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1 Jun 2010

Volume 107, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 107, 111101 (2010); http://dx.doi.org/10.1063/1.3386413 (22 pages)

John Federici and Lothar Moeller
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Review of terahertz and subterahertz wireless communications

John Federici and Lothar Moeller

J. Appl. Phys. 107, 111101 (2010); http://dx.doi.org/10.1063/1.3386413 (22 pages) | Cited 23 times

Online Publication Date: 9 June 2010

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According to Edholm’s law, the demand for point-to-point bandwidth in wireless short-range communications has doubled every 18 months over the last 25 years. It can be predicted that data rates of around 5–10 Gb/s will be required in ten years. In order to achieve 10 Gb/s data rates, the carrier frequencies need to be increased beyond 100 GHz. Over the past ten years, several groups have considered the prospects of using sub-terahertz (THz) and THz waves (100–2000 GHz) as a means to transmit data wirelessly. Some of the reported advantages of THz communications links are inherently higher bandwidth compared to millimeter wave links, less susceptibility to scintillation effects than infrared wireless links, and the ability to use THz links for secure communications. Our goal of this paper is to provide a comprehensive review of wireless sub-THz and THz communications.
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84.40.Ua Telecommunications: signal transmission and processing; communication satellites
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back to top Lasers, Optics, and Optoelectronics

In-plane poling characterization of organic electro-optical polymer

C. Palazzesi, F. Stella, F. De Matteis, and M. Casalboni

J. Appl. Phys. 107, 113101 (2010); http://dx.doi.org/10.1063/1.3380840 (5 pages)

Online Publication Date: 1 June 2010

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The purpose of this work is to investigate the in-plane poling technique and to make a comparison with the corona poling technique. To this end we chose as a test material a well known guest-host system, disperse red 1 in polymethyl methacrilate. The second harmonic generation and the order parameter, determined by means of polarized absorption spectroscopy, have been monitored to test the effectiveness of the poling. We found out that the shorter the gap distance between the electrodes, the higher is the maximum achievable value of the applied voltage, without occurrence of the electrical discharge, this increase in the electrical field enhances the poling efficiency thus enlarging the possibility to employ this configuration in electro-optical devices, such as Mach–Zehnder modulators. The use of quartz slide instead of BK7 and the careful tuning of the coplanar-electrode distance allowed to reach a high poling efficiency, yielding a nonlinear coefficient upto 25 pm/V while a value not higher than 8 pm/V was obtained with a traditional corona poling.
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82.35.Ej Nonlinear optics with polymers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.-k Nonlinear optics

Energy upconversion in holmium doped lead–germano–tellurite glass

Indumathi Kamma and B. Rami Reddy

J. Appl. Phys. 107, 113102 (2010); http://dx.doi.org/10.1063/1.3431386 (5 pages) | Cited 1 time

Online Publication Date: 1 June 2010

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Holmium doped lead–germano–tellurite glass was prepared by the melt quenching technique. The Judd–Ofelt intensity parameters were estimated as Ω2 = 7.6×10−20, Ω4 = 12.9×10−20, and Ω6 = 2.5×10−20 cm2. Radiative transition probabilities and lifetimes were also determined for some of the levels. Room temperature upconversion emissions have been observed from Ho3+ at 497 nm under 532 nm laser excitation, and at 557 and 668 nm under 762 nm laser excitation. The upconversion emission mechanisms were found to be due to a step wise excitation process. Upconversion emission intensity enhanced in a heat treated glass.
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61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
84.60.-h Direct energy conversion and storage
78.55.Hx Other solid inorganic materials
81.40.Gh Other heat and thermomechanical treatments

Mode characteristics of metallically coated square microcavity connected with an output waveguide

