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15 Jun 2007

Volume 101, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 101, 121301 (2007); http://dx.doi.org/10.1063/1.2749198 (46 pages)

Wai Lun Chan and Eric Chason
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Making waves: Kinetic processes controlling surface evolution during low energy ion sputtering

Wai Lun Chan and Eric Chason

J. Appl. Phys. 101, 121301 (2007); http://dx.doi.org/10.1063/1.2749198 (46 pages) | Cited 138 times

Online Publication Date: 20 June 2007

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When collimated beams of low energy ions are used to bombard materials, the surface often develops a periodic pattern or “ripple” structure. Different types of patterns are observed to develop under different conditions, with characteristic features that depend on the substrate material, the ion beam parameters, and the processing conditions. Because the patterns develop spontaneously, without applying any external mask or template, their formation is the expression of a dynamic balance among fundamental surface kinetic processes, e.g., erosion of material from the surface, ion-induced defect creation, and defect-mediated evolution of the surface morphology. In recent years, a comprehensive picture of the different kinetic mechanisms that control the different types of patterns that form has begun to emerge. In this article, we provide a review of different mechanisms that have been proposed and how they fit together in terms of the kinetic regimes in which they dominate. These are grouped into regions of behavior dominated by the directionality of the ion beam, the crystallinity of the surface, the barriers to surface roughening, and nonlinear effects. In sections devoted to each type of behavior, we relate experimental observations of patterning in these regimes to predictions of continuum models and to computer simulations. A comparison between theory and experiment is used to highlight strengths and weaknesses in our understanding. We also discuss the patterning behavior that falls outside the scope of the current understanding and opportunities for advancement.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.80.Jh Ion radiation effects
68.35.Fx Diffusion; interface formation
66.30.Lw Diffusion of other defects
01.30.Rr Surveys and tutorial papers; resource letters
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Carrier transport through a dry-etched InP-based two-dimensional photonic crystal

A. Berrier, M. Mulot, G. Malm, M. Östling, and S. Anand

J. Appl. Phys. 101, 123101 (2007); http://dx.doi.org/10.1063/1.2747222 (6 pages) | Cited 13 times

Online Publication Date: 18 June 2007

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The electrical conduction across a two-dimensional photonic crystal (PhC) fabricated by Ar/Cl2 chemically assisted ion beam etching in n-doped InP is influenced by the surface potential of the hole sidewalls, modified by dry etching. Carrier transport across photonic crystal fields with different lattice parameters is investigated. For a given lattice period the PhC resistivity increases with the air fill factor and for a given air fill factor it increases as the lattice period is reduced. The measured current-voltage characteristics show clear ohmic behavior at lower voltages followed by current saturation at higher voltages. This behavior is confirmed by finite element ISE TCAD™ simulations. The observed current saturation is attributed to electric-field-induced saturation of the electron drift velocity. From the measured and simulated conductance for the different PhC fields we show that it is possible to determine the sidewall depletion region width and hence the surface potential. We find that at the hole sidewalls the etching induces a Fermi level pinning at about 0.12 eV below the conduction band edge, a value much lower than the bare InP surface potential. The results indicate that for n-InP the volume available for conduction in the etched PhCs approaches the geometrically defined volume as the doping is increased.
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81.65.Cf Surface cleaning, etching, patterning
72.80.Ey III-V and II-VI semiconductors
52.77.Bn Etching and cleaning

Sub-wavelength resolution in linear arrays of plasmonic particles

Constantin R. Simovski, Ari J. Viitanen, and Sergei A. Tretyakov

J. Appl. Phys. 101, 123102 (2007); http://dx.doi.org/10.1063/1.2745315 (4 pages) | Cited 9 times

Online Publication Date: 19 June 2007

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Recently, we suggested the idea of an optical superlens based on the extraordinary dispersion properties of plasmonic nanochains. In the present paper we discuss the results of numerical simulations of the imaging of point sources in this superlens. The simulations show that sub-wavelength resolution can be obtained in much thicker structures than usual. A distance of nearly λ/2 between the source and the image plane is achieved. In addition the effects of stochastic deviations in geometrical parameters are studied.
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42.79.Bh Lenses, prisms and mirrors
42.15.Eq Optical system design

