bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theoretical studies of single magnetic impurities on the surface of semiconductors and topological insulators
Authors: Mahani M. R. , Pertsova A. , Canali C.M. , Islam M. F. , MacDonald A.H. 
Published: June 2019

ABSTRACTWe present results of theoretical studies of transition metal dopants in GaAs, based on microscopic tight-binding model and ab-initio calculations. We focus in particular on how the vicinity of surface affects the properties of the hole-acceptor state, its magnetic anisotropy and its magnetic coupling to the magnetic dopant. In agreement with STM experiments, Mn substitutional dopants on the (110) GaAs surface give rise to a deep acceptor state, whose wavefunction is localized around the Mn center. We discuss a refinement of the theory that introduces explicitly the d-levels for the TM dopant. The explicit inclusion of d-levels is particularly important for addressing recent STM experiments on substitutional Fe in GaAs. In the second part of the paper we discuss an analogous investigation of single dopants in Bi2Se3 three-dimensional topological insulators, focusing in particular on how substitutional impurities positioned on the surface affect the electronic structure in the gap. We present explicit results for BiSe antisite defects and compare with STM experiments.
Magnetic Domain Structure of Nanocrystalline Zr18-xHfxCo82 Ribbons: Effect of Hf
Authors: Yue Lanping , Al-Omari I. A. , Zhang Wenyong , Skomski Ralph , Sellmyer D. J. 
Published: June 2019

ABSTRACTThe effect of Hf on the permanent magnetism of nanocrystalline Zr18-xHfxCo82 ribbons (x = 0, 2, 4, and 6) was investigated by magnetic properties measurement and magnetic force microscopy (MFM). Emphasis is on the local magnetic domain structures in polycrystalline rapidly solidified Zr18-xHfxCo82 ribbons for four different samples with small fractions of Hf dopants (x ≤ 6). The investigation of the magnetic properties of the Zr18-xHfxCo82 ribbons revealed that all the samples under investigation are ferromagnetic at room temperature, and the corresponding MFM images show bright and dark contrast patterns with up-down magnetic domain structures. It is found that the saturation magnetization and the coercivity depend on Hf doping concentration x in the samples. For a sample with Hf concentration x = 4, the maximum energy product (BH)max value is 3.7 MGOe. The short magnetic correlation length of 131 nm and smallest root-mean-square phase shift value of 0.680 were observed for x = 4, which suggests the refinement of the magnetic domain structure due to weak intergranular exchange coupling in this sample. The above results indicate that suitable Hf addition is helpful for the magnetic domain structure refinement, the coecivity enhancement, and the energy-product improvement of this class of rare-earth-free nanocrystalline permanent-magnet materials.
Nanostructured ZnO–X Alloys with Tailored Optoelectronic Properties for Solar-energy Technologies
Authors: Dou Maofeng , Persson Clas 
Published: June 2019

ABSTRACTAlloying ZnO with isovalent compounds allows tailoring the material’s optoelectronic properties. In this work, we theoretically analyze the ZnO-based alloys ZnO–X ≡ (ZnO)1−x(X)x where X = GaN and InN, employing a first-principles Green’s function method GW0 based on the density functional approach. Since the alloy compounds are isovalent to ZnO, we find relatively small distortion of the crystalline structure, however, nanocluster structures are expected to be present in the alloy. ZnO–X reveal intriguing optoelectronic properties. Incorporating GaN or InN in ZnO strongly narrows the energy gap. The band gap energy is reduced from Eg = 3.34 eV in intrinsic ZnO to ∼2.17 and ∼1.89 eV in ZnO–X by alloying ZnO with 25% GaN and InN, respectively. Moreover, clustering enhances the impact on the electronic structure, and the gap energy in ZnO–InN is further reduced to 0.7–1.5 eV if the 25% compound contains nanoclusters. The dielectric function ε2(ω) varies weakly in ZnO–GaN with respect to alloy composition, while it varies rather strongly in ZnO–InN. Hence, by properly growing and designing ZnO–X, the alloy can be optimized for a variety of novel integrated optoelectronic nano-systems.
GaAs Pixel Detectors
Authors: Tyazhev A. , Budnitsky D. , Mokeev D. , Novikov V. , Zarubin A. , Tolbanov O. , Shelkov G. , Hamann E. , Fauler A , Fiederle M. , Procz S. 
Published: June 2019

