Growth dynamics of Ge1?xSix single crystals obtained by directional constitutional supercooling of the melt

The problem of growth dynamics for crystals of binary solid solutions, obtained by the constitutional supercooling of the melt with a silicon feeding rod, has been solved within the Pfann approximation. The dependences of the change in the axial growth rate of Ge_1−x Si _x crystals (0 ≤ x ≤ 0.3) are calculated. It is shown that the Ge_1−x Si _x crystallization rate significantly changes during growth. The results make it possible to determine the optimal conditions and technological parameters for growing Ge_1−x Si _x single crystals (0 ≤ x ≤ 0.3) with a specified concentration gradient along the crystallization axis.     

Si modified Ge10 cluster: the preparation and characterization of single crystal Na4(Ge,Si)9O20

A Si modified Ge₁₀ cluster with structure Na₄(Ge,Si)₉O₂₀ (denoted as HUT‐1) was synthesized by hydrothermal synthesis at 160 °C with a sodium silicate source. The compound was characterized by single crystal, powder X‐ray diffraction and TGA‐DSC analysis. HUT‐1 crystallizes in space group I4₁ (80) with calculated unit cell (a=14.966(5) Å, c=7.343(2) Å, V=1644.8(9) ų), which has the same structure as Na₄Ge₉O₂₀. HUT‐1 has a high Si/Ge ratio with an approximate formula of Na₄Ge_7.68Si_1.32O₂₀. Single crystal X‐ray structure refinements together with results from X‐ray powder diffraction (XRPD) confirm the occupancy of Si at two tetrahedral sites. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bridgman growth of langasite‐type piezoelectric crystals

Three langasite family crystals of Sr₃Ga₂Ge₄O₁₄ (SGG), Ca₃NbGa₃Si₂O₁₄ (CNGS), and Sr₃NbGa₃Si₂O₁₄ (SNGS) were successfully grown by the modified Bridgman method. Among them, SGG crystals up to 2 inches were obtained with the multi‐crucible industrial Bridgman furnace; SNGS crystal grown in any orientation direction other than along a‐axis was realized. Commercially availability SGG boules and the advantage in SNGS crystal indicated that the modified Bridgman technique is a prospective method to realize the mass‐production of the langasite‐type crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Evolution of the growth interface in liquid phase diffusion growth of bulk SiGe single crystals

The article presents a study for the evolution of growth interface in crystal growth by Liquid Phase Diffusion (LPD). Specific LPD experiments were designed to grow compositionally graded, germanium‐rich Si_xGe_1‐x single crystals of 25 mm in diameter with various thicknesses. Measured interface shapes show the evolution of the growth interface. Silicon compositions were measured by the Energy Dispersive X‐ray analysis (EDX) in the growth and radial directions. The study shows the feasibility of extracting the desired seeds of uniform composition from LPD grown crystals, for subsequent use in other epitaxial growth processes. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

The growth and structure of Pb3Ga2Ge4O14 and Ba3Ga2Ge4O14 single crystals

Conditions for the flux synthesis of Pb₃Ga₂Ge₄O₁₄ and Ba₃Ga₂Ge₄O₁₄ single crystals and their solid solutions Pb_{3 − x} Ba_xGa₂Ge₄O₁₄ are studied. Structural analysis showed that the Ga³⁺-and Ge⁴⁺-cation positions in flux-grown Pb₃Ga₂Ge₄O₁₄ and Ba₃Ga₂Ge₄O₁₄ single crystals are not mixed. __________ Translated from Kristallografiya, Vol. 49, No. 2, 2004, pp. 325–328. Original Russian Text Copyright ? 2004 by Bezmaternykh, Vasil’ev, Gudim, Temerov. This work was presented at the National Conference on Crystal Growth (NCCG-2002, Moscow).     

