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8 Feb 2010

Volume 96, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 96, 063101 (2010); http://dx.doi.org/10.1063/1.3308512 (3 pages)

Takashi Yokoyama
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Group velocity dispersion and self phase modulation in silicon nitride waveguides

D. T. H. Tan, K. Ikeda, P. C. Sun, and Y. Fainman

Appl. Phys. Lett. 96, 061101 (2010); http://dx.doi.org/10.1063/1.3299008 (3 pages) | Cited 9 times

Online Publication Date: 8 February 2010

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The group velocity dispersion (GVD) of silicon nitride waveguides, prepared using plasma enhanced chemical vapor deposition, is studied and characterized experimentally in support of nonlinear optics applications. We show that the dispersion may be engineered by varying the geometry of the waveguide and demonstrate measured anomalous GVD values as high as −0.57 ps2/m and normal GVD values as high as 0.86 ps2/m. We also experimentally demonstrate the absence of any observed nonlinear loss at the telecommunications wavelength at peak intensities of up to 12 GW/cm2. Spectral broadening due to self phase modulation in silicon nitride waveguides with a nonlinear parameter of 1.4 W−1/m is also demonstrated.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.79.Gn Optical waveguides and couplers

Efficiency droop in 245–247 nm AlGaN light-emitting diodes with continuous wave 2 mW output power

W. Sun, M. Shatalov, J. Deng, X. Hu, J. Yang, A. Lunev, Y. Bilenko, M. Shur, and R. Gaska

Appl. Phys. Lett. 96, 061102 (2010); http://dx.doi.org/10.1063/1.3302466 (3 pages) | Cited 20 times

Online Publication Date: 9 February 2010

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We report on 245–247 nm AlGaN-based deep ultraviolet (DUV) light-emitting diodes with continuous wave output power up to 2 mW. DUV diodes with peak emission wavelength of 245 and 247 nm exhibit turn-on voltage less than 10 V. At room temperature and cw operation the maximum external quantum efficiency was close to 0.18%, which is the highest value published to date for devices with peak emission wavelength shorter than 250 nm. A large external efficiency droop observed at current densities above 100 A/cm2 is attributed to self-heating, carrier spillover from the QWs into the barrier layers or the p-type cladding layer, and/or Auger recombination. A semiempirical equation was proposed to describe the efficiency droop in DUV diodes at a high current injection.
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85.60.Jb Light-emitting devices
72.80.Ey III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Reactive radical facilitated reaction-diffusion modeling for holographic photopolymerization

Jianhua Liu, Haihui Pu, Bin Gao, Hongyue Gao, Dejin Yin, and Haitao Dai

Appl. Phys. Lett. 96, 061103 (2010); http://dx.doi.org/10.1063/1.3298607 (3 pages) | Cited 1 time

Online Publication Date: 9 February 2010

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A phenomenological concentration of reactive radical is proposed to take the role of curing light intensity in explicit proportion to the reaction rate for the conventional reaction-diffusion model. This revision rationally eliminates the theoretical defect of null reaction rate in modeling of the postcuring process, and facilitates the applicability of the model in the whole process of holographic photopolymerizations in photocurable monomer and nematic liquid crystal blend system. Excellent consistencies are obtained in both curing and postcuring processes between simulated and experimentally measured evolutions of the first order diffraction efficiency of the formed composite Bragg gratings.
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82.50.-m Photochemistry
42.79.Dj Gratings
42.40.Eq Holographic optical elements; holographic gratings
61.30.-v Liquid crystals
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.35.-x Polymers: properties; reactions; polymerization

Single-walled carbon-nanotube-deposited tapered fiber for four-wave mixing based wavelength conversion

K. K. Chow, M. Tsuji, and S. Yamashita

Appl. Phys. Lett. 96, 061104 (2010); http://dx.doi.org/10.1063/1.3304789 (3 pages) | Cited 5 times

Online Publication Date: 9 February 2010

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We report the observation of four-wave mixing (FWM) in single-walled carbon nanotubes (CNTs) deposited around a tapered fiber. The third-order nonlinearity of CNTs is originated from the interband transitions of the π-electrons causing nonlinear polarization similar to other highly-nonlinear organic optical materials. CNTs with suitable distributed tube diameter are optically deposited around a tapered fiber and FWM effect is generated by launching a probe and a pump light into the fiber device. FWM-based wavelength conversion is further demonstrated using the generated nonlinear effects and tunable conversion of 10 Gb/s nonreturn-to-zero signal is obtained.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.81.Gs Birefringence, polarization

Soliton self-deflection via power-dependent walk-off

Armando Piccardi, Alessandro Alberucci, and Gaetano Assanto

Appl. Phys. Lett. 96, 061105 (2010); http://dx.doi.org/10.1063/1.3313932 (3 pages) | Cited 11 times

Online Publication Date: 9 February 2010

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We demonstrate, both experimentally and theoretically, excitation-dependent self-bending of spatial solitons in nematic liquid crystals. The observed deflection is explained by nonlinear changes in walk-off, as induced by the rotation of the optic axis via power-driven reorientation.
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78.20.Ek Optical activity
42.70.Df Liquid crystals
42.65.Tg Optical solitons; nonlinear guided waves