ABSTRACTResults of investigation of X-ray sensors on the basis of GaAs compensated with chromium (HR GaAs) are presented in this work. HR GaAs material is shown to have the following physical parameters: the resistivity about 1GOhm*cm, the nonequilibrium charge carrier lifetime – hundreds of nanoseconds. Prototypes of microstrip and array HR GaAs sensors have been manufactured and tested. It is demonstrated that the sensors provide spatial resolution according to the pixel pitch and allow obtaining high quality X-ray images.
New Flexible High Gamma Dose Dosimeter Based on Luminescent and Biodegradable Polymer Blend
Authors: Schimitberger T. , Franco M.R. , Lopes F.A. , Curti P.S. , Bianchi R.F. , Faria L.O. 
Published: June 2019

ABSTRACTIn this work we investigate the radio-degradation of MEH-PPV polymer film as a tool for measuring high doses of gamma radiation. In order to produce film samples with thickness in the micron range, we have mixed the photoluminescent poly(2-methoxy-5(2'-ethylhexyloxy)-p-phenylenevinylene) copolymer (MEH-PPV) with a biodegradable poly(butylene adipate-co-terephthalate) copolymers (PBAT). The system was irradiated with a Co-60 source with doses ranging from 1 to 1,000 kGy. Ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectroscopy have been used to investigate the radiation induced changes in the absorption and photon-emission spectra of the irradiated samples. Results indicate that the PL emission intensity varies exponentially with the applied gamma radiation dose for doses ranging from 30 to 500 kGy. The unambiguous relationship betweenPL & Dosetogether with the good flexibility of the copolymer films indicate that MEH-PPV/PBAT blends have great potential for applications in high gamma dose dosimetry.
HR XRD and Emission of InxGa1-xAs/GaAs quantum wells with embedded InAs quantum dots at the variation of InxGa1-xAs composition
Authors: Vega Macotela Leonardo G. , Tamayo Ricardo Cisneros , Polupan Georgiy 
Published: June 2019

ABSTRACTThe high resolution X ray diffraction (HR-XRD) diagrams have been studied in the GaAs /InxGa1-xAs /In0.15Ga0.85As/GaAs quantum wells with embedded InAs quantum dots (QDs) in dependence on the composition of the capping InxGa1-xAs layers. The parameter x in capping InxGa1-xAs layers varied from the range 0.10-0.25. These technological changes have been accompanied by the variation non-monotonously of InAs QD emission. Numerical simulation of HR-XRD results has shown that the level of elastic strains and the composition of quantum layers vary none monotonously in studied QD structures. Simultaneously it was revealed that the process of Ga/In inter diffusion at the InxGa1-xAs/InAs QD interface are characterized by the dependence non monotonous versus parameter x in capping InxGa1-xAs layers. The physical reasons of the mentioned optical and structural effects in studied structures have been discussed.
Size dependent optical properties in ZnO nanosheets
Authors: El Filali Brahim , Díaz Cano Aaron I. 
Published: June 2019

ABSTRACTPhotoluminescence (PL), scanning electronic microscopy (SEM) and Raman scattering have been studied in crystalline ZnO nanosheets with different sizes after the thermal annealing at 400 °C for 2 hours in ambient air. ZnO nanosheets were created by the electrochemical (anodization) method using the variation of the etching durations with obtained ZnO nanosheet sizes from the range 40-360 nm. Earlier it was shown using the X ray diffraction (XRD) method that thermal annealing performed the ZnO oxidation and crystallization with the creation of the wurtzite crystal lattice. Four PL bands are revealed in PL spectra with the PL peaks at 1.60, 2.08, 2.50 and 3.10 eV. Size decreasing of ZnO nanosheets stimulates tremendous changes of ZnO optical parameters. It is shown that decreasing the ZnO nanosheet sizes is accompanied by the intensity increase of a set of Raman peaks and the surface defect related PL bands. The reasons of emission transformation and the nature of optical transitions have been discussed as well.
Photoluminescence Study of ZnO Nanosheets with embedded Cu Nanocrystals.
Authors: Diaz Cano Aaron I. , El Filali Brahim 
Published: June 2019

