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15 Dec 2010

Volume 108, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 108, 121101 (2010); http://dx.doi.org/10.1063/1.3503505 (12 pages)

J. Martin, T. Tritt, and C. Uher
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High temperature Seebeck coefficient metrology

J. Martin, T. Tritt, and C. Uher

J. Appl. Phys. 108, 121101 (2010); http://dx.doi.org/10.1063/1.3503505 (12 pages) | Cited 24 times

Online Publication Date: 22 December 2010

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We present an overview of the challenges and practices of thermoelectric metrology on bulk materials at high temperature (300 to 1300 K). The Seebeck coefficient, when combined with thermal and electrical conductivity, is an essential property measurement for evaluating the potential performance of novel thermoelectric materials. However, there is some question as to which measurement technique(s) provides the most accurate determination of the Seebeck coefficient at high temperature. This has led to the implementation of nonideal practices that have further complicated the confirmation of reported high ZT materials. To ensure meaningful interlaboratory comparison of data, thermoelectric measurements must be reliable, accurate, and consistent. This article will summarize and compare the relevant measurement techniques and apparatus designs required to effectively manage uncertainty, while also providing a reference resource of previous advances in high temperature thermoelectric metrology.
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06.30.Ka Basic electromagnetic quantities
07.20.Ka High-temperature instrumentation; pyrometers
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back to top Lasers, Optics, and Optoelectronics

Thermoviscoelastic finite element modeling of laser-generated ultrasound in viscoelastic plates

Hong-xiang Sun and Shu-yi Zhang

J. Appl. Phys. 108, 123101 (2010); http://dx.doi.org/10.1063/1.3520675 (8 pages) | Cited 3 times

Online Publication Date: 16 December 2010

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Laser-generated ultrasound in a thin composite plate with thermoviscoelastic property has been studied quantitatively. According to thermoviscoelastic theory, considering the viscoelastic and thermophysical properties of materials, a numerical model for the laser-generated Lamb waves is established in the frequency domain by using a finite element method. It is confirmed that the temperature and displacement fields calculated in the frequency domain coincide well with those obtained in the time domain. In the numerical simulations of thermoviscoelastically generated Lamb waves, the effects of viscoelastic and elastic stiffness moduli, and the thickness of the materials have been taken into account in details. The characteristics of the Lamb waves in the numerical results agree well with the features of the disperse curves. The results show that the finite element method in this paper provides a useful technique to characterize mechanical properties of composite materials.
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68.60.Bs Mechanical and acoustical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.65.+k Acoustical properties of solids
62.20.de Elastic moduli
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
02.70.Dh Finite-element and Galerkin methods

Two-dimensional photonic crystal for absorption enhancement in hydrogenated amorphous silicon thin film solar cells

Guillaume Gomard, Emmanuel Drouard, Xavier Letartre, Xianqin Meng, Anne Kaminski, Alain Fave, Mustapha Lemiti, Enric Garcia-Caurel, and Christian Seassal

J. Appl. Phys. 108, 123102 (2010); http://dx.doi.org/10.1063/1.3506702 (8 pages) | Cited 14 times

Online Publication Date: 16 December 2010

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We propose a photovoltaic solar cell design based on a 100 nm thick absorbing layer made of hydrogenated amorphous silicon and patterned as a two-dimensional planar photonic crystal (PPC). After scanning the parameters of the PPC within the patterned cell, optical simulations performed on the best configuration obtained reveal that a relative increase in the integrated absorption inside the active layer of 28% can be expected between 300 and 720 nm compared to an equivalent but nonpatterned cell under normal incidence. Besides, this integrated absorption is found to be robust toward the angle of incidence. Incident light is efficiently coupled to leaky mode resonances of the PPC provided an appropriated tuning of its parameters. The effects of the reflectance of the back contact coupled to a conductive optical spacer on the absorption are also discussed.
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88.40.jj Silicon solar cells
88.40.H- Solar cells (photovoltaics)

Spectroscopic studies of the origin of radiation-induced degradation in phosphorus-doped optical fibers and preforms

