Chemical interaction of InAs,InSb, GaAs,and GaSb crystal surfaces with (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>Cr<Subscript>2</Subscript>O<Subscript>7</Subscript>–HBr–citric acid etching solutions

We have studied the chemical dissolution of InAs, InSb, GaAs, and GaSb crystals in (NH₄)₂Cr₂O₇–HBr–C₆H₈O₇ solutions. The dissolution rate of the crystals has been measured as a function of etchant composition, and the kinetics of the chemical interaction of the semiconductors with solutions have been investigated in detail. The dissolution rate has been shown to be diffusion-limited. Citric acid helps to reduce the etch rate and improves the polishing performance of the etching solutions.     

Influence of C<Subscript>4</Subscript>F<Subscript>8</Subscript>/Ar/O<Subscript>2</Subscript> plasma etching on SiO<Subscript>2</Subscript> surface chemistry

The plasma assisted etching of SiO₂ in a commercial RF reactor with a variety of C₄F₈/Ar/O₂ chemistries has been studied by XPS, SIMS and FTIR. A simple model of surface reactions is proposed. In particular, the role of oxygen in the etch process has been investigated. According to our experiments, oxygen inhibits the formation of CFH based polymeric films on the surface. As the etching process is due to an exchange reaction between the oxygen in the SiO₂ and the gaseous fluorine species in the plasma, the presence of oxygen in the etch hinders this process by occupying adsorption sites on the surface. The results would confirm that argon does not participate in chemical reactions with the SiO₂ substrate but provides energy for reactions in which F, C and O are involved. The results also indicate that a thick fluorocarbon layer only forms on the surface in the absence of oxygen, regardless of the oxygen source. Consequently, only when the SiO₂ layer has been substantially removed does this film form.     

Synthesis,crystallographic characterization and ionic conductivity of iron substituted sodium zirconium phosphate Na<Subscript>1.2</Subscript>Zr<Subscript>1.8</Subscript>Fe<Subscript>0.2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Sodium zirconium phosphate NaZr₂P₃O₁₂ (hereafter NZP) crystallizes in rhombohedral (hexagonal) symmetry with the space group R-3c. The NZP-related phase of synthetic iron substituted NZP has been prepared by partial substitution on zirconium site by Fe(III). The material has been synthesized by sintering the finely powdered oxide mixture in a muffle furnace at 1,050 °C. The polycrystalline phase of Na_1.2Zr_1.8Fe_0.2(PO₄)₃ has been characterized by its typical powder diffraction pattern. The powder diffraction data of 3,000 points have been subjected to general structural analysis system (GSAS) software to arrive at a satisfactory structural fit with R _p = 0.0623 and R _wp = 0.0915. The following unit cell parameters have been calculated: a = b = 8.83498(18) ?, c = 22.7821(8) ? and α = β = 90.0° γ = 120.0°. The structure of NZP consists of ZrO₆ octahedra and PO₄ tetrahedra linked by the corners to form a three-dimensional network. Each phosphate group is on a two-fold rotation axis and is linked to four ZrO₆ octahedra. Each zirconium octahedron lies on a threefold rotation axis and is connected to six PO₄ tetrahedra. AC conductivity of the solid solution has been measured between 303 and 773 K. The material exhibits temperature-dependent enhancement of ionic conduction by ≈400 times at elevated temperatures. The activation energies show significant change in slope at 1,000/T = 2.23(448 K).     

<Emphasis Type="Italic">Ab initio</Emphasis> studies on [bmim][PF<Subscript>6</Subscript>]-CO<Subscript>2</Subscript> mixture and CO<Subscript>2</Subscript> clusters

Ab initio molecular dynamics studies have been carried out on the room temperature ionic liquid, 1,n-butyl,3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) and supercritical carbon dioxide mixture at room temperature and experimental density. Partial radial distribution functions (RDF) for different sites have been computed to see the organization of CO₂ molecules around the ionic liquid. Several partial RDFs around the carbon atom of CO₂ molecule are compared to find out that the CO₂ has specific interaction with a carbon atom present in the imidazolium ring. The CO₂ is also found to be very well organized around the terminal carbon atom of the butyl chain. The partial RDFs for the oxygen atoms around oxygen and carbon atoms of the CO₂ suggests that there is very good organization of CO₂ molecules around themselves even in the [bmim][PF₆]-CO₂ mixture. The instantaneous quadrupole moment tensor has been calculated for the anion and the cation. The ensemble average of diagonal components of quadrupole moment tensor of the cation have finite values, whereas the off-diagonal components of the cation and both the diagonal and off-diagonal components of the anion have the value of zero with a large standard deviation. The CPMD studies performed on CO₂ clusters reveals the greater tendency of the clusters with more CO₂ units, to deviate from the linear geometry.     