Ultraviolet semiconductor laser diodes on bulk AlN

Michael Kneissl, Zhihong Yang, Mark Teepe, Cliff Knollenberg, Oliver Schmidt, Peter Kiesel, Noble M. Johnson, Sandra Schujman, and Leo J. Schowalter

J. Appl. Phys. 101, 123103 (2007); http://dx.doi.org/10.1063/1.2747546 (5 pages) | Cited 37 times

Online Publication Date: 20 June 2007

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Current-injection ultraviolet lasers are demonstrated on low-dislocation-density bulk AlN substrates. The AlGaInN heterostructures were grown by metalorganic chemical vapor deposition. Requisite smooth surface morphologies were obtained by growing on near-c-plane AlN substrates, with a nominal off-axis orientation of less than 0.5°. Lasing was obtained from gain-guided laser diodes with uncoated facets and cavity lengths ranging from 200 to 1500 μm. Threshold current densities as low as 13 kA/cm2 were achieved for laser emission wavelengths as short as 368 nm, under pulsed operation. The maximum light output power was near 300 mW with a differential quantum efficiency of 6.7%. This (first) demonstration of nitride laser diodes on bulk AlN substrates suggests the feasibility of using such substrates to realize nitride laser diodes emitting from the near to deep ultraviolet spectral regions.
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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
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Effects of laser-induced heating on Raman stress measurements of silicon and silicon-germanium structures

Carsten Georgi, Michael Hecker, and Ehrenfried Zschech

J. Appl. Phys. 101, 123104 (2007); http://dx.doi.org/10.1063/1.2743882 (6 pages) | Cited 14 times

Online Publication Date: 20 June 2007

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The authors investigate the effect of laser-induced heating on Raman measurements for different unpatterned and patterned substrates, including pure silicon, strained-silicon-on-insulator, and silicon-germanium layers on silicon. The relationship between heating and incident power of the laser used for Raman measurements is derived for unpatterned substrates, and the much stronger heating effects for line and island structures are shown. Additionally, the enormous heating of isolated silicon particles within the laser beam was investigated. The measured shifts clearly show that heating has to be considered even for moderate laser intensity when accurate stress measurements on such substrates are performed by Raman spectroscopy.
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78.30.Am Elemental semiconductors and insulators

Experimental and theoretical studies of particle generation after laser ablation of copper with a background gas at atmospheric pressure

Sy-Bor Wen, Xianglei Mao, Ralph Greif, and Richard E. Russo

J. Appl. Phys. 101, 123105 (2007); http://dx.doi.org/10.1063/1.2748635 (15 pages) | Cited 9 times

Online Publication Date: 21 June 2007

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Laser ablation has proven to be an effective method for generating nanoparticles; particles are produced in the laser induced vapor plume during the cooling stage. To understand the in situ condensation process, a series of time resolved light scattering images was recorded and analyzed. Significant changes in the condensation rate and the shape of the condensed aerosol plume were observed in two background gases, helium and argon. The primary particle shape and size distributions were measured using a transmission electron microscope, a scanning electron microscope, and a differential mobility analyzer. The gas dynamics simulation included nucleation and coagulation within the vapor plume, heat and mass transfer from the vapor plume to the background gas, and heat transfer to the sample. The experimental data and the calculated evolution of the shape of the vapor plume showed the same trend for the spatial distribution of the condensed particles in both background gases. The simulated particle size distribution also qualitatively agreed with the experimental data. It was determined that the laser energy, the physical properties of the background gas (conductivity, diffusivity, and viscosity), and the shape of the ablation system (ablation chamber and the layout of the sample) have strong effects on the condensation process and the subsequent sizes, shapes, and degree of aggregation of the particles.
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81.65.-b Surface treatments
42.62.-b Laser applications
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
51.20.+d Viscosity, diffusion, and thermal conductivity
51.10.+y Kinetic and transport theory of gases
82.70.Rr Aerosols and foams

Noncatalytic dissociation of MgO by laser pulses towards sustainable energy cycle