G. Origlio, F. Messina, S. Girard, M. Cannas, A. Boukenter, and Y. Ouerdane

J. Appl. Phys. 108, 123103 (2010); http://dx.doi.org/10.1063/1.3517479 (7 pages) | Cited 3 times

Online Publication Date: 17 December 2010

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In this paper, we study the radiation-induced point defects related to the phosphorus element that is commonly used to improve the optical properties of silica-based glasses but is responsible of a dramatic increase in their radiation sensitivity. To this aim, the influence of x-ray irradiation on prototype phosphorus-doped canonical fibers and their related preforms was investigated by in situ radiation induced attenuation (RIA), optical absorption, and electron spin resonance (ESR) spectroscopy. The RIA spectra in the (1.5–5 eV) range, can be explained by the presence of at least three absorption bands induced by radiation exposure. Additionally the X-dose dependence of such bands was studied. The main responsible defect for these absorption peaks was the phosphorus oxygen hole center (POHC) center, whose presence was also detected by ESR measurements both in irradiated fibers and preforms, together with the lineshape of the so called P2 defect. Correlations between the RIA bands and the ESR results allow us to assign the 2.3 and 3.0 eV bands to POHCs and to propose a scheme for the simultaneous creation of POHC and P2 defects after x-ray exposure.
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42.81.Dp Propagation, scattering, and losses; solitons
61.80.Cb X-ray effects
61.82.Ms Insulators
61.72.J- Point defects and defect clusters
61.05.Qr Magnetic resonance techniques; Mössbauer spectroscopy (for structure determination only)

Effects of strain on defect structure in II-VI green color converters

Y. Zhu (朱叶), S. McKernan, J. Xie, T. J. Miller, M. A. Haase, X. Sun (孙晓光), T. L. Smith, and C. A. Leatherdale

J. Appl. Phys. 108, 123104 (2010); http://dx.doi.org/10.1063/1.3517069 (4 pages) | Cited 2 times

Online Publication Date: 20 December 2010

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State-of-the-art green emission efficiency has been achieved with light-emitting diodes incorporating CdMgZnSe color-converting quantum well heterostructures, although dark line defects (DLDs) limit the device reliability. We have determined that misfit strain plays an important role in the formation of extended stacking faults (SFs) and DLDs in II-VI green converters. Even small strain causes SFs to extend to accommodate misfit strain and extended SFs further give rise to DLDs when they intersect active regions. Detailed strain relaxation mechanisms for both tensile and compressive strain have been investigated, which may apply for other semiconductor heterostructures with an fcc lattice. Careful control of the layer strain via close lattice matching prevents the extension of SFs and leads to DLD-free converters.
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85.60.Jb Light-emitting devices
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Nv Optical frequency converters
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
61.72.Nn Stacking faults and other planar or extended defects

Photoluminescence and photoreflectance characterization of ZnxCd1−xSe/MgSe multiple quantum wells

J. D. Wu, Y. S. Huang, B. S. Li, A. Shen, M. C. Tamargo, and K. K. Tiong

J. Appl. Phys. 108, 123105 (2010); http://dx.doi.org/10.1063/1.3520477 (5 pages) | Cited 1 time

Online Publication Date: 21 December 2010

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Photoluminescence (PL) and photoreflectance (PR) were used to characterize ZnxCd1−xSe/MgSe multiple quantum well (MQW) structures grown on InP substrates by molecular beam epitaxy for mid-infrared (IR) device applications. The PL spectra yielded information of the fundamental excitonic recombination and ZnxCd1−xSe cap/spacer band edge emission of the samples. The PR spectra revealed multitude of possible interband transitions in MQW structures. The ground state transitions were assigned by comparing with the PL emission signals taken from the same structures. A comprehensive analysis of the PR spectra led to the identification of various interband transitions. The intersubband transitions were then estimated and found to be in a good agreement with the previous report of Fourier-transform IR absorption measurements [ Li et al., Appl. Phys. Lett. 92, 261104 (2008)] . The results demonstrate the potential of using PL and PR as nondestructive optical techniques for characterization of ZnxCd1−xSe/MgSe MQWs for mid-IR device applications.
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73.21.Fg Quantum wells
73.63.Hs Quantum wells
78.67.De Quantum wells
81.07.St Quantum wells
78.55.Et II-VI semiconductors
81.05.Dz II-VI semiconductors

