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Journal of Applied Physics

C Flower, M S Freeman, M Plue, B Driehuys
High-volume production of hyperpolarized (129)Xe by spin-exchange optical pumping (SEOP) has historically fallen short of theoretical predictions. Recently, this shortfall was proposed to be caused by the formation of alkali metal clusters during optical pumping. However, this hypothesis has yet to be verified experimentally. Here, we seek to detect the presence of alkali particles using a combination of both transmission (TEM) and scanning (SEM) electron microscopy. From TEM studies, we observe the presence of particles exhibiting sizes ranging from approximately 0...
July 14, 2017: Journal of Applied Physics
V Mikhelashvili, G Ankonina, Y Kauffmann, G Atiya, W D Kaplan, R Padmanabhan, G Eisenstein
This paper describes a metal-insulator-semiconductor (MIS) capacitor with flat capacitance voltage characteristics and a small quadratic voltage capacitance coefficient. The device characteristics resemble a metal-insulator-metal diode except that here the capacitance depends on illumination and exhibits a strong frequency dispersion. The device incorporates Fe nanoparticles (NPs), mixed with SrF2, which are embedded in an insulator stack of SiO2 and HfO2. Positively charged Fe ions induce dipole type traps with an electronic polarization that is enhanced by photogenerated carriers injected from the substrate and/or by inter nanoparticle exchange of carriers...
June 7, 2017: Journal of Applied Physics
C McKeever, F Y Ogrin, M M Aziz
The high frequency dynamic behaviour of concentric permalloy nanorings with vortex domain structures with a thickness of 20 nm, a width in the range of 100 nm-250 nm, and a separation in the range of 10 nm-600 nm is investigated by micromagnetic simulations. The aim is to explore the ferromagnetic resonance of the concentric ring structure as a function of geometric parameters of the system. The dynamic susceptibility spectrum and spatial localization of the ferromagnetic resonance mode are investigated for varying ring widths and separations...
May 28, 2017: Journal of Applied Physics
J Gruber, X W Zhou, R E Jones, S R Lee, G J Tucker
We investigate the formation of extended defects during molecular-dynamics (MD) simulations of GaN and InGaN growth on (0001) and ([Formula: see text]) wurtzite-GaN surfaces. The simulated growths are conducted on an atypically large scale by sequentially injecting nearly a million individual vapor-phase atoms towards a fixed GaN surface; we apply time-and-position-dependent boundary constraints that vary the ensemble treatments of the vapor-phase, the near-surface solid-phase, and the bulk-like regions of the growing layer...
May 21, 2017: Journal of Applied Physics
Zhaojiang Chen, Shiyang Li, Yang Zhang, Wenwu Cao
Bipolar electric field induced degradation in [001]c poled Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-0.29PT) single crystals was investigated at megahertz frequencies. The electromechanical coupling factor kt , dielectric constant εr , dielectric loss D, and piezoelectric constant d33 were measured as a function of amplitude, frequency, and number of cycles of the applied electric field. Our results showed that samples degrade rapidly when the field amplitude is larger than a critical value due to the onset of domain switching...
May 7, 2017: Journal of Applied Physics
Dorian Ziss, Javier Martín-Sánchez, Thomas Lettner, Alma Halilovic, Giovanna Trevisi, Rinaldo Trotta, Armando Rastelli, Julian Stangl
In this paper, strain transfer efficiencies from a single crystalline piezoelectric lead magnesium niobate-lead titanate substrate to a GaAs semiconductor membrane bonded on top are investigated using state-of-the-art x-ray diffraction (XRD) techniques and finite-element-method (FEM) simulations. Two different bonding techniques are studied, namely, gold-thermo-compression and polymer-based SU8 bonding. Our results show a much higher strain-transfer for the "soft" SU8 bonding in comparison to the "hard" bonding via gold-thermo-compression...
April 2017: Journal of Applied Physics
Benoit Gaury, Paul M Haney
Analytic expressions are presented for the dark current-voltage relation J(V ) of a pn(+) junction with positively charged columnar grain boundaries with high defect density. These expressions apply to non-depleted grains with sufficiently high bulk hole mobilities. The accuracy of the formulas is verified by direct comparison to numerical simulations. Numerical simulations further show that the dark J(V ) can be used to determine the open-circuit potential Voc of an illuminated junction for a given short-circuit current density Jsc...
