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1 Oct 2009

Volume 106, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 106, 071101 (2009); http://dx.doi.org/10.1063/1.3216464 (13 pages)

M. D. McCluskey and S. J. Jokela
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Defects in ZnO

M. D. McCluskey and S. J. Jokela

J. Appl. Phys. 106, 071101 (2009); http://dx.doi.org/10.1063/1.3216464 (13 pages) | Cited 98 times

Online Publication Date: 5 October 2009

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Zinc oxide (ZnO) is a wide band gap semiconductor with potential applications in optoelectronics, transparent electronics, and spintronics. The high efficiency of UV emission in this material could be harnessed in solid-state white lighting devices. The problem of defects, in particular, acceptor dopants, remains a key challenge. In this review, defects in ZnO are discussed, with an emphasis on the physical properties of point defects in bulk crystals. As grown, ZnO is usually n-type, a property that was historically ascribed to native defects. However, experiments and theory have shown that O vacancies are deep donors, while Zn interstitials are too mobile to be stable at room temperature. Group-III (B, Al, Ga, and In) and H impurities account for most of the n-type conductivity in ZnO samples. Interstitial H donors have been observed with IR spectroscopy, while substitutional H donors have been predicted from first-principles calculations but not observed directly. Despite numerous reports, reliable p-type conductivity has not been achieved. Ferromagnetism is complicated by the presence of secondary phases, grain boundaries, and native defects. The famous green luminescence has several possible origins, including Cu impurities and Zn vacancies. The properties of group-I (Cu, Li, and Na) and group-V (N, P, As, and Sb) acceptors, and their complexes with H, are discussed. In the future, doping of ZnO nanocrystals will rely on an understanding of these fundamental properties.
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71.55.Gs II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
61.72.jj Interstitials
61.72.jd Vacancies
61.72.Mm Grain and twin boundaries
75.50.Dd Nonmetallic ferromagnetic materials
72.20.Fr Low-field transport and mobility; piezoresistance
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Advanced optical magnetic nanostructures fabricated by anodic aluminum oxide membranes and magnetic fluids

Ziyun Di, Xianfeng Chen, and Dongchen Zhang

J. Appl. Phys. 106, 073101 (2009); http://dx.doi.org/10.1063/1.3226861 (4 pages)

Online Publication Date: 2 October 2009

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Optical magnetic nanostructures, based on anodic aluminum oxide membranes and magnetic fluids, were fabricated and investigated in both transmission and magneto-optical properties. A strong enhancement in transmission property has been found compared with the traditional magnetic fluids. Excellent magneto-optical characteristic was obtained: a negative differential magnetic linear dichroism was observed, quite different from the traditional Langevin type of magnetic fluids. This phenomenon was interpreted by an antiferromagnetic coupling between two types of magnetic grains having different average diameters in the nanocomposites. Based on its outstanding magneto-optical effects, it may open potentials for future integral optical devices.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
78.20.Ls Magneto-optical effects
75.50.Mm Magnetic liquids
81.07.-b Nanoscale materials and structures: fabrication and characterization

Analysis of 1.2 μm InGaAs/GaAs quantum dot laser for high power applications

Q. Jiang, Z. Y. Zhang, D. T. D. Childs, and R. A. Hogg

J. Appl. Phys. 106, 073102 (2009); http://dx.doi.org/10.1063/1.3204660 (6 pages) | Cited 3 times

Online Publication Date: 5 October 2009

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The effect of modulation p-doping on the characteristics of 1.2 μm quantum dot lasers is reported. Compared to undoped devices, p-doped are shown to exhibit higher saturated gain, higher internal efficiency, improved T0, lower excited state lasing current densities, and higher internal loss. Both types of the device are analyzed with regard to high power applications in the extreme cases of complete and nonexistent gain clamping. Results from a laser optimized to have minimal threshold current are discussed.
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42.55.Px Semiconductor lasers; laser diodes
78.66.Fd III-V semiconductors
42.60.By Design of specific laser systems

