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1 Aug 2009

Volume 106, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 106, 031101 (2009); http://dx.doi.org/10.1063/1.3180960 (14 pages)

Jing Bai and D. S. Citrin
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Intracavity nonlinearities in quantum-cascade lasers

Jing Bai and D. S. Citrin

J. Appl. Phys. 106, 031101 (2009); http://dx.doi.org/10.1063/1.3180960 (14 pages) | Cited 3 times

Online Publication Date: 7 August 2009

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We discuss various intracavity optical nonlinearities up to the third order in quantum-cascade lasers. The discussions are based on two kinds of nonlinearities, each toward respective applications. The susceptibilities at the second-harmonic or third-harmonic frequencies lead to harmonic generation for multicolor emission; moreover, the third-order susceptibility at the fundamental frequency results in a nonlinear refractive index, i.e., the Kerr nonlinearity, which is associated with self-pulsations in quantum-cascade lasers. The review surveys the technology progression for the enhancement of nonlinear frequency generation as well as the investigation of the physics behind the multimode output of quantum-cascade lasers. In addition, a simulation model accounting for intracavity nonlinear interactions in quantum-cascade lasers is introduced, which can be used to evaluate and further optimize the nonlinear performance.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.An Optical susceptibility, hyperpolarizability
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
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Photonic bands in two-dimensional metallodielectric photonic crystals composed of metal coated cylinders

Chuan Cheng (程川) and Can Xu (徐灿)

J. Appl. Phys. 106, 033101 (2009); http://dx.doi.org/10.1063/1.3183934 (7 pages)

Online Publication Date: 6 August 2009

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Photonic bands in two-dimensional metallodielectric (MD) periodic systems composed of metal coated cylinders are investigated theoretically based on frequency dependent plane-wave expansion method. For the case of E-polarization, although the thickness of metal coating is less than half of the cylinder’s radius, most of MD photonic bands are the same as photonic bands composed of pure metal cylinders. This property provides us with a way to substitute metal photonic crystals with MD photonic crystals in many applications. In addition, flatbands are discovered in MD photonic band structures, which can be tuned by changing the thickness of metal coating while other photonic bands do not change their positions. For the case of H-polarization, the lowest frequency band gap (between the first and the second bands) can open up when the thickness of metal coating is thick enough. According to approximate calculation based on Maxwell–Garnett type effective medium theory and comparison with recent studies on three-dimensional MD photonic band structures, we predict that the lowest frequency band gap is not because of Bragg scattering but result from the individual metal coated dielectric cylinders, so that the gap is independent on geometry of photonic crystal lattices. Then, numerical calculation validates that our prediction is right.
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42.70.Qs Photonic bandgap materials
42.79.Wc Optical coatings
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Origin of giant polarization splitting in high quality organic microcavities

S. Stelitano, S. Savasta, S. Patané, G. De Luca, and L. Monsù Scolaro

J. Appl. Phys. 106, 033102 (2009); http://dx.doi.org/10.1063/1.3190517 (6 pages) | Cited 5 times

Online Publication Date: 7 August 2009

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We study the emission properties of a high quality monolithic microcavity with an embedded ultrathin organic tetrakis(4-methoxyphenyl)porphyrin layer. Spectral and angle-resolved photoluminescence measurements show a well defined polarized doublet at detection angles larger than 15°. The splitting energy ranges up to 70 meV. The usual employed mechanism, based on the mismatch between the center of the mirror stop band and the wavelength of the microcavity, accounts only for a small fraction of the observed splitting. A transfer matrix model taking into account the optical anisotropy of the organic layer, has been employed to reproduce the observed experimental results. The anisotropy of the organic layer, confirmed by optical absorption spectroscopy, origins from a local molecular order as inferred by atomic force microscopy measurements.
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78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials

Photoluminescence properties of Eu2+-activated CaSi2O2N2: Redshift and concentration quenching

Xiufeng Song, Renli Fu, Simeon Agathopoulos, Hong He, Xinran Zhao, and Shaodong Zhang

