Densities of Li2O–B2O3 melts

The densities have been systematically measured in xLi₂O–(1−x)B₂O₃ melts of different compositions with Li₂O content varying from x=0 to 0.68 from their respective melting points up to about 1450 K with a modified Archimedean method. The density decreased with increasing temperature for all the melts measured in this work. When x<0.15, the plot of temperature versus density could be well fitted by a quadratic polynomial function, and when x0.15, density decreased linearly with increasing temperature. At a fixed temperature, the density of the melts increased rapidly with Li₂O content, went through a maximum at about x=0.333 (Li₂O–2B₂O₃), and then decreased slowly as Li₂O content was further increased. In addition, the volume expansion coefficient (β) was calculated based on the densities measured in this work, and it was found that a maximum value appeared in the dependence of β on the molar ratio of Li₂O at about x=0.333.     

Hydrothermal growth of single-crystal CaV6O16·3H2O nanoribbons

CaV₆O₁₆·3H₂O nanoribbons have been prepared by the hydrothermal method in the presence of sodium dodecyl sulfate (SDS) at 160°C for 10 h. X-ray diffraction pattern indicates that the sample is monoclinic phase of CaV₆O₁₆·3H₂O with the lattice contents a=12.18 Å, b=3.598 Å, c=18.39 Å, β=118.03°. Field emission scanning electron microscopy shows that the nanoribbons have widths in the range of 150–500 nm, thicknesses of 30–60 nm and lengths of 500 mm X-ray photoelectron spectrum measurements further confirm the formation of the CaV₆O₁₆·3H₂O phase. The formation of CaV₆O₁₆·3H₂O nanoribbons is a self-assembling process, in which surfactant SDS plays the role of soft template.     

Growth of single crystals of the new double perovskite Ba2HoRu1−xCuxO6 from high temperature solutions

Single crystals of Ba₂HoRu_1−xCu_xO₆ have been grown from high temperature solutions using PbO–PbF₂ as solvent in the temperature range 1150–1250 °C. Crystals with a six sided plate like morphology measuring up to 3 mm across and 0.5 mm thick and polyhedral habit measuring up to 2 and 1 mm in thick mass were obtained. Powder X-ray diffraction patterns obtained on the crystals were indexed to give a monoclinic space group P2₁/n with lattice parameters a=5.875(2), b=5.874(3), c=8.960(1) and β=89.995(2)°. The crystals with x=0 show a single anomaly at 6.5 K corresponding to an antiferromagnetic phase with . The crystals containing Cu show additional anomalies at 18 and 48 K. The SEM and EDS analysis reveals a 2116 phase.     

A simple method to synthesize single-crystalline β-wollastonite nanowires

The single-crystalline β-wollastonite (β-CaSiO₃) nanowires were prepared via a simple hydrothermal method, in the absence of any template or surfactant using cheap and simple inorganic salts as raw materials. Xonotlite [Ca₆(Si₆O₁₇)(OH)₂] nanowires were first obtained after hydrothermal treatment at a lower temperature of 200 °C for 24 h, and after being calcinated at 800 °C for 2 h, xonotlite nanowires completely transformed into β-wollastonite nanowires and the wire-like structure was preserved. The synthesized β-wollastonite nanowires had a diameter of 10–30 nm, and a length up to tens of micrometers, and the single-crystalline monoclinic parawollastonite structured β-wollastonite was identified by XRD with the space group of P2₁/a and cell constants of a=15.42 Å, b=7.325 Å, c=7.069 Å and β=95.38°. A possible growth mechanism of β-wollastonite nanowires was also proposed. The advantages of this method for the nanowire synthesis lie in the high yield, low temperature and mild reaction conditions, which will allow large-scale production at low cost.     

Porous crystal structures obtained from directionally solidified eutectic precursors

Interconnecting cage-like porous structures of several halide compounds were prepared by the selective leaching of one eutectic phase method. The binary eutectic precursors were prepared by directional solidification using the Bridgman crystal growth technique. Porous NaMgF₃ (40% pore volume), CaF₂ (57% pore volume) and BaF₂ (43% pore volume) crystals were obtained after water leaching the NaF component of the directionally solidified NaF/NaMgF₃, NaF/CaF₂ and NaF/BaF₂ eutectics with the appropriate entangled microstructure. The growth conditions for eutectic-coupled growth and the morphology of the eutectics have been determined. In the coupled growth regime, the size of the eutectic phases “λ” is fairly uniform and varies with the eutectic growth rate “v” as λ²v=constant, which allows us to control the pore size within the 0.5–10 μm range. The simplicity and versatility of the eutectic growth also allows us to fabricate highly aligned porous structures at relatively high production rates.     

