Showing papers in "AIP Advances in 2015"
TL;DR: In this article, the uncertainty of the band-to-band absorption coefficient of crystalline silicon was analyzed using the Guide to the expression of uncertainty in measurement (GUM) as well as an extensive characterization of the measurement setups.
Abstract: We analyze the uncertainty of the coefficient of band-to-band absorption of crystalline silicon. For this purpose, we determine the absorption coefficient at room temperature (295 K) in the wavelength range from 250 to 1450 nm using four different measurement methods. The data presented in this work derive from spectroscopic ellipsometry, measurements of reflectance and transmittance, spectrally resolved luminescence measurements and spectral responsivity measurements. A systematic measurement uncertainty analysis based on the Guide to the expression of uncertainty in measurement (GUM) as well as an extensive characterization of the measurement setups are carried out for all methods. We determine relative uncertainties of the absorption coefficient of 0.4% at 250 nm, 11% at 600 nm, 1.4% at 1000 nm, 12% at 1200 nm and 180% at 1450 nm. The data are consolidated by intercomparison of results obtained at different institutions and using different measurement approaches.
332 citations
TL;DR: In this paper, the authors summarize the basics of fluctuational electrodynamics, a theoretical framework for the study of radiative heat transfer in terms of thermally excited propagating and evanescent electromagnetic waves.
Abstract: Radiative thermal transport via the fluctuating electromagnetic near-field has recently attracted increasing attention due to its fundamental importance and its impact on a range of applications from data storage to thermal management and energy conversion. After a brief historical account of radiative thermal transport, we summarize the basics of fluctuational electrodynamics, a theoretical framework for the study of radiative heat transfer in terms of thermally excited propagating and evanescent electromagnetic waves. Various approaches to modeling near-field thermal transport are briefly discussed, together with key results and proposals for manipulation and utilization of radiative heat flow. Subsequently, we review the experimental advances in the characterization of both near-field heat flow and energy density. We conclude with remarks on the opportunities and challenges for future explorations of radiative heat transfer at the nanoscale.
255 citations
TL;DR: In this paper, the authors review the basis of two-photon polymerization (TPP) micro/nanofabrication, including mechanism of TPP, experimental set-up for TPP and scaling laws of resolution of TPP.
Abstract: Two-photon polymerization (TPP) is a powerful and potential technology to fabricate true three-dimensional (3D) micro/nanostructures of various materials with subdiffraction-limit resolution. And it has been applied to microoptics, electronics, communications, biomedicine, microfluidic devices, MEMS and metamaterials. These applications, such as microoptics and photon crystals, put forward rigorous requirements on the processing accuracy of TPP, including the dimensional accuracy, shape accuracy and surface roughness and the processing accuracy influences their performance, even invalidate them. In order to fabricate precise 3D micro/nanostructures, the factors influencing the processing accuracy need to be considered comprehensively and systematically. In this paper, we review the basis of TPP micro/nanofabrication, including mechanism of TPP, experimental set-up for TPP and scaling laws of resolution of TPP. Then, we discuss the factors influencing the processing accuracy. Finally, we summarize the methods reported lately to improve the processing accuracy from improving the resolution and changing spatial arrangement of voxels.
241 citations
TL;DR: In this article, the Cattaneo-Christov heat flux model is used to investigate the rotating flow of viscoelastic fluid bounded by a stretching surface and the boundary layer equations are first modeled and then reduced to self-similar forms via similarity approach.
Abstract: In this paper Cattaneo-Christov heat flux model is used to investigate the rotating flow of viscoelastic fluid bounded by a stretching surface. This model is a modified version of the classical Fourier’s law that takes into account the interesting aspect of thermal relaxation time. The boundary layer equations are first modeled and then reduced to self-similar forms via similarity approach. Both analytical and numerical solutions are obtained and found in excellent agreement. Our computations reveal that velocity is inversely proportional to the viscoelastic fluid parameter. Further fluid temperature has inverse relationship with the relaxation time for heat flux and with the Prandtl number. Present consideration even in the case of Newtonian fluid does not yet exist in the literature.
