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1 Jul 2008

Volume 104, Issue 1, Articles (01xxxx)

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High-Tc superconducting quantum interference devices: Status and perspectives

Hong-Chang Yang, Ji-Chen Chen, Kuen-Lin Chen, Chiu-Hsien Wu, Herng-Er Horng, and S. Y. Yang

J. Appl. Phys. 104, 011101 (2008); http://dx.doi.org/10.1063/1.2948912 (12 pages) | Cited 3 times

Online Publication Date: 2 July 2008

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In this paper, an overview of the current status of high-Tc superconducting quantum interference devices (SQUIDs), from device engineering to biomagnetic applications, is given. The authors offer a description of the current status of SQUID sensors, challenges encountered, and the solution of fabricating SQUID sensors with low flux noises. The current challenge that we face is to fabricate high-Tc SQUIDs that are not only more reproducible than the current technology but also capable of providing a high IcRn product and fabricating SQUID with high yield. Improvement of flux noises and fabrication yield in the integrated multichoices directly coupled SQUID magnetometer or gradiometer with series SQUID array are presented. High-Tc SQUID magnetometers exhibiting magnetic field sensitivity of ∼ 30–50 fT/Hz1/2 or better at 100 Hz was demonstrated by incorporating serial SQUID into the pickup loop of the magnetometers. New technologies currently being developed and applications for high-Tc SQUIDs are addressed.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
07.55.Ge Magnetometers for magnetic field measurements
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Optimizing the Ar–Xe infrared laser on the Naval Research Laboratory’s Electra generator

J. P. Apruzese, J. L. Giuliani, M. F. Wolford, J. D. Sethian, G. M. Petrov, D. D. Hinshelwood, M. C. Myers, A. Dasgupta, F. Hegeler, and Ts. Petrova

J. Appl. Phys. 104, 013101 (2008); http://dx.doi.org/10.1063/1.2948934 (8 pages) | Cited 1 time

Online Publication Date: 2 July 2008

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The Ar–Xe infrared laser has been investigated in several series of experiments carried out on the Naval Research Laboratory’s Electra generator. Our primary goals were to optimize the efficiency of the laser (within Electra’s capabilities) and to gain understanding of the main physical processes underlying the laser’s output as a function of controllable parameters such as Xe fraction, power deposition, and gas pressure. We find that the intrinsic efficiency maximizes at ∼ 3% at a total pressure of 2.5 atm, Xe fraction of 1%, and electron beam power deposition density of 50–100 kW cm−3. We deployed an interferometer to measure the electron density during lasing; the ionization fractions of 10−5–10−4 that it detected well exceed previous theoretical estimates. Some trends in the data as a function of beam power and xenon fraction are not fully understood. The as-yet incomplete picture of Ar–Xe laser physics is likely traceable in large part to significant uncertainties still present in many important rates influencing the atomic and molecular kinetics.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems
52.57.-z Laser inertial confinement

Diode-pumped laser operation of Yb3+-doped Y2Ca3B4O12 crystal

Alain Brenier, Chaoyang Tu, Yan Wang, Zhenyu You, Zhaojie Zhu, and Jianfu Li

J. Appl. Phys. 104, 013102 (2008); http://dx.doi.org/10.1063/1.2948935 (5 pages) | Cited 5 times

Online Publication Date: 2 July 2008

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We report in the present paper the Yb3+-doped Y2Ca3B4O12 diode-pumped laser operation in both continuous-wave (cw) and passively Q-switched modes. The differential slopes of the cw output power are in the 22%–40% range under different experimental conditions. Continuous tuning of the laser wavelength is obtained in the 1020–1057 nm range, in agreement with the broad emission spectra. In pulsed regime the repetition rate occurs up to 1.6 kHz and pulse energies of 30–75 μJ with about 40 ns duration are obtained.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes

Reflectance analysis of a multilayer one-dimensional porous silicon structure: Theory and experiment