Kai-Jun Che and Yong-Zhen Huang

J. Appl. Phys. 107, 113103 (2010); http://dx.doi.org/10.1063/1.3431400 (4 pages)

Online Publication Date: 2 June 2010

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Mode characteristics of a square microcavity with an output waveguide on the middle of one side, laterally confined by an insulating layer SiO2 and a p-electrode metal Au, are investigated by two-dimensional finite-difference time-domain technique. The mode quality (Q) factors versus the width of the output waveguide are calculated for Fabry–Pérot type and whispering-gallery type modes in the square cavity. Mode coupling between the confined modes in the square cavity and the guided modes in the output waveguide determines the mode Q factors, which is greatly influenced by the symmetry behaviors of the modes. Fabry–Pérot type modes can also have high Q factors due to the high reflectivity of the Au layer for the vertical incident mode light rays. For the square cavity with side length 4 μm and refractive index 3.2, the mode Q factors of the Fabry–Pérot type modes can reach 104 at the mode wavelength of 1.5 μm as the output waveguide width is 0.4 μm.
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42.79.Gn Optical waveguides and couplers
02.70.Bf Finite-difference methods

Photoluminescence-induced oscillations in porous anodic aluminum oxide films grown on Si: Effect of the interface and porosity

S. Gardelis, A. G. Nassiopoulou, V. Gianneta, and M. Theodoropoulou

J. Appl. Phys. 107, 113104 (2010); http://dx.doi.org/10.1063/1.3432694 (5 pages)

Online Publication Date: 2 June 2010

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We report that porous anodic alumina (aluminum oxide: Al2O3) (PAA) thin films directly grown on Si show clear oscillations in their photoluminescence (PL) spectra which are ascribed to PL-induced interferences within the Fabry–Pérot optical cavity formed by the PAA film on Si, that involve the air/oxide and oxide/Si interfaces. The existence of the PL-induced oscillations is indicative of the high quality of the interface of the PAA film with Si, which is both planar and smooth. We show that by using these oscillations we can develop a sensitive optical method of measuring the porosity of PAA thin films on Si if we know the film thickness. The method is based on the calculation of the effective refractive index of the PAA film derived from the PL-induced oscillations, which is then introduced into the Bruggeman equation in order to derive the porosity of the film.
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68.55.-a Thin film structure and morphology
61.43.Gt Powders, porous materials

Investigations on terahertz radiation generated by two superposed femtosecond laser pulses

Anil K. Malik, Hitendra K. Malik, and Shigeo Kawata

J. Appl. Phys. 107, 113105 (2010); http://dx.doi.org/10.1063/1.3406257 (9 pages) | Cited 3 times

Online Publication Date: 3 June 2010

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The generation of terahertz (THz) radiation based on tunnel ionization of a gas jet is analytically investigated when two superposed short pulse lasers with finite initial phase difference are focused on to it after passing through an axicon. The phase difference between these two lasers plays an important role for the optimization of rate of ionization, evolution of plasma density, and subsequently the residual current due to dipole oscillations. The directionality of the emitted THz radiation can be controlled by tuning initial phase difference between the two laser pulses. Since a nonuniform plasma is produced during the tunnel ionization, the effect of radial variation in the electron density in the plasma channel is studied on the frequency of the emitted THz radiation and on its power. Higher power THz radiation is obtained for the higher fields of the lasers. With optimum initial phase of the laser envelope and the channel width, the mechanism seems to be much more efficient than some of the other mechanisms.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Photoinduced absorption study of carrier dynamics in Ru-doped Bi12SiO20 crystals after nanosecond laser pulse excitation

V. Marinova, I. Ahmad, and E. Goovaerts

J. Appl. Phys. 107, 113106 (2010); http://dx.doi.org/10.1063/1.3418443 (7 pages) | Cited 5 times

Online Publication Date: 4 June 2010

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The charge carrier dynamics in the sillenite type crystal Bi12SiO20 (BSO) doped with ruthenium is studied by monitoring the optical density changes after nanosecond laser pulse excitation using a frequency-doubled Nd:yttrium aluminum garnet laser. Ruthenium doping leads to a relatively high density of trap levels that significantly increase the relaxation time of excited charge carriers in comparison with a nondoped BSO. Relaxation dynamics with two different decay time constants is observed in BSO:Ru in the studied submicron to 100 s time range and their dependences on pump intensity and on temperature are investigated. From the observed temperature dependence of the slower and faster of the two decay components, thermal activation energies of Ea,s = 0.80±0.03 eV and Ea,f = 0.68±0.03 eV were determined, respectively. The results indicate that in BSO:Ru at least two different traps centers are involved in the long-lived photoinduced carrier dynamics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects
61.72.up Other materials
72.80.Sk Insulators