Enhanced efficiency of CdMgZnSe down-converted light emitting diodes using light extraction features fabricated by laser-speckle lithography

Zhaohui H. Yang, Michael A. Haase, Catherine A. Leatherdale, and Terry L. Smith

J. Appl. Phys. 108, 123106 (2010); http://dx.doi.org/10.1063/1.3524024 (4 pages) | Cited 1 time

Online Publication Date: 22 December 2010

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We report a method of making a wavelength converted, light-emitting diode (LED) having light extraction features based on coherent speckle patterns. These patterns have random feature size, random feature distribution, and random feature shape. The features were produced using a maskless lithography process based on exposing photoresist with a laser-induced coherent optical speckle pattern. A wet chemical etching process was then used to transfer the resist pattern into the underlying surface of the semiconductor wavelength converter layer. The external quantum efficiency of a wavelength converter with emitting surfaces having such extraction features showed a twofold increase compared to a wavelength converter without extraction features. While demonstrated here using semiconductor wavelength converters, this approach could also be applied to light extraction in conventional LED structures.
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85.60.Jb Light-emitting devices
85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning

A planar refractive x-ray lens made of nanocrystalline diamond

L. Alianelli, K. J. S. Sawhney, A. Malik, O. J. L. Fox, P. W. May, R. Stevens, I. M. Loader, and M. C. Wilson

J. Appl. Phys. 108, 123107 (2010); http://dx.doi.org/10.1063/1.3517060 (4 pages) | Cited 1 time

Online Publication Date: 23 December 2010

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Diamond has unique properties which make it the ideal material for use in synchrotron instrumentation. X-ray optics made of diamond are almost transparent, they possess strength, and are subject to very low thermal expansion; therefore they will be able to withstand the powerful beams generated by fourth-generation light sources without compromising brilliance. For this reason, several groups are attempting fabrication of refractive lenses and zone plates made of diamond. Lithography and, in general, microfabrication technology, are the ultimate tools for the innovation of synchrotron focusing optics. We propose to combine modern silicon microtechnology with advanced deposition methods to fabricate nanocrystalline-diamond lenses for third- and fourth-generation synchrotron sources. The fabrication method is described here and microfocusing synchrotron tests are illustrated.
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42.79.Bh Lenses, prisms and mirrors
41.85.Si Particle beam collimators, monochromators
29.20.dk Synchrotrons
42.82.Cr Fabrication techniques; lithography, pattern transfer

Thermomechanical properties of Yb3+ doped laser crystals: Experiments and modeling

Johan Petit, Bruno Viana, Philippe Goldner, Jean-Paul Roger, and Danièle Fournier

J. Appl. Phys. 108, 123108 (2010); http://dx.doi.org/10.1063/1.3520216 (11 pages) | Cited 3 times

Online Publication Date: 23 December 2010

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Thermal conductivity values of several laser materials were determined by photothermal measurements and compared to predicted values. The effect of the ytterbium doping concentration could be modeled using a simple cationic mass difference model. For ytterbium content corresponding to an absorption coefficient of 10 cm−1 (or 85% absorption of the pump power) Yb:GdVO4 (c-axis) and Yb:Gd3Ga5O12 laser materials present the highest measured thermal conductivity values of 8.1 W m−1 K−1 and 7.7 W m−1 K−1, respectively. Yb:Y3Al5O12, Yb:Lu3Al5O12, Yb:CaGdAlO4, and Yb:YAlO3 belong to the 6–7 W m−1 K−1 range while Yb:CaF2 and Yb:Lu2SiO5 are situated in the 5–6 W m−1 K−1 range. Other matrices such as Yb:SrLaGa3O7, Yb:CaGdAl3O7, Yb:SrGdGa3O7, and Yb:BaLaGa3O7 have thermal conductivity values lower than 5 W m−1 K−1. With the knowledge of the thermal conductivities and the determination of the thermal expansion coefficients, thermal shock parameters are evaluated for several ytterbium doped laser hosts.
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81.40.Gh Other heat and thermomechanical treatments
42.60.By Design of specific laser systems
42.70.Hj Laser materials
42.55.Rz Doped-insulator lasers and other solid state lasers

