Strain effects on thermal transport and anisotropy in thin-films of Si and Ge
We presentthermal conductivity calculations, performed in thin Si andGe strained films, using first principles calculations of vibrational frequencies under biaxial strain, along with a phononBoltzmann transport equation within therelaxation time approximation. We find that, while in-planetransport is not strongly dependent on strain, the cross-plane component of thethermal conductivity tensor shows a clear strain dependence, with up to 20% increase (decrease) at 4% compressive (tensile) strain in both Si andGe. We also uncover that strain emphasizes theanisotropy between in-plane and cross-planethermal conductivity across...
Source: Journal of Applied Physics - December 8, 2016 Category: Physics Authors: Cameron J. Foss and Zlatan Aksamija Source Type: research
Appropriate use of the particle-in-cell method in low temperature plasmas: Application to the simulation of negative ion extraction
TheParticle-In-Cell Monte Carlo Collision(PIC MCC) method has been used by different authors in the last ten years to describe negative ion extraction in the context of neutralbeam injection for fusion. Questionable results on the intensity and profile of the extracted negative ion beamlets have been presented in several recently published papers. Using a standard explicitPIC MCC method, we show that these results are due to a non-compliance with the constraints of the numerical method (grid spacing, number of particles per cell) and to a non-physical generation of the simulatedplasma. We discuss in detail the conditions o...
Source: Journal of Applied Physics - December 7, 2016 Category: Physics Authors: L. Garrigues, G. Fubiani and J. P. Boeuf Source Type: research
Actuation performances of anisotropic gels
We investigated the actuation performances ofanisotropicgels driven by mechanical and chemical stimuli, in terms of bothdeformation processes and stroke –curves, and distinguished between the fast response ofgels beforediffusion starts and the asymptotic response attained at the steady state. We also showed as the range of forces that ananisotropichydrogel can exert when constrained is especially wide; indeed, changing fiber orientation allows us to induce shear as well as transversely isotropic extensions. (Source: Journal of Applied Physics)
Source: Journal of Applied Physics - December 7, 2016 Category: Physics Authors: P. Nardinocchi and L. Teresi Source Type: research
Structural transition and its effect in La, Zr co-substituted mono-domain BiFeO3
A new approach was employed in explaining the weak ferromagnetic behavior of conventionally synthesized Zr4+ modified Bi0.8La0.2FeO3.Rietveld refinement of XRD patterns revealed a polar-to-non-polar R3c → Pnmastructural transition in Zr4+substituted samples. Magnetic properties were discovered to be remarkably enhanced, with extractedcoercivity and remanence as high as 14 kOe and 0.2 emu/g, respectively. More importantly, an answer to the essential question of the magnetic domain state of the samples has been put forward. Our analysis established, nearly without doubt, the presence of grains consisting of a single mag...
Source: Journal of Applied Physics - December 6, 2016 Category: Physics Authors: Hasan M. Usama, Ahmed Sharif, M. A. Zubair, M. A. Gafur and Sheikh Manjura Hoque Source Type: research
First-principles study on native point defects of cubic cuprite Ag2O
Using the first-principles calculations, we have systematically investigated the atomic configurations, electronic structures, formation energies and transition energies of native point defects in cupriteAg2O. Under the conditions of Ag-rich, we find that the oxygenvacancy (VO) and the oxygeninterstitial (Oi) have the lowest formation energies inp-type andn-type conditions, respectively.Silvervacancy (VAg) acts as a shallow acceptor, which has high formation energy inp-type sample. Oxygen anti-site (OAg) is the most stable state and acts as an acceptor-type point defect in the O-rich conditions.Aginterstitial(Agi) is a sha...
Source: Journal of Applied Physics - December 6, 2016 Category: Physics Authors: Yuan Yin, Guangde Chen, Xiangyang Duan, Honggang Ye, Wentao Jin, Youzhang Zhu and Yelong Wu Source Type: research
Unipolar resistive switching characteristics and scaling behaviors in La2Mo2O9 thin films for nonvolatile memory applications
La2Mo2O9 (LMO)thin films have beendeposited on Pt/Ti/SiO2/Si substrates by pulsed laser deposition and theresistive switching (RS) characteristics of the Au/LMO/Ptdevices has been investigated. The Au/LMO/Ptdevices show excellent unipolar RS characteristics with highresistance ratio between highresistance state and lowresistance state (LRS), good endurance, and retention performances. The results of temperature dependence ofresistance andx-ray photoelectron spectroscopy suggest that the observed RS characteristics can be explained by the formation and rupture ofconducting filaments composed of oxygenvacancies. Furthermore,...