The distribution of Ga and Sb impurities in Ge-Si crystals grown by the Bridgman method using a feeding rod

Gallium- and antimony-doped Ge_{1 ? x} Si _x crystals (0 ≤ x ≤ 0.25) have been grown by the improved Bridgman method using a silicon seed and a macrohomogeneous feeding Ge-Si rod of the corresponding composition. The impurity concentration profiles along the grown crystals were determined from Hall measurements. The mathematical problem of impurity distribution along two-component mixed crystals grown from a melt with uniform and graded composition is solved in the Pfann approximation and within the virtual-crystal model for the solid solution. It is shown that the experimental impurity distributions in Ge_{1 ? x} Si _x crystals are described well by the data calculated on the assumption of linear change in the impurity segregation coefficient with the crystal composition.     

Distribution of aluminum and indium impurities in crystals of Ge-Si solid solutions grown from the melt

The problem regarding the distribution of aluminum and indium impurities in bulk crystals of solid solutions with a variable composition Ge_1−x Si _x (0 ≤ x ≤ 0.3) is solved in order to establish regularities of the changes in the segregation coefficients of impurities with variations in the composition of the host lattice in the germanium-silicon system. Aluminum-and indium-doped crystals of Ge_1−x Si _x (0 ≤ x ≤ 0.3) solid solutions with a silicon content decreasing along the crystallization axis are grown by a modified Bridgman method with the use of a silicon seed. The concentration distribution of impurities over the length of the crystals is determined from Hall measurements. It is demonstrated that the experimental data on the concentration distribution of impurities in the crystals are in good agreement with the results obtained from the theory according to which the equilibrium segregation coefficients of impurities vary linearly with a change in the composition of Ge-Si solid solution crystals.

     

X‐ray Propagation in Distorted Crystals: From Dynamical to Kinematical Theory

The successive studies of the propagation of x‐rays in crystals distorted by a strain gradient whose magnitude is characterized by a parameter β are presented. It is shown how the new wavefield that appears when βΓ (Γ being the classical extinction length) is much larger than 1 pumps intensity out of the normal wavefield, which explains the transition from the dynamical to the kinematical theory. The quantity βΓ can be increased either by increasing the distortion or by using smaller wavelengths or structure factors as checked experimentally on Si_1‐xGe_x crystals.     

Distribution of Al and in impurities along homogeneous Ge-Si crystals grown by the Czochralski method using Si feeding rod

A distribution of Al and In impurities in Ge_{1 ? x} Si _x crystals (0 ≤ x ≤ 0.3) grown by a modified Czochralski method (with continuous feeding of melt using a Si rod) have been studied experimentally and theoretically. Experimental Al and In concentrations along homogeneous crystals have been determined from Hall measurements. The problem of Al and In impurity distribution in homogeneous Ge-Si single crystals grown in the same way is solved within the Pfann approximation. A set of dependences of Al and In concentrations on the crystal length obtained within this approximation demonstrates a good correspondence between the experimental and theoretical data.     

X-ray Photoelectron Spectroscopic Studies of Sellinite and Eulytite BGO and BSO Crystals

Single crystals of Bi₁₂GeO₂₀, Bi₁₂SiO₂₀, Bi₄Ge₃O₁₂, and Bi₄Si₃O₁₂ are grown by Floating zone and Czochralski techniques. The X-ray photoelectron spectroscopic (XPS) studies have been carried out on BSO and BGO crystals. XPS is employed to characterise the surface quality and bulk nature of the crystals. The surface contamination on both types of crystals are identified. In addition to the contamination, some amount of Bi atoms are observed with Bi ions on sellinite. It is demonstrated that the eulytite crystals are chemically more robust to degradation than the sellinite crystals. The predominant covalent and ionic character of Bi₄Ge₃O₁₂ and Bi₄Si₃O₁₂ respectively is explained from their oxygen 1s core level spectra.     