Absorption coefficients of intermediate-band media

Michael Y. Levy and Christiana Honsberg

J. Appl. Phys. 106, 073103 (2009); http://dx.doi.org/10.1063/1.3213337 (12 pages) | Cited 4 times

Online Publication Date: 6 October 2009

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This paper models the absorption coefficients of an intermediate-band (IB) absorbing medium. Equilibrium absorption coefficients are presented for several IB absorbers, each distinguished by their energy-wavevector dispersion and equilibrium temperature. Nonequilibrium absorption coefficients are also presented for solar cells implemented with IB absorbers. Several simplifying assumptions are made including that the energy-wavevector dispersions are parabolic. The model requires the absolute locations of three quasi-Fermi levels. This is made possible by using two balance equations. One of these, a charge-neutrality condition, necessitates the numerical computation of the carrier statistics in each band of the IB absorber. The use of the incomplete Fermi–Dirac functions makes this possible. The authors conclude that (i) if the concentration of intermediate states is greater than the concentration of carriers in the conduction band and greater than the concentration of carriers in the valence band, then the IB will be partially filled; (ii) an IB absorber may or may not absorb all photons with energies greater than the smallest bandgap in the system; (iii) an IB absorber may permit absorption overlap so that an absorbed photon would likely generate an electron-hole pair across a bandgap other than the largest bandgap less than the energy of the absorbed photon; (iv) as the temperature of the IB absorber approaches absolute zero, the absorption edges resulting from transitions at intermediate levels may blueshift.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.-b Electron density of states and band structure of crystalline solids
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Plasmon-induced terahertz radiation generation due to symmetry breaking in a nonlinear metallic nanodimer

A. A. Zharov, R. E. Noskov, and M. V. Tsarev

J. Appl. Phys. 106, 073104 (2009); http://dx.doi.org/10.1063/1.3225606 (5 pages) | Cited 4 times

Online Publication Date: 7 October 2009

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We suggest an alternative way of terahertz radiation generation utilizing the effect of spontaneous symmetry breaking in a nonlinear metallic nanodimer illuminated by light. We show that the symmetry breaking is caused by instability of plasmon eigenmodes of the system and can lead either to spontaneous magnetization of the dimer or to a periodic self-modulation regime of light scattering. We find that the modulation frequency lies in the terahertz band and may be tuned within a wide range.
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78.66.Bz Metals and metallic alloys
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
42.79.Hp Optical processors, correlators, and modulators

Thermomechanical model for the plastic deformation in high power laser diodes during operation

A. Martín-Martín, M. Avella, M. P. Iñiguez, J. Jiménez, M. Oudart, and J. Nagle

J. Appl. Phys. 106, 073105 (2009); http://dx.doi.org/10.1063/1.3236507 (8 pages) | Cited 1 time

Online Publication Date: 8 October 2009

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A thermomechanical model for the mechanism of rapid degradation of AlGaAs based high power laser bars (808 nm) is presented. Thermal stresses induced in the device by local heating around a facet defect by nonradiative recombination and self-absorption of photons are calculated, as well as the conditions for the beginning of plastic deformation, when these thermal stresses overcome the yield strength. The values of the power density and of the local temperature at which the yield limit is surmounted are in agreement with the threshold values for the degradation of Al based lasers given in the literature. The present model can also elucidate the role played by the packaging stress, being able to explain how this stress reduces the optical power density threshold for failure of these lasers.
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42.55.Px Semiconductor lasers; laser diodes
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
62.20.fq Plasticity and superplasticity

Tuning the emission profiles of various self-assembled InxGa1−xAs nanostructures by rapid thermal annealing

Jihoon H. Lee, Zhiming M. Wang, Vitaliy G. Dorogan, Yuiry I. Mazur, Morgan E. Ware, and Gregory J. Salamo

J. Appl. Phys. 106, 073106 (2009); http://dx.doi.org/10.1063/1.3213095 (6 pages) | Cited 6 times

Online Publication Date: 9 October 2009

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Tuning the emission profiles of various novel InxGa1−xAs nanostructures, such as quantum rods, quantum dot pairs (QDPs), bridged QDPs, dimpled quantum dots (QDs), and low-temperature-capped QDs, is demonstrated by postgrowth rapid thermal annealing. Specifically, improved optical properties, such as a much narrower full width at half maximum of 16 meV and a continuous blueshift, are demonstrated. The enhanced optical properties are attributed to the interchange of In and Ga atoms induced by both defect-assisted intermixing and strain-assisted intermixing. These results can find applications as an optical enhancement in nanostructures is critical for the improvements on device functionality.
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78.67.Hc Quantum dots
81.16.Dn Self-assembly
61.72.Cc Kinetics of defect formation and annealing
78.55.Cr III-V semiconductors

Near-field wire-based passive probe antenna for the selective detection of the longitudinal electric field at terahertz frequencies

Ronan Adam, Laurent Chusseau, Thierry Grosjean, Annick Penarier, Jean-Paul Guillet, and Daniel Charraut

