Interstitial Oxygen in Tin-Doped Indium Oxide Transparent Conductors

We report first-principles density functional theory calculations of interstitial oxygen in tin-doped indium oxide (ITO), a transparent conducting oxide. Interstitial oxygen plays a critical role in the defect of ITO because it is by removal of interstitial oxygen that n -type charge carriers are produced. The Frank and Köstlin defect model successfully rationalizes the observed conductivity, Sn-doping, and oxygen partial pressure dependencies of ITO by postulating that tin atoms, which substitute for indium, are clustered with interstitial oxygen. Structural evidence for such a clustering, however, remains ambiguous. Recently published Rietveld refinement results of X-ray and neutron diffraction data found interstitial oxygen to be significantly displaced (0.4 Å) from the ideal fourfold position. Our calculations show that the experimental position is plausible only if interstitial oxygen is clustered with Sn_In defects at any of the three d -type cation sites nearest to the interstitial, thereby providing direct structural confirmation of the Frank and Köstlin defect model.     

Defect structures and dopant solution states of Hf-doped Si3N4 ceramics

Transition-metal-doped silicon nitride ceramics have attracted much attention as gate materials for semiconductors because of their electrical properties as well as chemical and thermal stability. The present study aims to clarify the defect structures of Hf-doped β-Si₃N₄ by theoretical calculations and scanning transmission electron microscopy (STEM). First-principles calculations based on a hybrid functional method were performed. It was found that Hf dopants are mainly substituted for the Si sites and can be occasionally located at interstitial sites in the lattice of β-Si₃N₄. The substitution sites of Hf dopants predicted by the first-principles calculations were also confirmed by the high-resolution STEM images.     

Sol–Gel Processing and Characterization of Pure and Metal-Doped SnO2 Thin Films

A chloride-based inorganic sol–gel route was used for preparing pure and metal (osmium, nickel, palladium, platinum)-doped SnO₂ sol. SnCl₄ was first reacted with propanol, then the resulting compound was hydrolyzed and subsequently mixed with solutions of the metal dopants. The obtained sols were used for depositing thin films by spin coating or for preparing powders by solvent evaporation at 110°C. FTIR spectroscopy and thermal analysis of the powders revealed that chlorine still bound to tin stabilized the sol against gelation by hindering the condensation reactions. Film characterizations showed that platinum and palladium, unlike nickel and osmium, were likely to form nanoparticles in the SnO₂ lattice. This result was discussed with regard to the different ways that platinum and palladium, on one hand, and nickel and osmium, on the other, modified the growth of SnO₂ grains and the film roughness and morphology. Dopants that formed nanoparticles (platinum, palladium) resulted in the roughest film, while dopants that did not form particles (nickel, osmium) resulted in SnO₂ grain size very close to that of pure SnO₂.     

Atomistic Modeling of Effect of Mg on Oxygen Vacancy Diffusion in α‐Alumina

Oxygen diffusion plays an important role in grain growth and densification during the sintering of alumina ceramics and governs high‐temperature processes such as creep. The atomistic mechanism for oxygen diffusion in alumina is, however, still debated; atomistic calculations not being able to match experimentally determined activation energies for oxygen vacancy diffusion. These calculations are, however, usually performed for perfectly pure crystals, whereas virtually every experimental alumina sample contains a significant fraction of impurity/dopants ions. In this study, we use atomistic defect cluster and nudged elastic band (NEB) calculations to model the effect of Mg impurities/dopants on defect binding energies and migration barriers. We find that oxygen vacancies can form energetically favorable clusters with Mg, which reduces the number of mobile species and leads to an additional 1.5 eV energy barrier for the detachment of a single vacancy from Mg. The migration barriers of diffusive jumps change such that an enhanced concentration of oxygen vacancies is expected around Mg ions. Mg impurities were also found to cause destabilization of certain vacancy configurations as well as enhanced vacancy–vacancy interaction.     

Hydrolysis Deposition of Thin Films of Antimony-Doped Tin Oxide

Thin films of antimony-doped tin oxide have been obtained by a new technique, the so-called hydrolysis deposition method, in which hydrolyzed solids are precipitated from metal fluoride solutions. Mixed solutions of SnF₃ and SbF₃ produce antimony- and fluorine-doped tin oxide films. The amount of antimony can be controlled in a wide range by adjusting the initial fluoride concentrations of the solution. The film containing 2.9 mol% antimony heated at 500°C has an electrical resistivity of 1.0 × 10⁻³Ω·cm, which is lower than previously obtained by wet-chemical techniques.     

Investigations of Electrical Properties in Silica/Indium Tin Oxide Two-Layer Film for Effective Electromagnetic Shielding

The effect of zinc ions added to silica film on the electrical and structural properties of a silica/indium tin oxide two-layer film which had been prepared by solution coating for electromagnetic shielding of displays was studied. The volume resistivity of the undoped silica/indium tin oxide film was more than 3 times as high as that of the zinc-doped silica/indium tin oxide film. The addition of divalent cations, zinc ions, to the overcoated layer led volume resistivity of the two-layer film to decrease significantly and also caused a long-term increase in stability. The decrease in volume resistivity was due to the addition of zinc ions that changed the interface ionization and helped to enhance the electrical conductivity in the two-layer film.     