Jarkko J. Saarinen, Sharon M. Weiss, Philippe M. Fauchet, and J. E. Sipe

J. Appl. Phys. 104, 013103 (2008); http://dx.doi.org/10.1063/1.2949265 (7 pages) | Cited 5 times

Online Publication Date: 2 July 2008

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We present a method for treating birefringent effects in layered media and apply the formalism to analyze reflectance from a multilayer one-dimensional (1D) porous silicon (PS) structure at off-normal incidence. The approach is to characterize the fields in terms of s- and p-polarized amplitudes in each layer, and the calculations then naturally employ Fresnel reflection and transmission coefficients for the uniaxially anisotropic media. We observe an excellent agreement between the theoretical and experimental curves by including optical absorption and macroscale waviness of the PS layers, and the resolution of the spectrophotometer. In particular, we point out the importance of birefringent effects that cause the splitting of the resonance wavelengths between two different polarizations. The investigated 1D PS structure can be used, for example, as a polarization sensitive optical switch.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.20.Fm Birefringence
78.30.Am Elemental semiconductors and insulators

Effect of intensity noise of semiconductor lasers on the digital modulation characteristics and the bit error rate of optical communication systems

Moustafa Ahmed and Minoru Yamada

J. Appl. Phys. 104, 013104 (2008); http://dx.doi.org/10.1063/1.2949275 (7 pages) | Cited 2 times

Online Publication Date: 2 July 2008

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This paper presents theoretical evaluation of the digital modulation performance of semiconductor lasers in digital communication systems with gigabit rates. The study is based on numerical integration of the rate equations augmented by a nonreturn-to-zero (NRZ) bit generator. For solitary semiconductor lasers, the performance is evaluated in terms of the eye diagram, turn-on delay jitter (TOJ), and signal-to-noise ratio. In communication systems, the performance is evaluated by the bit error rate (BER) and power penalty induced by the laser noise. Contributions of both the intrinsic fluctuations and bit pattern to the TOJ and BER are assessed. The results show that when the modulation current is low and the semiconductor laser is biased relatively above threshold, the power penalty decreases although the eye diagram is not well open. When the modulation current is high enough, biasing the semiconductor laser far-above threshold achieves both lower power penalty and higher eye-diagram quality.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
84.40.Ua Telecommunications: signal transmission and processing; communication satellites

Space-charge-controlled electro-optic effect: Optical beam deflection by electro-optic effect and space-charge-controlled electrical conduction

Koichiro Nakamura, Jun Miyazu, Yuzo Sasaki, Tadayuki Imai, Masahiro Sasaura, and Kazuo Fujiura

J. Appl. Phys. 104, 013105 (2008); http://dx.doi.org/10.1063/1.2949394 (10 pages) | Cited 5 times

Online Publication Date: 2 July 2008

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This paper describes the experimental and theoretical studies of an anomalous optical beam deflection phenomenon based on electrooptic effect and space-charge-controlled electrical conduction. In the experiment, a large deflection angle of 250 mrad ( = 14.3°) has been observed by applying ±250 V to a 0.5‐mm-thick KTa1−xNbxO3 crystal with a short interaction length of 5.0 mm. The crystal has a rectangular shape with uniform electrodes and there is no prism shape involved which is a common geometrical shape of crystal, electrode, or ferroelectric domain in the conventional electro-optic deflectors. The operating principle is investigated and it is found that the space-charge-controlled electrical conduction in the crystal plays an essential role in this deflection phenomenon. The electrical conduction is carried by electrons injected from the Ohmic contact of the electrode with the crystal. The injected electrons induce the space-charge effect and the electric field becomes nonuniform between the electrodes. The theoretical analysis shows that the electric field has a square-root dependence on the distance from the cathode. As a result, a linearly graded refractive index is induced by the electrooptic Kerr effect of the crystal and the optical beam is cumulatively deflected as it propagates in the crystal. We named this effect the “space-charge-controlled electro-optic effect” and the factors related to the onset of this effect are also discussed.
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42.79.Fm Reflectors, beam splitters, and deflectors
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.25.-p Wave optics

Anisotropic exchange splitting of excitons in (001)GaAs/Al0.3Ga0.7As superlattice studied by reflectance difference spectroscopy