J. Appl. Phys. 106, 073107 (2009); http://dx.doi.org/10.1063/1.3236665 (7 pages) | Cited 5 times

Online Publication Date: 12 October 2009

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A passive probe antenna for cw near-field microscopy at millimeter and submillimeter wavelengths is defined. It is based on the coupling between a free-space linearly polarized propagating beam to a wire mode. This is obtained efficiently owing to a discontinuous phase plate. This passive “optical” structure allows either the generation of a subwavelength confinement of the longitudinal electric field (polarized along the wire antenna) or, due to reciprocity, the collection of the longitudinal component of the electric field (along the wire antenna) with subwavelength resolution. The emission and collection properties of the proposed antenna have been demonstrated experimentally using a preliminary realization designed to work at 0.1 THz. Experimental results are well supported by calculations.
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07.79.Fc Near-field scanning optical microscopes

Numerical simulation of laser-generated Lamb waves in viscoelastic materials by finite element method

Hongxiang Sun, Baiqiang Xu, and Rongzu Qian

J. Appl. Phys. 106, 073108 (2009); http://dx.doi.org/10.1063/1.3238247 (6 pages) | Cited 2 times

Online Publication Date: 12 October 2009

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The effect of material viscoelasticity on the propagation of Lamb wave in a viscoelastic thin plate has been investigated quantitatively. Based on the plane strain theory, a numerical model of the laser-generated Lamb wave is developed in the frequency domain by using the finite element (FE) method. To verify the correctness of the FE model in the frequency domain, a classical FE model in the time domain is established for an elastic plate. The transient waveforms calculated in the frequency domain are in very good agreement with those obtained in the time domain. And then, the laser-generated Lamb waves in the elastic and viscoelastic thin plates are calculated, respectively. By comparing the waveforms of Lamb wave in the two plates, the influence of the material viscoelasticity on the propagation of Lamb waves is studied. Moreover, the effect of the material viscoelastic rate on Lamb waves is analyzed in detail.
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43.35.Pt Surface waves in solids and liquids
46.35.+z Viscoelasticity, plasticity, viscoplasticity

Plasmonic absorption enhancement in organic solar cells with thin active layers

Honghui Shen, Peter Bienstman, and Bjorn Maes

J. Appl. Phys. 106, 073109 (2009); http://dx.doi.org/10.1063/1.3243163 (5 pages) | Cited 27 times

Online Publication Date: 13 October 2009

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The influence of silver nanoparticles on light absorption in organic solar cells based on poly(3-exylthiophene):(6,6)-phenyl-C61-butyric-acid-methyl ester is studied by means of finite element method simulations. The metallic nanoparticles are embedded directly inside the active layer. We investigate the enhancement mechanism and the influence of factors such as the spacing between neighboring nanoparticles, the particle diameter, and the coating thickness. The plasmonic resonance of the particles has a wideband influence on the absorption, and we observe a rich interaction between plasmonic enhancement and the absorption characteristics of the active layer material. An enhancement with a factor of around 1.56 is observed for nanoparticles with a diameter of 24 nm and a spacing of 40 nm, bringing the structure to the absorption level of much thicker active layers without nanoparticles. In addition, a significant effect of the particle coating thickness is observed.
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84.60.Jt Photoelectric conversion
73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Dielectric function of hydrogenated amorphous silicon near the optical absorption edge

E. Malainho, M. I. Vasilevskiy, P. Alpuim, and S. A. Filonovich

J. Appl. Phys. 106, 073110 (2009); http://dx.doi.org/10.1063/1.3240203 (9 pages) | Cited 3 times

Online Publication Date: 14 October 2009

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We report the results of the optical spectra modeling for hydrogenated amorphous silicon (a-Si:H) thin films produced for photovoltaic cell applications, which allowed us to accurately determine the material’s optical gap (Eg). While for thick films of a-Si:H, as well as for other amorphous semiconductors, Eg is normally estimated from a so called Tauc plot, this is hardly possible for thin films because of the interference effects. We developed a physically founded semianalytical model for the complex dielectric function of a-Si:H, valid below and above the optical gap and containing a small number of adjustable meaningful parameters, including Eg and the characteristic energy scales of the optical transition matrix element distribution and the joint density of states in the absorption tail region. With this model and using the transfer matrix formalism for multilayer optics, we have achieved a good agreement between the calculated and experimental transmittance spectra, which allowed us to self-consistently determine the values of the above parameters. We found that both Eg and the characteristic scale of the subgap absorption tail increase with the hydrogen addition. We have also determined the absorption rate spectra of the films, relevant to any optical spectroscopy of subgap states, such as the photothermal deflection spectroscopy and constant photocurrent measurements.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Jg Amorphous semiconductors; glasses
81.05.Gc Amorphous semiconductors
73.50.Pz Photoconduction and photovoltaic effects
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
84.60.Jt Photoelectric conversion
78.66.Db Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors

Optical description of solid-state dye-sensitized solar cells. I. Measurement of layer optical properties

Adam J. Moulé, Henry J. Snaith, Markus Kaiser, Heike Klesper, David M. Huang, Michael Grätzel, and Klaus Meerholz

J. Appl. Phys. 106, 073111 (2009); http://dx.doi.org/10.1063/1.3204982 (9 pages) | Cited 7 times

Online Publication Date: 14 October 2009

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The efficiency of a photovoltaic device is limited by the portion of solar energy that can be captured. We discuss how to measure the optical properties of the various layers in solid-state dye-sensitized solar cells (SDSC). We use spectroscopic ellipsometry to determine the complex refractive index of each of the various layers in a SDSC. Each of the ellipsometry fits is used to calculate a transmission spectrum that is compared to a measured transmission spectrum. The complexities of pore filling on the fitting of the ellipsometric data are discussed. Scanning electron microscopy and energy dispersive x-ray spectroscopy is shown to be an effective method for determining pore filling in SDSC layers. Accurate effective medium optical constants for each layer are presented and the material limits under which these optical constants can be used are discussed.
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84.60.Jt Photoelectric conversion
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Optical description of solid-state dye-sensitized solar cells. II. Device optical modeling with implications for improving efficiency

David M. Huang, Henry J. Snaith, Michael Grätzel, Klaus Meerholz, and Adam J. Moulé

J. Appl. Phys. 106, 073112 (2009); http://dx.doi.org/10.1063/1.3204985 (6 pages) | Cited 2 times

Online Publication Date: 14 October 2009

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We use the optical transfer-matrix method to quantify the spatial distribution of light in solid-state dye-sensitized solar cells (DSCs), employing material optical properties measured experimentally in the accompanying article (Part I) as input into the optical model. By comparing the optical modeling results with experimental photovoltaic action spectra for solid-state DSCs containing either a ruthenium-based dye or an organic indoline-based dye, we show that the internal quantum efficiency (IQE) of the devices for both dyes is around 60% for almost all wavelengths, substantially lower than the almost 100% IQE measured for liquid DSCs, indicating substantial electrical losses in solid-state DSCs that can account for much of the current factor-of-two difference between the efficiencies of liquid and solid-state DSCs. The model calculations also demonstrate significant optical losses due to absorption by 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene (spiro-OMeTAD) and TiO2 in the blue and to a lesser extent throughout the visible. As a consequence, the more absorptive organic dye, D149, should outperform the standard ruthenium complex sensitizer, Z907, for all device thicknesses, underlining the potential benefits of high extinction coefficient dyes optimized for solid-state DSC operation.
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84.60.Jt Photoelectric conversion
42.30.Lr Modulation and optical transfer functions
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Electron beam and plasma modes of a channel spark discharge operation

S. Gleizer, D. Yarmolich, J. Felsteiner, Ya. E. Krasik, P. Nozar, and C. Taliani

J. Appl. Phys. 106, 073301 (2009); http://dx.doi.org/10.1063/1.3234376 (10 pages) | Cited 1 time

Online Publication Date: 1 October 2009

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Parameters of a modified pulsed channel spark discharge (CSD), operating at a repetition rate up to 100 Hz at Ar gas pressures of 10−3 and 10−4 Torr and of the generated electron beam, were studied using different electrical, optical, and x-ray diagnostics. It was shown that efficient (up to ∼ 74%) transfer of the initially stored energy to the energetic electron beam is realized only at the pressure of 10−4 Torr. Conversely, at the pressure of 10−3 Torr, less than 10% of the stored energy is acquired by the energetic electrons. It was found that the energetic electron beam generation is limited by the expansion of the cathode and anode plasmas and by the formation of plasma inside the gap between the CSD capillary output and the anode. It was also found that the plasma, which acquires the hollow cathode potential, is already formed at the beginning of the CSD operation inside the capillary, and the electron emission occurs from the capillary output plasma boundary. Finally, it was shown that the electron beam energy spectrum differs significantly from the energy spectrum, which one may expect in the case of the planar diode operation.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.70.La X-ray and γ-ray measurements
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.70.Ds Electric and magnetic measurements

Absolute nitrogen atom density measurements by two-photon laser-induced fluorescence spectroscopy in atmospheric pressure dielectric barrier discharges of pure nitrogen