Investigation of nonlinear optical properties of gold nanograins embedded in indium oxide films by reflection Z-scan using continuous laser

F. Z. Henari and A. A. Dakhel

J. Appl. Phys. 108, 123109 (2010); http://dx.doi.org/10.1063/1.3524281 (5 pages) | Cited 1 time

Online Publication Date: 23 December 2010

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Nanograins of gold-embedded in indium oxide thin films were fabricated by vacuum evaporation on silicon substrate. The gold concentrations were 3, 5, and 7 at. % as measured by x-ray fluorescence method. The x-ray diffraction results reveal that pure gold was crystallized into nanograins embedded in the indium oxide medium. The nonlinear optical properties of films on silicon substrate were investigated by reflection z-scan technique, using cw laser at 514 nm. Measurements of nonlinear refractive index and nonlinear absorption coefficient on these films are reported and the mechanism responsible for the process of optical nonlinearities is discussed.
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81.16.-c Methods of micro- and nanofabrication and processing
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.55.Hx Other solid inorganic materials
78.70.En X-ray emission spectra and fluorescence
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.-a Thin film structure and morphology

Transient Raman response and soliton self-frequency shift in tellurite microstructured fiber

Xin Yan, Guanshi Qin, Meisong Liao, Takenobu Suzuki, and Yasutake Ohishi

J. Appl. Phys. 108, 123110 (2010); http://dx.doi.org/10.1063/1.3525595 (5 pages) | Cited 3 times

Online Publication Date: 28 December 2010

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We report on the Raman response function and the soliton self-frequency shift in a tellurite microstructured fiber pumped at 1557 nm. The Raman response function in a tellurite fiber quantifies a contribution of the Raman fraction to the nonlinear optical response. Continuous soliton wavelength shift from 1582 to 1851 nm is observed in a tellurite microstructured optical fiber with the length of 6.5 cm. The experimental results strongly correlated with the numerical simulations based on a generalized nonlinear Schrödinger equation.
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42.81.Wg Other fiber-optical devices
42.81.Dp Propagation, scattering, and losses; solitons
42.65.Tg Optical solitons; nonlinear guided waves
42.70.Ce Glasses, quartz

Enhancement of ultrathin film emission using a waveguiding active layer

R. Aad, S. Blaize, A. Bruyant, C. Couteau, and G. Lérondel

J. Appl. Phys. 108, 123111 (2010); http://dx.doi.org/10.1063/1.3524537 (7 pages) | Cited 1 time

Online Publication Date: 29 December 2010

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We present a theoretical study on the impact of a waveguiding active layer on the emission properties of an ultrathin luminescent film. While the study can be generalized to any material, we focus here on a simple layered medium composed of a conjugated polymers (CPs) thin film, a zinc oxide layer (ZnO) and a sapphire substrate. The study spreads throughout variable aspects including the effect of the structure parameters on the CP luminescence and radiation pattern and more specifically the influence of the absorption and emission properties of the active layer. Comparing between the passive and active layer cases, the obtained results show that an enhancement of the CP luminescence of more than 20 times can be obtained by using an optically active waveguiding underlying layer. The results can be explained in terms of photon recycling where the optically active layer acts as a photon reservoir and a secondary light source for the ultrathin film. This general concept is of a special interest for ultratrace chemosensor.
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78.55.Kz Solid organic materials
78.66.Qn Polymers; organic compounds

