Stabilization of silicon-based devices in ion-containing media using thin Al2O3 platelets and MoS2 oriented thin films

A simplified analogue to an Ion-Sensitive Field-Effect Transistor (ISFET) was tested in the presence of ions. The gate electrode in an ISFET is an aqueous solution, unlike in a Metal-Oxide Field-Effect Transistor (MOSFET) where the gate is a metal. A problem with the ISFET is that the insulating oxide between the silicon and the solution is slowly penetrated by various ions such as OH^– or Na⁺ causing a change in the characteristics of the device.The application of thin alumina platelets and thin MoS₂ films as a protective insulating layer, when deposited over the insulating silicon oxide, was tested against the penetration of ions. It is shown that there is a significant decrease in the ion penetration through to the silicon oxide layer, depending on the applied bias, when the oxide is covered with thin alumina or MoS2 layers. The effect of different ions and ion concentrations are presented. Suggestions for further improvement are made.     

Effect of a quantizing magnetic field on the capacitance of MOS structures of small-gap semiconductors

An attempt is made to investigate the effect of a quantizing magnetic field on the capacitance of MOS structures of small-gap semiconductors havingn-channel inversion layers under the weak electric-field limit. It is found, takingn-channel InSb as an example, that both the MOS and surface capacitances show spiky oscillations with changing magnetic field. It is further observed that the sharpness and the depths of the spikes increase with increasing magnetic field whereas the depths are found to decrease with increasing thickness of the insulating layer. On leave of absence from the Department of Physics, Patna University, Patna, India     

The effect of photoelectrochemical etching on the performance of CdS based photoelectrochemical cells

A photoelectrochemical etching technique which was formerly used to improve the performance of CdSe¹ and Cd(Se, Te)² based photoelectrochemical cells (PEC's) was further used to improve the short-circuit current and the fill factor of CdS based PEC's. It is suggested that this method can be used to improve photovoltaic cells having CdS as one of their components.     

On the gate capacitance of MOS structures of kane-type semiconductors under magnetic quantization

An attempt is made to formulate the gate capacitance of MOS structures of Kane-type semiconductors under magnetic quantization, without any approximations of weak or strong electric field limits, on the basis of the fourth-order effective mass theory and taking into account the interactions of the conduction, light-hole, heavy-hole, and split-off bands. It is found, taking n-channel Hg_1–x Cd _x Te as an example, that the gate capacitance exhibits spiky oscillations with changing magnetic field, which is in qualitative agreement with experimental observations, reported elsewhere, in MOS structures of the same semiconductor. The corresponding results for n-channel inversion layers on parabolic semiconductors are also obtained from the expressions derived.     

Molecular dynamic simulation of the CsCl–Al2O3 interface

The interface between solid cesium chloride and α-aluminum oxide was simulated by molecular dynamics technique. It was shown that due to a misfit between lattices of the components the interfacial contact may be presented as a small-angle boundary saturated with dislocations. Also a domain structure is formed. The dislocations and interdomain boundaries act as a source of defects and give rise to the total ionic mobility along the interface and boundaries. According to the calculation at a temperature of nearly 70% of the melting point, the diffusion coefficients of ions along misfit dislocation cores and domain walls, ∼ 10^– 6 cm²/s, are only an order of magnitude lower than the corresponding values for molten salts.     

Application of BaF2-B2O3-GeO2-SiO2 glasses to metal-oxide-silicon field-effect transistors

The capacitance and voltage characteristics of field effect transistors passivated by BaF₂-B₂O₃-GeO₂-SiO₂ glasses with various water contents were investigated. As the OH absorption coefficients of the glass increased, adverse effects on the recovery of hysteresisC-V curve shifts was seen. The water content is related to the fluoride content of the BaF₂–B₂O₃–GeO₂–SiO₂ glass. The viscous flow point of the glass was lowered with increasing ionic character obtained from Hannay's equation. The source-drain current and voltage (I-V) characteristics of typical enhancement and depletion mode field effect transistors passivated with these glasses were investigated.     

Viscous How and MOS properties of CaF2-B2O3-GeO2-SiO2 glasses with ionic bonds

The capacitance and voltage (C-V) characteristics of Metal-Oxide-silicon (MOS) capacitors passivated by CaF₂B₂O₃-GeO₂-SiO₂ glasses with OH^– ions, water and fluoride contents were investigated. As the OH^– absorption coefficients of the glass increased, adverse effects on the recovery of hysteresis C-V curve shifts was observed. The content of OH^– ions is closely related to the fluoride content in the CaF2 B₂O₃-GeO₂-SiO₂ glass. The viscous-flow point of the glass was lowered with increasing degree of ionic character obtained from Hannay's equation.     