Interdiffusion effects and line broadening of hole intersubband absorption in complex GaAs/AlGaAs quantum well structures

Zoran Ikonić, Oana Malis, Loren N. Pfeiffer, Kenneth W. West, and Paul Harrison

J. Appl. Phys. 107, 113107 (2010); http://dx.doi.org/10.1063/1.3402289 (6 pages)

Online Publication Date: 8 June 2010

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Detailed modeling of intersubband absorption in p-doped GaAs quantum wells embedded in GaAs/AlAs superlattice barriers is performed. It is shown that a careful analysis of measurements provides valuable information on the structure details, like the extent of interdiffusion and different sources of line broadening, which can be useful for further design of emitters and detectors based on this and other material systems.
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78.67.De Quantum wells
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.66.Fd III-V semiconductors
73.21.Fg Quantum wells
68.35.Fx Diffusion; interface formation

Highly polarized polymer-based light-emitting diodes fabricated by using very thin photoaligned polyimide layers

Kenji Sakamoto, Kazushi Miki, Masahiro Misaki, Koichi Sakaguchi, Yuzuru Hijikata, Masayuki Chikamatsu, and Reiko Azumi

J. Appl. Phys. 107, 113108 (2010); http://dx.doi.org/10.1063/1.3445774 (9 pages) | Cited 7 times

Online Publication Date: 9 June 2010

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Polarized polymer-based light-emitting diodes (PLEDs) have been fabricated by inserting a very thin photoaligned polyimide film into the device structure. The photoaligned polyimide film was used to form a highly oriented layer of light-emitting polymer, poly (9,9-dioctylfluorenyl-2,7-diyl) (PFO). The polyimide contains azobenzene in the backbone structure, allowing us to control the alignment of its backbone structure by optical treatment. Since the photoalignment treatment is scratch-free, the thickness of the photoaligned film can be reduced below 4 nm without decreasing its alignment ability for PFO. Even though polyimide is a good insulator, such a very thin photoaligned film can be inserted into PLED structures. We examined the influence of the thickness of the photoaligned polyimide film and the light-emitting layer on the polarization ratio and the current efficiency of the polarized PLEDs. Using a 2.9 nm-thick polyimide photoalignment layer and a 101 nm-thick PFO light-emitting layer, we have succeeded in fabricating a polarized PLED with a current efficiency of 0.3 cd/A at 150 cd/m2 and polarization ratios of 46 at 434 nm, 27 at 460 nm, and 20 for integrated intensity from 400 to 600 nm.
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85.60.Jb Light-emitting devices

Relative contribution of geometric shape and periodicity to resonant terahertz transmission

J. W. Lee and D. S. Kim

J. Appl. Phys. 107, 113109 (2010); http://dx.doi.org/10.1063/1.3445780 (6 pages)

Online Publication Date: 9 June 2010

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We report the terahertz (THz) transmission characteristics of subwavelength slit arrays with a variety of structures ranging from periodic to random. THz electromagnetic wave transmission experiments clarify the relative contributions of the periodicity and the geometric shape effects to transmission enhancement. In the spectral region slightly below the first Rayleigh minimum, strong transmission enhancement is achieved through the contributions of both effects. In the long-wavelength region, however, enhancement is achieved even in the random arrays of slits because the slit shape has its fundamental resonance. The understanding of the mechanisms of resonant THz transmission is elucidated by using a theoretical approach that is based on a perfect conductor model.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
42.79.-e Optical elements, devices, and systems

