Nonlinear optical properties of antimony–germanium–sulfur glasses at 1560 nm

Nonlinear (NL) optical properties of antimony–germanium–sulfur (Sb–Ge–S) glasses were investigated using laser pulses of 65 fs at 1560 nm. Samples having concentration ratio [S]/[Ge]=2.69 with different antimony concentrations were studied. Glasses with different oxidation states of Sb were investigated using the thermally managed Z -scan technique. The influence of the Sb oxidation state on the NL properties was evaluated. NL refraction indices of electronic origin, n ₂≈10⁻¹³ cm²/W, two-orders of magnitude larger than for fused silica and NL absorption coefficients smaller than 0.55 cm/GW were measured. Appropriate figures-of-merit for photonic applications were determined.     

Thermodynamics and surface properties of liquid Al–Ga and Al–Ge alloys

The surface properties of Al–Ga and Al–Ge liquid alloys have been theoretically investigated at a temperature of 1100 K and 1220 K respectively. For the Al–Ga system, the quasi chemical model for regular alloy and a model for phase segregating alloy systems were applied, while for the Al–Ge system the quasi chemical model for regular and compound forming binary alloys were applied. In the case of Al–Ga, the models for the regular alloys and that for the phase segregating alloys produced the same value of order energy and same values of thermodynamic and surface properties, while for the Al–Ge system, the model for the regular alloy reproduced better the thermodynamic properties of the alloy. The model for the compound forming systems showed a qualitative trend with the measured values of the thermodynamic properties of the Al–Ge alloy and suggests the presence of a weak complex of the form Al₂Ge₃. The surface concentrations for the alloys show that Ga manifests some level of surface segregation in Al–Ga liquid alloy while the surface concentration of Ge in Al–Ge liquid alloy showed a near Roultian behavior below 0.8 atomic fraction of Ge.     

Thermophysical properties of Ni-5%Sn alloy melt

The surface tension and specific heat of Ni-5%Sn alloy melt were measured by the oscillating drop method and the drop calorimetric method using electromagnetic levitation, respectively. The temperature coefficient of surface tension is 6.43×10⁻⁴ N·m⁻¹K⁻¹ within the temperature regime of 1464–1931 K. The enthalpy change was measured in the temperature range from 1461 to 1986 K, and the average specific heat was obtained as 43.03 J·mol⁻¹K⁻¹. Some other thermophysical properties, such as viscosity, solute diffusion coefficient, density, thermal diffusivity and thermal conductivity of this alloy melt, were derived based on the experimentally measured surface tension and specific heat. Using these thermophysical parameters, the relation between solute trapping and undercooling in rapidly solidified α-Ni was calculated, and the theoretical prediction shows a good agreement with experimental data.     

Er<Superscript>3+</Superscript> as glass structure modifier of Ga–Ge–S chalcogenide system

Er³⁺ clustering phenomenon in Ga–Ge–S chalcogenide system is studied using Raman spectroscopy. The Raman spectra from 10 to 500 cm⁻¹ for glasses (100−y)[15Ga₂S₃–85GeS₂]–yEr₂S₃ (y=0.08−5.00 mol. %) have been analyzed. To reveal the influence of the chemical composition on the glass structure the intensity of the peak corresponding to Ge–Ge (Ga–Ga) homopolar bonds has been examined. The peak intensity increase with Er₂S₃ concentration change in the region 0<C(Er₂S₃)<2 mol. % has been interpreted in terms of the sulphur deficiency in the glass resulting in the formation of S₃Ge–GeS₃ (S₃Ga-GaS₃) structural units. The further increase in concentration beyond 2 mol. % reduces the sulphur deficiency, which can be attributed to the formation of the ternary compound Er₃GaS₆. The structural units Er₃GaS₆ contain a large mol. fraction of Er³⁺ or, in other words, Er³⁺ clusters. The data obtained from the low-frequency Raman spectra (boson band) indicate strong variations of the medium-range order (MRO) in the glasses induced by Er³⁺. The observed behavior of the MRO size (the correlation length) with increasing of Er₂S₃ concentration provides for additional evidence of the Er³⁺ clustering.     

Mössbauer study of the disorder in crystalline and amorphous Ge implanted with 125mTe ions

Crystalline and amorphous Ge and amorphous Ge_0.8Te_0.2 were implanted with ^125mTe. The Mössbauer spectra showed quadrupole split doublets. The isomer shift and quadrupole split values suggested that the atomic configuration around Te after implantation in Ge is similar to that of amorphous GeTe.     

