Advances in Condensed Matter Physics
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Open Access journal
ISSN (Print) 1687-8108 - ISSN (Online) 1687-8124
Published by Hindawi Publishing Corporation [403 journals]
- Formation of Porous Apatite Layer during In Vitro Study of
Hydroxyapatite-AW Based Glass Composites
Abstract: This research discussed the fabrication, characterization, and in vitro study of composites based on the mixture of hydroxyapatite powder and apatite-wollastonite (AW) based glass. AW based glass was prepared from the SiO2-CaO-MgO-P2O5-CaF2 glass system. This study focuses on the effect of composition and sintering temperature that influences the properties of these composites. Microstructural study revealed the formation of apatite layer on the composite surfaces when immersed in simulated body fluid (SBF) solution at 37°C. Composites containing ≥50 wt% AW based glass showed good bioactivity after 7 days of immersion in the SBF. A porous calcium phosphate (potentially hydroxycarbonate apatite, HCA) layer formed at the SBF-composite interface and the layer became denser at longer soaking period, for periods ranging from 7 to 28 days. Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) analysis showed that early stage of soaking occurred with the release of Ca and Si ions from the composites and the decrease of P ions with slow exchange rate.
PubDate: Thu, 30 Jul 2015 13:44:59 +000
- Analysis of Eu3+ Emission from Mg2TiO4 Nanoparticles by Judd-Ofelt Theory
Abstract: Eu3+ doped Mg2TiO4 (2 at% of Eu) nanoparticles which are 5 to 10 nm in diameter are prepared by Pechini-type polymerized complex route followed with the calcination in the temperature range from 400°C to 700°C. Emission spectra display characteristic (, 1, 2, 3, and 4) spin forbidden f-f electronic transitions of the Eu3+ ions with the most pronounced emission coming from transition and with the emission decays varying between 0.57 and 0.87 ms for samples prepared at different temperatures. Judd-Ofelt theoretical analysis of the emission spectra of Eu3+ ions was performed, which allowed calculating radiative and nonradiative emission probabilities, Judd-Ofelt intensity parameters, and the quantum efficiency of the Eu3+ emission in the Mg2TiO4 nanoparticles. The analyses showed the existence of high asymmetry around the metal ion sites. Also, the largest quantum efficiency of emission of 58.5% is found in nanoparticles prepared at 600°C.
PubDate: Mon, 27 Jul 2015 13:09:43 +000
- Experimental and Theoretical Studies on the Structure and Photoluminescent
Properties of New Mononuclear and Homodinuclear Europium(III)
Abstract: Two novel europium(III) complexes, a monomer and a homodimer, with 1-(4-chlorophenyl)-4,4,4-trifluoro-1,3-butanedione (Hcbtfa) and 5-chloro-1,10-phenanthroline (cphen) ligands, formulated as [Eu(cbtfa)3(cphen)] and [Eu2(cbtfa)4(cphen)2(CH3O)2], have been synthesized. Their structures have been elucidated by X-ray diffraction and their absorption and emission properties have been studied in the solid state. The experimental data has then been used to test the recently released LUMPAC software, a promising tool which can facilitate the design of more efficient lanthanide light-conversion molecular devices by combining ground state geometry, excited state energy, and luminescent properties calculations.
PubDate: Mon, 27 Jul 2015 12:29:11 +000
- Exotic Superconductivity in Correlated Electron Systems
PubDate: Wed, 22 Jul 2015 12:44:23 +000
- Gap Structure of the Overdoped Iron-Pnictide Superconductor
Ba(Fe0.942Ni0.058)2As2: A Low-Temperature Specific-Heat Study
Abstract: Low-temperature specific heat (SH) is measured on the postannealed Ba(Fe1−xNix)2As2 single crystal with x = 0.058 under different magnetic fields. The sample locates on the overdoped sides and the critical transition temperature is determined to be 14.8 K by both the magnetization and SH measurements. A simple and reliable analysis shows that, besides the phonon and normal electronic contributions, a clear term emerges in the low temperature SH data. Our observation is similar to that observed in the Co-doped system in our previous work and is consistent with the theoretical prediction for a superconductor with line nodes in the energy gap.