T. Yabe, M. S. Mohamed, S. Uchida, C. Baasandash, Y. Sato, M. Tsuji, and Y. Mori

J. Appl. Phys. 101, 123106 (2007); http://dx.doi.org/10.1063/1.2743730 (7 pages) | Cited 7 times

Online Publication Date: 22 June 2007

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We succeeded in dissociating MgO using laser pulses without a reducing agent. The energy efficiency from laser to magnesium reaction energy exceeded 42.5%. Although 1 kW CO2 cw laser and Nd-YAG pulse laser are used in this experiment, the laser can be pumped by natural resources such as solar light or wind power. Thus natural resources are stored in the form of magnesium, which can be used through the reaction with water whenever we need the energy, and thus a renewable energy system will be established. This paper reports the preliminary experiments of MgO reduction toward a sustainable energy cycle.
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82.50.-m Photochemistry
89.30.-g Fossil fuels and nuclear power

Destruction and enhancement of photonic band gap and coherent localization of optical fields in functional photonic crystals

S. M. Sadeghi, X. Li, W.-P. Huang, and W. Li

J. Appl. Phys. 101, 123107 (2007); http://dx.doi.org/10.1063/1.2749422 (6 pages) | Cited 3 times

Online Publication Date: 22 June 2007

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We use electromagnetically induced transparency combined with coherent enhancement of refractive index in the conduction intersubband transitions of a n-doped quantum well structure to study one-dimensional functional (active) photonic band gap structures. In the absence of a control laser field, such structures act as conventional photonic band gaps created by off-resonant (background) refractive index perturbations. In the presence of the control field, they are transformed into resonant structures with transitions around the Bragg wavelength. We show that this process can be used to (i) destroy the band gap, making the structure fully transparent around the Bragg wavelength, or (ii) coherently tune the band gap while enhancing its width by nearly a factor of 2. Using these phenomena we then study coherent localization of electromagnetic modes in photonic band gap structures without having any structural defects. Such a localization process here happens via partial illumination of such structures by the control field, generating electromagnetically induced optical defects. We show that the phase associated with such defects can be adjusted by the control field, allowing us to generate tunable electromagnetically induced transmission resonances (or photonic electromagnetically induced transparency) within the band gap.
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42.70.Qs Photonic bandgap materials
42.65.-k Nonlinear optics
78.67.De Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Intersubband transitions in asymmetric AlxGa1−xN/GaN double quantum wells

S. Y. Lei, B. Shen, L. Cao, Z. J. Yang, and G. Y. Zhang

J. Appl. Phys. 101, 123108 (2007); http://dx.doi.org/10.1063/1.2745422 (5 pages) | Cited 7 times

Online Publication Date: 26 June 2007

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Influence of the width and Al composition of one well in asymmetric Al0.85Ga0.15N/GaN double quantum wells (DQWs) on the absorption coefficients and the wavelengths of the intersubband transitions (ISBTs) has been investigated by solving the Schrödinger and Poisson equations self-consistently. When the well width is chosen to be 1.91 nm, the three-energy-level DQWs are realized. The ISBT between the first odd order and the second even order subbands (the 1odd-2even ISBT) has comparable absorption coefficient with the 1odd-2odd ISBT. Their wavelengths are located at 1.3 and 1.54 μm, respectively. When the well width is 2.77 nm, the four-energy-level DQWs are realized. The 1odd-2even and the 1even-2odd ISBTs have comparable absorption coefficients. Their wavelengths are located at 1.41 and 2.54 μm, respectively. The energy separation between the excited subbands is determined to have the minimum value of 144 meV due to the band anticrossing interaction. The calculated results give possible application to ultrafast two-color optoelectronic devices operating within the optical communication wavelength range.
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78.67.De Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.65.Hb Quantum dots (patterned in quantum wells)

H+ ion-implantation energy dependence of electronic transport properties in the MeV range in n-type silicon wafers using frequency-domain photocarrier radiometry