ABSTRACTIn this work a simple method to produce the ZnO nanosheets (NSs) with inclusions of Cu nanocrystals by means of electrochemical etching without the necessity of any surfactant has been presented. The Raman spectroscopy demonstrates that the amorphous samples of ZnO-Cu present appreciable changes in its vibrational behavior after the thermal treatment at 400°C in ambient atmosphere. The study of Photoluminescence (PL) shows monotonous increasing the bands centered in 3.07, 2.41, 2.03 and 1.57 eV versus etching time in freshly prepared samples. The intensity variation of the PL bands, the changes in vibrational behavior, as well as the impact of the copper content and preparation conditions allow identifying emission inside the visible spectral range related to the surface defects that is interesting for the future possible application this ZnO system in room temperature “white” light-emitting diodes.
Colloidal indium sulfide quantum dots in water: synthesis and optical properties
Authors: Ivanchenko Mariia V. , Rayevska Oleksandra E. , Stroyuk Oleksandr L. , Kuchmiy Stepan Ya. 
Published: June 2019

ABSTRACTColloidal β-In2S3 quantum dots stabilized in water by a number of polymers or sodium polyphosphate and mercaptoacetate were synthesized. An increase in the stabilizer content was found to result in a decrease in the average dot size from 20–30 to 5–10 nm and formation of a narrow absorption band centered at 290 nm. The position and spectral width of the band were found to be independent on stabilizer concentration, synthesis temperature and molar In:S ratio. The band was assumed to belong to a molecular cluster smaller than 1 nm which is a precursor for formation of larger regular indium sulfide quantum dots.
Photoluminescence and Structural Properties of CdSe Quantum Dot-Polymer Composite Films
Authors: Borkovska L. , Korsunska N. , Stara T. , Bondarenko V. , Gudymenko O. , Stroyuk O. , Raevska O. , Kryshtab T. 
Published: June 2019

ABSTRACTThermal stability of the luminescent properties of CdSe and CdSe/ZnS quantum dots (QDs) in polymer films of gelatin and polyvinyl alcohol (PVA) is studied. Thermal annealing of the films at the air ambience at 100 °C is found to result in two effects in the photoluminescence (PL) spectra: (i) an enhancement of the PL intensity and (ii) a red spectral shift of the PL bands. The first effect is observed in both QDs-gelatin and QDs-PVA composites, while the second one - in the QDs-gelatin only. The passivation of CdSe QDs with ZnS shell reduces the effects. The enhancement of the PL intensity is supposed to be due to the decrease of nonradiative defect density. The red shift is explained by dissociation of coordination bonds between surface Cd atoms and amino-groups of gelatin. This dissociation decreases the PL intensity too. This effect competes with the effect of PL enhancement and is supposed to be responsible for non-monotonous dependence of the PL intensity versus annealing time in the QDs-gelatin composite.
Spatial resonances of the Cherenkov emission in dispersive metamaterials
Authors: Burlak Gennadiy , Martinez-Sanchez Erika 
Published: June 2019

ABSTRACTWe systematically study the Cherenkov optical emission by a nonrelativistic modulated source crossing 3D dispersive metamaterial. It is found that the interference of the field produced by the modulated source with the periodic plasmonic-polariton excitations leads to the specific interaction in the frequency range where the dispersive refractive index of a metamaterial is negative. Such resonance considerably modifies the spatial structure of the Cherenkov fieldand the reversed Cherenkov emission. In our study parameters of metamaterial and modulated source are fixed while the frequency spectrum of the plasmonic excitations is formed due to the fields interplay in the frequency domain.
Plasmon-polariton signature in the transmission and reflection spectra of one-dimensional metamaterial heterostructures
Authors: Reyes-Gómez E. , Cavalcanti S. B. , Oliveira L. E. 
Published: June 2019