J. Appl. Phys. 106, 033103 (2009); http://dx.doi.org/10.1063/1.3190522 (5 pages) | Cited 9 times

Online Publication Date: 7 August 2009

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Highly efficient CaSi2O2N2:Eu2+ green phosphors were synthesized via solid-state reaction method. The produced phosphors are effectively excited with UV-vis light of wavelength between 300 and 460 nm and emit a single, intense, and broad emission band centered at 538 nm. The experimental results and their analysis suggest that the energy transfer mechanism should occur due to dipole-dipole interactions among Eu2+ ions, resulting in a shift in emission spectrum toward longer wavelengths with increasing Eu2+ concentration. The quenching concentration of Eu2+ (i.e., where the emission intensity maximizes) is approximately 2 at. %. Accordingly, the produced CaSi2O2N2:Eu2+ green phosphors are qualified for further consideration and experimentation for potential use in white light emitting diodes.
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78.55.Hx Other solid inorganic materials
81.20.-n Methods of materials synthesis and materials processing
85.60.Jb Light-emitting devices
61.72.sd Impurity concentration

Low-voltage onset of electroluminescence in nanocrystalline-Si/SiO2 multilayers

A. Anopchenko, A. Marconi, E. Moser, S. Prezioso, M. Wang, L. Pavesi, G. Pucker, and P. Bellutti

J. Appl. Phys. 106, 033104 (2009); http://dx.doi.org/10.1063/1.3194315 (8 pages) | Cited 19 times

Online Publication Date: 11 August 2009

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Thin film metal-oxide-semiconductor light emitting devices (LEDs) based on nanocrystalline silicon multilayer structure were grown by plasma-enhanced chemical vapor deposition. Room temperature electroluminescence was studied under direct current and time-resolved pulsed-current injection schemes. Multilayer LEDs operating at voltages below 5 V and electroluminescence turn-on voltage of 1.4–1.7 V are demonstrated. The turn-on voltage is less than 3.2 V which corresponds to the barrier height at the silicon oxide interface for electrons. Electrical injection in the multilayer LED is controlled by direct tunneling of electrons and holes among silicon nanocrystals. This injection regime is different than the Fowler–Nordheim tunneling that controls the electron injection in single thick layer LED operating at high voltages. A comparison of the power efficiency for the multilayer based LED and a similar single thick layer LED shows larger power efficiency for the former than for the second. Our results open new directions in the development of highly efficient room temperature silicon based LED.
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85.60.Jb Light-emitting devices
81.07.Bc Nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Thermoluminescence properties of carbon doped Y3Al5O12 (YAG) crystal

Xin-Bo Yang, Jun Xu, Hong-Jun Li, Qun-Yu Bi, Liang-Bi Su, Yan Cheng, and Qiang Tang

J. Appl. Phys. 106, 033105 (2009); http://dx.doi.org/10.1063/1.3194794 (5 pages) | Cited 1 time

Online Publication Date: 11 August 2009

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In this work, carbon doped yttrium aluminum garnet (YAG) (YAG:C) crystal was grown by the temperature gradient technique in a reducing atmosphere. The optical and thermoluminescence (TL) properties of the as-grown YAG:C crystal were investigated. Four absorption bands at 235, 255, 298, and 370 nm and a main blue emission peak at 400 nm are observed in the YAG:C crystal. The absorption coefficients of the bands at 235 and 370 nm, which are associated with the F+-center, increase sharply in YAG crystal by the introduction of carbon. As-grown YAG:C crystal shows high TL sensitivity, and three main glow peaks at 390 K (P1), 465 K (P2), 524 K (P3) and two weak glow peaks at 580 and 625 K are found. The TL dose responses of the three main glow peaks show linear-supralinear characteristic, and wide linearity dose response are found in P1 and P2 glow peaks. The temperature position and TL intensity of three main glow peaks show a strong dependence of heating rate in YAG:C crystal.
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78.60.Kn Thermoluminescence
78.20.-e Optical properties of bulk materials and thin films
78.40.Ha Other nonmetallic inorganics
78.30.Hv Other nonmetallic inorganics
81.10.-h Methods of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
81.40.Gh Other heat and thermomechanical treatments

Theoretical investigation of 1.3 μm dots-under-a-well and dots-in-a-well InAs/GaAs quantum dot vertical-cavity surface-emitting lasers