Measurement and simulation of specific heat for metastable liquid Ni80Fe10Cu10 alloy

The specific heat of undercooled liquid Ni₈₀Fe₁₀Cu₁₀ alloy was experimentally measured by electromagnetic levitation drop calorimeter, and also numerically simulated by the molecular dynamics method. The achieved maximum undercooling is up to 252 K (0.15 T _L) in the experiments, and the measured result is 41.67 J mol⁻¹ K⁻¹. The simulation provides calculated data within 0∼702 K undercooling range, which is much broader than the experimental regime. The simulated value is 37.02 J mol⁻¹ K⁻¹. Although there exists a difference of 4.65 J mol⁻¹ K⁻¹ between them, the result is quite acceptable for simulation. Furthermore, the liquid structure of undercooled Ni₈₀Fe₁₀Cu₁₀ alloy is studied in terms of the total and partial pair distribution functions, which display that the ordered degree of atoms enhances from a normal liquid to metastable state.     

Formation mechanism of the primary faceted phase and complex eutectic structure within an undercooled Ag–Cu–Ge alloy

The solidified microstructure of bulk undercooled Ag₄₀Cu₃₀Ge₃₀ alloy consists of three parts: primary (Ge) phase, the complex structure of (Ag + Ge) and (Ag + ε ₂) pseudobinary eutectics, and (Ag + Ge + ε ₂) ternary eutectic. In comparison, the pseudobinary eutectic no longer appears in an alloy droplet solidified in a drop tube. Once the undercooling exceeds 225 K and the cooling rate is greater than 2×10³ K s⁻¹, the microstructure of the solidified droplet is totally composed of anomalous ternary eutectic. In both cases, the primary (Ge) phase exhibits various faceted growth morphologies at different undercoolings, such as columnar block, long dendrite, equiaxed dendrite and rod-like crystal. Some refined side branches grow from the equiaxed (Ge) dendritic branches composed of {111} twins, which is ascribed to the rapid epitaxial growth of (Ag + Ge) pseudobinary eutectic from the (Ge) dendritic branches. Moreover, both the primary (Ge) phase and the (Ge) phase in the (Ag + Ge) pseudobinary eutectic are effective heterogeneous nuclei for the (Ag+ε ₂) pseudobinary eutectic. As undercooling increases, the (Ge) phase in the (Ag + Ge+ε ₂) ternary eutectic transforms from faceted to non-faceted phase, while the independent nucleation and growth of the (Ag) and ε ₂ phases in the ternary eutectic displaces their previous cooperative growth. These growth kinetics transitions result in the formation of anomalous ternary eutectic.     

Average and recommended half-life values for two-neutrino double-beta decay: Upgrade ’05

All existing “positive” results on two-neutrino double-beta decay in different nuclei were analyzed. Using the procedure recommended by the Particle Data Group, weighted average values for half-lives of ⁴⁸Ca, ⁷⁶Ge, ⁸²Se, ⁹⁶Zr, ¹⁰⁰Mo, ¹⁰⁰Mo−¹⁰⁰Ru(0 ₁ ⁺ ), ¹¹⁶Cd, ¹⁵⁰Nd, ¹⁵⁰Nd− ¹⁵⁰Sm(0 ₁ ⁺ ) and ²³⁸U were obtained. Existing geochemical data were analyzed and recommended values for half-lives of ¹²⁸Te, ¹³⁰Te, and ¹³⁰Ba are proposed. We recommend the use of these results as presently the most precise and reliable values for half-lives. Presented by A.S. Barabash at the Workshop on calculation of double-beta-decay matrix elements (MEDEX’05), Corfu, Greece, September 26–29, 2005.     

The Peierls phase transition in <Emphasis Type="Italic">n</Emphasis>-Ge caused by impurity interaction

The study of the electron paramagnetic resonance in Ge:As has revealed that the insulating state in uncompensated semiconductors is preserved near the insulator-metal phase transition because of the appearance of lattice distortions. The latter are caused by the interaction of the spins localized on impurity atoms due to the spin-Peierls transition. In Ge:As, this effect manifests itself in the concentration range n = n = 3 × 10¹⁷–3.7 × 10¹⁷ cm⁻³.     