December 21, 2016: Journal of Applied Physics
Jeong Hoon Ryou, Jason J Gorman
An analytical comparison between the fundamental mode and higher modes of vibration for an electrostatic beam resonator is presented. Multiple mode numbers can be matched to a desired resonance 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 motional resistance for each mode. The resulting equation provides the basis for comparing performance between modes using motional resistance and quality factor...
December 7, 2016: Journal of Applied Physics
John F Roller, Yu-Tai Li, Mario Dagenais, Behrang H Hamadani
Charge carrier lifetimes in photovoltaic-grade silicon wafers were measured by a spectral-dependent, quasi-steady-state photoconductance technique. Narrow bandwidth light emitting diodes (LEDs) were used to excite excess charge carriers within the material, and the effective lifetimes of these carriers were measured as a function of wavelength and intensity. The dependence of the effective lifetime on the excitation wavelength was then analyzed within the context of an analytical model relating effective lifetime to the bulk lifetime and surface recombination velocity of the material...
December 2016: Journal of Applied Physics
B P Burton, A K Singh
A first principles phase diagram calculation, that included van der Waals interactions, was performed for the 3D bulk system (1 - X) · MoS2 - (X) · MoTe2. Surprisingly, the predicted phase diagram has at least two ordered phases, at X ≈ 0:46, even though all calculated formation energies are positive; in a ground-state analysis that examined all configurations with 16 or fewer anion sites. The lower-temperature I-phase is predicted to transform to a higher-temperature I'-phase at T ≈ 500 K, and I' disorders at T ≈ 730 K...
October 2016: Journal of Applied Physics
Paul M Haney, Heayoung P Yoon, Benoit Gaury, Nikolai B Zhitenev
Electron beam induced current (EBIC) is a powerful characterization technique which offers the high spatial resolution needed to study polycrystalline solar cells. Current models of EBIC assume that excitations in the p-n junction depletion region result in perfect charge collection efficiency. However we find that in CdTe and Si samples prepared by focused ion beam (FIB) milling, there is a reduced and nonuniform EBIC lineshape for excitations in the depletion region. Motivated by this, we present a model of the EBIC response for excitations in the depletion region which includes the effects of surface recombination from both charge-neutral and charged surfaces...
September 7, 2016: Journal of Applied Physics
N M Bruno, Y J Huang, C L Dennis, J G Li, R D Shull, J H Ross, Y I Chumlyakov, I Karaman
The influence of grain constraint on the magnetic field levels required to complete the isothermal martensitic transformation in magnetic shape memory alloys has been demonstrated for a NiCoMnSn alloy, and the magnetocaloric performance of an optimally heat treated alloy was quantified. Ni45CoxMn45-xSn10 melt spun ribbons with x = 2, 4, 5, and 6 were characterized. The x = 5 sample was determined to exhibit the lowest transformation thermal hysteresis (7 K) and transformation temperature range during transformation from paramagnetic austenite to nonmagnetic martensite, as well as a large latent heat of transformation (45 J kg(-1) K(-1))...
August 2016: Journal of Applied Physics
Angela N Fioretti, Craig P Schwartz, John Vinson, Dennis Nordlund, David Prendergast, Adele C Tamboli, Christopher M Caskey, Filip Tuomisto, Florence Linez, Steven T Christensen, Eric S Toberer, Stephan Lany, Andriy Zakutayev
Semiconductor materials that can be doped both n-type and p-type are desirable for diode-based applications and transistor technology. Copper nitride (Cu3N) is a metastable semiconductor with a solar-relevant bandgap that has been reported to exhibit bipolar doping behavior. However, deeper understanding and better control of the mechanism behind this behavior in Cu3N is currently lacking in the literature. In this work, we use combinatorial growth with a temperature gradient to demonstrate both conduction types of phase-pure, sputter-deposited Cu3N thin films...