C. Z. Tong, D. W. Xu, and S. F. Yoon

J. Appl. Phys. 106, 033106 (2009); http://dx.doi.org/10.1063/1.3191660 (8 pages)

Online Publication Date: 11 August 2009

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The threshold characteristic and output power of 1.3 μm quantum dot (QD) vertical-cavity surface-emitting laser (VCSEL) with dots-under-a-well and dots-in-a-well InAs/GaAs QD structures are investigated by using rate equation model and output power model. The influence of VCSEL and QD structures on the modal gain of VCSEL is analyzed. Threshold current density, quantum efficiency, and characteristic temperature are simulated for different QD structures. The dependence of output power of 1.3 μm QD VCSEL on the QD structure, threshold current, quantum efficiency, and oxide-aperture size is investigated in detail.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
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Control of plasma uniformity in a capacitive discharge using two very high frequency power sources

Kallol Bera, Shahid Rauf, Kartik Ramaswamy, and Ken Collins

J. Appl. Phys. 106, 033301 (2009); http://dx.doi.org/10.1063/1.3183946 (7 pages) | Cited 14 times

Online Publication Date: 4 August 2009

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Very high frequency (VHF) capacitively coupled plasma (CCP) discharges are being employed for dielectric etching due to VHF’s various benefits including low plasma potential, high electron density, and controllable dissociation. If the plasma is generated using multiple VHF sources, one can expect that the interaction between the sources can be important in determining the plasma characteristics. The effects of VHF mixing on plasma characteristics, especially its spatial profile, are investigated using both computational modeling and diagnostic experiments. The two-dimensional plasma model includes the full set of Maxwell equations in their potential formulation. The plasma simulation results show that electron density peaks at the center of the chamber at 180 MHz due to the standing electromagnetic wave. Electrostatic effects at the electrode edges tend to get stronger at lower VHFs such as 60 MHz. When the two rf sources are used simultaneously and power at 60 MHz is gradually increased, the ion flux becomes uniform and then transitions to peak at electrode edge. These results are corroborated by Langmuir probe measurements of ion saturation current. VHF mixing is therefore an effective method for dynamically controlling plasma uniformity. The plasma is stronger and more confined when the 60 MHz source is connected to the smaller bottom electrode compared to the top electrode.
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52.80.Pi High-frequency and RF discharges
52.65.-y Plasma simulation
52.25.Fi Transport properties
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.40.Hf Plasma-material interactions; boundary layer effects
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma

Plasma parameters of pulsed-dc discharges in methane used to deposit diamondlike carbon films

C. Corbella, M. Rubio-Roy, E. Bertran, and J. L. Andújar

J. Appl. Phys. 106, 033302 (2009); http://dx.doi.org/10.1063/1.3183945 (11 pages) | Cited 4 times

Online Publication Date: 5 August 2009

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Here we approximate the plasma kinetics responsible for diamondlike carbon (DLC) depositions that result from pulsed-dc discharges. The DLC films were deposited at room temperature by plasma-enhanced chemical vapor deposition (PECVD) in a methane (CH4) atmosphere at 10 Pa. We compared the plasma characteristics of asymmetric bipolar pulsed-dc discharges at 100 kHz to those produced by a radio frequency (rf) source. The electrical discharges were monitored by a computer-controlled Langmuir probe operating in time-resolved mode. The acquisition system provided the intensity-voltage (I-V) characteristics with a time resolution of 1 μs. This facilitated the discussion of the variation in plasma parameters within a pulse cycle as a function of the pulse waveform and the peak voltage. The electron distribution was clearly divided into high- and low-energy Maxwellian populations of electrons (a bi-Maxwellian population) at the beginning of the negative voltage region of the pulse. We ascribe this to intense stochastic heating due to the rapid advancing of the sheath edge. The hot population had an electron temperature Tehot of over 10 eV and an initial low density nehot which decreased to zero. Cold electrons of temperature Tecold ∼ 1 eV represented the majority of each discharge. The density of cold electrons necold showed a monotonic increase over time within the negative pulse, peaking at almost 7×1010 cm−3, corresponding to the cooling of the hot electrons. The plasma potential Vp of ∼ 30 V underwent a smooth increase during the pulse and fell at the end of the negative region. Different rates of CH4 conversion were calculated from the DLC deposition rate. These were explained in terms of the specific activation energy Ea and the conversion factor xdep associated with the plasma processes. The work deepens our understanding of the advantages of using pulsed power supplies for the PECVD of hard metallic and protective coatings for industrial applications (optics, biomedicine, and electronics).
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52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Fq High-field and nonlinear effects
52.80.-s Electric discharges
52.70.Ds Electric and magnetic measurements
68.55.aj Insulators