Manifestation of anomalous properties of HgTe lattice vibrations in Hg1 ? xZxTe (Z = Cd, Mn, Zn) alloys

Alloys (solid solutions) Hg_{1 − x} Z _x Te (Z = Cd, Mn, Zn) with a variation in their composition are characterized by the double-mode type of rearrangement of the vibrational spectrum of the crystal lattice, and these alloys retain the properties of lattice vibrations of the binary alloy components. The HgTe-enriched alloys under consideration also retain the anomalous properties of HgTe lattice vibrations with their additional low-frequency 105 cm⁻¹ mode, which is forbidden according to the symmetry selection rules. An analysis has been made of the specific features of the manifestation of the 105 cm⁻¹ mode in the alloys as compared to HgTe, in particular, its splitting into several modes ω _n (n = 0, 1, 2) due to the presence of two cations Hg and Z (Cd, Mn, Zn) in the cation sublattice. The thermal activation of the low-frequency 105 cm⁻¹ mode in the HgMnTe and HgZnTe alloys almost coincides with that observed in HgTe, but the activation energy of the mode for HgCdTe differs substantially from that for HgTe. Moreover, the conditions providing the activation of the 105 cm⁻¹ mode in the n-HgCdTe and p-HgCdTe alloys are different.     

Anisotropic μ+ shift in bismuthshift in bismuth

μSR studies in the semi metal Bi have revealed pronounced anisotropies in the μ⁺ Knightshift which vary strongly with temperature. Above 10 K the anisotropy is well described by a P₂(cosθ) distribution with a change of sign around 60 K. Below 10 K we find a very unusual angular dependence in that the anisotropy is described only by terms of fourth order in the direction cosines. Such a dependence is allowed by symmetry arguments, considering that the pointgroup of the crystalline μ⁺ site is D_3d, but requires that the electrons, responsible for the μ⁺ Knight shift, are subject to strong spin orbit coupling or involve effective, field induced moments of orbital origin. The various types of anisotropies seem to be associated with the different site occupations of the μ⁺. The total Knightshift is generally regative which is to be contrasted with the huge positive Knightshift found in the other semimetal Sb /1/.     

Specific heat and related thermophysical properties of liquid Fe-Cu-Mo alloy

The specific heat and related thermophysical properties of liquid Fe77.5Cu13Mo9.5 monotectic alloy were investigated by an electromagnetic levitation drop calorimeter over a wide temperature range from 1482 to 1818 K. A maximum undercooling of 221 K (0.13 Tm) was achieved and the specific heat was determined as 44.71 J·mol-1·K-1. The excess specific heat, enthalpy change, entropy change and Gibbs free energy difference of this alloy were calculated on the basis of experimental results. It was found that the calculated results by traditional estimating methods can only describe the solidification process under low undercooling conditions. Only the experimental results can reflect the reality under high undercooling conditions. Meanwhile, the thermal diffusivity, thermal conductivity, and sound speed were derived from the present experimental results. Furthermore, the solidified microstructural morphology was examined, which consists of (Fe) and (Cu) phases. The calculated interface energy was applied to exploring the correlation between competitive nucleation and solidification microstructure within monotectic alloy.     

Raman scattering in germanium at high pressure: Isotope effects

The first-order Raman scattering in isotopically enriched samples of germanium ⁷⁰Ge, ⁷²Ge, and ⁷⁴Ge and germanium with the natural isotopic composition is investigated at high pressures. It is found that the isotopic dependence of the frequency of the LTO(Γ) mode in isotopically pure germanium samples can be described in the harmonic approximation (ν∝m ^−1/2). At the same time, the frequency of the LTO(Γ) mode of germanium of natural isotopic composition apparently contains a contribution due to isotopic disorder effects. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 3, 211–214 (10 February 1999)     

Suche nach dem Isomer74mAs

An activity with the decay propertiesT _1/2=(8.0±0.3)sec andE _γ=(283±5)keV has been produced bySchardt andGoodman by proton irradiation of thin layers of evaporated⁷³Ge and⁷⁴Ge on thick gold backings. This activity was interpreted as the new isomer^74mAs. In the present experiment a search for^74mAs was carried out using the reactions⁷⁵As(n, 2n),⁷¹Ga(α, n) and⁷⁴Ge(d, 2n).^74mAs could not be detected. Upper limits for the reaction cross sections were determined. It is discussed that the reported properties of^74mAs resemble the known properties of^197mAu.     