ABSTRACTThe transmission and reflection properties of a meta-stack composed of a periodic AB arrangement of an air(A)/metamaterial(B) bilayer is presented, with the multi layered system embedded between two semi-infinite layers of the A material. For oblique incidence, a finite projection along the growth direction of the electric or magnetic field of the incident wave associated with the TM or TE modes, respectively, leads to a coupling of the photon modes with the bulk electric or magnetic metamaterial plasmons, in each layer of the meta-stack. This field-matter coupling gives rise to plasmon-polariton modes and signatures of electric or magnetic longitudinal bulk-plasmon polariton modes in the transmission, as well as in the reflection properties of the meta-stack, by means of a plasmon-polariton gap. Such features survive even in the case of a single bilayer and experimental observation should be, therefore, easily achieved.
Polarization Control of Optically Pumped Terahertz Lasers
Authors: Slavcheva Gabriela , Kavokin Alexey V. 
Published: June 2019

ABSTRACTTwo-photon pumping of excited exciton states in semiconductor quantum wells is a tool for realization of ultra-compact terahertz (THz) lasers based on stimulated optical transition between excited 2p and ground 1s exciton state. We show that the probability of two-photon absorption by a 2p-exciton is strongly dependent on the polarization of both photons. Variation of the threshold power for THz lasing by a factor of 5 is predicted by switching from linear to circular pumping. We calculate the polarization dependence of the THz emission and identify photon polarization configurations for achieving maximum THz photon generation quantum efficiency.
Glass-Oxide Nanocomposites as Effective Thermal Insulation Materials
Authors: Hao Qing , Li Minqing , Coleman Garrett Joseph , Li Qiang , Lucas Pierre 
Published: June 2019

ABSTRACTWith extremely disordered atomic structures, a glass possesses a thermal conductivitykthat approaches the theoretical minimum of its composition, known as the Einstein’s limit.1Depending on the material composition and the extent of disorder, the thermal conductivity of some glasses can be down to 0.1-0.3 W/m∙K at room temperature,2,3representing some of the lowestkvalues among existing solids. Such a lowkcan be further reduced by the interfacial phonon scattering within a nanocomposite that can be used for thermal insulation applications. In this work, nanocomposites hot pressed from the mixture of glass nanopowder (GeSe4or Ge20Te70Se10) and commercial SiO2nanoparticles, or pure glass nanopowder, are investigated for the potentialkreduction. It is found that adding SiO2nanoparticles will instead increasekif the measuredkvalues for usually porous nanocomposites are converted into those for the corresponding solid (kSolid) with Eucken’s formula. In contrast, pure glass nano-samples always showkSoliddata significantly reduced from that for the starting glass. For a pure GeSe4nano-sample,kSolidwould beat the Einstein’s limit for its composition.
Optically Active Nanoparticle Coated Polystyrene Spheres
Authors: Kinkead Brandy , Ali Abdiwali A. , Boyer John-C. , Gates Byron D. 
Published: June 2019

ABSTRACTNanoparticles (NPs) with either plasmonic or upconverting properties have been selectively coated onto the surfaces of polystyrene (PS) spheres, imparting their optical properties to the PS colloids. These NP coated PS spheres have many potential applications, such as in medicine as drug-delivery systems or diagnostic tools. To prepare the NP coated PS spheres, gold or core-shell NaYF4Tm0.5Yb30/NaYF4NPs were synthesized and separately combined with amino-functionalized PS spheres. The mechanism by which the NPs adhered to the PS spheres is attributed to interactions of the NP and a polyvinylpyrrolidone additive with the surfaces of the PS spheres. Two-photon fluorescence microscopy and SERS analysis demonstrate the potential applications of these NP coated PS spheres.
Size Controlled Synthesis of Silicon Nanocrystals within Inverse Micelles
Authors: Linehan Keith , Doyle Hugh 
Published: June 2019

ABSTRACTAlkyl-terminated Si nanocrystals (NCs) are synthesized at room temperature by hydride reduction of SiCl4 within inverse micelles. Highly monodisperse Si NCs (2 – 6 nm) are produced by variation of the cationic quaternary ammonium salts used to form the inverse micelles. Transmission electron microscopy imaging confirms the NCs are highly crystalline, while FTIR spectra confirm that the NCs are passivated by covalent attachment of alkanes, with minimal surface oxidation. The photoluminescence intensity of the Si NCs exhibits an inverse relationship with the mean NC diameter, with a quantum yield of 12 % recorded for 2 nm NCs.
Colloidal Synthesis of Luminescent Quantum Dots in Macadamia Oil
Authors: Li Menglu , Chan Weng Leong , Gardner Hannah C. 
Published: June 2019

