Indirect exciton transition in silicon under [111] uniaxial compression

Transverse electroabsorption and absolute absorption spectra in silicon at 1.8° K in the presence of [111] uniaxial compression are reported. The relative strengths of the phonon-assisted transitions and the change of exciton binding energy are found to be in agreement with predictions. The effect of strain upon spectral broadening is also discussed.     

The single crystal diffraction patterns of silicon

A triple-crystal diffractometer is used to study the single crystal diffraction patterns of Si (111), (220), (333) and good agreement with the dynamical theory of X-ray diffraction on perfect single crystals is found. This proves the possibility of using Si single crystals as in X-ray spectroscopy for a double-crystal spectrometer with a high resolving power as well as for studying very narrow diffraction patterns by means of a triple-crystal diffractometer.

---

Si

Si (111), (220), (333); . Si , .

---

---

The authors thank R. ida and F. Hájek for designing and making the automatic equipment for measuring the curves and V. Smutná and A. Irra for carefully performing the auxiliary work.     

Phonon focusing in [001] germanium

Phonon focusing in [001]-oriented Ge crystals has been studied at temperatures near 2.0K using electron-beam scanning for phonon generation and thin-film bolometers with an effective area of 10 m×10 m or smaller for phonon detection. The thickness of the Ge crystals was 2 or 3 mm. In our experiments the angular resolution appeared to be dominated by effective diameter of the local region heated by the beam and acting as phonon source. Whereas metallic overlay films did not appreciably effect the angular resolution, a distinct increase in resolution due to high-frequency beam modulation has been observed which can be understood in terms of the thermal skin effect. From a comparison between theoretical calculations and our experimental results the effective diameter of the phonon source has been found to be 20–30 m. Our focusing images show appreciable deviations from theoretical calculations in the low-frequency limit. However, excellent agreement is obtained, if dispersion is included and if the dominant phonon frequencies are place in the range 300–400 GHz.     

Electrical and magnetic properties of single crystal [NEt4]2[CuII(mnt)2]

We report electrical and magnetic studies of [NEt₄]₂[Cu^II(mnt)₂]. This crystal is composed of chains of theplanar [Cu^II(mnt)₂]^?2 anions (space group $\text{P}\text{1}$ and z = 1) which exhibit only weak magnetic interactions. The material behaves as a semiconductor; from 300–400°K the conductivity increases by six orders of magnitude and the resistivity values above 300°K are comparable to those of some of the better known wide band-gap inorganic semiconductors. In contrast with the behavior of other linear chain systems, at room temperature the conductivity along the chain (σ_∥) is less than that perpendicular to the chain (σ_⊥). As the temperature is increase, the anisotropy ratio, σ_∥/σ_⊥, becomes greater than unity and increases to 1.6 × 10² at 400°K.     

Evidence for molecular hydrogen in single crystal silicon

Rutherford backscattering in channeling in combination with elastic recoil detection analysis has been used to study the formation and destruction of hydrogen “supermolecular” complexes (H₂)_n formed in single crystal silicon after hydrogen implantation and annealing in the range 150–800°C. Secondary ion mass spectroscopy has been used to confirm this interpretation by giving direct evidence for H₂. The supermolecular configuration can be interpreted as the nucleus for the formation of bubbles.     

Ab initio study of [001] GaN nanowires

We present the results of a study of structural, electronic, and optical properties of the unpassivated and H-passivated GaN nanowires having diameters in the range of 3.29 to 18.33 Å grown along [001] direction by employing the first-principles pseudopotential method within density functional theory in the local density approximation. Two types of nanowires having hexagonal and triangular cross-sections have been investigated. The binding energy increases with the diameter of the nanowire because of a decrease in the relative number of the unsaturated surface bonds. The binding energies of the triangular cross-sectional nanowires are somewhat smaller than those of the hexagonal cross-sectional nanowires in accordance with the Wulff’s rule except the smallest diameter triangular cross-sectional nanowire, where the binding energy is comparable with the corresponding hexagonal cross-sectional nanowires. The band gap varies rapidly with the diameter of the nanowire in the case of the smaller diameter nanowires, and quite slowly for the larger diameter nanowires. After atomic relaxation, appreciable distortion occurs in the nanowires, where the chains of Ga- and N-atoms are curved in different directions. These distortions are reduced with the diameters of the nanowires. The optical absorption in the GaN nanowires is quite strong in the ultra-violet region but an appreciable absorption is also present in the visible region for the larger diameter nanowires. The present results indicate the possibility of engineering the properties of nanowires by manipulating their diameter and surface structure. The presently predicted smaller diameter GaN nanowire possessing the triangular cross-section should be observable in the experiments.     

