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15 Jun 2012

Volume 111, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 111, 123510 (2012); http://dx.doi.org/10.1063/1.4729803 (4 pages)

Sz-Chin Steven Lin, Bernhard R. Tittmann, and Tony Jun Huang
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back to top Lasers, Optics, and Optoelectronics

Thermal lens study of thermo-optical properties and concentration quenching of Er3+-doped lead pyrophosphate-based glasses

C. C. Santos, U. Rocha, I. Guedes, M. V. D. Vermelho, L. A. Boatner, and C. Jacinto

J. Appl. Phys. 111, 123101 (2012); http://dx.doi.org/10.1063/1.4729295 (7 pages) | Cited 1 time

Online Publication Date: 18 June 2012

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In this work, we have used the thermal lens technique combined with conventional spectroscopy to characterize the thermo-optical properties of Er3+-doped lead pyrophosphate-based glasses. More precisely, we have investigated and quantified experimentally the fluorescence quantum efficiencies of the Er3+ levels, and we describe the role of concentration quenching effects. The fluorescence quantum efficiency of the 4I13/2 level is very high when compared to other phosphate glasses, while that of the green-coupled levels is very small. Other important photonic materials parameters, such as the thermal diffusivity and temperature coefficient of the optical path length change, were obtained and compared with those of other glass systems. The cumulative results obtained here for the Er-doped lead pyrophosphate glass show that this material is a good candidate for photonic applications with a characteristic Er3+ infrared emission around 1550 nm.
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81.05.Kf Glasses (including metallic glasses)
66.70.Hk Glasses and polymers
78.20.N- Thermo-optic effects
66.30.Xj Thermal diffusivity
78.55.Hx Other solid inorganic materials

Investigations of Bragg reflectors in nanowire lasers

Guro K. Svendsen, Helge Weman, and Johannes Skaar

J. Appl. Phys. 111, 123102 (2012); http://dx.doi.org/10.1063/1.4729529 (11 pages) | Cited 1 time

Online Publication Date: 18 June 2012

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The reflectivity of various Bragg reflectors in connection to waveguide structures, including nanowires, has been investigated using modal reflection and transmission matrices. A semi-analytical model was applied yielding increased understanding of the diffraction effects present in such gratings. Planar waveguides and nanowire lasers are considered in particular. Two geometries are compared; Bragg reflectors within the waveguides are shown to have significant advantages compared to Bragg reflectors in the substrate, when diffraction effects are significant.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Bh Lenses, prisms and mirrors
42.79.Dj Gratings
42.60.By Design of specific laser systems

Exploration of nano-element array architectures for substrate solar cells using an a-Si:H absorber

Wook Jun Nam, Liming Ji, Vasundara V. Varadan, and Stephen J. Fonash

J. Appl. Phys. 111, 123103 (2012); http://dx.doi.org/10.1063/1.4729539 (6 pages) | Cited 1 time

Online Publication Date: 19 June 2012

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Architectures involving Ag and transparent conducting oxide (TCO) nano-element arrays for light and photocarrier collection management in substrate solar cells are numerically explored and compared. Some architectures with TCO nano-elements are shown to perform better than the best reported Ag arrays and (1) increase JSC at least 57% over that of a planar 200 nm a-Si:H control, (2) attain absorber utilization <7 mg/W, and (3) have only 224 nm as the longest collection length. Photonic effects are the cause of the light trapping enhancement in these devices. While the computations were done for a-Si:H, the insight provided is equally applicable to other absorbers.
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88.40.jj Silicon solar cells