Et-Touhami Es-Sebbar, Christian Sarra-Bournet, Nicolas Naudé, Françoise Massines, and Nicolas Gherardi

J. Appl. Phys. 106, 073302 (2009); http://dx.doi.org/10.1063/1.3225569 (7 pages) | Cited 6 times

Online Publication Date: 7 October 2009

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In this paper, two-photon absorption laser induced fluorescence spectroscopy is used to follow the nitrogen atom density in flowing dielectric barrier discharges fed with pure nitrogen and operating at atmospheric pressure. Two different dielectric barrier discharge regimes are investigated: the Townsend regime, which is homogeneous although operating at atmospheric pressure, and the more common filamentary regime. In both regimes, densities as high as 3×1014/cm3 are detected. However, the N atoms kinetic formation depends on the discharge regime. The saturation level is reached more rapidly with a filamentary discharge. For a given discharge regime, the N atom density depends strongly on the energy dissipated in the plasma between the gas inlet and the measurement position, whether the energy is varied by varying the position of the measurements, the gas flow, or the dissipated power. Experiments performed in the postdischarge show that the N atom decay cannot be simply attributed to three-body recombination of atomic nitrogen with nitrogen molecules, meaning that other mechanisms such as surface recombination or gas impurities play a role.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Dy Low-field and Townsend discharges
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.40.Hf Plasma-material interactions; boundary layer effects
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Vy Impurities in plasmas

Accurate control of ion bombardment in remote plasmas using pulse-shaped biasing

P. Kudlacek, R. F. Rumphorst, and M. C. M. van de Sanden

J. Appl. Phys. 106, 073303 (2009); http://dx.doi.org/10.1063/1.3225690 (8 pages) | Cited 11 times

Online Publication Date: 7 October 2009

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This paper deals with a pulsed biasing technique employed to a downstream expanding thermal plasma. Two pulsed biasing approaches are presented: asymmetric rectangular pulses and modulated pulses with a linear voltage slope during the pulse, and their applicability is discussed on the basis of the intrinsic capacitance of the processed substrate-layer system. The substrate voltage and current waveforms are measured, and the relation to the obtained ion energy distributions is discussed. Accurate control of the ion bombardment is demonstrated for both aforementioned cases, and the cause of broadening of the peaks in the ion energy spectra is determined as well. Moreover, several methods to determine the modulated pulse duration, such that the sloping voltage exactly compensates for the drop of the substrate sheath potential due to charging, are presented and their accuracy is discussed.
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52.77.Dq Plasma-based ion implantation and deposition

Influence of gas pressure and applied voltage on Xe excimer radiation from a micro dielectric barrier discharge for plasma display panel

Giichiro Uchida, Satoshi Uchida, Hiroshi Kajiyama, and Tsutae Shinoda

J. Appl. Phys. 106, 073304 (2009); http://dx.doi.org/10.1063/1.3236508 (9 pages) | Cited 2 times

Online Publication Date: 8 October 2009

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We present the influence of gas pressure and applied voltage on Xe excimer radiation from a microdielectric barrier discharge (micro-DBD) in Ne/Xe gas mixture for plasma display panel. Measurements show that the excimer radiation with the 172 nm band lines is strongly observed in the afterglow, and drastically increases with an increase in gas pressure and applied voltage. It is also found that for high gas pressure and low voltage, excimer molecule (Xe2∗) is efficiently produced because of less infrared emission from Xe excited atom. The reaction processes of Xe metastable atom (Xe1s5∗), which is a precursor for Xe2∗, are theoretically analyzed using a one-dimensional fluid model. Increasing gas pressure results in large excimer radiation due to the enhancement of the following three processes, i.e., the conversion process from Xe1s5∗ to Xe2∗, the direct electron impact excitation from ground state to Xe1s5∗, and the collisional de-excitation process from upper level (Xe∗∗) to Xe1s5∗. The simulation analytical result shows that for lower voltage, Xe1s5∗ is efficiently produced due to the increase in the ratio of direct excitation to Xe1s5∗ from ground state and the suppression of the stepwise ionization from Xe1s5∗ by electron collisions. While for high voltage operation of micro-DBD, the recombination process with Xe molecular ion (Xe2+) and electron contributes to the total excimer radiation, which can be responsible for the large excimer radiation observed in experiment.
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52.75.-d Plasma devices
52.77.-j Plasma applications
52.80.Hc Glow; corona

