Growth and scintillation properties of the Na2W2O7 crystal

The growth and scintillation properties of the Na₂W₂O₇ crystal are reported. The solid reaction between Na₂CO₃ and WO₃ is used to synthesise the Na₂W₂O₇ material. The Na₂W₂O₇ single crystal has been grown by the Bridgman method. And the Na₂W₂O₇ single crystal with sizes 14×7×6 mm³ has been achieved. The transmission spectra, the Ultraviolet fluorescence spectra and the X-ray excited luminescence spectra of the Na₂W₂O₇ crystal are measured. The measurement results show that the Na₂W₂O₇ crystal is a promising intrinsic scintillator.     

Effect of lattice oxygen on optical absorption, radiation hardness and thermally stimulated luminescence of BaF2 crystal

The influence of the presence of BaO impurity on the optical absorption, radiation hardness and thermally stimulated luminescence of BaF₂ has been investigated. The presence of oxygen impurity gives rise to three absorption bands in the UV region, peaking around 220, 280 and 335 nm. Further, the impurity is found to be detrimental to crystal hardness against ionizing radiations. The thermally stimulated luminescence (TSL) has been studied from gamma-irradiated crystals containing different fractions of BaO impurity. Four prominent glow peaks around 100°C (peak I), 150°C (peak II), 220°C (peak III) and 290°C (peak IV) are observed for crystals containing BaO impurity concentrations lower than 0.5% (by wt). For crystals containing higher impurity concentrations, two additional peaks around 75°C and 260°C are also observed. The kinetics of TSL emission is observed to be of first order, implying that the absorption and the emission centers responsible for TSL are the same. The normalized TSL output for peak I is found to vary linearly with the concentration of oxide impurity. This fact can be utilized to detect the presence of minute amounts of oxygen in BaF₂ lattice, which is crucial to the growth of crystals exhibiting high radiation hardness.     

Growth and characterization of organic material 4-nitrobenzaldehyde single crystal using modified vertical Bridgman technique

The organic material 4-nitrobenzaldehyde single crystal has been grown using the single wall ampoule with nano-translation by modified vertical Bridgman technique. The grown crystal was confirmed by single and powder X-ray diffraction (XRD). Fourier transform infrared (FTIR) analysis was used to identify the functional groups present in the grown crystal. The optical property of the grown crystal was analyzed by UV–vis–NIR and photoluminescence (PL) spectral measurements. The thermal characteristics of the grown crystal were analyzed by thermogravimetric (TG) and differential thermal analyses (DTA). The dielectric measurements were carried out with four different frequencies and the results indicate an increase in dielectric and conductivity parameters with the increase of temperature at all frequencies. The microhardness measurements were used to analyze the mechanical property of the grown crystal.     

Estimation of growth rate in unidirectionally solidified multicrystalline silicon by the growth-induced striation method

Multicrystalline silicon was grown by unidirectional solidification method using the accelerated crucible rotation technique. The application of the accelerated crucible rotation technique in unidirectional solidification method induced growth striations across the axial direction of the grown crystal. This striation pattern was observed from carbon concentration distribution, obtained by using Fourier transform infrared spectroscopy. The generated striation pattern was found to be weak and discontinuous. Some striations were absent, probably due to back melting, caused during each crucible rotation. From the growth striations and applied time period in crucible rotation, the growth rate was estimated by using Fourier transformation analysis.     

Bridgman growth and site occupation in LuAG:Ce scintillator crystals

LuAG:Ce single crystals with various activator concentrations were grown by the vertical Bridgman technique. Characterization of crystals was done in terms of actual doping level, macroscopic defects and degree of non-equivalent substitutions by Lu for Al in octahedral lattice sites. Scintillation measurements were performed using 2×2×8 mm³ shaped samples with Ce concentration in the range 0.05–0.55 at%. Essential improvement of performance was demonstrated in samples containing ≥0.2 at% of Ce; the light yield measured in LuAG:Ce (0.55 at%) was about 26000 ph/MeV, or close to that of LSO.     

Impurity segregation in directional solidified multi-crystalline silicon

In this paper numerical results on the impurity segregation in directional solidified multi-crystalline silicon are presented and compared with experimental results. A solute transport model has been established to predict the final segregation pattern of impurities in the ingot. The segregation is analyzed experimentally on the basis of Fourier transform infrared (FTIR) spectroscopy and glow-discharge mass spectrometry (GDMS). Precipitates were located by IR-transmission microscopy (IRM). Qualitative agreement between simulation and experiment is found. It is demonstrated how the flow pattern can influence the final solute distribution. The simulation also shows that the solubility limit of carbon and nitrogen is reached locally in the ingot and SiC and Si₃N₄ precipitates are likely to form.     

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.     