ABSTRACTSemiconductor nanocrystals or quantum dots are becoming increasingly popular in research fields as wide ranging as cancer therapies, solar energy and disease detection. Colloidal synthesis provides a low-cost method of producing high quality quantum dots with narrow size distributions. The controllable nature of colloidal synthesis allows researchers to design the size, shape and surface functionalization of the resulting particles.Here we investigate a simple low temperature method to produce CdSe quantum dots. The quantum dots were grown in solution by dissolving the CdO precursor in a mixture of macadamia oil, and oleic acid. Elemental Se was heated separately before the two mixtures were combined under an inert atmosphere. The injection temperature, reaction temperature and oleic acid concentration were all varied.Optical absorption and photoluminescence spectroscopies showed the size of the quantum dots increased with time, temperature and oleic acid concentration. Dynamic light scattering has shown the hydrodynamic particle size to range from 7 to 22nm and the samples for up to 6 months.
Degradation of Transparent Conductive Oxides, and the Beneficial Role of Interfacial Layers
Authors: Lemire Heather M. , Peterson Kelly A. , Breslau Mona S. , Singer Kenneth D. , Martin Ina T. , French Roger H. 
Published: June 2019

ABSTRACTThe lifetime performance and reliability of photovoltaic (PV) modules are critical factors in their successful deployment. Interfaces in thin film PV, such as that between the transparent conductive oxide (TCO) electrode and the absorber layer, are frequently an avenue for degradation; this degradation is promoted by exposure to environmental stressors such as irradiance, heat and humidity. Understanding and suppressing TCO degradation is critical to improving stability and extending the lifetime. Commercially available indium tin oxide (ITO), fluorine doped tin oxide (FTO) and aluminum doped zinc oxide (AZO) were exposed to damp heat (DH), ASTM G154 cycle 4, and modified ASTM G154 for up to 1000 hours. The TCOs’ electrical and optical properties and surface energies were determined before and after each exposure and their relative degradation classified. Data demonstrate that AZO degraded most rapidly of all the TCOs, whereas ITO and FTO degraded at lower to non-quantifiable rates. One approach to suppress degradation could be to use interfacial layers (IFLs), including organofunctional silane layers, to modify the TCO. We modified the TCO surfaces using a variety of organofunctional silanes, and determined a range of surface energies could be obtained without affecting the electrical and optical properties of the TCO. Degradation studies of TCOs with a silane layer were also conducted. We found that an inhomogeneous silane layer was able to delay the resistivity increase for ITO in DH.
Effects of Vapor Grown Carbon Fiber Substitution for Conductive Carbon in Anode Systems for LiB Applications
Authors: Kambe Yu , Fernandes Alberto J. , Archer Lynden A. 
Published: June 2019

ABSTRACTIsotropic and anisotropic conductive carbon particles, carbon black (CB) and vapor grown carbon fiber (VGCF), were incorporated into a Lithium Titanate (LTO) battery anode material composition, and their effect on conductivity and electrochemical properties investigated. Nanocomposite electrodes comprised of LTO, polyvinyldine floride (PVDF) and as little as 5 wt% VGCF are reported to manifest more than one order of magnitude enhancement in conductivity over their CB counterparts. VGCF-based anodes are also found to exhibit more stable voltage discharge profiles and as much as 20% improvement in capacity retention during extended electrochemical cycling at charge/discharge rates as high as 2.625 A/g (15 C). Remarkably, we find that the benefits of VGCF relative to CB conductivity aids diminish at higher particle loadings and that a LTO anode formulation containing 5 wt% CB | 5 wt% VGCF yields optimal capacity retention. At 5C, this composite system outperformed both the 10 wt% VGCF and 10 wt% CB electrode systems by delivering 20% higher capacity during extended charge/discharge cycling. We explain this finding in terms of two synergetic effects: enhanced electrode conductivity facilitated by incorporation of a percolated network of anisotropic VGCF particles; and shorter transport distances between the insulative LTO and high surface area CB.