Atomic hydrogen interactions with amorphous carbon thin films

Bhavin N. Jariwala, Cristian V. Ciobanu, and Sumit Agarwal

J. Appl. Phys. 106, 073305 (2009); http://dx.doi.org/10.1063/1.3238305 (9 pages) | Cited 6 times

Online Publication Date: 9 October 2009

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The atomic-scale interactions of H atoms with hydrogenated amorphous carbon (a-C:H) films were identified using molecular dynamics (MD) simulations and experiments based on surface characterization tools. Realistic a-C:H films developed using MD simulations were impinged with H atoms with a kinetic energy corresponding to a temperature of 700 K. The specific chemical reactions of the H atoms with the a-C:H surface were identified through a detailed analysis of the MD trajectories. The MD simulations showed that hydrogenation occurs primarily at the sp2 sites and converts them to sp3-hybridized C atoms. Depending on the hybridization of the next-nearest neighbor, a dangling bond may or may not be created. The hydrogenation reaction is highly exothermic, >2.5 eV, and proceeds with a negligible activation energy barrier via a mechanism similar to Eley–Rideal. In certain cases hydrogenation may also cleave a C–C bond. The reaction events observed through MD simulations are consistent with the surface characterization of D-exposed a-C:H films using Raman spectroscopy, spectroscopic ellipsometry, and in situ attenuated total reflection Fourier-transform infrared spectroscopy.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
78.30.Hv Other nonmetallic inorganics
81.65.-b Surface treatments
82.30.-b Specific chemical reactions; reaction mechanisms

Production of hydrogen in a conventional microwave oven

Shinfuku Nomura, Hiromichi Toyota, Shinobu Mukasa, Hiroshi Yamashita, Tsunehiro Maehara, and Ayato Kawashima

J. Appl. Phys. 106, 073306 (2009); http://dx.doi.org/10.1063/1.3236575 (4 pages) | Cited 3 times

Online Publication Date: 12 October 2009

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Hydrogen is produced by generating in-liquid plasma in a conventional microwave oven. A receiving antenna unit consisting of seven copper rods is placed at the bottom of the reactor furnace in the microwave oven. 2.45 GHz microwave in-liquid plasma can be generated at the tips of the electrodes in the microwave oven. When the n-dodecane is decomposed by plasma, 74% pure hydrogen gas can be achieved with this device. The hydrogen generation efficiency for a 750 W magnetron output is estimated to be approximately 56% of that of the electrolysis of water. Also, in this process up to 4 mg/s of solid carbon can be produced at the same time. The present process enables simultaneous production of hydrogen gas and the carbide in the hydrocarbon liquid.
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89.20.Kk Engineering
07.20.Hy Furnaces; heaters
84.40.-x Radiowave and microwave (including millimeter wave) technology

Investigation on oblique shock wave control by arc discharge plasma in supersonic airflow

Jian Wang, Yinghong Li, and Fei Xing

J. Appl. Phys. 106, 073307 (2009); http://dx.doi.org/10.1063/1.3236658 (7 pages) | Cited 1 time

Online Publication Date: 12 October 2009

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Wedge oblique shock wave control by arc discharge plasma in supersonic airflow was investigated theoretically, experimentally, and numerically in this paper. Using thermal choking model, the change in oblique shock wave was deduced, which refer that the start point of shock wave shifts upstream, the shock wave angle decreases, and its intensity weakens. Then the theoretical results were validated experimentally in a Mach 2.2 wind tunnel. On the test conditions of arc discharge power of ∼1 kW and arc plasma temperature of ∼3000 K, schlieren photography and gas pressure measurements indicated that the start point of shock wave shifted upstream of ∼4 mm, the shock wave angle decreased 8.6%, and its intensity weakened 8.8%. The deduced theoretical results match the test results qualitatively, so thermal mechanism and thermal choking model are rational to explain the problem of oblique shock wave control by arc discharge plasma. Finally, numerical simulation was developed. Based on thermal mechanism, the arc discharge plasma was simplified as a thermal source term that added to the Navier–Stokes equations. The simulation results of the change in oblique shock wave were consistent with the test results, so the thermal mechanism indeed dominates the oblique shock wave control process.
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52.35.Tc Shock waves and discontinuities
52.25.-b Plasma properties
52.80.-s Electric discharges
52.70.-m Plasma diagnostic techniques and instrumentation
52.65.-y Plasma simulation

Addressing the efficiency of the energy transfer to the water flow by underwater electrical wire explosion

