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1 Aug 2012

Volume 112, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 112, 031101 (2012); http://dx.doi.org/10.1063/1.4738372 (16 pages)

Ali Oguz Er, Jie Chen, and Peter M. Rentzepis
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Ultrafast time resolved x-ray diffraction, extended x-ray absorption fine structure and x-ray absorption near edge structure

Ali Oguz Er, Jie Chen, and Peter M. Rentzepis

J. Appl. Phys. 112, 031101 (2012); http://dx.doi.org/10.1063/1.4738372 (16 pages) | Cited 2 times

Online Publication Date: 2 August 2012

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Ultrafast time resolved x-ray absorption and x-ray diffraction have made it possible to measure, in real time, transient phenomena structures and processes induced by optical femtosecond pulses. To illustrate the power of these experimental methods, we present several representative examples from the literature. (I) Time resolved measurements of photon/electron coupling, electron/phonon interaction, pressure wave formation, melting and recrystallization by means of time resolved x-ray diffraction. (II) Ultrafast x-ray absorption, EXAFS, for the direct measurement of the structures and their kinetics, evolved during electron transfer within molecules in liquid phase. (III) XANES experiments that measure directly pathway for the population of high spin states and the study of the operating mechanism of dye activated TiO2 solar cell devices. The construction and use of novel polycapillary x-ray lenses that focus and collimate hard x-rays efficiently are described.
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78.47.je Time resolved light scattering spectroscopy
88.40.H- Solar cells (photovoltaics)
42.79.Bh Lenses, prisms and mirrors
78.70.Dm X-ray absorption spectra
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
63.20.kd Phonon-electron interactions
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back to top Lasers, Optics, and Optoelectronics

Transmission through stacked 2D periodic distributions of square conducting patches

Chandra S. R. Kaipa, Alexander B. Yakovlev, Francisco Medina, and Francisco Mesa

J. Appl. Phys. 112, 033101 (2012); http://dx.doi.org/10.1063/1.4740054 (11 pages) | Cited 4 times

Online Publication Date: 1 August 2012

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In this paper, we study the transmissivity of electromagnetic waves through stacked two-dimensional printed periodic arrays of square conducting patches. An analytical circuit-like model is used for the analysis. The model accounts for the details of the transmission spectrum provided that the period of the unit cell of each patterned layer is well below the wavelength in the dielectric slabs separating the printed surfaces. In particular, we analyze the low-pass band and rejection band behavior of the multilayer structure, and the results are validated by comparison with a computationally intensive finite element commercial electromagnetic solver. The limiting case of an infinite periodic structure is analytically solved and the corresponding band structure is used to explain the passband/stopband behavior of finite structures. In addition, we study in depth the elementary unit cell consisting of a single dielectric slab coated by two metal patch arrays, and its resonance behavior is explained in terms of Fabry-Pérot resonances when the electrical thickness of the slab is large enough. In such case, the concept of equivalent thickness of the equivalent ideal Fabry-Pérot resonator is introduced. For electrically thinner slabs it is also shown that the analytical model is still valid, and its corresponding first transmission peak is explained in terms of a lumped-circuit LC resonance.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
07.60.Ly Interferometers

Optimization of extreme ultraviolet photons emission and collection in mass-limited laser produced plasmas for lithography application

T. Sizyuk and A. Hassanein

J. Appl. Phys. 112, 033102 (2012); http://dx.doi.org/10.1063/1.4740230 (6 pages) | Cited 1 time

Online Publication Date: 2 August 2012

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The progress in development of commercial system for next generation EUV lithography requires, among other factors, significant improvement in EUV photon sources such as discharge produced plasma (DPP) and laser produced plasma (LPP) devices. There are still many uncertainties in determining the optimum device since there are many parameters for the suitable and efficient energy source and target configuration and size. Complex devices with trigger lasers in DPP or with pre-pulsing in LPP provide wide area for optimization in regards to conversion efficiency (CE) and components lifetime. We considered in our analysis a promising LPP source configuration using 10–30 μm tin droplet targets, and predicted conditions for the most efficient EUV radiation output and collection as well as calculating photons source location and size. We optimized several parameters of dual-beam lasers and their relationship to target size. We used our HEIGHTS comprehensive and integrated full 3D simulation package to study and optimize LPP processes with various target sizes to maximize the CE of the system.
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52.77.-j Plasma applications
85.40.Hp Lithography, masks and pattern transfer
42.72.Bj Visible and ultraviolet sources
52.25.Tx Emission, absorption, and scattering of particles
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.65.-y Plasma simulation