Synthesis, thermal and magnetic properties of new metal iodate: (LiFe1/3)(IO3)2

This paper reports the detail synthesis of a new kind of metal iodate, anhydrous (LiFe_1/3)(IO₃)₂, from aqueous solutions. The synthesized compound shows spinal morphology and is chemical stable up to 400°C. The iodate shows paramagnetic behavior from room temperature down to 4.2 K. At room temperature, the new compound has a hexagonal structure with the lattice parameters a=5.4632(2) Å, c=5.0895(6) Å, Z=1, space group of P6₃.     

Metalorganic vapor-phase epitaxy of III/V phosphides with tertiarybutylphosphine and tertiarybutylarsine

Indium phosphide, gallium arsenide phosphide, and aluminum indium phosphide have been deposited by metalorganic vapor-phase epitaxy using tertiarybutylphosphine and tertiarybutylarsine. The effects of growth temperature and V/III ratio on the amount of silicon, sulfur, carbon, and oxygen in InP have been determined. Minimum incorporation was observed at 565 °C and a V/III ratio of 32. In this case, the material contained a background carrier concentration of 2.7×10¹⁴ cm⁻³, and the Hall mobilities were 4970 and 135,000 cm²/V s at 300 and 77 K. The oxygen contamination in AlInP was found to be only 9.0×10¹⁵ cm⁻³ for deposition at 650 °C and a V/III ratio of 35. The relative distribution of arsenic to phosphorus in GaAs_yP_1−y was determined at temperatures between 525 and 575 °C. The distribution coefficient [(N_As/N_P)_film/(P_TBAs/P_TBP)_gas] ranged from 25.4 to 8.4, and exhibited an Arrhenius relationship with an apparent activation energy of 1.2 eV.     

Mechanochemical–hydrothermal synthesis of hydroxyapatite from nonionic surfactant emulsion precursors

Nanocrystalline hydroxyapatite [HA, Ca₁₀(PO₄)₆(OH)₂] powders were synthesized by the mechanochemical–hydrothermal method using emulsion systems consisting of aqueous phase, petroleum ether (PE) as the oil phase and biodegradable Tomadol 23–6.5 as the nonionic surfactant. (NH₄)₂HPO₄ and Ca(NO₃)₂ or Ca(OH)₂ were used as the phosphorus and calcium sources, respectively. The calcium source and emulsion composition had significant effects on the stoichiometry, crystallinity, thermal stability, particle size and morphology of final products. Disperse HA crystals with a 160 nm length and aspect ratio of ca. 6 were formed in an emulsion system containing 10 wt% PE, 60 wt% water and 30 wt% surfactant. The HA particles had needle morphology with a specific surface area of . With this technique, HA nanopowders with specific surface areas in the range of 72– were produced.     

Diffusion of Zn in stoichiometric LiTaO3

As stoichiometric LiTaO₃ (LT) draws a considerable attention for integrated optical waveguide devices, we have investigated Zn diffusion into this material by diffusing 70- nm-thick ZnO films deposited on y-cut LT substrates at 700–900 °C under various atmospheres. It was observed that the surface quality was very sensitive to pressure, but weakly affected by other diffusion conditions such as temperature and atmosphere. While the surface degraded, being covered with some residuals after heat treatment at the atmospheric pressure, it was very smooth and clear when the pressure was lowered below about 10 Torr. Another feature of Zn-diffused stoichiometric LT is that the crystal maintains its transparency even after diffusion at a pressure as low as 0.1 Torr, thus without a post-annealing step required. The diffusion coefficient varied from D=1.1×10^-2 to 5.5×10⁻¹ μm²/h in the given temperature range, with an activation energy of .     

A study of the degree of relaxation of AlGaN epilayers on GaN template

The strain state of 570 nm Al_xGa_1−xN layers grown on 600 nm GaN template by metal organic chemical vapor deposition was studied using Rutherford backscattering (RBS)/channeling and triple-axis X-ray diffraction measurements. The results showed that the degree of relaxation (R) of Al_xGa_1−xN layers increased almost linearly when x0.42 and reached to 70% when x=0.42. Above 0.42, the value of R varied slowly and Al_xGa_1−xN layers almost full relaxed when x=1 (AlN). In this work the underlying GaN layer was in compressive strain, which resulted in the reduction of lattice misfit between GaN and Al_xGa_1−xN, and a 570 nm Al_xGa_1−xN layer with the composition of about 0.16 might be grown on GaN coherently from the extrapolation. The different shape of (0 0 0 4) diffraction peak was discussed to be related to the relaxation.     

