Temperature-dependent structural changes in liquid Ge15Te85

The structure of liquid Ge₁₅Te₈₅ has been studied with neutron diffraction in the liquid state up to 740 °C and in the supercooled liquid state down to 345 °C. The temperature dependences of the diffraction patterns are analyzed. It is shown that the liquid Ge₁₅Te₈₅ can be described by the model of heterogeneous structure, which assumes that the melt consists of atoms joined in clusters and a proportion of atoms with higher mobility that fill the space in between clusters. The number and the size of clusters decrease while the volume fraction of ‘free’ atoms increases under heating.     

Structural and dynamical properties of Fe78Si9B13 alloy during rapid quenching by first principles molecular dynamic simulation

Structural evolution of the Fe₇₈Si₉B₁₃ alloy during rapid quenching was investigated by ab initio molecular dynamics simulation. The second peak splitting has been perceived even at 1473 K in the partial pair correlation functions though not in the total pair correlation function. The (0, 3, 6, 0) polyhedra are abundant in the liquid state while the distorted (0, 3, 6, 0) polyhedra are the featured local structure around B atoms in the amorphous state. The diffusion coefficients of the three elements are evaluated to understand the dynamics of quenching. From 1173 to 873 K the three coefficients are coherent. We think this temperature range corresponds to the supercooled liquid region, and 873 K serves as the glass transition temperature.     

Correlation between the photoluminescence and different types of Si nano-clusters in amorphous silicon

This paper presents the results of PL spectrum study for Si nano-clusters in amorphous silicon matrix. The hydrogenated amorphous Si layers were prepared by the hot-wire CVD method on glass substrates. The layers were deposited at different wafer temperatures 280, 360, 420 and 460 °C and at one filament temperature of 1650 °C. The joint analysis of PL and X-ray diffraction spectra in dependence on the technological conditions and on different sizes of Si nano-clusters has been done. The mechanisms of PL are discussed as well.     

Effect of temperature on the structure of liquid In20Sn80

X-ray diffraction, density and dynamic viscosity measurements on liquid In₂₀Sn₈₀ have been carried out between 300 and 800 °C. An effect of temperature on the atomic structure of molten In₂₀Sn₈₀ is discussed in terms of the model of inhomogeneous structure. It is shown that the structure of liquid In₂₀Sn₈₀ can be presented by atomic clusters with stable composition and atomic packing and a portion of free atoms with higher mobility. The number and the size of clusters decrease and the volume fraction of free atoms increases under heating.     

Electromagnetic stirring and retention to improve segregation in silicon for photovoltaics

The segregation of impurities was investigated during the crystallization of upgraded metallurgical grade silicon (UMG Si). An experimental solidification system has been developed, including a strong electromagnetic stirring in order to mix the melt, to increase the effective segregation coefficient.Our crucible has a slit-like opening at the bottom of a face, to be adapted to ribbon pulling for future developments of a crystallization system for the photovoltaic industry. The electromagnetic system allowed retaining the liquid silicon inside the crucible during the crystallization of an ingot (thickness ～5 cm), or make it flow out after the partial crystallization of a bottom layer (thickness ～2 mm).Starting from UMG Si of known composition, the chemical analysis of the impurity concentrations in that multicrystalline material shows an efficient purification, despite the rather high crystallization speed (estimated between 9 and 20 cm/h). Phosphorous concentration was reduced from 6 to 1.7 ppm during the segregation, which is difficult to achieve for this impurity, which has a segregation coefficient close to unity (k₀=0.3).     

Internal friction behavior of liquid AsxTe1−x mixtures

The internal friction technique was applied to investigate the structure properties of liquid As_xTe_1−x mixtures. A well-pronounced peak was observed in the curve of internal friction as a function of temperature in the liquid As_xTe_1−x (x ⩽ 40 at.%), suggesting that an abnormal structural change may take place in this system. The appearance of this internal friction peak during both heating and cooling processes indicates that the abnormal behavior is reversible in the molten As–Te system. Further analysis indicates that the internal friction peak observed in As_xTe_1−x (x ⩽ 40 at.%) melts may be associated with the decomposition of As₂Te₃ clusters with the increase in temperature.     