Sensitized Yb3+ emission in (Nd, Yb):Y3Al5O12 transparent ceramics

V. Lupei, A. Lupei, C. Gheorghe, and A. Ikesue

J. Appl. Phys. 108, 123112 (2010); http://dx.doi.org/10.1063/1.3525269 (5 pages) | Cited 1 time

Online Publication Date: 29 December 2010

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The characteristics of Nd→Yb energy transfer in (Nd, Yb):Y3Al5O12 (YAG) transparent ceramics, obtained from steady state and dynamic spectral studies on different single doped and codoped samples, prepared by solid state synthesis, are presented. The Yb3+ emission in codoped (Nd, Yb):YAG samples under cw excitation of the donors (Nd3+) revealed efficient energy transfer to Yb3+ (at low temperatures too), due to the overlap of the Nd3+ 4F3/2→4I9/2 emission and Yb3+ 2F7/2→2F5/2 absorption. From the global decays of the Nd3+ 4F3/2 level in single and codoped samples, the transfer efficiencies were estimated; they increase with Yb3+ content reaching ∼ 93% for 1 at. % Nd, 5 at. % Yb:YAG sample. The mechanisms and parameters of the Nd→Yb energy transfer were inferred from the Nd3+ decays in the codoped samples, after the separation of the self-quenching inside the donors (Nd3+) from the transfer to acceptors (Yb3+). It was proved that the Nd→Yb energy is resonant and dominated by dipole-dipole interactions. Due to the large transfer efficiencies, (Nd, Yb):YAG ceramic could be a promising material for Yb3+ emission under pumping in strong Nd3+ absorption lines.
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78.55.Hx Other solid inorganic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Thermomechanical mechanism of orientational optical nonlinearity in twisted nematic liquid crystals

J. B. Poursamad, A. K. Aleksanyan, and R. S. Hakobyan

J. Appl. Phys. 108, 123113 (2010); http://dx.doi.org/10.1063/1.3525992 (5 pages) | Cited 1 time

Online Publication Date: 30 December 2010

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In a nonuniform nematic liquid crystal director reorientation may take place as a result of a temperature gradient. We formulated a two-dimensional model of the temperature gradient caused by the light absorption of a Gaussian laser beam impinging normally on the liquid crystal cell. Within this model, we calculated the director reorientation and the subsequent optical nonlinearity of the liquid crystal.
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42.70.Df Liquid crystals
81.40.Gh Other heat and thermomechanical treatments
78.15.+e Optical properties of fluid materials, supercritical fluids and liquid crystals
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
back to top Plasmas and Electrical Discharges

Modeling electron flow produced by a three-dimensional spatially periodic field emitter

A. Rokhlenko and J. L. Lebowitz

J. Appl. Phys. 108, 123301 (2010); http://dx.doi.org/10.1063/1.3520672 (6 pages) | Cited 1 time

Online Publication Date: 17 December 2010

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We study the space charge limited field emission from an emitter whose surface has a simple periodic structure with bumps. The shape of each bump is represented by a smooth function and the emission is governed by the Fowler–Nordheim–Schottky law. A mathematical scheme for modeling the potential and current structure by a set of elementary functions is developed and implemented numerically with the help of a special least square procedure. Our results show that such emitters are more efficient than emitters with long ridges only in weak electric fields. In stronger fields the latter give larger currents and they should be more durable. The emission by an individual bump in our periodic structure is compared also with that of a single emitter bump of the same shape, they appear to be quite close.
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85.45.Db Field emitters and arrays, cold electron emitters
85.45.Bz Vacuum microelectronic device characterization, design, and modeling
79.70.+q Field emission, ionization, evaporation, and desorption

Self-field effects on instability of wave modes in a free-electron laser with background plasma

Atefeh Ghazavi, Behrouz Maraghechi, and Taghi Mohsenpour

J. Appl. Phys. 108, 123302 (2010); http://dx.doi.org/10.1063/1.3520664 (7 pages) | Cited 1 time

Online Publication Date: 21 December 2010

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A dispersion relation for the plasma loaded free-electron laser (FEL), with a helical wiggler and an axial magnetic field is derived. The cold fluid formulation is used with self-fields of the electron beam taken into account. By solving the dispersion relation numerically the influence of self-fields on the FEL resonance and the two-stream instability is investigated. It was found that although self-fields have strong effect on the FEL resonance, their effects on the two-stream instability is much weaker.
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41.60.Cr Free-electron lasers
41.75.Ht Relativistic electron and positron beams
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Excitation of terahertz plasmons eigenmode of a parallel plane guiding system by an electron beam