Chinhua Wang, Andreas Mandelis, Jordan Tolev, Bernd Burchard, and Jan Meijer

J. Appl. Phys. 101, 123109 (2007); http://dx.doi.org/10.1063/1.2748868 (11 pages) | Cited 2 times

Online Publication Date: 27 June 2007

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Industrial n-type Si wafers (resistivity of 5–10 Ω cm) were H+ ion implanted with energies between 0.75 and 2.00 MeV, and the electronic transport properties of the implanted layer (recombination lifetime, carrier diffusion coefficient, and front-surface and implanted-interface recombination velocities s1 and s2) were studied using photocarrier radiometry (PCR). A quantitative fitting procedure to the diffusing photoexcited free-carrier density wave was introduced using a relatively simple two-layer PCR model in lieu of the more realistic but substantially more complicated three-layer model. The experimental trends in the transport properties of H+-implanted Si layers extracted from the PCR amplitude and phase data as functions of implantation energy corroborate a physical model of the implanted layer in which (a) overlayer damage due to the light H+ ions decreases with increased depth of implantation at higher energies, (b) the implanted region damage close to the interface is largely decoupled from the overlayer crystallinity, and (c) the concentration of implanted H+ ions decreases at higher implantation energies at the interface, thus decreasing the degree of implantation damage at the interface proper.
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73.61.Cw Elemental semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.25.+i Surface conductivity and carrier phenomena
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uf Ge and Si
61.82.Fk Semiconductors

Diffusion lengths of silicon solar cells from luminescence images

P. Würfel, T. Trupke, T. Puzzer, E. Schäffer, W. Warta, and S. W. Glunz

J. Appl. Phys. 101, 123110 (2007); http://dx.doi.org/10.1063/1.2749201 (10 pages) | Cited 55 times

Online Publication Date: 27 June 2007

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A method for spatially resolved measurement of the minority carrier diffusion length in silicon wafers and in silicon solar cells is introduced. The method, which is based on measuring the ratio of two luminescence images taken with two different spectral filters, is applicable, in principle, to both photoluminescence and electroluminescence measurements and is demonstrated experimentally by electroluminescence measurements on a multicrystalline silicon solar cell. Good agreement is observed with the diffusion length distribution obtained from a spectrally resolved light beam induced current map. In contrast to the determination of diffusion lengths from one single luminescence image, the method proposed here gives absolute values of the diffusion length and, in comparison, it is much less sensitive to lateral voltage variations across the cell area as caused by local variations of the series resistance. It is also shown that measuring the ratio of two luminescence images allows distinguishing shunts or surface defects from bulk defects.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
06.30.Ka Basic electromagnetic quantities
84.60.Jt Photoelectric conversion

Excited state dynamics of the Ho3+ ions in holmium singly doped and holmium, praseodymium-codoped fluoride glasses

André Felipe Henriques Librantz, Stuart D. Jackson, Fabio Henrique Jagosich, Laércio Gomes, Gaël Poirier, Sidney José Lima Ribeiro, and Younes Messaddeq

J. Appl. Phys. 101, 123111 (2007); http://dx.doi.org/10.1063/1.2749285 (9 pages) | Cited 21 times

Online Publication Date: 27 June 2007

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The deactivation of the two lowest excited states of Ho3+ was investigated in Ho3+ singly doped and Ho3+, Pr3+-codoped fluoride (ZBLAN) glasses. We establish that 0.1–0.3 mol % Pr3+ can efficiently deactivate the first excited (5I7) state of Ho3+ while causing a small reduction of ∼ 40% of the initial population of the second excited (5I6) state. The net effect introduced by the Pr3+ ion deactivation of the Ho3+ ion is the fast recovery of the ground state of Ho3+. The Burshstein model parameters relevant to the Ho3+→Pr3+ energy transfer processes were determined using a least squares fit to the measured luminescence decay. The energy transfer upconversion and cross relaxation parameters for 1948, 1151, and 532 nm excitations of singly Ho3+-doped ZBLAN were determined. Using the energy transfer rate parameters we determine from the measured luminescence, a rate equation model for 650 nm excitation of Ho3+-doped and Ho3+, Pr3+-doped ZBLAN glasses was developed. The rate equations were solved numerically and the population inversion between the 5I6 and the 5I7 excited states of Ho3+ was calculated to examine the beneficial effects on the gain associated with Pr3+ codoping.
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42.70.Ce Glasses, quartz
78.55.Hx Other solid inorganic materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Influence of unit cell rotated on the focusing in a two-dimensional photonic-crystal-based flat lens

Zhifang Feng, Xiuguo Wang, Zhiyuan Li, and DaoZhong Zhang

J. Appl. Phys. 101, 123112 (2007); http://dx.doi.org/10.1063/1.2745374 (6 pages) | Cited 1 time

Online Publication Date: 27 June 2007

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Focusing in photonic crystal (PC) slab has been studied theoretically and experimentally. PCs are composed of a unit cell repeated periodically. In this article, we investigate in detail the influence of the continuous rotation of the unit cell on the focus in a two-dimensional photonic-crystal-based flat lens by the finite-difference time-domain method and experimental measurement. It is found that the focusing can appear within a large range of rotated angle of the unit cell. When the rotation exceeds a certain angle, the focusing disappears. However, it is interesting that the focusing does not depart from the symmetric center because of rotation of the unit cell.
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42.79.Bh Lenses, prisms and mirrors
42.70.Qs Photonic bandgap materials

