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One-dimensional silicon-based photonic crystals are formed by the electrochemical anodization of silicon substrates in hydrofluoric acid-based solution using an appropriate current density profile. In order to create a multi-band optical filter, two fabrication approaches are compared and discussed. The first approach utilizes a current profile composed of a linear combination of sinusoidal current waveforms having different frequencies. The individual frequency of the waveform maps to a characteristic stop band in the reflectance spectrum. The stopbands of the optical filter created by the second approach, on the other hand, are controlled by stacking multiple porous silicon rugate multilayers having different fabrication conditions. The morphology of the resulting optical filters is tuned by controlling the electrolyte composition and the type of the silicon substrate. The reduction of sidelobes arising from the interference in the multilayers is observed by applying an index matching current profile to the anodizing current waveform. In order to stabilize the resulting optical filters against natural oxidation, atomic layer deposition of silicon dioxide on the pore wall is employed. [ABSTRACT FROM AUTHOR]

Light-induced degradation due to BO defects in silicon consists of a fast initial decay within a few seconds followed by a slower decay within hours to days. Determination of injection dependent charge carrier lifetime curves during the initial decay is challenging due to this short timeframe. We have developed a suitable measurement technique based on in situ photoluminescence measurements and present results of our studies of the fast degradation component. The temporal evolution of the recombination activity is studied and assessed by means of a two-level Shockley-Read-Hall statistics. A quadratic dependence of the fast defect activation on the hole concentration during illumination is demonstrated. We suggest a new parameterization of the recombination activity introduced by fast-formed BO defects featuring energy levels 0.34 eV below the conduction band and 0.31 eV above the valence band. The capture asymmetry ratio determined for the donor level of 18.1 is significantly smaller than previous parameterizations in literature suggest. [ABSTRACT FROM AUTHOR]

We report the development of a powerful method for quantum transport calculations of nanowire/nanobeam structures with large cross sectional area. Our approach to quantum transport is based on Green's functions and tight-binding potentials. A linear algebraic formulation allows us to harness the massively parallel nature of Graphics Processing Units (GPUs) and our implementation is based on a heterogeneous parallel computing scheme with traditional processors and GPUs working together. Using our software tool, the electronic and quantum transport properties of silicon nanobeams with a realistic cross sectional area of ~22.7nm2 and a length of ~81.5nm—comprising 105 000 Si atoms and 24 000 passivating H atoms in the scattering region—are investigated. The method also allows us to perform significant averaging over impurity configurations—all possible configurations were considered in the case of single impurities. Finally, the effect of the position and number of vacancy defects on the transport properties was considered. It is found that the configurations with the vacancies lying closer to the local density of states (LDOS) maxima have lower transmission functions than the configurations with the vacancies located at LDOS minima or far away from LDOS maxima, suggesting both a qualitative method to tune or estimate optimal impurity configurations as well as a physical picture that accounts for device variability. Finally, we provide performance benchmarks for structures as large as ~42.5nm2 cross section and ~81.5nm length. [ABSTRACT FROM AUTHOR]

Electrically-inactive arsenic (As) complexes in silicon are investigated using time-of-flight medium-energy ion scattering spectroscopy. In heavily As-doped Si, the As atoms that are segregated in the Si interface region just below the SiO2 are found to be in interstitial forms (Asi), while the As atoms in the bulk Si region are found to be in the substitutional form (AsSi). Despite the substitutional form of As, most of the As are found to be electrically inactive in the bulk region, and we identify the As to be in the form of a 〈111〉-oriented AsSi-Si-vacancy (AsSi-VSi) complex. The Asi atoms in the interface Si region are found to exist together with Si-interstitial atoms (Sii), suggesting that the Asi atoms in the interface Si region accompany the Sii atoms. [ABSTRACT FROM AUTHOR]

This paper reports the results of atomistic and ab initio simulation of several different tilt grain boundaries in silicon. The boundary structures obtained with genetic algorithm turned out to have no coordination defects, i.e., all silicon atoms restored their tetrahedral coordination during the structure optimisation. That concerns previously known symmetric Σ5 (130), Σ3 (211), and Σ29 (520) boundaries and previously unknown asymmetric Σ9 (̄255)/(̄211), Σ3 (̄255)/(̄211), and Σ13 (790)/(3 11 0) structures. An extensive study has been performed on defect segregation on the boundaries, including neutral vacancy and carbon, phosphorus, and boron impurities. A clear correlation has been revealed between the segregation energy of the defect and local geometry of the boundary site where the defect is segregated. The authors propose a simple purely geometric model for evaluating approximate segregation energies of the listed defects. [ABSTRACT FROM AUTHOR]

The evolution of radiation defects after the thermalization of collision cascades often plays the dominant role in the formation of stable radiation disorder in crystalline solids of interest to electronics and nuclear materials applications. Here, we explore a pulsed-ion-beam method to study defect interaction dynamics in Si crystals bombarded at room temperature with 500 keV Ne, Ar, Kr, and Xe ions. The effective time constant of defect interaction is measured directly by studying the dependence of lattice disorder, monitored by ion channeling, on the passive part of the beam duty cycle. The effective defect diffusion length is revealed by the dependence of damage on the active part of the beam duty cycle. Results show that the defect relaxation behavior obeys a second order kinetic process for all the cases studied, with a time constant in the range of ~4-13 ms and a diffusion length of ~15-50 nm. Both radiation dynamics parameters (the time constant and diffusion length) are essentially independent of the maximum instantaneous dose rate, total ion dose, and dopant concentration within the ranges studied. However, both the time constant and diffusion length increase with increasing ion mass. This demonstrates that the density of collision cascades influences not only defect production and annealing efficiencies but also the defect interaction dynamics. [ABSTRACT FROM AUTHOR]