Gain enhancement in graphene terahertz amplifiers with resonant structures

Yuya Takatsuka, Kazuhiro Takahagi, Eiichi Sano, Victor Ryzhii, and Taiichi Otsuji

J. Appl. Phys. 112, 033103 (2012); http://dx.doi.org/10.1063/1.4742998 (4 pages) | Cited 1 time

Online Publication Date: 3 August 2012

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Terahertz (THz) devices have been investigated over the last decade to utilize THz waves for non-destructive sensing and high-speed wireless communications. Graphene with gapless and linear energy spectra is expected to exhibit population inversion and has negative dynamic conductivity in the THz range when it is illuminated by infrared light. We analyze a THz amplifier utilizing this negative dynamic conductivity combined with electric field enhancements due to surface plasmon polaritons induced on a metal mesh and with a resonant structure. We evaluate its characteristics through finite-difference time-domain electromagnetic simulations. The amplifier is expected to remarkably enhance THz emissions compared with amplifiers without the resonant structure.
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84.30.Le Amplifiers
84.40.-x Radiowave and microwave (including millimeter wave) technology
85.65.+h Molecular electronic devices
02.70.Bf Finite-difference methods

Study of optical anisotropy in nonpolar and semipolar AlGaN quantum well deep ultraviolet light emission diode

Chang-Pei Wang and Yuh-Renn Wu

J. Appl. Phys. 112, 033104 (2012); http://dx.doi.org/10.1063/1.4742050 (7 pages)

Online Publication Date: 3 August 2012

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This paper analyzes the optical polarization characteristics and internal quantum efficiency (IQE) of an AlGaN based polar, nonpolar, and semipolar deep ultra-violet (UV) light emitting diode (LED). A one dimensional model is used to solve drift-diffusion, Poisson equations, and 6 × 6 k·p Schrodinger equations to investigate band structure and emission characteristics. The light emission polarization ratios of c-plane, nonpolar, and semipolar AlGaN based deep UV LEDs with different Al compositions and injection current were studied. The study shows that the optical polarization of the c-plane AlGaN based deep UV LED is dominated by the out-plane polarization as the Al composition increases. For nonpolar and semipolar structures, the light polarization direction is mainly dominated by the in-plane polarized light which is good for the surface emitting. Finally, influences of the IQE by changing the p-type activation energy, growth orientation, and nonradiatve lifetime are studied in this paper.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Photoexpansion and nano-lenslet formation in amorphous As2S3 thin films by 800 nm femtosecond laser irradiation

A. Velea, M. Popescu, F. Sava, A. Lőrinczi, I. D. Simandan, G. Socol, I. N. Mihailescu, N. Stefan, F. Jipa, M. Zamfirescu, A. Kiss, and V. Braic

J. Appl. Phys. 112, 033105 (2012); http://dx.doi.org/10.1063/1.4745021 (4 pages) | Cited 1 time

Online Publication Date: 6 August 2012

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Two step laser processing has been used for the formation of nano-lenslets transmitting in red/infrared region of the optical spectrum on the surface of arsenic sulphide glass films. In the first step the films were obtained by pulsed laser deposition (248 nm), while in the second step the lenslets were created by low power femtosecond (800 nm) laser irradiation. Photoexpansion of the material along with simultaneous migration of chalcogen atoms in the irradiated area was the main phenomena involved in the generation of these structures. The maximum photoexpansion observed was 5.1%. At higher laser power, material ablation was evidenced.
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81.16.-c Methods of micro- and nanofabrication and processing
68.55.-a Thin film structure and morphology
78.30.Hv Other nonmetallic inorganics
78.40.Fy Semiconductors
78.66.Jg Amorphous semiconductors; glasses
81.15.Fg Pulsed laser ablation deposition

Analysis of statistical compositional alloy fluctuations in InGaN from aberration corrected transmission electron microscopy image series