Bridgman and Czochralski growth of Ge?Si alloy crystals

Ge_1–xSi_x crystals were grown with the Bridgman and the Czochralski method over a wide concentration range. With the Bridgman process single crystals up to 40 at.% Si were possible. The reasons for polycrystalline growth were the permanent contact of the interface with the crucible wall in combination with curvature towards the crystal and inclusions of high Si concentration. Analysis of striations in Czochralski grown material showed that in this process the crystal does not continuously grow in one direction but consists of piece-wise grown crystals in which the composition permanently changes. According to that fact the main reason for polycrystalline growth in the Czochralski process is common due to lattice mismatch between the seed and equilibrium concentration transients in the crystal corresponding to the microscopic growth rates.     

Growth and characterization of a new langasite‐type single crystal Sr3NbAl1.5Ga1.5Si2O14

Single crystals of Sr₃NbAl_1.5Ga_1.5Si₂O₁₄ (SNAGS) with langasite structure have been successfully grown by Czochralski method. The X‐ray diffraction (XRD) verified that the as‐grown crystal was isostructural with A₃BC₃D₂O₁₄ structure and the lattice parameters were calculated as follows: a = 8.242 Å, c = 5.041 Å, V = 296.6 ų. The piezoelectric coefficient d₁₁ was 5.7pC/N, which was 2.47 times of α‐quartz (d₁₁=2.31pC/N). The electric resistivity was up to 3.04×10⁶ Ωcm at 700 °C for X‐cut sample. In addition, the transmission spectrum of the SNAGS crystal showed that it had a high transmittance (>80%) in the range of 350‐800 nm and exceeded 90% above 520 nm. These results suggest that the SNAGS crystals have potential applications in high‐temperature piezoelectric sensors and optical techniques. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrothermal synthesis of ultralong single‐crystalline α‐Ni(OH)2 nanobelts and corresponding porous NiO nanobelts

Ultralong α‐Ni(OH)₂ nanobelts with uniform size have been prepared on large scale via a facile template‐free hydrothermal method. The as‐prepared nanobelts were single crystals, with several tens of microns in length and about 100 nm in width. For the whole process, a novel nucleation–aggregation–dissolution–seed‐directed growth mechanism was proposed based on the experimental results. The roles of aqueous ammonia and hydrothermal temperature were also discussed. Furthermore, porous NiO nanobelts were obtained by annealing the as‐prepared Ni(OH)₂ nanobelts. This facile, template‐free, and low cost method might feasibly be scaled up for industrial production. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Advanced deposition phase diagrams for guiding Si:H-based multijunction solar cells

Phase diagrams have been established to describe very high frequency (vhf) plasma-enhanced chemical vapor deposition (PECVD) of intrinsic hydrogenated silicon (Si:H) and silicon–germanium alloy (Si_1?xGe_x:H) thin films on crystalline Si substrates that have been over-deposited with n-type amorphous Si:H (a-Si:H). The Si:H and Si_1?xGe_x:H films are prepared under conditions used for the top and middle i-layers of high efficiency triple-junction a-Si:H-based n–i–p solar cells. Identical n/i cell structures were co-deposited in this study on textured (stainless steel)/Ag/ZnO which serve as substrate/back-reflectors in order to relate the phase diagrams to the performance parameters of single-junction solar cells. This study has reaffirmed that the highest efficiencies for a-Si:H and a-Si_1?xGe_x:H solar cells are obtained when the i-layers are prepared under previously-described maximal H₂ dilution conditions.     

Dependence of the surface topology and raman scattering spectra of Ge x Si1−x /Si films on the composition variation over the layer thickness

The surface topology and Raman scattering spectra of Ge _x Si_{1 ? x} /Si(100) films are investigated in dependence of the composition variation over the film thickness. It is shown that the character of the Ge content variation in the Ge _x Si_{1 ? x} alloy at the constant cumulative Ge fraction in the film (x _int = 0.5) affects the surface morphology of the grown Ge _x Si_{1 ? x} /Si layer. The heterostructures were grown by molecular-beam epitaxy.     