217 citations
TL;DR: In this paper, Nanocrystalline tin oxide (SnO2) powders with different grain size were prepared by chemical precipitation method using X-ray powder diffractometer and transmission electron microscopy.
Abstract: Nanocrystalline tin oxide (SnO2) powders with different grain size were prepared by chemical precipitation method. The reaction was carried out by varying the period of hydrolysis and the as-prepared samples were annealed at different temperatures. The samples were characterized using X-ray powder diffractometer and transmission electron microscopy. The microstrain and crystallite size were calculated for all the samples by using Williamson-Hall (W-H) models namely, isotropic strain model (ISM), anisotropic strain model (ASM) and uniform deformation energy density model (UDEDM). The morphology and particle size were determined using TEM micrographs. The directional dependant young’s modulus was modified as an equation relating elastic compliances (sij) and Miller indices of the lattice plane (hkl) for tetragonal crystal system and also the equation for elastic compliance in terms of stiffness constants was derived. The changes in crystallite size and microstrain due to lattice defects were observed while ...
215 citations
TL;DR: In this paper, the average valence of the oxygen anions in the perovskite oxide BaTiO3 was found using O1s photoelectron spectra to be −1.55.
Abstract: The average valence, ValO, of the oxygen anions in the perovskite oxide BaTiO3, was found using O1s photoelectron spectra to be −1.55. This experimental result is close to the theoretical value for BaTiO3 (−1.63) calculated by Cohen [Nature 358, 136 (1992)] using density functional theory. Using the same approach, we obtained values of ValO for several monoxides, and investigated the dependence of ValO and the ionicity on the second ionization energy, V(M2+), of the metal cation. We found that the dependence of the ionicity on V(M2+) in this work is close to that reported by Phillips [Rev. Mod. Phys. 42, 317 (1970)]. We therefore suggest that O1s photoelectron spectrum measurements should be accepted as a general experimental method for estimating the ionicity and average valence of oxygen anions.
180 citations
TL;DR: In this paper, hole conducting, optically transparent Cu2O thin films on glass substrates have been synthesized by vacuum annealing (5×10−6 mbar at 700 K for 1 hour) of magnetron sputtered (at 300 K).
Abstract: Hole conducting, optically transparent Cu2O thin films on glass substrates have been synthesized by vacuum annealing (5×10−6 mbar at 700 K for 1 hour) of magnetron sputtered (at 300 K) CuO thin films. The Cu2O thin films are p-type and show enhanced properties: grain size (54.7 nm), optical transmission 72% (at 600 nm) and Hall mobility 51 cm2/Vs. The bulk and surface Valence band spectra of Cu2O and CuO thin films are studied by temperature dependent Hall effect and Ultra violet photo electron Spectroscopy (UPS). CuO thin films show a significant band bending downwards (due to higher hole concentration) than Cu2O thin films.
165 citations
TL;DR: In this paper, the boundary layer flow of Maxwell fluid over a stretching sheet with variable thickness is analyzed and the behavior of various pertinent parameters on the velocity and temperature distributions are analyzed and discussed.
Abstract: The present analysis concentrates on the boundary layer flow of Maxwell fluid over a stretching sheet with variable thickness. Cattaneo-Christov heat flux model is used instead of classical Fourier’s law to explore the heat transfer characteristics with variable thermal conductivity. Suitable transformations are employed to achieve the nonlinear ordinary differential equations. Convergent series solutions of the momentum and energy equations are obtained. Behavior of various pertinent parameters on the velocity and temperature distributions are analyzed and discussed.
157 citations
TL;DR: In this paper, the incompressible two-dimensional mixed convection flow of MHD Eyring-Powell nanofluid over a stretching sheet is investigated numerically.
Abstract: In the present analysis incompressible two dimensional mixed convection flow of MHD Eyring-Powell nanofluid over a stretching sheet is investigated numerically. The governing highly nonlinear partial differential equations are converted into ordinary differential equations by using a similarity approach. Numerical solutions of the nonlinear ordinary differential equations are found by using a shooting method. Effects of various parameters are displayed graphically for velocity, temperature and concentration profiles. Also quantities of practical interest i.e skin friction coefficient, Nusselt number and Sherwood number are presented graphically and tabularly.