S. Efimov, V. Tz. Gurovich, G. Bazalitski, A. Fedotov, and Ya. E. Krasik

J. Appl. Phys. 106, 073308 (2009); http://dx.doi.org/10.1063/1.3243233 (8 pages) | Cited 4 times

Online Publication Date: 13 October 2009

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Experimental and hydrodynamic simulation results of submicrosecond time scale underwater electrical explosions of planar Cu and Al wire arrays are presented. A pulsed low-inductance generator having a current amplitude of up to 380 kA was used. The maximum current rise rate and maximum power achieved during wire array explosions were dI/dt ≤ 830 A/ns and ∼ 10 GW, respectively. Interaction of the water flow generated during wire array explosion with the target was used to estimate the efficiency of the transfer of the energy initially stored in the generator energy to the water flow. It was shown that efficiency is in the range of 18%–24%. In addition, it was revealed that electrical explosion of the Al wire array allows almost double the energy to be transferred to the water flow due to efficient combustion of the Al wires. The latter allows one to expect a significant increase in the pressure at the front of converging strong shock waves in the case of cylindrical Al wire array underwater explosion.
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52.80.Qj Explosions; exploding wires
47.40.Rs Detonation waves
52.65.-y Plasma simulation
47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.11.-j Computational methods in fluid dynamics
52.35.Tc Shock waves and discontinuities

Optimization of a gas discharge plasma source for extreme ultraviolet interference lithography at a wavelength of 11 nm

K. Bergmann, S. V. Danylyuk, and L. Juschkin

J. Appl. Phys. 106, 073309 (2009); http://dx.doi.org/10.1063/1.3243287 (5 pages) | Cited 1 time

Online Publication Date: 15 October 2009

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In this work, we report about the optimization of the spectral emission characteristic of a gas discharge plasma source for high-resolution extreme ultraviolet (EUV) interference lithography based on achromatic Talbot self-imaging. The working parameters of the source are optimized to achieve a required narrowband emission spectrum and to fulfill the necessary coherence and intensity requirements. The intense 4f-4d transitions around 11 nm in a highly ionized (Xe8+–Xe12+) xenon plasma are chosen to provide the working wavelength. This allows us to increase the available radiation intensity in comparison with an in-band EUV xenon emission at 13.5 nm and opens up the possibility to strongly suppress the influence of the 5p-4d transitions at wavelengths between 12 and 16 nm utilizing a significant difference in conditions for optical thickness between 4f-4d and 5p-4d transitions. The effect is achieved by using the admixture of argon to the pinch plasma, which allows keeping the plasma parameters approximately constant while, at the same time, reducing the density of xenon emitters. It is demonstrated that with this approach it is possible to achieve a high intensity 11 nm EUV radiation with a bandwidth of 3%–4% without the use of multilayer mirrors or other additional spectral filters in the vicinity of the working wavelength. The achieved radiation parameters are sufficient for high-performance interference lithography based on the achromatic Talbot effect.
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52.50.Dg Plasma sources
52.55.Ez Theta pinch
52.80.-s Electric discharges
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Characterization of damage induced by heavy neutron irradiation on multilayered 6LiF-single crystal chemical vapor deposition diamond detectors

S. Almaviva, M. Angelone, Marco Marinelli, E. Milani, M. Pillon, G. Prestopino, A. Tucciarone, C. Verona, and G. Verona-Rinati

J. Appl. Phys. 106, 073501 (2009); http://dx.doi.org/10.1063/1.3224869 (10 pages) | Cited 1 time

Online Publication Date: 2 October 2009

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High performance neutron detectors sensitive to both thermal and fast neutrons are of great interest to monitor the high neutron flux produced, e.g., by fission and fusion reactors. An obvious requirement for such an application is neutron irradiation hardness. This is why diamond based neutron detectors are currently under test in some of these facilities. In this paper the damaging effects induced in chemical vapor deposition (CVD) diamond based detectors by a neutron fluence of ∼ 2×1016 neutrons/cm2 have been studied and significant changes in spectroscopic, electrical, and optical properties have been observed. The detectors are fabricated using high quality synthetic CVD single crystal diamond using the p-type/intrinsic/Schottky metal/6LiF layered structure recently proposed by Marinelli et al. [Appl. Phys. Lett. 89, 143509 (2006)] , which allows simultaneous detection of thermal and fast neutrons. Neutron radiation hardness up to at least 2×1014 n/cm2 fast (14 MeV) neutron fluence has been confirmed so far [see Pillon et al., (Fusion Eng. Des. 82, 1174 (2007) ]. However, at the much higher neutron fluence of ∼ 2×1016 neutrons/cm2 damage is observed. The detector response to 5.5 MeV 241Am α-particles still shows a well resolved α-peak, thus confirming the good radiation hardness of the device but a remarkable degradation and a significant instability with time of charge collection efficiency and energy resolution arise. Symmetric, nearly Ohmic I-V (current-voltage) characteristics have been recorded from the metal/intrinsic/p-doped diamond layered structure, which before neutron irradiation acted as a Schottky barrier diode with a strong rectifying behavior. The nature and the distribution of the radiation induced damage have been deeply examined by means of cathodoluminescence spectroscopy. A more heavily damaged area into the intrinsic diamond at the same position and with the same extension of the 6LiF layer has been found, the increased damage being ascribed to the highly ionizing particles produced in the 6LiF layer by thermal neutrons through the nuclear reaction 6Li(n,α)T.
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85.30.Kk Junction diodes
78.60.Hk Cathodoluminescence, ionoluminescence
85.30.Hi Surface barrier, boundary, and point contact devices
29.40.-n Radiation detectors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.80.Hg Neutron radiation effects

