Precipitation of nanometer-sized SnO2 crystals and Sn depth profile in heat-treated float glass

The effect of oxygen diffusion from the atmosphere on tin depth profile in the bottom face of a soda-lime-silica float glass at temperatures above T_g was investigated. The heat treatment was performed in ¹⁸O₂/N₂ and argon (Ar) atmospheres. The significant diffusion of tin to the surface was observed for the glass heat-treated in ¹⁸O₂/N₂ atmosphere, resulting in the formation of a tin-enriched layer near the surface region. It was found that the tin was supplied from the region shallower than the ‘hump’ which is commonly observed in the tin profile of a commercial soda-lime-silica float glass. No significant change in the tin depth profile was observed for the glass heat-treated in Ar atmosphere. These results indicate that ¹⁸O diffusion into the glass, which causes the change in chemical state of tin from Sn²⁺ to Sn⁴⁺, induces the significant diffusion of tin. Furthermore, the precipitation of crystalline SnO₂ particles with a diameter of ∼1 nm was clearly recognized in the tin-enriched layer. This fact indicates that a phase separation was induced by the oxygen diffusion into the glass. Consequently, Sn²⁺ may be supplied to the surface in order to compensate for the marked decrease in Sn²⁺ concentration in the glass system. The significant diffusion of tin to the surface was suppressed by increasing the iron content in the glass. This suppression was ascribed to the increase in Sn⁴⁺ concentration as a result of the redox reaction between tin and iron because the diffusion coefficient of Sn⁴⁺ is much smaller than that of Sn²⁺.     

Structure and optical properties of chalcohalide glasses doped with Pr and Yb ions

Glasses of systems 100-y((GeS₂)₈₀(Sb₂S₃)_20−x(PbI₂)_x)yPr₂S₃, x = 0; 2; 5, 8; y = 0; 0.01; 0.1; 0.5 and 99.9-z((GeS₂)₈₀(Sb₂S₃)₁₈(PbI₂)₂)0.1Pr₂S₃zYb₂S₃, z = 0.05; 0.1; 0.15) were synthesized in high purity. Optically well transparent glasses were obtained for x  5 mol.% PbI₂, for y  0.1 mol.% Pr₂S₃ and for z  0.15 mol.% Yb₂S₃. The glasses were stable and homogeneous, as confirmed by X-ray diffraction and electron microscopy, with high optical transmittivity from visible (red) region up to infrared region (900 cm⁻¹). The density of the glasses was 3.26–3.33 gcm⁻³ for PbI₂ containing glasses. The glass transition temperature, T_g, was 320–336 °C. The optical absorption bands in rare-earth doped glasses corresponded to ³H₄–³F₄, ³H₄–³F₃, ³H₄–(³F₂ + ³H₆) f–f electron transitions of Pr³⁺ ions and to ²F_7/2–²F_5/2 f–f electron transitions of Yb³⁺ ions. Strong luminescence band with maximum near 1340 nm (electron transition ¹G₄–³H₅) was found in Pr₂S₃ doped glasses. The intensity of this band was rising with doping by Yb³⁺ ions. The possible mechanism of the luminescence enhancement is suggested.     

Tin valence and local environments in silicate glasses as determined from X-ray absorption spectroscopy

X-ray absorption spectroscopy (XAS) was used to characterize the tin (Sn) environments in four borosilicate glass nuclear waste formulations, two silicate float glasses, and three potassium aluminosilicate glasses. Sn K-edge XAS data of most glasses investigated indicate Sn⁴⁺O₆ units with average Sn-O distances near 2.03 Å. XAS data for a float glass fabricated under reducing conditions show a mixture of Sn⁴⁺O₆ and Sn²⁺O₄ sites. XAS data for three glasses indicate Sn-Sn distances ranging from 3.43 to 3.53 Å, that suggest Sn⁴⁺O₆ units linking with each other, while the 4.96 Å Sn-Sn distance for one waste glass suggests clustering of unlinked Sn⁴⁺O₆ units.     

Optical and spectroscopic characterization of germanium selenide glass films

A previews study of germanium selenide glass films by scanning electron microscopy and atomic force microscopy revealed a heterogeneous surface morphology consisting of granular regions 15–50 nm in size, which cause high optical losses. The present work was performed in order to further characterize such materials using spectroscopic ellipsometry, infrared (IR) and Raman spectroscopies. Chalcogenide glass films with GeSe₂, Ge₂₈Sb₁₂Se₆₀ and GeSe compositions have been deposited on single crystal silicon and silica glass substrates by vacuum thermal evaporation. The film thickness and the optical constants were obtained from spectroscopic ellipsometry using the Tauc-Lorenz dispersion formula. A model was derived for the film structure, which included a roughness layer at the surface. This top layer was found to have a thickness of 5–15 nm, of the order of the size of the granular regions previously reported. The optical bandgap of the samples increased with increasing selenium content, while the refractive index decreased. Despite a previous report of large scale phase separation in bulk Ge₂₆Sb₁₄Se₆₀ glass, the fundamental IR and Raman spectra obtained in the present work did not provide any clear evidence for such phase separation which could be associated with the heterogeneous nanostructure observed at the surface of the films.     

