Novel Method of Preparation of Gold‐Nanoparticle‐Doped TiO2 and SiO2 Plasmonic Thin Films: Optical Characterization and Comparison with Maxwell–Garnett Modeling

SiO₂ and TiO₂ thin films with gold nanoparticles (NPs) are of particular interest as photovoltaic materials. A novel method for the preparation of spin‐coated SiO₂–Au and TiO₂–Au nanocomposites is presented. This fast and inexpensive method, which includes three separate stages, is based on the in situ synthesis of both the metal‐oxide matrix and the Au NPs during a baking process at relatively low temperature. It allows the formation of nanocomposite thin films with a higher concentration of Au NPs than other methods. High‐resolution transmission electron microscopy studies revealed a homogeneous distribution of NPs over the film volume along with their narrow size distribution. The optical manifestation of localized surface plasmon resonance was studied in more detail for TiO₂‐based Au‐doped nanocomposite films deposited on glass (in absorption and transmittance) and silicon (in specular reflectance). Maxwell–Garnett effective‐medium theory applied to such metal‐doped nanocomposite films describes the peculiarities of the experimental spectra, including modification of the antireflective properties of bare TiO₂ films deposited on silicon by varying the concentration of metal NPs. The antireflective capabilities of the film are increased after a wet etching process.     

High-Conductivity–Dispersibility Graphene Made by Catalytic Exfoliation of Graphite for Lithium-Ion Battery

Despite the progress made on the production of graphene using liquid-phase exfoliation methods, the fabrication of graphene with both high conductivity and dispersibility remains challenging. Through catalytic exfoliation of graphite, an effective synthesis method for graphene with large lateral size (≈10 µm), high conductivity (926 S cm^–1), and excellent water solubility (≈10 mg mL^–1) is reported herein. Such graphene can be used broadly for applications such as lithium ion batteries, where both high conductivity and dispersibility are required. As an example, the synthesis of graphene and lithium-iron-phosphate composites is demonstrated, which leads to electrodes with dramatically improved cycling stability and rate performance. Adaption of such material leads to electrodes with volumetric energy density as high as 658.7 and 287.6 W h L^–1 under 0.5 and 20 C, respectively, which is significantly higher than that of commercial LiFePO₄ (394.7 and 13.5 W h L^–1 at 0.5 and 20 C, respectively). This work provides a new method of making high-conductivity–dispersibility graphene for various applications.     

Improved Scalar Multiplication on Elliptic Curves Defined over F2mn

We propose two improved scalar multiplication methods on elliptic curves over F_qn where q = 2^m using Frobenius expansion. The scalar multiplication of elliptic curves defined over subfield F_q can be sped up by Frobenius expansion. Previous methods are restricted to the case of a small m. However, when m is small, it is hard to find curves having good cryptographic properties. Our methods are suitable for curves defined over medium‐sized fields, that is, 10 ≤ m ≤ 20. These methods are variants of the conventional multiple‐base binary (MBB) method combined with the window method. One of our methods is for a polynomial basis representation with software implementation, and the other is for a normal basis representation with hardware implementation. Our software experiment shows that it is about 10% faster than the MBB method, which also uses Frobenius expansion, and about 20% faster than the Montgomery method, which is the fastest general method in polynomial basis implementation.     

Rapid Synthesis of Various Electrocatalysts on Ni Foam Using a Universal and Facile Induction Heating Method for Efficient Water Splitting

Electrocatalytic water splitting for the production of hydrogen proves to be effective and available. In general, the thermal radiation synthesis usually involves a slow heating and cooling process. Here, a high-frequency induction heating (IH) is employed to rapidly prepare various self-supported electrocatalysts grown on Ni foam (NF) in liquid- and gas-phase within 1–3 min. The NF not only serves as an in situ heating medium, but also as a growth substrate. The as-synthesized Ni nanoparticles anchored on MoO₂ nanowires supported on NF (Ni-MoO₂/NF-IH) enable catalysis of hydrogen evolution reaction (HER), showing a low overpotential of −39 mV (10 mA cm⁻²) and maintaining the stability of 12 h in alkaline condition. Moreover, the NiFe layered double hydroxide (NiFe LDH/NF-IH) is also synthesized via IH and affords outstanding oxygen evolution reaction (OER) activity with an overpotential of 246 mV (10 mA cm⁻²). The Ni-MoO₂/NF-IH and NiFe LDH/NF-IH are assembled to construct a two-electrode system, where a small cell voltage of ≈1.50 V enables a current density of 10 mA cm⁻². More importantly, this IH method is also available to rapidly synthesize other freestanding electrocatalysts on NF, such as transition metal hydroxides and metal nitrides.     