May 14, 2016: Journal of Applied Physics
Cedric J Powell, Xavier Llovet, Francesc Salvat
We analyzed calculated cross sections for K-, L-, and M-shell ionization by electron impact to determine the energy ranges over which these cross sections are consistent with the Bethe equation for inner-shell ionization. Our analysis was performed with K-shell ionization cross sections for 26 elements, with L-shell ionization cross sections for seven elements, with L3-subshell ionization cross sections for Xe, and with M-shell ionization cross sections for three elements. The validity or otherwise of the Bethe equation could be checked with Fano plots based on a linearized form of the Bethe equation...
May 14, 2016: Journal of Applied Physics
Lawrence H Friedman, Igor Levin, Robert F Cook
The random buckling patterns of nanoscale dielectric walls are analyzed using a nonlinear multi-scale stochastic method that combines experimental measurements with simulations. The dielectric walls, approximately 200 nm tall and 20 nm wide, consist of compliant, low dielectric constant (low-k) fins capped with stiff, compressively stressed TiN lines that provide the driving force for buckling. The deflections of the buckled lines exhibit sinusoidal pseudoperiodicity with amplitude fluctuation and phase decorrelation arising from stochastic variations in wall geometry, properties, and stress state at length scales shorter than the characteristic deflection wavelength of about 1000 nm...
March 2016: Journal of Applied Physics
Benoit Gaury, Paul M Haney
The determination of minority-carrier lifetimes and surface recombination velocities is essential for the development of semiconductor technologies such as solar cells. The recent development of two-photon time-resolved microscopy allows for better measurements of bulk and subsurface interfaces properties. Here we analyze the diffusion problem related to this optical technique. Our three-dimensional treatment enables us to separate lifetime (recombination) from transport effects (diffusion) in the photoluminescence intensity...
March 2016: Journal of Applied Physics
Zhangyi Huang, Jianqi Qi, Li Zhou, Zhao Feng, Xiaohe Yu, Yichao Gong, Mao Yang, Qiwu Shi, Nian Wei, Tiecheng Lu
We investigate the ionization and displacement effects of an electron-beam (e-beam) on amorphous Gd2Zr2O7 synthesized by the co-precipitation and calcination methods. The as-received amorphous specimens were irradiated under electron beams at different energies (80 keV, 120 keV, and 2 MeV) and then characterized by X-ray diffraction and transmission electron microscopy. A metastable fluorite phase was observed in nanocrystalline Gd2Zr2O7 and is proposed to arise from the relatively lower surface and interface energy compared with the pyrochlore phase...
December 7, 2015: Journal of Applied Physics
Xinghao Hu, Roozbeh Abedini-Nassab, Byeonghwa Lim, Ye Yang, Marci Howdyshell, Ratnasingham Sooryakumar, Benjamin B Yellen, CheolGi Kim
We investigate the non-linear dynamics of superparamagnetic beads moving around the periphery of patterned magnetic disks in the presence of an in-plane rotating magnetic field. Three different dynamical regimes are observed in experiments, including (1) phase-locked motion at low driving frequencies, (2) phase-slipping motion above the first critical frequency fc1, and (3) phase-insulated motion above the second critical frequency fc2. Experiments with Janus particles were used to confirm that the beads move by sliding rather than rolling...
November 28, 2015: Journal of Applied Physics
Fridon Shubitidze, Katsiaryna Kekalo, Robert Stigliano, Ian Baker
[This corrects the article , PMID: 25825545.].
November 7, 2015: Journal of Applied Physics
Rohan Dhavalikar, Lorena Maldonado-Camargo, Nicolas Garraud, Carlos Rinaldi
Magnetic Particle Imaging (MPI) is an emerging imaging technique that uses magnetic nanoparticles as tracers. In order to analyze the quality of nanoparticles developed for MPI, a Magnetic Particle Spectrometer (MPS) is often employed. In this paper, we describe results for predictions of the nanoparticle harmonic spectra obtained in a MPS using three models: the first uses the Langevin function, which does not take into account finite magnetic relaxation; the second model uses the magnetization equation by Shliomis (Sh), which takes into account finite magnetic relaxation using a constant characteristic time scale; and the third model uses the magnetization equation derived by Martsenyuk, Raikher, and Shliomis (MRSh), which takes into account the effect of magnetic field magnitude on the magnetic relaxation time...
November 7, 2015: Journal of Applied Physics
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