Textural properties of synthetic nano-calcite produced by hydrothermal carbonation of calcium hydroxide

The hydrothermal carbonation of calcium hydroxide (Ca(OH)₂) at high pressure of CO₂ (initial P_CO2=55 bar) and moderate to high temperature (30 and 90 °C) was used to synthesize fine particles of calcite. This method allows a high carbonation efficiency (about 95% of Ca(OH)₂–CaCO₃ conversion), a significant production rate (48 kg/m³ h) and high purity of product (about 96%). However, the various initial physicochemical conditions have a strong influence on the crystal size and surface area of the synthesized calcite crystals. The present study is focused on the estimation of the textural properties of synthesized calcite (morphology, specific surface area, average particle size, particle size distribution and particle size evolution with reaction time), using Rietveld refinements of X-ray diffraction (XRD) spectra, Brunauer–Emmett–Teller (BET) measurements, and scanning electron microscope (SEM) and transmission electron microscope (TEM) observations. This study demonstrate that the pressure, the temperature and the dissolved quantity of CO₂ have a significant effect on the average particle size, specific surface area, initial rate of precipitation, and on the morphology of calcium carbonate crystals. In contrast, these PTx conditions used herein have an insignificant effect on the carbonation efficiency of Ca(OH)₂.

Finally, the results presented here demonstrate that nano-calcite crystals with high specific surface area (S_BET=6–10 m²/g) can be produced, with a high potential for industrial applications such as adsorbents and/or filler in papermaking industry.     

Boron segregation control in silicon crystal ingots grown in Czochralski process

Boron-doped silicon single crystals of 207 mm diameter with various growing conditions are grown from a large amount of the melt in the cusp-magnetic Czochralski method, and the effects of growing parameters on dopant concentrations in the crystals are experimentally investigated. Equilibrium distribution coefficient of boron calculated by BPS model is 0.716. With the crystal rotation (ω) of 13 rpm and the crucible rotation of , the effective distribution coefficient (k_e) is 0.751 in zero magnetic strength and increases up to 0.78 in the magnetic strength of 640 G. For , there is no significant influence of ω on k_e. With , k_e is almost unity. The experimental results are compared with theory.     

Nucleation of AlN on SiC substrates by seeded sublimation growth

The nucleation of aluminum nitride (AlN) on silicon carbide (SiC) seed by sublimation growth was investigated. Silicon-face, 8 off-axis 4H-SiC (0 0 0 1) and on-axis 6H-SiC (0 0 0 1) were employed as seeds. Initial growth for 15 min and extended growth for 2 h suggested that 1850 °C was the optimum temperature of AlN crystal growth: on an 8 off-axis substrate, AlN grew laterally forming a continuous layer with regular “step” features; on the on-axis substrate, AlN grew vertically as well as laterally, generating an epilayer with hexagonal sub-grains of different sizes. The layer's c-lattice constant was larger than pure AlN, which was caused by the compression of the AlN film and impurities (Si, C) incorporation. Polarity sensitive and defect selective etchings were performed to examine the surface polarity and dislocation density. All the samples had an Al-polar surface and no N-polar inversion domains were observed. Threading dislocations were present regardless of the substrate misorientation. Basal plane dislocations (BPDs) were revealed only on the AlN films on the 8 off-axis substrates. The total dislocation density was in the order of when the film was 20– thick.     

Synthesis and characteristics of Na-doped Bi4Ti3O12 thin films on Si substrate

Bi_3.25Na_2.25Ti₃O₁₂ thin films were prepared on p-Si(1 1 1) substrate by a metalorganic solution decomposition (MOSD) method. The structural characteristic and crystallization of the films were examined by X-ray diffraction. The current–voltage characteristic shows ohmic conductivity in the lower voltage range and space-charge-limited conductivity in the higher voltage range. The dielectric constant is 53 at a frequency of 100 kHz at room temperature and the dissipation factor exists at a minimal value of 0.02 at a frequency of 200 kHz. The retention time estimated by measuring capacitance is about 10⁶ s. Nonhysteretic C–V curves at various frequencies were also collected.     

Determination of kinetic parameters of crystal growth rate of borax in aqueous solution by using the rotating disc technique

Growth rate of polycrystalline disc of borax compressed at different pressure and rotated at various speed has been measured in a rotating disc crystallizer under well-defined conditions of supersaturation. It was found that the mass transfer coefficient, K, increased while overall growth rate constant, K_g, and surface reaction constant, k_r, decreased with increasing smoothness of the disc. It was also determined that kinetic parameters (k_r,r,K,g) of crystal growth rate of borax decreased with increasing rotating speed of the polycrystalline disc. The effectiveness factor was calculated from the growth rate data to evaluate the relative magnitude of the steps in series bulk diffusion through the mass transfer boundary layer and the surface integration. At low rotating speed of disc, the crystal growth rate of borax is mainly controlled by integration. However, both diffusion and integration steps affect the growth rate of borax at higher rotating speed of polycrystalline disc.     