136 citations
TL;DR: In this article, the magneto-hydro-dynamic flow and heat transfer of Casson nanofluid over a non-linearly stretching sheet is considered and numerical solutions are computed through fourth-fifth-order Runge-Kutta integration approach combined with the shooting technique.
Abstract: Present work deals with the magneto-hydro-dynamic flow and heat transfer of Casson nanofluid over a non-linearly stretching sheet. Non-linear temperature distribution across the sheet is considered. More physically acceptable model of passively controlled wall nanoparticle volume fraction is accounted. The arising mathematical problem is governed by interesting parameters which include Casson fluid parameter, magnetic field parameter, power-law index, Brownian motion parameter, thermophoresis parameter, Prandtl number and Schmidt number. Numerical solutions are computed through fourth-fifth-order-Runge-Kutta integration approach combined with the shooting technique. Both temperature and nanoparticle volume fraction are increasing functions of Casson fluid parameter.
131 citations
TL;DR: In this article, the authors describe stimulating recent developments in the three caloric strands that are now being studied collectively, namely magnetocaloric, electrocaloric and mechanocaloric (elastocaloric or barocaloric) effects.
Abstract: Caloric materials are in the spotlight as candidates for future environmentally friendly cooling technologies. We describe stimulating recent developments in the three caloric strands that are now being studied collectively, namely magnetocaloric, electrocaloric and mechanocaloric (elastocaloric or barocaloric) effects.
TL;DR: In this article, the boundary layer flow and heat transfer to a Carreau model over a nonlinear stretching surface is discussed and the numerical solution of the resulting equations are obtained by using the Runge-Kutta Fehlberg method along with shooting technique.
Abstract: This article studies the Carreau viscosity model (which is a generalized Newtonian model) and then use it to obtain a formulation for the boundary layer equations of the Carreau fluid. The boundary layer flow and heat transfer to a Carreau model over a nonlinear stretching surface is discussed. The Carreau model, adequate for many non-Newtonian fluids, is used to characterize the behavior of the fluids having shear thinning properties and fluids with shear thickening properties for numerical values of the power law exponent n. The modeled boundary layer conservation equations are converted to non-linear coupled ordinary differential equations by a suitable transformation. Numerical solution of the resulting equations are obtained by using the Runge-Kutta Fehlberg method along with shooting technique. This analysis reveals many important physical aspects of flow and heat transfer. Computations are performed for different values of the stretching parameter (m), the Weissenberg number (We) and the Prandtl number (Pr). The obtained results show that for shear thinning fluid the fluid velocity is depressed by the Weissenberg number while opposite behavior for the shear thickening fluid is observed. A comparison with previously published data in limiting cases is performed and they are in excellent agreement.
TL;DR: In this paper, the stagnation point flow of carbon nanotubes over an impermeable stretching cylinder with homogeneous-heterogeneous reactions was studied and the impacts of various pertinent parameters on the velocity, temperature and concentration distributions were discussed graphically.
Abstract: This work addresses the stagnation point flow of carbon nanotubes over an impermeable stretching cylinder with homogeneous-heterogeneous reactions. Modern heat transfer technique (i.e., Newtonian heating) and Carbon nanotubes (CNTs) and water are used to explore the impacts of heat transfer characteristics. Two types of CNTs are used as nanoparticles (i) Single-wall carbon nanotubes (SWCNTs) and (ii) multi-wall carbon nanotubes (MWCNTs). A system of ordinary differential equations is obtained by using suitable transformations. Convergent series solutions are derived via homotopic procedure. Impacts of various pertinent parameters on the velocity, temperature and concentration distributions are discussed graphically. Numerical values of skin friction coefficient and Nusselt number are computed and analyzed.
TL;DR: In this paper, Ni substituted cobalt ferrite nanoparticles with composition Co1−xNixFe2O4 (0.0 ≤ x ≤ 1.0) was synthesized using simple, low temperature auto combustion method.