Millisecond annealing for advanced doping of dirty-silicon solar cells

S. Prucnal, B. Abendroth, K. Krockert, K. König, D. Henke, A. Kolitsch, H. J. Möller, and W. Skorupa

J. Appl. Phys. 111, 123104 (2012); http://dx.doi.org/10.1063/1.4729812 (5 pages) | Cited 1 time

Online Publication Date: 19 June 2012

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Cost reduction is the overall goal in the further development of solar cell technologies. Multicrystalline silicon has attracted considerable attention because of its high stability against light soaking. In case of solar grade mc-Si, the rigorous control of metal impurities is desirable for solar cell fabrication. Although ion implantation doping got very recently distinct consideration for doping of monocrystalline solar material, efficient doping of multicrystalline solar material remains the main challenge to reduce costs. The influence of different annealing techniques on the optical and electrical properties of mc-Si solar cells was investigated. Flash lamp annealing (FLA) in the ms-range is demonstrated here as a very promising technique for the emitter formation at an overall low thermal budget. It could be presented that FLA at 1000 °C for 3 ms even without preheating is sufficient to recrystallize implanted silicon. The sheet resistance of FLA samples shows the values of about 50 Ω/sq. Especially, the minority carrier diffusion length for the FLA samples is in the range of 80 μm without surface passivation. This is up to one order of magnitude higher than that observed from rapid thermal annealing or furnace annealing samples. This technology shows great promise to replace the conventional POCl3-doping.
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88.40.jj Silicon solar cells
81.40.Gh Other heat and thermomechanical treatments
88.40.hm Cost of production of solar cells

Visible light emission and energy transfer processes in Sm-doped nitride films

A. R. Zanatta

J. Appl. Phys. 111, 123105 (2012); http://dx.doi.org/10.1063/1.4729911 (8 pages) | Cited 1 time

Online Publication Date: 20 June 2012

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Even though the great interest in studying the near-infrared light emission due to Er3+ ions for telecommunication purposes, efficient visible radiation can be achieved from many different rare-earth (RE) ions. In fact, visible and/or near-infrared light emission takes place in RE-doped wide bandgap semiconductors following either photon or electron excitation, suggesting their technological potential in devices such as light-emitting diodes (LED's) and flat-panel displays, for example. Taking into consideration these aspects, the present contribution reports on the investigation of AlN, BeN, GeN, and SiN thin films doped with samarium. The samples were prepared by sputtering and as a result of the deposition method and conditions they present an amorphous structure and Sm concentrations in the low 0.5 at. %. After deposition, the samples were submitted to thermal annealing treatments and investigated by different spectroscopic techniques. A detailed examination of the experimental data allowed to identify optical transitions due to Sm3+ and Sm2+ ions as well as differences in their mechanisms of photon excitation and recombination. Moreover, it is shown that the Sm-related spectral features and emission intensity are susceptible, respectively, to the atomic environment the Sm3+/Sm2+ ions experience and to the presence of non-radiative recombination centers.
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78.66.Fd III-V semiconductors
81.15.Cd Deposition by sputtering
61.72.uj III-V and II-VI semiconductors
68.55.ag Semiconductors
78.55.Cr III-V semiconductors
78.55.Hx Other solid inorganic materials

Construction of invisibility cloaks of arbitrary shape and size using planar layers of metamaterials

Oliver Paul, Yaroslav Urzhumov, Christoffer Elsen, David Smith, and Marco Rahm

J. Appl. Phys. 111, 123106 (2012); http://dx.doi.org/10.1063/1.4729012 (8 pages)

Online Publication Date: 20 June 2012

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Transformation optics (TO) is a powerful tool for the design of electromagnetic and optical devices with novel functionality derived from the unusual properties of the transformation media. In general, the fabrication of TO media is challenging, requiring spatially varying material properties with both anisotropic electric and magnetic responses. Though metamaterials have been proposed as a path for achieving such complex media, the required properties arising from the most general transformations remain elusive, and cannot implemented by state-of-the-art fabrication techniques. Here, we propose faceted approximations of TO media of arbitrary shape in which the volume of the TO device is divided into flat metamaterial layers. These layers can be readily implemented by standard fabrication and stacking techniques. We illustrate our approximation approach for the specific example of a two-dimensional, omnidirectional “invisibility cloak,” and quantify its performance using the total scattering cross section as a practical figure of merit.
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42.70.-a Optical materials
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.25.Dd Wave propagation in random media

