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Search Results: 1 - 10 of 434250 matches for " S. H. Phark "
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Initial stages of nickel oxide growth on Ag(001) by pulsed laser deposition
S. H. Phark,Y. J. Chang,T. W. Noh,J. -S. Kim
Physics , 2009, DOI: 10.1103/PhysRevB.80.035426
Abstract: Submonolayers of nickel oxide films were grown on an Ag(001) by pulsed laser deposition, and characterized in-situ by both scanning tunneling microscopy and X-ray photoelectron spectroscopy. We observed quasi-two-dimensional growth of the film, and clearly identified several kinds of defects, such as embedded metallic Ni clusters and, notably, oxygen atoms, even while looking deeply into the substrate. These originated from Ni and O hyperthermal projectiles as well as from NiO clusters that were formed during laser ablation of a NiO target. Those defects played a role of nucleation sites in extending the nucleation stage of thin film growth.
Fundamental thickness limit of itinerant ferromagnetic SrRuO$_3$ thin films
Young Jun Chang,Choong H. Kim,S. -H. Phark,Y. S. Kim,J. Yu,T. W. Noh
Physics , 2009, DOI: 10.1103/PhysRevLett.103.057201
Abstract: We report on a fundamental thickness limit of the itinerant ferromagnetic oxide SrRuO$_3$ that might arise from the orbital-selective quantum confinement effects. Experimentally, SrRuO$_3$ films remain metallic even for a thickness of 2 unit cells (uc), but the Curie temperature, T$_C$, starts to decrease at 4 uc and becomes zero at 2 uc. Using the Stoner model, we attributed the T$_C$ decrease to a decrease in the density of states (N$_o$). Namely, in the thin film geometry, the hybridized Ru-d$_yz,zx$ orbitals are terminated by top and bottom interfaces, resulting in quantum confinement and reduction of N$_o$.
Reduction of charge fluctuation energies in ultrathin NiO films on Ag(001)
Seolun Yang,H. -K. Park,J. -S. Kim,H. -N. Hwang,C. -C. Hwang,S. -H. Phark,Y. J. Chang,T. W. Noh,H. -D. Kim
Physics , 2011,
Abstract: We investigate on-site Coulomb interaction energy between two 3p holes U(Ni 3p) of ultrathin NiO films on Ag(001) by both x-ray photoelectron spectroscopy and Auger electron spectroscopy. As the film becomes thin, U(Ni 3p) monotonically decreases, and the difference of U(Ni 3p) for 1 monolayer (ML) film from that of bulk-like thick film \delta U(Ni 3p) reaches ~ -2.2 eV. The observed \delta U(Ni 3p) for 1 ML film is well reproduced by the differences of both the image potential and polarization energies between 1 ML film and the bulk-like thick film. Hence, the present results provide an evidence for the picture originally proposed by Duffy et al. [J. Phys. C: Solid State Phys., 16, 4087 (1983)] and Altieri et al. [Phys. Rev. B 59, R2517 (1999)]
Selective growth of perovskite oxides on SrTiO3 (001) by control of surface reconstructions
Soo-hyon Phark,Young Jun Chang,Tae Won Noh
Physics , 2010, DOI: 10.1063/1.3583443
Abstract: We report surface reconstruction (RC)-dependent growths of SrTiO3 and SrVO3 on a SrTiO3 (001) surface with two different coexisting surface RCs, namely (2x1) and c(6x2). Up to the coverage of several layers, epitaxial growth was forbidden on the c(6x2) RC under the growth conditions that permitted layer-by-layer epitaxial growth on the (2x1) RC. Scanning tunneling microscopy examination of the lattice structure of the c(6x2) RC revealed that this RC-selective growth mainly originated from the significant structural/stoichiometric dissimilarity between the c(6x2) RC and the cubic perovskite films. As a result, the formation of SrTiO3 islands was forbidden from the nucleation stage.
Superparamagnetic response of Fe-coated W tips in spin-polarized scanning tunneling microscopy
Soo-hyon Phark,Jeison A. Fischer,Marco Corbetta,Dirk Sander,Jürgen Kirschner
Physics , 2013,
Abstract: We performed spin-polarized scanning tunneling spectroscopy on biatomic-layer-high Co nanoislands grown on Cu(111) in magnetic fields oriented normal to the sample surface, with Fe-coated W tips. Increasing the temperature from 10 to 30 K, we observe a reduced slope of the differential conductance around zero field. A quantitative analysis of the field- and temperature-dependent differential conductance data in the framework of superparamagnetism as described by a Langevin function gives an excellent description of the experimental results. The analysis suggests that a Fe nano-apex at the W tip, which is composed of 220-300 Fe atoms, determines the magnetic response of the tip.