This paper reports initial the demonstration of prototype Ge1-x-ySixSny light emitting diodes with distinct direct and indirect edges and high quality I-V characteristics. The devices are fabricated on Si (100) wafers in heterostructure pin geometry [n-Ge/i-Ge1-x-ySixSny/p-Ge(Sn/Si)] using ultra low-temperature (T<300 °C) depositions of the highly reactive chemical sources Si4H10, Ge4H10, Ge3H8, and SnD4. The Sn content in the i-Ge1-x-ySixSny layer was varied from ~3.5% to 11%, while the Si content was kept constant near 3%. The Si/Sn amounts in the p-layer were selected to mitigate the lattice mismatch so that the top interface grows defect-free, thereby reducing the deleterious effects of mismatch-induced dislocations on the optical/electrical properties. The spectral responsivity plots of the devices reveal sharp and well-defined absorption edges that systematically red-shift in the mid-IR from 1750 to 2100 nm with increasing Sn content from 3.5% to 11%. The electroluminescence spectra reveal strong direct-gap emission peaks and weak lower energy shoulders attributed to indirect gaps. Both peaks in a given spectrum red-shift with increasing Sn content and their separation decreases as the material approaches direct gap conditions in analogy with binary Ge1-ySny counterparts. These findings-combined with the enhanced thermal stability of Ge1-x-ySixSny relative to Ge1-ySny and the observation that ternary alloy disorder does not adversely affect the emission properties—indicate that Ge1-x-ySixSny may represent a practical target system for future generations of group-IV light sources on Si. [ABSTRACT FROM AUTHOR]

The diffusion and dissociation mechanisms governing the evolution of oxygen and vacancyoxygen defects in Czochralski-grown Si samples have been studied. The samples were irradiated at (i) room temperature or (ii) elevated temperature (350 °C) by MeV electrons and then isothermally annealed at 8 different temperatures in the range of 300 °C to 500 °C. The evolution of the concentrations of oxygen complexes (On, n≤3) and mono-vacancy-oxygen defects (VOn, n≤4) have been followed by infrared absorption measurements of local vibrational modes originating from the individual defects. The experimental kinetics data have been compared with simulation results based on the theory for diffusion limited reactions, assuming a model where sequential build-up of the VOn defects is a key ingredient. A close quantitative agreement is obtained for both sets of samples despite quite different initial conditions prior to the annealing, which adds evidence to the validity of the model. Values for the diffusivity and dissociation rates of VOn (n≤4) and On (n≤3) have been deduced and in general, the mobility and stability of VOn decrease and increase with n, respectively. For all the defects, partial dissociation appears as a prevailing process during diffusion, while full dissociation of VOn is limited by an energy barrier identical to that of interstitial oxygen (Oi) diffusion (~2.55 eV). The oxygen dimer and trimer are fast diffusers but slower than substitutional oxygen, i.e., VO; VO is found to be the most mobile species, whilst Oi is the slowest one with a difference in diffusivity of up to 7 orders of magnitude in the studied temperature range. [ABSTRACT FROM AUTHOR]

A new concept, using a negatively charged tunnel layer as a hole collector, is proposed and theoretically investigated for application in amorphous silicon thin-film solar cells. The concept features a glass/transparent conductive oxide/ultra-thin negatively charged tunnel layer/intrinsic a-Si:H/n-doped a-Si:H/metal structure. The key feature of this so called t+-i-n structure is the introduction of a negatively charged tunnel layer (attracting holes from the intrinsic absorber layer), which substitutes the highly recombination active p-doped a-Si:H layer in a conventional p-i-n configuration. Atomic layer deposited aluminum oxide (ALD AlOx) is suggested as a potential candidate for such a tunnel layer. Using typical ALD AlOx parameters, a 27% relative efficiency increase (i.e., from 9.7% to 12.3%) is predicted theoretically for a single-junction a-Si:H solar cell on a textured superstrate. This prediction is based on parameters that reproduce the experimentally obtained external quantum efficiency and current-voltage characteristics of a conventional processed p-i-n a-Si:H solar cell, reaching 9.7% efficiency and serving as a reference. Subsequently, the p-doped a-Si:H layer is replaced by the tunnel layer (studied by means of numerical device simulation). Using a t+-i-n configuration instead of a conventional p-i-n configuration will not only increase the short-circuit current density (from 14.4 to 14.9 mA/cm2, according to our simulations), it also enhances the open-circuit voltage and the fill factor (from 917mV to 1.0V and from 74% to 83%, respectively). For this concept to work efficiently, a high work function front electrode material or a high interface charge is needed. [ABSTRACT FROM AUTHOR]

By using first-principles calculations, we investigated how to achieve a strong ferromagnetism in Cr-doped Si by controlling the atomic structure and Cr concentration as well as carrier densities. We found that the configuration in which the Cr atom occupies the tetrahedral interstitial site can exist stably and the Cr atom has a large magnetic moment. Using this doping configuration, room-temperature ferromagnetism can be achieved in both n-type and p-type Si by tuning Cr concentration and carrier densities. The results indicate that the carrier density plays a crucial role in realizing strong ferromagnetism in diluted magnetic semiconductors. [ABSTRACT FROM AUTHOR]