PubDate: Wed, 22 Jul 2015 06:38:18 +000
- Pressure Induced Suppression to the Valence Change Transition in EuPdAs
Abstract: By applying a hydrostatic pressure, we have successfully suppressed the valence change transition in EuPdAs. The studied compound EuPdAs crystallizes in a P63/mmc space group. Through resistivity and magnetic susceptibility measurements, we find that EuPdAs shows a phase transition at 180 K and another transition below 10 K at ambient pressure, as was reported before. The overall transport and magnetic behavior is to some extent similar to that of the parent phase of iron based superconductors. With application of a hydrostatic pressure, the transition at 180 K is sensitively suppressed with a pressure as low as 0.48 GPa. However, superconductivity has not been induced with pressure up to 1.90 GPa.
PubDate: Tue, 21 Jul 2015 13:31:22 +000
- Improving Breakdown Voltage for a Novel SOI LDMOS with a Lateral Variable
Doping Profile on the Top Interface of the Buried Oxide Layer
Abstract: In order to achieve a high breakdown voltage (BV) for the SOI (Silicon-On-Insulator) power device in high voltage ICs, a novel high voltage n-channel lateral double-diffused MOS (LDMOS) with a lateral variable interface doping profile (LVID) placed at the interface between the SOI layer and the buried-oxide (BOX) layer (LVID SOI) is researched. Its breakdown mechanism is investigated theoretically, and its structure parameters are optimized and analyzed by 2D simulation software MEDICI. In the high voltage blocking state, the high concentration ionized donors in the depleted LVID make the surface electric field of SOI layer () more uniform and enhance the electric field of BOX layer (), which can prevent the lateral premature breakdown and result in a higher BV. Compared with the conventional uniformly doped (UD) SOI LDMOS, of the optimized LVID SOI LDMOS is enhanced by 79% from 119 V/μm to 213 V/μm, and BV is increased by 33.4% from 169 V to 227 V. Simulations indicate that the method of LVID profile can significantly improve breakdown voltage for the SOI LDMOS.
PubDate: Tue, 21 Jul 2015 13:01:49 +000
- “Nodal Gap” Induced by the Incommensurate Diagonal Spin
Density Modulation in Underdoped High- Superconductors
Abstract: Recently it was revealed that the whole Fermi surface is fully gapped for several families of underdoped cuprates. The existence of the finite energy gap along the -wave nodal lines (nodal gap) contrasts the common understanding of the -wave pairing symmetry, which challenges the present theories for the high- superconductors. Here we propose that the incommensurate diagonal spin-density-wave order can account for the above experimental observation. The Fermi surface and the local density of states are also studied. Our results are in good agreement with many important experiments in high- superconductors.
PubDate: Tue, 21 Jul 2015 11:27:14 +000
- Inelastic Neutron Scattering Studies on the Crystal Field Excitations in
Abstract: Inelastic neutron scattering experiments were performed on polycrystalline samples of NdFeAsO0.85F0.15 over a wide temperature range (3 K–250 K). Based on the analysis of the experimental data, a Nd3+ CF energy level scheme is proposed to give a consistent explanation about the observed CF transitions. The observed extra ground-state CF transitions could not be simply explained by the transitions between five Kramers doublets split from the Nd3+ ground state in the point symmetry. A reliable explanation would be a superposition of crystal fields due to different local symmetries around the Nd3+ ions induced by the fluorine doping.
PubDate: Tue, 21 Jul 2015 11:26:12 +000
- The Insulator to Superconductor Transition in Ga-Doped Semiconductor Ge
Single Crystal Induced by the Annealing Temperature
Abstract: We have fabricated the heavily Ga-doped layer in Ge single crystal by the implantation and rapid thermal annealing method. The samples show a crossover from the insulating to the superconducting behavior as the annealing temperature increases. Transport measurements suggest that the superconductivity is from the heavily Ga-doped layer in Ge.