Abstract: Nickel substituted cobalt ferrite nanoparticles with composition Co1−xNixFe2O4 (0.0 ≤ x ≤ 1.0) was synthesized using simple, low temperature auto combustion method. The X-ray diffraction patterns reveal the formation of cubic phase spinel structure. The crystallite size varies from 30-44 nm with the nickel content. Porous and agglomerated morphology of the bulk sample was displayed in the scanning electron microscopy. Micro Raman spectroscopy reveals continuous shift of Eg and Eg(2) stokes line up to 0.8 Ni substitution. The dispersion behavior of the dielectric constant with frequency and the semicircle nature of the impedance spectra show the cobalt nickel ferrite to have high resistance. The ferromagnetic nature is observed in all the samples, however, the maximum saturation magnetization was achieved by the 0.4 Ni substituted cobalt ferrite, which is up to the 92.87 emu/gm at 30K.
TL;DR: In this paper, the influence of gold nanoparticles (GNPs) on graphene was studied by Raman spectroscopy and it was found that the contact of GNPs could induce the whole Raman spectrum of graphene to redshift.
Abstract: The influence of gold nanoparticles (GNPs) on graphene was studied by Raman spectroscopy. It was found that the contact of GNPs could induce the whole Raman spectrum of graphene to redshift. And the shift of the 2D peak is more obvious than that of the G peak. A model of local strain was brought forward to explain the shift of Raman spectrum, which comes from the charges transfer between the GNPs and graphene. The observation of the Raman shifts helps us to gain more physical insights into the graphene-related systems.
TL;DR: In this article, the MHD steady flow of viscous nanofluid due to a rotating disk was investigated, where water was treated as a base fluid and copper as nanoparticle.
Abstract: This paper investigates MHD steady flow of viscous nanofluid due to a rotating disk. Water is treated as a base fluid and copper as nanoparticle. Nanofluid fills the porous medium. Effects of partial slip, viscous dissipation and thermal radiation are also considered. Similarity transformations reduce the nonlinear partial differential equations to ordinary differential equations. Flow and heat transfer characteristics are computed by HAM solutions. Also computations for skin friction coefficient and Nusselt number are presented and examined for pertinent parameters. It is noted that higher velocity slip parameter decreases the radial and azimuthal velocities while temperature decreases for larger values of the thermal slip parameter. Also the rate of heat transfer enhances when the nanoparticle volume fraction increases.
TL;DR: In this paper, a review of the many directions of realizing phononic computing and information processing is examined, given the relative similarity of vibrational transport at different length scales, the related fields of acoustic, phononic, and thermal information processing are all included, as are quantum and classical computer implementations.
Abstract: Phonons, the quanta of mechanical vibration, are important to the transport of heat and sound in solid materials. Recent advances in the fundamental control of phonons (phononics) have brought into prominence the potential role of phonons in information processing. In this review, the many directions of realizing phononic computing and information processing are examined. Given the relative similarity of vibrational transport at different length scales, the related fields of acoustic, phononic, and thermal information processing are all included, as are quantum and classical computer implementations. Connections are made between the fundamental questions in phonon transport and phononic control and the device level approach to diodes, transistors, memory, and logic.
TL;DR: In this paper, the authors have studied ionic conductivity and dielectric permittivity of PEO-LiClO4 solid polymer electrolyte plasticized with propylene carbonate.
Abstract: We have studied ionic conductivity and dielectric permittivity of PEO-LiClO4 solid polymer electrolyte plasticized with propylene carbonate. Differential scanning calorimetry and X-ray diffraction studies confirm minimum volume fraction of crystalline phase for the polymer electrolyte with 40 wt. % propylene carbonate. The ionic conductivity exhibits a maximum for the same composition. The temperature dependence of the ionic conductivity has been well interpreted using Vogel-Tamman-Fulcher equation. Ion-ion interactions in the polymer electrolytes have been studied using Raman spectra and the concentrations of free ions, ion-pairs and ion-aggregates have been determined. The ionic conductivity increases due to the increase of free ions with the increase of propylene carbonate content. But for higher content of propylene carbonate, the ionic conductivity decreases due to the increase of concentrations of ion-pairs and ion-aggregates. To get further insights into the ion dynamics, the experimental data for the complex dielectric permittivity have been studied using Havriliak–Negami function. The variation of relaxation time with temperature obtained from this formalism follows Vogel-Tamman-Fulcher equation similar to the ionic conductivity.
