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]
- Rare Earth-Doped BiFeO3 Thin Films: Relationship between Structural and
Abstract: Rare Earth- (RE-) doped BiFeO3 (BFO) thin films were grown on LaAlO3 substrates by using pulsed laser deposition technique. All of BFO films doped with 10% of RE show a single phase of rhombohedral structure. The saturated magnetization in the Ho- and Sm-doped films is much larger than those reported in literature and was observed at a quite low field as of 0.2 T. As for Pr- and Nd-doped BFO films, Fe2+ amount is not dominant; thus, ferromagnetism is not favored. As the RE concentration goes up to 20%, all compounds have drastically gone through a structural transition. The RE-doped BFO films have changed from rhombohedral to either pure orthorhombic phase (for Ho, Sm), or a mixed phase of orthorhombic and tetragonal (for Pr, Nd), or pure tetragonal (for Eu). We observed magnetic properties of RE-doped BFO films have significantly changed. While 20% Ho/Sm-doped BFO films have ferromagnetism degraded in comparison with the 10% doping case, the 20% Pr/Nd-doped BFO thin films, whose structure is a mixed phase, have magnetic ordering improved due to the fact that the Fe2+ amount has become greater. It seems that one can control the magnetic properties of BFO films by using appropriate RE dopants and concentrations.
PubDate: Mon, 31 Aug 2015 11:57:14 +000
- An Infrared Spectroscopy Study of the Conformational Evolution of the
Bis(trifluoromethanesulfonyl)imide Ion in the Liquid and in the Glass
Abstract: We measure the far-infrared spectrum of N,N-Dimethyl-N-ethyl-N-benzylammonium (DEBA) bis(trifluoromethanesulfonyl)imide (TFSI) ionic liquid (IL) in the temperature range between 160 and 307 K. Differential scanning calorimetry measurements indicate that such IL undergoes a glass transition around 210 K. DFT calculations allow us to assign all the experimental absorptions to specific vibrations of the DEBA cation or of the two conformers of the TFSI anion. We find that the vibration frequencies calculated by means of the PBE0 functional are in better agreement with the experimental ones than those calculated at the B3LYP level, largely used for the attribution of vibration lines of ionic liquids. Experimentally we show that, in the liquid state, the relative concentrations of the two conformers of TFSI depend on temperature through the Boltzmann factor and the energy separation, H, is found to be 2 kJ/mol, in agreement with previous calculations and literature. However, in the glassy state, the concentrations of the cis-TFSI and trans-TFSI remain fixed, witnessing the frozen state of this phase.
PubDate: Sun, 30 Aug 2015 12:20:27 +000
- Photoproducts Formation from Salicylic Acid and Poly(allylamine
hydrochloride) in Aqueous Solution Induced by UV-B Radiation
Abstract: We report on the investigation of the influence of UV-B radiation (306 nm) on the salicylic acid mixed with poly(allylamine hydrochloride), PAH, in aqueous solution. UV-Vis spectra versus irradiation time reveal kinetics of photoproducts formation. At pH 9 and 10 are found a growth regime and another of decay of photoproducts formation. In addition, the growth does not depend on temperature, whereas the decay showed a significant dependence on this parameter suggesting a thermally activated process. These processes were well fitted with first-order exponential functions.
PubDate: Wed, 26 Aug 2015 14:21:12 +000
- Self-Organization of Polymeric Fluids in Strong Stress Fields
Abstract: Analysis of literature data and our own experimental observations have led to the conclusion that, at high deformation rates, viscoelastic liquids come to behave as rubbery materials, with strong domination by elastic deformations over flow. This can be regarded as a deformation-induced fluid-to-rubbery transition. This transition is accompanied by elastic instability, which can lead to the formation of regular structures. So, a general explanation for these effects requires the treatment of viscoelastic liquids beyond critical deformation rates as rubbery media. Behaviouristic modeling of their behaviour is based on a new concept, which considers the medium as consisting of discrete elastic elements. Such a type of modeling introduces a set of discrete rotators settled on a lattice with two modes of elastic interaction. The first of these is their transformation from spherical to ellipsoidal shapes and orientation in an external field. The second is elastic collisions between rotators. Computer calculations have demonstrated that this discrete model correctly describes the observed structural effects, eventually resulting in a “chaos-to-order” transformation. These predictions correspond to real-world experimental data obtained under different modes of deformation. We presume that the developed concept can play a central role in understanding strong nonlinear effects in the rheology of viscoelastic liquids.
PubDate: Wed, 26 Aug 2015 09:45:22 +000
- Assessment of Functionals for First-Principle Studies of the Structural
and Electronic Properties of -Bi2O3
Abstract: Fully relativistic full-potential density functional calculations with an all-electron linearized augmented plane waves plus local orbitals method were carried out to perform a comparative study on the structural and electronic properties of the cubic oxide -Bi2O3 phase, which is considered as one of the most promising materials in a variety of applications including fuel cells, sensors, and catalysts. Three different density functionals were used in our calculations, LDA, the GGA scheme in the parametrization of Perdew, Burke, and Ernzerhof (PBE96), and the hybrid scheme of Perdew-Wang B3PW91. The examined properties include lattice parameter, band structure and density of states, and charge density profiles. For this modification the three functionals reveal the characteristics of a metal and the existence of minigaps at high symmetry points of the band structure when spin-orbit coupling is taken into account. Density of states exhibits hybridization of Bi 6s and O 2p orbitals and the calculated charge density profiles exhibit the ionic character in the chemical bonding of this compound. The B3PW91 hybrid functional provided a better agreement with the experimental result for the lattice parameter, revealing the importance of Hartree-Fock exchange in this compound.
