the wind force and the electrostatic Z_el appear to be small. The Z¹_ss, appeared to increase slightly with concentration. The transient measurements were in general less precise, but were consistent with the steady state results within their experimental accuracy. The values of $\text{D}{}_{\mathrm{ch}}\text{D}{}^1$ appeared to be unity within the same accuracy for a range of composition up to 510 at ppm Cd. To a standard dissociation model for impurity mobility we have added a rather extended atomic exciton mechanism to help explain the diffusion kinetics.     

Evidence of complex positron-ammonia interaction in ammonia gas

Positron annihilation in ammonia gas at temperatures of ?19°C, 22,5°C, and 95°C in the density range 1.76 × 10^?4 g/cm³ to 6.63 × 10^?3 g/cm³ is investigated. ¹Z_eff for orthopositronium annihilation is 0.58 ± 0.04 Z_eff/ Z for positrons not forming positronium varies from about 117 to 1329.     

Magnetic susceptibility of solid and liquid metals

Apparatus for the measurement of the magnetic susceptibilities of solid and liquid metals at temperatures up to 800°C is described. Prior to studying the susceptibilities of various metals through the melting point, the apparatus was tested by measuring the susceptibilities of tin and lead at room temperature, and the temperature dependences of susceptibility of several pure copper specimens enclosed in quartz bulbs. For copper, in the temperature range 20°C to 700°C,? _χ /?T = 1.9₂ × 10^?11 emu/g · deg C. This result is discussed in terms of the change of electronic susceptibility with volume expansion.     

Matter transport in pure gold induced by high direct current densities

In a new investigation the temperature dependence of electromigration in gold was measured by applying an improved tracer method. The results are in good agreement with those of Gilder and Lazarus. In the temperature range between 1137K and 1235K the effective charge varies from ?7.7 e to ?6.7 e. However, the linear relation betweenz _eff and 1/?, predicted from theory, could not be confirmed unequivocally. The activation enthalpy of electromigration,Q _E =42.3±1.1 kcal/mole, is practically identical to that for self-diffusion. A temperature independent value was found for the residual resistivity of the thermally activated ion-vacancy complexes, ? _d =1.76 µΩ cm/at-%, which is close to the residual resistivity of vacancies in gold. In addition, our earlier investigations are reviewed, in which electromigration in gold was measured using a marker method and a tracer method simultaneously. The results are critically examined in connexion with a theory proposed by Guy.     

Kernrelaxations-Untersuchung der Selbstdiffusion in festem Kupfer

We report on measurements of the⁶³Cu nuclear spin relaxation time in the rotating frame,T _1ρ, in solid copper as a function of temperature and Larmor frequency, from which the temperature dependence of the self-diffusion coefficient was evaluated using Torrey's theory. Within the relatively small temperature range (572 °C ≦ ? ≦ 838 °C) in which diffusion relaxation dominates, the temperature dependence of the diffusion coefficient is compatible with a simple Arrhenius law. However, in an evaluation including recent tracer results in an essentially larger temperature range (353 °C≦?≦1079 °C) clear deviations from this standard interpretation were found, as implied by Seeger's divacancy formalism. From those deviations we have calculated a more reliable set of diffusion parameters than comparable data in the literature.     

In situ electron microscopy investigations of solid-state synthesis in Al/Au thin bilayer films

In situ transmission electron microscopy investigations of solid-state synthesis in Al/Au thin bilayer films are conducted. The samples are heated in the column of a transmission electron microscope. The heating temperature is changed from room temperature to 300°C with a heating rate of up to 120°C min^?1. It is found that solid-phase synthesis starts at ≈100°C. At 140 ± 5°C, two crystal phases, Al₂Au (Fm3m) and AlAu₂ (I4/mmm), are simultaneously observed, while at 235 ± 5°C and higher (up to 300°C) only Al₂Au phase is detected.     

The non-mesonic to π− mesonic decay ratio and Λ-neutron stimulation fraction for p-shell hypernuclei

Kinematic analysis of simple hypernuclear production reactions has produced a sample of hypernuclei of _ΛB, _ΛC and _ΛN with negligible background, and a much smaller sample of _ΛBe. The values of the non-mesonic to π^? mesonic ratio Q^? for the above samples are 5.5 ± 0.5 and 4.3 ± 1.1, respectively. A sub-sample of ¹¹_ΛB hypernuclei was separated on the basis of production via an excited state of _Λ¹²C, giving Q^? = 4.8 ± 1.1 for _Λ¹¹B. Assuming the Fermi gas model is applicable to nuclei of mass A ≈ 11, two independent means of analysis of the non-mesonic decays give values for the Λ-neutron stimulation fraction n of 0.41 ± 0.09 and 0.34 ± 0.07 for hypernuclei of charge 5 ≦ Z ≦ 7.     