Photon induced far-infrared absorption in pure single crystal silicon

Illumination of silicon by direct sunlight was found to cause a significant increase in the far-infrared (FIR) absorption of silicon. The effect was observed during a recent measurement campaign using a 2.5 THz airborne heterodyne spectrometer for atmospheric measurements together with a silicon aircraft window. In this work, the absorption increase was reproduced in the laboratory by illumination of a silicon sample with a halogen lamp. The analysis of the energy flux dependence and the wavenumber dependence support the assumption that the increased absorption in the FIR is due to photon induced transitions of electrons from the valence band to the conduction band. This effect might be of importance to a number of instruments using silicon components.     

Surface metal-insulator transition on a vanadium pentoxide (001) single crystal

In situ band gap mapping of the V2O5(001) crystal surface revealed a reversible metal-to-insulator transition at 350-400 K, which occurs inhomogeneously across the surface and expands preferentially in the direction of the vanadyl (V=O) double rows. Supported by density functional theory and Monte Carlo simulations, the results are rationalized on the basis of the anisotropic growth of vanadyl-oxygen vacancies and a concomitant oxygen loss driven metal-to-insulator transition at the surface. At elevated temperatures irreversible surface reduction proceeds sequentially as V2O5(001) --> V6O13(001) --> V2O3(0001).     

Abnormal thermal conductivity of [720]‐oriented BaTiO3 single crystal

The 3ω ‐scanning thermal microscopy and piezoresponse force microscopy techniques were combined to characterize the local thermal conductivity (λ) of ferroelastic domains in [720]‐oriented and [001]‐oriented BaTiO₃ single crystal. The [720]‐oriented BaTiO₃ showed a local λ value of 3.39 W/m·K, while it was 5.95 W/m·K for [001]‐oriented BaTiO₃. The underlying mechanism for such drastic thermal conductivity reduction in [720]‐oriented BaTiO₃ is ascribed to a stronger phonon‐scattering effect due to the high strains appearing in [720]‐oriented BaTiO₃ single crystals. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microstructure evolution of a [011] orientation single crystal nickel-base superalloy during tensile creep

Microstructure of [011] oriented single crystal nickel-base superalloy consists of the cubical γ′ phase embedded coherently in the γ matrix, and arranged regularly along 〈100〉 orientations. After tensile creep, the cubical γ′ phase in the alloy is transformed into the strip-like rafted structure along [001] direction under the ordering transformation free-energy and strain energy change. And the directional growing of γ′ phase is attributed to the atoms Al and Ta into (001) plane to form the stable stacking mode.     

Resonant transverse differential conductivity of heavy holes inp-type diamond and silicon in fields E∥H∥ [001]

We show that, in comparison top-Ge,p-Si is the most promising material for extending the generation of electromagnetic waves into the high-frequency region. Diamond is unsuitable for this purpose because of its small transverse negative differential conductivity.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 45–48, August, 1993.     

Shock compression of solids

This review contains a brief, comprehensive, critical assessment of the status of investigations concerning the response of solids to shock compression. Mechanical, metallurgical, electrical, optical and other phenomena occurring in substances subjected to shock pressures covering the range from about 0.1 to 6000 GPa are considered. Emphasis is placed on physical interpretation of observations peculiar to the shock environment and on the relationships among observations in the various areas of investigation.     

Electrical properties and diffusion behavior of hafnium in single crystal silicon

Electrical properties and diffusivity of Hf in single crystal Si have been studied. Several deep level defects were found for Hf in both the upper and lower half of the silicon band gap, and their parameters were measured. Energy levels, concentrations, and capture cross sections were determined for all Hf defects. The DLTS spectra depend on the cooling rate. Analysis of electrical properties yielded a dominant deep level defect at E_C -0.27 eV, which showed field enhanced emission due to Poole–Frenkel effect, confirming its donor nature. This agreed with results obtained using CV and TSCAP. In the lower half of the bandgap, a defect level at E_V +0.24 eV was found to have a capture barrier of 0.04 eV. Diffusivity of Hf was studied using two methods for Hf incorporation in Si – ion implantation and sputtering. Analysis of broadening of the Hf profile in implanted samples, which were annealed for 168 h, allowed us to estimate the diffusivity of Hf as 1.7×10^-15 cm²/s at 1250 °C: the spreading of implanted profiles at lower temperatures was too small. Analysis of Hf depth profiles in the sputtered and annealed samples reveals that Hf appears to have a fast and slow component to its diffusivity whose migration energy was determined to be 3.5±0.3 eV and 4.1±0.3 eV respectively. The fast and slow component are ascribed to interstitial and substitutional Hf with an energy level of E_C -0.27 eV and E_V +0.43 eV respectively. The mechanism for the fast component seems to indicate a direct interstitial diffusion mechanism whereas the diffusion of the substitutional Hf seems most consistent with the concerted exchange diffusion mechanism. In addition, estimates of solubility for both, interstitial and substitutional Hf, are included. PACS 61.72.Tt; 66.30.Jt; 71.55.Cn