Optical gain characteristics of staggered InGaN quantum wells lasers

Hongping Zhao and Nelson Tansu

J. Appl. Phys. 107, 113110 (2010); http://dx.doi.org/10.1063/1.3407564 (12 pages) | Cited 29 times

Online Publication Date: 9 June 2010

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Staggered InGaN quantum wells (QWs) are analyzed as improved gain media for laser diodes (LDs) lasing at 440 and 500 nm. The calculation of band structure is based on a 6-band k⋅p method taking into account the valence band mixing, strain effect, and spontaneous and piezoelectric polarizations as well as the carrier screening effect. Staggered InGaN QWs with two-layer and three-layer step-function like In-content InGaN QWs structures are investigated to enhance the optical gain as well as to reduce the threshold current density for LDs emitting at 440 and 500 nm. Our analysis shows that the optical gain is enhanced by 1.5–2.1 times by utilizing the staggered InGaN QW active region emitting at 440 nm, which leads to a reduction of the threshold current density up to 24% as compared to that of the conventional InGaN QW laser. Staggered InGaN QWs with enhanced optical gain shows significantly reduced blue-shift as carrier density increases, which enables nitride QWs with high optical gain in the green spectral regime. The use of green-emitting three-layer staggered InGaN QW is also expected to lead to reduction in the threshold carrier density by 30%.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Enhancement of dye fluorescence recovery in nematic liquid crystals using a spatial optical soliton

J. F. Henninot, J. F. Blach, and M. Warenghem

J. Appl. Phys. 107, 113111 (2010); http://dx.doi.org/10.1063/1.3446091 (6 pages) | Cited 3 times

Online Publication Date: 10 June 2010

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Up to now, spatial optical solitons have been mostly studied for their particular nature (a nonlinear mode of propagation); with a potential application in steering and routing beams. In this paper, we propose another use of spatial optical solitons: the enhancement of the fluorescence recovery. As a spatial soliton can be excited in a luminescent medium, the luminescence excited by this collimated beam will be partly trapped within the self created waveguide and then driven up to a collection fiber facing the soliton. We demonstrate the feasibility of such concept by comparing the collected fluorescence signals of a dye in a nematic liquid crystal host, excited either by a Gaussian beam or a spatial soliton, in both cases, emerging out of a source fiber and collected via another fiber. We found that, the fluorescence signal collected as the excitation source, is a soliton, is larger than the one collected as the source, is a Gaussian beam, with an enhancement factor which depends on the fibers distance. Actually, we found that, for a soliton excitation source, the signal slightly increases as the distance between the fibers varies from 0.5 to 2 Rayleigh range, contrarily to the case of a Gaussian beam excitation source for which the signal severely decreases with that distance. A simple model confirms such a behavior.
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42.65.Tg Optical solitons; nonlinear guided waves
42.81.Dp Propagation, scattering, and losses; solitons
42.65.Wi Nonlinear waveguides
42.81.-i Fiber optics
42.70.Df Liquid crystals
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Effect of particle size on the UV pulsed-laser scribing in computational fluid dynamics-based simulations

Kwan-Woo Park and Suck-Joo Na

J. Appl. Phys. 107, 113112 (2010); http://dx.doi.org/10.1063/1.3436588 (7 pages)

Online Publication Date: 14 June 2010

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A computational model for UV pulsed-laser scribing of silicon target is presented and compared with experimental results. The experiments were performed with a high-power Q-switched diode-pumped solid state laser which was operated at 355 nm. They were conducted on n-type 500 μm thick silicon wafers. The scribing width and depth were measured using scanning electron microscopy. The model takes into account major physics, such as heat transfer, evaporation, multiple reflections, and Rayleigh scattering. It also considers the attenuation and redistribution of laser energy due to Rayleigh scattering. Especially, the influence of the average particle sizes in the model is mainly investigated. Finally, it is shown that the computational model describing the laser scribing of silicon is valid at an average particle size of about 10 nm.
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81.65.-b Surface treatments
47.27.te Turbulent convective heat transfer
78.35.+c Brillouin and Rayleigh scattering; other light scattering
47.11.-j Computational methods in fluid dynamics
42.62.-b Laser applications
back to top Plasmas and Electrical Discharges

