Dipole formation and electrical properties of high-k/SiO2 interface according to the density of SiO2 interfacial layer

The effect of SiO₂ buffer layers with various atomic densities on the interface dipole of high-k/SiO₂ is confirmed. An ultrathin SiO₂ layer is formed on Si using the plasma-enhanced chemical vapor deposition (PECVD), H₂O₂ oxidation and nitric acid oxidation (NAOS). The atomic density ratio between the SiO₂ layer with various methods and the high-k is calculated respectively. As the oxygen density of the SiO₂ increased, the amount of the dipole and the flatband voltage (V_FB) shift decreased. Furthermore, leakage current density of the H₂O₂ (0.9 × 10⁻² A/cm²) due to the formation of low-density SiO₂, decreases by approximately six orders of magnitude when SiO₂ buffer layer is inserted using the NAOS (5.13 × 10^-8 A/cm²). Consequently, it is demonstrated that the dipoles that affects the V_FB shift is formed by the diffusion of oxygen ions between the high-k and SiO₂ interface, which has a significant effect of the MOS capacitor.     

Controlled SnO2 nanocrystal growth in SiO2–SnO2 glass‐ceramic monoliths

Crack‐free (100–x) SiO₂–x SnO₂ glass‐ceramic monoliths have been prepared by the sol–gel method obtaining for the first time SnO₂ concentrations of 20% with annealing at 1100 °C. Heat‐treatment resulted in the formation and growth of SnO₂ nanocrystals within the silica matrices. Combined use of Fourier transform–Raman spectroscopy and in situ high‐temperature X‐Ray diffraction shows that SnO₂ particles begin to crystallize in the cassiterite‐type phase at 80 °C and that their average apparent size remains around 7 nm, even after annealing at 1100 °C. Nanocrystal sizes and size distributions determined by low‐wavenumber Raman are in good agreement with those obtained from transmission electron microscopy measurements. Results indicate that the formation and the growth of SnO₂ nanocrystals impose a residual porosity in the silica matrix. Copyright © 2011 John Wiley & Sons, Ltd.     

Designing Zwitterionic SiO2NH2‐Au Particles with Tunable Patchiness using Wrinkles

A facile template‐based approach toward zwitterionic SiO₂NH₂‐Au patchy particles is presented. Therefore, wrinkle templates prepared by stress release in a bilayer system comprised of an elastic PDMS fundament and a thin SiO_x top layer are used. After aligning positively charged, amine‐functionalized silica particles in wrinkle grooves, their surfaces are partially modified with negatively charged gold nanoparticles in an electrostatic adsorption step. Patchiness is precisely controlled by the degree of immersion of the initial particles into wrinkles of varying dimensions. By ultrasonication or wetting with a water droplet, patchy particles are easily released from the substrate‐yielding particles with two oppositely charged hemispheres. Interfacial tension measurements prove the surface activity of the SiO₂NH₂‐Au particles in an oil/water system and are explained in the view of the Janus‐type surface charges of the particles and the charge of the oil/water interface.     

Tunable n‐ and p‐type doping of single‐layer graphene by engineering its interaction with the SiO2 support

We report a technique to tune the excess charge concentration in single‐layer graphene from p‐ to n‐type up to densities of |n | ～ 1.2 × 10¹³ cm^–2, corresponding to a displacement electric field of ～2.5 V/nm. The tuning is achieved by engineering the interaction between graphene and the underlying Si/SiO₂ substrate with an amino group‐terminated self‐assembled monolayer, and subsequent rinsing in aqueous solutions at controlled pH. Raman spectroscopy and electrical measurements on treated graphene devices confirm the occurrence of doping. Interestingly, we found the field‐effect mobility not to be significantly affected by the procedure. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Assessment of the illumination dependency of Al2O3 and SiO2 rear‐passivated p‐type silicon solar cells

This Letter discusses an important difference between positively charged SiO₂ and negatively charged Al₂O₃ rear‐passivated p‐type Si solar cells: their illumination level dependency. For positively charged SiO₂ rear‐passivated p‐type Si solar cells, a loss in short circuit current (J_SC) and open circuit voltage (V_OC) as a function of illumination level is mainly caused by parasitic shunting and a decrease in surface recombination, respectively. Hence, the relative loss in cell conversion efficiency, J_SC, and V_OC as a function of the illumination level for SiO₂ compared to Al₂O₃ rear‐passivated p‐type Si solar cells has been measured and discussed. Subsequently, an exponential decay fit of the loss in cell efficiency is applied in order to estimate the difference in the energy output for both cell types in three different territories: Belgium (EU), Seattle and Austin (US). The observed trends in the difference in energy output between both cells, as a function of time of the year and region, are as expected and discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination of the Al content in aluminum‐modified SiO2 stationary phases using X‐ray scattering spectroscopy

This paper describes the determination of aluminum in the presence of silica using a method based on X‐ray scattering spectrometry coupled with chemometric tools (principal component analysis and partial least squares) that treat samples according to their Al concentrations. Samples were prepared by mixing Al and Si oxides. X‐ray spectra of all samples, including pure oxides of aluminum and silicon, were submitted to the chemometric tools. Principal component analysis results show that it is possible to classify three subgroups of Al (low, medium and high Al content), whereas partial least squares 1 was used to construct calibration and cross‐validation models for Al in the presence of Si. The method is simple, fast, does not require sample dissolution prior to analysis, is of low cost and can be applied as a routine procedure. The method was used to quantify Al in some chromatographic stationary phases covered with a layer of Al₂O₃. Good correlations with low errors were obtained. Copyright © 2013 John Wiley & Sons, Ltd.     