PubDate: Tue, 21 Jul 2015 11:17:26 +000
- A Novel Orange-Red Emitting ZnB4O7:Eu3+ Phosphor with Urchin-Like
Abstract: A novel phosphor, ZnB4O7:Eu3+, with urchin-like structure consisting of radially arranged high density nanorods was successfully synthesized by hydrothermal process at 150°C for 24 h. The nanorods were measured from 200 to 400 nm in diameter and several µm in length. The urchins were few µm to 40 µm in diameter. The ZnB4O7:Eu3+ phosphors were efficiently excited by ultraviolet (UV ~ 254 nm) to visible light of ~ 220 to 450 nm and exhibited intense orange-red emission consisting of main peaks at 590, 615, and 695 nm due to the charge transfer in the host and transitions (5D0 to 7F1,2,4) of the Eu3+ ions. Effect of the Eu3+ ions concentration on the photoluminescence (PL) emission intensity was investigated and it was found that 5 at% Eu3+ is the optimum concentration. Meanwhile, the concentration quenching mechanism was discussed. The key parameters, such as temperature dependent PL and CIE values of ZnB4O7:Eu3+ phosphors, were studied. The ZnB4O7:Eu3+ phosphor exhibited good thermal stability and better absorption cross section compared to the commercial Y2O2S:Eu3+ phosphor. All these characteristics indicate that the phosphor will be a potential candidate for the UV based white LEDs.
PubDate: Wed, 15 Jul 2015 10:25:28 +000
- Influence of Fe Buffer Layer on Co-Doped BaFe2As2 Superconducting Thin
Abstract: A systematic characterization of Co-doped BaFe2As2 (Ba-122) thin films has been carried out. Two samples were available, one grown on CaF2 substrate and the other on MgO with an Fe buffer layer. The goal was to investigate films’ magnetic and superconducting properties, their reciprocal interplay, and the role played by the Fe buffer layer in modifying them. Morphological characterization and Energy Dispersive X-ray analyses on the Fe-buffered sample demonstrate the presence of diffused Fe close to the Co-doped Ba-122 outer surface as well as irregular holes in the overlying superconducting film. These results account for hysteresis loops obtained with magneto-optic Kerr effect measurements and observed at both room and low temperatures. The magnetic pattern was visualized by magneto-optical imaging with an indicator film. Moreover, we investigated the onset of superconductivity through a measure of the superconducting energy gap. The latter is strictly related to the decay time of the excitation produced by an ultrashort laser pulse and has been determined in a pump-probe transient reflectivity experiment. A comparison of results relative to Co-doped Ba-122 thin films with and without Fe buffer layer is finally reported.
PubDate: Tue, 14 Jul 2015 09:03:43 +000
- Effects of Low Ag Doping on Physical and Optical Waveguide Properties of
Highly Oriented Sol-Gel ZnO Thin Films
Abstract: A sol-gel dip-coating process was used to deposit almost stress-free highly c-axis oriented zinc oxide (ZnO) thin films onto glass substrates. The effects of low silver doping concentration (Ag/Zn < 1%) on the structural, morphological, optical, and waveguide properties of such films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy, UV-Visible spectrophotometry, and M-lines spectroscopy (MLS). XRD analysis revealed that all the films were in single phase and had a hexagonal wurtzite structure. The grain size values were calculated and found to be about 24–29 nm. SEM micrographs and AFM images have shown that film morphology and surface roughness were influenced by Ag doping concentration. According to UV-Vis. measurements all the films were highly transparent with average visible transmission values ranging from 80% to 86%. It was found that the Ag contents lead to widening of the band gap. MLS measurements at 632.8 nm wavelength put into evidence that all thin film planar waveguides demonstrate a well-guided fundamental mode for both transverse electric and transverse magnetic polarized light. Moreover, the refractive index of ZnO thin films was found to increase by Ag doping levels.
PubDate: Mon, 13 Jul 2015 11:44:30 +000
- Weakly Bound States of Elementary Excitations in Graphene Superlattice in
Quantizing Magnetic Field
Abstract: The spectrum of allowed energy of electron in graphene superlattice in the quantizing magnetic field is investigated. Such spectrum consists of number of so-called magnetic minibands. The width of these minibands depends on the superlattice barriers power and on the magnetic field intensity. The explicit form of electron spectrum is derived in the case of weak magnetic field. The possibility of electron-electron and electron-phonon bound states is shown. The binding energies of these states are calculated. The binding energy is shown to be the function of magnetic field intensity.