Efficient optical gain media comprising binary blends of poly(3-hexylthiophene) and poly(9,9-dioctylfluorene-co-benzothiadiazole)

R. Xia, P. N. Stavrinou, D. D. C. Bradley, and Y. Kim

J. Appl. Phys. 111, 123107 (2012); http://dx.doi.org/10.1063/1.4730041 (8 pages) | Cited 2 times

Online Publication Date: 21 June 2012

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We report the results of a study of the optical gain properties of binary blend films of regioregular poly(3-hexylthiophene) (RR-P3HT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT). Efficient optical gain is observed in the 10–20 wt. % RR-P3HT composition range and can be tuned to the ∼650 nm window utilised for polymer optical fibre data-communications, with maximum gain ∼50 cm−1. At higher P3HT fractions, gain thresholds increase substantially, consistent with the observed concomitant improvement in photocharge generation. Distributed feed back lasers with one-dimensional gratings exhibit pump pulse thresholds as low as 8 nJ (26 μJ cm−2, 2.17 kW cm−2), lower than many other polymer-based gain media in this wavelength range. They also provide relatively high slope efficiencies >2%. The confluence of efficient optical gain with electronic properties that are conducive to charge carrier injection and transport is relatively novel and is expected to be a necessary requirement for the achievement of electrically pumped lasing.
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42.70.Hj Laser materials
42.70.Jk Polymers and organics
78.66.Qn Polymers; organic compounds

Determination of the melting threshold of TiO2 thin films processed by excimer laser irradiation

O. Van Overschelde, T. Delsate, and R. Snyders

J. Appl. Phys. 111, 123108 (2012); http://dx.doi.org/10.1063/1.4728159 (4 pages) | Cited 1 time

Online Publication Date: 22 June 2012

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Processing surfaces by laser needs an understanding of the mechanisms generated by irradiation. In this work, to gain understanding of the mechanisms occurring during irradiation of TiO2 thin films by means of KrF excimer laser, we have performed infrared time resolved reflectivity measurements. This experimental investigation revealed modifications of the heating/cooling cycle as a function of the fluence (F). These modifications start appearing for a fluence value of about ∼0.25 J/cm2 which is associated with the melting threshold of the film. Additionally, we have solved numerically the heat equation of the system with specific boundary conditions. From these calculations, we have established the thermal history of the film during the 25 ns irradiation pulse. The data reveal that a part of the medium liquefies around a fluence of 0.23 J/cm2 in good agreement with the experimental data.
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64.70.dj Melting of specific substances
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.40.Gh Other heat and thermomechanical treatments
79.20.Ds Laser-beam impact phenomena

A new architecture for solar cells involving a metal bridge deposited between active TiO2 particles

Sahrul Saehana, Pepen Arifin, Khairurrijal, and Mikrajuddin Abdullah

J. Appl. Phys. 111, 123109 (2012); http://dx.doi.org/10.1063/1.4730393 (7 pages) | Cited 1 time

Online Publication Date: 22 June 2012

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The efficiency of titanium dioxide (TiO2)-based film solar cells fabricated by combined spray and electroplating methods was improved by forming metal bridges in the pores between TiO2 nanoparticles. The interfaces between TiO2 nanoparticles and metal bridges formed Schottky contacts, which minimized recombination of electron-hole pairs and increased electron transfer. A maximum efficiency of 4.38% was achieved for cells plated at 50 mA and 55 °C. This efficiency is higher than that reported for solar cells with a similar structure [Saehana et al., AIP Conf. Proc. 1284, 154 (2010); 1415, 163 (2011); IJBAS/IJENS 11, 15 (2011)]. We also identified that both current and temperature influence the morphology of the metal bridges and efficiency of the solar cell.
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88.40.J- Types of solar cells
88.40.hj Efficiency and performance of solar cells

Controlled growth and multi-photon luminescence of hexagonal arrays of Au nanoparticles on anodic aluminum oxide templates