Source: Journal of Applied Physics - December 6, 2016 Category: Physics Authors: L. Hu, G. T. Lin, X. Luo, R. H. Wei, X. B. Zhu, W. H. Song, J. M. Dai and Y. P. Sun Source Type: research
Carrier transport mechanism of highly-sensitive niobium doped titanium dioxide/p-Si heterojunction photodiode under illuminations by solar simulated light
Nano-crystallineNbdoped anatase TiO2 (NTO) thin film wasdeposited onp-type Si substrate for fabrication ofn-NTO/p-Siheterojunctionphotodiode using RF magnetronsputtering technique. Rutherford backscattering spectrometry and Raman spectroscopy results suggest the substitutional incorporation ofNb5+ ions in anatase TiO2 lattice, which is evidenced from large stiffening ofEg(1) and softening ofB1g Raman modes. The current density-voltage (J-V) characteristics are measured and important diode parameters ofn-NTO/p-Siheterojunction diode are determined, such as ideality factor, barrier height, and series resistance. Diode exhibi...
Source: Journal of Applied Physics - December 6, 2016 Category: Physics Authors: Subodh K. Gautam, Arkaprava Das, R. G. Singh, V. V. S. Kumar and Fouran Singh Source Type: research
Mode selection for electrostatic beam resonators based on motional resistance and quality factor
An analytical comparison between the fundamental mode and higher modes of vibration for anelectrostaticbeam resonator is presented. Multiple mode numbers can be matched to a desiredresonance frequency through appropriate scaling. Therefore, it is important to determine which mode yields the best performance. A dynamic model of the resonator is derived and then used to determine the motionalresistance for each mode. The resulting equation provides the basis for comparing performance between modes using motionalresistance and quality factor. As a demonstration of the approach, a quality factor model that has been previously ...
Source: Journal of Applied Physics - December 6, 2016 Category: Physics Authors: Jeong Hoon Ryou and Jason J. Gorman Source Type: research
Ramifications of codoping SrI2:Eu with isovalent and aliovalent impurities
Eu2+doped SrI2 is an important scintillator having applications in the field of radiation detection.Codoping techniques are often useful to improve the electronic response of such insulators. Using first-principles based approach, we report on the properties of SrI2:Eu and the influence ofcodoping with aliovalent(Na, Cs) and isovalent (Mg, Ca, Ba, and Sn) impurities. These codopants do not preferably bind with Eu and are expected to remain as isolated impurities in the SrI2 host. As isolated defects they display amphoteric behavior having, in most cases, significant ionization energies of the donor and acceptor levels. Fur...
Source: Journal of Applied Physics - December 6, 2016 Category: Physics Authors: Qingguo Feng and Koushik Biswas Source Type: research
VQS (vapor-quasiliquid-solid, vapor-quasisolid-solid) mechanism lays down general platform for the syntheses of graphene by chemical vapor deposition
Graphene is a relatively new material. The current state-of-the-art of thegraphene synthesis has been reviewed. Existing mechanism for thegraphene synthesis has been examined. The flaws of this mechanism have been described. Attempts have been made to present a new mechanism called the vapor-quasiliquid (quasisolid)-solid mechanism. For this, various physicochemical processes contributing tographene synthesis have been considered. These processes include the substratesurface morphology, substratesurface energy,carbonsolubility in the substratesurface, temperature, and pressure.Surface disturbance andsurface amorphicity of ...