PubDate: Tue, 25 Aug 2015 12:43:32 +000
- Particle and Particle-Surfactant Mixtures at Fluid Interfaces: Assembly,
Morphology, and Rheological Description
Abstract: We report here a review of particle-laden interfaces. We discuss the importance of the particle’s wettability, accounted for by the definition of a contact angle, on the attachment of particles to the fluid interface and how the contact angle is strongly affected by several physicochemical parameters. The different mechanisms of interfacial assembly are also addressed, being the adsorption and spreading the most widely used processes leading to the well-known adsorbed and spread layers, respectively. The different steps involved in the adsorption of the particles and the particle-surfactant mixtures from bulk to the interface are also discussed. We also include here the different equations of state provided so far to explain the interfacial behavior of the nanoparticles. Finally, we discuss the mechanical properties of the interfacial particle layers via dilatational and shear rheology. We emphasize along that section the importance of the shear rheology to know the intrinsic morphology of such particulate system and to understand how the flow-field-dependent evolution of the interfacial morphology might eventually affect some properties of materials such as foams and emulsions. We dedicated the last section to explaining the importance of the particulate interfacial systems in the stabilization of foams and emulsions.
PubDate: Thu, 20 Aug 2015 12:44:13 +000
- New Topological Configurations in the Continuous Heisenberg Spin Chain:
Lower Bound for the Energy
Abstract: In order to study the spin configurations of the classical one-dimensional Heisenberg model, we map the normalized unit vector, representing the spin, on a space curve. We show that the total chirality of the configuration is a conserved quantity. If, for example, one end of the space curve is rotated by an angle of 2π relative to the other, the Frenet frame traces out a noncontractible loop in and this defines a new class of topological spin configurations for the Heisenberg model.
PubDate: Wed, 19 Aug 2015 11:30:33 +000
- Characterisation of PMMA/ATH Layers Realised by Means of Atmospheric
Pressure Plasma Powder Deposition
Abstract: We report on the characteristics of aluminium trihydrate filled poly(methyl methacrylate) composite (PMMA/ATH) coatings realised by plasma deposition at atmospheric pressure. For this purpose, PMMA/ATH powder was fed to a plasma jet where the process and carrier gas was compressed air. The deposited coatings were investigated by X-ray photoelectron spectroscopy and water contact angle measurements. Further, the raw material was characterised before deposition. It was found that, with respect to the raw material, aluminium was uncovered in the course of the plasma deposition process which can be explained by plasma-induced etching of the PMMA matrix. As a result, the wettability of plasma-deposited PMMA/ATH was significantly increased. Even though a uniform coating film could not be realised as ascertained by confocal laser scanning microscopy, the deposited coatings feature notably enhanced characteristics which could be advantageous for further processing.
PubDate: Mon, 17 Aug 2015 13:54:49 +000
- Indentation Depth Dependent Mechanical Behavior in Polymers
Abstract: Various experimental studies have revealed size dependent deformation of materials at micro and submicron length scales. Among different experimental methods, nanoindentation testing is arguably the most commonly applied method of studying size effect in various materials where increases in the hardness with decreasing indentation depth are usually related to indentation size effects. Such indentation size effects have been observed in both metals and polymers. While the indentation size effects in metals are widely discussed in the literature and are commonly attributed to geometrically necessary dislocations, for polymer the experimental results are far sparser and there does not seem to be a common ground for their rationales. The indentation size effects of polymers are addressed in this paper, where their depth dependent deformation is reviewed along with the rationale provided in the literature.
PubDate: Mon, 17 Aug 2015 07:28:39 +000
- Strain-Dependence of the Structure and Ferroic Properties of Epitaxial
NiTiO3 Thin Films Grown on Different Substrates
Abstract: Polarization-induced weak ferromagnetism has been predicted a few years back in perovskite MTiO3 (M = Fe, Mn, and Ni). We set out to stabilize this metastable perovskite structure by growing NiTiO3 epitaxially on different substrates and to investigate the dependence of polar and magnetic properties on strain. Epitaxial NiTiO3 films were deposited on Al2O3, Fe2O3, and LiNbO3 substrates by pulsed laser deposition and characterized using several techniques. The effect of substrate choice on lattice strain, film structure, and physical properties was investigated. Our structural data from X-ray diffraction and electron microscopy shows that substrate-induced strain has a marked effect on the structure and crystalline quality of the films. Physical property measurements reveal a dependence of the weak ferromagnetism and lattice polarization on strain and highlight our ability to control the ferroic properties in NiTiO3 thin films by the choice of substrate. Our results are also consistent with the theoretical prediction that the ferromagnetism in acentric NiTiO3 is polarization induced. From the substrates studied here, the perovskite substrate LiNbO3 proved to be the most promising one for strong multiferroism.
