MOCVD growth and optical properties of non-polar (1 1–2 0) a-plane GaN on (1 0–1 2) r-plane sapphire substrate

Non-polar a-plane GaN film with crystalline quality and anisotropy improvement is grown by use of high temperature AlN/AlGaN buffer, which is directly deposited on r-plane sapphire by pulse flows. Compared to the a-plane GaN grown on AlN buffer, X-ray rocking curve analysis reveals a remarkable reduction in the full width at half maximum, both on-axis and off-axis. Atomic force microscopy image exhibits a fully coalesced pit-free surface morphology with low root-mean-square roughness (∼1.5 nm). Photoluminescence is carried out on the a-plane GaN grown on r-plane sapphire. It is found that, at low temperature, the dominant emission at ∼3.42 eV is composed of two separate peaks with different characteristics, which provide explanations for the controversial attributions of this peak in previous studies.     

Thermomagnetic study of the amorphous cobalt-erbium borides Co80ErxB20−x (0 ? x ? 4)

Calorimetric, magnetic and X-ray diffraction measurements have been used to study the magnetic susceptibility and thermal stability of Co₈₀Er_xB_20−x with (0 ? x ? 4) amorphous ribbons. The compounds are found to crystallize in Co₂B and β-Co, after precipitation of the tetragonal Co₃B phase. The addition of erbium shifts up the crystallization temperature leading to the increase in the stability of the amorphous state. Magnetic susceptibility measurements show that the addition of erbium increases the Curie temperature and induces noncollinear magnetic behavior. This latter fact is explained on the basis of random local magnetic anisotropy related to the rare earth atoms in amorphous materials.     

Incorporation of group III,IV and V elements in 3C–SiC(1 1 1) layers grown by the vapour–liquid–solid mechanism

We report on a comparative investigation of the incorporation of group III, IV and V impurities in 3C–SiC heteroepitaxial layers grown by the vapour–liquid–solid (VLS) mechanism on on-axis α-SiC substrates. To this end, various Si-based melts have been used with addition of Al, Ga, Ge and Sn species. Homoepitaxial α-SiC layers grown using Al-based melts were used for comparison purposed for Al incorporation. Nitrogen incorporation depth profile systematically displays an overshoot at the substrate/epilayer interface for all the layers. Ga and Al incorporations follow the same distribution shape as N whereas this is not the case for the isoelectronic impurities Ge and Sn. This suggests some interaction between Ga/Al and N coming from the high bonding energy between the group III and V elements, which does not exist with Ge and Sn. This is why both incorporate as a cluster. A model of incorporation is proposed taking into account metal-N and metal-C bonding energies together with the solid solubility of the corresponding nitrides.     

Epitaxial lateral overgrowth of non-polar GaN(1 1̄ 0 0) on Si(1 1 2) patterned substrates by MOCVD

m-Plane GaN was grown selectively by metal–organic chemical vapor deposition (MOCVD) on patterned Si(1 1 2) substrates, where grooves aligned parallel to the Si〈1 1 0〉 direction were formed by anisotropic wet etching to expose the vertical Si{1 1 1} facets for growth initiation. The effect of growth conditions (substrate temperature, chamber pressure, and ammonia and trimethylgallium flow rates) on the growth habits of GaN was studied with the aim of achieving coalesced m-plane GaN films. The epitaxial relationship was found to be GaN(1 1? 0 0) || Si(1 1 2), GaN[0 0 0 1] || Si[1 1 –1], GaN[1? 1? 2 0] || Si[1 1? 0]. Among all growth parameters, the ammonia flow rate was revealed to be the critical factor determining the growth habits of GaN. The distribution of extended defects, such as stacking faults and dislocations, in the selectively grown GaN were studied by transmission electron microscopy in combination with spatially resolved cathodoluminescence and scanning electron microscopy. Basal-plane stacking faults were found in the nitrogen-wing regions of the laterally overgrown GaN, while gallium-wings were almost free of extended defects, except for the regions near the GaN/Si{1 1 1} vertical sidewall interface, where high dislocation density was observed.     