Oriented growth of large size calcium fluoride single crystals for optical lithography

We report (1 1 1), (1 1 0) and (1 0 0) growth of CaF₂ by the vertical Bridgman method. Crystals up to 250 mm diameter were grown and various growth parameters such as growth rate, temperature gradient and post-growth cooling rate were studied. It was found that the growth rate and the cooling rate are slower for the larger diameter crystals with a fixed temperature gradient. These growth parameters were optimized for growing the crystals along specific orientation after realizing that CaF₂ has a tendency to grow along an orientation close to 1 1 0. Degradation in optical transmittance was evaluated by irradiating the crystal to γ-rays up to a dose of 10⁵ rad. Optimized scavenger addition resulted in crystals with better radiation resistance and excellent VUV transmittance.     

High-temperature growth of very high germanium content SiGe virtual substrates

We have first of all studied (in reduced pressure–chemical vapour deposition) the high-temperature growth kinetics of SiGe in the 0–100% Ge concentration range. We have then grown very high Ge content (55–100%) SiGe virtual substrates at 850 °C. We have focused on the impact of the final Ge concentration on the SiGe virtual substrates’ structural properties. Polished Si_0.5Ge_0.5 virtual substrates were used as templates for the growth of the high Ge concentration part of such stacks, in order to minimize the severe surface roughening occurring when ramping up the Ge concentration. The macroscopic degree of strain relaxation increases from 99% up to values close to 104% as the Ge concentration of our SiGe virtual substrates increases from 50% up to 100% (discrepancies in-between the thermal expansion coefficients of Si and SiGe). The surface root mean square roughness increases when the Ge concentration increases, reaching values close to 20 nm for 100% of Ge. Finally, the field (the pile-up) threading dislocations density (TDD) decreases as the Ge concentration increases, from 4×10⁵ cm⁻² (1–2×10⁵ cm⁻²) for [Ge]=50% down to slightly more than 1×10⁵ cm⁻² (a few 10⁴ cm⁻²) for [Ge]=88%. For [Ge]=100%, the field TDD is of the order of 3×10⁶ cm⁻², however.     

Compositional plane of a wide-gap semiconductor CaCdSeS lattice-matched to InP and GaAs

We have investigated compositional plane of a wide band gap solid solution semiconductor Ca_1−xCd_xSe_1−yS_y (x0.32) using powder synthesis under thermal equilibrium condition. The solubility limit at 1273 K varies with respect to the Se concentration y, taking a minimum Cd solubility limit of 0.12 at y=0.8 and a maximum limit of 0.32 at y=1.0. It is found that the system can be lattice-matched to GaAs and InP under covering the energy band gap of ultraviolet–visible region. These results allow to design optoelectronic devices adopting the Ca_1−xCd_xSe_1−yS_y system.     

Growth and morphology of ruby crystals with unusual chromium concentration

Single crystals of ruby have been obtained from fluxed melts based on the systems Li₂O–MoO₃, Li₂O–WO₃, Na₂O–WO₃, 2PbO–3V₂O₅, PbO–V₂O₅–WO₃, PbF₂–Bi₂O₃ and Na₃AlF₆ by both the TSSG method and spontaneous crystallization at the temperatures 1330–900 °C. Al₂O₃ solubility has been measured for the flux composition of 2Bi₂O₃–5PbF₂ in the temperature range 1200–1000 °C and dissolution enthalpy has been defined as 29.4 KJ/Mol. The composition of grown crystals was studied by electron microprobe analysis. The synthetic ruby contains from 0.51 to 6.38 at% of chromium admixture depending on the crystal growth conditions. Experimental results on growth conditions, composition and morphology of grown crystals are presented for each flux and temperature interval.     

Diffusion of vanadium in GaAs

The diffusion of Vanadium has been studied in V-doped GaAs layers (GaAs:V) grown by Metal-Organic Chemical Vapour Deposition (MOCVD) using secondary ion mass spectroscopy (SIMS). The vanadium (V) concentration profiles of sandwiched structures made of alternatively undoped and V doped GaAs layers have shown a concentration independent diffusion coefficient (D_V) for varying V doping levels from 10¹⁸ to 10¹⁹ cm⁻³. Measurements of D_V at 550, 615 and 680 °C indicate that the temperature dependence of D_V can be represented by the Arrhenius equation:  cm² s⁻¹. It is suggested that V diffuses via interstitial sites.