Characterization and coagulation performance of solid poly-silicic–ferric (PSF) coagulant

An inorganic polymer, liquid poly-silicic–ferric (PSF) coagulant, with different Si/Fe molar ratios was prepared using water glass, FeSO₄ · 7H₂O and NaClO₃ by co-polymerization. The solid PSF made from liquid PSF by two different solidification approaches was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. A comparison of coagulation behavior between PSF and polyferric sulfate (PFS) was explored. The results indicate that PSF is a complexation compound of Si, Fe and other ions, instead of a simple mixture of raw materials. The surface morphology of solid PSF is a function of the solidification method and the Si/Fe ratio. The reaction time needed in preparing solid PSF with excellent coagulation performance is shorter than that in liquid PSF. The solidification process is not a simple dehydration from liquid coagulant, but a re-preparation process. The optimal dose by PSF is 7.5 mg/L according to residual turbidity, in comparison with 10.5 mg/L by PFS. PSF has higher UV₂₅₄ removal than PFS, with a difference from 10% to 60% at given dose range. When settling time with solid PSF as coagulant increases, the slight reduction of turbidity removal caused by solidification can be retarded, and the removal of dissolved organic matters can be improved.     

Ion beam synthesis of C-based optically-active nanoclusters in silica

Carbon nanoclusters formed using ion implantation and thermal annealing are shown to photoluminescence in the visible range. Silica samples were implanted with a fluence of 2 × 10¹⁷ atoms/cm², 70 keV carbon ions and thermally annealed for 4 h at 1100 °C. Photoluminescence measurement made at select intervals during the anneal process show continued growth of the nanoclusters within the silica throughout the process. However, Rutherford backscattering showed a rapid loss of carbon during the initial 15 min of annealing indicating a competition between the growth of the second-phase nanoparticles and the formation of CO, a volatile form of carbon.     

The effect of copper ions addition on structural and optical properties of zinc borate glasses

Glasses in the ternary system xCuO?(100 ? x)[55B₂O₃·45ZnO] (0 ≤ x ≤ 20 mol%) have been prepared by melting at 1200 °C and rapidly cooling at room temperature. The effect of copper ions addition in 55B₂O₃·45ZnO glass matrix together with the matrix effect on paramagentic behavior has been investigated using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, differential thermal analysis (DTA), electron paramagnetic resonance (EPR), ultraviolet–visible (UV–VIS) spectroscopy and density measurements. The increase of the number of non-bridging oxygen (NBO) atoms as a function of CuO content in these glasses leads to the decrease of glass polymerization which reduces the stability of the glasses and favors the association of copper ions in clusters. This leads to the major changes of structural and optical properties of the studied glasses as can be seen from the data obtained by FTIR and EPR spectroscopies.     

Electronic structure and properties of liquid caesium up to critical point by LMTO calculations

It is well-known that liquid caesium shows some unusual properties at low densities. We used supercell technique within linear muffin-tin orbital method to investigate this phenomenon. Electronic structure of liquid caesium for different temperatures from the melting point up to critical point was obtained. The atomic structure was simulated for a cluster of 2000 atoms by the Reatto method on the base of experimental structure factors of Cs obtained by Winter and co-workers for different temperatures (from 323 K up to 1923 K). The Kubo–Greenwood formula was applied for the calculations of melts conductivity. The received results indicate that metal–nonmetal transition in liquid cesium is connected not to the gap at Fermi energy in density of electronic states, but more likely with electrons localization on some kind of atomic clusters.     

Solid–liquid interface energies in the succinonitrile and succinonitrile–carbon tetrabromide eutectic system

The equilibrated grain boundary groove shapes for the commercial purity succinonitrile (SCN) and succinonitrile–carbon tetrabromide (CTB) eutectic system were directly observed. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficients for the solid SCN–liquid SCN and solid SCN–liquid SCN CTB have been determined to be (5.43±0.27)×10⁻⁸ Km and (5.56±0.28)×10⁻⁸ Km, respectively, with numerical method. The solid–liquid interface energies for the solid SCN–liquid SCN and solid SCN–liquid SCN CTB have been obtained to be (7.86±0.79)×10⁻³ J m⁻² and (8.80±0.88)×10⁻³ J m⁻², respectively from the Gibbs–Thomson equation. The grain boundary energies in the SCN and SCN rich phase of the SCN–CTB system have been calculated to be (15.03±1.95)×10⁻³ J m⁻² and (16.51±2.15)×10⁻³ J m⁻², respectively, from the observed grain boundary groove shapes. The thermal conductivity ratios of the liquid phase to the solid phase for SCN and SCN–4 mol% CTB alloy have also been measured.     