Production of high purity TeO2 single crystals for the study of neutrinoless double beta decay

High purity TeO₂ crystals are produced to be used for the search for the neutrinoless double beta decay of ¹³⁰Te. Dedicated production lines for raw material synthesis, crystal growth, and surface processing were built compliant with radio-purity constraints specific to rare event physics experiments. High sensitivity measurements of radio-isotope concentrations in raw materials, reactants, consumables, ancillaries, and intermediary products used for TeO₂ crystals production are reported. Indications are given on the crystals perfection and how it is achieved and maintained in a large scale production process. Production and certification protocols are presented and resulting ready-to-use TeO₂ crystals are described.     

Growth and properties of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 single crystals directly from melt

Pb[(Zn_1/3Nb_2/3)_0.91Ti_0.09]O₃ (PZNT91/9) single crystals were grown by a modified Bridgman method directly from melt using an allomeric Pb[(Mg_1/3Nb_2/3)_0.69Ti_0.31]O₃ (PMNT69/31) single crystal as a seed. X-ray diffraction (XRD) measurement confirmed that the as-grown PZNT91/9 single crystals are of pure perovskite structure. Electrical properties and thermal stabilization of PZNT91/9 crystals grown directly from melt exhibit different characters from those of PZNT91/9 crystals grown from flux, although segregation and the variation of chemical composition are not seriously confirmed by X-ray fluorescence analysis (XPS). The [0 0 1]-oriented PZNT91/9 crystals cut from the middle part of the as-grown crystal boules exhibit broad dielectric-response peaks at around 105 °C, accompanied by apparent frequency dispersion. The values of piezoelectric constant d₃₃, remnant polarization P_r, and induced strain are about 1800–2200 pC/N, 38.8 μC/cm², and 0.3%, respectively, indicating that the quality of PZNT crystals grown directly from melt can be comparable to those of PZNT91/9 single crystals grown from flux. However, further work deserves attention to improve the dielectric properties of PZNT crystals grown directly from melt. Such unusual characterizations of dielectric properties of PZNT crystals grown directly from melt are considered as correlating with defects, microinhomogeneities, and polar regions.     

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 NaBi(WO4)2 crystal by modified-Bridgman method

NaBi(WO₄)₂ (NBW) crystals have been grown for the first time by modified-Bridgman method. Influences of some factors on the crystal growth process are discussed. X-ray powder diffraction experiments show that the unit cell parameters of NBW crystal are a=b=0.5284 nm, c=1.1517 nm, and V=0.3215 nm³. The differential thermal analysis shows that the NBW crystal melts at 923°C.     

Growth and properties of Nd:Lu3Ga5O12 laser crystal by floating-zone method

Neodymium (Nd) doped lutetium gallium garnet (Nd:Lu₃Ga₅O₁₂, Nd:LuGG) single crystal was successfully grown by the optical floating-zone method for the first time to our knowledge. Its absorption and luminescence spectra at room temperature were measured. By using the J–O theory, the spectral parameters of Nd:LuGG were calculated, which indicated that Nd:LuGG should possess comparable and even better laser properties than Nd:YAG. The maximum output power of 855 mW at 1062 nm was achieved with slope efficiency of 23.4% under a pump power of 5.2 W, and optical conversion efficiency of 16.4%. All the results show that Nd:LuGG is a potential laser material.     

Defect characterization and composition distributions of mercury indium telluride single crystals

A mercury indium telluride (MIT) ingot was grown by the vertical Bridgman method. The defects in MIT crystals were characterized by the chemical etching method. A defect etchant for MIT crystals was developed. The etch pits of dislocations, microcracks and boundary was observed by scanning electron microscopy. It was elucidated that the etch pits density of dislocations of MIT wafers was about 4×10⁵ cm⁻². Te and In reduced at the grain boundaries, but were homogeneously distributed within the grains in the as-grown MIT crystals. The distribution of In in MIT crystals along the growth direction and radial direction was analyzed by electronic probe microscopy. It was found that In concentration was higher in the initial part and lower in the final part of the MIT ingot, which indicated that the segregation coefficient of In in MIT crystals was 1.15. The radial In concentration increased from the center to edge of the wafers and homogeneous in the middle part.     

Unidirectional seeded single crystal growth from solution of benzophenone

A novel crystal growth method has been established for the growth of single crystal with selective orientation at room temperature. Using volatile solvent, the saturated solution containing the material to be crystallized was taken in an ampoule and allowed to crystallize by slow solvent evaporation assisted with a ring heater. The orientation of the growing crystal was imposed by means of a seed fixed at the bottom of the ampoule. By selecting a suitable ring heater voltage and by controlling the ring heater voltage, nucleation and the growth rate of the crystal were controlled more effectively. By employing this novel method, benzophenone single crystal ingots of diameters 10 and 20 mm and length more than 50 mm were successfully grown using xylene as solvent. The ease in scaling up of diameter from 10 to 20 mm shows the vital advantage of this technique. It was possible to achieve solute–crystal conversion efficiency of 100 percent. The grown benzophenone crystal was characterized by FTIR, TG and DTA, powder X-ray diffraction, X-ray rocking curve, optical transmission study and powder SHG measurement. The results show that the crystal quality is at least as good as the quality of the crystal grown by other known methods. Also, microbial growth was naturally avoided in this method, as the fresh solution is constantly made available for the growing crystal.     