High‐Performance Polyaniline Prepared via Polymerization in a Self‐Stabilized Dispersion

We report a new synthetic method for the preparation of high‐performance polyaniline, implementing a new concept of self‐stabilized dispersion polymerization. In contrast with conventional homogeneous or dispersion polymerization methods that use an aqueous medium containing aniline, acid, and oxidant, our new polymerization is performed in a heterogeneous biphasic system of organic and aqueous medium without any stabilizers. Here, the monomers and growing polymer chains act as stabilizers, resulting in excellent dispersion of the organic phase inside the aqueous reaction medium. Polymerization based on this concept has produced high‐quality samples with few structural defects; the doped polyanilines exhibit conductivities (σ_DC ～ 600–800 S cm^–1) almost three times that of the samples prepared using conventional methods. Moreover, the new polyaniline system shows a honeycomb‐like morphology with great porosity, leading to a system with excellent processibility.     

Reflectance of a PbSb<Subscript>2</Subscript>Te<Subscript>4</Subscript> crystal in a wide spectral range

For the anisotropic PbSb₂Te₄ single crystal with a high hole concentration (p ≈ 3 × 10²⁰ cm^–3) and high conductivity (σ ≈ 2500 Ω^–1 cm^–1), the reflectance spectrum for a cleavage plane orthogonal to the trigonal axis C₃ is recorded in a wide spectral range from 50 to 50000 cm^–1. It is shown that, in the long-wavelength and mid-infrared regions, the reflectance can be described with consideration for the contribution of plasma vibrations and two crystal-lattice vibrations. The quantitative characteristics of these vibrations are determined. The characteristics are in satisfactory agreement with the electrical parameters. The discrepancies between the values of the hole effective mass calculated by different methods are attributed to the complex structure of the crystal’s valence band.     

Accurate series resistance measurement of solar cells

The series resistance (R_s) of a solar cell is commonly represented as a constant resistance value. However, because of the distributed nature of series resistance, the effective lumped R_s vary with current density and illumination intensity. Treating R_s as a constant is usually insufficient for an accurate analysis of its J–V curve. This work first presents a review of the distributed nature of series resistance and commonly applied methods to measure R_s. Particular attention is given to the multi‐light method (MLM) and it is discussed in detail, where R_s in both the light and dark can be measured as a function of current by extracting R_s from a set of current–voltage (J–V) curves attained at different illumination intensities. The principle behind this method is discussed, and the results are then compared with those of other known methods of R_s measurement. The accurate measurement of R_s(J) attained with the MLM permits the extraction of an R_s‐corrected J–V curve, which is theoretically more accurate than that attained by alternative methods because of negligible error from injection dependence and spectral mismatch. With the solar cell equation modified to include R_s(J), we attain a much better fit to experimental data, finding a significant reduction in error compared with using a constant R_s. Copyright © 2011 John Wiley & Sons, Ltd.     

Interaction of infrared radiation with free carriers in mesoporous silicon

Features of absorption and reflection of infrared radiation in the range 500–6000 cm^?1 are investigated; these features are associated with free carriers in the layers of mesoporous Si (porosity, 60–70%) formed in single-crystal p-Si(100) wafers with a hole concentration of N _p ≈10²⁰ cm^?3. It is found that the contribution of free holes to the optical parameters of the samples decreases as the porosity of the material increases and further falls when the samples are naturally oxidized in air. The experimental results are explained in the context of a model based on the Bruggeman effective medium approximation and the Drude classical theory with a correction for additional carrier scattering in silicon residues (nanocrystals). A comparison between the calculated and experimental dependences yields a hole concentration in nanocrystals of N _p ≈10¹⁹ cm^?3 for as-prepared layers and shows a reduction of N _p when they are naturally oxidized.     

