Effect Of Strain Field Research Articles

De Haas-van Alphen study of conduction electron scattering and impurity screening for dilute Co impurities in Au

High precision de Haas-van Alphen (dHvA) Dingle temperature measurements were carried out for six orbits in the (110) plane, in six different samples of Au (150 atomic p.p.m. Co) annealed under different conditions. No significant differences in Dingle temperature was observed due to annealing. Waveshape analysis, and observations of both fundamental and second harmonic spin-splitting zeros, revealed no significant spin-dependent scattering or exchange energy shifts of the electronic Landau level. A phase-shift analysis of the measured Dingle temperature anisotropy was carried out, with the result that d-d interaction and d wave scattering is heavily dominant. Both the Friedel sum and the impurity resistivity are correctly calculated using the dHvA-derived phase shifts, if the effect of impurity-induced strain fields is taken into account. An approximate method for obtaining a phase-shift description of these strain fields is demonstrated using the measured dHvA phase shifts and the experimental resistivity value. Finally a connection between dHvA scattering measurements and the screening of impurity states is shown.

Non-Conventional Electron Microscopy in Small Defect Characterization

The conventional bright field (Fig. 1a) and dark-field images of small (<200Å) def ects are beset with several disadvantages: The image sizes (≃300Å) are two or three times the defect size; the image shift from core position may be larger than the defects; (Table 1a); the images are dominated by strain field effects and give no clue to defect shape and habit. Conventional images are therefore unsuitable for the size, nature and habit plane determination of small defects.

The transport of heat in isotopic mixtures of solid neon: an experimental study concerning the possibility of second-sound propagation

The thermal transport properties of solid mixtures of the neon isotopes 20Ne and 22Ne have been studied by means of heat-pulse and steady-state thermal conductivity measurements. The results have been interpreted numerically using the Callaway formalism to establish the relaxation rates for phonon scattering. The rate for three-phonon normal processes which is of particular interest can be represented by tau N-1=(4.5+or-0.5)*105x2T4s-1, where x=h(cross) omega /kT and W is the phonon frequency. The phonon scattering by isotopic impurity atoms was found to be 40% stronger than that predicted on the basis of the mass difference alone, but accords well with calculations that include the effects of strain field scattering. The intrinsic process relaxation rates have been used to assess the possibility of second-sound propagation in perfect neon crystals.

Effect of Dislocation Strain Field on Lattice Specific Heat

The change of the lattice specific heat caused from the strain fields of dislocations has been evaluated on the basis of the higher order elasticity theory. The variations of the lattice vibrational frequencies due to strains were calculated using the quasi-harmonic approximation, and the usual and the higher order mode Gruneisen parameters were expressed as functions of the second-, third-, and fourth-order elastic constants. The displacement fields of an edge and a screw dislocation were also calculated with taking into account the elastic anisotropy of the crystal. These results were combined with the Debye theory of specific heat to obtain the expression for the specific heat change from dislocations. Numerical evaluation has been done for the case of copper, and it was found that the specific heat was increased several per cent at liquid helium temperature by dislocations with density of 10 12 cm -2 and the effect was larger for edge dislocations.

Biaxial stress relaxation in glassy polymers: polymethylmethacrylate

Biaxial stress relaxation studies were performed on glassy polymethylmethacrylate in combined torsion-tension strain fields using a specially designed apparatus with exceptionally high stiffness and low cross talk between the torsional and tensile load measuring transducers. It was found that at low strain levels uniaxial tension relaxation is slower than pure torsion relaxation; tensile-component relaxation rates are unaffected by the level of torsional strain; torsional-component relaxation rates decrease as tensile strain is increased; uniaxial tension relaxation rates approach the pure torsion rates at higher strains (∼2%). A phenomenological treatment is presented which shows that relaxation rates can be coupled to the strain fields in which they are observed and yet be consistent with the concepts of linear viscoelasticity and the Boltzmann superposition integral. It is concluded that the mean normal strain, and not the octahedral shear strain, is the principal factor that governs both the effect of strain field on relaxation kinetics and the onset of nonlinear viscoelastic behavior. A mechanistic interpretation based on long-term relaxation processes in glassy polymers is offered to explain the effects of mean normal strain on relaxation kinetics.