Pawan Kumar, Manish Kumar, and V. K. Tripathi

J. Appl. Phys. 108, 123303 (2010); http://dx.doi.org/10.1063/1.3524368 (4 pages) | Cited 2 times

Online Publication Date: 23 December 2010

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Two parallel semiconductor plates, separated by a short distance, support surface plasmon eigenmode with amplitude maxima at the inner surfaces of the plates and minimum at the center. A relativistic sheet electron beam propagating through the space between the planes resonantly excites the surface plasma wave (SPW). The frequency of the driven SPW decreases with the energy of the beam while the growth rate increases. At the beam current ≈168 A the growth rate of 5.93×108 rad/s is achieved at the frequency ≈0.51 THz of SPW for the 5 mm math width and spacing between the two plates of ≈2.83 mm. The growth rate scales as 1/3 root of the electron beam current.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Electrical double layers at shock fronts in glow discharges and afterglows

Nicholas S. Siefert

J. Appl. Phys. 108, 123304 (2010); http://dx.doi.org/10.1063/1.3511745 (11 pages)

Online Publication Date: 28 December 2010

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This paper examines the propagation of spark-generated shockwaves (1.0<Mach<2.0) into argon and nitrogen glow discharges and their afterglow. Diagnostic methods were employed and expanded in order to capture the dynamics of the shock front in these weakly-ionized, nonmagnetized, collisional plasmas. We used a microwave hairpin resonator to measure the electron number density, and, for all cases, we measured an increase in the electron number density at the shock front. By comparing the increase in electron number density at the shock front in the active discharge and in the afterglow, we conclude that electrons with a temperature much greater than room temperature can be compressed at the shock front. The ratio of electron number density before and after the shock front can be approximately predicted using the Rankine–Hugoniot relationship. The large gradient in electron density, and hence a large gradient in the flux of charged species, created a region of space-charge separation, i.e., a double layer, at the shock front. The double layer balances the flux of charged particles on both sides of the shock front. The double layer voltage drop was measured in the current-carrying discharge using floating probes and compared with previous models. As well, we measured argon 1s5 metastable-state density and demonstrate that metastable-state neutral species can be compressed across a shock front and approximately predicted using the Rankine–Hugoniot relationship.
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52.35.Tc Shock waves and discontinuities
52.80.Hc Glow; corona
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.25.-b Plasma properties
52.70.Ds Electric and magnetic measurements

Microwave air plasma source at atmospheric pressure: Experiment and theory

E. Tatarova, F. M. Dias, E. Felizardo, J. Henriques, M. J. Pinheiro, C. M. Ferreira, and B. Gordiets

J. Appl. Phys. 108, 123305 (2010); http://dx.doi.org/10.1063/1.3525245 (18 pages) | Cited 3 times

Online Publication Date: 29 December 2010

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An experimental and theoretical investigation of the axial structure of a surface wave (2.45 GHz) driven atmospheric plasma source in air with a small admixture (1%) of water vapor has been performed. Measurements of the gas temperature and of the intensities of the O(777.4 nm), O(844.6 nm), and O(630 nm) atomic lines and the NO(γ) molecular band versus input power and axial position were carried out. Amplitude and phase sensitive measurements have also been performed to derive the surface wave dispersion characteristics. The experimental results are analyzed in terms of a one-dimensional theoretical model based on a self-consistent treatment of particle kinetics, gas dynamics, and wave electrodynamics. The predicted gas temperature and emission line intensities variations with power and axial position are shown to compare well with experiment. “Hot” excited O atoms (with kinetic energy ∼ 2 eV) have been detected.
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52.50.Dg Plasma sources
52.25.Dg Plasma kinetic equations
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Compression and strong rarefaction in high power impulse magnetron sputtering discharges