Growth of Ba2Re(Y,Pr)Ru1‐xCuxO single crystals in a high temperature solution drop using an infrared imaging system

Infrared imaging furnace was used to grow single crystals of Ba₂YRu_1‐xCu_xO₆ and Ba₂PrRu_1‐xCu_xO₆ using high temperature solutions of PbO‐PbF₂ in the form of a bubble attached to the feed rods. Several small crystals were found deposited on the cooler portions of the sintered rod as well as in the drop like portion at the end of the rod. These crystals were collected and the morphology, microstructure and magnetic properties were studied. The details of these investigations are presented. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Laterally‐Graded SiGe Crystals for High Resolution Synchrotron Optics

A novel type of optical element for synchrotron radiation applications in the X‐ray region: namely laterally‐graded aperiodic crystals on the basis of Si_1‐xGe_x mixed crystal is presented. The lattice parameter of such gradient crystals containing up to some at. % Ge changes nearly linearly along the plane of diffraction. Thus the variation of the Bragg angle of divergent incident light on the crystal can be compensated. This opens up the possibility to operate a crystal monochromator in nearly crystal limited resolution in the whole energy range above 2 keV at the full vertical synchrotron source divergence without a collimating pre‐mirror. Simultaneously the reflected spectral intensity can be increased considerably as compared with a conventional Si‐crystal monochromator.     

Effective electro‐optic coefficient of (1–x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 single crystals

Refractive indices and effective electro‐optic coefficient γ_c of (1–x)Pb(Zn_1/3Nb_2/3)O₃–xPbTiO₃ (PZN‐xPT, x = 0.05, 0.09 and 0.12) single crystals were measured at 532 nm wavelength. Orientation and temperature dependences of the electro‐optic coefficient were investigated. Large electro‐optic coefficient (γ_c = 470 pm/V) was observed in [001]‐poled PZN‐0.09PT crystal. More importantly, γ_c of tetragonal PZN‐0.12PT is almost unchanged in a temperature range −20 ∼ 80 °C. The γ_c of PZN‐xPT single crystals are much higher than that of widely used electro‐optic crystal LiNbO₃ (γ_c = 20 pm/V). These results show that PZN‐xPT single crystals are very promising materials for electro‐optic modulators in optical communications.     

One‐step fabrication of SnxTi1‐xO2 rutile‐type core‐shell microspheres and their electrochemical properties

Sn_xTi_1‐xO₂ core‐shell microspheres were synthesized through a simple one‐step hydrothermal method. The structural and morphologic properties were unambiguously characterized, and the electrochemical performance of the Sn_xTi_1‐xO₂ microspheres was determined by cyclic voltammetry. The possible formation mechanism of Sn_xTi_1‐xO₂ microspheres was also proposed.     

Growth of big single crystals of a new magnetic superconducting double perovskite Ba2PrRu1–xCuxO6

Single crystals of Ba₂PrRu_1–xCu_xO₆ with x = 0 to 0.2, have been grown from high temperature solutions of a mixture of PbO‐PbF₂ in the temperature range 1100–1200 °C. Thin crystals with mostly a hexagonal and triangular plate like habit measuring up to 1–2 mm across and 0.1–0.2 mm thick were obtained. The size, quality and morphology of the crystals were improved by varying the solution volume as well as additives like B₂O₃. Large crystals measuring up to 3 mm across and 0.3 to 0.5 mm thick were obtained with 5–7 wt% solute concentration and 0.51 wt% of B₂O₃. The ZFC curves exhibit a spin glass like behavior with x = 0 and a superconducting transition at 8 to 11 K depending on x = 0.05 to 0.1. The transition was also influenced by the growth temperature and post growth annealing. Powder x‐ray diffraction, EDS and Raman spectroscopic measurements confirm the presence of Cu in the crystals. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)