Jian-Bo Li, Ying Yu, Xiao-Niu Peng, Zhong-Jian Yang, Zhang-Kai Zhou, and Li Zhou

J. Appl. Phys. 111, 123110 (2012); http://dx.doi.org/10.1063/1.4730629 (4 pages)

Online Publication Date: 22 June 2012

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Au nanoparticles were deposited onto anodic aluminum oxide (AAO) templates by using a rotating sputtering technique. Interestingly, hexagonal arrays of Au nanoparticles were obtained at an appropriate rotating rate and deposition time. Strong three-photon luminescence was observed from the hexagonally arrayed Au nanoparticles, which is attributed to the strong enhancements of local electromagnetic fields at both excitation and emission wavelengths. Our findings provide a new method to prepare Au nanoparticle arrays with large field enhancements and could have prospective applications in plasmonic nanodevices, such as surface-enhanced Raman scattering substrates, and biosensors.
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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)
78.55.Hx Other solid inorganic materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
81.15.Cd Deposition by sputtering
FREE

Terahertz imaging system using high-Tc superconducting oscillation devices

M. Tsujimoto, H. Minami, K. Delfanazari, M. Sawamura, R. Nakayama, T. Kitamura, T. Yamamoto, T. Kashiwagi, T. Hattori, and K. Kadowaki

J. Appl. Phys. 111, 123111 (2012); http://dx.doi.org/10.1063/1.4729799 (4 pages) | Cited 2 times

Online Publication Date: 22 June 2012

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Microwatt power oscillation devices at sub-terahertz frequency region between 0.3 and 1.0 terahertz (THz) were fabricated from high-Tc superconducting single crystalline Bi2Sr2CaCu2O8+δ and used as a source of the transmission terahertz imaging system. As test examples, terahertz images of coins and a razor blade placed inside the brownish paper envelopes with the spatial resolution of 1 mm are presented. The signal-to-noise ratio exceeds 130 in these images. Using a simple wedge-shaped interferometer and analysing the interference fringe pattern, the wavelength of the terahertz wave is calibrated within 0.1% accuracy. This interferometer also provides a simple method to measure the absorption coefficient of the liquid sample. Two test measurements for distilled water and ethanol are demonstrated and their absorption coefficients are obtained with 99.2% accuracy. This suggests that our terahertz imaging system can be applied to many practical applications, such as biological and biomedical imaging, environmental monitoring, microanalysis of impurities, structure and dynamical analyses of large molecules and ions in solution.
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85.25.Cp Josephson devices
84.40.-x Radiowave and microwave (including millimeter wave) technology

High optical quality polycrystalline indium phosphide grown on metal substrates by metalorganic chemical vapor deposition

Maxwell Zheng, Zhibin Yu, Tae Joon Seok, Yu-Ze Chen, Rehan Kapadia, Kuniharu Takei, Shaul Aloni, Joel W. Ager, Ming Wu, Yu-Lun Chueh, and Ali Javey

J. Appl. Phys. 111, 123112 (2012); http://dx.doi.org/10.1063/1.4730442 (6 pages) | Cited 2 times

Online Publication Date: 25 June 2012

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III–V semiconductor solar cells have demonstrated the highest power conversion efficiencies to date. However, the cost of III-V solar cells has historically been too high to be practical outside of specialty applications. This stems from the cost of raw materials, need for a lattice-matched substrate for single-crystal growth, and complex epitaxial growth processes. To address these challenges, here, we explore the direct non-epitaxial growth of thin poly-crystalline films of III-Vs on metal substrates by using metalorganic chemical vapor deposition. This method minimizes the amount of raw material used while utilizing a low cost substrate. Specifically, we focus on InP which is known to have a low surface recombination velocity of carriers, thereby, making it an ideal candidate for efficient poly-crystalline cells where surface/interface properties at the grain boundaries are critical. The grown InP films are 1-3 μm thick and are composed of micron-sized grains that generally extend from the surface to the Mo substrate. They exhibit similar photoluminescence peak widths and positions as single-crystalline InP, as well as excellent crystallinity as examined through TEM and XRD analyses. This work presents poly-InP as a promising absorber layer for future photovoltaics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors

Franz-Keldysh electro-absorption modulation in germanium-tin alloys

R. A. Soref, G. Sun, and H. H. Cheng

J. Appl. Phys. 111, 123113 (2012); http://dx.doi.org/10.1063/1.4730404 (7 pages) | Cited 1 time

Online Publication Date: 26 June 2012

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The direct-bandgap Franz-Keldysh theory has been applied to relaxed crystalline Ge1-xSnx alloys for 0 ≤ x ≤ 0.1 taking into account the light- and heavy-hole contributions. For electro-absorption modulation, the change-in-absorption spectrum Δα(ω, ɛ) was calculated for an applied electric field ɛ of 33 to 100 kV/cm using a B parameter determined by curve-fitting the zero-field absorption spectrum α(ω, ɛ) for each alloy. At a photon energy ∼10 meV below the gap, it was found that the figure of merit Δα(ω, ɛ)/α(ω, 0) ranged from 0.4 to 1.0 for 2% Sn, 0.5 to 1.2 for 5% Sn, 0.6 to 1.4 for 7.5% Sn, and 0.7 to 1.6 for 10% Sn. For a figure of merit ∼1, the waveguided resonant low-Q GeSn microdisk-and-bus modulator is expected to give a higher on/off contrast ratio than the non-resonant GeSn channel waveguide modulator.
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78.20.Jq Electro-optical effects

Modal approach for tailoring the absorption in a photonic crystal membrane

Romain Peretti, Guillaume Gomard, Christian Seassal, Xavier Letartre, and Emmanuel Drouard

J. Appl. Phys. 111, 123114 (2012); http://dx.doi.org/10.1063/1.4730443 (7 pages) | Cited 1 time

Online Publication Date: 26 June 2012

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In this paper, we propose a method for tailoring the absorption in a photonic crystal membrane. For that purpose, we first applied time domain coupled mode theory to such a subwavelength membrane and demonstrated that 100% resonant absorption can be reached even for a symmetric membrane, if degenerate modes are involved. Design rules were then derived from this model in order to tune the absorption. Subsequently, finite difference time domain simulations were used as a proof of concept and carried out on a low absorbing material (extinction coefficient = 10−2) with a high refractive index corresponding to the optical indices of amorphous silicon at around 720 nm. In doing so, 85% resonant absorption was obtained, which is significantly higher than the commonly reported 50% maximum value. Those results were finally analyzed and confronted to theory so as to extend our method to other materials, configurations and applications.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Am Elemental semiconductors and insulators
78.40.Fy Semiconductors

Simulation of trap-assisted tunneling effect on characteristics of gallium nitride diodes

Konrad Sakowski, Leszek Marcinkowski, Stanislaw Krukowski, Szymon Grzanka, and Elzbieta Litwin-Staszewska

J. Appl. Phys. 111, 123115 (2012); http://dx.doi.org/10.1063/1.4730772 (7 pages)

Online Publication Date: 27 June 2012

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In this paper, simulations of I-V characteristics and band structures of magnesium and silicon doped gallium nitride diodes are presented. The numerical algorithm is based on the drift-diffusion semi-classic model, with the van Roosbroeck differential equation system involved. The model accounts for trap-assisted tunneling, which provides better agreement between the predicted and experimental I-V characteristics of p-n junctions in the low-bias range. We have performed one-dimensional simulations of devices. We compare the results with the results obtained from the standard drift-diffusion model. It is shown that taking the trap-assisted tunneling into account leads to good agreement with experimental data. We also demonstrate that a high doping of the p-n junctions may significantly increase the nonradiative recombination rate due to the prescribed effect.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.De Semiconductor-device characterization, design, and modeling

Shift of indirect to direct bandgap and optical response of LaAlO3 under pressure

