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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
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
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
Waylin J Wing, Seyed M Sadeghi, Rithvik R Gutha, Quinn Campbell, Chuanbin Mao
We investigate the shape and size effects of gold metallic nanoparticles on the enhancement of exciton-plasmon coupling and emission of semiconductor quantum dots induced via the simultaneous impact of metal-oxide and plasmonic effects. This enhancement occurs when metallic nanoparticle arrays are separated from the quantum dots by a layered thin film consisting of a high index dielectric material (silicon) and aluminum oxide. Our results show that adding the aluminum oxide layer can increase the degree of polarization of quantum dot emission induced by metallic nanorods by nearly two times, when these nanorods have large aspect ratios...
September 28, 2015: Journal of Applied Physics
Yohei Shiokawa, JinWon Jung, Takahiko Otsuka, Masashi Sahashi
Nano-contact magnetoresistance (NCMR) spin-valves (SVs) using an AlO x nano-oxide-layer (NOL) have numerous nanocontacts in the thin AlOx oxide layer. The NCMR theoretically depends on the bulk scattering spin asymmetry ([Formula: see text]) of the ferromagnetic material in the nanocontacts. To determine the relationship between NCMR and [Formula: see text], we investigated the dependence of NCMR on the composition of the ferromagnetic material Co1-xFex. The samples were annealed at 270 °C and 380 °C to enhance the MR ratio...
August 7, 2015: Journal of Applied Physics
Jesus Cantu-Valle, Israel Betancourt, John E Sanchez, Francisco Ruiz-Zepeda, Mazin M Maqableh, Fernando Mendoza-Santoyo, Bethanie J H Stadler, Arturo Ponce
Using off-axis electron holography under Lorentz microscopy conditions to experimentally determine the magnetization distribution in individual cobalt (Co) nanowires, and scanning precession-electron diffraction to obtain their crystalline orientation phase map, allowed us to directly visualize with high accuracy the effect of crystallographic texture on the magnetization of nanowires. The influence of grain boundaries and disorientations on the magnetic structure is correlated on the basis of micromagnetic analysis in order to establish the detailed relationship between magnetic and crystalline structure...
July 14, 2015: Journal of Applied Physics
Daniel B Reeves, John B Weaver
Magnetic nanoparticles are promising tools for a host of therapeutic and diagnostic medical applications. The dynamics of rotating magnetic nanoparticles in applied magnetic fields depend strongly on the type and strength of the field applied. There are two possible rotation mechanisms and the decision for the dominant mechanism is often made by comparing the equilibrium relaxation times. This is a problem when particles are driven with high-amplitude fields because they are not necessarily at equilibrium at all...
June 21, 2015: Journal of Applied Physics
Yang Shen, Zhibin Pei, Yongqiang Pang, Jiafu Wang, Anxue Zhang, Shaobo Qu
This paper presents a three-dimensional microwave metamaterial absorber based on the stand-up resistive film patch array. The absorber has wideband absorption, lightweight, and polarization-independent properties. Our design comes from the array of unidirectional stand-up resistive film patches backed by a metallic plane, which can excite multiple standing wave modes. By rolling the resistive film patches as a square enclosure, we obtain the polarization-independent property. Due to the multiple standing wave modes, the most incident energy is dissipated by the resistive film patches, and thus, the ultra-wideband absorption can be achieved by overlapping all the absorption modes at different frequencies...
June 14, 2015: Journal of Applied Physics
Maki Tokii, Eiji Kita, Chiharu Mitsumata, Kanta Ono, Hideto Yanagihara, Makoto Matsumoto
Visualization of the magnetic domain structure is indispensable to the investigation of magnetization processes and the coercivity mechanism. It is necessary to develop a reconstruction method from the reciprocal-space image to the real-space image. For this purpose, it is necessary to solve the problem of missing phase information in the reciprocal-space image. We propose the method of extend Fourier image with mean-value padding to compensate for the phase information. We visualized the magnetic domain structure using the Reverse Monte Carlo method with simulated annealing to accelerate the calculation...
May 7, 2015: Journal of Applied Physics
Y L Xie, L Lin, Z B Yan, J-M Liu
In this work, we explore the spin ice model under uniaxial pressure using the Monte Carlo simulation method. For the known spin ices, the interaction correction (δ) introduced by the uniaxial pressure varies in quite a wide range from positive to negative. When δ is positive, the ground state characterized by the ferromagnetic spin chains is quite unstable, and in real materials it serves as intermediate state connecting the ice state and the long range ordered dipolar spin ice ground state. In the case of negative δ, the system relaxes from highly degenerate ice state to ordered ferromagnetic state via a first order phase transition...
May 7, 2015: Journal of Applied Physics
Sunghan Kim, Yan Zhou, Jeffrey D Cirillo, Andreas A Polycarpou, Hong Liang
Bacteria introduce diseases and infections to humans by their adherence to biomaterials, such as implants and surgical tools. Cell desorption is an effective step to reduce such damage. Here, we report mechanisms of bacteria desorption. An alumina nanopore structure (ANS) with pore size of 35 nm, 55 nm, 70 nm, and 80 nm was used as substrate to grow Escherichia coli (E. coli) cells. A bacteria repelling experimental method was developed to quantitatively evaluate the area percentage of adherent bacterial cells that represent the nature of cell adhesion as well as desorption...
April 21, 2015: Journal of Applied Physics
N S Susan Mousavi, Sachin D Khapli, Sunil Kumar
Evolution of microstructures in magnetite-based ferrofluids with weak dipolar moments (particle size ≤ 10 nm) is studied with an emphasis on examining the effects of particle concentration (ϕ) and magnetic field strength (H) on the structures. Nanoparticles are dispersed in water at three different concentrations, ϕ = 0.15%, 0.48%, and 0.59% (w/v) [g/ml%] and exposed to uniform magnetic fields in the range of H = 0.05-0.42 T. Cryogenic transmission electron microscopy is employed to provide in-situ observations of the field-induced assemblies in such systems...
March 14, 2015: Journal of Applied Physics
Fridon Shubitidze, Katsiaryna Kekalo, Robert Stigliano, Ian Baker
Magnetic nanoparticles (MNPs), referred to as the Dartmouth MNPs, which exhibit high specific absorption rate at low applied field strength have been developed for hyperthermia therapy applications. The MNPs consist of small (2-5 nm) single crystals of gamma-Fe2O3 with saccharide chains implanted in their crystalline structure, forming 20-40 nm flower-like aggregates with a hydrodynamic diameter of 110-120 nm. The MNPs form stable (>12 months) colloidal solutions in water and exhibit no hysteresis under an applied quasistatic magnetic field, and produce a significant amount of heat at field strengths as low as 100 Oe at 99-164 kHz...
March 7, 2015: Journal of Applied Physics
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