Resonant Raman scattering by strained and relaxed germanium quantum dots

This paper reports on the results of resonant Raman scattering investigations of the fundamental vibrations in Ge/Si structures with strained and relaxed germanium quantum dots. Self-assembled strained Ge/Si quantum dots are grown by molecular-beam epitaxy on Si(001) substrates. An ultrathin SiO₂ layer is grown prior to the deposition of a germanium layer with the aim of forming relaxed germanium quantum dots. The use of resonant Raman scattering (selective with respect to quantum dot size) made it possible to assign unambiguously the line observed in the vicinity of 300 cm^?1 to optical phonons confined in relaxed germanium quantum dots. The influence of confinement effects and mechanical stresses on the vibrational spectra of the structures with germanium quantum dots is analyzed.     

Refraction of surface spin waves in spatially inhomogeneous ferrodielectrics with biaxial magnetic anisotropy

The refractive index of surface spin waves propagating in a ferromagnetic medium with a nonuniform distribution of the parameters of uniaxial and orthorhombic magnetic anisotropies and exchange coupling is determined within the spin-density formalism. The coefficients of reflection and transmission of spin waves at the interface between two homogeneous magnets with different constants of uniaxial and orthorhombic magnetic anisotropies, exchange coupling, and saturation magnetization are calculated. The dependences of the intensity of a reflected wave and the refractive index on the wave frequency and the strength of an external dc homogeneous magnetic field are determined.     

Giant piezoelectric and dielectric enhancement in disordered heterogeneous systems

Effective complex piezoelectric and dielectric constants of disordered heterogeneous systems, such as statistical mixtures consisting of spheroidal particles of the same orientation but with random distribution in space, are studied. It is found for the first time that, in such systems, there exists giant piezoelectric enhancement accompanied by giant relaxation of piezoelectric coefficients and permittivity. The piezoelectric and dielectric spectra differ considerably from the Debye spectra and have a Cole-Cole character. The dependence of the effects considered on the aspect ratios of the spheroids is investigated. The physical mechanisms responsible for the anomalous behavior of the piezoelectric coefficients and permittivity are considered.     

Stress relaxation and viscosity of a bulk Pd<Subscript>40</Subscript>Cu<Subscript>30</Subscript>Ni<Subscript>10</Subscript>P<Subscript>20</Subscript> metallic glass under isochronous heating conditions

Isochronous relaxation of tensile stresses is measured in a bulk Pd₄₀Cu₃₀Ni₁₀P₂₀ metallic glass in the initial state and after certain thermal treatments. The results of measurements are used to find the energy spectrum of irreversible structural relaxation, from which the temperature dependence of shear viscosity is then calculated. This dependence is also found independently from measurements of creep in the same glass. The calculated viscosity is shown to agree well with the experimental data.     

Growth of germanium nanoislands and nanowires on singular and vicinal Si(111) surfaces prior to the formation of a wetting layer

Physics of the Solid State - The growth of germanium nanoislands and nanowires on singular and vicinal Si(111) surfaces is investigated by scanning tunneling microscopy (STM). It is shown that the...     

Distribution of a local magnetic field in superconductors with an uncorrelated random lattice of abrikosov vortices

The distribution of a local magnetic field near the surface of a uniaxial anisotropic type-II superconductor is determined in the framework of the London model in the case when the Abrikosov vortices are randomly distributed in the superconductor. The distribution of a local magnetic field is obtained as a function of the distance from the surface of the superconductor. It is demonstrated that the shape of the distribution of the local magnetic field near the surface differs substantially from that in the bulk of the superconductor. This difference should be taken into account in interpreting experimental data on the local magnetic field in the surface region of the superconductor and in thin superconducting films (with a thickness of less than or equal to λ, where λ is the depth of penetration of the magnetic field into the superconductor). It is shown that, as in the case of a regular lattice of vortices, the value of λ can be determined from observations of the distribution of the local magnetic field in type-II superconductors with an uncorrelated random lattice of vortices.     

Threshold character of the magnetoplastic effect in twinning of bismuth crystals

It is found that, when a bismuth crystal is subjected simultaneously to concentrated loading and a dc magnetic field, the magnetoplastic effect manifests itself as an abrupt decrease in the average length of wedge twins on the (111) cleavage plane (and, hence, as a decrease in the total twinned volume of the crystal) as a threshold value of the magnetic field is reached. However, the magnetic field stimulates glide deformation, which is indicated by an increase in the size of dislocation rosettes. The microhardness of a crystal varies smoothly and tends to increase with increasing magnetic field. The last phenomenon is accounted for by hardening of the crystal under the indenter in the presence of a magnetic field, because several slip systems become operative.     

Chain decay of low-angle tilt boundaries in nanocrystalline materials

In terms of two-dimensional dislocation-disclination dynamics, a theoretical model is developed to describe the decay of a low-angle tilt boundary in a deformed nanocrystalline material under the action of an externally applied elastic stress and of the elastic field of a neighboring decayed boundary. The critical external stresses are calculated at which the boundary decays and the dislocations making up this boundary either are trapped by the boundary that decayed earlier or break away from both boundaries. The decay of a low-angle tilt boundary is shown to result in a substantial decrease in the critical decay stresses for the neighboring boundaries, which can cause an avalanche-like chain decay of low-angle boundaries yielding high-density ensembles of mobile dislocations capable of carrying substantial plastic deformations and of forming shear bands in deformed nanocrystalline materials.     

Modification of the physical properties of chemical vapor-deposited nanostructure diamond by argon-hydrogen plasma surface treatment

Nanostructure diamond (NSD) film with a hardness as high as 70 GPa and an average surface roughness of 10 nm has been synthesized by the two-step negative substrate bias method combined with post-growth Ar-H₂ plasma irradiation. The Ar-H₂ plasma irradiation has been confirmed to improve the uniformity of grain size and shape and increase the hardness of the NSD film.     

Perpendicular magnetic anisotropy in single-crystal Co<Subscript>50</Subscript>Pt<Subscript>50</Subscript>/MgO(100) films

The crystal structure and hysteretic magnetic properties of equiatomic single-crystal CoPt films applied on MgO substrates by magnetron sputtering, as well as modification of these properties by thermal annealing, are studied. Heat-treated films of thickness in the range 2<d≤16 nm exhibit perpendicular magnetic anisotropy. A correlation between the crystalline anisotropy constant of the CoPt films and the order parameter of the LI₀ superstructure in these alloys is found. The effect of a single-crystalline MgO substrate on the structure and magnetic properties of equiatomic CoPt films is revealed.