Effect of radio frequency discharge power on dusty plasma parameters

T. E. Sheridan

J. Appl. Phys. 106, 033303 (2009); http://dx.doi.org/10.1063/1.3186022 (6 pages) | Cited 4 times

Online Publication Date: 5 August 2009

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The parameters of a two-dimensional dusty plasma consisting of six, 9 μm diameter particles trapped inside a radio frequency (rf) plasma sheath have been measured as a function of rf power in a 13.5 mtorr (1.8 Pa) argon discharge. The center-of-mass and breathing frequencies are found by projecting the cluster’s Brownian motion onto the associated normal mode. The center-of-mass frequency (i.e., radial confinement) is insensitive to rf power. The Debye shielding parameter κ, as found from the breathing frequency, increases from ≈0.5 to 2 as the square root of rf power. The Debye length decreases from ≈2.7 to 0.7 mm as the inverse of the square root of rf power. The average particle charge q ≈ −17 000e is effectively independent of rf power. These results are consistent with an electron temperature that is independent of rf power and an ion density that is directly proportional to rf power, where the Debye length is determined by the ion density in combination with the electron temperature.
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52.80.Pi High-frequency and RF discharges
52.25.-b Plasma properties
52.27.Lw Dusty or complex plasmas; plasma crystals
52.55.-s Magnetic confinement and equilibrium
52.40.Kh Plasma sheaths

Mechanism of laser and rf plasma in vibrational nonequilibrium CO–N2 gas mixture

Guofeng Lou and Igor V. Adamovich

J. Appl. Phys. 106, 033304 (2009); http://dx.doi.org/10.1063/1.3159893 (7 pages)

Online Publication Date: 5 August 2009

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This paper investigates the mechanism of plasma created by focused CO laser and rf electric field. The plasma is created in a CO/N2 environment, at a total pressure of 600 torr. Ionization of the gases occurs by an associative ionization mechanism, in collisions of two highly vibrationally excited molecules. These highly vibrationally excited states are populated by resonance absorption of the CO radiation followed by anharmonic vibration-vibration (V-V) pumping. Moreover N2 also becomes vibrationally excited due to collisions with vibrationally excited CO. The coupled rf reduced electric field E/N is sufficiently low to prevent electron impact ionization that may create plasma individually, so when a subbreakdown rf field is applied to the plasma, collisions between the free electrons heated by the field and the diatomic species create additional vibrational excitation both in the region occupied by the CO laser beam and outside of the laser beam region. The numerical results show plasma created in both regions (in and out of the CO laser beam region) with the associative ionization mechanism. This suggests a method for creating a stable nonequilibrium plasma. The calculation result is verified by comparison the synthetic spectrum to a measured one.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.20.Fs Electron collisions
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams

Quantum cascade laser investigations of CH4 and C2H2 interconversion in hydrocarbon/H2 gas mixtures during microwave plasma enhanced chemical vapor deposition of diamond

Jie Ma, Andrew Cheesman, Michael N. R. Ashfold, Kenneth G. Hay, Stephen Wright, Nigel Langford, Geoffrey Duxbury, and Yuri A. Mankelevich