T. Schulz, T. Remmele, T. Markurt, M. Korytov, and M. Albrecht

J. Appl. Phys. 112, 033106 (2012); http://dx.doi.org/10.1063/1.4742015 (9 pages) | Cited 4 times

Online Publication Date: 6 August 2012

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We propose an approach that improves the measuring precision of lattice parameters in semiconductor alloys from high resolution transmission electron microscopy images on the unit cell scale. The method is based on the evaluation of a series of images taken under optimized imaging conditions in an aberration corrected microscope. By comparing image simulations with experimental images, we show that hardly avoidable amorphous surface layers are the main cause for the limited measuring precision. We use our approach to analyze the In distribution within a nominal In0.09Ga0.91N and In0.16Ga0.84N layer and show that both layers do not show a deviation from a random alloy. In addition, we are able to resolve local variations of the in-plane (a-lattice) and out of plane (c-lattice) parameter at the unit cell scale. These fluctuations are due to the local strain within the InGaN alloy caused by the different atomic radii of In and Ga.
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61.66.Fn Inorganic compounds
02.50.-r Probability theory, stochastic processes, and statistics

1.3 μm InAs/GaAs quantum dot lasers on Si substrates by low-resistivity, Au-free metal-mediated wafer bonding

Tomohiko Tatsumi, Katsuaki Tanabe, Katsuyuki Watanabe, Satoshi Iwamoto, and Yasuhiko Arakawa

J. Appl. Phys. 112, 033107 (2012); http://dx.doi.org/10.1063/1.4742198 (5 pages)

Online Publication Date: 7 August 2012

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Low-resistivity GaAs/Si metal-mediated wafer bonding has been investigated for silicon photonics applications. Ag thin-film bonding agent was found to significantly reduce interfacial resistivity relative to the previous bonding mediated by Au-based alloy. Lowering of the interfacial resistivity was found to saturate at 1–2 h of bonding time. A bonding temperature around 300 °C was found optimal to balance the trade-off between elemental interdiffusion and oxidation. On the basis of the bonding investigation, 1.3 μm InAs/GaAs ridge-type quantum dot lasers on Si substrates with Au-free GaAs/Si heterointerfaces have been fabricated. The laser device exhibited a significantly lower device series resistivity and threshold current density than the previous Au-mediated-bonded and direct-grown lasers.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.82.Cr Fabrication techniques; lithography, pattern transfer

Cavity mode gain alignment in GaAsSb-based near-infrared vertical cavity lasers studied by spectroscopy and device measurements

G. Blume, K. Hild, I. P. Marko, T. J. C. Hosea, S.-Q. Yu, S. A. Chaparro, N. Samal, S. R. Johnson, Y.-H. Zhang, and S. J. Sweeney

J. Appl. Phys. 112, 033108 (2012); http://dx.doi.org/10.1063/1.4744985 (7 pages) | Cited 1 time

Online Publication Date: 8 August 2012

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We present a combination of spectroscopy and device measurements on GaAsSb/GaAs vertical-cavity surface-emitting laser (VCSEL) structures to determine the temperature at which the wavelength of the VCSEL cavity mode (CM) aligns with that of the quantum well (QW) ground-state transition (GST), and therefore the gain peak. We find that, despite the achievement of room temperature (RT) continuous wave lasing in VCSEL devices, the QW transition and the CM are actually slightly misaligned at this temperature; room temperature electroluminescence measurements from a cleaved edge of the VCSEL wafer indicate that the 300 K QW GST energy is at 0.975 ± 0.005 eV, while the CM measured in the VCSEL surface reflectivity spectra is at 0.9805 ± 0.0002 eV. When the wafer sample is cooled, the CM and QW GST can be brought into alignment at 270 ± 10 K, as confirmed by temperature-dependent electro-modulated reflectance (ER) and edge-electroluminescence spectroscopic studies. This alignment temperature is further confirmed by comparing the temperature dependence of the emission energy of a fabricated VCSEL device with that of an edge-emitting laser structure with a nominally identical active region. The study suggests that for further device improvement, the room temperature CM and QW GST energies should be more closely matched and both designed to a smaller energy of about 0.95 eV, somewhat closer to the 1.31 μm target. The study amply demonstrates the usefulness of non-destructive ER characterisation techniques in VCSEL manufacturing with GaAsSb-based QWs.
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42.55.Px Semiconductor lasers; laser diodes
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques

Simulation of N-face InGaN-based p-i-n solar cells

Jih-Yuan Chang (張誌原) and Yen-Kuang Kuo (郭艷光)

J. Appl. Phys. 112, 033109 (2012); http://dx.doi.org/10.1063/1.4745043 (5 pages) | Cited 2 times

Online Publication Date: 8 August 2012

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GaN/InGaN p-i-n solar cells with N-face are simulated. In contrast to the detrimental effect of normal polarization, the internal electric field induced by reversed polarization enhances the efficiency of carrier collection by enlarging the energy band tilting to the favorable direction in the InGaN absorption layer. This beneficial effect becomes more remarkable when the indium composition of the InGaN absorption layer is higher.
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88.40.jm Thin film III-V and II-VI based solar cells
88.40.hj Efficiency and performance of solar cells

Spacer and well pumping of InGaN vertical cavity semiconductor lasers with varying number of quantum wells

R. Debusmann, U. Brauch, V. Hoffmann, M. Weyers, and M. Kneissl

J. Appl. Phys. 112, 033110 (2012); http://dx.doi.org/10.1063/1.4745025 (6 pages)

Online Publication Date: 9 August 2012

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We have investigated the dependence of the threshold pump power and slope efficiency of 415 nm (In)GaN vertical cavity surface emitting lasers on the wavelength of the pump source and the number of quantum wells. InGaN double quantum well resonant-periodic-gain structures with 6, 8, and 10 periods have been compared. By barrier and well pumping of the samples with a 375 nm dye laser, a nearly 10 times reduction of the laser threshold was observed compared to pumping with a 337 nm nitrogen laser source. The laser threshold was found to be independent of the number of quantum wells. The slope efficiency seems to be not affected by the pump wavelength and resonant-periodic-gain periods. The results are discussed with a rate equation model that takes into account the inhomogeneous pumping of the quantum wells and optical thickness variations in the resonant-periodic-gain structure.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.-e Optical elements, devices, and systems

Properties of coupled surface plasmon-polaritons in metal-dielectric-metal structures

N. C. Chen, C. Y. Lu, Y. L. Huang, C. C. Liao, W. C. Ke, and B. R. Huang

J. Appl. Phys. 112, 033111 (2012); http://dx.doi.org/10.1063/1.4745051 (7 pages) | Cited 1 time

Online Publication Date: 9 August 2012

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The properties of surface plasmon-polaritons (SPPs) in symmetrical metal-dielectric-metal (MDM) structures were theoretically investigated and experimentally demonstrated. These SPPs exhibit several intriguing properties that are not observed in single-interface SPPs: they can directly couple to radiation outside the MDM structure; their frequency may fall within the plasmon gap; their group velocities can be positive, negative, or even zero, and their density of states can be tuned. All of these properties are favorable in devices that exploit the Purcell effect of SPPs to improve performance. Analytical descriptions of the dispersion curves in some important regions are presented.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.At Surface states, band structure, electron density of states

Band structure of photonic crystal with dispersive and lossy materials using Dirichlet-to-Neumann wave vector eigen equation method

Bin Jiang, Yejin Zhang, Yufei Wang, and Wanhua Zheng

J. Appl. Phys. 112, 033112 (2012); http://dx.doi.org/10.1063/1.4740176 (5 pages)

Online Publication Date: 14 August 2012

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We present the Dirichlet-to-Neumann wave vector eigen equation (DtN-WVEE) method to calculate the band structure of photonic crystal (PhC) with dispersive and lossy materials, and then use finite-difference time-domain method to verify the validity of the results of the DtN-WVEE method. Since the material is lossy with a non-zero imaginary part of epsilon, the wave vector of PhC band structure also has a non-zero imaginary part which results in the reduction of the intensity of the mode. We further present the band structure which gives the relationship among the normalized frequency, the real part of the wave vector, and the imaginary part of the wave vector. To our knowledge, the band structure of lossy PhC has not been well studied yet, and our results can be useful in designing the devices using surface plasmon polariton effect.
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71.20.-b Electron density of states and band structure of crystalline solids
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Qs Photonic bandgap materials
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