We report on the growth and structural and morphologic characterization of stacked layers of self-assembled GeSn dots grown on Si (100) substrates by molecular beam epitaxy at low substrate tem-perature T = 350°C. Samples consist of layers (from 1 up to 10) of Ge0.96Sn0.04 self-assembled dots separated by Si spacer layers, 10 nm thick. Their structural analysis was performed based on transmission electron microscopy, atomic force microscopy, and Raman scattering. We found that up to 4 stacks of dots could be grown with good dot layer homogeneity, making the GeSn dots interesting candidates for optoelectronic device applications. [ABSTRACT FROM AUTHOR]

Energy storage is a key challenge in solar-driven renewable energy conversion. We promote a photochemical diode based on dilute nitride GaPN grown lattice-matched on Si(100), which could reach both high photovoltaic efficiencies and evolve hydrogen directly without external bias. Homoepitaxial GaP(100) surface preparation was shown to have a significant impact on the semiconductor-water interface formation. Here, we grow a thin, pseudomorphic GaP nucleation buffer on almost single-domain Si(100) prior to GaPN growth and compare the GaP0.98N0.02/Si(100) surface preparation to established P- and Ga-rich surfaces of GaP/Si(100). We apply reflection anisotropy spectroscopy to study the surface preparation of GaP0.98N0.02 in situ in vapor phase epitaxy ambient and benchmark the signals to low energy electron diffraction, photoelectron spectroscopy, and x-ray diffraction. While the preparation of the Ga-rich surface is hardly influenced by the presence of the nitrogen precursor 1,1-dimethylhydrazine (UDMH), we find that stabilization with UDMH after growth hinders well-defined formation of the V-rich GaP0.98N0.02/Si(100) surface. Additional features in the reflection anisotropy spectra are suggested to be related to nitrogen incorporation in the GaP bulk. [ABSTRACT FROM AUTHOR]

High temperature nanoindentation has been performed on pure ion-implanted amorphous silicon (unrelaxed a-Si) and structurally relaxed a-Si to investigate the temperature dependence of mechanical deformation, including pressure-induced phase transformations. Along with the indentation load-depth curves, ex situ measurements such as Raman micro-spectroscopy and crosssectional transmission electron microscopy analysis on the residual indents reveal the mode of deformation under the indenter. While unrelaxed a-Si deforms entirely via plastic flow up to 200 °C, a clear transition in the mode of deformation is observed in relaxed a-Si with increasing temperature. Up to 100 °C, pressure-induced phase transformation and the observation of either crystalline (r8/bc8) end phases or pressure-induced a-Si occurs in relaxed a-Si. However, with further increase of temperature, plastic flow rather than phase transformation is the dominant mode of deformation. It is believed that the elevated temperature and pressure together induce bond softening and "defect" formation in structurally relaxed a-Si, leading to the inhibition of phase transformation due to pressure-releasing plastic flow under the indenter. [ABSTRACT FROM AUTHOR]

In recent years, it has been recognized that medium range ordering (MRO) in amorphous silicon (a-Si:H) plays a role in controlling its solid phase crystallization (SPC) behavior. Information on the MRO can be obtained from the width of the first X-ray diffraction (XRD) peak of a-Si:H centered around 2θ = 27.5°. The broader the full width half maximum (FWHM) of the first XRD peak, the less ordered the a-Si:H material in the medium range length scale (up to 5 nm). In this work, it was found that the FWHM of the first XRD peak changes with the pressure used during the deposition of a-Si:H. A threshold SPC behavior was observed as a function of the a-Si:H deposition pressure and a good correlation between the SPC behavior and the a-Si:H XRD peak width was found. Results in this study indicate that higher MRO in a-Si:H led to faster SPC rates and smaller grain sizes, suggesting the presence of relatively active and high density of nucleation sites. High angle annular dark field scanning transmission electron microscopy and ultraviolet reflectance indicate that films with higher MRO yielded polycrystalline silicon (poly-Si) grains which were more defective and non-columnar in morphology. Results suggest that a-Si:H material with lower MRO were preferred as a precursor for SPC, which forms a better quality poly-Si thin film material. It was proposed that ion bombardment seems to play a role in altering the a-Si:H properties. [ABSTRACT FROM AUTHOR]

This paper describes Raman spectroscopy of microstructured silicon (Si), which is used for electronic displays, solar cells, and other applications. Enhanced Raman scattering was found for excimer laser crystallized polycrystalline Si (ELC poly-Si) thin films, texture-structured Si, black Si, and porous Si. Raman scattering of those materials reflects mainly the conditions at projections on their surfaces. Atomic force microscopy and Raman spectroscopy for ELC poly-Si indicated that hillocks and ridges are located at grain boundaries where the defect density is relatively large and the thermal stress in the films is somewhat relaxed. The enhancement effect was shown to be useful for detecting a local vibration mode that could not be easily detected for mirror-finished Si. The variation in the enhancement ratio with the incident light wavelength was examined for comparison with the electromagnetic model. [ABSTRACT FROM AUTHOR]