SiO2/Ge:SiO2/SiO2夹层结构红外光发射的起源

我们借助傅立叶变换红外光谱（FT－IR）以及光致激发谱（PLE）,研究SiO2/Ge:SiO2/SiO2夹层结构红外光发射的起源。谱分析表明,该红外光发射并非起源于纳米锗、硅的量子限制效应以及锗、硅的中性氧空位,而与锗的氧化物紧密相关。PLE的结果证实它们来源于GeO色心TⅡ‘→S0的光学跃迁,给出的GeO电子态模型描述了载流子激发和复合的过程。     

Micro‐PIXE analysis of doped SiO2 fibres intended as TL dosimeters for radiation measurements

Sample elemental concentrations can be determined using the microbeam proton‐induced X‐ray emission (PIXE) technique, providing non‐destructive simultaneous low‐background multi‐element analysis. Present interest concerns analysis of Ge‐doped SiO₂ fibres intended as high spatial‐resolution thermoluminescence (TL) dosimeters for radiation measurements in place of their more typical applications in telecommunications. During fibres fabrication, defined amounts of the Ge dopant are added, the dopant more usually having a determining role in the transmission properties of the fibre. Characteristic X‐rays produced in PIXE analysis provide information on the relative distribution of elements within a sample, as in for instance Ge and Si concentrations, the Ge acting as point defect centres that promote TL. With the dopant tending to diffuse in and away from the fibre core, it is essential to define the sample matrix composition in order to accurately evaluate the X‐ray yield. This is determined in part using simultaneous Rutherford Back Scattering analysis. In present work, PIXE/Rutherford Back Scattering measurements have been employed to ascertain dopant concentrations of fibres that have been fabricated at the University of Malaya with a view to improving TL yield. Present results concern cylindrical fibres, nominally with 4%, 6% and 8% weight peak Ge concentrations and flat fibres of nominal 6% weight Ge concentration. For the cylindrical fibres, Ge dopant concentration has been found to be in the range of 2.41–4.56%, 6.44–8.29% and 10.27–12.25% weight, respectively, while for the flat fibres, the Ge concentration range is broader, at 0.07–6.55% weight. Copyright © 2014 John Wiley & Sons, Ltd.     

Beryllium Silicate,Be2SiO4 (phenakite) – a Novel Trigonal SRS‐Active Crystal

In single crystals of the beryllium silicate Be₂SiO₄ with trigonal symmetry , known also as the mineral phenakite, χ⁽³⁾‐nonlinear lasing by stimulated Raman scattering (SRS) is investigated. All observed Stokes and anti‐Stokes lasing components are identified and ascribed to a single SRS‐promoting vibration mode with ω_SRS ≈876 cm⁻¹. With picosecond single‐wavelength pumping at one micrometer the generation of an octave‐spanning Stokes and anti‐Stokes comb is observed.     

Dynamic moderation of an electric field using a SiO2 switching layer in TaOx ‐based ReRAM

ReRAMs using oxygen vacancy drift in their resistive switching are promising candidates as next generation memory devices. One remaining issue is degradation of the on/off ratio down to 10² or less with an increased number of switching cycles. Such degradation is caused by a local hard breakdown in a set process due to a very high electric field formed just before the completion of a conductive filament formation. We found that introducing an ultra‐thin SiO₂ layer prevents the hard breakdown by dynamical moderation of the electric field formed in the TaO_x matrix, resulting in repeated switching while retaining a higher on/off ratio of about 10⁵. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Organic light‐emitting transistors with voltage‐tunable lit area and full channel illumination

Organic light‐emitting transistors (OLETs) are multifunctional optoelectronic devices that hold great promise for a variety of applications, including flat panel displays, integrated light sources for sensing and optical communication systems. The narrow illumination area within the device channel is considered intrinsic to the device architecture and is a severe technological drawback for all those applications where a controlled, wide and homogeneous emission area is required. Here it is shown that not only the position but also the extension of the emission area is voltage‐tunable, and the entire channel of the transistor can be homogeneously illuminated. The modeling of the exciton distribution within the channel at the different bias conditions coupled to the modeling of the device emission profile highlights that excitons are spread through the entire channel width and across the bulk of the central emission layer of the p‐channel/emitter/n‐channel trilayer active heterostructure.     

A Particle‐in‐Cell Simulation of the Breakdown Mechanism in Microdischarges with an Improved Secondary Emission Model

In this paper, the failure of the breakdown voltage from the Paschen's law at extremely small electrode separations is studied. The electrical breakdown in microgaps occurs at the voltages far below the Paschen curve minimum breakdown limit and the modified Paschen curve should be used. Offered explanation for the departure from the Paschen's law at small gap spacings is based on the increasing of the yield of the secondary electrons. The high electric fields existing in small gaps may enhance the secondary electron yield and this would lead to a lowering of the breakdown voltage and to the departure from the Paschen's law. Particlein‐cell/Monte‐Carlo (PIC/MCC) simulations with a new secondary emission model have been performed to estimate the importance of this mechanism in the discharge breakdown. Obtained simulation results suggest that deviations from the Paschen curve across the micron and submicorn gap spacing can be attributed to the ion‐enhanced field emissions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)