Growth and structure properties of La1−xSrxMnO3−σ (x=0.2, 0.3, 0.45) thin film grown on SrTiO3 (0 0 1) single-crystal substrate by laser molecular beam epitaxy

La_1−xSr_xMnO_3−σ (LSMO) thin films have been grown on SrTiO₃ (0 0 1) single-crystal substrates using the laser molecular beam epitaxy (MBE) technique. The two-dimensional layer-by-layer growth was in-situ monitored by reflection high-energy electron diffraction (RHEED). Kinetic growth with surface relaxation was also observed, and crystallinity of the thin films was investigated by high-resolution X-ray diffraction. Results of 2θ−ω scans revealed a strong correlation between out-of-plane lattice constant and oxygen content as well as strontium doping concentration. However, further analysis of rocking curve measurements around (0 0 2) plane of thin films grown under different oxygen pressure (P_O2) shown the effects of oxygen content on the crystal structure. An exceptionally low full-width at half-maximum (FWHM) of 0.02° was measured from the sample grown at P_O2 of 5.0 Pa, indicating the almost perfect epitaxial growth of LSMO thin films.     

Role of interfacial crystallites in the crystallization of α-Fe2O3/α-Al2O3(0 0 0 1) thin films

In situ crystallization of α-Fe₂O₃/α-Al₂O₃(0 0 0 1) thin films was studied in real-time synchrotron X-ray scattering experiments. We find the coexistence of α-Fe₂O₃ (hexagonal) and Fe₃O₄ (cubic) interfacial crystallites (∼50-Å-thick), well aligned [0.02° full-width at half-maximum (FWHM)] to the α-Al₂O₃[0 0 0 1] direction, in the sputter-grown amorphous films. As the annealing temperature increases up to 750°C, the cubic stacking of the Fe₃O₄ crystallites gradually changes to the hexagonal α-Fe₂O₃ stacking, together with the growth of the well-aligned (WA) (0.02° FWHM) grains from the α-Fe₂O₃ crystallites. In the meanwhile, heterogeneous nucleation starts to occur on the substrate at ∼600°C, resulting in the formation of misaligned (1.39° FWHM) α-Fe₂O₃ grains. Our study reveals that the interfacial crystallites act as a template for the growth of the WA α-Fe₂O₃ grains.     

Gain cross-section of 1.06 μm emission in Nd-doped SiO2-LaF3 glass-ceramics prepared by sol-gel method

The room temperature near-infrared emission at 1.06 μm corresponding to the ⁴F_3/2 → ⁴I_11/2 laser transition in Nd³⁺-doped SiO₂-LaF₃ transparent glass-ceramics prepared by sol-gel method has been characterized in terms of the product of emission cross-section and fluorescence lifetime. Stimulated emission cross-sections have been calculated from experimental emission spectra using the Füchtbauer-Ladenburg equation. The precipitation of LaF₃ nanocrystals after heat-treatment, confirmed by X-ray diffraction, induces a significant increment of the 1.06 μm near-infrared emission compared with the as made sample. An enhancement of emission cross-section of about 10% has been achieved with increasing temperature of heat-treatment of the nano-ceramming process from 800 to 1000 °C, which is related to the growth of LaF₃ nanocrystals.     

Growth of Sm1 – ySryF3 – y (0 < y ≤ 0.31) Crystals and Investigation of Their Properties

Crystallography Reports - Sm1&nbsp;–&nbsp;ySryF3&nbsp;–&nbsp;y (0 &lt; y ≤ 0.31) crystals have been grown from melt by directional solidification in a...     