David Horwat and André Anders

J. Appl. Phys. 108, 123306 (2010); http://dx.doi.org/10.1063/1.3525986 (6 pages) | Cited 15 times

Online Publication Date: 29 December 2010

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Gas compression and strong rarefaction have been observed for high power impulse magnetron sputtering (HIPIMS) discharges using a copper target in argon. Time-resolved ion saturation currents of 35 probes were simultaneously recorded for HIPIMS discharges operating far above the self-sputtering runaway threshold. The argon background pressure was a parameter for the evaluation of the spatial and temporal development of the plasma density distribution. The data can be interpreted by a massive onset of the sputtering flux (sputter wind) that causes a transient densification of the gas, followed by rarefaction and the replacement of gas plasma by the metal plasma of sustained self-sputtering. The plasma density pulse follows closely the power pulse at low pressure. At high pressure, the relatively remote probes recorded a density peak only after the discharge pulse, indicative for slow, diffusive ion transport.
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52.80.Sm Magnetoactive discharges (e.g., Penning discharges)
52.25.Fi Transport properties
52.70.Ds Electric and magnetic measurements
52.40.Hf Plasma-material interactions; boundary layer effects
52.50.Dg Plasma sources
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

On the assumed impact of germanium doping on void formation in Czochralski-grown silicon

Jan Vanhellemont, Xinpeng Zhang, Wubing Xu, Jiahe Chen, Xiangyang Ma, and Deren Yang

J. Appl. Phys. 108, 123501 (2010); http://dx.doi.org/10.1063/1.3503154 (4 pages) | Cited 2 times

Online Publication Date: 16 December 2010

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The assumed impact of Ge doping on void formation during Czochralski-growth of silicon single crystals, is studied using scanning infrared microscopy. It has been reported that Ge doping leads to a reduction in the flow pattern defect density and of the crystal originated particle size, both suggesting an effect of Ge on vacancy concentration and void formation during crystal growth. The present study however reveals only a marginal-if any-effect of Ge doping on grown-in single void size and density. Double and multiple void formation might however be suppressed partially by Ge doping leading to the observed decrease in flow pattern defect density. The limited effect of Ge doping on single void formation is in agreement with earlier findings that Ge atoms are only a weak trap for vacancies at higher temperatures and therefor should have a smaller impact on the vacancy thermal equilibrium concentration and on single void nucleation than, e.g., interstitial oxygen and nitrogen.
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81.10.Fq Growth from melts; zone melting and refining

Localized surface plasmon resonance effects by naturally occurring Chinese yam particles

Quanshui Li, Zhili Zhang, Sara S. Haque, Mingjun Zhang, and Lijin Xia

J. Appl. Phys. 108, 123502 (2010); http://dx.doi.org/10.1063/1.3520667 (5 pages) | Cited 1 time

Online Publication Date: 16 December 2010

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In this paper, localized surface plasmon resonance (LSPR) effects by naturally occurring Chinese yam particles are observed and quantified. Chinese yam particles were found by atomic force microscope and high-speed optical dark-field microscope. The particles with diameters greater than 200 nm are found to contribute most of ultraviolet and visible absorption. LSPR effects of silver nanoparticles by the Chinese yam particles lead to the redshifts in the extinction peaks of the silver nanoparticles. The wavelength shifts are quantitatively predicted based on discrete dipole approximation of the LSPR effects, which are sensitive to the local dielectric constant changed by the Chinese yam particles. The finding may open a new avenue to detect the biological submicron particles or virus in solution.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.40.-q Absorption and reflection spectra: visible and ultraviolet
77.22.Ch Permittivity (dielectric function)

Electron delocalization of tensily strained GaAs quantum dots in GaSb matrix

T. C. Lin, Y. H. Wu, L. C. Li, Y. T. Sung, S. D. Lin, L. Chang, Y. W. Suen, and C. P. Lee

J. Appl. Phys. 108, 123503 (2010); http://dx.doi.org/10.1063/1.3520669 (5 pages)

Online Publication Date: 16 December 2010

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The magneto-optical response of type-II tensily strained GaAs self-assembled quantum dots in GaSb was investigated in magnetic fields up to 14 T. By depositing different GaAs amount, the dot sizes and the corresponding emission energies were varied. We analyzed the carrier wave function extent of different dots using the diamagnetic shift results. It was found that, with the increase in the energy (the reduction in the dot size), the diamagnetic coefficient first rises quickly and then saturates at around 21 μeV/T2. Based on a simple calculation model, this unusual tendency is attributed to the electrons gradually spilling out of the quantum dot to the wetting layer as the dots get smaller. This delocalization effect is enhanced in this material system due to the tensile strain relaxation within the dots, which raises the conduction band edge over that in the wetting layer.
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78.20.Ls Magneto-optical effects
73.21.La Quantum dots
73.20.At Surface states, band structure, electron density of states
68.08.Bc Wetting
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
68.35.Ct Interface structure and roughness