Scaling Laws for Plasma Focus Machines from Numerical Experiments  [PDF]
S. H. SAW, S. LEE
Energy and Power Engineering (EPE) , 2010, DOI: 10.4236/epe.2010.21010
Abstract: Numerical experiments carried out systematically using the Lee Model code unveil insightful and practical wide-ranging scaling laws for plasma focus machines for nuclear fusion energy as well as other applications. An essential feature of the numerical experiments is the fitting of a measured current waveform to the computed waveform to calibrate the model for the particular machine, thus providing a reliable and rigorous determination of the all-important pinch current. The thermodynamics and radiation properties of the resulting plasma are then reliably determined. This paper provides an overview of the recently published scaling laws for neutron (Yn) and neon soft x-ray, SXR (Ysxr) yields: Yn = 3.2x1011 Ipinch4.5; Yn = 1.8x1010 Ipeak3.8; Ipeak (0.3 to 5.7), Ipinch (0.2 to 2.4) in MA. Yn~E02.0 at tens of kJ to Yn~E00.84 at MJ level (up to 25MJ) and Ysxr = 8.3x103 Ipinch3.6; Ysxr = 6x102 Ipeak3.2; Ipeak (0.1 to 2.4), Ipinch (0.07 to1.3) in MA. Ysxr~E01.6 (kJ range) to Ysxr~E00.8 (towards MJ).
A New Neural Network Structure: Node-to-Node-Link Neural Network  [PDF]
S. H. Ling
Journal of Intelligent Learning Systems and Applications (JILSA) , 2010, DOI: 10.4236/jilsa.2010.21001
Abstract: This paper presents a new neural network structure and namely node-to-node-link neural network (N-N-LNN) and it is trained by real-coded genetic algorithm (RCGA) with average-bound crossover and wavelet mutation [1]. The N-N-LNN exhibits a node-to-node relationship in the hidden layer and the network parameters are variable. These characteristics make the network adaptive to the changes of the input environment, enabling it to tackle different input sets distributed in a large domain. Each input data set is effectively handled by a corresponding set of network parame-ters. The set of parameters is governed by other nodes. Thanks to these features, the proposed network exhibits better learning and generalization abilities. Industrial application of the proposed network to hand-written graffiti recognition will be presented to illustrate the merits of the network.
Superficial tribological transformation of a ferritic stainless steel by dynamic microindentation  [PDF]
H. Boudoukha, S. Djabi
Natural Science (NS) , 2013, DOI: 10.4236/ns.2013.511147
Abstract:

Currently, the stainless steel starts to widen its fields of application in an extraordinary way in medicine and surgery, in the domestic utensils (flatware) and in heavy industry (petrochemistry, nuclear industry and transport). This work consists of making an experimental study on a type of ferritic stainless steel having undergone the test of the microindentation at controlled load and knowing the Superficial Tribological Transformations (STT) caused by this test. It is supposed that it is a simulation with the damages caused on the stainless steels which are in the environment (the effect of hail) or in industry (shot-blasting of the turbines). The analysis of the repeated shocks is based on the mechanical characterization (microhardness, microstructures of the impacts) and geometrical to see the evolution of the diameter and depth of the impacts according to the number of shocks (cycles of impact), in order to know the plastic deformation.

Iterated Function System-Based Crossover Operation for Real-Coded Genetic Algorithm  [PDF]
S. H. Ling
Journal of Intelligent Learning Systems and Applications (JILSA) , 2015, DOI: 10.4236/jilsa.2015.72004
Abstract: An iterated function system crossover (IFSX) operation for real-coded genetic algorithms (RCGAs) is presented in this paper. Iterated?function system (IFS) is one type of fractals that maintains a similarity characteristic. By introducing the IFS into the crossover operation, the RCGA performs better searching solution with a faster convergence in a set of benchmark test functions.
RF Field-Driven Electron Tunneling through Mesoscale Junctions  [PDF]
Masroor H. S. Bukhari
Journal of Modern Physics (JMP) , 2017, DOI: 10.4236/jmp.2017.812117
Abstract: Preliminary results of a study are reported here investigating mesoscopic tunnel junctions irradiated with coherent low-intensity (-50 to -10 dB) pulsed microwave RF fields at moderately low (LN2) temperatures. Quantum tunneling of electrons was observed through fabricated mesoscale gap junctions as a result of coherent irradiating fields at low temperatures around 77 - 100 K. The tunneling current was seen as a result of applied microwave fields across the junctions, distinguishable from shot noise and resistance effects. The form of tunneling behavior does not lead to any conductance quantization effects which could manifest the junction as a Quantum Point Contact (QPC), hence it is surmised that the phenomenon is purely low intensity RF field-induced tunneling of electrons across the mesoscale junctions at low temperatures.
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