Electric transport in gallium antimonide single crystals involving molten GaSb-Sn inclusions

Electromigration of molten tin-based inclusions in single-crystal p-GaSb:Zn(111) was studied. It was shown that molten inclusions are displaced by a current (j=(1–4)×10⁵ A/m²) toward a negative electrode in the temperature range T=750–920 K. The mechanism of this phenomenon was shown to be related to concentration changes in the bulk of molten inclusions. It was noted that the inclusion transport is initiated by two competing processes: the temperature changes at phase interfaces caused by the Peltier heat and the electric transport, leading to the redistribution of components, depending on their effective charges in the melt. The size dependence of the velocity of inclusion motion W in the bulk of a single-crystal matrix was determined: W increases with the inclusion size. The numerical values of the thermoelectric parameters of all the contacting phases were experimentally determined using independent methods. This made it possible, fitting the theory to the experimental data, not only to estimate quantitatively the effective charge Z* of a molten semiconductor, but also to explain the size dependence of the activation barrier overcome by a drifting inclusion.     

Effect of Nanopores on the Phonon Conductivity of Crystalline CoSb3: A Molecular Dynamics Study

Molecular dynamics simulations have been performed to investigate the effect of nanometer-size pores on the phonon conductivity of single-crystal bulk CoSb₃. The cylindrical pores are uniformly distributed along two vertical principal crystallographic directions of a square lattice. Because pore diameter and porosity are two key factors that could affect the performance of the materials, they were varied individually in the ranges a ₀–6a ₀ and 0.1–5%, respectively, where a ₀ is the lattice constant of CoSb₃. The simulation results indicate that the phonon conductivity of nanoporous CoSb₃ is significantly lower than that of no-pore CoSb₃. The reduction of phonon conductivity in this simulation was consistent with the ballistic–diffusive microscopic effective medium model, demonstrating the ballistic character of phonon transport when the phonon mean-free-path is comparable with or larger than the pore size. Reducing pore diameter or increasing porosity are alternative means of effective reduction of the thermal conductivity of CoSb₃. These results are expected to provide a useful basis for the design of high-performance skutterudites.     

The concentration dependence of acceptor-state radii in p-Hg0.78Cd0.22Te crystals

Hopping conduction in undoped p-Hg_0.78Cd_0.22Te crystals containing native double-charged acceptors (Hg vacancies) with concentrations of 10¹⁶–10¹⁸cm^?3 was studied. Electrical conduction with a variable hopping range is dominant in the entire concentration range at temperatures below 6–16 K. The measured parameters of this conduction were used to calculate the acceptor-state radius as a function of vacancy concentration N _A . It is shown that, for N _A <4×10¹⁷ cm^?3, the low-temperature conduction occurs via the vacancy states whose radius is independent of N _A . For N _A >5×10¹⁷ cm^?3, the hopping conduction is governed by the states of uncontrolled shallow-level impurity acceptors. The radius of the state for these defects increases with increasing N _A owing to an increase in the effective permittivity of the medium.     

Determination of the diffusion length of minority charge carriers in a semiconductor from the dynamic nonequilibrium I–V characteristics of MIS structures

A method for determination of the diffusion length L _de of minority charge carriers in a semiconductor from the dynamic nonequilibrium I–V characteristics of metal-insulator-semiconductor (MIS) structures is proposed. The method makes it possible to exclude the effect of bulk generation in a semiconductor on L _de and decrease the temperature of measurements. The possibility of investigating the effective L _de profile in the semiconductor surface layer is shown for the case of nonuniform depth distribution of electrically active defects in a material. The values of L _de in MIS structures on silicon used in integrated-circuit technology are investigated. The effect of the internal gettering of defects in silicon and the irradiation of MIS structures by low-energy electrons (10–30 keV) on the effective L _de profiles in the surface layer of a semiconductor is considered.     