Source: Journal of Applied Physics - December 6, 2016 Category: Physics Authors: S. Noor Mohammad Source Type: research
Effect of Nb and more Fe ions co-doping on the microstructures, magnetic, and piezoelectric properties of Aurivillius Bi5Ti3FeO15 phases
Aurivillius Bi5Ti3 −2xFe1+xNbxO15 (BTFNO, x = 0.1, 0.2, 0.3, and 0.4) phases were prepared by solid state reaction method. The structures and dielectric responses were studied, and especially the effects ofNb with a higher valence and more Fe co-doping on the magnetic andpiezoelectricproperties were addressed in detail. The BTFNO samples were well crystallized with no detectable impurities, and plate-likemicrostructures with various sizes demonstrate the typicalcharacteristics of bismuth-layer Aurivilliusmaterials. It is found that a dielectric loss peak appears in theNb and Fe co-doped Bi5Ti3FeO15 (BTFO)ceramics, and it...
Source: Journal of Applied Physics - December 5, 2016 Category: Physics Authors: Chao Chen, Kun Song, Wei Bai, Jing Yang, Yuanyuan Zhang, Pinghua Xiang, Muyang Qin, Xiaodong Tang and Junhao Chu Source Type: research
Modeling of reduced effective secondary electron emission yield from a velvet surface
Complexstructures on amaterialsurface can significantly reduce totalsecondary electron emission from thatsurface. A velvet is asurface that consists of an array of vertically standingwhiskers. The reduction occurs due to the capture of low-energy, truesecondary electrons emitted at the bottom of thestructure and on the sides of the velvetwhiskers. We performed numerical simulations and developed an approximate analytical model that calculates the netsecondary electron emission yield from a velvetsurface as a function of the velvetwhisker length and packing density, and the angle of incidence of primaryelectrons. We found t...
Source: Journal of Applied Physics - December 5, 2016 Category: Physics Authors: Charles Swanson and Igor D. Kaganovich Source Type: research
Controlling energy transfer time between two coupled magnetic vortex-state disks
The influence of the in-plane uniaxialanisotropy (IPUA) in the mutualenergy transfer time (τ) between two identical coupled nanodisks was studied. Using an analytical dipolar model, we obtained the interactions between the disks along x and y directions (the coupling integrals) as a function of the uniaxialanisotropy constant (K σ) and the distance. We find that the IPUA increases the interaction between the disks allowing shorterenergy transfer times. For our range of K σ values, we get a drop in the values ofτ of up to about 70%. From theLagrangian of the system, we obtained theequations of motion and the couplin...
Source: Journal of Applied Physics - December 5, 2016 Category: Physics Authors: H. Vigo-Cotrina and A. P. Guimar ães Source Type: research
Theoretical analysis of 1D resonant tunneling behavior in ion-enhanced cold field and thermo-field emission
In cold field and thermo-field emission, positive ions oradsorbates very close to thecathode surface can enhance emission current by bothresonant and non-resonant processes. In this paper,resonant tunneling behavior is investigated by solving the one-dimensional Schr ödinger equation in the presence of an ion, and the enhancement due toresonant processes is evaluated. Results shows that as the appliedelectric field increases, theresonant states move from higher to lower energies as the ion energy levels are shifted down. Conversely, as the ion position moves closer to thecathode, theresonant states shift up in energy. Fur...
Source: Journal of Applied Physics - December 5, 2016 Category: Physics Authors: Xi Tan, Paul Rumbach, Nathaniel Griggs, Kevin L. Jensen and David B. Go Source Type: research
Instability of phosphorous doped SiO2 in 4H-SiC MOS capacitors at high temperatures
In this paper, the effect of inclusion of phosphorous (at a concentration below 1%) on thehigh temperaturecharacteristics (up to 300 °C) of the SiO2/SiC interface is investigated. Capacitance –voltagemeasurements taken for a range of frequencies have been utilized to extract parameters including flatband voltage, threshold voltage, effective oxide charge, and interface state density. The variation of these parameters withtemperature has been investigated for bias sweeps in opposing directions and a comparison made between phosphorousdoped and as-grown oxides. At roomtemperature, the effective oxide charge for SiO2 ma...
Source: Journal of Applied Physics - December 5, 2016 Category: Physics Authors: M. I. Idris, M. H. Weng, H.-K. Chan, A. E. Murphy, D. T. Clark, R. A. R. Young, E. P. Ramsay, N. G. Wright and A. B. Horsfall Source Type: research