Z. Y. Zhou, C. G. Tang, Y. H. Chen, and Z. G. Wang

J. Appl. Phys. 104, 013106 (2008); http://dx.doi.org/10.1063/1.2947602 (6 pages)

Online Publication Date: 3 July 2008

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Anisotropic exchange splitting (AES) is induced by the joint effects of the electron-hole exchange interaction and the symmetry reduction in quantum wells and quantum dots. A model has been developed to quantitatively obtain the electron-hole exchange energy and the hole-mixing energy of quantum wells and superlattices. In this model, the AES and the degree of polarization can both be obtained from the reflectance difference spectroscopy. Thus the electron-hole exchange energy and the hole-mixing energy can be completely separated and quantitatively deduced. By using this model, a (001)5 nm GaAs/7 nm Al0.3Ga0.7As superlattice sample subjected to [110] uniaxial strains has been investigated in detail. The n = 1 heavy-hole (1H1E) exciton can be analyzed by this model. We find that the AES of quantum wells can be linearly tuned by the [110] uniaxial strains. The small uniaxial strains can only influence the hole-mixing interaction of quantum wells, but have almost no contribution to the electron-hole exchange interaction.
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68.65.Cd Superlattices
71.70.Gm Exchange interactions
78.67.De Quantum wells
71.35.-y Excitons and related phenomena
68.65.Fg Quantum wells
68.65.Hb Quantum dots (patterned in quantum wells)

Highly localized mode in a pair structure made of epsilon-negative and mu-negative metamaterials

Tuanhui Feng, Yunhui Li, Jiyong Guo, Li He, Hongqiang Li, Yewen Zhang, Yunlong Shi, and Hong Chen

J. Appl. Phys. 104, 013107 (2008); http://dx.doi.org/10.1063/1.2949264 (5 pages) | Cited 4 times

Online Publication Date: 3 July 2008

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In this paper, the tunneling phenomenon occurring in a pair structure made of epsilon-negative (ENG) and mu-negative (MNG) metamaterials is experimentally studied. The ENG and MNG metamaterials are fabricated using coplanar waveguide loading with lumped-element series capacitors and shunt inductors. The properties of the tunneling mode are investigated by means of the transfer-matrix method, based on the experiment parameters of effective permittivity and permeability. The results show that the tunneling frequency is independent of the pair length and the electric field is highly localized at the interface of the ENG-MNG pair. These features illustrate that the pair behaves as a cavity with strongly enhanced electric field and with dimensions beyond the half-wavelength limit.
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73.40.Gk Tunneling
77.22.Ch Permittivity (dielectric function)
63.20.Pw Localized modes
68.35.Ct Interface structure and roughness
42.70.-a Optical materials

Energy transfer in hybrid quantum dot light-emitting diodes

Patrick T. K. Chin, Rifat A. M. Hikmet, and René A. J. Janssen

J. Appl. Phys. 104, 013108 (2008); http://dx.doi.org/10.1063/1.2932149 (6 pages) | Cited 8 times

Online Publication Date: 7 July 2008

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Energy transfer in a host-guest system consisting of a blue-emitting poly(2,7-spirofluorene) (PSF) donor and red-emitting CdSe/ZnS core shell quantum dots (QDs) as acceptor is investigated in solid films, using time-resolved optical spectroscopy, and in electroluminescent diodes. In the QD:PSF composite films, the Förster radius for energy transfer is found to be 4–6 nm. In electroluminescent devices lacking an electron transport layer, the electroluminescence (EL) spectrum of the QD:PSF polymer composite is similar to the photoluminescence (PL), giving evidence for energy transfer from PSF to the QDs. The addition of an electron transport layer between the emitting layer and the cathode results in a significant change in the EL spectrum and a considerable improved device performance, providing almost pure monochromatic emission at 630 nm with a luminance efficiency of 0.32 cd/A. The change in spectrum signifies that the electron transport layer changes the dominant pathway for QD emission from energy transfer from the polymer host to direct electron-hole recombination on the QDs.
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85.60.Jb Light-emitting devices
78.67.Hc Quantum dots

A first-principles survey of the partitioning behaviors of alloying elements on γ/γ′ interface

Yun-Jiang Wang and Chong-Yu Wang

J. Appl. Phys. 104, 013109 (2008); http://dx.doi.org/10.1063/1.2953077 (5 pages) | Cited 5 times

Online Publication Date: 8 July 2008

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A first-principles approach is proposed to investigate the partitioning behaviors of the alloying elements Re, Co, and Cr, and the influence of Ru and Ir addition on them. The results show that Re, Co, and Cr all partition strongly to the γ matrix. The Ru addition decreases the γ phase partitioning trend of Re, Co, and Cr. The results are consistent with the early experimental work. Besides Ru, Ir results in Re less strongly partitioning to γ. Our study shows that the influence of Ru (or Ir) on the partitioning characteristics of alloying elements originates from the strong interactions between Ru(Ir)-Re-Ni through the d−d orbitals hybridization.
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71.20.Be Transition metals and alloys
71.20.Lp Intermetallic compounds
61.50.Lt Crystal binding; cohesive energy
62.20.-x Mechanical properties of solids