Demonstration of a single-photon router with a cavity electromechanical system

Cheng Jiang, Bin Chen, and Ka-Di Zhu

J. Appl. Phys. 112, 033113 (2012); http://dx.doi.org/10.1063/1.4746741 (5 pages)

Online Publication Date: 14 August 2012

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We demonstrate theoretically a scheme for realizing a single-photon router in a cavity electromechanical system. When a weak probe field is tuned on resonance with the microwave cavity, we can use a strong control field to choose to what output port of this probe field is delivered, which is based on the analogue of electromagnetically induced transparency effect in this coupled system. Routing between the reflection output port and the transmission output port can be achieved by turning off and on the control field. The router proposed here opens a good perspective for its applications in photonic quantum information networks.
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42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption

Correlation between charge transport and electroluminescence properties of Si-rich oxide/nitride/oxide-based light emitting capacitors

Y. Berencén, J. M. Ramírez, O. Jambois, C. Domínguez, J. A. Rodríguez, and B. Garrido

J. Appl. Phys. 112, 033114 (2012); http://dx.doi.org/10.1063/1.4742054 (5 pages) | Cited 1 time

Online Publication Date: 14 August 2012

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The electrical and electroluminescence (EL) properties at room and high temperatures of oxide/nitride/oxide (ONO)-based light emitting capacitors are studied. The ONO multidielectric layer is enriched with silicon by means of ion implantation. The exceeding silicon distribution follows a Gaussian profile with a maximum of 19%, centered close to the lower oxide/nitride interface. The electrical measurements performed at room and high temperatures allowed to unambiguously identify variable range hopping (VRH) as the dominant electrical conduction mechanism at low voltages, whereas at moderate and high voltages, a hybrid conduction formed by means of variable range hopping and space charge-limited current enhanced by Poole-Frenkel effect predominates. The EL spectra at different temperatures are also recorded, and the correlation between charge transport mechanisms and EL properties is discussed.
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84.32.Tt Capacitors
85.60.Jb Light-emitting devices
61.72.up Other materials
72.20.Ee Mobility edges; hopping transport
73.40.-c Electronic transport in interface structures
78.60.Fi Electroluminescence
back to top Plasmas and Electrical Discharges

Generation and diagnostics of atmospheric pressure CO2 plasma by laser driven plasma wind tunnel

Makoto Matsui, Kensaku Tanaka, Satoshi Nomura, Kimiya Komurasaki, Yoshiki Yamagiwa, and Yoshihiro Arakawa

J. Appl. Phys. 112, 033301 (2012); http://dx.doi.org/10.1063/1.4739259 (6 pages) | Cited 2 times

Online Publication Date: 1 August 2012

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Atmospheric pressure CO2 plasma was generated by a laser driven plasma wind tunnel. At an ambient pressure of 0.38 MPa, a stable plasma was maintained by a laser power of 1000 W for more than 20 min. The translational temperature was measured using laser absorption spectroscopy with the atomic oxygen line at 777.19 nm. The measured absorption profiles were analyzed by a Voigt function considering Doppler, Stark, and pressure-broadening effects. Under the assumption of thermochemical equilibrium, all broadening effects were consistent with each other. The measured temperature ranged from 8500 K to 8900 K.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.-b Plasma properties
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.30.-q Plasma dynamics and flow

Plasma parameters and electromagnetic forces induced by the magneto hydro dynamic interaction in a hypersonic argon flow experiment