Redox profile of the glass surface

The redox profiles of tin, iron and sulfur at the float glass surface were determined on purposely cut samples by Electron Probe Micro Analysis (EPMA), X-ray Fluorescence mapping and X-ray Absorption Spectroscopy (XAS) at the micron scale. Going inward from the surface to the bulk, it was observed that (features do not depend on the glass thickness (holding time) though they extend over depths that vary from ca. 25 to 50 μm): (i) after a diffusion-driven decrease and prior to vanishing, the tin concentration passes through a local maximum (the tin hump), where stannous ions, which dominate the shallow layers, switch to stannic ions; (ii) the iron concentration decreases, passes through a minimum at the tin hump where iron is in the more reduced form (lowest Fe³⁺/Fe²⁺ ratio); it then increases and, after a hump which appears as a chemical echo of the tin hump, it reaches the bulk value; (iii) the concentration of sulfur increases up to reach the bulk concentration beyond the tin hump region. In a mixed S⁶⁺/S^2? form at the surface, sulfur is only in sulfate form in the bulk.In the case under study, the iron concentration is much too low to balance the redox reaction Sn²⁺ → Sn⁴⁺ that occurs at the tin hump. Sulfur is shown to play the role usually attributed to iron, according to the reaction4Sn²⁺ + S⁶⁺ → 4Sn⁴⁺ + S^2?The occurrence of that reaction is supported by the appearance of sulfide S^2? in the tin hump region with an appropriate concentration profile of a much stronger S^2?/S⁶⁺ ratio on the tin side than on the atmosphere side of the float glass. The conclusions drawn herein likely apply to the many cases in which the glass composition is similar as that encountered herein.     

Optical properties of chalcogenide multilayer deposited on Au layer

The chalcogenide multilayers were prepared as dielectric mirrors having the first order stop bands in the near infrared region 1.55 μm. The 7.5 layer pairs of the alternating amorphous Sb–Se and As–S layers were deposited on glass substrates using a conventional thermal evaporation method. To center the stop bands of the 15-layer dielectric mirrors at 1.55 μm, the layer thicknesses 117 nm for Sb–Se and 169 nm for As–S single layers were calculated from the quarter wave stack condition. The optical reflection and transmission spectra of the prepared mirrors were measured using a UV/VIS/NIR and FT-IR spectroscopy at the ambient and elevated temperatures. The optical reflection of the annealed 15-layer chalcogenide mirror was found higher than 99% in the range of 1440–1600 nm. As the 200 nm thick gold layer was added between the substrate and the chalcogenide mirror, the stop band of the annealed Au/multilayer system broadened to 1360–1740 nm simultaneously with an appearance of the 15% transmission peak at 1.55 μm. A preparation of similar metal/multilayer systems is one of the possible ways how to design the dielectric filters for near infrared region exploiting the good optical quality of the chalcogenide films and their simple deposition.     

Synthesis and characterization of tin containing molybdophosphate and tungstophosphate glasses

Two series of tin containing molybdophosphate and tungstophosphate glasses and glass-ceramics were achieved by means of a domestic microwave oven under air. During melting, a redox reaction takes place between Sn²⁺ and Mo⁶⁺ generating the crystallization of a Na(Sn^IV,Mo^IV)(PO₄)₃ solid solution with a NZP (NaZr₂P₃O₁₂) type structure. Such reactivity was not underlined in the case of the W-series. All the samples were characterized from a thermal and mechanical point of view as a function of the RO₃ (R = Mo, W) for SnO substitution. Two types of behaviors were identified. For the Mo-series, all the characteristics, except density, present an extremum value for the chemical composition with a 1:1 SnO-MoO₃ molar ratio. This is strongly correlated to the amount of NZP crystals present in the glass ceramic, the different behavior observed for the density being due to the low compactness of the NZP phase. For the W-series, all these different characteristics varies monotonously according to a progressive strengthening of the network by replacement of a low field strength ion (Sn²⁺) by a higher field strength ion (W⁶⁺). In addition, the solid state reactivity of a 1:1 SnO-RO₃ mixture was examined confirming the absence of any redox process between SnO and WO₃ during the glass synthesis.     