Atomistic modeling of lattice frame effects on laser-induced dislocation behaviors in nanopore mending processes

Pei-Hsing Huang and Hsin-Yi Lai

J. Appl. Phys. 108, 123504 (2010); http://dx.doi.org/10.1063/1.3517788 (10 pages) | Cited 1 time

Online Publication Date: 16 December 2010

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In recent years, the femtosecond laser technique has emerged as an effective tool for defect mending, especially for fault repairs of the conducting wire in three-dimensional integrated circuits. However, the nanodefect mending mechanism subjected to photothermal and mechanical stress introduced by ultrafast laser dynamics is still not well understood so far. In this paper, the microscopic dislocation behaviors of the lattice mending of metallic nanopore defects induced by femtosecond laser is presented using a modified continuum-atomistic modeling approach and the quantitative dislocation-based analysis. Two different cases of lattice frame effects are elaborated to characterize the dislocation behaviors and the nanopore mending mechanisms. The lattice frame is found to possess a direct effect on controlling the mechanisms of nucleation and growth of dislocation during laser interaction with metallic microdefects. The nanopore defect with a symmetric lattice frame is observed to form a prismaticlike slip structure around the pore region, and the dislocation loop consequently expands along its glide-prism plane. The growth of the loops continues even after they are fully mended to form sessile junctions by creating a local anisotropic hardening structure. On the other hand, the nanopore defect of an asymmetric lattice frame induces drastically irregular lattice glides, forming a tight network of junction loops around the mended area. It was found that the fast shock wave enhanced by the stress concentration factor around the pore that enabled a cooperative movement of sheets of atoms around the pore. This particular mechanism causes a rapid mending of the hole with a metastable lattice structure. The heterogeneous reaction dynamics of dislocation nucleation on the pore defect surface is analyzed in detail in this study. The photomechanical and thermally-activated plastic flow of mending processes is also clearly elucidated. The results provide vital insights into better dynamic behavior characterization of how the ultrafast laser interacts with metallic microdefects.
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64.60.Q- Nucleation
82.60.Nh Thermodynamics of nucleation
79.20.Ds Laser-beam impact phenomena
42.60.-v Laser optical systems: design and operation

Spectral finite element method modeling of ultrasonic guided waves propagation in layered viscoelastic film/substrate materials

Ying Luo, Hong Li, BaiQiang Xu, and Gui Dong Xu

J. Appl. Phys. 108, 123505 (2010); http://dx.doi.org/10.1063/1.3520572 (6 pages) | Cited 2 times

Online Publication Date: 20 December 2010

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The propagation of ultrasonic guided waves in layered viscoelastic film/substrate materials has been investigated. Based on the plane strain theory, a numerical model of the guided waves propagating in thin film on the substrate is developed in the frequency domain by employing the spectral finite element method. The surface normal displacement and the propagating characteristic are obtained and analyzed, which depends not only on the material parameters of the film, but also on those of the substrate. If the substrate velocity is faster than that of the film, the dispersion takes on the normal, otherwise, the anomalous dispersion will appear, and thin film properties for different film/substrate systems can be identified. The guided wave is attenuated gradually due to energy dissipation caused by material viscosity and rapidly at the location near the source. With the receiver distance increasing, it becomes slower. Clearly models for ultrasonic generation and propagation in layered viscoelastic film/substrate materials must include the effect of viscoelasticity on the dispersive wave.
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68.60.Bs Mechanical and acoustical properties
62.65.+k Acoustical properties of solids
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
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