PubDate: Thu, 13 Aug 2015 13:29:35 +000
- Computational Investigation of the Electronic and Optical Properties of
Planar Ga-Doped Graphene
Abstract: We simulate the optical and electrical responses in gallium-doped graphene. Using density functional theory with a local density approximation, we simulate the electronic band structure and show the effects of impurity doping (0–3.91%) in graphene on the electron density, refractive index, optical conductivity, and extinction coefficient for each doping percentage. Here, gallium atoms are placed randomly (using a 5-point average) throughout a 128-atom sheet of graphene. These calculations demonstrate the effects of hole doping due to direct atomic substitution, where it is found that a disruption in the electronic structure and electron density for small doping levels is due to impurity scattering of the electrons. However, the system continues to produce metallic or semimetallic behavior with increasing doping levels. These calculations are compared to a purely theoretical 100% Ga sheet for comparison of conductivity. Furthermore, we examine the change in the electronic band structure, where the introduction of gallium electronic bands produces a shift in the electron bands and dissolves the characteristic Dirac cone within graphene, which leads to better electron mobility.
PubDate: Thu, 13 Aug 2015 12:15:14 +000
- High Performance Enhancement-Mode AlGaN/GaN MIS-HEMT with Selective
Abstract: A novel enhancement-mode (E-mode) Metal-Insulator-Semiconductor- (MIS-) HEMT with selective fluorine ion (F−) treatment is proposed and its mechanism is investigated. The HEMT features the Selective F− treatment both in the AlGaN channel region and in the thick passivation layer between the gate and drain (SFCP-MIS-HEMT). First, the F− in the passivation layer not only extends the depletion region and thus enhances the average electric field (-field) between the gate and drain by the assisted depletion effect but also reduces the -field peak at the gate end, leading to a higher breakdown voltage (BV). Second, in the AlGaN channel region, the F− region realizes the E-mode and the region without F− maintains a high drain current (). Third, MIS structure suppresses the gate leakage current, increasing the gate swing voltage and the BV. Compared with a MIS-HEMT with F− treatment in whole channel (FC-MIS-HEMT), SFCP-MIS-HEMT increases the BV by 46% and the saturation drain current () by 28%.
PubDate: Mon, 10 Aug 2015 12:00:31 +000
- Chemical Functionalization Effects on Cubane-Based Chain Electronic
Abstract: We report electronic structure calculations in chemically functionalized linear cubane-based chains. The effects of covalent chemical attachments on chain transport properties are examined with nonorthogonal tight-binding model (NTBM) considering Landauer-Büttiker formalism. The covalent bonding of even a single-type functional group is shown to considerably alter the conductance of the chain. For similar radical doping density, electronic characteristics are found to range from insulator to narrow-gap semiconductor depending on the nature of the covalent bonding. Therefore it has become possible to tune electronic properties of the cubane-based one-dimensional oligomers by the functionalization for nanoelectronic applications.
PubDate: Sun, 09 Aug 2015 12:08:26 +000
- The Intramolecular Pressure and the Extension of the Critical
Point’s Influence Zone on the Order Parameter
Abstract: The critical point affects the coexistence behavior of the vapor-liquid equilibrium densities. The length of the critical influence zone is under debate because for some properties, like shear viscosity, the extension is only a few degrees, while for others, such as the density order parameter, the critical influence zone covers up to hundreds of degrees below the critical temperature. Here we show that, for ethane, the experimental critical influence zone covers a wide zone of tens of degrees (below the critical temperature) down to a transition temperature, at which the apparent critical influence zone vanishes, and the transition temperature can be predicted through a pressure analysis of the coexisting bulk liquid phase, using a simple molecular potential. The liquid phases within the apparent critical influence zone show low densities, making them behave internally like their corresponding vapor phases. Therefore, Molecular Dynamics simulations reveal that the experimentally observed wide extension of the critical influence zone is the result of a vapor-like effect due to low bulk liquid phase densities.
PubDate: Thu, 06 Aug 2015 12:28:11 +000
- Microscale Fragmentation and Small-Angle Scattering from Mass Fractals
Abstract: Using the small-angle scattering method, we calculate here the mono- and polydisperse structure factor from an idealized fragmentation model based on the concept of renormalization. The system consists of a large number of fractal microobjects which are randomly oriented and whose positions are uncorrelated. It is shown that, in the fractal region, the monodisperse form factor is characterized by a generalized power-law decay (i.e., a succession of maxima and minima superimposed on a simple power-law decay) and whose scattering exponent coincides with the fractal dimension of the scatterer. The present analysis of the scattering structure factor allows us to obtain the number of fragments resulted at a given iteration. The results could be used to obtain additional structural information about systems obtained through microscale fragmentation processes.
PubDate: Wed, 05 Aug 2015 17:15:43 +000
- 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