The radiation from a planar metamaterial waveguide

A. A. Basharin, N. P. Balabukha, and V. N. Semenenko

J. Appl. Phys. 107, 113301 (2010); http://dx.doi.org/10.1063/1.3428479 (5 pages) | Cited 1 time

Online Publication Date: 1 June 2010

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Propagation of electromagnetic waves in planar waveguides made of metamaterials with negative values of the relative permittivity and relative permeability is analyzed. The specific features of radiation from antennas manufactured on the basis of planar metamaterial waveguides are studied. It is shown that radiation of such antennas is characterized by the backward radiation effect, i.e., the maximum of the radiation pattern is formed at 180°. The causes of this effect and the conditions for its appearance are revealed. It is proved that this effect appears only in the antennas manufactured on the basis of metamaterial waveguides with negative values of the relative permittivity and relative permeability. A design version of a scanning two-mode antenna operating on the basis of this effect is proposed.
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42.70.-a Optical materials
42.79.Gn Optical waveguides and couplers
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Modeling of ac dielectric barrier discharge

J. S. Shang and P. G. Huang

J. Appl. Phys. 107, 113302 (2010); http://dx.doi.org/10.1063/1.3415526 (7 pages) | Cited 1 time

Online Publication Date: 2 June 2010

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The qualitative electrodynamic field of the dielectric barrier discharge in air is studied by a three-component, drift-diffusion plasma model including the Poisson equation of plasmadynamics. The critical media interface boundary conditions independent of the detailed mechanisms of surface absorption, diffusion, recombination, and charge accumulation on electrode or dielectrics are developed from the theory of electromagnetics. The computational simulation duplicates the self-limiting feature of dielectric barrier discharge for preventing corona-to-spark transition, and the numerical results of the breakdown voltage are compared very well with data. According to the present modeling, the periodic electrodynamic force due to charge separation over the electrodes also exerts on alternative directions from the exposed to encapsulated electrodes over a complete ac cycle as experimental observations.
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52.80.-s Electric discharges
52.25.Fi Transport properties

Modeling of radiative properties of Sn plasmas for extreme-ultraviolet source

Akira Sasaki, Atsushi Sunahara, Hiroyuki Furukawa, Katsunobu Nishihara, Shinsuke Fujioka, Takeshi Nishikawa, Fumihiro Koike, Hayato Ohashi, and Hajime Tanuma

J. Appl. Phys. 107, 113303 (2010); http://dx.doi.org/10.1063/1.3373427 (11 pages) | Cited 6 times

Online Publication Date: 2 June 2010

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Atomic processes in Sn plasmas are investigated for application to extreme-ultraviolet (EUV) light sources used in microlithography. We develop a full collisional radiative (CR) model of Sn plasmas based on calculated atomic data using Hebrew University Lawrence Livermore Atomic Code (HULLAC). Resonance and satellite lines from singly and multiply excited states of Sn ions, which contribute significantly to the EUV emission, are identified and included in the model through a systematic investigation of their effect on the emission spectra. The wavelengths of the 4d−4f+4p−4d transitions of Sn5+ to Sn13+ are investigated, because of their importance for determining the conversion efficiency of the EUV source, in conjunction with the effect of configuration interaction in the calculation of atomic structure. Calculated emission spectra are compared with those of charge exchange spectroscopy and of laser produced plasma EUV sources. The comparison is also carried out for the opacity of a radiatively heated Sn sample. A reasonable agreement is obtained between calculated and experimental EUV emission spectra observed under the typical condition of EUV sources with the ion density and ionization temperature of the plasma around 1018 cm−3 and 20 eV, respectively, by applying a wavelength correction to the resonance and satellite lines. Finally, the spectral emissivity and opacity of Sn plasmas are calculated as a function of electron temperature and ion density. The results are useful for radiation hydrodynamics simulations for the optimization of EUV sources.
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52.80.Yr Discharges for spectral sources (including inductively coupled plasma)
52.65.-y Plasma simulation
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.25.Jm Ionization of plasmas
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
42.72.Bj Visible and ultraviolet sources

Nanostructural evolution during emission of CsI-coated carbon fiber cathodes

Lawrence F. Drummy, Scott Apt, Don Shiffler, Ken Golby, Matt LaCour, Benji Maruyama, and Richard A. Vaia