TL;DR: In this paper, the exact solution of convective heat transfer of a magnetohydrodynamic (MHD) Jeffrey fluid over a stretching sheet was studied in the presence of a transverse magnetic field for two types of boundary heating process.
Abstract: This article focuses on the exact solution regarding convective heat transfer of a magnetohydrodynamic (MHD) Jeffrey fluid over a stretching sheet. The effects of joule and viscous dissipation, internal heat source/sink and thermal radiation on the heat transfer characteristics are taken in account in the presence of a transverse magnetic field for two types of boundary heating process namely prescribed power law surface temperature (PST) and prescribed heat flux (PHF). Similarity transformations are used to reduce the governing non-linear momentum and thermal boundary layer equations into a set of ordinary differential equations. The exact solutions of the reduced ordinary differential equations are developed in the form of confluent hypergeometric function. The influence of the pertinent parameters on the temperature profile is examined. In addition the results for the wall temperature gradient are also discussed in detail.
TL;DR: In this paper, the authors present the results of a thermo-mechanical characterization conducted on a specific type of twisted polymeric fiber (i.e., nylon-made coiled actuators) that is considered particularly promising.
Abstract: The discovery of an innovative class of thermally activated actuators based on twisted polymeric fibres has opened new horizons toward the development of effective devices that can be easily manufactured using inexpensive materials such as fishing lines or sewing threads. These new devices show large deformations when heated together with promising performance in terms of energy and power densities. With the aim of providing information and data useful for the future engineering applications, we present the results of a thermo-mechanical characterization conducted on a specific type of twisted polymeric fibre (i.e. nylon-made coiled actuators) that is considered particularly promising. A custom experimental test-bench and procedure have been developed and employed to run isothermal and isometric tensile tests on a set of specimens that are fabricated with a simple and repeatable process. The results of the experiments highlight some important issues related to the response of these actuators such as hysteresis, repeatability, predictability and stored elastic energy.
TL;DR: In this paper, the authors investigated the band gap and defect states of MgO thin films by using reflection electron energy loss spectroscopy (REELS) and high-energy resolution REELS (HR-REELS).
Abstract: The band gap and defect states of MgO thin films were investigated by using reflection electron energy loss spectroscopy (REELS) and high-energy resolution REELS (HR-REELS) HR-REELS with a primary electron energy of 03 keV revealed that the surface F center (FS) energy was located at approximately 42 eV above the valence band maximum (VBM) and the surface band gap width (EgS) was approximately 63 eV The bulk F center (FB) energy was located approximately 49 eV above the VBM and the bulk band gap width was about 78 eV, when measured by REELS with 3 keV primary electrons From a first-principles calculation, we confirmed that the 42 eV and 49 eV peaks were FS and FB, induced by oxygen vacancies We also experimentally demonstrated that the HR-REELS peak height increases with increasing number of oxygen vacancies Finally, we calculated the secondary electron emission yields (γ) for various noble gases He and Ne were not influenced by the defect states owing to their higher ionization energies, but
TL;DR: In this article, structural, vibrational, resonance and magnetic properties of nanoscale NiO powders prepared by ball milling process under different milling speeds for 30 hours of milling were investigated.
Abstract: We report systematic investigations of structural, vibrational, resonance and magnetic properties of nanoscale NiO powders prepared by ball milling process under different milling speeds for 30 hours of milling. Structural properties revealed that both pure NiO and as-milled NiO powders exhibit face centered cubic structure, but average crystallite size decreases to around 11 nm along with significant increase in strain with increasing milling speed. Vibrational properties show the enhancement in the intensity of one-phonon longitudinal optical (LO) band and disappearance of two-magnon band due to size reduction. In addition, two-phonon LO band exhibits red shift due to size-induced phonon confinement effect and surface relaxation. Pure NiO powder exhibit antiferromagnetic nature, which transforms into induced ferromagnetic after size reduction. The average magnetization at room temperature increases with decreasing the crystallite size and a maximum moment of 0.016 μB/f.u. at 12 kOe applied field and coe...