Mixed Electronic and Ionic Conduction Properties of Lithium Lanthanum Titanate

With the continued increase in Li‐metal anode rate capability, there is an equally important need to develop high‐rate cathode architectures for solid‐state batteries. A proposed method of improving charge transport in the cathode is introducing a mixed electronic and ionic conductor (MEIC) which can eliminate the need for conductive additives that occlude electrolyte–electrode interfaces and lower the net additive required in the cathode. This study takes advantage of a reduced perovskite electrolyte, Li_0.33La_0.57TiO₃ (LLTO), to act as a model MEIC. It is found that the ionic conductivity of reduced LLTO is comparable to oxidized LLTO (σ_bulk = 10^?3–10^?4 S cm^?1, σ_GB = 10^?5–10^?6 S cm^?1) and the electronic conductivity is 1 mS cm^?1. The ionic transference numbers are 0.9995 and 0.0095 in the oxidized and reduced state, respectively. Furthermore, two methods for controlling the transference numbers are evaluated. It is found that the electronic conductivity cannot easily be controlled by changing O₂ overpressures, but increasing the ionic conductivity can be achieved by increasing grain size. This work identifies a possible class of MEIC materials that may improve rate capabilities of cathodes in solid‐state architectures and motivate a deeper understanding of MEICs in the context of solid‐state batteries.     

Density functional theory calculations for estimation of gettering sites of C,H, intrinsic point defects and related complexes in Si wafers

Very recently, a C₃H₅ cluster ion implantation technique for proximity gettering has been reported with the low energy of around 10¹⁵/cm² dose without recovery heat treatments. The main feature of this technique is that the gettering efficiency is higher than that by C monomer implantation, even though irradiation defects are too small to clarify by TEM observation. In the present work, we evaluate the binding energies of metal atoms with candidate gettering sites of C, H, intrinsic point defects and related complexes in Si wafers induced by C₃H₅ cluster ion implantation or different methods, for example, H implantation etc. by using density functional theory calculations. In addition to C and H atoms, we consider donor P and O atoms contained in an n- CZ-Si wafer for use in a CMOS image sensor. The simplest complexes of substitutional/interstitial C (C_s/C_i), H_i, P_s, O_i, and incorporated intrinsic point defects (vacancy (V) and self-interstitial Si (I)) by C₃H₅ implantation were also considered. We found that C_s–I (= C_i), C_i–C_i, H_i–I, VH_n (n=1–3), and VO complexes are the best candidates for gettering sites. Gettering by C₃H₅ cluster ion implantation is more effective than that by C monomer implantation due to the formation of VH_n (n=1–3) and H_i–I complexes, which provides more effective gettering sites.     

Investigation of electron properties of semiconductor surface by modulation spectroscopy of electroreflection

The relation of the Franz-Keldysh oscillations to electronic parameters of semiconductor materials is analyzed using the high-field measurement mode. The potential of using modulation spectroscopy of electroreflection for investigating electronic properties of a semiconductor surface is shown by the example of electroreflection spectra of n-GaAs (100) homoepitaxial films with the electron concentration of 10¹⁷–10¹⁸ cm^?3. The spectra are measured by the Schottky-barrier method at a room temperature using unpolarized light in the spectral range of 1.3–1.65 eV in the vicinity of the transition E ₀ (Γ_8V -Γ_6C ). From the quantitative analysis of electroreflection spectra, electronic parameters of films are obtained: the electron-transition energy E ₀, the electro-optical energy ??, the surface electric field F _s, the energy-relaxation time τ of charge carriers, the oscillation length λ_KF of the wave function of a quantum-mechanical particle with a reduced effective mass μ for a given surface electric field F _s, and the electron mobility μ_e.     

Electrical Transport and Oxygen Exchange in the Superoxides of Potassium,Rubidium, and Cesium

Conductivity, ionic transference number, and chemical diffusion coefficients are determined for KO₂, RbO₂, and CsO₂. Based on such results, a defect‐chemical model is constructed. These superoxides are found to exhibit a total conductivity in the range of 3 × 10^–7 to 5 × 10^–5 S cm^–1 at 200 °C with contributions from ionic and electronic carriers. The ionic conductivity is caused by alkali interstitials and superoxide vacancies as mobile defects, and is found to exceed the n‐type electronic conductivity. ¹⁸O isotope exchange on powder samples (monitoring the gas phase composition) shows that essentially all oxygen can be exchanged. At high pO₂ this largely occurs without breaking of the O–O bond—indicating a sufficient mobility of molecular superoxide species in the solid—and with an effective rate constant that is much higher than for other large‐bandgap mixed conducting materials such as SrTiO₃.     