Non-invasive temperature mapping using MRI: comparison of two methods based on chemical shift and T1-relaxation

Purpose: To implement and evaluate the accuracy of non-invasive temperature mapping using MRI methods based on the chemical shift (CS) and T₁ relaxation in media of various heterogeneity during focal (laser) and external thermal energy deposition.Materials and Methods: All measurements were performed on a 1.5 T superconducting clinical scanner using the temperature dependence of the water proton chemical shift and the T₁ relaxation time. Homogeneous gel and heterogeneous muscle phantoms were heated focally with a fiberoptic laser probe and externally of varying degree ex vivo by water circulating in a temperature range of 20–50°C. Magnetic resonance imaging data were compared to simultaneously recorded fiberoptic temperature readings.Results: Both methods provided accurate results in homogeneous media (turkey) with better accuracy for the chemical shift method (CS: ±1.5°C, T₁: ±2.0°C). In gel, the accuracy with the CS method was ±0.6°C. The accuracy decreased in heterogeneous media containing fat (T₁: ±3.5°C, CS: +5°C). In focal heating of turkey muscle, the accuracy was within 1.5°C with the T₁ method.Conclusion: Temperature monitoring with the chemical shift provides better results in homogeneous media containing no fat. In fat tissue, the temperature calculation proved to be difficult.     

Diffusion of titanium in slightly reduced rutile

The self-diffusion of ⁴⁴Ti in slightly reduced rutile. TiO_2?δ, was measured along the c axis over the temperature range of 1000–1100°C between 0.2 and 1 × 10^?18atm. oxygen pressure. These measurements enabled the determination of the defect structure of TiO_2-δ for 0.02 ?gd ? 0.001. For oxygen pressures between 1 × 10^?13 and 1 × 10^?16atm. at 1058.4°C random tetravalent titanium atoms are the predominant defects evident from self-diffusion. The enthalpy of motion was determined as ΔH_m = 57.03 ± 4.9% kcal/mole. From the activation energy at 1.69 × 10^?16atm., the enthalpy of formation for tetravalent titanium interstitials was determined as ΔH_f = 276 ± 15.6% kcal/mole.For oxygen pressures less than 1 × 10^?16atm. at 1058.4°C, the tracer diffusion coefficient shows a continuous decline as the oxygen pressure is lowered. Comparisons with thermogravimetric studies and consideration of the similarity in structure between nonstoichiometric point defect phases and the first homologous series phase indicate that the order-disorder transition retains a considerable degree of short range order below the critical concentration in the form of Wadsley defects.     

Perturbed angular distribution of recoil implanted19F-nuclei in a cobalt and copper environment

The magnetic hyperfine field acting on¹⁹F nuclei in a cubic cobalt lattice at a temperature of 450 °C has been investigated. Time dependent spin rotation has been observed following the excitation and recoil implantation with a pulsed α-particle beam using the reaction¹⁹F(α,α′)¹⁹F*. The hyperfine field isH _hf (450 °C)=31.4 ± 0.5 kG. The measured amplitude of the spin rotation is only 18% of the amplitude expected for the case where all¹⁹F* nuclei are assumed to be subject to the same hyperfine field without any further perturbation. This was established by means of other implantation experiments with a copper backing using first the pulsed beam technique followed by a γ-ray angular distribution measurement in coincidence with backscattered α-particles. In copper a fast perturbation was found, which reduces the anisotropy to about 80% within a short time interval immediately after the excitation.     

Mössbauer and optical evidence for a crystallographic transition in AFeF4 compounds

The thermal variation of the quadrupole splitting of ⁵⁷Fe in NH₄FeF₄ and RbFeF₄ gives a strong evidence of a phase transition taking place at 120° and 110°C respectively. Birefringence in the a, b plane is observed at room temperature and disappears when approaching the reported temperatures. KFeF₄ does not show any sizeable change in the range 20–200°C. CsFeF₄ behaves in a more complicated way and does not lead to definite conclusions.     

Effect of the deviation from stoichiometry on cation self-diffusion and isotope effect in wüstite,Fe1−xO

Diffusion of ⁵⁹Fe in Fe_1xO crystals has been measured by a serial-sectioning technique as a function of temperature and deviation from stoichiometry. The results indicate that the diffusivity increases slightly at 1200°C, decreases at 802°C with an increase in x, and is insensitive to change in x at 1003°C. The temperature dependence of the cation diffusivity in Fe_0.94O is given by the expression, $\text{D=(0.6±0.5)×10}{}^{\mathrm{?3}}\text{exp(?29350 ±}\text{300}\text{RT}\text{)cm}{}^2\text{/se}$ the temperature range 700–1340°C. The isotope effect for cation self-diffusion was measured by simultaneous diffusion of ⁵²Fe and ⁵⁹Fe in Fe_1?xO at various temperatures and values of x. Although the measured values of fΔK are independent of temperature within the limits of experimental error, they decrease with an increase in the deviation from stoichiometry. The experimental results appeared to be consistent with the diffusion of Fe ions via “free mobile vacancies” that coexist with defect clusters. As a consequence of a “site-blocking” effect, the mobility of “free mobile vacancies” and the apparent correlation factor for cation tracer diffusion decrease with an increase in deviation from stoichiometry.     