TL;DR: In this article, a simple chemical method based on sol-gel processing was proposed to deposit metastable orthorhombic tin oxide (SnOx) thin films on glass substrates at room temperature.
Abstract: A novel and simple chemical method based on sol-gel processing was proposed to deposit metastable orthorhombic tin oxide (SnOx) thin films on glass substrates at room temperature. The resultant samples are labeled according to the solvents used: ethanol (SnO-EtOH), isopropanol (SnO-IPA) and methanol (SnO-MeOH). The variations in the structural, morphological and optical properties of the thin films deposited using di ff erent solvents were characterized by X-ray diff raction, atomic force microscopy, Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy and photoluminescence (PL) analysis. The XRD patterns confirm that all the films, irrespective of the solvents used for preparation, were polycrystalline in nature and contained a mixed phases of tin (II) oxide and tin (IV) oxide in a metastable orthorhombic crystal structure. FTIR spectra confirmed the presence of Sn=O and Sn-O in all of the samples. PL spectra showed a violet emission band centered at 380 nm (3.25 eV) for all of the solvents. The UV-vis spectra indicated a maximum absorption band shown at 332 nm and the highest average transmittance around 97% was observed for the SnO-IPA and SnO-MeOH thin film samples. The AFM results show variations in the grain size with solvent. The structural and optical properties of the SnO thin films indicate that this method of fabricating tin oxide is promising and that future work is warranted to analyze the electrical properties of the films in order to determine the viability of these films for various transparent conducting oxide applications. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4909542]
TL;DR: In this article, a microwave sintered nanocrystalline BiFeO3 (BFO) ceramic was used to reduce the sintering time and increase the final density.
Abstract: In this paper, major reduction in sintering time,temperautre and significant improvement over final density of sitnered sample is reported for the microwave sintered nanocrystalline BiFeO3 (BFO) ceramic. Also, different sintering time and temperatures have been used to tailor the grain size and the final density of the resulting BFO ceramics synthesized from phase pure BFO nanoparticles (d ≈10 nm). Microwave sintering resulted in reducing the sintering time substantially (by 1h), and has resulted in submicron sized grains and high resistivity ∼1.8 GΩ-cm. The AC conductivity is seen to follow the Jonscher’s power law behavior, suggesting correlated barrier hopping (CBH) mechanism in the sample. The role of oxygen vacancies at high temperature, due to volatility of bismuth, in dielectric and conductivity behavior is also discussed. Further, the sample displayed dielectric anomaly near magnetic transition temperature (∼180 °C) indicating bearing of magnetic moments on the dielectric properties. Using Impeda...
TL;DR: In this article, the formation of TiO2 thin films via DC reactive magnetron sputtering was discussed and the oxygen concentration during sputtering proved to be a crucial parameter with respect to the final film structure and properties.
Abstract: We discuss the formation of TiO2 thin films via DC reactive magnetron sputtering. The oxygen concentration during sputtering proved to be a crucial parameter with respect to the final film structure and properties. The initial deposition provided amorphous films that crystallise upon annealing to anatase or rutile, depending on the initial sputtering conditions. Substoichiometric films (TiOx<2), obtained by sputtering at relatively low oxygen concentration, formed rutile upon annealing in air, whereas stoichiometric films formed anatase. This route therefore presents a formation route for rutile films via lower (<500 °C) temperature pathways. The dynamics of the annealing process were followed by in situ ellipsometry, showing the optical properties transformation. The final crystal structures were identified by XRD. The anatase film obtained by this deposition method displayed high carriers mobility as measured by time-resolved microwave conductance. This also confirms the high photocatalytic activity of the anatase films.
TL;DR: In this paper, the effects of inclined magnetic field and heat transfer in the flow of a third-grade fluid by an exponentially stretching surface were examined with heat source and sink, and the governing boundary layer equations and boundary conditions were simplified through appropriate transformations.
Abstract: This paper examines effects of inclined magnetic field and heat transfer in the flow of a third-grade fluid by an exponentially stretching surface. Formulation and analysis are given with heat source and sink. Thermal conductivity is taken temperature dependent. The governing boundary layer equations and boundary conditions are simplified through appropriate transformations. Resulting equations are solved for the approximate solutions. Convergence of governed problems is explicitly discussed. Influences of various dimensionless parameters such as on the flow and thermal fields are discussed. Local skin friction coefficient and the local Nusselt number are analyzed through tabulated values.