Laser ablation-induced spectral plasma characteristics in optical far- and near fields

David J. Hwang, Hojeong Jeon, Costas P. Grigoropoulos, Jong Yoo, and Richard E. Russo

J. Appl. Phys. 104, 013110 (2008); http://dx.doi.org/10.1063/1.2939587 (12 pages) | Cited 8 times

Online Publication Date: 8 July 2008

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The aim of this work is to elucidate the ablation-induced plasma physics for chemical species analysis by laser-induced breakdown spectroscopy at higher spatial resolution. To accomplish this, the effect of the laser spot size on the laser ablation-induced plasma characteristics is experimentally investigated, both in optical far-field and near-field ablation configurations, utilizing a Cr thin film of ∼ 200 nm thickness on quartz substrate as a target. The far-field ablation is affected under tight focusing conditions, wherein nanosecond laser pulses of 532 nm wavelength are focused to laser focal spot diameters of ∼ 7 and 1.5 μm. The measured results show that the ablation-induced plasma from sub-10 μm ablation craters exhibits complex three-dimensional behavior, leading to greatly reduced laser-plasma interaction and an order of magnitude shorter plasma lifetime. Nanosecond laser pulses of 532 nm wavelength are also coupled to a pulled fiber based near-field scanning optical microscopy probe. Due to the sharp tip presence in close proximity of the ablation craters, entirely different plasma evolution behavior is observed, highlighted by orders of magnitude shorter plasma lifetime and strongly directional material ejection. The ablation-induced plasma from reduced lateral crater dimensions both in far- and near-field shows improved contrast of atomic transition signals with respect to the wide-spectrum background, hence confirming the potential for laser-induced breakdown spectroscopy with high spatial resolution.
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52.38.Mf Laser ablation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Theoretical study of terahertz current oscillation in GaAs1−xNx

W. Feng and J. C. Cao

J. Appl. Phys. 104, 013111 (2008); http://dx.doi.org/10.1063/1.2952017 (4 pages) | Cited 5 times

Online Publication Date: 10 July 2008

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We have theoretically investigated current self-oscillation in doped n+nn+ GaAs1−xNx diodes driven by direct current (dc) electric field. The current self-oscillation is associated with negative differential velocity effect in the highly nonparabolic conduction band of this unique material system. By solving a time-dependent drift-diffusion model that takes into account the negative differential velocity effect, we provide a detailed analysis of the current oscillations. The frequencies of current oscillations are in the gigahertz to terahertz region, depending on the doping concentration and the applied dc electric field. The calculated average current density is in qualitative agreement with the measured result.
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85.30.Kk Junction diodes
85.30.De Semiconductor-device characterization, design, and modeling
61.72.uj III-V and II-VI semiconductors

Laser irradiation in Nd3+ doped strontium barium niobate glass

P. Haro-González, I. R. Martín, E. Arbelo-Jorge, S. González-Pérez, J. M. Cáceres, and P. Núñez

J. Appl. Phys. 104, 013112 (2008); http://dx.doi.org/10.1063/1.2952011 (5 pages) | Cited 7 times

Online Publication Date: 11 July 2008

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A local nanocrystalline formation in a neodymium doped strontium barium niobate (SBN) glass has been obtained under argon laser irradiation. The intense emission around 880 nm, originated from the 4F3/2 (4F5/2) thermalized level when the glass structure changes to a glass ceramic structure due to the irradiation of the laser beam, has been studied. The intensities and lifetimes change from this level inside and outside the irradiated area made by the laser excitation. They have been analyzed and demonstrated that the desvitrification process has been successfully achieved. These results confirm that nanocrystals of SBN have been created by the laser action confirming that the transition from glass to glass ceramic has been completed. These results are in agreement with the emission properties of nanocrystals of the bulk glass ceramic sample. The present study also suggests that the SBN nanocrystal has a potential application as temperature detector.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.43.Fs Glasses
81.07.Bc Nanocrystalline materials
61.46.Hk Nanocrystals
64.70.ph Nonmetallic glasses (silicates, oxides, selenides, etc.)