Synthesis and Structural Characterization by X-ray Absorption Spectroscopy of Tin-Doped Mullite Solid Solutions

The formation of solid solutions between tin cations and mullite by calcination at 1400°C of amorphous precursors prepared by pyrolysis of aerosols is reported. The oxidation state of the tin cations and the position that they occupy in the mullite structure have been analyzed using XAS (XANES and EXAFS) spectroscopy, which shows that the tetravalent tin cations are located at the octahedral positions of the Al³⁺ ions, which induces cell expansion. The limit of tin incorporation under the experimental conditions reported here correspond to a tin/mullite mole ratio of ∼5%, which is within the range previously reported for other tetravalent cations (4%–6%).     

Effect of Dopants on Zirconia Stabilization—An X-ray Absorption Study: I, Trivalent Dopants

Local atomic structures of Zr and dopant cations in zirconia solid solutions with Fe₂O₃, Ga₂O₃, Y₂O₃, and Gd₂O₃ have been determined. The Zr ions in both partially stabilized tetragonal and fully stabilized cubic zirconia have their own characteristic structures which are dopant-independent. The dopant cations substitute for Zr ions despite severe local distortions necessitated by the large difference in dopant–O distance ana Zr─O distance. Dopant ionic size determines the preferred locations of oxygen vacancies. Vacancies introduced by oversized dopants (Y and Gd) are located as nearest neighbors to Zr atoms, leaving 8-fold oxygen coordination to dopant cations. Undersized dopants (Fe and Ga) compete with Zr ions for the oxygen vacancies in zirconia, resulting in 6-fold oxygen coordination and a large disturbance to the surrounding next nearest neighbors. Since oxygen vacancies associated with Zr can provide stability for tetragonal and cubic zirconia, these results suggest an explanation for the observation that oversized trivalent dopants are more effective than undersized trivalent dopants in stabilizing cubic and tetragonal phases.     

Preparation and optical properties of Sn- and Ga-doped indium oxide semiconductor nanoparticles

Indium tin oxide (ITO) nanoparticles and gallium-doped indium tin oxide (GITO) nanoparticles with various molar ratios of dopants were prepared by a solution method in oleylamine. Characterization of crystal, morphology, and optical properties was carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible (UV–Vis), photoluminescent (PL), and Fourier transform infrared spectroscopy (FT-IR). XRD patterns show that with increasing of Sn, the crystal structure of ITO nanoparticles varies gradually from standard cubic bixbyite In₂O₃ to amorphous and to standard tetragonal SnO₂, whereas the GITO nanoparticles retain the crystal structure of ITO. The smallest particle size is around 10 nm, and the morphology of the particles is nearly spherical. The smallest particles, though coated with oleylamine, tend to aggregate forming larger flower-like particles. Defect level emission at the present of dopants was observed in the PL spectra of the ITO and GITO nanoparticles.     

Growth and characterization of ZnO/ZnTe core/shell nanowire arrays on transparent conducting oxide glass substrates

ABSTRACT: We report the growth and characterization of ZnO/ZnTe core/shell nanowire arrays on indium tin oxide. Coating of the ZnTe layer on well-aligned vertical ZnO nanowires has been demonstrated by scanning electron microscope, tunneling electron microscope, X-ray diffraction pattern, photoluminescence, and transmission studies. The ZnO/ZnTe core/shell nanowire arrays were then used as the active layer and carrier transport medium to fabricate a photovoltaic device. The enhanced photocurrent and faster response observed in ZnO/ZnTe, together with the quenching of the UV emission in the PL spectra, indicate that carrier separation in this structure plays an important role in determining their optical response. The results also indicate that core/shell structures can be made into useful photovoltaic devices.     

Effective Doping in Cubic Si3N4 and Ge3N4: A First-Principles Study

First-principles calculations have been conducted to investigate impurities in cubic Si₃N₄ and Ge₃N₄. Impurity species suitable for n - and p -type doping are suggested, in terms of the formation and ionization energies. The suggested species are P and O as n -type dopants and Al as a p -type dopant for c -Si₃N₄, and Sb and O as n -type dopants and Al as a p -type dopant for c -Ge₃N₄. The dependence of the formation energies on the chemical potentials indicates that a proper choice of growth conditions is mandatory for suppressing the incorporation of these impurities into anti and interstitial sites, where the impurities can be charged to compensate carriers.     

Effects of electrostatic field strength on grain-boundary core structures in SrTiO3

Understanding interactions between externally applied electric fields and the interfacial structures of nanoscale ceramics is important for controlling their functional properties. In ceramic oxides, functional properties are determined by oxygen vacancy concentrations near and within grain-boundary core structures. In this study it is shown that the application of electrostatic fields ranging from 0 to nominally 170 V/cm during diffusion bonding of bicrystals alters the atomic and electronic core structures of (100) twist grain boundaries in SrTiO₃. The applied electric field strength affects local oxygen vacancy concentrations and ordering of the oxygen sublattice. Results for this model system indicate that electrostatic fields applied during ceramic manufacturing can be employed as a new processing parameter to tailor defect structure configurations and obtain unprecedented ceramic microstructures. The ability to manipulate interface configurations with electric fields in the absence of any sintering additives may have far reaching implications for tuning polarization and band structures in electroceramics while avoiding effects of often unwanted dopants.     