Andrea Cristofolini, Gabriele Neretti, and Carlo A. Borghi

J. Appl. Phys. 112, 033302 (2012); http://dx.doi.org/10.1063/1.4740052 (11 pages)

Online Publication Date: 8 August 2012

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This work proposes an experimental analysis on the magneto hydro dynamic (MHD) interaction induced by a magnetic test body immersed into a hypersonic argon flow. The characteristic plasma parameters are measured. They are related to the voltages arising in the Hall direction and to the variation of the fluid dynamic properties induced by the interaction. The tests have been performed in a hypersonic wind tunnel at Mach 6 and Mach 15. The plasma parameters are measured in the stagnation region in front of the nozzle of the wind tunnel and in the free stream region at the nozzle exit. The test body has a conical shape with the cone axis in the gas flow direction and the cone vertex against the flow. It is placed at the nozzle exit and is equipped with three permanent magnets. In the configuration adopted, the Faraday current flows in a closed loop completely immersed into the plasma of the shock layer. The electric field and the pressure variation due to MHD interaction have been measured on the test body walls. Microwave adsorption measurements have been used for the determination of the electron number density and the electron collision frequency. Continuum recombination radiation and line radiation emissions have been detected. The electron temperature has been determined by means of the spectroscopic data by using different methods. The electron number density has been also determined by means of the Stark broadening of Hα and the Hβ lines. Optical imaging has been utilized to visualize the pattern of the electric current distribution in the shock layer around the test body. The experiments show a considerable effect of the electromagnetic forces produced by the MHD interaction acting on the plasma flow around the test body. A comparison of the experimental data with simulation results shows a good agreement.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
47.40.Ki Supersonic and hypersonic flows
47.40.Nm Shock wave interactions and shock effects
52.20.Fs Electron collisions
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Extraction of negative ions from pulsed electronegative capacitively coupled plasmas

Ankur Agarwal, Shahid Rauf, and Ken Collins

J. Appl. Phys. 112, 033303 (2012); http://dx.doi.org/10.1063/1.4745877 (10 pages) | Cited 1 time

Online Publication Date: 9 August 2012

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Charge buildup during plasma etching of dielectric features can lead to undesirable effects, such as notching, bowing, and twisting. Pulsed plasmas have been suggested as a method to achieve charge-free plasma etching. In particular, electronegative plasmas are attractive as the collapse of the plasma potential during the after-glow period of pulsed capacitively coupled plasmas (CCPs) can allow for extraction of negative ions into the feature. The extraction of negative ions in the after-glow of pulsed CCPs sustained in CF4 containing gas mixtures is computationally investigated. In this paper, the consequences of pulse frequency and gas chemistry on negative ion flux to the wafer are discussed. A low negative ion flux to the wafer was observed only in the late after-glow period of low pulse frequencies. The negative ion flux was found to significantly increase with the addition of highly electronegative gases (such as thermally attaching Cl2) even at a high pulse frequency of 10 kHz. As the production of negative ions during the after-glow diminishes, alternative strategies to enhance the flux were also pursued. The flux of negative ions was found to increase by the addition of a pulsed dc voltage on the top electrode that is 180° out-of-phase with the rf pulse.
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52.77.Bn Etching and cleaning
52.80.Hc Glow; corona
52.80.Pi High-frequency and RF discharges
52.25.Fi Transport properties

Impact of Xe partial pressure on the production of excimer vacuum ultraviolet emission for plasma display panels

Di Zhu, Xiong Zhang, and Hiroshi Kajiyama

J. Appl. Phys. 112, 033304 (2012); http://dx.doi.org/10.1063/1.4745898 (10 pages)

Online Publication Date: 13 August 2012

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In this work, the effect of the Xe partial pressure on the excimer vacuum ultraviolet (VUV) emission intensity of the plasma display panels is investigated, both by measuring the spectral emission directly and by two-dimensional simulations. Experimentally, we find that at the high Xe partial pressure levels, there is an supra-linear increase of excimer VUV radiation and that determines the strong increase of luminance at the high pressures and high voltage. Due to the increase of the luminance and the almost unchanged discharge current, the luminous efficacy strongly increases with the Xe partial pressure. In addition, we also investigated the dynamics of the VUV generation, by measuring the decay time of the excimer VUV light as a function of the gas pressure. It is found that the decay time decreases with the increase of gas pressure. The spatial characteristics of the excimer VUV emission are also discussed. Different from the Ne and near-infrared emission, the excimer VUV emission is generated near the surface of the electrodes and increases uniformly on both sides of the anode and cathode (i.e., the bulk plasma region). Most importantly, it is found that the VUV production occurs during the afterglow period, while it is almost zero at the moment of the discharge itself. From the simulations, it can be seen that the Xe2*(3Σu+) excimer species, which are generated from Xe*(1s5), play a dominant role in the excimer VUV emission output at the high Xe partial pressure. The two-dimensional simulations also show that the strong increase of Xe excimer excitation states in the case of high pressure is mainly the result of the high conversion efficiency of the Xe excimer states, especially in the afterglow period. Due to the high conversion efficiency of Xe excitation species to Xe excimer species by the high collision rate in the case of high pressure, there is a strong increase of excimer VUV production, especially from the cathode.
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85.60.Pg Display systems
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.65.-y Plasma simulation
52.75.-d Plasma devices
52.80.Hc Glow; corona
52.80.Yr Discharges for spectral sources (including inductively coupled plasma)