J. Appl. Phys. 106, 033305 (2009); http://dx.doi.org/10.1063/1.3176971 (15 pages) | Cited 3 times

Online Publication Date: 5 August 2009

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CH4 and C2H2 molecules (and their interconversion) in hydrocarbon/rare gas/H2 gas mixtures in a microwave reactor used for plasma enhanced diamond chemical vapor deposition (CVD) have been investigated by line-of-sight infrared absorption spectroscopy in the wavenumber range of 1276.5−1273.1 cm−1 using a quantum cascade laser spectrometer. Parameters explored include process conditions [pressure, input power, source hydrocarbon, rare gas (Ar or Ne), input gas mixing ratio], height (z) above the substrate, and time (t) after addition of hydrocarbon to a pre-existing Ar/H2 plasma. The line integrated absorptions so obtained have been converted to species number densities by reference to the companion two-dimensional (r,z) modeling of the CVD reactor described in Mankelevich et al. [J. Appl. Phys. 104, 113304 (2008)] . The gas temperature distribution within the reactor ensures that the measured absorptions are dominated by CH4 and C2H2 molecules in the cool periphery of the reactor. Nonetheless, the measurements prove to be of enormous value in testing, tensioning, and confirming the model predictions. Under standard process conditions, the study confirms that all hydrocarbon source gases investigated (methane, acetylene, ethane, propyne, propane, and butane) are converted into a mixture dominated by CH4 and C2H2. The interconversion between these two species is highly dependent on the local gas temperature and the H atom number density, and thus on position within the reactor. CH4→C2H2 conversion occurs most efficiently in an annular shell around the central plasma (characterized by 1400<Tgas<2200 K), while the reverse transformation C2H2→CH4 is favored in the more distant regions where Tgas<1400 K. Analysis of the multistep interconversion mechanism reveals substantial net consumption of H atoms accompanying the CH4→C2H2 conversion, whereas the reverse C2H2→CH4 process only requires H atoms to drive the reactions; H atoms are not consumed by the overall conversion.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.at Other materials
78.35.+c Brillouin and Rayleigh scattering; other light scattering
52.77.Dq Plasma-based ion implantation and deposition
78.66.Nk Insulators
81.05.U- Carbon/carbon-based materials

Temporal evolution of the laser-induced plasma generated by IR CO2 pulsed laser on carbon targets

J. J. Camacho, L. Díaz, M. Santos, L. J. Juan, and J. M. L. Poyato

J. Appl. Phys. 106, 033306 (2009); http://dx.doi.org/10.1063/1.3190542 (11 pages) | Cited 5 times

Online Publication Date: 5 August 2009

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Time-resolved optical emission analysis was carried out for the plasma plume, produced by high-power tunable IR CO2 pulsed laser ablation of graphite, at λ = 10.591 μm and in a regime of relatively high laser fluences (123–402 J/cm2). Wavelength-dispersed spectra of the plasma plume, at medium-vacuum conditions (4 Pa) and at 9.0 mm from the target, show ionized species (C+, C2+, C3+, C4+, N2+ , N+, and O+), neutral atoms (C, H, N, and O), and neutral diatomic molecules (C2, CN, OH, CH, and N2). In this work, we focus our attention on the temporal evolution of different atomic/ionic and molecular species over a broad spectral range from 190 to 1000 nm. The results show a faster decay for ionic fragments than for neutral atomic and molecular species. The velocity and kinetic energy distributions for different species were obtained from time-of-flight measurements using time-resolved optical emission spectroscopy. Possible mechanisms for the production of these distributions are discussed. Excitation temperature, electron density, and vibrational temperature in the laser-induced plasma were estimated from the analysis of spectral data at various times from the laser pulse incidence.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

A comparative study of single and double pulse laser induced breakdown spectroscopy

Rizwan Ahmed and M. Aslam Baig

J. Appl. Phys. 106, 033307 (2009); http://dx.doi.org/10.1063/1.3190516 (6 pages) | Cited 5 times

Online Publication Date: 7 August 2009

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A comparative study of single and double pulse laser induced breakdown spectroscopy (LIBS) using the fundamental (1064 nm) and the second harmonics (532 nm) of Nd:YAG lasers is presented. The double pulse collinear configuration yields more than three hundred times signal enhancement in the singly ionized aluminum lines as compared to the single pulse LIBS spectrum. The effect of interpulse delay between the two laser pulses and the laser pulses energies ratio in the double pulse spectrum are studied. A comparison of variations of plasma parameters along the plume axis in the single and the double pulse has also been studied.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
42.62.-b Laser applications

High efficiency annular magnetically insulated line oscillator-transit time oscillator with three separate frequencies in three bands

Renzhen Xiao, Jun Sun, Changhua Chen, Yongpeng Zhang, and Hao Shao

J. Appl. Phys. 106, 033308 (2009); http://dx.doi.org/10.1063/1.3190532 (4 pages) | Cited 3 times

Online Publication Date: 7 August 2009

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To increase the efficiency of the magnetically insulated line oscillator (MILO) and expand its frequency band, a coaxial transit time oscillator (TTO) is introduced to use the load currents of an annular MILO, called the annular MILO-TTO, which comprises an inward-emitting MILO, an outward-emitting MILO, and a coaxial TTO. In simulation, when the input power is 78 GW and the diode voltage is 520 kV, three microwaves with powers of 3.2, 9.6, and 7.0 GW are generated, with a total efficiency of 25.4%, in the inward-emitting MILO, the outward-emitting MILO, and the coaxial TTO, and the frequencies are 1.7, 3.3, and 4.2 GHz, corresponding to L, S, and C bands, respectively.
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84.30.Ng Oscillators, pulse generators, and function generators
85.70.-w Magnetic devices