Defect structure of Ge(111)/cubic Pr2O3(111)/Si(111) heterostructures: Thickness and annealing dependence

A. Giussani, P. Zaumseil, P. Rodenbach, G. Weidner, M. A. Schubert, D. Geiger, H. Lichte, P. Storck, J. Wollschläger, and T. Schroeder

J. Appl. Phys. 106, 073502 (2009); http://dx.doi.org/10.1063/1.3224947 (8 pages) | Cited 8 times

Online Publication Date: 5 October 2009

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The defect structure of Ge(111) epilayers grown by molecular beam epitaxy on cubic Pr2O3(111)/Si(111) support systems was investigated by means of transmission electron microscopy and laboratory-based x-ray diffraction techniques. Three main types of defects were identified, namely, rotation twins, microtwins, and stacking faults, and studied as a function of Ge film thickness and after annealing at 825 °C in ultrahigh vacuum. Rotation twins were found to be localized at the Ge(111)/cubic Pr2O3(111) interface and their amount could be lowered by the thermal treatment. Microtwins across {11math} were detected only in closed Ge films, after Ge island coalescence. The fraction of Ge film volume affected by microtwinning is constant within the thickness range of ∼ 20–260 nm. Beyond 260 nm, the density of microtwins is clearly reduced, resulting in thick layers with a top part of higher crystalline quality. Microtwins resulted insensitive to the postdeposition annealing. Instead, the density of stacking faults across {11math} planes decreases with the thermal treatment. In conclusion, the defect density was proved to diminish with increasing Ge thickness and after annealing. Moreover, it is noteworthy that the annealing generates a tetragonal distortion in the Ge films, which get in-plane tensely strained, probably due to thermal mismatch between Ge and Si.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.J- Morphology of films
61.72.Mm Grain and twin boundaries
61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Dd Experimental determination of defects by diffraction and scattering

Lower limit to the lattice thermal conductivity of nanostructured Bi2Te3-based materials

Catalin Chiritescu, Clay Mortensen, David G. Cahill, David Johnson, and Paul Zschack

J. Appl. Phys. 106, 073503 (2009); http://dx.doi.org/10.1063/1.3226884 (5 pages) | Cited 4 times

Online Publication Date: 5 October 2009

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We investigate the lower limit to the lattice thermal conductivity of Bi2Te3 and related materials using thin films synthesized by the method of elemental reactants. The thermal conductivities of single layer films of (Bi0.5Sb0.5)2Te3 and multilayer films of (Bi2Te3)m(TiTe2)n and [(BixSb1−x)2Te3]m(TiTe2)n are measured by time-domain thermoreflectance; the thermal conductivity data are compared to our prior work on nanocrystalline Bi2Te3 and a Debye–Callaway model of heat transport by acoustic phonons. The homogeneous nanocrystalline films have average grain sizes 30<d<100 nm as measured by the width of the (003) x-ray diffraction peak. Multilayer films incorporating turbostratic TiTe2 enable studies of the effective thermal conductivity of Bi2Te3 layers as thin as 2 nm. In the limit of small grain size or layer thickness, the thermal conductivity of Bi2Te3 approaches the predicted minimum thermal conductivity of 0.31 W/m K. The dependence of the thermal conductivity on grain size is in good agreement with our Debye–Callaway model. The use of alloy (Bi,Sb)2Te3 layers further reduces the thermal conductivity of the nanoscale layers to as low as 0.20 W/m K.
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73.63.Bd Nanocrystalline materials
62.65.+k Acoustical properties of solids
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
61.46.-w Structure of nanoscale materials
68.55.ag Semiconductors
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
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