Synthesis,Characterization and Crystal Structure of the Bis(2,4-dinitrobenzoato)tetrabutyldistannoxane(IV) Dimer

Abstract The title compound, bis(2,4-dinitrobenzoato)tetrabutyldistannoxane(IV), was obtained from the reaction of di-n-butyltin(IV) oxide with 2,4-dinitrobenzoic acid. It crystallizes out as the usual dicarboxylatotetrabutyldistannoxane(IV) dimer. In the monoclinic system P2₁/c, a = 12.391(3) ?, b = 19.937(5) ?, c = 15.026(4) ?, α = γ = 90°, β = 102.857(2)°, V = 3618.95(16) ?³ and Z = 2. A crystal structure determination of the title compound reveals the presence of a centrosymmetric planar Sn₂O₂, with two different environments for tin atoms and two distinct carboxylate groups. Two of the carboxylate groups are bonded to the exocyclic tin atom in a bidentate bridging manner and the remaining two carboxylate groups are bonded to the tin atom in a monodentate manner. As a result, both the tin atoms moieties in the complex are five coordinate and exhibit trigonal bipyramid geometry. Index Abstract Synthesis, Characterization and Crystal Structure of the Bis(2,4-dinitrobenzoato)tetrabutyldistannoxane(IV) Dimer Yip Foo Win, Teoh Siang Guan, Lim Eng Khoon, Shea Lin Ng, Hoong Kun Fun A crystal structure determination of the title compound reveals the presence of a centrosymmetric planar Sn₂O₂, with two different environments for tin atoms and two distinct carboxylate groups.      

Effect of silver doping on the structure and phase separation of sulfur-rich As–S glasses: Raman and SEM studies

We report on the structural details and microphase separation of the bulk glasses Ag_x·(As₃₃S₆₇)_100-x for 0x25. Glass–glass phase separation occurs over a wide range of Ag content, i.e. 4x20. An off-resonant polarized Raman spectroscopic study has been carried out to elucidate structural aspects at the short- and medium-range structural order of the glasses. Analysis of Raman spectra revealed quantitative changes of the sulfur-rich microenvironments that reduce upon adding Ag. Scanning electron microscopy combined with X-rays microanalysis have been utilized to examine the type and extent of phase separation, and to provide quantitative details on the atomic concentrations in the Ag-poor and Ag-rich phases. It has been shown that at 7 at.% Ag the Ag-rich phase percolates through the structure; this effect can be associated with an ionic-to-superionic behavior of these glasses in accordance with similar studies on the stoichiometric arsenic sulfide glass; although the phase separation observed in the present glasses is qualitatively different.     

Effect of tin-oxide on the physical properties of soda-lime–silica glass

The effect of tin-oxide on the physical properties of soda-lime–silica glasses was investigated. Glasses containing tin-oxide concentrations ranging from 0 to 3 mol% were synthesized in the laboratory. In some of the glasses, an attempt was made to control the ratio of Sn²⁺ to Sn⁴⁺ present in the glass. Dilatometry, beam-bending viscosity, and sonic resonance experiments were performed on the glasses to determine the role of tin on the thermal expansion, glass transition temperature, dilatometric softening temperature, annealing temperature, strain temperature, and elastic modulus of the glass. Mössbauer spectroscopy was used to determine the presence and relative amount of Sn²⁺ and Sn⁴⁺ in the glasses. The data suggest that the substitution of relatively small amounts of tin for a modifier species in the glass composition results in an increase in the network connectivity. In addition, the results suggest that this increase in network connectivity is more apparent in glasses containing higher relative amounts of Sn⁴⁺ compared to Sn²⁺.     

Growth and characterization of pendeo-epitaxial GaN on 4H–SiC substrates

Growth on AlN/4H–SiC substrates of coalesced, non-polar GaN films having volumes of material with reduced densities of dislocations and stacking faults has been achieved from etched stripes via the statistical and experimental determination of the effect of temperature and V/III ratio on the lateral and vertical growth rates of the GaN{0 0 0 1} faces combined with pendeo-epitaxy. AFM of the uncoalesced GaN(0 0 0 1) and GaN vertical faces revealed growth steps with some steps terminating at dislocations on the former and a pitted surface without growth steps, indicative of decomposition, on the latter. Coalescence was achieved via (a) a two-step route and the parameters of (1) and V/III=1323 for 40 min and (2) 1020 °C and V/III=660 for 40 min and (b) a one-step route that employed and a V/III ratio=660 for 6 h. The densities of dislocations in the GaN grown vertically over and laterally from the stripes were 4×10¹⁰ cm⁻² and 2×10⁸ cm⁻², respectively; the densities of stacking fault in these volumes were 1×10⁶ cm⁻¹ and 2×10⁴ cm⁻¹, respectively. The defects in the wing material were observed primarily at the bottom of the film where lateral growth of the GaN occurred from the AlN and the SiC. Plan view AFM also revealed different microstructures and a reduction in the RMS roughness values from 1.2 to 0.95 nm in these respective regions.     