Influence of helium mole fraction distribution on the properties of cold atmospheric pressure helium plasma jets

Ranhua Xiong, Qing Xiong, Anton Yu. Nikiforov, Patrick Vanraes, and Christophe Leys

J. Appl. Phys. 112, 033305 (2012); http://dx.doi.org/10.1063/1.4746700 (8 pages) | Cited 3 times

Online Publication Date: 14 August 2012

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The influence of helium mole fraction distribution in air on the cold atmospheric plasma jets excited by 1.5 kHz rectangular high voltage pulse is studied in this work. Computational fluid dynamics (CFD) with incorporation of large eddy simulation (LES) model is used to simulate the helium mole fraction distribution in air under the helium flow from laminar to turbulent regime with increasing helium outlet velocity. Numerical simulation results are combined with experimental results in order to determine the influence of helium distribution on the cold plasma jets. It reveals that the structure of the helium distribution caused by diffusion or by turbulent mixing in turbulent regime determines the characteristics of the cold plasma jets. On the other hand, the curves of plasma jet length (L) versus helium outlet velocity (V) at different jet diameters (D) are unified in a map of jet Reynolds number (Re = ρHe·V·D/μHe, where μHe is the helium viscosity constant) versus dimensionless plasma jet length (l = L/D). The map is allowed to predict the flow pattern of helium jet in order to estimate and control the plasma jet length at different jet diameters.
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52.75.-d Plasma devices
45.70.Qj Pattern formation
47.11.-j Computational methods in fluid dynamics
47.27.Cn Transition to turbulence
47.27.ek Direct numerical simulations
47.54.-r Pattern selection; pattern formation
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Quantum molecular dynamics simulations for the nonmetal-metal transition in fluid nitrogen oxide

Yujuan Zhang, Cong Wang, Fawei Zheng, and Ping Zhang

J. Appl. Phys. 112, 033501 (2012); http://dx.doi.org/10.1063/1.4739716 (5 pages) | Cited 1 time

Online Publication Date: 1 August 2012

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First-principle molecular-dynamics simulations based on density-functional theory have been used to study the thermophysical properties of fluid nitrogen oxide under extreme conditions. We have presented wide range equation of states, from which the principal Hugoniot were derived up to 200 GPa, and the results are well accordant with the experimental and theoretical data. The optical conductivity is calculated via the Kubo-Greenwood formula, from which the dc conductivity is obtained. The nonmetal-metal transition is observed at about 40 GPa, and is attributed to the dissociation of nitrogen oxide molecules. Additionally, the density of states and the distribution of the electronic charge are also investigated to study the complex behavior of fluid nitrogen oxide.
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71.30.+h Metal-insulator transitions and other electronic transitions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
62.50.-p High-pressure effects in solids and liquids
64.30.Jk Equations of state of nonmetals
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

Effect of hydrofluoric acid concentration on the evolution of photoluminescence characteristics in porous silicon nanowires prepared by Ag-assisted electroless etching method