G. Murtaza and Iftikhar Ahmad

J. Appl. Phys. 111, 123116 (2012); http://dx.doi.org/10.1063/1.4729264 (8 pages) | Cited 2 times

Online Publication Date: 28 June 2012

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The structural and optoelectronic properties of LaAlO3 under pressure have been investigated for the first time using the highly accurate all electrons full potential linearized augmented plane wave method. The calculated lattice parameter at zero pressure is found in excellent agreement with the experimental results. Furthermore, with the increase in the external pressure, the lattice constant as well as bonds length decreases in accordance with the experimental results. The compound at zero pressure is an indirect bandgap semiconductor, while interestingly the indirect nature shifts to direct one with the increase of the pressure. The bonding in the material is of mixed covalent and ionic nature. In optical properties, frequency dependent parameters such as real and imaginary parts of dielectric function, refractive index, reflectivity, optical conductivity, absorption coefficient, and sumrules are calculated under pressure.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.50.Lt Crystal binding; cohesive energy
61.66.Fn Inorganic compounds
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.20.Ps Other inorganic compounds

Complete polarization analysis of high energy soft x-rays by combining a multilayer phase retarder with crystal analyzer

H. Wang, S. S. Dhesi, F. Maccherozzi, and K. J. S. Sawhney

J. Appl. Phys. 111, 123117 (2012); http://dx.doi.org/10.1063/1.4730899 (4 pages) | Cited 2 times

Online Publication Date: 29 June 2012

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We demonstrate a complete polarization analysis of soft x-rays with an energy of 1.1 keV using a free-standing W/B4C multilayer phase retarders and a beryl crystal analyzer. The W/B4C multilayer exhibits five times increase in transmission over that previously reported. The beryl crystal proves to be a suitable analyzer for the polarization analysis with a 10% s-component of reflectivity resulting in an extinction ratio close to 0.002 at 1.1 keV. The combination of multilayer phase retarders and crystal analyzers should open up the field of the soft x-ray polarization analysis in the energy range between 1 keV and 2 keV.
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07.85.-m X- and γ-ray instruments
back to top Plasmas and Electrical Discharges

Molecular dynamics simulation of Si nanoclusters in high rate and low temperature epitaxy

L. W. Chen, Y. Shibuta, M. Kambara, and T. Yoshida

J. Appl. Phys. 111, 123301 (2012); http://dx.doi.org/10.1063/1.4729057 (6 pages) | Cited 2 times

Online Publication Date: 19 June 2012

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Si nanocluster formation during rapid cooling from high temperature Si vapors and its subsequent interaction with substrate was simulated by molecular dynamics. It was confirmed that several nm sized clusters with a loosely bound structure form during rapid cooling and their metastable structures are retained even at temperatures below the Si melting point. Such globular clusters tend to rearrange themselves upon impingement to be a similar structure to that of the substrate, at least near the cluster/substrate interface. This is suggestive of the role of clusters formed under the mesoplasma condition as growth precursors for fast rate epitaxy.
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81.16.-c Methods of micro- and nanofabrication and processing
64.70.dj Melting of specific substances
52.77.-j Plasma applications
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Plasma-wall interaction in Hall thrusters with magnetic lens configuration

Lubos Brieda and Michael Keidar

J. Appl. Phys. 111, 123302 (2012); http://dx.doi.org/10.1063/1.4730340 (8 pages)

Online Publication Date: 21 June 2012

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Some recently developed Hall thrusters utilize a magnetic field configuration in which the field lines penetrate the thruster walls at a high incidence angle. This so-called magnetic lens leads to an electric field pointing away from the walls, which is expected to reduce ion losses and improve thruster efficiency. This configuration also introduces an interesting behavior in the sheath formation. At sufficiently large angles, ions are repelled from the wall, and sheath collapse is expected. We use a plasma simulation code to investigate this phenomenon in detail. We consider the role of the magnetic field incidence angle, secondary electron emission, and a magnetic mirror. Numerical study confirms the theoretical predictions, and at large angles, ions are seen to turn away from the wall. We also consider the role of the magnetic field geometry on ion wall flux and channel erosion, and observe reduction in both quantities as the magnetic field incidence angle is increased.
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28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.40.Kh Plasma sheaths
52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.40.Hf Plasma-material interactions; boundary layer effects