EPR study of Mn2+ around the ferroelastic transition point of Pb3(PO4)2

The spin Hamiltonian parameters of Mn²⁺ have been measured above and below the transition point (180°C) of the lead phosphate. They show that Mn²⁺ substitutes a Pb_I ion. Between 175 and 180°C the principal axis OX of the fine tensor is parallel to the wave vector of the soft mode which condensates at the transition point. An exaltation of the linewidth is observed. The linewidth remains constant within 5°C of T_c; in this temperature range, the “static regime” is achieved, and the correlation time of the fluctuations is less than 10^?8 sec.     

Fission yields at different fission-product kinetic energies for thermal-neutron-induced fission of 239Pu

At the recoil spectrometer “Lohengrin” of the Institut Laue-Langevin in Grenoble, the yields of the light fission products from the thermal-neutron-induced fission of ²³⁹Pu were measured as a function of A, Z, the kinetic energy E and the ionic charge states q. The nuclear charge and mass distributions summed over all ionic charge states were determined for different light fissionproduct kinetic energies between 93 and 112 MeV. The proton odd-even effect which was measured to be (11.6 ± 0.6)% causes considerable fine structure in the yields. The average kinetic energy of even-Z elements in the light fission-product group is 0.3 ± 0.1 MeV larger than for odd-Z elements. The neutron odd-even effect is (6.5 ± 0.7)%. The comparison with previously published data ¹) for thermal-neutron-induced fission of ²³⁵U reveals a correlation between the proton odd-even effect in the yield and in the kinetic energy of the elements. The dependence of the proton odd-even effect on the fragmentation is very similar for ²³⁵U and ²³⁹Pu when it is considered as a function of the nuclear charge of the heavy fission products. The isobaric variances σ_z². for thermal-neutron fission of ²³⁵U and ²³⁹Pu coincide at all kinetic energies if the influence of the proton odd-even effect is averaged out. This supports the hypothesis that the magnitude of σ_z² is determined only by quantum-mechanical zero-point fluctuations. The influence of the spherical shells Z = 50 and N = 82 on the fragmentation is discussed.     

Electromigration in polycrystalline and single crystal magnesium

The electromigration of magnesium single and polycrystal samples was measured under the influence of a d.c. current density of approximately $\text{6×10}{}^3\text{A}\text{cm}{}^2$ using the vacancy flux technique. The single crystal data were taken on samples with the c-axis of the metal making angles of 22° and 63° respectively with the cylindrical axis of the specimen. Accurate measurements of the longitudinal and transverse motion were made over a period of several weeks and used to calculate a value for the atom drift velocity, V_a. The atom drift velocity is used to calculate Z¹, the effective eiectromigration charge on the ion. All of the observed motion was directed toward the anode. The polycrystal runs yielded an average value of $\text{Z}{}^1\text{?}\text{= ?2.03 ±0.33}$. The single crystal runs resulted in an anisotropic drift velocity ratio of $\text{V}{}_{\mathrm{a\perp }}\text{V}{}_{\mathrm{a\parallel }}\text{= 1.4}$. However, the product of diffusivity times resistivity is anisotropic by the same ratio as the atom drift velocity and the correlation factor f is nearly isotropic for magnesium. As a result Z¹ is isotropic and turns out to be ?1.6.     

Azimuthal anisotropy of the emission of fragments and relativistic particles in collisions between iron nuclei of momentum 2.5 GeV/<Emphasis Type="Italic">c</Emphasis> per nucleon and photoemulsion nuclei

The azimuthal anisotropy of the emission of fragments and relativistic particles in collisions between ⁵⁶Fe nuclei of momentum 2.5 GeV/c per nucleon and photoemulsion nuclei is measured. For semicentral collisions at impact-parameter values in the range 0.12 ≤ b/b_max ≤ 0.70, charged fragments and relativistic particles are predominantly emitted in the direction orthogonal to the nuclear-reaction plane. The azimuthal-asymmetry parameter P₂ for fragments whose charge numbers are Z = 1, 2 and Z ≥ 3 takes values of, respectively, ?0.192±0.057, ?0.28±0.07, and ?0.39±0.12. Evaporated b particles have an isotropic azimuthal distribution.     

Die Temperaturabhängigkeit des Bandabstandes von Bleiselenid,gemessen an photoleitenden Schichten

The temperature dependence of spectral distribution of photoconductivity was measured on evaporated polycrystalline layers of lead-selenide in the range from 80 to 300 °K. The method ofBardeen, Blatt andHall was used, to calculate the band gap for direct and indirect transitions. A linear positive temperature coefficient was obtained for both transitions. The values areβ _dir=+(4.5±0.2) · 10^?4 eV/°K andβ _ind=+(3.0±0.2)· 10^?4eV/°K.