Modeling of the gain and temperature in high pressure, ejector type chemical oxygen-iodine lasers and comparison to experiments

K. Waichman, B. D. Barmashenko, and S. Rosenwaks

J. Appl. Phys. 104, 013113 (2008); http://dx.doi.org/10.1063/1.2955727 (8 pages) | Cited 4 times

Online Publication Date: 15 July 2008

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The results of three-dimensional computational fluid dynamics model calculations are compared to available experimental results [ V. D. Nikolaev et al., IEEE J. Quantum Electron. 38, 421 (2002) ]. It is shown that the model is applicable to high pressure, ejector type chemical oxygen-iodine laser (COIL), reasonably reproducing the measured gain, temperature, static pressure, and gas velocity. A previous model, which included I2(A′3Π2u), I2(A3Π1u), and O2(a1Δg,v) as significant intermediates in the dissociation of I2 [ K. Waichman et al., J. Appl. Phys. 102, 013108 (2007) ], reproduced the measured gain and temperature of a low pressure supersonic COIL. The previous model is complemented here by adding the effects of turbulence, which play an important role in high pressure COILs.
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42.55.Ks Chemical lasers
47.11.-j Computational methods in fluid dynamics

Modeling of avalanche multiplication and excess noise factor in In0.52Al0.48As avalanche photodiodes using a simple Monte Carlo model

S. C. Liew Tat Mun, C. H. Tan, Y. L. Goh, A. R. J. Marshall, and J. P. R. David

J. Appl. Phys. 104, 013114 (2008); http://dx.doi.org/10.1063/1.2952003 (6 pages) | Cited 3 times

Online Publication Date: 15 July 2008

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A simple Monte Carlo model has been developed to simulate the avalanche multiplication process in In0.52Al0.48As. The model reproduces avalanche multiplication and excess noise factor measured on a wide range of In0.52Al0.48As p+-n-n+, n+-n-p+, and p+-n+ diodes and confirms that very low excess noise factor can be obtained using pure electron injection in very thick diodes with avalanche region greater than 2.21 μm or in very thin diodes with avalanche region lesser than 0.11 μm. In addition we investigated the effect of an electric field gradient in the avalanche region of avalanche photodiodes and found that the excess noise factor can be reduced with electric field gradients. However in thin diodes with avalanche region lesser than 0.20 μm, the onset of tunneling current negates the excess noise reduction achieved using the electric field gradient. Therefore ideal p+-i-n+ diodes still provide the overall preferred structure.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.De Semiconductor-device characterization, design, and modeling
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Laser-rf creation and diagnostics of seeded atmospheric pressure air and nitrogen plasmas

Siqi Luo, C. Mark Denning, and John E. Scharer

J. Appl. Phys. 104, 013301 (2008); http://dx.doi.org/10.1063/1.2946718 (11 pages) | Cited 12 times

Online Publication Date: 2 July 2008

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A laser initiation and radio frequency (rf) sustainment technique has been developed and improved from our previous work to create and sustain large-volume, high-pressure air and nitrogen plasmas. This technique utilizes a laser-initiated, 15 mTorr partial pressure tetrakis (dimethylamino) ethylene seed plasma with a 75 Torr background gas pressure to achieve high-pressure air/nitrogen plasma breakdown and reduce the rf power requirement needed to sustain the plasma. Upon the laser plasma initiation, the chamber pressure is raised to 760 Torr in 0.5 s through a pulsed gas valve, and the end of the chamber is subsequently opened to the ambient air. The atmospheric-pressure plasma is then maintained with the 13.56 MHz rf power. Using this technique, large-volume (1000 cm3), high electron density (on the order of 1011–12 cm−3), 760 Torr air and nitrogen plasmas have been created while rf power reflection is minimized during the entire plasma pulse utilizing a dynamic matching method. This plasma can project far away from the antenna region (30 cm), and the rf power budget is 5 W/cm3. Temporal evolution of the plasma electron density and total electron-neutral collision frequency during the pulsed plasma is diagnosed using millimeter wave interferometry. Optical emission spectroscopy (OES) aided by SPECAIR, a special OES simulation program for air-constituent plasmas, is used to analyze the radiating species and thermodynamic characteristics of the plasma. Rotational and vibrational temperatures of 4400–4600±100 K are obtained from the emission spectra from the N2(2+) and N2+(1−) transitions by matching the experimental spectrum results with the SPECAIR simulation results. Based on the relation between the electron collision frequency and the neutral density, utilizing millimeter wave interferometry, the electron temperature of the 760 Torr nitrogen plasma is found to be 8700±100 K (0.75±0.1 eV). Therefore, the plasma deviates significantly from local thermal equilibrium.
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52.50.-b Plasma production and heating
52.70.-m Plasma diagnostic techniques and instrumentation
52.25.-b Plasma properties
52.65.-y Plasma simulation