Homogeneous Precipitation of Hydrous Tin Oxide Powders at Room Temperature Using Enzymatically Induced Gluconic Acid as a Precipitant

Hydrous tin oxide powders were precipitated at room temperature via the neutralization of sodium stannate with gluconic acid. The gluconic acid was generated by the oxidation of glucose, with the assistance of a glucose oxidase/catalase system. The hydrous tin oxide, which had a large surface area, was obtained when a high concentration of enzymes was used as a solution. However, the apparent sizes of the precipitates were ∼0.3 μm, independent of the enzyme concentration. The precipitates were converted to tin oxide via calcination at temperatures >400°C.     

浅谈浮法工艺中锡缺陷的产生及有效控制

通过对锡槽内部气氛的全面分析,以及氧、硫对锡槽的污染,了解锡缺陷的产生机理和切实可行的控制方案。     

锡污染的防止与清除

从生产的机理和如何控制等方面对沾锡、光畸变、虹彩三种缺陷进行了分析和探讨,着重阐述了对锡槽锡液中含氧量的控制方法和措施,在提高浮法玻璃质量,防止浮法玻璃污染,减少玻璃表面缺陷等方面采取切实可靠的技术措施.     

Mechanisms of Dopant-Induced Changes in Intergranular SiO2 Viscosity in Polycrystalline Silicon Nitride

Mechanical spectroscopic methods and first-principles density functional calculations were applied to attempt a quantitative analysis of both atomic structure and viscous behavior of Si₃N₄ grain boundaries. In particular, the effect on the intergranular structure/viscosity of small fractions of selected anion/cation dopants was examined in comparison with the undoped polycrystal. From the point of view of mechanical spectroscopy, emphasis was placed on the morphologic analysis, as a function of frequency of oscillation, of a relaxation peak that originates from grain-boundary sliding. The morphologic characteristics of the grain-boundary peak clearly revealed the presence of significant chemical gradients among different grain boundaries for particular dopants (e.g., Cl and Ba). On dopant addition, a reduction in activation energy for viscous intergranular flow was observed which broadened the grain-boundary peak. Chemical inhomogeneities also broadened the peak shape by generating a spectrum of activation energies. First-principles density functional calculations were conducted for cluster fragment models representative of the amorphous SiO₂ intergranular film. The results explicitly showed the mechanism by which the respective dopants break bonds in the host, an action that directly reduces the viscosity of the SiO₂ film. These complementary theoretical studies assist understanding and atomic-scale rationalization of the differences in segregation behavior of different dopants incorporated into the SiO₂ film.     

降低浮法锡耗的探讨

根据浮法玻璃生产中锡耗以不同锡质缺陷的表现形式,分析了其产生的原因、特征以及如何采取措施减少锡质缺陷,降低浮法锡耗。     

Fabrication of Low-Porosity Indium Tin Oxide Ceramics in Air from Hydrothermally Prepared Powder

Compositionally homogeneous indium tin oxide (ITO) ceramics with low porosity were obtained successfully by sintering hydrothermally prepared powders. The fabrication technique began with the preparation of microcrystalline, homogeneously tin-doped (5 wt%) indium oxyhydroxide powder, under hydrothermal conditions. Low-temperature (∼500°C) calcination of the hydrothermally derived powder led to the formation of a substitutional-vacancy-type solid solution of In₂Sn_{1− x} O_{5− y} , and further heating of this phase at temperatures of >1000°C resulted in the formation of the tin-doped indium oxide phase, which had the C -type rare-earth-oxide structure. The sintering of uniformly packed, calcined powder compacts at 1450°C for 3 h in air resulted in low-porosity (∼0.7%) ITO ceramics.     

Vacancy clusters as entry ports for cesium intercalation in graphite

Graphite has been subjected to surface damage by Ar⁺ ion bombardment. It has been found by scanning tunneling microscopy (STM) that deposited Cs atoms preferentially cluster at the artificially-produced vacancy clusters in the basal plane at 300 K. Density functional theory calculations show that Cs is more strongly bound at these defect sites than at basal plane step edges, providing a plausible explanation for the experimental observation. STM reveals that Cs intercalation into graphite occurs by diffusion through these vacancy clusters, acting as entry ports to the interior, at 700 K. DFT calculations show that these defects must consist of more than four contiguous atoms in order for Cs intercalation to be energetically easy. Experimentally, Cs atom nucleation at defect sites seems to culminate at Cs cluster heights near 1 nm and cluster diameters near 5 nm. Intercalated Cs produces coherent single Cs islands in the galleries as well as layered structures caused by superposition of overlapping individual islands. Oxygen exposure to graphite containing Ar⁺-produced defects does not influence Cs clustering at the defects or Cs entry into galleries beneath the defect. However, large oxygen exposures these clusters results in diminution of Cs intercalation, probably due to surface oxidation of Cs clusters.