Preparation of high-purity SF<Subscript>6</Subscript> and AsH<Subscript>3</Subscript> using gas centrifuges

We have developed centrifugal separation technology for ultrapurification of sulfur hexafluoride (SF₆) and arsine (AsH₃). The content of volatile impurities in sulfur hexafluoride (∼0.15 mol %) was reduced by more than a factor of 1500. The purity of the resultant product was 99.9999+ mol %. The impurity content of arsine (∼0.02 mol %) was reduced by more than a factor of 20. The purity of the resultant product was 99.999+ mol %.     

High-temperature heat capacity and vibrational spectra of Eu<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript>

The Eu₂Sn₂O₇ compound has been prepared by solid-state reaction (by sequentially firing a stoichiometric mixture of Eu₂O₃ and SnO₂ in air at 1273 and 1473 K) and its heat capacity has been determined by differential scanning calorimetry in the temperature range 370–1000 K. The heat capacity data have been used to evaluate the thermodynamic properties of europium stannate: enthalpy increment H°(T)–H°(370 K), entropy change S°(T)–S°(370 K), and reduced Gibbs energy Ф°(T). Raman spectra of Eu₂Sn₂O₇ polycrystals with the pyrochlore structure have been measured in the range 200–1200 cm^–1.     

Thermodynamic Properties of FeNb<Subscript>2</Subscript>O<Subscript>6</Subscript> and FeTa<Subscript>2</Subscript>O<Subscript>6</Subscript>

Empirical calculational approaches have been used to evaluate the enthalpy, entropy, heat capacity, and melting point of iron(II) niobate and iron(II) tantalate and the coefficients A, B, and C in an equation for the temperature dependence of their heat capacity. The melting point of FeTa₂O₆ has been experimentally determined to be 1891 ± 5 K. The calculated heat capacity (C°_p (298.15 K)) of iron tantalate and the Gibbs energies of formation of FeN₂O₆ and FeTa₂O₆ have been compared to previously reported data.     

Catalytic effect of Ti<Subscript>5</Subscript>Si<Subscript>3</Subscript> on thermal decomposition of Li<Subscript>3</Subscript>AlH<Subscript>6</Subscript>

Fine Ti₅Si₃ powder has been mechanochemically synthesized from a mixture of elemental Ti and Si powders. When Ti₅Si₃ is added as a catalyst into Li₃AlH₆, it shows a good catalytic ability by reducing the decomposition temperature and improving the decomposition kinetics as well. Although its catalytic effect is not as good as well-known TiCl₃, the use of Ti₅Si₃ has a benefit of releasing more hydrogen than TiCl₃ during dehydrogenation. This can be explained by that Ti₅Si₃, unlike TiCl₃, does not incur any chemical reactions with Li₃AlH₆ and thus remains inert during milling for dispersion.     

Threshold electron impact ionization of SF<Subscript>6</Subscript> molecule

The relative cross sections of a dissociative ionization of SF₆ molecules by electron impact in the near-threshold energy region have been determined. The experiments were performed on a setup providing for ion mass separation and detection using a monopole mass spectrometer. The energy dependences of the cross sections of fragment ion formation have been measured and the corresponding appearance thresholds are determined.     

Low-loss,high-purity (TeO<Subscript>2</Subscript>)<Subscript>0.75</Subscript>(WO<Subscript>3</Subscript>)<Subscript>0.25</Subscript> glass

By melting a mixture of high-purity oxides in a platinum crucible under flowing purified oxygen, we have prepared (TeO₂)_0.75(WO₃)_0.25 glass with a total content of 3d transition metals (Fe, Ni, Co, Cu, Mn, Cr, and V) within 0.4 ppm by weight, a concentration of scattering centers larger than 300 nm in size below 10² cm⁻³, and an absorption coefficient for OH groups (λ ∼ 3 μm) of 0.008 cm⁻¹. The absorption loss in the glass has been determined to be 115 dB/km at λ = 1.06 μm, 86 dB/km at λ = 1.56 μm, and 100 dB/km at λ = 1.97 μm. From reported specific absorptions of impurities in fluorozirconate glasses and the impurity composition of the glass studied here, the absorption loss at λ ∼ 2 μm has been estimated at ≤100 dB/km. The glass has been drawn into a glass-polymer fiber, and the optical loss spectrum of the fiber has been measured.     