Growth and spectroscopic characterization of Er3+:CaWO4

Francesco Cornacchia, Alessandra Toncelli, Mauro Tonelli, Elena Favilla, Kirill A. Subbotin, Valerii A. Smirnov, Denis A. Lis, and Evgenii V. Zharikov

J. Appl. Phys. 101, 123113 (2007); http://dx.doi.org/10.1063/1.2749403 (7 pages) | Cited 1 time

Online Publication Date: 28 June 2007

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In this work we present the growth and spectroscopic investigation of Er3+ in CaWO4 single crystals. Er3+ polarized absorption has been measured at room temperature from UV to 1700 nm, and the fluorescence from the most important emitting states from the visible to the infrared has been recorded at 10 and 300 K in the two possible polarizations. The lifetimes of the lower lying excited states have been measured as a function of the temperature to evaluate the contribution of nonradiative decay processes. The absorption spectra enabled us to determine radiative lifetimes of the emitting states by means of the the Judd-Ofelt approach. The stimulated emission cross section has been estimated for the 1.5 μm transition. A comparison of the theoretical and experimental results permitted to obtain an estimate of the actual Er3+ doping level. A calculation of the effective gain cross section for the 1.5 μm transition is also presented. These experimental results are discussed in order to evaluate the potentialities of Er3+ in this material as active medium in solid state laser devices.
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42.70.Hj Laser materials
78.40.Ha Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials
78.45.+h Stimulated emission
61.72.S- Impurities in crystals

Semiconducting polymers and quantum dots in luminescent solar concentrators for solar energy harvesting

V. Sholin, J. D. Olson, and S. A. Carter

J. Appl. Phys. 101, 123114 (2007); http://dx.doi.org/10.1063/1.2748350 (9 pages) | Cited 23 times

Online Publication Date: 28 June 2007

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We compare the performance of luminescent solar concentrators (LSCs) fabricated with polymers and quantum dots to the behavior of laser dye LSCs. Previous research, centered around the use of small molecule laser dyes, was hindered by the lack of materials with small absorption/emission band overlap and longer lifetime. Materials such as semiconducting polymers and quantum dots present qualities that are desirable in LSCs, for example, smaller absorption/emission band overlap, tunable absorption, and longer lifetimes. In this study, the efficiency of LSCs consisting of liquid solutions of semiconducting polymers encased in glass was measured and compared to the efficiency of LSCs based on small molecule dyes and on quantum dots. Factors affecting the optical efficiency of the system such as the luminescing properties of the organic materials were examined. The experimental results were compared to Monte Carlo simulations. Our results suggest that commercially available quantum dots cannot serve as viable LSC dyes because of their large absorption/emission band overlaps and relatively low quantum yields. Materials such as Red F demonstrate that semiconducting polymers with high quantum yield and small absorption/emission band overlap are good candidates for LSCs.
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42.79.Ek Solar collectors and concentrators

Heating-induced carrier accumulation in the optical confinement layer and the output power in broadened symmetric and narrow asymmetric waveguide laser diodes

Boris Ryvkin and Eugene Avrutin

J. Appl. Phys. 101, 123115 (2007); http://dx.doi.org/10.1063/1.2749464 (5 pages) | Cited 6 times

Online Publication Date: 28 June 2007

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We analyze the thermal effects in carrier accumulation (leakage) in the optical confinement layer of high-power λ = 1.06 μm semiconductor lasers. The experimental data for the symmetric broadened-cavity lasers are analyzed to extract the information on the current dependence of the internal loss and laser temperature. These data are used to predict the thermal behavior and output power-current dependence of a proposed asymmetric nonbroadened construction operating at the same wavelength, and a significant improvement is predicted.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Optical properties of Y2O3 thin films doped with spatially controlled Er3+ by atomic layer deposition