Microstructural,chemical bonding,stress development and charge storage characteristics of Ge nanocrystals embedded in hafnium oxide

We have grown Ge nanocrystals (NCs) (4.0–9.0 nm in diameter) embedded in high-k HfO₂ matrix for applications in floating gate memory devices. X-ray photoelectron spectroscopy has been used to probe the local chemical bonding of Ge NCs. The analysis of Ge–Ge phonon vibration using Raman spectroscopy has shown the formation of compressively stressed Ge NCs in HfO₂ matrix. Frequency dependent electrical properties of HfO₂/Ge-NCs in HfO₂/HfO₂ sandwich structures have been studied. An anticlockwise hysteresis in the capacitance–voltage characteristics suggests electron injection and trapping in embedded Ge NCs. The role of interface states and deep traps in the devices has been thoroughly examined and has been shown to be negligible on the overall device performance.     

Transmission spectra of epitaxial layers of Pb1 ? xEuxTe (0 ≤ x ≤ 0.37) solid solutions in the frequency range 7–4000 cm?1

The spectra of epitaxial Pb_{1 − x} Eu _x Te (0 ≤ x ≤ 0.37) solid solution layers grown on BaF₂ and Si substrates have been investigated over a wide frequency range 7–4000 cm⁻¹ at temperatures of 5–300 K. Apart from the phonon and impurity absorption lines, the absorption in a local mode in PbEuTe layers of substrates and buffer layers has been observed in the frequency range 110–114 cm⁻¹. As the temperature decreases from 300 to 5 K, the transverse phonon mode softens from 33.0 to 19.5 cm⁻¹.     

Fabrication of multilayered Ge nanocrystals embedded in SiOxGeNy films

Multilayered Ge nanocrystals embedded in SiO_xGeN_y films have been fabricated on Si substrate by a (Ge + SiO₂)/SiO_xGeN_y superlattice approach, using a rf magnetron sputtering technique with a Ge + SiO₂ composite target and subsequent thermal annealing in N₂ ambient at 750 °C for 30 min. X-ray diffraction (XRD) measurement indicated the formation of Ge nanocrystals with an average size estimated to be 5.4 nm. Raman scattering spectra showed a peak of the Ge-Ge vibrational mode downward shifted to 299.4 cm⁻¹, which was caused by quantum confinement of phonons in the Ge nanocrystals. Transmission electron microscopy (TEM) revealed that Ge nanocrystals were confined in (Ge + SiO₂) layers. This superlattice approach significantly improved both the size uniformity of Ge nanocrystals and their uniformity of spacing on the ‘Z’ growth direction.     

Search for the invisible axion emitted in the M1 transition in 125m Te

A method of searching for the invisible axion emitted in M transitions of isomeric nuclei is proposed. It is determined experimentally that the probability of emission of an axion in the M1 transition in ^125m Te is ⩽1.3⋅10⁻⁵ (90% confidence level). Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 576–580 (25 April 1997)     

XPS study of the chemical bonding in hydrogenated amorphous germanium–carbon alloys

A systematic study of the chemical bonding in hydrogenated amorphous germanium–carbon (a-Ge_1-xC_x:H)alloys using X-ray photoelectron spectroscopy (XPS) is presented. The films, with carbon content ranging from 0 at. % to 100 at. %, were prepared by the rf co-sputtering technique. Raman spectroscopy was used to investigate the carbon hybridization. Rutherford backscattering spectroscopy (RBS) and XPS were used to determine the film stoichiometry. The Ge 3d and C 1s core levels were used for investigating the bonding properties of germanium and carbon atoms, respectively. The relative concentrations of C–Ge, C–C, and C–H bonds were calculated using the intensities of the chemically shifted C 1s components. It was observed that the carbon atoms enter the germanium network with different hybridization, which depends on the carbon concentration. For concentrations lower than 20 at. %, the carbon atoms are preferentially sp³ hybridized, and approximately randomly distributed. As the carbon content increases the concentration of sp² sites also increases and the films are more graphitic-like. Received: 4 May 1999 / Accepted: 24 November 1999 / Published online: 24 March 2000     

Dielectric properties of epitaxial Pb1−x Sn x Te layers at microwave frequencies

The dielectric properties of epitaxial Pb_1−x Sn _x Te layers are investigated at 9 GHz in a composition range betweenx=0 and 0.225. The samples are characterized by fairly low carrier concentrations between 1.4×10¹⁶ and 32×10¹⁶ cm⁻³. Data of the static dielectric constant (ε ^s ) are obtained at temperatures of 77 and 300 K. The results of ε ^s are 25% to 100% higher compared to previous measurements in bulk material from other authors. The observed higher values of ε ^s in the investigated samples may be due to the reduced number of point defects in epitaxially grown Pb_1−x Sn _x Te layers. The model of Kawamura which predicts a dependence of ε ^s on the effective band gap cannot be verified.