J. Appl. Phys. 107, 113304 (2010); http://dx.doi.org/10.1063/1.3428463 (6 pages) | Cited 1 time

Online Publication Date: 2 June 2010

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Carbon-based nanofiber and microfiber cathodes exhibit very low voltages for the onset of electron emission, and thus provide exciting opportunities for applications ranging from high power microwave sources to field emission displays. CsI coatings have been experimentally shown to lower the work function for emission from the fiber tips, although little is known about the microstructure of the fibers themselves in their as-received state, after coating with CsI, or after being subjected to high voltage cycling. Longitudinal cross sections of the original, unused CsI-coated fibers produced by focused ion beam lift-out revealed a nanostructured graphitic core surrounded by an amorphous carbon shell with submicron sized islands of crystalline CsI on the outer surface. Aberration-corrected high resolution electron microscopy (HREM) of the fiber core achieved 0.10 nm resolution, with the graphite (200) clearly visible in digital fast Fourier transformations of the 2–4 nm highly ordered graphitic domains. As the cathode fibers are cycled at high voltage, HREM demonstrates that the graphitic ordering of the core increases with the number of cycles, however the structure and thickness of the amorphous carbon layer remains unchanged. These results are consistent with micro-Raman measurements of the fiber disordered/graphitic (D/G) band ratios. After high voltage cycling, a uniform ∼ 100 nm film at the fiber tip was evident in both bright field transmission electron microscopy (TEM) and high angle annular dark field scanning TEM (STEM). Low-dose electron diffraction techniques confirmed the amorphous nature of this film, and STEM with elemental mapping via x-ray energy dispersive spectroscopy indicates this layer is composed of CsIO. The oxidative evolution of tip composition and morphology due to impurities in the chamber, along with increased graphitization of the fiber core, contributes to changes in emission behavior with cycling.
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81.07.Bc Nanocrystalline materials
79.70.+q Field emission, ionization, evaporation, and desorption
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
82.45.Fk Electrodes

Molecular dynamics simulations of Cl+ etching on a Si(100) surface

F. Gou, E. Neyts, M. Eckert, S. Tinck, and A. Bogaerts

J. Appl. Phys. 107, 113305 (2010); http://dx.doi.org/10.1063/1.3361038 (6 pages) | Cited 4 times

Online Publication Date: 3 June 2010

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Molecular dynamics simulations using improved Tersoff–Brenner potential parameters were performed to investigate Cl+ etching of a {2×1} reconstructed Si(100) surface. Steady-state Si etching accompanying the Cl coverage of the surface is observed. Furthermore, a steady-state chlorinated reaction layer is formed. The thickness of this reaction layer is found to increase with increasing energy. The stoichiometry of SiClx species in the reaction layer is found to be SiCl:SiCl2:SiCl3 = 1.0:0.14:0.008 at 50 eV. These results are in excellent agreement with available experimental data. While elemental Si products are created by physical sputtering, most SiClx (0<x<4) etch products are produced by chemical-enhanced physical sputtering.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.47.Fg Semiconductor surfaces
81.05.Cy Elemental semiconductors
61.66.Bi Elemental solids
61.66.Dk Alloys

Modeling and simulation of anode melting pool flow under the action of high-current vacuum arc

Lijun Wang, Shenli Jia, Yu Liu, Bin Chen, Dingge Yang, and Zongqian Shi

J. Appl. Phys. 107, 113306 (2010); http://dx.doi.org/10.1063/1.3386568 (12 pages) | Cited 2 times

Online Publication Date: 4 June 2010

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In this paper, a transient magnetohydrodynamic (MHD) model of an anode melting pool (AMP) flow (AMPF) is established. Mass equation, momentum equations along axial, radial and azimuthal directions, energy equation, and current continuity equations are considered in the model. In the momentum equations, the influence of electromagnetic force, viscosity force and Marangoni force (anode surface shear stress) are included. Joule heating is also included in the energy equations. According to the MHD model of AMPF, the influence of different heat flux densities to melting pool flow velocities (including azimuthal, radial, and axial velocity), anode temperature, fraction of liquid, melting depth, melting radius, and anode vapor flux will be analyzed. In the AMP, the azimuthal velocity is dominant, whose value approximately approaches velocity magnitude, the radial velocity is much smaller than azimuthal velocity, and the axial velocity is the smallest one compared with radial and azimuthal velocity. According to simulation results, anode surface temperature, melting width, melting depth, and anode vapor flux are increased with the increase in heat flux densities, but the increase in azimuthal velocity is not significant. Simulation results also show that the maximum anode temperature appears near 6.5–7 ms (50 Hz), but the maximum velocity of AMPF appears near 8–10 ms, which is in agreement with the experimental observation. Simulation result of AMPF swirl velocity (about 0.4 m/s) is approximately close to experimental result (about 0.6 m/s) based on high-speed camera data. Simulation results also show that the influence of joule heating and radiation on anode temperature can be neglected. The influence of Marangoni force on AMPF is significant.
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52.65.-y Plasma simulation
52.80.Vp Discharge in vacuum
52.25.-b Plasma properties
52.50.-b Plasma production and heating
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Rotating cylindrical magnetron sputtering: Simulation of the reactive process