J. Hoang, T. T. Van, M. Sawkar-Mathur, B. Hoex, M. C. M. Van de Sanden, W. M. M. Kessels, R. Ostroumov, K. L. Wang, J. R. Bargar, and J. P. Chang

J. Appl. Phys. 101, 123116 (2007); http://dx.doi.org/10.1063/1.2748629 (8 pages) | Cited 9 times

Online Publication Date: 29 June 2007

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We report in this work the optical properties of Er3+-doped Y2O3, deposited by radical enhanced atomic layer deposition. Specifically, the 1.53 μm absorption cross section of Er3+ in Y2O3 was measured by cavity ring-down spectroscopy to be (1.9±0.5)×10−20 cm2, about two times that for Er3+ in SiO2. This is consistent with the larger Er3+ effective absorption cross section at 488 nm, determined based on the 1.53 μm photoluminescence yield as a function of the pump power. X-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy were used to determine the film composition, which in turn was used to analyze the extended x-ray absorption fine structure data, showing that Er was locally coordinated to only O in the first shell and its second shell was a mixture of Y and Er. These results demonstrated that the optical properties of Er3+-doped Y2O3 are enhanced, likely due to the fully oxygen coordinated, spatially controlled, and uniformly distributed Er3+ dopants in the host. These findings are likely universal in rare-earth doped oxide materials, making it possible to design materials with improved optical properties for their use in optoelectronic devices.
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78.66.-w Optical properties of specific thin films
78.55.Hx Other solid inorganic materials
78.70.Dm X-ray absorption spectra
79.60.Dp Adsorbed layers and thin films
61.72.S- Impurities in crystals
42.70.-a Optical materials
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The role of the defect levels in MgO in the low firing voltage, wide driving voltage margin operation of an alternate current plasma display panel

Chang Hoon Ha, Joong Kyun Kim, and Ki-Woong Whang

J. Appl. Phys. 101, 123301 (2007); http://dx.doi.org/10.1063/1.2747228 (5 pages) | Cited 8 times

Online Publication Date: 19 June 2007

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In order to study the relationship between the discharge characteristics of an ac plasma display panel and the surface conductivity of a MgO thin film, we measured the surface current across a ring-shaped MgO film temporally induced by exposure to monochromatic vacuum ultraviolet radiation from a synchrotron radiation source whose wavelength ranges from 60 to 240 nm (5.5−25 eV). The experimental results show that the surface current begins to increase rapidly at a photon energy of about 9 eV which might correspond to the valence band edge of MgO. The differences in the surface current level correlate well with the differences in the preparation method of the MgO films and their respective discharge characteristics, such as firing, minimum sustained voltages, address voltage margins, and address discharge delay times. Surface charge measurements using the linear electro-optic effect also show consistent correlations with the surface current measurement of each MgO sample.
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71.55.Ht Other nonmetals
73.61.Ng Insulators
73.25.+i Surface conductivity and carrier phenomena
52.75.-d Plasma devices
78.20.Jq Electro-optical effects
78.66.Nk Insulators

Characteristics of atmospheric-pressure, radio-frequency glow discharges operated with argon added ethanol

Wen-Ting Sun, Guo Li, He-Ping Li, Cheng-Yu Bao, Hua-Bo Wang, Shi Zeng, Xing Gao, and Hui-Ying Luo

J. Appl. Phys. 101, 123302 (2007); http://dx.doi.org/10.1063/1.2748430 (6 pages) | Cited 4 times

Online Publication Date: 20 June 2007

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Rf, atmospheric-pressure glow discharge (APGD) plasmas with bare metal electrodes have promising prospects in the fields of plasma-aided etching, thin film deposition, disinfection and sterilization, etc. In this paper, the discharge characteristics are presented for the rf APGD plasmas generated with pure argon or argon-ethanol mixture as the plasma-forming gas and using water-cooled, bare copper electrodes. The experimental results show that the breakdown voltage can be reduced significantly when a small amount of ethanol is added into argon, probably due to the fact that the Penning ionization process is involved, and a pure α-mode discharge can be produced more easily with the help of ethanol. The uniformity of the rf APGDs of pure argon or argon-ethanol mixtures using bare metallic electrodes is identified with the aid of the intensified charge coupled device images.
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52.80.Hc Glow; corona
52.80.Pi High-frequency and RF discharges
52.50.Dg Plasma sources
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Carbon dioxide reforming of methane by pulsed glow discharge at atmospheric pressure: The effect of pulse compression