Spectral photoluminescence imaging is able to provide quantitative bulk lifetime and doping images if applied on silicon bricks or thick silicon wafers. A comprehensive study of this new method addresses previously reported artefacts in low lifetime regions and provides a more complete understanding of the technique. Spectrally resolved photoluminescence measurements show that luminescence originating from sub band gap defects does not cause those artefacts. Rather, we find that optical light spreading within the silicon CCD is responsible for most of the distortion in image contrast and introduce a method to measure and remove this spreading via image deconvolution. Alternatively, image blur can be reduced systematically by using an InGaAs camera. Results of modelling this alternative camera type and experiments are shown and discussed in comparison. In addition to eliminating the blur effects, we find a superior accuracy for lifetimes above 100 μs with significantly shorter, but dark noise limited exposure times. [ABSTRACT FROM AUTHOR]

Amorphous silicon oxide SiO2, silicon nitride Si3N4, and silicon oxynitride SiOxNy are three key dielectrics in silicon devices. Implementation of nitrided oxide (oxynitride SiOxNy) as a gate dielectric in metal-oxide-semiconductor field effect transistors has been shown to significantly improve the reliability and lifetime of devices. Also, amorphous oxynitride is used as a tunnel dielectric in nonvolatile flash memory devices. The present paper is devoted to the experimental and theoretical study of silicon oxynitride electronic structure. The ionic formula of crystalline Si2N2O is deduced from the first principles. Effective masses of charge carriers in Si2N2O are calculated and compared with experimental data on tunnel injection in amorphous SiNxOy samples. Also experimental x-ray absorption and emission spectra are compared with the theoretically calculated ones. [ABSTRACT FROM AUTHOR]

In this paper, we report large mid-wave infrared photoconductivity in highly textured, nanocrystalline PbTe films thermally evaporated on Si at room temperature. Responsivity as high as 25 V/W is measured at the 3.5 μm wavelength. The large photoconductivity is attributed to the oxygen incorporation in the films by diffusion. Carrier concentration as low as 1017 cm-3 is identified to be the consequence of Fermi level pinning induced by the diffused oxygen. The successful demonstration of IR-sensitive PbTe films without the need for high-temperature processing presents an important step toward monolithic integration of mid-wave PbTe infrared detectors on Si read-out integrated circuits (ROICs). [ABSTRACT FROM AUTHOR]

The early stages of crystallization of tetrahedral systems remain largely unknown, due to experimental limitations in spatial and temporal resolutions. Computer simulations, when combined with advanced sampling techniques, can provide valuable details about nucleation at the atomistic level. Here we describe a computational approach that combines the forward flux sampling method with molecular dynamics, and we apply it to the study of nucleation in supercooled liquid silicon. We investigated different supercooling temperatures, namely, 0.79, 0.86, and 0.95 of the equilibrium melting point Tm. Our results show the calculated nucleation rates decrease from 5.52±1.75×1028 to 4.77±3.26×1011 m-3 s-1 at 0.79 and 0.86 Tm, respectively. A comparison between simulation results and those of classical nucleation theory shows that the free energy of the liquid solid interface γls inferred from our computations differ by about 28% from that obtained for bulk liquid solid interfaces. However the computed values of γls appear to be rather insensitive to supercooling temperature variations. Our simulations also yield atomistic details of the nucleation process, including the atomic structure of critical nuclei and lifetime distributions of subcritical nuclei. [ABSTRACT FROM AUTHOR]

Silicon light emitting diode arrays made by industrial planar technology and operating at T>300 K in the double injection mode have been shown to be an efficient emitters of the infrared (IR) radiation in the 3–12 μm spectral band. We show that due to free carrier injection in an optically thin base, which makes its emissivity to increase at the wavelengths of the free carrier absorption, the devices have thermal emission output power of 2–3 mW and local power density up to 1 mW/mm2 at T=473 K. The 0.5-mm-thick 6×6 mm2 emitting pixel of an array demonstrates the power conversion efficiency of 13%, a time response of 300 μs, and an apparent temperature of the IR radiation of 400 K, which make the device practical for use in IR dynamic scene simulation techniques. [ABSTRACT FROM AUTHOR]

Substitutionally doped Si1-xMnx thin films were fabricated by a magnetron cosputtering method at a low growth temperature. X-ray absorption fine structure (XAFS) and x-ray diffraction (XRD) techniques were used to investigate the structures of the Si1-xMnx thin films. The XRD results exhibit that no secondary phases such as metallic Mn or Mn–Si compound can be detected. The detailed analysis of the extended XAFS together with the x-ray absorption near-edge structure spectra at the Mn K-edge unambiguously reveals that the doped Mn atoms are incorporated into the Si matrix and substitute for the Si sites in the Si lattice. The results clearly indicate that the Mn occupations in silicon thin films are quite sensitive to the growth conditions and the postannealing treatment. [ABSTRACT FROM AUTHOR]