119Sn Mössbauer studies of glassy and crystalline compounds in the chalcogenide system SeSnAs

¹¹⁹Sn Mössbauer measurements have been carried out on 18 chalcogenide glasses of different composition in the system SeSnAs. In all cases tin is four-coordinated and appears to be tetrahedrally surrounded by selenium. Two of the glasses (Se₆₀Sn₃As₃₇ and Se₄₇Sn₃As₅₀) were crystallized by heat treatment, and their Mössbauer spectra have been measured as a function of crystallization temperature and annealing time. As a result of the heat treatment, crystalline SnSe and SnSe₂ are precipitated. The amount of each compound is determined by the composition of the original glass and the remaining glassy or crystalline phase (As₂Se₃ and As₄Se₄). The degree of the crystallization depends on the temperature and the annealing time, but not the mass ratio of the tin selenides formed.     

Preparation and the growth mechanism of zinc blende structure tin sulfide films by successive ionic layer adsorption and reaction

Zinc blende structure tin sulfide (SnS) films have been prepared by successive ionic layer adsorption and reaction (SILAR) method. It is found that both the annealing and addition of NH₄Cl or NaCl to cation solution during the SILAR process can promote the crystallization of SnS films. The growth mechanism for this novel structure considered that the initial distribution of cations on the substrate surface during the cation adsorption process is the crucial factor that determines the structure of the final production. Because Cl⁻ anions can complex with Sn²⁺ cations, when the concentration of Cl⁻ in the cation precursor solution increases, more [SnCl]⁺ complex ions are adsorbed on the substrate. These [SnCl]⁺ ions assemble more orderly than Sn²⁺ ions because of the polarity of ions, so crystallized SnS films can be obtained when NH₄Cl or NaCl is added to the cation solution.     

The phase transformation behaviors of Sn2+-doped Titania gels

The transformation behaviors of Sn²⁺-doped titania gels, such as transformation temperature, conversion rate and the crystal granularity, were studied by using thermo-gravimetric/differential thermal analysis and X-ray diffraction methods. Experimental results show that, anatase, rutile and SnO₂ phases can exist in the sintering products by varying Sn²⁺ content and sintering temperature. Sn²⁺-doping greatly depresses the growth of anatase and rutile crystals and so obtaining nanosized crystals The transformation temperatures of gel to anatase and anatase to rutile first decrease and then increase with an increase of Sn²⁺ content, while both of the transformation rates are associated with Sn²⁺ content, change in its valence and the sintering temperature. It is suggested that by adjusting Ti⁴⁺/Sn⁴⁺ ratio and sintering temperature, the crystal granularity and the ratio of anatase to rutile can be tailored to optimize properties of TiO₂–SnO₂ humidity sensing ceramics.     

Epitaxial growth of tin oxide film on TiO2(1 1 0) using molecular beam epitaxy

Growth of tin oxide thin films using molecular beam epitaxy in a pyrolyzed nitrogen dioxide atmosphere on a titanium dioxide (1 1 0) substrate was investigated using X-ray photoelectron spectroscopy (XPS), electron diffraction, and atomic force microscopy (AFM). Properties of deposited films were studied for their dependence on substrate temperature and oxidation gas pressure. Analyses using XPS data revealed that tin atoms were fully oxidized to Sn⁴⁺ and SnO₂ films were grown epitaxially in deposition conditions of substrate temperatures of 627 K or higher and NO₂ pressure greater than 3×10⁻³ Pa. At a substrate temperature of 773 K, a smooth surface with atomic steps was visible in the SnO₂ films, but above or below this temperature, fine grains with crystal facets or porous structures appeared. At pressures of 8×10⁻⁴ to 3×10⁻⁴ Pa, the randomly oriented SnO phase was dominantly grown. Further decreasing the pressure, the Sn metal phase, which was epitaxially crystallized at less than 500 K, was also grown.     