TL;DR: In this article, an initially transparent light shutter using polymer-networked liquid crystals with crossed patterned electrodes was proposed, which is switchable between the transparent and opaque states, and exhibits a fast response time and a low operating voltage.
Abstract: We propose an initially transparent light shutter using polymer-networked liquid crystals with crossed patterned electrodes. The proposed light shutter is switchable between the transparent and opaque states, and it exhibits a fast response time and a low operating voltage. In the transparent state, the light shutter has high transmittance; in the opaque state, it can block the background image and provides black color. We expect that the proposed light shutter can be applied to see-through displays and smart windows.
TL;DR: In this article, the authors show that the typical strains in a semiconductor nanostructure from metal gates are large enough to create strain-induced quantum dots, which can be eliminated by replacing the metal gates with poly-silicon gates.
Abstract: A long-standing mystery in the field of semiconductor quantum dots (QDs) is: Why are there so many unintentional dots (also known as disorder dots) which are neither expected nor controllable. It is typically assumed that these unintentional dots are due to charged defects, however the frequency and predictability of the location of the unintentional QDs suggests there might be additional mechanisms causing the unintentional QDs besides charged defects. We show that the typical strains in a semiconductor nanostructure from metal gates are large enough to create strain-induced quantum dots. We simulate a commonly used QD device architecture, metal gates on bulk silicon, and show the formation of strain-induced QDs. The strain-induced QD can be eliminated by replacing the metal gates with poly-silicon gates. Thus strain can be as important as electrostatics to QD device operation operation.
TL;DR: In this article, the authors reported the first time, experimentally extracted electronic parameters, i.e., fixed charge density (Qf) and interface-trap charge density(Dit), for as-deposited (AD) and post-deposition annealed (PDA) ALD Al2O3 films on CIGS surfaces using capacitance-voltage (C-V) and conductance-frequency (G-f) measurements.
Abstract: Atomic layer deposited (ALD) Al2O3 films on Cu(In,Ga)Se2 (CIGS) surfaces have been demonstrated to exhibit excellent surface passivation properties, which is advantageous in reducing recombination losses at the rear metal contact of CIGS thin-film solar cells. Here, we report, for the first time, experimentally extracted electronic parameters, i.e. fixed charge density (Qf) and interface-trap charge density (Dit), for as-deposited (AD) and post-deposition annealed (PDA) ALD Al2O3 films on CIGS surfaces using capacitance–voltage (C-V) and conductance-frequency (G-f) measurements. These results indicate that the AD films exhibit positive fixed charges Qf (approximately 1012 cm−2), whereas the PDA films exhibit a very high density of negative fixed charges Qf (approximately 1013 cm−2). The extracted Dit values, which reflect the extent of chemical passivation, were found to be in a similar range of order (approximately 1012 cm−2 eV−1) for both AD and PDA samples. The high density of negative Qf in the bulk of the PDA Al2O3 film exerts a strong Coulomb repulsive force on the underlying CIGS minority carriers (ns), preventing them to recombine at the CIGS/Al2O3 interface. Using experimentally extracted Qf and Dit values, SCAPS simulation results showed that the surface concentration of minority carriers (ns) in the PDA films was approximately eight-orders of magnitude lower than in the AD films. The electrical characterization and estimations presented in this letter construct a comprehensive picture of the interfacial physics involved at the Al2O3/CIGS interface.
TL;DR: For the mixed initial boundary value problem in the context of micropolar bodies with double porosity, this article proved the existence of the solution, its uniqueness as well as some considerations on stability of solution.
Abstract: In this study we want to extend the results of B Straughan, which quite recently addressed the issue of double porosity structure for classical elastic bodies In this case, the double porosity structure of the body is not influenced by the displacement field, which is not consistent with reality For the mixed initial boundary value problem in the context of micropolar bodies with double porosity, we prove the existence of the solution, its uniqueness as well as some considerations on stability of solution