An analytical model to determine equilibrium quantities of azimuthally symmetric and mismatched charged particle beams under linear focusing

R. P. Nunes, R. Pakter, and F. B. Rizzato

J. Appl. Phys. 104, 013302 (2008); http://dx.doi.org/10.1063/1.2949270 (10 pages) | Cited 6 times

Online Publication Date: 3 July 2008

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The model developed here analytically allows to obtain equilibrium quantities of interest from high-intensity charged particle beams such as the emittance, beam envelope, and the number of beam halo particles. The results obtained in this work have been particularized to the case of initially homogeneous beams, with azimuthal symmetry, and focused by a constant magnetic field while confined in a linear channel. For validation, full self-consistent N-particle beam simulations have been carried out and its results compared with the predictions supplied by the developed hybrid numerical-analytical model. The agreement has been reasonable. Also, the model revealed to be useful to understand the basic physical aspects of the problem.
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41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
41.75.-i Charged-particle beams

Experimental investigation of ultraviolet laser induced plasma density and temperature evolution in air

Magesh Thiyagarajan and John Scharer

J. Appl. Phys. 104, 013303 (2008); http://dx.doi.org/10.1063/1.2952540 (12 pages) | Cited 15 times

Online Publication Date: 11 July 2008

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We present measurements and analysis of laser induced plasma neutral densities and temperatures in dry air by focusing 200 mJ, 10 MW high power, 193 nm ultraviolet ArF (argon fluoride) laser radiation to a 30 μm radius spot size. We examine these properties that result from multiphoton and collisional cascade processes for pressures ranging from 40 Torr to 5 atm. A laser shadowgraphy diagnostic technique is used to obtain the plasma electron temperature just after the shock front and this is compared with optical emission spectroscopic measurements of nitrogen rotational and vibrational temperatures. Two-color laser interferometry is employed to measure time resolved spatial electron and neutral density decay in initial local thermodynamic equilibrium (LTE) and non-LTE conditions. The radiating species and thermodynamic characteristics of the plasma are analyzed by means of optical emission spectroscopy (OES) supported by SPECAIR, a special OES program for air constituent plasmas. Core plasma rotational and vibrational temperatures are obtained from the emission spectra from the N2C-B(2+) transitions by matching the experimental spectrum results with the SPECAIR simulation results and the results are compared with the electron temperature just behind the shock wave. The plasma density decay measurements are compared with a simplified electron density decay model that illustrates the dominant three-and two-body recombination terms with good correlation.
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52.25.-b Plasma properties

An experimental and theoretical investigation of a magnetically confined dc plasma discharge

Maurizio Rondanini, Carlo Cavallotti, Daria Ricci, Daniel Chrastina, Giovanni Isella, Tamara Moiseev, and Hans von Känel

J. Appl. Phys. 104, 013304 (2008); http://dx.doi.org/10.1063/1.2948927 (13 pages) | Cited 10 times

Online Publication Date: 11 July 2008

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A magnetically confined dc plasma discharge sustained by a thermionic source was investigated using a combined experimental and theoretical approach. The discharge originates in an arc plasma source and is expanded in a cylindrical chamber, where it is stabilized by an annular anode. The plasma expansion is contained by an axial magnetic field generated by coils positioned at the top and the bottom of the reactor. The plasma reactor design allows control of the energy of ions impinging on the substrate and thus a high electron density of about 1017 m−3 at 1 Pa can be reached. The plasma is studied using a model composed of the Poisson and of the charged species continuity equations, solved in the flow and temperature fields determined by solving the Navier–Stokes and Fourier equations. The model equations are integrated using the finite element method in a two-dimensional axial symmetric domain. Ionization rates are either assumed constant or determined by solving the Boltzmann transport equation in the local electric field with the Monte Carlo (MC) method. Electron and ion transport parameters are determined by accounting for magnetic confinement through a simplified solution of the ion and electron momentum conservation equations, which yielded parameters in good agreement with those determined with the MC simulations. Calculated electron densities and plasma potentials were satisfactorily compared to those measured using a Langmuir probe. The model demonstrates that the intensity of the magnetic field greatly influences the electron density, so that a decrease by a factor of 2 in its intensity corresponds to a decrease by almost an order of magnitude of the electron and ion concentrations.
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52.65.Pp Monte Carlo methods
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.50.Dg Plasma sources