Phase Equilibria in the Tl<Subscript>2</Subscript>S-Tl<Subscript>2</Subscript>Te-Tl<Subscript>9</Subscript>BiTe<Subscript>6</Subscript>-TlBiS<Subscript>2</Subscript> system

The phase equilibria in the Tl₂S-Tl₂Te-Tl₉BiTe₆-TlBiS₂ system have been studied by differential thermal analysis and x-ray diffraction. The results have been used to construct the T-x phase diagram along the Tl₂S-Tl₉BiTe₆ ([TlBi_0.333S_0.5Te_0.5]) and TlBiS₂-Tl₂Te(Tl₉BiTe₆) joins, the 500-K section of the phase diagram of the Tl₂S-Tl₂Te-Tl₉BiTe₆-TlBiS₂ system, and its liquidus diagram. The invariant and univariant phase equilibria involved have been identified. The system has been shown to contain wide regions of Tl₂Te-and Tl₉BiTe₆-based quaternary solid solutions.     

Texturization of ZnO:Al surface by reactive ion etching in SF<Subscript>6</Subscript>/Ar,CHF<Subscript>3</Subscript>/Ar plasma for application in thin film silicon solar cells

As-deposited sputtered ZnO:Al (AZO) thin films having high transparency (T?≥?85% at 550 nm of wavelength) and good electrical properties (ρ?=?2.59?×?10^?04 Ω cm) are etched to get suitable light trapping in thin film solar cells, using reactive ion etching method in sulfur hexafluoride–argon (SF₆/Ar) plasma and trifluoromethane–argon (CHF₃/Ar) plasma to texture their surface. Though the electrical properties of the films are not affected much by the etching process but significant increment in the average haze values in the wave length range of 350–1100 nm in the etched AZO films (19.21% for SF₆/Ar and 22.07% for CHF₃/Ar plasma etched) are found compared to as-deposited AZO films (5.61%). Increment in haze value is due to more scattering of light from the textured surface. These textured substrates are used as front transparent conducting oxide electrode for the fabrication of amorphous silicon solar cells. Solar cells fabricated on etched AZO substrates show 7.76% increase in conversion efficiency compared to as-deposited AZO substrates.     

Enhancement in electrical conductivity of Li<Subscript>2</Subscript>O: B<Subscript>2</Subscript>O<Subscript>3</Subscript>: V<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

The study of electrical conductivity of 30Li₂O: (70 − x) B₂O₃: xV₂O₅ glass samples has been carried out. The results have been explained by dividing the temperature range into two regions. In region I, conductivity shows Arrhenius behaviour for all the samples. The conductivity increases with addition of V₂O₅. The results have been explained in the light of Anderson and Stuart Model. In region II, an anomalous enhancement in the conductivity is observed for all the samples up to certain temperature beyond which the conductivity decreases. The enhancement in the conductivity in the annealed glass sample has been attributed to nanocrystallization.     

Phase relations in the Ag<Subscript>8</Subscript>SnS<Subscript>6</Subscript>-Ag<Subscript>2</Subscript>SnS<Subscript>3</Subscript>-AgBr system and crystal structure of Ag<Subscript>6</Subscript>SnS<Subscript>4</Subscript>Br<Subscript>2</Subscript>

The T-x phase diagram of the Ag-Sn-S-Br system has been studied in the composition region Ag₈SnS₆-Ag₂SnS₃-AgBr, and a compound of composition Ag₆SnS₄Br₂ has been identified. Ag₆SnS₄Br₂ has a new structure, closely related to that of Ag₆GeS₄Br₂: sp. gr. Pnma, a = 6.67050(10), b = 7.82095(9), c = 23.1404(3) Å, Z = 4, R _B = 0.0519, R _wp = 0.0782, χ² = 1.36.     

Synthesis and luminescence properties of a Li<Subscript>3</Subscript>BaCaY<Subscript>3</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>8</Subscript>:Er<Superscript>3+</Superscript> phosphor with a layered scheelite-like structure

A Li₃BaCaY₃(MoO₄)₈:Er³⁺ phosphor with a scheelite-like structure (sp. gr. C2/c) has been synthesized and its luminescence properties have been studied. The phosphor has been characterized by X-ray diffraction, differential thermal analysis, and IR spectroscopy.     