Cationic transport mechanism in α-Ag<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>I(0 < <Emphasis Type="Italic">x</Emphasis> < 0.25): Molecular-dynamics simulation

The structural and transport characteristics of an Ag_{1 ? x} Cu _x I(0 < x < 0.25) solid solution have been simulated by the molecular-dynamics method. It is found that the cation diffusion coefficient decreases with increasing copper concentration; this correlation is in agreement with the experimentally observed decrease in ionic conductivity. It is shown that the cationic transport in disordered Ag_{1 ? x} Cu _x I phases is mainly due to the migration of silver cations, whereas the mobility of copper cations is much lower. Cu⁺ cations are found to reside in the 8c positions in a bcc cell; this finding suggests the existence of nanoscale α-CuI regions.     

中温SOFC La0．9Sr0．1Ga0．8Mg0．203-δ固体电解质的电性能研究

采用固相反应法制备了 La0．9Sr0．1Ga0．8Mg0．203-δ(LSGM)固体电解质，XRD测试表明，经1500℃煅烧24h后得到LSGM单相结构，采用交流阻抗测试技术对 La0．9Sr0．1Ga0．8Mg0．203-δ的电性能进行了研究，结果表明 La0．9Sr0．1Ga0．8Mg0．203-δ低温区电导率主要取决于晶界电导；而在高温区电导率主要取决于晶粒电导。低温下导电率激活能较高为1．09eV，高温的激活能较低为0．8eV。     

Study of structural properties of In<Subscript>x</Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>As/In<Subscript>y</Subscript>Al<Subscript>1−<Emphasis Type="Italic">y</Emphasis></Subscript>As heterosystems on InP substrates

The structural properties of In_xGa_1?xAs/In_yAl_1?yAs samples on InP substrates are studied as functions of growth conditions by the method of high-resolution diffractometry. The results obtained and the photoluminescence spectroscopy data are used to optimize the technology of preparation of high-quality heterostructures with sharp interfaces. The parameters of the two-dimensional electron gas of such heterostructures measured at 77 and 300 K are comparable with the best world standards in this field, so these heterostructures may be used to manufacture transistors and integral amplifiers operating at the frequency 40 GHz and even higher.     

Comparative Analysis of the Methods for Obtaining Superconducting Fe1 + ySexTe1 – x Single Crystals

Crystallography Reports - The Fe1&nbsp;+&nbsp;ySexTe1&nbsp;–&nbsp;x single crystals grown by the KCl flux and Bridgman methods have been compared using the same investigation...     

Growth and dielectric properties of KTiOPO<Subscript>4</Subscript> and K<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Rb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiOPO<Subscript>4</Subscript> crystals

Methods of growth of KTiOPO₄ and K_{1 ? x} Rb _x TiOPO₄ crystals of high optical quality have been optimized. The dielectric properties (permittivity and conductivity) of the crystals grown have been investigated at frequencies from 10² to 10⁶ Hz in the temperature range from 100 to 350 K, along the [001] crystallographic direction. It is established that partial substitution of K⁺ ions with Rb⁺ ions leads to a decrease in the permittivity and conductivity.     

Synthesis and crystal structure of [(C<Subscript>7</Subscript>H<Subscript>10</Subscript>N)<Subscript>2</Subscript>]<Superscript>2+</Superscript> [Sb<Subscript>2</Subscript>Cl<Subscript>8</Subscript>]<Superscript>2−1</Superscript>

The reaction of 2,6-dimethylpyridine with SbCl₃ and HCl affords the title compound, the structure of which is ascertained by X-ray diffraction. The unit cell consists of one bridged Sb₂Cl₈²⁻ anion and two 2,6-dimethylpyridinium cations. The trivalent antimony ion is bonded not only directly to chlorine anions, but also is coordinated with chlorine anions by secondary bonds. In the crystal, there exists infinite coordinated chains of [Sb₂Cl₈] _n ²ⁿ⁻ anions running along the a axis, which link 2,6-dimethylpyridinium cations by N-H…Cl hydrogen bonds.     