Characterization of out-of-band radiation and plasma parameters in laser-produced Sn plasmas for extreme ultraviolet lithography light sources

S. Namba, S. Fujioka, H. Sakaguchi, H. Nishimura, Y. Yasuda, K. Nagai, N. Miyanaga, Y. Izawa, K. Mima, K. Sato, and K. Takiyama

J. Appl. Phys. 104, 013305 (2008); http://dx.doi.org/10.1063/1.2952033 (5 pages) | Cited 7 times

Online Publication Date: 14 July 2008

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Out-of-band (OOB) radiation, in contrast to the in-band radiation at 13.5 nm in a 2% bandwidth, emitted from dense tin plasmas generated by a laser was investigated for application as an extreme ultraviolet lithography light source. It was found that the continuum spectrum, which overwhelms the atomic and ionic line emissions, is responsible for the intense OOB radiation. The spectral distribution of the continuum emission matches that of blackbody radiation with a temperature of about 10 eV. The OOB radiation can be considerably suppressed by employing a minimum-mass target and short-pulse laser irradiation. Spectroscopic observations were made to examine the spatiotemporal behavior of the plasma immediately after laser irradiation. Prominent line broadening due to the Stark effect in the high-density plasma was observed, from which the variation of the electron density was deduced. The electron density and temperature on the target surface were 1017–1018 cm−3 and a few eV’s, respectively, in the first 200 ns after laser illumination. In addition, the expansion velocities of neutral and singly ionized tin atoms were deduced from time-of-flight transients in the spectral emission.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
52.77.-j Plasma applications

Effect of electrode polarity on wire explosion in vacuum

A. G. Rousskikh, D Pil’tikhina, R. B. Baksht, I. I. Beilis, and S. A. Chaikovsky

J. Appl. Phys. 104, 013306 (2008); http://dx.doi.org/10.1063/1.2952041 (6 pages) | Cited 2 times

Online Publication Date: 14 July 2008

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This paper presents experimental results on electrical explosions of thin tungsten wires at wire currents of 0.04–0.4 kA and current rise times of several tens of nanoseconds. The experiment was performed for both negative and positive polarity of the high-voltage electrode. In addition to conventional current and voltage measurements, the current to a grounded cylindrical collector placed between the exploded wire and the return conductor was measured. The collector current was observed only for a 6 μm wire exploded with the high-voltage electrode being at a negative potential. In all other test modes (a 6 μm wire exploded with electrode positive polarity, 6 μm wire exploded with electrodes enclosed in ceramic tubes, 30 μm wires exploded with electrode negative and positive polarities) no collector current was detected. A model of the discharge initiation during a wire explosion (WE) in vacuum has been proposed which is based on the supposition that a surface discharge develops over the electrodes. The presence of plasma-emitted electrons at the cathode surface makes it possible to interpret the experimental results on WEs at different electrode polarities reported both in this paper and in previous publications.
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52.80.Qj Explosions; exploding wires
52.80.Vp Discharge in vacuum
52.50.Lp Plasma production and heating by shock waves and compression
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Tensile strength of randomly perforated aluminum plates: Weibull distribution parameters

Claude A. Klein

J. Appl. Phys. 104, 013501 (2008); http://dx.doi.org/10.1063/1.2948942 (6 pages) | Cited 1 time

Online Publication Date: 1 July 2008

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Recently, Yanay and collaborators [J. Appl. Phys. 101, 104911 (2007)] addressed issues regarding the fracture strength of randomly perforated aluminum plates subjected to tensile loads. Based on comprehensive measurements and computational simulations, they formulate statistical predictions for the tensile strength dependence on the hole density but conclude that their data are inadequate for the purpose of deriving the strength distribution function. The primary purpose of this contribution is to demonstrate that, on dividing the totality of applicable data into seven “bins” of comparable population, the strength distribution of perforated plates of similar hole density obeys a conventional two-parameter Weibull model. Furthermore, on examining the fracture stresses as recorded in the vicinity of the percolation threshold, we find that the strength obeys the expression σo(P−Pth)β with Pth ≃ 0.64 and β ≃ 0.4. In this light, and taking advantage of percolation theory, we formulate equations that specify how the two Weibull parameters (characteristic strength and shape factor) depend on the hole density. This enables us to express the failure probability as a function of the tensile stress, over the entire range of hole densities, i.e., P = 0.02 up to the percolation threshold.
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46.70.De Beams, plates, and shells
62.20.mm Fracture
81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
02.50.Ng Distribution theory and Monte Carlo studies