PubDate: Thu, 09 Jul 2015 08:16:00 +000
- Electrical Characterization and Modeling of a Gelatin/Graphene System
Abstract: A gelatin/graphene composite has been analyzed by means of current density-voltage and the electrical impedance measurements. The DC electrical behavior has been interpreted in terms of an equivalent Thévenin model taking into account the open circuit voltage and the series resistance. A model based on the effect of the electrical double layer and on the diffusion of the charge carriers is used for the analysis of the experimental data, obtained in the frequency domain. The model reveals for any applied voltages a marked diffusion process at low frequencies. In particular, where the charge transfer mechanism is dominant, the time distribution of the reaction rates reveals that several multiple step reactions occur in the materials, especially at high values of the applied forward bias voltages.
PubDate: Thu, 09 Jul 2015 07:15:51 +000
- Formation of Nanoporous Tin Oxide Layers on Different Substrates during
Anodic Oxidation in Oxalic Acid Electrolyte
Abstract: Nanoporous tin oxide layers were obtained on various Sn substrates including high- and low-purity foils and wire by one-step anodic oxidation carried out in a 0.3 M oxalic acid electrolyte at various anodizing potentials. In general, amorphous oxide layers with the atomic ratio of Sn : O (1 : 1) were grown during anodization, and a typical structure of the as-obtained film consists of the “outer” layer with less regular, interconnetted pores and the “inner” layer with much more uniform and regular channels formed as a result of vigorous gas evolution. It was found that the use of electrochemical cell with the sample placed horizontally on the metallic support and stabilized by the Teflon cover, instead of the typical two-electrode system with vertically arranged electrodes, can affect the morphology of as-obtained layers and allows fabrication of nanoporous oxides even at anodizing potentials up to 11 V. An average pore diameter in the “outer” oxide layer increases with increasing anodizing potential, and no significant effect of substrate purity on the structure of anodic film was proved, except better uniformity of the oxides grown on high-purity Sn. A strong linear relationship between the average steady-state current density and anodizing potential was also observed.
PubDate: Sun, 05 Jul 2015 08:40:29 +000
- Optical Properties of Sol-Gel Nb2O5 Films with Tunable Porosity for
Abstract: Thin Nb2O5 films with tunable porosity are deposited by the sol-gel and evaporation induced self-assembly methods using organic template Pluronic PE6100 with different molar fractions with respect to NbCl5 used as a precursor for synthesis of Nb sol. Surface morphology and structure of the films are studied by Transmission Electron Microscopy and Selected Area Electron Diffraction. The optical characterization of the films is carried out through reflectance spectra measurements of the films deposited on silicon substrates and theoretical modeling in order to obtain refractive index, extinction coefficient, and thickness of the films. The overall porosity of the films and the amount of adsorbed acetone vapors in the pores are quantified by means of Bruggeman effective medium approximation using already determined optical constants. The sensing properties of the samples are studied by measuring both the reflectance spectra and room-temperature photoluminescence spectra prior to and after exposure to acetone vapors and liquid, respectively. The potential of using the studied mesoporous Nb2O5 films for chemooptical sensing is demonstrated and discussed.
PubDate: Mon, 29 Jun 2015 11:42:59 +000
- Characterization of Precipitation in Al-Li Alloy AA2195 by means of Atom
Probe Tomography and Transmission Electron Microscopy
Abstract: The microstructure of the commercial alloy AA2195 was investigated on the nanoscale after conducting T8 tempering. This particular thermomechanical treatment of the specimen resulted in the formation of platelet-shaped precipitates within the Al matrix. The electrochemically prepared samples were analyzed by scanning transmission electron microscopy and atom probe tomography for chemical mapping. The platelets, which are less than 2 nm thick, have the stoichiometric composition consistent with the expected Al2Cu equilibrium composition. Additionally, the Li distribution inside the platelets was found to equal the same value as in the matrix. The equally thin platelet deviates from the formula (Al2CuLi) in its stoichiometry and shows Mg enrichment inside the platelet without any indication of a higher segregation level at the precipitate/matrix interface. The deviation from the (Al2CuLi) stoichiometry cannot be simply interpreted as a consequence of artifacts when measuring the Cu and Li concentrations inside the platelet. The results show rather a strong hint for a true lower Li and Cu contents, hence supporting reasonably the hypothesis that the real chemical composition for the thin platelet in the T8 tempering condition differs from the equilibrium composition of the thermodynamic stable bulk phase.