D. Depla, X. Y. Li, S. Mahieu, K. Van Aeken, W. P. Leroy, J. Haemers, R. De Gryse, and A. Bogaerts

J. Appl. Phys. 107, 113307 (2010); http://dx.doi.org/10.1063/1.3415550 (9 pages) | Cited 4 times

Online Publication Date: 7 June 2010

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A rotating cylindrical magnetron consists of a cylindrical tube, functioning as the cathode, which rotates around a stationary magnet assembly. In stationary mode, the cylindrical magnetron behaves similar to a planar magnetron with respect to the influence of reactive gas addition to the plasma. However, the transition from metallic mode to poisoned mode and vice versa depends on the rotation speed. An existing model has been modified to simulate the influence of target rotation on the well known hysteresis behavior during reactive magnetron sputtering. The model shows that the existing poisoning mechanisms, i.e., chemisorption, direct reactive ion implantation and knock on implantation, are insufficient to describe the poisoning behavior of the rotating target. A better description of the process is only possible by including the deposition of sputtered material on the target.
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81.15.Cd Deposition by sputtering

Brillouin shifted third harmonic generation of a laser in a plasma

Ranjeet Singh and V. K. Tripathi

J. Appl. Phys. 107, 113308 (2010); http://dx.doi.org/10.1063/1.3431402 (4 pages)

Online Publication Date: 8 June 2010

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The process of Brillouin shifted resonant third harmonic generation of an intense laser of finite spot size in a plasma is investigated. The laser of frequency ω0 and wave number math0 excites an ion acoustic wave of frequency ω ≈ kcs and wave number math ≈ 2math0, where cs is the ion acoustic speed, in the primary stimulated Brillouin scattering process. The laser also exerts a second harmonic ponderomotive force on electrons. This imparts them an oscillatory velocity v2ω0,2k0. This velocity beats with the electron density perturbation associated with the ion acoustic wave to produce a density perturbation at Brillouin shifted second harmonic. This perturbation couples with the oscillatory velocity vω0,k0 due to the laser to produce Brillouin shifted third harmonic current density and the radiation field. The phase matching is satisfied when plasma density is two third critical.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.25.-b Plasma properties
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

The effect of hot captured electrons on dust particle charge in a dusty plasma

J. M. A. Ashbourn

J. Appl. Phys. 107, 113309 (2010); http://dx.doi.org/10.1063/1.3415549 (6 pages)

Online Publication Date: 11 June 2010

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We consider the effect of allowing the capture of hot electrons by a dust particle in a dusty plasma by considering the temperature gradient created between these and the ambient plasma and by calculating the contribution to the electron current which results. A graph of the curve for the contribution from the temperature gradient to the electron current at the dust particle and the curve for the function without the temperature gradient included for a variety of values of the effective reduced potential of the dust particle shows a significant reduction in the charge on the dust particle when the temperature gradient is included. We present results for the percentage differences between the function with and without the temperature gradient included for a range of values of the reduced potential. These show that the effect of hot electrons can reduce the electron current contribution to the dust charge by up to 38% when the ion temperature is equal to the ambient electron temperature and that it can increase the electron current contribution to the dust charge by up to 33% when the ion temperature is a tenth of the ambient electron temperature.
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52.27.Lw Dusty or complex plasmas; plasma crystals

Etching characteristics of organic low-k films interpreted by internal parameters employing a combinatorial plasma process in an inductively coupled H2/N2 plasma