The formation of nearly wavelength-sized laser-induced periodic surface structures (LIPSSs) on single-crystalline silicon upon irradiation with single or multiple femtosecond-laser pulses (pulse duration τ=130 fs and central wavelength λ=800 nm) in air is studied experimentally and theoretically. In our theoretical approach, we model the LIPSS formation by combining the generally accepted first-principles theory of Sipe and co-workers with a Drude model in order to account for transient intrapulse changes in the optical properties of the material due to the excitation of a dense electron-hole plasma. Our results are capable to explain quantitatively the spatial periods of the LIPSSs being somewhat smaller than the laser wavelength, their orientation perpendicular to the laser beam polarization, and their characteristic fluence dependence. Moreover, evidence is presented that surface plasmon polaritons play a dominant role during the initial stage of near-wavelength-sized periodic surface structures in femtosecond-laser irradiated silicon, and it is demonstrated that these LIPSSs can be formed in silicon upon irradiation by single femtosecond-laser pulses. [ABSTRACT FROM AUTHOR]

We report the results of the optical spectra modeling for hydrogenated amorphous silicon (a-Si:H) thin films produced for photovoltaic cell applications, which allowed us to accurately determine the material’s optical gap (Eg). While for thick films of a-Si:H, as well as for other amorphous semiconductors, Eg is normally estimated from a so called Tauc plot, this is hardly possible for thin films because of the interference effects. We developed a physically founded semianalytical model for the complex dielectric function of a-Si:H, valid below and above the optical gap and containing a small number of adjustable meaningful parameters, including Eg and the characteristic energy scales of the optical transition matrix element distribution and the joint density of states in the absorption tail region. With this model and using the transfer matrix formalism for multilayer optics, we have achieved a good agreement between the calculated and experimental transmittance spectra, which allowed us to self-consistently determine the values of the above parameters. We found that both Eg and the characteristic scale of the subgap absorption tail increase with the hydrogen addition. We have also determined the absorption rate spectra of the films, relevant to any optical spectroscopy of subgap states, such as the photothermal deflection spectroscopy and constant photocurrent measurements. [ABSTRACT FROM AUTHOR]

The change in the diffracted intensity of a silicon 400 Bragg peak is measured in situ while the sample is exposed to a thermal treatment up to 1150 °C. The experiments are set up in focusing Laue geometry with polychromatic and divergent x-rays generated by a high voltage tube. Changes in peak intensity and shape are only observed for Czochralski grown samples and not for the float zone grown reference group. Thus, they are attributed to oxygen related defects emerging at these temperatures. [ABSTRACT FROM AUTHOR]

Raman shifts are investigated on silicon and germanium substrates under the uniaxial tensile strain on various substrate orientations. The strain splits the triply degenerate optical (LO, TO) phonons at the zone center (kvector ≈0). The redshifts of Si Raman peaks induced by the tensile strain on all substrate orientations are observed. With the specific polarization of the incident light, however, the unusual blueshifts of Ge Raman peaks induced by the tensile strain are observed on (110) and (111) Ge substrates. By using the suitable phenomenological constants and taking the Raman selection rules into consideration, the experimental results are in reasonable agreement with the lattice dynamical theory. [ABSTRACT FROM AUTHOR]

In addition to the development of the nano-wire device, the vertical gate-all-around (V-GAA) Si nano-tube (NT) device structure is proposed with the promising device performance in this work. The vertical device structure makes the transistor easy to be scaled down continuously to meet the complementary metal-oxide-semiconductor scaling needs of the 10/7 nm technology node and beyond. The NT device with the center hollow structure has the capability to deplete the out-of gate control carriers in the center of the nano-wire device and further results in the better device short channel control. Based on the simulation data, the V-GAA Si NT device can keep the Ion-state current the same and reduce the Ioff-state stand-by power. With the demonstration of the promising device performance, the proposed V-GAA Si NT device can be regarded as one of the most promising candidates for the future application of the sub-10/7 nm logic device. [ABSTRACT FROM AUTHOR]

We have investigated the electronic structure of anionic and neutral Bi2Si5 by means of anion photoelectron spectroscopy and density functional calculations. Both the experiments and calculations reveal that the Bi2Si5- anion prefers to adopt a distorted trigonal-bipyramidal structure with Bi2 bridges. Following the isolobal analogy between divalent Si and B–H group, we show that both neutral Bi2Si5 and neutral Bi2B5H5 adopt similar pentagonal-bipyrmidal geometries and have analogous orbital energy patterns. [ABSTRACT FROM AUTHOR]

We have investigated the electronic structure of anionic and neutral Bi2Si5 by means of anion photoelectron spectroscopy and density functional calculations. Both the experiments and calculations reveal that the Bi2Si5- anion prefers to adopt a distorted trigonal-bipyramidal structure with Bi2 bridges. Following the isolobal analogy between divalent Si and B–H group, we show that both neutral Bi2Si5 and neutral Bi2B5H5 adopt similar pentagonal-bipyrmidal geometries and have analogous orbital energy patterns. [ABSTRACT FROM AUTHOR]

We describe a method to study diffusion of rhodamine 6G dye in single silica nanochannels using arrays of silica nanochannels. Dynamics of the molecules inside single nanochannel is found from the change of the dye concentration in solution with time. A 108 decrease in the dye diffusion coefficient relative to water was observed. In comparison to single fluorescent molecule studies, the presented method does not require fluorescence of the diffusing molecules. [ABSTRACT FROM AUTHOR]

Using various junction space-charge techniques, annealing, and simulation, a metastable defect in 6H SiC have been characterized. We suggest a configuration coordinate diagram with three configurations, where two of them can only exist when the defect is occupied by one or more electrons. The thermal ionization energies for the different configurations were measured and the thermal barriers for two of the transitions have been determined. It is also shown that the transformation process is governed by electron capturing to the defect. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the characteristics of high-temperature-sputtered cobalt (Co) and strained silicon-germanium (Si-Ge) layer. Analysis of the Ge-Si ratio; Role of Co sputtering in the silicidation process; Comparison between room- and high-temperature sputtered samples; Inhibition of lattice relaxation.