Influence of electron velocity distribution on the plasma expansion features

R. Shokoohi and H. Abbasi

J. Appl. Phys. 106, 033309 (2009); http://dx.doi.org/10.1063/1.3168437 (5 pages)

Online Publication Date: 10 August 2009

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Collisionless plasma expansion into vacuum is addressed emphasizing on the kinetic effects associated with the plasma electrons. It is an important issue since there are situations in which the plasmas are in nonequilibrium state. Thus, the electron distribution function (DF) that is generally non-Maxwellian has to be modeled. For this purpose, the generalized Lorentzian (kappa) DF is used to simulate the electron DF. The Maxwellian and kappa distributions differ substantially in a high-energy tail. Thus, the electron dynamics is studied by the Vlasov equation. Neglecting the ion temperatures, fluid equations are used for them. It is shown that by increasing the population of energetic electrons, the expansion takes place faster, the resulting electric field is stronger, and the ions are accelerated to higher energy.
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52.25.Fi Transport properties
52.65.Ff Fokker-Planck and Vlasov equation

Experimental scaling law for mass ablation rate from a Sn plasma generated by a 1064 nm laser

Russell A. Burdt, Sam Yuspeh, Kevin L. Sequoia, Yezheng Tao, Mark S. Tillack, and Farrokh Najmabadi

J. Appl. Phys. 106, 033310 (2009); http://dx.doi.org/10.1063/1.3190537 (5 pages) | Cited 9 times

Online Publication Date: 10 August 2009

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The ablation depth in planar Sn targets irradiated with a pulsed 1064 nm laser was investigated over laser intensities from 3×1011 to 2×1012 W/cm2. The ablation depth was measured by irradiating a thin layer of Sn evaporated onto a Si wafer, and looking for signatures of Si ions in the expanding plasma with spectroscopic and particle diagnostics. It was found that ablation depth scales with laser intensity to the (5/9)th power, which is consistent with analytical models of steady-state laser ablation, as well as empirical formulae from previous studies of mass ablation rate in overlapping parameter space. In addition, the scaling of mass ablation rate with atomic number of the target as given by empirical formulae in previous studies using targets such as C and Al, are shown to remain valid for the higher atomic number of the target (Z = 50) used in these experiments.
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52.38.Mf Laser ablation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
52.70.Nc Particle measurements
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
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First-principles study of structural, thermodynamic, elastic, and magnetic properties of Cr2GeC under pressure and temperature

Wei Zhou, Lijuan Liu, and Ping Wu

J. Appl. Phys. 106, 033501 (2009); http://dx.doi.org/10.1063/1.3187912 (7 pages) | Cited 2 times

Online Publication Date: 3 August 2009

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The dependences of the structural, thermodynamic, elastic, and magnetic properties of Cr2GeC on pressure and temperature were investigated with the quasiharmonic Debye model and the first-principles method based on the density functional theory. Our calculated data, which were obtained at different pressures and temperatures, are in good agreement with the experimental results. Cr2GeC is mechanically stable in the pressure range of 0–50 GPa and the compressibility along the a axis is greater than along the c axis indicating that the presence of C in the interstitial sites of the Cr octahedra can enhance the stability of the Cr–Ge bonds. It is also found that the antiferromagnetic state is the ground state of Cr2GeC and the total induced magnetic moment of the metastable ferromagnetic state decreases with pressure and completely vanishes at about 25 GPa.
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61.66.Fn Inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
75.30.Cr Saturation moments and magnetic susceptibilities
71.20.Ps Other inorganic compounds
65.40.De Thermal expansion; thermomechanical effects