Chang Sung Moon, Keigo Takeda, Makoto Sekine, Yuichi Setsuhara, Masaharu Shiratani, and Masaru Hori

J. Appl. Phys. 107, 113310 (2010); http://dx.doi.org/10.1063/1.3415535 (8 pages) | Cited 2 times

Online Publication Date: 14 June 2010

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The development of plasma etching technology is being held back due to the use of trial and error methods when scaling down and high integration. Such a continuous development could result in enormous losses in term of cost and time. It is impossible to overcome without a different approach. In this study, we have tried to accumulate a large amount of data on internal parameters and based on database, the etching characteristics could be interpreted with a high reproducibility. In order to realized faster data acquisitions, we developed a combinatorial plasma process (CPP) for obtaining a large amount of data in a single trial from spatially inhomogeneous plasma distribution regarding etching of organic low-k films in H2/N2 plasmas. In addition, synergetic effects of other internal parameters such as vacuum ultraviolet radiation and radicals without ion bombardment were clarified. Finally, the high performance of CPP for faster data acquisitions was shown and the etching characteristics in terms of internal parameters such as ion fluxes and the H/(H+N) radical flux ratio were demonstrated.
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52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
77.55.Bh Low-permittivity dielectric films
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Transformation twinning of Ni–Mn–Ga characterized with temperature-controlled atomic force microscopy

Matthew Reinhold, Chad Watson, William B. Knowlton, and Peter Müllner

J. Appl. Phys. 107, 113501 (2010); http://dx.doi.org/10.1063/1.3429090 (7 pages)

Online Publication Date: 1 June 2010

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The magnetomechanical properties of ferromagnetic shape memory alloy Ni–Mn–Ga single crystals depend strongly on the twin microstructure, which can be modified through thermomagnetomechanical training. Atomic force microscopy (AFM) and magnetic force microscopy (MFM) were used to characterize the evolution of twin microstructures during thermomechanical training of a Ni–Mn–Ga single crystal. Experiments were performed in the martensite phase at 25 °C and in the austenite phase at 55 °C. Two distinct twinning surface reliefs were observed at room temperature. At elevated temperature (55 °C), the surface relief of one twinning mode disappeared while the other relief remained unchanged. When cooled back to 25 °C, the twin surface relief recovered. The relief persisting at elevated temperature specifies the positions of twin boundaries that were present when the sample was polished prior to surface characterization. AFM and MFM following thermomechanical treatment provide a nondestructive method to identify the crystallographic orientation of each twin and of each twin boundary plane. Temperature dependent AFM and MFM experiments reveal the twinning history thereby establishing the technique as a unique predictive tool for revealing the path of the martensitic and reverse transformations of magnetic shape memory alloys.
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61.72.Mm Grain and twin boundaries
75.80.+q Magnetomechanical effects, magnetostriction
81.30.Kf Martensitic transformations
62.20.fg Shape-memory effect; yield stress; superelasticity
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Persistent template effect in InAs/GaAs quantum dot bilayers

E. Clarke, P. Howe, M. Taylor, P. Spencer, E. Harbord, R. Murray, S. Kadkhodazadeh, D. W. McComb, B. J. Stevens, and R. A. Hogg

J. Appl. Phys. 107, 113502 (2010); http://dx.doi.org/10.1063/1.3429226 (6 pages) | Cited 7 times

Online Publication Date: 1 June 2010

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The dependence of the optical properties of InAs/GaAs quantum dot (QD) bilayers on seed layer growth temperature and second layer InAs coverage is investigated. As the seed layer growth temperature is increased, a low density of large QDs is obtained. This results in a concomitant increase in dot size in the second layer, which extends their emission wavelength, reaching a saturation value of around 1400 nm at room temperature for GaAs-capped bilayers. Capping the second dot layer with InGaAs results in a further extension of the emission wavelength, to 1515 nm at room temperature with a narrow linewidth of 22 meV. Addition of more InAs to high density bilayers does not result in a significant extension of emission wavelength as most additional material migrates to coalesced InAs islands but, in contrast to single layers, a substantial population of regular QDs remains.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.Hc Quantum dots
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