Presents information on a study which investigated the surface reactions of hydrogenated amorphous silicon films which were exposed to electron cyclotron resonance plasma using in situ polarization modulation infrared reflection absorption spectroscopy. Experimental details; Results and discussion; Conclusions.

Abstract We report the experimental study of changes in optical properties of oxidised porous silicon induced by pore filling with salts from aqueous solutions. Our experiments demonstrate that pore filling is a simple and effective method for tuning the refractive index of porous silicon, which can be applied locally. This method can be used for creation of waveguides and other planar optical components. Our results correlate with previously reported works on the subject and provide information, which can be useful for the future investigation of porous materials. Our samples were thin porous layers on top of Si wafers. We used aqueous solutions of several phosphate salts with various concentrations for filling the pores. After the pore filling, the dry samples were examined using optical spectrometry, microscopy (optical and electron) and EDS methods. The paper provides description of the experimental procedures, data analysis and comparison with theoretical calculations. Highlights • Simple method for tuning the refractive index of porous silicon in lateral directions over a wide range. • Description of the experimental procedures and comparison with theoretical calculations. • The process, if applied locally would enable the creation of planar optical components. [ABSTRACT FROM AUTHOR]

Ideal thermoelectric materials should possess low thermal conductivity κ along with high electrical conductivity σ. Thus, strategies are needed to impede the propagation of phonons mostly responsible for thermal conduction while only marginally affecting charge carrier diffusion. Defect engineering may provide tools to fulfill this aim, provided that one can achieve an adequate understanding of the role played by multiple morphological defects in scattering thermal energy carriers. In this paper, we study how various morphological defects such as grain boundaries and dispersed nanovoids reduce the thermal conductivity of silicon. A blended approach has been adopted, using data from both simulations and experiments in order to cover a wide range of defect densities. We show that the co-presence of morphological defects with different characteristic scattering length scales is effective in reducing the thermal conductivity. We also point out that non-gray models (i.e. models with spectral resolution) are required to improve the accuracy of predictive models explaining the dependence of κ on the density of morphological defects. Finally, the application of spectral models to Matthiessen’s rule is critically addressed with the aim of arriving at a compact model of phonon scattering in highly defective materials showing that non-local descriptors would be needed to account for lattice distortion due to nanometric voids. [ABSTRACT FROM AUTHOR]

The development of a spectroscopy device on a chip that could realize real-time fingerprinting with label-free and high-throughput detection of trace molecules represents one of the big challenges in sensing. Dual-comb spectroscopy (DCS) in the mid-infrared is a powerful technique offering high acquisition rates and signal-to-noise ratios through use of only a single detector with no moving parts. Here, we present a nanophotonic silicon-oninsulator platform designed for mid-infrared (mid-IR) DCS. A single continuous-wave lowpower pump source generates two mutually coherent mode-locked frequency combs spanning from 2.6 to 4.1 μm in two silicon microresonators. A proof-of-principle experiment of vibrational absorption DCS in the liquid phase is achieved acquiring spectra of acetone spanning from 2900 to 3100 nm at 127-GHz (4.2-cm-1) resolution. These results represent a significant step towards a broadband, mid-IR spectroscopy instrument on a chip for liquid/ condensed matter phase studies. [ABSTRACT FROM AUTHOR]

Transparent thermoluminescent alumino-phosphate‑sodium glass system of 15Al 2 O 3 -35P 2 O 5 -25CaO-25Na 2 CO 3 (all in mol%) doped with different concentrations of SiO 2 were prepared by conventional melt quenching technique. X-ray diffraction (XRD) studies checked the amorphous nature of the prepared glass. Fourier Transform Infrared (FTIR) of the glass system was investigated to find the effect of SiO 2 -dopant concentrations on the absorption spectra in comparison with that of bulk sample (without dopants). Direct and indirect energy band gaps (E opt ) were determined and found to be in the range of 2.47–3.65 eV for m = ½ and 2.24–3.3 eV for m = 2. Refractive index (n) for each E opt value vary from 2.42 to 2.55 and from 2.32 to 2.63 for the direct and indirect transition, respectively. Urbach energy values of the newly prepared glasses are found to be from 0.57 to 0.98 eV. In addition, effect of UV exposure on thermoluminescence (TL) sensitivity was also examined for APCNSi 5 (contains 500 ppm SiO 2 concentration) and a linear response to dose was obtained, indicating that this type of glass is promising as a TL dosimeter within the UV range. [ABSTRACT FROM AUTHOR]

Self-propagating high-temperature synthesis as a low energy consumption and simple approach was employed to synthesise silicon nanocrystal from the monolithic silica cryogel prepared by freeze drying. The recrystallisation process of silicon was investigated under combustion at 800, 900 and 1000°C and the uniform coral-like structure was achieved at 1000°C. The results of Raman and X-ray diffraction analysis showed the decrease in ignition time to 40 s for 1000°C temperature, leading to the decrement of crystalline size to 10.85 A° and the raise of average lattice strain to 0.152% due to accelerating recrystallisation. In addition, NaCl diluent consumed the excess heat generated during exothermic reaction and decreased the crystalline size to 10.79 A° thanks to its 0.8 W/m K thermal conductivity. [ABSTRACT FROM AUTHOR]