Stimulated interdiffusion and optical recording in Sb/As2S3 nanomultilayers

The role of the compositional modulation at nano-scale dimensions (2–10 nm) in the enhancement of optical recording parameters in nanomultilayers, which contain Sb as active, optical absorbing and diffusing layers and As₂S₃ as barrier (matrix) layers was investigated. Comparison was made with single homogeneous layers made of ternary (As₂S3)_xSb_1−x glasses and co-deposited from Sb and As₂S₃. It was shown that essential increase of the recording efficiency, sensitivity of the bleaching process, broadening of its spectral range occurs due to the stimulated interdiffusion of adjacent components in Sb/As₂S₃ nanomultilayers with optimized Sb layer thickness.     

Peculiarities of photoluminescence excited by 157 nm wavelength F2 excimer laser in fused and unfused silicon dioxide

Photoluminescence (PL) spectra and kinetics of high purity amorphous silicon dioxide with ultra low hydroxyl content is studied under the excitation by F₂ excimer laser (157 nm wavelength) pulses. Materials synthesized in the SPCVD plasma chemical process are studied before and after fusion. Two bands are found in the PL spectra: one centered at 2.6–2.9 eV (a blue band) and the other at 4.4 eV (a UV band). Luminescence intensity of unfused material is found to increase significantly with exposure time starting from a very small level, whereas in fused counterpart it does not depend on irradiation time. Both bands show complicated decay kinetics, to which add exponential and hyperbolic functions. The UV band of the unfused material is characterized by decay with exponential time constant τ  4.5 ns and hyperbolic function t⁻ⁿ, where n = 1.5 ± 0.4. For the blue band the hyperbolic decay kinetics with n  1.5 extends to several milliseconds, gradually transforming to the exponential one with τ = 11 ± 0.5 ms. In fused glass relative contribution of the fast component to the UV band is small whereas for the blue one it is great, that allows one to more accurately determine the hyperbolic law factor n = 1.1 ± 0.1 typical for tunneling recombination. Simultaneous intracenter and recombination luminescence, the later occurring with the participation of laser radiation induced defects, add particular features to the decay kinetics. Spectra of the above luminescence processes are different. A less sharp position of bands is associated with the recombination luminescence. The origin of the observed PL features we attribute to the presence of oxygen deficient centers in glass network in the form of twofold coordinated silicon. Such centers being affected by network irregularities can be responsible for the recombination PL component. A great variety of network irregularities is responsible for centers’ structural inequivalence, which causes a non-uniform broadening of PL spectral and kinetic parameters.     

Spontaneous growth of single crystals of various shapes in tin-fullerite films

Changes in the structure and elemental and phase compositions of tin-fullerite films after their storage in air are investigated by X-ray diffraction, scanning electronic microscopy, atomic force microscopy, X-ray spectroscopic microanalysis, and Auger electron spectroscopy. Formation of the new phase Sn_xC₆₀, whisker tin and Sn_xC₆₀ crystals, and petal and flowerlike fullerite crystals under the action of internal stress is established.     

Study on the crystal and molecular structure of triphenyl tin methacrylate: (C6H5)3SnOCOCCH2CH3

The crystal and molecular structure of (C₆H₅)₃SnOCOCCH₂CH₃ has been determined by a single crystal X-ray diffraction study. The crystal is monoclinic with space group P2₁/c,a=11.902(3),b=10.104(4),c=16.721(2) Å,=97.56(1)°,V=1930.4 ų,Z=4 andD _c =1.495 g/ cm³,F(0,0,0)=872,(CuK)=1.5418 Å. The structure was solved by the heavy-atom method and refined by full-matrix least-squares procedures to anR factor of 0.060 based on 2157 independent reflections. The results showed that the Sn-O bond distance is 2.064(4) Å. The average Sn-C bond distance is 2.126 Å. There is a weak coordination through the O of the CO group of the methacrylate residue (Sn-O(2) 2.774(5) Å) except for four normal coordinations. The coordination number at the Sn⁴⁺ is 5.     

Mercury(II) complex with terpyridine: structure of the 2∶1 solvate of [Hg(terpy)2](CF3SO3)2 with acetone

[Hg(terpy)₂](CF₃SO₃)₂·0.5(CH₃)₂CO crystallizes in the triclinic space group witha=14.631(6),b=15.258(4),c=18.785(7) Å, =69.66(2), =70.72(1), =88.55(1)°. The crystal structure consists of two independent [Hg(terpy)₂]²⁺ cations, four trifluoromethanesulfonate anions and an acetone molecule in the asymmetric unit. Each mercury atom is coordinated by two tridentate terpyridine ligands forming an irregular six-coordination polyhedron. The Hg–N bond lengths range from 2.27(2) to 2.53(2) Å.