Conductivity of nanosecond discharges in nitrogen and sulfur hexafluoride studied by particle-in-cell simulations

D. Levko, V. Tz. Gurovich, and Ya. E. Krasik

J. Appl. Phys. 111, 123303 (2012); http://dx.doi.org/10.1063/1.4730373 (4 pages) | Cited 1 time

Online Publication Date: 22 June 2012

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The conductivity of the discharge gap during the nanosecond high-voltage pulsed discharge in nitrogen and sulfur hexafluoride is studied using particle-in-cell numerical simulations. It is shown that the conductivity in different locations of the cathode-anode gap is not uniform and that the conductivity is determined by both the runaway and the plasma electrons. In addition, it is shown that runaway electrons generated prior to the virtual cathode formation pre-ionize the discharge gap, which makes it conductive.
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52.25.Fi Transport properties
52.25.Jm Ionization of plasmas
52.80.-s Electric discharges
02.60.Cb Numerical simulation; solution of equations
52.65.Rr Particle-in-cell method

Angular emission of ions and mass deposition from femtosecond and nanosecond laser-produced plasmas

B. Verhoff, S. S. Harilal, and A. Hassanein

J. Appl. Phys. 111, 123304 (2012); http://dx.doi.org/10.1063/1.4730444 (7 pages) | Cited 1 time

Online Publication Date: 25 June 2012

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We investigated the angular distribution of ions and atoms emanating from femto- and nanosecond laser-produced metal plasmas under similar laser fluence conditions. For producing plasmas, aluminum targets are ablated in vacuum employing pulses from a Ti:Sapphire ultrafast laser (40 fs, 800 nm) and an Nd:YAG laser (6 ns, 1064 nm). The angular distribution of ion emission as well as the kinetic energy distribution is characterized by a Faraday cup, while a quartz microbalance is used for evaluating deposited mass. The ion and deposited mass features showed that fs laser ablated plasmas produced higher kinetic energy and more mass per pulse than ns plumes over all angles. The ion flux and kinetic energy studies show fs laser plasmas produce narrower angular distribution while ns laser plasmas provide narrower energy distribution.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.38.Mf Laser ablation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Assessment of the roles of various inactivation agents in an argon-based direct current atmospheric pressure cold plasma jet

Qian Zhang, Peng Sun, Hongqing Feng, Ruixue Wang, Yongdong Liang, Weidong Zhu, Kurt H. Becker, Jue Zhang, and Jing Fang

J. Appl. Phys. 111, 123305 (2012); http://dx.doi.org/10.1063/1.4730627 (6 pages) | Cited 1 time

Online Publication Date: 26 June 2012

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Three types of gases, pure argon (99.999%), argon with 2% oxygen, and argon with 2% oxygen and 10% nitrogen were used as operating gases of a direct current atmospheric pressure cold plasma jet to inactivate Staphylococcus aureus (S. aureus) suspended in a liquid. The inactivation efficacies for the plasma jets operating in the three gases decrease from Ar/O2(2%) to Ar/O2(2%)/N2(10%) to pure Ar. Optical emission spectroscopy, electron spin resonance spectroscopy, high performance liquid chromatography, and atomic absorption spectrophotometry were employed to identify and monitor the reactive species in the plasma-liquid system for the three operating gases and revealed the presence of O, 1O2, OH, NO, H2O2, O3, and NO3−/NO2− as well as Cu+/Cu2+. The S. aureus inactivation results indicate that atomic oxygen (O) is the key inactivation agent, while other species play a lesser role in the inactivation progress studied here.
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87.15.M- Spectra of biomolecules
87.15.R- Reactions and kinetics
52.77.Fv High-pressure, high-current plasmas (plasma spray, arc welding, etc.)
82.70.Kj Emulsions and suspensions
82.80.Bg Chromatography
82.80.Dx Analytical methods involving electronic spectroscopy