The present scientific opinion deals with the safety of orthosilicic acid-vanillin complex (OSA-VC) as a novel food ingredient for use as a source of silicon (Si) in food supplements and with the bioavailability of Si from this source. OSA-VC is stable in liquid solution at low pH values. OSA from OSA-VC was available as revealed by the increase in plasma Si concentrations after oral ingestion in human volunteers. The toxicological data provided in support of the current application were not in accordance with the Tier 1 requirement of the 'Guidance for submission for food additive evaluations'; however, this was considered justified by the Panel given that OSA-VC at pH 6.8 dissociates into orthosilicic acid and vanillin. The daily consumption of OSA-VC at the dose recommended by the applicant would provide a supplemental intake of Si of approximately 10-18 mg Si/day which would result in an estimated total intake of roughly 30-70 mg Si/day. The maximum vanillin intake resulting from the consumption of OSA-VC would be less than 5% of the acceptable daily intake (ADI) value for vanillin of 10 mg/kg body weight (bw) per day established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) in 2002. The Panel concluded that there would be no safety concern with the proposed use and use level of OSA-VC as a novel food ingredient intended to be used as a source of Si in food supplements for the adult population. The Panel concluded that OSA, measured as Si, is bioavailable following ingestion of OSA-VC and appears similar to values reported in the literature for other established sources of OSA. [ABSTRACT FROM AUTHOR]

Nanocrystalline diamond films with bright photoluminescence of silicon-vacancy colour centres have been grown using a microwave plasma enhanced CVD technique. The influence of substrate material (quartz, Al2O3, Mo and Si) on a reproducible fabrication of diamond thin films with Si-V optical centres is presented. Film quality and morphology are characterized by Raman spectroscopy and SEM technique. SEM shows well faceted diamond grains with sizes from 170 to 300 nm. The diamond peak is confirmed in Raman spectra for all samples. In the case of the quartz substrate, a redshift of the diamond peak is observed (≈3.5 cm-1) due to tension in the diamond film. The steady-state photoluminescence intensity was measured in the temperature range from 11 K to 300 K. All spectra consist of a broad emission band with a maximum near 600 nm and of a sharp zero phonon line in the vicinity of 738 nm corresponding to Si-V centres that is accompanied with a phonon sideband peaking at 757 nm. Activation energies for the thermal quenching of Si-V centre photoluminescence were determined and the effect of the substrate on photoluminescence properties is discussed too. [ABSTRACT FROM AUTHOR]

Point defects, particularly vacancies, exist abundantly in the structure of a variety of clay minerals (e.g., kaolinite). Such defects significantly alter the physical/chemical characteristics of the minerals. Dissolution of kaolinite in an alkali medium is a critical step in the geopolymerization process and it determines the properties of the final product. In this work, a series of molecular dynamics (MD) simulations were carried out in the isothermal-isobaric (NPT) ensemble at 298 K and 1 atm to study the influence of structural vacancies (Al and Si vacancies in particular) on the interaction/dissolution of the two basal surfaces of kaolinite (partially deprotonated octahedral and tetrahedral surfaces) exposed to alkali media. Two different alkali media were used. One contained sodium cation (Na + ) only while the other potassium cation (K + ) and their concentrations were 3 M and 5 M. The MD results showed that regardless of the type of cation and cation concentration, Al vacancies on the octahedral surface promoted the dissolution of Al into the solution compared to the surface without Al vacancies. However, there existed a vacancy concentration (2 Al vacancies per 576 Al atoms) at which the dissolution amount was the maximum and above which the dissolution decreased with increasing Al vacancy concentration. The presence of Si vacancies in the tetrahedral surface did not show significant effect on the dissociation of Si. Radial distribution function (RDF) analyses indicated that the degree of crystallinity of the octahedral surface decreased as the number of Al vacancies increased but this was not the case for the tetrahedral surface. [ABSTRACT FROM AUTHOR]

The infrared spectra of SiH 4 in natural abundance (92.23% of 28 SiH 4 , 4.68% of 29 SiH 4 , and 3.09% of 30 SiH 4 ) were measured in the region of 600–1200 cm −1 with a Bruker IFS 120HR Fourier transform spectrometer, analyzed and compared with the results available in the literature. More than 3500 transitions with J max . = 27 were assigned to the dyad bands ν 4 and ν 2 of 28 SiH 4 (the band ν 2 is allowed in Raman, but forbidden in absorption spectra for symmetry reasons, and its transitions appear in absorption spectra only because of strong Coriolis interaction with the ν 4 band). Rotational, centrifugal distortion, tetrahedral splitting, and interaction parameters for the ground, (0100) and (0001) vibrational states were determined from the fit of experimental line positions. The obtained set of parameters reproduces the initial experimental data with accuracy close to experimental uncertainties. The results of the analogous analyses of the 29 SiH 4 and 30 SiH 4 isotopologues are also presented (the numbers of the assigned transitions are here more than 1360 and 1120). An further analysis of about 790 experimental ro-vibrational lines in the dyad region of 28 SiH 4 was performed using the Voigt profile to simulate the measured line shape and to determine experimental line intensities. A set of 4 effective dipole moment parameters for the dyad of 28 SiH 4 was obtained on that basis from the weighted fit, which reproduce the initial experimental intensities of about 790 lines with the d rms = 5.6 % . Analogous analyses were made for the two other isotopic species, 29 SiH 4 , and 30 SiH 4 . A detailed line list of transitions in the region of 750–1150 cm −1 is generated. The half-widths of 40 ro-vibrational lines ( J up . max . = 16 ) are studied from the multi-spectrum analysis, and self-pressure broadening coefficients are determined. [ABSTRACT FROM AUTHOR]

