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.     

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.     

Growth of Na modified potassium lithium niobate crystal by the Czochralski method

Transparent Na modified potassium lithium niobate (Na_0.23K_2.60Li_1.82Nb_5.35O_15.70; NKLN) crystal was successively grown by the Czochralski method using RF induction heating from melt composition Na₂O:K₂O : Li₂O:Nb₂O₅=2:30:25:43 mol%. NKLN crystal showed a tetragonal tungsten bronze structure with lattice constants a=12.5446±0.0010 Å and c=4.0129±0.0005 Å at room temperature. The dielectric constant along the c-axis ε₃₃ showed a sharp maximum around 480 °C. Optical transmission edge was 370 nm and optical transmission spectra showed no absorption at wavelengths ranging from 380 to 800 nm. The structural and optical properties of NKLN were similar to those of the near stoichiometric KLN crystals. We believe that the growth of NKLN by the Czochralski method has an advantage for a large size and high-quality crystal.     

Oxygen-pressure dependence of the crystallinity of MgO films grown on Si(1 0 0) by PLD

Effects of the oxygen partial pressure on pulsed-laser deposition of MgO buffer layers on silicon substrates were investigated. The overall growth process was monitored in situ by reflection high-energy electron diffraction (RHEED) method. It was found that the crystallinity and surface morphology of the MgO films were strongly affected by oxygen partial pressure in the deposition chamber. The oxygen-pressure dependence could be explained in terms of interactions of oxygen with species in the plume-like plasma. The MgO film obtained at an optimal oxygen-pressure range of 1×10⁻²–1 Pa exhibited an atomic-smooth and defect-free surface (the root-mean-square roughness being as low as 0.82 nm). For the metal–insulator–metal (MIM) structure of Au/MgO (150 nm)/TiN prepared at the optimal growth conditions achieved a very low leak current density of 10⁻⁷ A cm⁻² at an electric field of 8×10⁵ V cm⁻¹ and the permittivity (ε_r) of about 10.6, virtually the same as that of the bulk MgO single crystals.     

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.     

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.     

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.     

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.     

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 of Y2O3:Eu phosphors by bicontinuous cubic phase process

A novel approach for preparation of red-emitting europium-doped yttrium oxide phosphor (Y₂O₃:Eu) by using the bicontinuous cubic phase (BCP) process was reported in this paper. The BCP system was composed of anionic surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and aqueous yttrium nitrate/europium nitrate solution. Energy dispersive spectrometer analysis revealed the homogeneous precipitation occurred in the BCP structure. Thermogravimetric analysis measurements indicated the precursor powder was europium-doped yttrium hydroxide, Y_1−xEu_x(OH)₃. Scanning electron microscopy micrographs showed the precursor powder had a primary size about 30 nm and narrow size distribution. After heat treatment in furnace above 700 °C for 4 h, high crystallinity Y₂O₃:Eu phosphors was obtained. However, the primary size of particles grew to 50–200 nm and the dense agglomerates with a size below 1 μm were formed. X-ray diffraction patterns indicated the crystal structure of precursor powders and Y₂O₃:Eu phosphors were amorphous and body-centered cubic structure, respectively. The photoluminescence analysis showed that the obtained Y₂O₃:Eu phosphor had a strong red emitting at 612 nm and the quenching started at a Eu concentration of 10 mol%. This study indicated that the BCP process could be used to prepare the highly efficient oxide-based phosphors.     

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.     

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.     

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.     

The tri-methyl-Sb flow and the surfactant time effect on InGaAsN/GaAs-strained MQWs grown by MOCVD

The tri-methyl-Sb flow and the surfactant time dependence of photocurrent (PC) spectra was studied on InGaAsN/GaAs-strained multiple quantum wells (MQWs) structures grown by using metalorganic chemical vapor deposition (MOCVD). The structural properties of InGaAsN/GaAs-strained MQWs were investigated by using high-resolution X-ray diffraction (HRXRD). In the case of InGaAsN/GaAs-strained MQWs, an increase in compressive strain from an analysis of the satellite peaks in HRXRD was observed on increasing the tri-methyl-Sb flow and the surfactant time. For InGaAsN/GaAs-strained MQWs, the peaks observed in the photocurrent spectra were preliminarily assigned to electron–heavy hole (e₁–hh) and electron–light hole (e₁–lh) fundamental excitonic transitions. Their peaks are red-shifted with increasing tri-methyl-Sb flow and surfactant time. But the photocurrent peak is blue-shifted at the surfactant time of . It seems to be due to the improvement of structure properties at interface owing to a surfactant-suppressing surface diffusion phenomenon during growth. We compared this with the result of the experimental energies for InGaAsN/GaAs-strained MQWs.     

Kinetics of dopant incorporation in GaAs grown by organometallic vapor-phase epitaxy

A diffusive capture reaction of dopant atoms by relevant host atoms, via the Rideal–Eley mechanism, in GaAs grown by organometallic vapor-phase epitaxy is shown to result in the dopant concentration in the crystal acquiring a dependence on p_Ga (which is proportional to the growth rate) in agreement with data on S_As, Zn_Ga, and Si_Ga where p_Ga is the partial pressure of trimethylgallium in the input gas stream.     

Ambient-condition growth of superconducting YBa2Cu4O8 single crystals using KOH flux

YBa₂Cu₄O₈ is a stoichiometric oxide superconductor of T_c80 K. Unlike YBa₂Cu₃O_7−δ, this compound is free from oxygen vacancy or twin formation and does not have any microscopic disorder in the crystal. Doping with Ca raises its T_c to 90 K. The compound is a promising superconductor for technological application. Up to now, single crystals have not been grown without using specialized apparatus with extremely high oxygen pressure up to 3000 bar and at over 1100 °C due to the limited range of reaction kinetics of the compound. This fact has delayed the progress in the study of its physical properties and potential applications. We present here a simple growth method using KOH as flux that acts effectively for obtaining high-quality single crystals in air/oxygen at the temperature as low as 550 °C. As-grown crystals can readily be separated from the flux and exhibit a perfect orthorhombic morphology with sizes up to 0.7×0.4×0.2 mm³. Our results are reproducible and suggest that the crystals can be grown using a conventional flux method under ambient condition.     

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.     

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.     

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.     

Edge-defined film-fed growth of Yb:YVO4 single crystal plates

The applicability of the edge-defined film-fed growth (EFG) technique for Yb_xY_(1−x)VO₄ (x=0.05, 0.1 and 1) was approved by successful growth of crystals up to 80 mm in length as the thin plates. Low-angle grain boundaries and the crystal coloration as main defects were found. Optimal seed orientation was suggested on the strength of vanadate crystal plate morphology. Optical properties, chemical composition and the crystalline quality were investigated.