X-ray diffraction measurements for liquid Ge–Si alloys using synchrotron radiation

Energy dispersive X-ray diffraction measurements have been carried out for liquid Ge_1−xSi_x alloys (x = 0.0, 0.3, 0.5, 1.0) using synchrotron radiation at SPring-8. We measured the X-ray diffraction spectra of liquid Ge and Si up to a high temperature range, (liquid Ge from 1270 to1870 K and liquid Si from 1680 to 2020 K), liquid Ge_0.7Si_0.3 at 1620 K, and liquid Ge_0.5Si_0.5 at 1540, 1590, 1670 and 1720 K. The total structure factors of the liquid Ge–Si alloys have a characteristic shoulder on the high-wave-vector side of the first peak. We deduced a pair distribution function from the Fourier transform of the observed structure factor, which was weakly dependent on the temperature. The nearest-neighbor coordination number of liquid Ge–Si alloys is close to that of pure liquid Ge and Si. The first peak of the pair distribution function moved to a shorter distance with increasing Si concentration. These results may indicate that the atomic radii of the Si and Ge atoms in the pure liquid are preserved in the liquid alloys.     

Magnetostatic bias in soft/hard bi-phase layered materials based on amorphous ribbons and microwires

Bi-phase soft/hard magnetic systems have been prepared by electroplating CoNi alloy with relative hard magnetic character (10² Oe coercivity) onto ultrasoft (coercivity less than 1 Oe) FeCo-based amorphous alloys prepared by rapid solidification techniques. Experiments have been performed in planar (ribbons) and cylindrical (microwires) configuration. Low-field hysteresis loops after premagnetizing to saturation are ascribed to the magnetization reversal process of the soft inner phase, while harder component remains close to its remanence. Such low-field loops exhibit a shift typical of magnetic bias phenomena which in this case is ascribed to the magnetostatic coupling originated through the stray fields created by uncompensated charges at the ends of the harder phase.     

The preferential orientation of the directionally solidified Si–TaSi2 eutectic in situ composite

The Si–TaSi₂ eutectic in situ composite is a favorable field emission material due to relatively low work function, good electron conductivity, and three-dimensional array of Schottky junctions grown in the composite spontaneously. The preferential orientation during directional solidification is determined by the growth anisotropy. In order to obtain the preferential direction of the steady-state crystal growth, the transmission electron microscopy (TEM) is used for analysis. It is found that the preferential orientation of the Si-TaSi₂ eutectic in situ composite prepared by Czochralski (CZ) technique is [3 3¯ 2¯] Si∥[0 0 0 1] TaSi₂, (2 2 0)Si∥(2 2¯ 0 0) TaSi₂. Whereas the preferential orientation of the Si–TaSi₂ eutectic in situ composite prepared by electron beam floating zone melting (EBFZM) technique is [0 1¯ 1¯ ]] Si∥[0 0 0 1] TaSi₂,(0 1¯ 1) Si∥(0 1¯ 1 1)TaSi₂. The preferential directions of the Si-TaSi₂ eutectic in situ composites prepared by two kinds of crystal growth techniques are distinctly different from each other, which results from different solid–liquid interface temperatures on account of the different crystal growth conditions, e.g. different solidification rate, different temperature gradient, different solid–liquid interface curvature and different kinetic undercooling.     

Electronic properties of liquid noble metal–Si alloys

The electrical resistivity, ρ, of liquid noble metal–Si alloys (M_1−cSi_c, M = Cu, Ag, Au) increases rapidly with the addition of Si to liquid noble metals. The composition dependence of ρ exhibits a maximum at the composition c = 0.3, 0.4 and 0.4 for liquid Cu–Si, Ag–Si and Au–Si, respectively. A positive to negative transition of thermoelectric power, S, is observed at c = 0.3, 0.15 and 0.1 for liquid Cu–Si, Ag–Si and Au–Si, respectively. Their composition dependence of S reaches a minimum value in the composition range c = 0.6–0.8. The experimental results of ρ and S have been analyzed using the Faber–Ziman theory. The composition dependence of χ for liquid Cu–Si and Au–Si alloys exhibits a clear deviation from a straight line on the noble metal-rich side. As a result, liquid Cu–Si and Au–Si alloys have a minimum in the composition dependence of paramagnetic susceptibility.     