A. M. Ghorbanzadeh and H. Modarresi

J. Appl. Phys. 101, 123303 (2007); http://dx.doi.org/10.1063/1.2745425 (10 pages) | Cited 5 times

Online Publication Date: 20 June 2007

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Methane reforming by carbon dioxide in pulsed glow discharge at atmospheric pressure is examined. The plasma pulse is compressed to less than 50 ns. This compression enables one to work at higher frequencies, over 3 kHz, without glow-arc transition. The main products of the reaction are synthetic gases (H2, CO) and C2 hydrocarbons. Approximately 42% of plasma energy goes to the chemical dissociation, when the reactant ratio is CO2/CH4 = 1. At this point, the energy expense is less than 3.8 eV per converted molecule while reactant conversions are relatively high reaching to 55% (CH4) and 42% (CO2). The reactor energy performance even gets better at higher CO2/CH4 ratios. While energy efficiency reached about 45%, at feed ratio of CO2/CH4 = 5, the conversions of about 65% and 45% were obtained for methane and carbon dioxide, respectively. A model describing dissociation through molecular vibrations is introduced. According to the model, the high nonequilibrium state of vibrational energy at short pulses leads to this improvement, especially in carbon dioxide.
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52.80.Hc Glow; corona
52.77.Fv High-pressure, high-current plasmas (plasma spray, arc welding, etc.)
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Bc State selected dynamics and product distribution
82.20.Hf Product distribution

Cathode sputtering and the resulting formation of carbon nanometer-size dust

C. Dominique and C. Arnas

J. Appl. Phys. 101, 123304 (2007); http://dx.doi.org/10.1063/1.2748365 (8 pages) | Cited 14 times

Online Publication Date: 20 June 2007

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Nanometer-size particles are produced in parallel electrode glow discharges. Supersaturated carbon vapor produced by the sputtering of a graphite cathode is at the origin of their formation. In this context, the energy distribution and the flux of the sputtering particles are estimated. The energy distribution of the emitted carbon atoms is also evaluated as a function of the distance to the cathode, taking into account the collisions with the discharge gas atoms. These collisions induce the carbon vapor cooling and then, a nucleation-condensation phase giving rise to dust precursor clusters. A linear scaling law of growth is established experimentally as a function of time when the dust size is higher than 20 nm. Within the considered time range, this scaling law shows that the growth comes from neutral deposition on the dust surface.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.05.U- Carbon/carbon-based materials

Deviations from the local field approximation in negative streamer heads

Chao Li, W. J. M. Brok, Ute Ebert, and J. J. A. M. van der Mullen

J. Appl. Phys. 101, 123305 (2007); http://dx.doi.org/10.1063/1.2748673 (14 pages) | Cited 26 times

Online Publication Date: 21 June 2007

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Negative streamer ionization fronts in nitrogen under normal conditions are investigated both in a particle model and in a fluid model in local field approximation. The parameter functions for the fluid model are derived from swarm experiments in the particle model. The front structure on the inner scale is investigated in a one-dimensional setting, allowing reasonable run time and memory consumption and high numerical accuracy without introducing superparticles. If the reduced electric field immediately before the front is ⩽ 50 kV/(cm bar), solutions of fluid and particle model agree very well. If the field increases up to 200 kV/(cm bar), the solutions of particle and fluid model deviate, in particular, the ionization level behind the front becomes up to 60% higher in the particle model while the velocity is rather insensitive. Particle and fluid model deviate because electrons with high energies do not yet fully run away from the front, but are somewhat ahead. This leads to increasing ionization rates in the particle model at the very tip of the front. The energy overshoot of electrons in the leading edge of the front actually agrees quantitatively with the energy overshoot in the leading edge of an electron swarm or avalanche in the same electric field.
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52.80.-s Electric discharges
52.25.Jm Ionization of plasmas
52.65.Pp Monte Carlo methods
52.65.Kj Magnetohydrodynamic and fluid equation
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