Relaxation times in AgAu and AgCu alloys

Calculations have been made of the relaxation times for electrons on the Fermi surface of Ag due to scattering from dilute concentrations of Au and Cu impurities. In the case of AgAu alloys it has been found that the relaxation times are primarily determined by the mass-velocity and Darwin relativistic corrections to the potential seen by an electron. In AgCu alloys the relativistic corrections are still important and the calculated relaxation times depend critically on cancellation between `potential' scattering and `relativistic scattering' and possibly the effects of the strain field.

Donor-acceptor pairing in the system GaP(Zn, O)

Equilibrium concentrations of Zn-O nearest-neighbor pairs in GaP have been calculated for Zn and O concentrations between 10 16 and 10 19 cm −3 at temperatures between 400 and 1200°K. The discrete nature of the host lattice is taken into account and the effects of strain-fields, bond mismatch, and electrostatic interactions on the Zn-O binding energy are discussed. The discrete and fluid models of ion pairing are compared and it is shown that for the case of substitutional pairing in compound semiconductors, the fluid model can underestimate the pairing by as much as a factor of 3 depending on the temperature and ion concentrations.

Electron diffraction contrast from ledges at the interfaces of faceted θ′ precipitates

Abstract Ledges have been observed at the habit-plane interface of faceted ø’ precipitates in an aluminium-copper alloy. The ledges are between 15 and 65 Å in height and are visible both by strain field and thickness contrast effects. The strain field behaves qualitatively as a prismatic dislocation loop lying at the precipitate-matrix interface. When a precipitate reflection only is excited, a characteristic black-white contrast is observed in dark field and this enables the sense of the loop to be determined, i.e. growth or dissolution ledges can be distinguished.

Effective mass theoretical approach to optical and microwave phenomena in semiconductors—II: Theory of the Faraday and Voigt effects due to excitons in germanium

The oscillatory Faraday and Voigt spectra observed by Nishina and Lax near the direct band gap of germanium have been analysed on the effective mass theory of the excitons in a strong magnetic field. The effective mass equation is solved variationally and assignment of each rotational singularity is made. The exciton binding turns out to be essential for the interpretation of the rotation spectra at room temperature as well as at low temperature. The effect of the existing strain is emphasized in the low temperature spectrum. The sign reversal of the first Faraday singularity observed at low temperatures is accounted for as an interplay between the effects of strain and magnetic field on a degenerate band.

Interband Faraday rotation and Voigt effect in Ge

The interband Faraday and Voigt effect near the direct edge of Ge were measured near liquid helium temperature in the magnetic fields up to 56.7 kG applied in the [110] axis. The sample, about 4 μ thick, was backed by the glass substrate of 3 mm thick. In the low temperature the difference in the linear expansion coefficients of the sample and substrate induced a uniaxial stress equivalently in the direction perpendicular to the surface of the sample. Consequently the strain removed the four-fold degeneracy of the valence bands at Γ point, so that each of the observed Faraday singularities could be interpreted as caused by electronic transition to a non-degenerate excitonic state. An anomalous reversal in the sign of the Faraday peak was observed near the field of 45 kG, corres- ponding to the magneto-absorption line of the lowest photon energy. This phenomenon is due to the competitive effects of strain and magnetic field.

Effect of coherency strain fields on the flow stress of a copper-3·12% cobalt alloy

Abstract The reversible flow stress ratio in a polycrystalline Cu-3·12% Co alloy was investigated by temperature changes below 303°K as a function of the strain and of the precipitation structure determined by transmission electron microscopy. Shear modulus values determined with a torsion pendulum were used to correct the data. Coherent precipitates of about 15 Å diameter produced by ageing at 923°K resulted in an anomalous increased temperature dependence of the flow stress, whereas those over about 25 Å diameter gave an anomalous reversed temperature dependence, the alloy becoming softer on cooling. The maximum anomalous softening occurred in the peak-hardened condition, and at zero strain and 0°K was estimated to be 16% of the flow stress at 303°K. Straining progressively removed the effect. The proportional decrease in flow stress (for zero strain) on cooling from 303° to 77°K for the peak aged alloy is in excellent agreement with the proportional decrease in mis-match determined by x-ray parameter measurements on a Cu-20% Co alloy homogenized at 923°K. The anomalous softening effect disappeared on gross overageing which resulted in loss of coherency. The results support the concept of coherency hardening.