PubDate: Mon, 22 Jun 2015 08:41:05 +000
- A Study on the Stoichiometry of One-Dimensional Nanostructures
Abstract: While attributes such as small dimensions, low power consumption, fast sensor response, and a wide range of detection give one-dimensional nanostructures excellent potential to revolutionize sensor and detector industries, challenges to achieving uniform stoichiometry pose significant obstacles to their commercial use. Diverse characteristics arise from nanostructures with variable compositions and morphologies. Thus, investigation of physical properties of nanostructures would be pointless if one cannot assure the exact stoichiometry of the material. We studied the stoichiometry of ZnTe nanowires grown via the vapor-liquid-solid method. Different microscopy and composition analysis methods were exploited to study the stoichiometry of the nanowires. It was observed that nonstoichiometric wires had relatively higher defect concentrations. The temperature profile along the substrate during nanowire growth was found to be the reason for the formation of nanowires with different stoichiometries.
PubDate: Thu, 18 Jun 2015 11:51:42 +000
- The Quantum Well of One-Dimensional Photonic Crystals
Abstract: We have studied the transmissivity of one-dimensional photonic crystals quantum well (QW) with quantum theory approach. By calculation, we find that there are photon bound states in the QW structure , and the numbers of the bound states are equal to . We have found that there are some new features in the QW, which can be used to design optic amplifier, attenuator, and optic filter of multiple channel.
PubDate: Thu, 18 Jun 2015 07:58:49 +000
- An Efficient Compact Finite Difference Method for the Solution of the
Abstract: We present an efficient, unconditionally stable, and accurate numerical method for the solution of the Gross-Pitaevskii equation. We begin with an introduction on the gradient flow with discrete normalization (GFDN) for computing stationary states of a nonconvex minimization problem. Then we present a new numerical method, CFDM-AIF method, which combines compact finite difference method (CFDM) in space and array-representation integration factor (AIF) method in time. The key features of our methods are as follows: (i) the fourth-order accuracy in space and rth () accuracy in time which can be achieved and (ii) the significant reduction of storage and CPU cost because of array-representation technique for efficient handling of exponential matrices. The CFDM-AIF method is implemented to investigate the ground and first excited state solutions of the Gross-Pitaevskii equation in two-dimensional (2D) and three-dimensional (3D) Bose-Einstein condensates (BECs). Numerical results are presented to demonstrate the validity, accuracy, and efficiency of the CFDM-AIF method.
PubDate: Tue, 09 Jun 2015 16:05:58 +000
- Elastic Properties of Liquid Surfaces Coated with Colloidal Particles
Abstract: The physical mechanism of elasticity of liquid surfaces coated with colloidal particles is proposed. It is suggested that particles are separated by water clearings and the capillary interaction between them is negligible. The case is treated when the colloidal layer is deformed normally to its surface. The elasticity arises as an interfacial effect. The effective Young modulus of a surface depends on the interfacial tension, equilibrium contact angle, radius of colloidal particles, and their surface density. For the nanometrically scaled particles the line tension becomes essential and has an influence on the effective Young modulus.
PubDate: Sun, 31 May 2015 13:35:55 +000
- Analytical Model of Subthreshold Drain Current Characteristics of
Ballistic Silicon Nanowire Transistors
Abstract: A physically based subthreshold current model for silicon nanowire transistors working in the ballistic regime is developed. Based on the electric potential distribution obtained from a 2D Poisson equation and by performing some perturbation approximations for subband energy levels, an analytical model for the subthreshold drain current is obtained. The model is further used for predicting the subthreshold slopes and threshold voltages of the transistors. Our results agree well with TCAD simulation with different geometries and under different biasing conditions.
PubDate: Sun, 31 May 2015 11:58:01 +000
- Single Mobile Micro Droplet-Particle Pairs Spatially Captured by Macro
Host Droplets on a Superhydrophobic Surface
Abstract: In this preliminary study, we demonstrate how small single water droplets can be spatially captured on the surface of individual micron sized hydrophobic coated particles (C18) which adhere to the surface of a nonmobile larger host water droplet resting on a superhydrophobic surface. The formation of the larger droplet, particle adhesion to that droplet, and smaller droplet formation on the particle all take place spontaneously from condensation conditions. These micro droplet-particle pairs are confined to the surface (liquid-air interface) of the larger host droplet; however, they are free to engage with external forces to promote mobility. This response may find applications for particle pair transport on liquid surfaces. We also demonstrate that droplets can be captured or removed from the larger droplet surface via a self-propulsion mechanism.
