High-pressure Mössbauer study of SnSe

SnSe is a member of the IV-VI family of binary compounds which have orthorhombic structure and are layered, exhibiting properties that place SnSe intermediate between two- and three-dimensional crystals. Mössbauer measurements have been made on SnSe under hydrostatic pressure in the range 0.001 to 55 kbar. The results are interpreted with respect to interlayer and intralayer bonding. Two ranges of response to the pressure were found: (1) a lower-pressure range (below 30 kbar), in which measurable changes in isomer shift and quadrupole splitting were found, and (2) a higher-pressure range (between 30 and 55 kbar), where no further changes were found. The lower-pressure range is interpreted as a range in which the interlayer bonds are changed

Effect of pressure on the resistivity and Hall coefficient of amorphous metallic alloys

Measurements have been made of the resistivity as a function of hydrostatic pressure in the range 0-5 kbar in the temperature interval 180-330 K for the amorphous alloys Fe80B20(Metglas 2605), Fe19Ni61P14B6, Fe32Ni36Cr14P12B6 (Metglas 2826A), Pd82Si18, and Cu42Zr58. Measurements of the Hall coefficient were also made in Fe19Ni61P14B6 and Metglas 2826A. The pressure coefficients of resistivity were uniformly negative and, with the exception of Fe80B20, insensitive to temperature. The contributions of thermal and magnetic scattering to the resistivity are negligible. The simple formulation of the Ziman theory is found to be inadequate to account for the observed pressure dependence of the resistivity

Pressure-amorphized SiO2 ±-quartz: An anisotropic amorphous solid

Recent experiments [Kruger and Jeanloz, Science 249, 647 (1990)] have shown that the pressure-induced amorphous form of AlPO4 reverts to its original single-crystal form on release of pressure. Here we present the results of a Brillouin scattering study of the sister compound ±-quartz, SiO2 (which can also be pressure amorphized but retains its amorphous structure on release of pressure), which shows that the recovered material is not elastically isotropic but retains a memory of its original crystallographic orientation

Photodarkening in amorphous Ge1-xSnxSe2 films

Photodarkening experiments have been performed on evaporated films of Ge1-xSnxSe2 in the composition range 0x0.60 at 78 K. Thermal cycling between room temperature and 78 K was observed to reduce the optical absorption of the films. The photodarkening response is slightly enhanced at x=0.1 but is suppressed for higher Sn concentrations

Elastic constants of As2S3

We have used Brillouin scattering to measure ten of the thirteen independent elastic constants of crystalline As2S3. We find that the phonon propagation within the layer plane is largely controlled by the orthorhombic symmetry of the layer rather than the monoclinic symmetry of the crystal. The stiffness within the plane displays a large anisotropy, and the smaller of the stiffnesses within the plane is less than that along the axis perpendicular to the plane, an unexpected result for a layered crystal. For phonons propagating near the [001] direction the two branches of the velocity show a mode repulsion and exchange their polarizations. In this direction the velocity of the shear wave is larger than that of the compressional wave

Effect of impurities on the electronic phase transition in graphite in the magnetic quantum limit

The electronic phase transition in graphite under strong magnetic fields is studied by magneto-transport measurement for a wide variety of single-crystal samples for a field range up to 280 kG and temperatures down to 0.41 K. The magnetic field dependence of the transition temperature is fitted to a functional form Tc(B)=T*exp(-B* B), where the parameters T* and B* are approximately 100 K and 1000 kG, respectively. This functional form is consistent with Yoshioka and Fukuyama's model of a magnetic-field- induced charge-density-wave instability. We have found two types of samples, each of which exhibit distinctive magnetotransport behavior at the onset of the phase transition. For one sample type, we have observed a suppression of Tc and a less sharp conductivity change at the transition point, relative to the other type. This difference in behavior is correlated with the difference in the ionized impurity concentration between the two types of samples as deduced from the high-field Hall measurements. The differences between the types can be understood by taking account of the "pair-breaking" effect of the impurities

Structural and elastic properties of Ge after Kr-ion irradiation at room temperature

Changes in the elastic properties of Ge induced by room-temperature irradiation with 3.5-MeV Kr ions have been determined and correlated with changes in the microstructure determined by transmission electron microscopy. Elastic-shear-moduli changes were measured by Brillouin scattering, and changes in local atomic arrangement were determined by Raman scattering. Amorphization decreased the elastic shear modulus of Ge by 17%. The fractional decrease was correlated with the amorphous volume fraction with a cross section of 4.5±0.5 nm2/ion. No change was observed in the shear modulus during void formation and growth. The elastic properties of the voided material are described by the Voigt averaging. However, as the voids evolved into a fibrous spongelike microstructure, a second dramatic elastic softening occurs which we attribute to the inability of the fibrous structure to support shear stresses. Raman scattering showed that, once formed, there was no change in the structure of the amorphous material at the atomic scale during void formation and subsequent void coalescence

Molecular motion and mobility in an organic single crystal: Raman study and model

We report Raman spectra of the organic semiconductor 5,6,11,12- tetraphenyltetracene (rubrene) in the temperature range 30-300 K. The linewidths of certain low-frequency peaks increase significantly, especially in the range 150-200 K. These peaks correspond to the vibrations of the phenyl side groups of the rubrene molecules, and their couplings to intermolecular vibrational modes. We propose a model in which the strong increase in mobility observed with increasing temperature between 30 and 150 K results from disorder as the phenyl groups exchange sides of the backbone plane and break the symmetry. This model explains previous experimental observations of structural and calorimetric changes near 150 K

Electroluminescence in silicon oxynitride films

Electroluminescence (EL) was reported from 50 nm silicon oxynitride films on p-type crystalline silicon substrates in a Au/silicon oxynitride/Si structure. The EL intensity is consisted with radiative recombination of injected carriers, and has a peak below 2.45 eV. The EL can only be seen in annealed samples with the emission similar to the photoluminescence from the same samples

Measurement of the In0.52Al0.48As valence-band hydrostatic deformation potential and the hydrostatic-pressure dependence of the In0.52Al0.48As/InP valence-band offset

We have measured the In0.52Al0.48As valence-band hydrostatic deformation potential from the hydrostatic-pressure dependence of the In0.52Al0.48As/InP valence-band offset which was measured from 0 to 35 kbar at room temperature. Due to the type-II band lineup, the radiative recombinations across the InP band gap and between the InP conduction band and the In0.52Al0.48As valence band were both observed in the photoluminescence spectra. This enables us to measure directly the changes of the valence-band offset under pressure. The hydrostatic-pressure derivative of the valence-band offset was measured to be 0.00.4 meV/kbar. The predictions of the pressure dependence from band-offset models (dielectric midgap and model-solid theories) agree with the measurement to within 1 meV/kbar. The In0.52Al0.48As valence-band hydrostatic deformation potential is found to be -0.8 eV which compares well with the dielectric midgap theory. Using the reported pressure dependence of the GaAs/AlAs valence-band offset, the valence-band hydrostatic deformation potentials of InxAl1-xAs (0x0.52) are linearly interpolated as -1.9x+0.2 eV