Ionic character of SrF2-B2O3-GeO2-SiO2 glasses for viscous flow and their applications to MOS capacitors

The capacitance and voltage (C-V) characteristics of metal, oxide, and semiconductors (MOS) capacitors passivated by SrF₂-B₂O₃-GeO₂-SiO₂ glasses with various water and fluoride contents were investigated. As the OH^– absorption coefficient of a glass increased, adverse effects on the recovery of shifts of the hysteresisC-V curve have been observed. The water content of ions is closely related to the fluoride content in the SrF₂-B₂O₃-GeO₂-SiO₂ glass. The viscous-flow transition point of glass was lowered with increasing degree of ionic character obtained from Hannay's equation.     

An anomalous enhancement in the electrical conductivity of Li2O : B2O3 : Al2O3 glasses

The study of electrical conductivity of 27.5 Li₂O : (72.5 − x) B₂O₃ : x Al₂O₃ glass samples has been carried out. It has been observed that the conductivity exhibits Arrhenius behavior for all samples up to glass transition temperature T_g. Beyond T_g, an anomalous enhancement followed by decrease in conductivity has been observed. The results have been explained by dividing the temperature range into two regions. In region-I, it has been observed that the conductivity variation exhibits a maximum at 2.5 mol% Al₂O₃, which has been explained on the basis of Mixed Glass Former Effect (MGFE). An anomalous enhancement in the conductivity observed in region-II has been attributed to the nucleation in the glass. The subsequent decrease in the conductivity has been attributed to the crystallization of the glass samples.     

XRD and Mössbauer spectroscopy investigation of Fe2O3–Al2O3 nano-composite

Fe₂O₃–Al₂O₃ nano-composites were synthesized by sol–gel means. The properties of samples sintered at various thermal treatment temperatures were investigated by X-ray diffraction (XRD) and Mössbauer spectroscopy (MS). The experimental results show that the γ- to α-Al₂O₃ transformation occurs at lower temperature after iron oxide doping. The samples obtained at 1173 K contained poorly crystallized γ-Al₂O₃ phase and an amorphous iron oxide. When the temperature of heating was increased to 1373 K, the sample was composed of α-Fe₂O₃/α-Al₂O₃ nano-composite and some solid solution. A superparamagnetic phenomenon was observed until the thermal treatment temperature reached 1373 K.     

Electronic transport properties of graphene/Al2O3 (0001) interface

The electronic structure and transport properties of a single layer of graphene (Gr) on α-Al₂O₃ surface are studied using the density functional theory (DFT). We present three models that take into account the atom at the termination of the alumina surface: a) Al atoms, with the center of the Gr hexagon directly over an Al atom; b) Al atoms, with a carbon directly positioned above an Al atom; c) oxygen atoms. Two processes of geometric optimization were used: (i) All the atoms of the supercell were allowed to move in accordance with the BFGS quasi-Newton algorithm; (ii) The atoms of the three topmost layers of the α-Al₂O₃ (0001) slab, including the C atoms, were allowed to move, whereas the atoms of the remaining layers were frozen in their respective atomic bulk positions. The first two models preserve qualitatively the electronic structure of the pristine Gr using the geometric optimization process (i) whereas, in the third model this structure was lost due to a significant charge transfer between the carbon and oxygen atoms irrespective of the optimization procedure. However, models (a) and (b) with the optimization (ii) reveal a p-type semiconducting behavior.     

Double correlation technique (DDLTS) for the analysis of deep level profiles in semiconductors

A very sensitive technique is presented which can be applied to determine deep level profiles in space-charge layers of Schottky barriers orpn-junctions. The method uses an extended transient capacitance technique with correlation similar to Lang's DLTS technique. The extension of DLTS to double correlation DDLTS is necessary to resolve the deep level profile and to exclude the field dependence of the capture cross-section and contact effects. By using a double-pulse capacitance transient and correlation, these undesired effects can be subtracted. Profiles can be determined for deep levels at concentrations 10⁴ times lower than the background doping. Results are reported for epitaxial GaAs which showed one major deep level at 0.18 eV below the conduction band. Near the interface to the substrate, a slight shift in energy from 0.18 to 0.19 eV is observed. A second level at 0.43 eV decays into the epi-layer in the form of a diffusion tail.     