To quantify the resolution limits of scanning microwave impedance microscopy (sMIM), we created scanning tunneling microscope (STM)-patterned donor nanostructures in silicon composed of 10 nm lines of highly conductive silicon buried under a protective top cap of silicon, and imaged them with sMIM. This dopant pattern is an ideal test of the resolution and sensitivity of the sMIM technique, as it is made with nm-resolution and offers minimal complications from topography convolution. It has been determined that typical sMIM tips can resolve lines down to ∼80 nm spacing, while resolution is independent of tip geometry as extreme tip wear does not change the resolving power, contrary to traditional scanning capacitance microscopy (SCM). Going forward, sMIM is an ideal technique for qualifying buried patterned devices, potentially allowing for quantitative post-fabrication characterization of donor structures, which may be an important tool for the study of atomic-scale transistors and state of the art quantum computation schemes. [ABSTRACT FROM AUTHOR]

The effects of neutrally charged silicon vacancies on the atomic structure and the lattice dynamics of -quartz were studied. This theoretical study focuses on modeling of the equilibrium local structure and the symmetrized local density of vibrational states. The frequencies of localized vibrations of A- and B-symmetries induced by silicon vacancies were obtained. The contribution of atoms located around silicon vacancies in the formation of localized symmetrized vibrations was analyzed. [ABSTRACT FROM AUTHOR]

An experimental study on the hydrodynamic behavior of silicon particles with a wide size distribution in a draft tube spout-fluid bed was performed in a 182 diameter cylindrical column with a flat gas distributor. Effects of spouting and fluidizing gas velocity, static bed height, entrainment zone height and draft tube diameter on the maximum spouting pressure drop, minimum stable spouting velocity and solids circulation rate were investigated. The results show that the maximum spouting pressure drop increases with static bed height, entrainment zone height, draft tube diameter and fluidizing gas velocity. The minimum spouting velocity increases with entrainment zone height, while it decreases with static bed height, draft tube diameter and fluidizing gas velocity. Two correlations on the maximum pressure drop and minimum spouting velocity are proposed respectively based on the experimental data, which are in good agreement with the present experiments. In addition, the solids circulation rate increases with static bed height, draft tube diameter, fluidizing and spouting gas velocity. It also increases with entrainment zone height at a lower fluidizing gas velocity, however it decreases with entrainment zone height at a higher fluidizing gas velocity. [ABSTRACT FROM AUTHOR]

The inherent brittleness of crystalline silicon is a cause of concern for processing, handling and application of the material. Here a simulation-based design is proposed to reduce the risk of catastrophic brittle fracture of devices and components made of silicon. In this scheme, ultrathin layers of amorphous silicon are introduced within the crystalline silicon to create a multilayered laminated structure. Using molecular dynamics simulations, we demonstrate that in this nanolaminate, a crack growing within the crystalline region gets pinned at the amorphous layers. This phenomenon occurs due to the observed ductility in amorphous silicon, which resembles the shear-band mediated deformation of metallic glasses. As a consequence, the catastrophic failure is averted by localizing the damage and preventing it from extending across the material. [ABSTRACT FROM AUTHOR]

Based on the transmission properties and the photon location characteristics of the Surface plasmon polaritons (SPPs) sub-wavelength structure, a metal–dielectric–metal (MDM) waveguide coupled rectangular cavity structure is proposed. Dielectric material silicon (Si) is introduced in the structure to overcome the high loss of the metal materials. Due to the large refractive index difference between silicon and air, the reflections of SPPs and the incident light at the two ends of the Si–air–Si cavity in the sub-wavelength structure are small meanwhile the transmissions are high, which leads to a wider continuous spectrum. And when the SPPs enter the rectangular cavity in the metal and the phase matching condition is satisfied, the resonance will occur and a narrow transmission spectrum peak will be generated. Through the coupling of the wider continuous state and the narrower isolated state, the Fano resonance will occur. According to the phase-matching condition of resonance, the relationship model between the effective refractive index of the waveguide and the wavelength shift of the resonant peak is established. And with the increase of the length L of the rectangular cavity, the red shift of the resonant peak will occur, which can improve the sensitivity of the sensing structure. The influences of structural parameters L , W and g on Fano resonance are analyzed respectively to optimize the structural parameters by the finite element methods. The Figure of merit (FOM) value can be adjusted and controlled with the change of the structural parameters L , W and g . The FOM value of the optimized structure parameters can attain to 1.19 × 10 4 . The optimized structure parameters are adopted to discuss the sensing performances of the structure. The results show that the sensitivity of the sensor is about 1612 nm/RIU. The waveguide structure mentioned above can provide effective theoretical references for the miniaturization and high integration of photonic devices and refractive index sensing. [ABSTRACT FROM AUTHOR]