Deformation pathway to high-pressure phases of silicon during nanoindentation

Dong Earn Kim and Soo Ik Oh

J. Appl. Phys. 104, 013502 (2008); http://dx.doi.org/10.1063/1.2949404 (6 pages) | Cited 5 times

Online Publication Date: 1 July 2008

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The deformation pathway of silicon induced by nanoindentation is investigated in detail at the atomic level using molecular dynamics. Due to the complex stresses associated with the directional loading along a specific crystallographic orientation, the initial Si I lattice is transformed into two different high-pressure phases, namely, Si II and BCT5-Si. The Si II phase, where atoms have the six nearest neighbors, is generated through the tetragonal deformation caused by the compressive loading along the [001] direction. In contrast, the BCT5-Si phase, where each silicon atom has the five nearest neighbors, is formed by flattening the initially stepped sixfold rings of the diamond lattice onto the (110) plane of the BCT lattice. These reconstructive transformations are accomplished only by adding additional bonds and do not involve any bond breaking.
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81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
62.20.F- Deformation and plasticity

Pressure-induced metallization and resonant Raman scattering in Zn1−xMnxTe

Y. C. Lin, W. C. Fan, C. H. Chiu, F. K. Ke, S. L. Yang, D. S. Chuu, M. C. Lee, W. K. Chen, W. H. Chang, W. C. Chou, J. S. Hsu, and J. L. Shen

J. Appl. Phys. 104, 013503 (2008); http://dx.doi.org/10.1063/1.2949707 (5 pages) | Cited 3 times

Online Publication Date: 1 July 2008

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Pressure-induced resonant Raman scattering is adopted to analyze the zone-center optical phonon modes and crystal characteristics of Zn1−xMnxTe (0≦x≦0.26) thin films. The pressure (Pt) at which the semiconducting undergoes a transition to the metallic phase declines as a function of Mn concentration (x) according to the formula Pt(x) = 15.7−25.4x+19.0x2 (GPa). Pressure-dependent longitudinal and transverse optical phonon frequencies and the calculated mode Grüneisen parameters were adopted to investigate the influence of Mn2+ ions on the iconicity. The experimental results indicate that the manganese ions tend to increase the iconicity of ZnTe under ambient conditions, whereas an external hydrostatic pressure tends to reduce the iconicity and the bond length of Zn1−xMnxTe.
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75.50.Pp Magnetic semiconductors
78.30.Hv Other nonmetallic inorganics
71.55.Gs II-VI semiconductors
68.35.Rh Phase transitions and critical phenomena
64.70.kg Semiconductors
61.66.Fn Inorganic compounds

Electric field modulation of exciton recombination in InAs/GaAs quantum dots emitting at 1.3 μm

Toshiyuki Miyazawa, Toshihiro Nakaoka, Tatsuya Usuki, Jun Tatebayashi, Yasuhiko Arakawa, Shinichi Hirose, Kazuya Takemoto, Motomu Takatsu, and Naoki Yokoyama

J. Appl. Phys. 104, 013504 (2008); http://dx.doi.org/10.1063/1.2947603 (8 pages) | Cited 1 time

Online Publication Date: 2 July 2008

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Changing the electric field applied to InAs quantum dots embedded in a p-i-n diode was found to modulate the radiative recombination rate of excitons in the dots. The quantum dots were capped with a strain-reducing layer to realize 1.3 μm photoemission and a large dipole moment to the exciton states. The exciton states in a quantum dot were investigated by measuring the quantum-confined Stark shift for various applied electric fields and were compared with the theoretical electron and hole wave functions calculated using an eight-band k⋅p model. When the absolute value of the applied electric field was reduced from −82.4 kV/cm to 0, the radiative recombination rate increased from 0.88 to 1.11 ns−1. Comparison of the experimental rate with the calculated one revealed that the increase in the radiative recombination rate was due to a decrease in the overlap integral between the electrons and holes. These optical characteristics of InAs quantum dots are especially important for developing optical devices that use single photons and single charges because the contribution of nonradiative processes is smaller than that of the radiative process.
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73.21.La Quantum dots
85.30.Kk Junction diodes
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