Growth,electronic properties and thermal stability of the Fe/Al2O3 interface

Soft X-ray photoelectron spectroscopy and resonant photoemission have been used to study the growth and electronic properties of Fe ultrathin films deposited on Al₂O₃ substrates. A simultaneous multilayer growth mode has been found for Fe growth at room temperature. For iron coverages below 1 ML, Fe²⁺ species are formed at the Fe/Al₂O₃ interface, followed by the formation of a metallic iron overlayer. The bonding of Fe at very low coverages occurs by charge transfer from Fe to surface oxygen atoms, and neither hybridisation of Fe and Al states nor reduction of the Al₂O₃ substrate are observed. The thermal stability of the interface has been also studied in the range 673–873 K. Annealing produces Fe agglomeration in such a way that some areas of the Al₂O₃ substrate become fully Fe-depleted. In these Fe-depleted areas, Fe²⁺ completely disappears and Al⁰ reduced species are formed. This behaviour would explain the decrease in the magnetoresistance performance of magnetic tunnel junctions after annealing above 573 K.     

蓝宝石冲击消光晶向效应的第一性原理

蓝宝石的冲击消光现象是高压领域中的研究热点.低压段(86 GPa范围内)的实验研究表明蓝宝石的冲击消光与晶向相关,但在高压段(压力范围:131255 GPa)是否也具有晶向相关性目前尚不清楚.为此,利用第一性原理方法,分别计算了八个不同晶向的蓝宝石理想晶体和含氧离子空位缺陷晶体在高压段的光吸收性质,结果发现:1)蓝宝石在高压段的冲击消光表现出明显的晶向效应,且该效应还随压力增大而增强;一步的数据分析可以看出,在冲击实验采用的波段内,a晶向的消光最弱(透明性最好),c晶向的消光最强与c晶向的消光接近,g晶向的消光要弱于s晶向的消光.鉴于此,如果在高压段开展加窗冲击波实验,建议选择a晶向或m晶向的蓝宝石作为其光学窗口.本文结果不仅有助于深入地认识蓝宝石在极端条件下的光学性质,而且对未来的实验研究有重要的参考作用.     

The effect of supports (Al2O3, Al2O3-CeO2 and Al2O3-CeZrO2) on the nature of gold-species in supported gold catalysts

This work is concerned with the study of Au specimens produced by gold deposition on nanosized mixed oxides (alumina, ceria, zirconia) prepared by the sol-gel method using organometallic precursors. According to X-ray absorption near edge structure, extended X-ray absorption fine structure, transmission electron microscopy data, and ultraviolet-visible and X-ray photoelectron spectroscopy measurements, mixed Al-Ce-Zr oxides are quite effective for stabilization of different gold specimens. The samples pre- treated in hydrogen at 150°C are characterized by the presence of gold Au³⁺ cations located on the surface in slightly disordered octahedral oxygen coordination. Metallic gold nanoparticles with a size of about 2 nm and gold clusters were found in the samples treated in hydrogen at 300°C.     

Two-dimensional spatially ordered Al2O3 systems: Small-angle neutron scattering investigation

The structure of anodized aluminum oxide films has been investigated by the small-angle neutron scattering method. A theoretical solution is obtained for describing neutron scattering from the Al₂O₃ ordered porous structure. Analysis of the neutron-experiment data shows the possibility of obtaining porous membranes with ideally periodic hexagonal packed pores on a large area (～0.5 cm²).     

Thermal instability of HfO2 on InP structure with ultrathin Al2O3 interface passivation layer

We studied the thermal stability of HfO₂ on an InP structure when an Al₂O₃ interface passivation layer (PL) was introduced. In contrast to the thick (～4 nm) Al₂O₃‐PL, an almost complete disappearance of the thin (～1 nm) Al₂O₃‐PL was observed after a post‐deposition anneal at 600 °C. Based on various chemical and electrical analyses, this was attributed to the intermixing of the thin Al₂O₃‐PL with HfO₂, which might have been accompanied by the out‐diffusion of a substantial amount of substrate elements. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An X-ray investigation of the high temperature anomaly in pure V2O3

An X-ray investigation of pure V₂O₃ in the temperature region 300 to 700 K has revealed the presence of more than one phase coexisting from ≈450 to at least 700 K. This observation can be correlated with the high temperature resistivity anomaly and with recent nmr studies on this material.