O2(1Δ) production in high pressure flowing He/O2 plasmas: Scaling and quenching

Natalia Y. Babaeva, Ramesh Arakoni, and Mark J. Kushner

J. Appl. Phys. 101, 123306 (2007); http://dx.doi.org/10.1063/1.2743878 (13 pages) | Cited 4 times

Online Publication Date: 22 June 2007

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Chemical oxygen-iodine lasers (COILs) oscillate on the 2P1/2→2P3/2 transition of atomic iodine at 1.315 μm by a series of excitation transfers from O2(1Δ). In electrically excited COILs (eCOILs), the O2(1Δ) is produced in a flowing plasma, typically He/O2, at a few to tens of Torr. Many system issues motivate operating eCOILs at higher pressures to obtain larger absolute densities of O2(1Δ) for a given yield and to provide higher back pressure for expansion. In this paper, we discuss results from a computational investigation of O2(1Δ) production in flowing plasmas sustained at moderate pressures ( ⩽ 50 Torr). Power deposition and flow rates were scaled such that in the absence of second order effects, yield should be constant and absolute O2(1Δ) production should scale linearly with pressure. We found in many cases that absolute O2(1Δ) production scaled sublinearly with pressure. Ozone is found to be one of the major quenchers of O2(1Δ) and its production increases with pressure. Gas heating also increases with increasing pressure due to exothermic three-body reactions. The gas heating reduces O3 production, increases O3 destruction and, for certain conditions, restores yields. With increasing pressure and increasing absolute densities of atomic oxygen and pooling reactions of O2(1Δ), quenching by these species also becomes important, though the influence of O-atom quenching can be controlled by managing the density of O atoms with additives. The yield of O2(1Δ) is also determined by discharge stability which becomes problematic at higher pressure.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Fi Transport properties
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

A miniature electrothermal thruster using microwave-excited microplasmas: Thrust measurement and its comparison with numerical analysis

Yoshinori Takao, Koji Eriguchi, and Kouichi Ono

J. Appl. Phys. 101, 123307 (2007); http://dx.doi.org/10.1063/1.2749336 (10 pages) | Cited 9 times

Online Publication Date: 26 June 2007

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A microplasma thruster has been developed, consisting of a cylindrical microplasma source 10 mm long and 1.5 mm in inner diameter and a conical micronozzle 1.0–1.4 mm long with a throat of 0.12–0.2 mm in diameter. The feed or propellant gas employed is Ar at pressures of 10–100 kPa, and the surface-wave-excited plasma is established by 4.0 GHz microwaves at powers of <10 W. The thrust has been measured by a combination of target and pendulum methods, exhibiting the performance improved by discharging the plasma. The thrust obtained is 1.4 mN at an Ar gas flow rate of 60 SCCM (1.8 mg/s) and a microwave power of 6 W, giving a specific impulse of 79 s and a thrust efficiency of 8.7%. The thrust and specific impulse are 0.9 mN and 51 s, respectively, in cold-gas operation. A comparison with numerical analysis indicates that the pressure thrust contributes significantly to the total thrust at low gas flow rates, and that the micronozzle tends to have an isothermal wall rather than an adiabatic.
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52.75.Di Ion and plasma propulsion
52.50.Dg Plasma sources
52.80.Pi High-frequency and RF discharges
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma

Modeling plasma actuators with air chemistry for effective flow control

Kunwar Pal Singh and Subrata Roy

J. Appl. Phys. 101, 123308 (2007); http://dx.doi.org/10.1063/1.2749467 (8 pages) | Cited 20 times

Online Publication Date: 29 June 2007

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An asymmetric dielectric barrier discharge model is presented for real gas air chemistry using a self-consistent multibody system of plasma, dielectric, and neutral gas modeled together to predict the electrodynamic force imparted to the working gas. The equations governing the motion of charged and neutral species are solved with Poisson equation using finite element method using a Galerkin weak formulation. Electric field profile changes with the increase in grounded electrode and the density increases downstream. The electrodynamic force development mechanism is studied over a flat plate due to charge and neutral species production from adjacent air in a radio frequency driven barrier discharge. The time average of the force shows mostly acceleration above the actuator. Numerical simulation confirms that the magnitude of force increases very slightly with the increase in the length of grounded electrode.
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52.75.-d Plasma devices
52.30.-q Plasma dynamics and flow
52.25.Fi Transport properties
52.25.Ya Neutrals in plasmas
52.80.Pi High-frequency and RF discharges
07.07.Tw Servo and control equipment; robots
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