Rapid calculation of the ion energy distribution on a plasma electrode

Paola Diomede, Demetre J. Economou, and Vincent M. Donnelly

J. Appl. Phys. 111, 123306 (2012); http://dx.doi.org/10.1063/1.4728997 (9 pages) | Cited 1 time

Online Publication Date: 27 June 2012

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A model was developed to rapidly calculate the ion energy distribution (IED) on an electrode immersed in plasma, for a given voltage waveform applied to the electrode through a blocking capacitor. The model combined an equivalent circuit representation of the system, with an equation for a damped potential to which ions respond, during their transit through the sheath. Predicted IEDs on both conducting and insulating surfaces for a variety of applied voltage waveforms (spike, staircase, square wave, etc.) agreed with published experimental data. For these comparisons with experiments, peak broadening due to the resolution of the ion energy analyzer was also taken into account. Using “tailored” waveforms of the applied voltage, desired IEDs may be obtained in terms of peak energies and fraction of ions under each peak.
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52.59.Mv High-voltage diodes
52.65.Pp Monte Carlo methods
52.65.Rr Particle-in-cell method
52.77.Bn Etching and cleaning
52.40.Kh Plasma sheaths
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Thermochemical modeling of temperature controlled shock-induced chemical reactions in multifunctional energetic structural materials under shock compression

X. F. Zhang, A. S. Shi, J. Zhang, L. Qiao, Y. He, and Z. W. Guan

J. Appl. Phys. 111, 123501 (2012); http://dx.doi.org/10.1063/1.4729048 (9 pages) | Cited 3 times

Online Publication Date: 18 June 2012

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Multifunctional energetic structural materials (MESMs) are a new class of energetic materials which release energy due to exothermic chemical reactions initiated under shock loading conditions. In order to analyze shock-induced chemical reactions (SICR) for MESMs, theoretical models have been developed to calculate the Hugoniot data which include the heat released by shock temperature controlled reactions. The temperature rise of porous materials due to shock compression is first calculated using a constant volume and pressure adjustment. Then the Arrhenius reaction rate and Avrami-Erofeev kinetic models are used to calculate the extent of reaction of MESMs under shock compression. Thermochemical models for shock-induced reactions, in which the reaction efficiency is considered, are given by combining the shock temperature rise with the chemical reaction kinetics. The Hugoniot relations and temperatures are calculated by using the proposed method. The models developed have been validated against the experimental SICR data involving Fe2O3/Al, Al/Ni, and Ti/Ni mixtures. It has been shown that the theoretical calculations correlate reasonably well with the corresponding experimental and simulation results. The models presented can be used to predict the reaction results of MESMs over a wide range of pressure satisfactorily.
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82.30.-b Specific chemical reactions; reaction mechanisms
82.33.Vx Reactions in flames, combustion, and explosions
64.75.Ef Mixing
61.43.Gt Powders, porous materials

Superfluid ultra-dense deuterium D(−1) on polymer surfaces: Structure and density changes at a polymer-metal boundary

Frans Olofson and Leif Holmlid

J. Appl. Phys. 111, 123502 (2012); http://dx.doi.org/10.1063/1.4729078 (7 pages) | Cited 1 time

Online Publication Date: 18 June 2012

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Ultra-dense deuterium D(−1) with D-D bond distance 2.3 pm is the first ultra-dense material studied. It is a superfluid quantum material and may also be superconductive. Its interaction with metal and polymer surfaces is of immediate interest. D(−1) exists on organic polymer surfaces like (poly(methyl methacrylate)) PMMA even at a distance of a few millimeter from a metal in contact with the polymer. The density of D(−1) decreases from the metal surface to the open polymer surface, and is to some extent replaced by D(1) on the polymer surface. At low surface density of D(−1), the long chain-clusters appear to lie parallel the surface, while at large densities the clusters stand vertical to the surface. Various polymers give different structures of D(−1), for example fewer non-superfluid clusters D4 are observed on fluorocarbon surfaces relative to hydrogen containing polymers. Isotope exchange reactions in four-atom clusters are probably observed between deuterium in D(−1) and protium atoms in the hydrogenated polymer surface.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
05.30.-d Quantum statistical mechanics
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
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