Power modulation based fiber-optic loop-sensor having a dual measurement range

Nguyen Q. Nguyen and Nikhil Gupta

J. Appl. Phys. 106, 033502 (2009); http://dx.doi.org/10.1063/1.3187917 (5 pages) | Cited 2 times

Online Publication Date: 3 August 2009

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A fiber-optic sensor is investigated in this work for potential applications in structural health monitoring. The sensor, called fiber-loop-sensor, is based on bending an optical fiber beyond a critical radius to obtain intensity losses and calibrating the losses with respect to the applied force or displacement. Additionally, in the present case, the use of single-mode optical fibers allows the appearance of several resonance peaks in the transmitted power-displacement graph. The intensity of one of these resonances can be tracked in a narrow range to obtain high sensitivity. Experimental results show that the resolution of 10−4 N for force and 10−5 m for displacement can be obtained in these sensors. The sensors are calibrated for various loop radii and for various loading rates. They are also tested under loading-unloading conditions for over 104 cycles to observe their fatigue behavior. The sensors show very repeatable response and no degradation in performance under these test conditions. Simple construction and instrumentation, high sensitivity, and low cost are the advantages of these sensors.
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42.81.Pa Sensors, gyros
42.81.Dp Propagation, scattering, and losses; solitons
89.20.Kk Engineering

Water diffusion and fracture behavior in nanoporous low-k dielectric film stacks

Han Li, Ting Y. Tsui, and Joost J. Vlassak

J. Appl. Phys. 106, 033503 (2009); http://dx.doi.org/10.1063/1.3187931 (8 pages) | Cited 3 times

Online Publication Date: 5 August 2009

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Among various low-dielectric constant (low-k) materials under development, organosilicate glasses (OSGs) containing nanometer-size pores are leading candidates for use as intrametal dielectrics in future microelectronics technologies. In this paper, we investigate the direct impact of water diffusion on the fracture behavior of film stacks that contain porous OSG coatings. We demonstrate that exposure of the film stacks to water causes significant degradation of the interfacial adhesion energy, but that it has negligible effect on the cohesive fracture energy of the nanoporous OSG layer. Isotope tracer diffusion experiments combined with dynamic secondary ion mass spectroscopy show that water diffuses predominantly along the interfaces, and not through the porous films. This unexpected result is attributed to the hydrophilic character of the interfaces.
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77.55.-g Dielectric thin films
81.05.Kf Glasses (including metallic glasses)
66.30.hh Glasses
62.20.mm Fracture
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.35.Gy Mechanical properties; surface strains
68.35.Fx Diffusion; interface formation
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Chemical and physical sputtering effects on the surface morphology of carbon films grown by plasma chemical vapor deposition

Luis Vázquez and Josephus G. Buijnsters

J. Appl. Phys. 106, 033504 (2009); http://dx.doi.org/10.1063/1.3184349 (8 pages) | Cited 3 times

Online Publication Date: 6 August 2009

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We have studied the influence of chemical and physical sputtering on the surface morphology of hydrogenated carbon films deposited on silicon substrates by bias-enhanced electron cyclotron resonance chemical vapor deposition. Atomic force microscopy based power spectrum density (PSD) and roughness analysis have been used to investigate the film morphology. This study has been possible due to the appropriate choice of the experimental variables, in particular, gas mixture, resulting in either nitrogen-free (a-C:H) or nitrogenated carbon (a-CN:H) films, and substrate bias (Vb). Under these conditions, chemical sputtering is present for a-CN:H deposition but it is negligible for a-C:H film growth, while physical sputtering processes appear for both systems for Vb ≤ −85 V. When physical sputtering does not operate, the film growth with simultaneous chemical sputtering leads to a characteristic a-CN:H granular surface morphology. Furthermore, PSD analysis reveals that a spatial correlation of the a-CN:H film surface roughness, up to distances ∼ 300 nm, becomes a fingerprint of the coexistence of growth and chemical erosion processes on the film morphology. However, once physical sputtering takes place, the influence of chemical sputtering by reactive nitrogen species on the final surface morphology becomes negligible and both a-CN:H and a-C:H film morphologies are ultrasmooth.
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68.55.aj Insulators
68.55.J- Morphology of films
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
68.35.bt Other materials
68.37.Ps Atomic force microscopy (AFM)
76.40.+b Diamagnetic and cyclotron resonances