Local symmetry breaking for negatively charged impurity centers in SrTi<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript>

First-principles calculations of the geometry and electronic structure of the impurity center in SrTi_{1 − x} Mn _x O₃ have been performed. Neutral and negatively charged defects are considered. It is found that the doubly charged impurity center is polar; it has C _4v symmetry and electronic state ⁴ B ₁ with electron polaron localized at one of the neighboring titanium atoms. It is shown that this state is due to the spontaneous breaking of the defect local symmetry: O _h (⁴ A _1g ) → D _4h (⁴ B _1g ) → C _4ν(⁴ B ₁).     

Growth of ZnSe<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> solid solution crystals from vapor phase

Partially faceted ZnSe_{1 − x} S _x solid solution crystals have been grown from a vapor phase in a closed stationary horizontal system. The growth has been performed in cylindrical quartz ampoules—∼10 mm in diameter and evacuated to a residual pressure of less than ∼10⁻³ Pa-at a temperature of 1050°C and a temperature drop between the source and growth zones of 10–16°C. The crystal structure, optical absorption, and composition inhomogeneity along the ingot length have been investigated by X-ray diffractometry and optical spectroscopy in the wavelength range of 300–3000 nm. The solid-solution composition range corresponding to cubic polymorphs is determined. The concentration dependences of the lattice parameter and band gap are presented.     

Structure and magnetism of low-doped monoclinic crystals of (Ga<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>Se<Subscript>3</Subscript>

The influence that doping with Mn³⁺ ions has on the fine crystal structure of the monoclinic compound Ga₂Se₃ was studied by single-crystal neutron diffraction and the measurements of magnetic properties. It was found that the structural state of the crystals changes even at relatively low doping levels (x = 0.04). Local Jahn-Teller distortions were shown to be responsible for the formation of the fine structure and magnetism in this type of compounds.     

Synthesis and Crystal Structure of (PzCH<Subscript>2</Subscript>CHOHCH<Subscript>2</Subscript>PzH)·(Ph<Subscript>2</Subscript>SnCl<Subscript>3</Subscript>) (Pz = 3,5-dimethylpyrazol-1-yl)

Abstract  

Reaction of Ph₂SnCl₂ with 1,3-bis(3,5-dimethylpyrazol-1-yl)-2-propanol (L) in a 1:1 ratio yields L(SnPh₂Cl₂)₂ adduct, which partly hydrolyzes to the title complex (C₂₅H₃₁Cl₃N₄OSn, Mr = 628.58) during crystal growing in the air. The title complex is of monoclinic, space group P2₁/n with a = 9.0338(9), b = 17.890(1), c = 17.340(1) ?, β = 95.533(1)^o, V = 2798.9(5) ?³, Z = 4, Dc = 1.492 Mg/m³, λ(MoKα) = 0.71073 ?, μ = 1.224 mm⁻¹, F(000) = 1272, R = 0.023, wR = 0.054 for 4212 observed reflections with I ≥ 2σ(I). The crystal structure indicates that there is no direct interaction between the pyrazolyl ligand and the tin atom, but this complex forms a supramolecular structure through weak intermolecular C–H⋯Cl and O–H⋯Cl hydrogen bonds.     

Investigation of the possibility of obtaining homogeneous Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>In<Subscript>x</Subscript>Sb crystals under weak flow conditions

The possibility of growing macrohomogeneous Ga_{1 ? x}In_xSb crystals with x = 0.2 was studied using the axial heating process close to the melt/crystal interface. The grown ingots were analyzed by a JSM-5300 scanning electron microscope and the experimental results were compared with the results of numerical simulation. It was shown that, as a whole, the mathematical model adequately describes the processes of the steady-state heat and mass transfer. It was found that, at the crystallization of Ga_{1 ? x}In_xSb by the axial heating process under conditions of weak laminar flows, longitudinal homogeneity is observed when a dead zone is formed in the melt and that the crystallization regime is similar to diffusion. It was shown that the composition of the grown crystals strongly depends on the structure of a melt flow and its dynamics.