A. Najar, A. B. Slimane, M. N. Hedhili, D. Anjum, R. Sougrat, T. K. Ng, and B. S. Ooi

J. Appl. Phys. 112, 033502 (2012); http://dx.doi.org/10.1063/1.4740051 (6 pages) | Cited 1 time

Online Publication Date: 1 August 2012

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We report on the structural and optical properties of porous silicon nanowires (PSiNWs) fabricated using silver (Ag) ions assisted electroless etching method. Silicon nanocrystallites with sizes <5 nm embedded in amorphous silica have been observed from PSiNW samples etched using the optimum hydrofluoric acid (HF) concentration. The strongest photoluminescence (PL) signal has been measured from samples etched with 4.8 M of HF, beyond which a significant decreasing in PL emission intensity has been observed. A qualitative model is proposed for the formation of PSiNWs in the presence of Ag catalyst. This model affirms our observations in PL enhancement for samples etched using HF < 4.8 M and the eventual PL reduction for samples etched beyond 4.8 M of HF concentration. The enhancement in PL signals has been associated to the formation of PSiNWs and the quantum confinement effect in the Si nanocrystallites. Compared to PSiNWs without Si-Ox, the HF treated samples exhibited significant blue PL peak shift of 100 nm. This effect has been correlated to the formation of defect states in the surface oxide. PSiNWs fabricated using the electroless etching method can find useful applications in optical sensors and as anti-reflection layer in silicon-based solar cells.
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78.55.Ap Elemental semiconductors
81.07.Gf Nanowires

Analysis of doping induced wafer bow during GaN:Si growth on sapphire

F. Brunner, A. Mogilatenko, A. Knauer, M. Weyers, and J.-T. Zettler

J. Appl. Phys. 112, 033503 (2012); http://dx.doi.org/10.1063/1.4739278 (5 pages) | Cited 1 time

Online Publication Date: 2 August 2012

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In-situ curvature measurements were employed to quantify stress generation during metalorganic vapor phase epitaxy growth of Si-doped GaN sandwiched between undoped GaN layers. It is shown that the creation of tensile stress in Si-doped GaN is closely linked to the density of threading dislocations in the material. Accompanying characterization by in-situ reflectance measurements and TEM analysis supports the model that the doping induced stress formation is caused by a surface-mediated dislocation climb process. In addition, curvature measurements reveal an unusual partial relaxation in GaN:nid grown atop of highly doped GaN:Si layers. This relaxation is assigned to a notable dislocation annihilation at the upper GaN:Si+/GaN:nid interface found by TEM probably due to the formation of a thin SiNx masking layer.
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68.55.ag Semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.40.Jj Elasticity and anelasticity, stress-strain relations

Thermal conductivity of solid deuterium by the 3ω method

R. Q. Gram, A. She, R. S. Craxton, and D. R. Harding

J. Appl. Phys. 112, 033504 (2012); http://dx.doi.org/10.1063/1.4739285 (8 pages)

Online Publication Date: 2 August 2012

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The thermal conductivity of solid D2 is measured by the 3ω method, in which a wire embedded in the medium serves as both a heater and a temperature sensor. Conductivity values are obtained by fitting experimental data with a two-dimensional model that calculates heat flow in both the axial and radial directions as a function of frequency. The model provides the thermal conductivity of D2 from the measurement of the 3ω voltage and published values of specific heat and density of D2 and of the sensor wire, and thermal conductivity values for the sensor wire. Data for D2 gas and liquid are obtained for comparison to solid D2. Conductivity values obtained for solid D2 range from 0.35 ± 0.01 W/(m K) at 18.6 K to 0.75 ± 0.02 W/(m K) at 13.4 K and are the same for normal and ortho D2. These values are acquired at lower temperatures than the 3ω method has previously been used for.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
65.40.Ba Heat capacity

Study of exciton-polariton modes in nanocrystalline thin films of CuCl using reflectance spectroscopy

Barry Foy, Enda McGlynn, Aidan Cowley, Patrick J. McNally, and Martin O. Henry

J. Appl. Phys. 112, 033505 (2012); http://dx.doi.org/10.1063/1.4739726 (10 pages)

Online Publication Date: 2 August 2012

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CuCl thin films grown on (100) Si by thermal evaporation are studied using reflectance spectroscopy. The reflectance spectra in the near UV spectral range close to the CuCl bandgap are modeled using a dielectric response function based on an exciton-polariton response with various models involving dead layers and reflected waves in the thin film. The exciton-polariton structure obtained is compared to other studies of bulk CuCl crystals. These different models are analyzed using a matrix-based approach and they yield theoretical spectra of reflected intensity. The fits provide parameter values which can be compared to bulk data known for CuCl and provide a non-destructive means of quantitative analysis of CuCl thin films. The best models are shown to match the experimental data quite well, with the closest fits produced when thin film front and rear interfaces are included. This model also accurately simulates the Fabry-Perot fringes present at energies lower than the Z3 free exciton position in CuCl (at 3.272 eV).
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71.35.-y Excitons and related phenomena
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.66.Nk Insulators
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
68.55.aj Insulators
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