Stable growth of large-area single crystalline thin films from an organic semiconductor/polymer blend solution for high-mobility organic field-effect transistors

We developed an effective and steady solution-processing technique for a small molecule–type semiconductor, C₁₀–DNBDT–NW, by adding an amorphous PMMA polymer to produce stable growth of a two-dimensional large-area single-crystalline thin film by effective phase separation at a crucially faster processing speed compared to the case without the addition of a polymer. By using this solution-processing technique, it is noteworthy that the single-crystalline films of C₁₀–DNBDT–NW/PMMA exhibit the highest and average mobilities of 17 and 10.6 cm²/Vs, respectively. Furthermore, we also show the limitations of two-dimensional continuous growth of a single-crystalline film in terms of the solution technique.     

Properties of Sb2S3 and Sb2Se3 thin films obtained by pulsed laser ablation

The properties of Sb₂S₃ and Sb₂Se₃ thin films of variable thickness deposited onto Al₂O₃, Si, and KCl substrates are investigated by the method of pulsed laser ablation. The samples are obtained at a substrate temperature of 180°C in a vacuum chamber with a residual pressure of 10^?5 Torr. The thickness of the films amounted to 40–1500 nm. The structure of the bulk material of the targets and films is investigated by the methods of X-ray diffraction and transmission high-energy electron diffraction, respectively. The electrical properties of the films are investigated in the temperature range of 253–310 K. It is shown that the films have semiconductor properties. The structural features of the films determine their optical parameters.     

Novel construction of quasi-cyclic low-density parity-check codes with variable code rates for cloud data storage systems

This paper proposed a novel method for constructing quasi-cyclic low-density parity-check (QC-LDPC) codes of medium to high code rates that can be applied in cloud data storage systems, requiring better error correction capabilities. The novelty of this method lies in the construction of sparse base matrices, using a girth greater than 4 that can then be expanded with a lift factor to produce high code rate QC-LDPC codes. Investigations revealed that the proposed large-sized QC-LDPC codes with high code rates displayed low encoding complexities and provided a low bit error rate (BER) of 10⁻¹⁰ at 3.5 dB E_b/N₀ than conventional LDPC codes, which showed a BER of 10⁻⁷ at 3 dB E_b/N₀. Subsequently, implementation of the proposed QC-LDPC code in a software-defined radio, using the NI USRP 2920 hardware platform, was conducted. As a result, a BER of 10⁻⁶ at 4.2 dB E_b/N₀ was achieved. Then, the performance of the proposed codes based on their encoding–decoding speeds and storage overhead was investigated when applied to a cloud data storage (GCP). Our results revealed that the proposed codes required much less time for encoding and decoding (of data files having a 10 MB size) and produced less storage overhead than the conventional LDPC and Reed–Solomon codes.     

Adhesion and Percolation Parameters in Two Dimensional Pd–LSCM Composites for SOFC Anode Current Collection

This paper is concerned with palladium–(La_0.75Sr_0.25)_0.97Cr_0.5Mn_0.5O₃ (LSCM) composite current collectors for solid oxide fuel cells (SOFCs); the composites, which are in a 2D configuration (thickness of about 8–10 µm), are deposited upon an LSCM electrode layer on top of an yttria zirconia electrolyte substrate. The influence of the LSCM particle size on the adhesion between palladium and LSCM are reported and discussed. Compositions using four different LSCM particle sizes (0.21, 0.49, 0.64, and 0.81 µm) with sintered Pd particle sizes approaching 10 µm are investigated. The best bonding is obtained when smaller particles are used. The electrical dc conductivity of the composite is reported as a function of the palladium volume fraction for all used LSCM particle sizes. The measured experimental values present typical insulating–conductive percolation. However, the transition occurs at ～33% of the conductive phase, that is, a lower percentage than for 2D ideal systems and a higher percentage than for 3D ideal systems. This is consistent with lower‐dimension percolation for a system of large‐grained conductors and small‐grained insulators. The general effective media (GEM) equation is used to fit the experimental data, and the two main parameters (the threshold point ?_c and the exponent t) are defined.