Characterization of AlN single crystal fabricated by a novel growth technique, “pyrolytic transportation method”

Aluminum nitride single crystal fabricated by a novel growth technique “pyrolytic transportation method”, which is advantageous for industrial process because of using α-Al₂O₃ as a source material instead of aluminum nitride, was characterized. This growth technique shows high growth rate up to 1.6 mm/h. High crystalline quality was indicated by X-ray topogragh and X-ray rocking curve. Full width at half maximum of (0 0 0 2) and (1 0 −1 0) were excellent values of 90 and 148 arcsec, respectively. Homoepitaxial overgrowth by hydride vapor phase epitaxy was successfully conducted. No dislocation was observed at the interface between the substrate and overgrowth layer by transmission electron microscopy.     

CrO2 (1 0 0) and TiO2 (1 0 0) film heteroepitaxy on a BaF2 (1 1 1)/Si (1 0 0) substrate

Multi-domained heteroepitaxial rutile-phase TiO₂ (1 0 0)-oriented films were grown on Si (1 0 0) substrates by using a 30-nm-thick BaF₂ (1 1 1) buffer layer at the TiO₂–Si interface. The 50 nm TiO₂ films were grown by electron cyclotron resonance oxygen plasma-assisted electron beam evaporation of a titanium source, and the growth temperature was varied from 300 to 600 °C. At an optimal temperature of 500 °C, X-ray diffraction measurements show that rutile phase TiO₂ films are produced. Pole figure analysis indicates that the TiO₂ layer follows the symmetry of the BaF₂ surface mesh, and consists of six (1 0 0)-oriented domains separated by 30° in-plane rotations about the TiO₂ [1 0 0] axis. The in-plane alignment between the TiO₂ and BaF₂ films is oriented as [0 0 1] TiO₂ || BaF₂ or [0 0 1] TiO₂ || BaF₂ . Rocking curve and STM analyses suggest that the TiO₂ films are more finely grained than the BaF₂ film. STM imaging also reveals that the TiO₂ surface has morphological features consistent with the BaF₂ surface mesh symmetry. One of the optimally grown TiO₂ (1 0 0) films was used to template a CrO₂ (1 0 0) film which was grown via chemical vapor deposition. Point contact Andreev reflection measurements indicate that the CrO₂ film was approximately 70% spin polarized.     

X-ray characterization of detached-grown germanium crystals

Germanium (1 1 1)-oriented crystals have been grown by the vertical Bridgman technique, in both detached and attached configurations. Microstructural characterization of these crystals has been performed using synchrotron white beam X-ray topography (SWBXT) and double axis X-ray diffraction. Dislocation densities were measured from X-ray topographs obtained using the reflection geometry. For detached-grown crystals, the dislocation density is on the order of 10⁴ cm⁻² in the seed region, and decreases in the direction of growth to less than 10³ cm⁻², and in some crystals reaches less than 10² cm⁻². For crystals grown in the attached configuration, dislocation densities were on the order of 10⁴ cm⁻² in the middle of the crystals, increasing to greater than 10⁵ cm⁻² near the edge. The measured dislocation densities are in excellent agreement with etch pit density (EPD) results. Broadening and splitting of the rocking curve linewidths was observed in the vicinity of subgrain boundaries identified by X-ray topography in some of the attached-grown crystal wafers. The spatial distribution of rocking curve linewidths across the wafers corresponds to the spatial distribution of defect densities measured in the X-ray topographs and EPD micrographs.     

Detached solidification of InSb on earth

Detached solidification of lightly gallium-doped indium antimonide was achieved in the laboratory only when the ampoule was coated with hexagonal boron nitride and when the material appeared to be oxide-free. A furnace was constructed with the temperature increasing with height in order to minimize bouyancy-driven convection, so as to maximize transport of segregated dissolved gases into the gap between the growing solid and the ampoule wall. There appeared to be no difference in results with freezing rates of 5 and 10 mm/h. Best results were obtained when the ampoule was backfilled with 20 kPa of Ar-10% H₂ prior to sealing. The detached portions were depressed by several μm from adjacent attached regions, were dull, and sometimes had microfacets and steps.     

Metastable PbO crystal grown through alcohol-thermal process

An alcohol-thermal route has been developed to the growth of single crystals of yellow metastable PbO in largest dimensions of 11×1×0.1 mm³, using freshly synthesized β-PbO crystallites as seeds. The transformation of metastable β-PbO to stable form (-PbO) can be slowed down by choosing appropriate solvent as the growth medium. The obtained β-PbO crystals have a strong orientational growth parallel to the (0 0 1) plane and exhibit a lath shape. Studies found that cooling rate and NaOH concentration also have great influence on the crystallographic forms of the final products during the alcohol-thermal process.