Ho<Subscript>2</Subscript>S<Subscript>3</Subscript>-Ga<Subscript>2</Subscript>S<Subscript>3</Subscript> phase diagram

The Ho₂S₃-Ga₂S₃ system has been studied using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements, and its phase diagram has been constructed. The system contains three ternary compounds: Ho₃GaS₆, HoGaS₃, and Ho₆Ga_10/3S₁₄. Their melting behavior has been studied for the first time. The compound Ho₆Ga_10/3S₁₄ melts congruently at 1435 K; Ho₃GaS₆ and HoGaS₃ melt incongruently at 1370 and 1250 K, respectively. The Ho₂S₃-Ga₂S₃ system is a pseudobinary join of the ternary system Ho-Ga-S. At room temperature, the β-Ga₂S₃-based solid solution extends to 1.5 mol % Ho₂S₃; the Ho₂S₃ solubility in γ-Ga₂S₃ is 10 mol %. The compounds HoGaS₃ and Ho₃GaS₆ crystallize in orthorhombic symmetry (Ho₃GaS₆: a = 10.40 Å, b = 13.20 Å, c = 6.44 Å, Z = 4; HoGaS₃: a = 6.8 Å, b = 9.92 Å, a = 3.08 Å, Z = 4). Ho₆Ga_10/3S₁₄ has a hexagonal structure (a = 9.62 Å, c = 6.04 Å).     

Synthesis and crystal structure CoNi<Subscript>2</Subscript>(BO<Subscript>3</Subscript>)<Subscript>2</Subscript>

A new metal orthoborate compound, cobalt dinickel orthoborate, CoNi₂(BO₃)₂ has been successfully synthesized for the first time. The title compound was synthesized by thermally-induced solid-state chemical reaction at 900°C between the initial reagents of Co(NO₃)₂ · 6H₂O, Ni(NO₃)₂ · 6H₂O and H₃BO₃ which were mixed with the mol ratio of 1: 2: 2 respectively. The obtained product was structurally characterized by X-ray powder diffraction technique. It has been found that the CoNi₂(BO₃)₂ crystallizes in the kotoite type and isostructural with the compounds having the chemical formula M₃(BO₃)₂ where M—Mg, Co and Ni. The synthesized compound belongs to the orthorhombic crystal system with the refined unit cell parameters of a = 5.419(9) Å, b = 8.352(0) Å, c = 4.478(8) Å and Z = 2. The space group was determined as Pnmn. Further characterizations by FTIR, elemental analysis and thermal analysis were also performed.     

Synthesis,structure, and thermal expansion of M<Subscript>2</Subscript>Fe<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>16</Subscript> and MFeTiO<Subscript>4</Subscript> compounds

Compounds that crystallize in four structure types in M₂O-Fe₂O₃-TiO₂ systems have been prepared by solid-state reactions. The M₂Fe₂Ti₆O₁₆ (M = Rb, Cs) compounds have been prepared for the first time. The thermal expansion coefficients of the MFeTiO₄ (M = Li, Na) and M₂Fe₂Ti₆O₁₆ (M = Na, K, Rb, Cs) compounds have been determined by high-temperature X-ray diffraction.     

Liquid-phase epitaxy of NdAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> and Yb-doped YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>

Epitaxial layers of NaAl₃(BO₃)₄ (NAB) and YAl₃(BO₃)₄〈Yb〉 (YAB〈Yb〉) containing up to 10 at % Yb have been grown by liquid-phase epitaxy on YAB substrates. Their growth kinetics have been studied at relative supersaturations of the high-temperature solution from 2 × 10^?2 to 16 × 10^?2. The ytterbium concentration in YAB〈Yb〉 has been shown to vary little during the epitaxial process. Near the edges of the substrate, the surface morphology of the layers is complicated by vicinals, which have a spiral form in the case of YAB〈Yb〉. On \(\{ 10\overline 1 1\} \) YAB substrates, homogeneous single-crystal NAB films have been grown.     

Synthesis and x-ray diffraction study of solid solutions in the Zn<Subscript>2</Subscript>SnO<Subscript>4</Subscript>-Zn<Subscript>2</Subscript>TiO<Subscript>4</Subscript>-Zn<Subscript>2</Subscript>ZrO<Subscript>4</Subscript> system

The multicomponent refractory oxide system Zn₂(Ti_aSn_b)_{1 ? x} Zr_xO₄ (a + b = 1; a: b = 1: 5, 1: 4, 1: 3, 1: 2, 1: 1, 1: 0, 2: 1, 3: 1, 4: 1; x = 0?1.0; Δx = 0.05) has been studied by x-ray diffraction, using samples prepared by melting appropriate oxide mixtures in a low-temperature hydrogen-oxygen plasma. Two phases, both with wide homogeneity ranges, have been identified: α-phase, with a cubic inverse spinel structure, and β-phase, with a tetragonal spinel structure. The phase boundaries in the system have been determined. Structural data are presented for about 100 solid solutions of different compositions.