Effects of vicinal angles from (0 0 1) surface on the Boron-doping features of high-quality homoepitaxial diamond films grown by the high-power microwave plasma chemical-vapor-deposition method

Vicinal surface effects on homoepitaxial growth and boron-doping processes have been studied in case of single-crystalline diamond (0 0 1) surfaces grown using the high-power microwave plasma chemical-vapor-deposition (MWPCVD) method. The off-angles inclined from the on-orientation (0 0 1) surfaces ranged to 5° along the [1 1 0] or [1 0 0] direction, while the concentration of doping B(CH₃)₃ gas was kept constant with a B/C ratio of 50 ppm. Although a number of square-like growth hillocks often appeared, depending substantially on the crystalline quality of the high-pressure/high-temperature-synthesized (HPHT) Ib diamond substrates employed, the number and shape of the hillocks changed significantly with the increasing off-angle. For the vicinal surfaces with off-angles of ≈3° inclined along the [1 1 0] direction, macroscopically flat surfaces were obtained, compared with the other off-angle cases examined. Furthermore, the growth rate and acceptor density of substitutional boron atoms in the homoepitaxial layers were found to substantially increase with the increasing off-angle. These indicate that the step density can play important roles not only in the homoepitaxial growth but also in the boron-incorporation process during the high-power MWPCVD growth.     

Self-assembling of supramolecular erbium–oxygen clusters in magnetron plasma,and the optimization of erbium luminescence in a-SiOx:H〈Er, O〉 films

Films of erbium-doped amorphous hydrogenated silicon a-SiO_x:H〈Er, O〉 were fabricated by dc-magnetron sputtering at different concentrations of oxygen in the magnetron plasma and different areas of erbium metallic target. It was demonstrated that the increase of oxygen concentration in the plasma gaseous phase above ∼5 mol% leads to a sharp rise in the amount of oxygen bound to erbium in the a-SiO_x:H〈Er, O〉 films. Simultaneously, a smooth increase in the concentration of oxygen bound to matrix-forming elements (silicon, hydrogen) is observed. The increase of the area of erbium target, corresponding to the rise of concentration of erbium ions in the plasma, also favors the binding of erbium with oxygen. However, the content of erbium in the a-SiO_x:H〈Er, O〉 film (in atomic percents) significantly drops with intense binding of erbium with oxygen. These facts point to the formation of erbium–oxygen clusters, with a large number of oxygen atoms, which are probably formed in the magnetron plasma but are deposited as a separate species on the substrate in the reaction chamber. The intensity of erbium photoluminescence rises significantly in the region of formation of these large erbium–oxygen clusters. A ‘phase-transition’ model is formulated, describing the properties of a-SiO_x:H〈Er, O〉 films, based on the assumption of the formation of large erbium–oxygen clusters in the magnetron plasma. The size and composition of these clusters are determined. The model is semi-quantitatively consistent with all the experimental findings.     

Atomic order in magnetic Mn inclusions in Si crystals: XAS and TEM studies

A Si (1 0 0) crystal implanted with Mn⁺ ions, exhibiting ferromagnetic properties, was studied with XAS and TEM to examine the local atomic order around Mn atoms. The advantage of the XAS technique was its elemental selectivity, which allowed extracting information on the atomic surroundings of Mn atoms even at very low concentrations of this element, incapable of producing a signal in X-ray diffraction. It is very important to find out what is responsible for the ferromagnetism of this new class of materials. The knowledge of the location of Mn atoms in the Si crystal lattice is crucial in developing models of ferromagnetic interactions. The performed studies have proven beyond doubt that Mn atoms are not located randomly in the Si crystalline matrix but form Mn–Si clusters immersed in a strained Si matrix. Assuming the atomic order and dimensions of the cluster found through EXAFS and HRTEM, we have reproduced the electronic structure of Mn atoms by modeling the XANES spectrum in agreement with the experimental one.     

Computer simulation of GeO2 liquid

The local structure and dynamic of liquid GeO₂ have been investigated by mean of molecular dynamics simulation. We have prepared 13 systems upon pressure ranging from −0.41 to 48.9 GPa. The local structure was analyzed through the pair radial distribution function, coordination number and bond-angle statistics, the characteristics of voids and void aggregations. Two kinds of void aggregations have been examined: void clusters and void tubes. It was found a large number of vacancy-like voids and microscopic cavities in low-density system. Furthermore, there is a large void tube consisting of 94% oxygen vacancy-like voids and it spreads over whole system. The considerable changes in dynamic and local structure between high-density and low-density systems indicated the possibility of the liquid–liquid phase transition.