Charged particle-display

Sung Nae Cho

J. Appl. Phys. 106, 033505 (2009); http://dx.doi.org/10.1063/1.3176485 (13 pages)

Online Publication Date: 6 August 2009

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An optical shutter based on charged particles is presented. The output light intensity of the proposed device has an intrinsic dependence on the interparticle spacing between charged particles, which can be controlled by varying voltages applied to the control electrodes. The interparticle spacing between charged particles can be varied continuously and this opens up the possibility of particle based displays with continuous grayscale.
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42.79.Kr Display devices, liquid-crystal devices

Measurement and calculation of surface tension for undercooled liquid nickel and its alloy

H. P. Wang, J. Chang, and B. Wei

J. Appl. Phys. 106, 033506 (2009); http://dx.doi.org/10.1063/1.3187793 (4 pages) | Cited 11 times

Online Publication Date: 6 August 2009

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The surface tensions of metastable undercooled liquid nickel and its alloy are experimentally measured and theoretically calculated by electromagnetic levitation oscillating droplet method and molecular dynamics method, respectively. The experimental undercoolings for liquid Ni and Ni90.1Si9.9 alloy are 201 and 206 K, whereas the calculated undercoolings are up to 426 and 323 K. The measured surface tension displays the same undercooling dependence as the molecular dynamics calculation. The surface tension increases linearly with the increase in undercooling and no break occurs at the melting temperature. It is found that the correlation of surface tension with temperature predicted by molecular dynamics calculation agrees with the experimental results for both pure Ni and its alloy.
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68.03.Cd Surface tension and related phenomena
61.25.Mv Liquid metals and alloys
64.70.dj Melting of specific substances
61.20.Ja Computer simulation of liquid structure

Temperature dependence of the optical transitions in Ga0.64In0.36N0.046As0.954 multiquantum wells of various widths studied by photoreflectance

R. Kudrawiec, P. Poloczek, J. Misiewicz, F. Ishikawa, A. Trampert, and K. H. Ploog

J. Appl. Phys. 106, 033507 (2009); http://dx.doi.org/10.1063/1.3187789 (5 pages)

Online Publication Date: 7 August 2009

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The temperature dependencies of optical transitions in as-grown Ga0.64In0.36N0.046As0.954 multiple quantum wells (QWs) of various widths (ranging from 3.9 to 8.1 nm) grown at the low temperature of 375 °C were studied by photoreflectance (PR). In addition to the 11H transition, which is the fundamental transition for this QW, the optical transitions between excited states (22H and 33H transitions, where the notation klH denotes the transition between the kth heavy-hole valence subband and the lth conduction subband) were clearly observed in the PR spectra. The temperature dependencies of the QW transition energies were analyzed using Varshni and Bose–Einstein expressions. It was found that with increasing temperature, both the ground-state and the excited-state transitions shift to the red without showing S-shape-type behaviors, which are typical for photoluminescence from this system. This shift does not depend on the QW width and amounts to ∼ 80 meV for the 11H transition and ∼ 100 meV for the 22H and 33H transitions in the temperature range of 10–300 K. These shifts are comparable to those of N-free QWs.
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78.67.De Quantum wells
68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.St Quantum wells

Shock compression of cubic boron nitride

Nobuaki Kawai, Manabu Yokoo, Ken-ichi Kondo, Takashi Taniguchi, and Fumikazu Saito

J. Appl. Phys. 106, 033508 (2009); http://dx.doi.org/10.1063/1.3187922 (4 pages) | Cited 1 time

Online Publication Date: 7 August 2009

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Hugoniot measurements have been performed on high-purity cubic boron nitride polycrystals in the pressure range up to 296 GPa using a two-stage light-gas gun. Hugoniot parameters have been measured by a line reflection method and Fabry–Pérot velocimetry. The Hugoniot elastic limit (HEL) is determined to be 44.3 GPa, which is the second highest value after that of diamond. Above the HEL, the Hugoniot compression curve shows a considerable offset from its hydrodynamic compression curve, which is calculated from static-compression data. This result shows that cubic boron nitride preserves its shear strength in the plastic region. Hugoniot data indicate that the cubic phase of boron nitride is stable in the pressure range up to 296 GPa.
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81.40.Lm Deformation, plasticity, and creep
62.50.Ef Shock wave effects in solids and liquids
62.20.fq Plasticity and superplasticity
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