PubDate: Thu, 28 May 2015 14:12:15 +000
- Effects of the Junction Functionality and Chain Entanglements in
Chemomechanical Behavior of Polyelectrolyte Gels
Abstract: By considering the functionality of junctions and entanglements of polymer chains for polyelectrolyte gels, a new free energy density function is presented via combining Edwards-Vilgis slip-link model with Flory-Huggins theory. On this basis, the effects of the functionality of network junctions and entanglements of polymer chains are systematically analyzed for free swelling of a cubic polyelectrolyte gel and constrained swelling of a blanket layer of the gel. Analytical results show that the functionality of junctions and chains entanglements plays an important role in the coupled chemomechanical deformation of polyelectrolyte gels.
PubDate: Tue, 26 May 2015 09:02:59 +000
- Structural and Electronic Properties of GaN (0001)/α-Al2O3 (0001)
Abstract: Structural and electronic properties of the interface between α-Al2O3 (0001) and GaN (0001) surfaces are investigated through ab initio calculations within the density functional theory. Two different structural models have been investigated interface N(Ga)-terminated. The interface N-terminated GaN surface seems to exhibit the lowest formation energy. The studied interface models are metallic, with the levels at energy spatially confined in the interface region. Our calculations show strong hybridization between atoms in the interface region.
PubDate: Wed, 20 May 2015 11:34:49 +000
- Shape-Dependent Energy of an Elliptical Jellium Background
Abstract: The jellium model is commonly used in condensed matter physics to study the properties of a two-dimensional electron gas system. Within this approximation, one assumes that electrons move in the presence of a neutralizing background consisting of uniformly spread positive charge. When properties of bulk systems (of infinite size) are studied, shape of the jellium domain is irrelevant. However, the same cannot be said when one is dealing with finite systems of electrons confined in a finite two-dimensional region of space. In such a case, geometry and shape of the jellium background play a role on the overall properties of the system. In this work, we assume that the region where the electrons are confined is represented by a jellium background charge with an elliptical shape. It is shown that, in this case, the Coulomb self-energy of the elliptically shaped region can be exactly calculated in closed analytical form by using suitable mathematical transformations. The results obtained reveal the external influence of geometry/shape on the properties of two-dimensional systems of few electrons confined to a small finite region of space.
PubDate: Sun, 17 May 2015 11:33:31 +000
- Band Structure Analysis of La0.7Sr0.3MnO3 Perovskite Manganite Using a
Abstract: Oxide semiconductors and their application in next-generation devices have received a great deal of attention due to their various optical, electric, and magnetic properties. For various applications, an understanding of these properties and their mechanisms is also very important. Various characteristics of these oxides originate from the band structure. In this study, we introduce a band structure analysis technique using a soft X-ray energy source to study a (LSMO) oxide semiconductor. The band structure is formed by a valence band, conduction band, band gap, work function, and electron affinity. These can be determined from secondary electron cut-off, valence band spectrum, O 1s core electron, and O K-edge measurements using synchrotron radiation. A detailed analysis of the band structure of the LSMO perovskite manganite oxide semiconductor thin film was established using these techniques.
PubDate: Thu, 14 May 2015 08:34:54 +000
- Influence of Size Effect on the Electronic and Elastic Properties of
Graphane Nanoflakes: Quantum Chemical and Empirical Investigations
Abstract: By application of empirical method it is found that graphene nanoflake (graphane) saturated by hydrogen is not elastic material. In this case, the modulus of the elastic compression of graphane depends on its size, allowing us to identify the linear parameters of graphane with maximum Young’s modulus for this material. The electronic structure of graphane nanoflakes was calculated by means of the semiempirical tight-binding method. It is found that graphane nanoflakes can be characterized as dielectric. The energy gap of these particles decreases with increasing of the length tending to a certain value. At the same time, the ionization potential of graphane also decreases. A comparative analysis of the calculated values with the same parameters of single-walled nanotubes is performed.
PubDate: Mon, 04 May 2015 09:34:36 +000
- Si- and Ge-Based Electronic Devices
PubDate: Mon, 27 Apr 2015 12:44:44 +000