High-Q silica microsphere by poly(methyl methacrylate) coating and modifying

C.-H. Dong, F.-W. Sun, C.-L. Zou, X.-F. Ren, G.-C. Guo, and Z.-F. Han

Appl. Phys. Lett. 96, 061106 (2010); http://dx.doi.org/10.1063/1.3313939 (3 pages) | Cited 8 times

Online Publication Date: 9 February 2010

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We experimentally characterize the Q-factor in a silica microsphere with the poly(methyl methacrylate) coating. Experimental results demonstrated that the Q-factor of the coated microcavity is higher than 108. Moreover, this coating is able to eliminate scattering from the unsmoothed surface and tune the optical field in the cavity. In the cavity interaction with quantum dots, the coating can not only increase the Q-factor of the microsphere with deposited quantum dots but also draw the maximal field to the interface where the quantum dots exist. Therefore, this coating method can highly enhance the interaction strength, and it will contribute to the cavity quantum electrodynamics study.
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42.79.Wc Optical coatings
78.67.Hc Quantum dots
42.70.Jk Polymers and organics
81.65.-b Surface treatments

Integrated terahertz pulse generation and amplification in quantum cascade lasers

S. S. Dhillon, S. Sawallich, N. Jukam, D. Oustinov, J. Madéo, S. Barbieri, P. Filloux, C. Sirtori, X. Marcadet, and J. Tignon

Appl. Phys. Lett. 96, 061107 (2010); http://dx.doi.org/10.1063/1.3306733 (3 pages) | Cited 7 times

Online Publication Date: 10 February 2010

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Integrated terahertz (THz) pulse generation and amplification in a THz quantum cascade laser (QCL) is demonstrated. Intracavity THz pulses are generated by exciting the facet of the QCL with an ultrafast Ti:Sapphire laser ( ∼ 100 fs) and detected using electro-optic sampling. Maximum THz field emission is found with an interband transition of 1.535 eV (809 nm) and by narrowing the excitation laser bandwidth to ∼ 3 THz. These resonance conditions correspond to the narrowband excitation of the quantum cascade miniband, indicating that the THz pulse is generated by the photoexcited carriers that are accelerated by the applied field. The generated pulse is subsequently amplified by the narrowband gain of the laser as it propagates through the QCL cavity.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.-v Laser optical systems: design and operation

Raman scattered photon transmission through a single nanoslit

Chang Chen (陈昌), Francesca Clemente, Ronald Kox, Liesbet Lagae, Guido Maes, Gustaaf Borghs, and Pol Van Dorpe

Appl. Phys. Lett. 96, 061108 (2010); http://dx.doi.org/10.1063/1.3309689 (3 pages) | Cited 2 times

Online Publication Date: 10 February 2010

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We demonstrate excitation and detection of Raman scattering of a silicon substrate through a 15 nm gold nanoslit. Along with the nanoslit, a plasmonic cavity is fabricated to optimize optical transmission through the slit. Using a polarization analysis we prove that the plasmons enhanced transmission is responsible for the detection of the Raman scattered photons of the silicon substrate through the nanoslit. The optical cavity between the nanoslit and the Si substrate further enhances this backward photon transmission. This opens up prospects for new tools for near-field Raman spectroscopy and sub-wavelength measurements.
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78.66.Bz Metals and metallic alloys
81.07.Bc Nanocrystalline materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
78.30.Er Solid metals and alloys

A direct comparison of single-walled carbon nanotubes and quantum-wells based subpicosecond saturable absorbers for all optical signal regeneration at 1.55 μm

H. Nong, M. Gicquel, L. Bramerie, M. Perrin, F. Grillot, C. Levallois, A. Maalouf, and S. Loualiche

Appl. Phys. Lett. 96, 061109 (2010); http://dx.doi.org/10.1063/1.3309712 (3 pages) | Cited 3 times

Online Publication Date: 10 February 2010

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Subpicosecond optical transmission experiments are used to compare saturable absorber (SA) based on bundled single-walled carbon nanotubes (SWNT) and iron-doped InGaAs/InP epitaxial multiple quantum wells (MQW) at 1.55 μm telecom wavelength. The SA key parameters (contrast ratio, saturation fluence, and recovery time) relevant for high speed all optical signal regeneration (AOSR) are extracted from the normalized differential transmission (NDT). Although both SA exhibit good contrast ratios, SWNT show a full signal recovery as well as a much faster response time than MQW. This original work on SA shows that SWNT are excellent candidates for future low cost AOSR.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption

Strain modulation-enhanced Mg acceptor activation efficiency of Al0.14Ga0.86N/GaN superlattices with AlN interlayer

Lei Wang, Rui Li, Ding Li, Ningyang Liu, Lei Liu, Weihua Chen, Cunda Wang, Zhijian Yang, and Xiaodong Hu

Appl. Phys. Lett. 96, 061110 (2010); http://dx.doi.org/10.1063/1.3315887 (3 pages) | Cited 6 times

Online Publication Date: 11 February 2010

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AlN layer was grown as interlayer between undoped GaN and Mg doped Al0.14Ga0.86N/GaN superlattices (SLs) epilayer to modulate the strain distribution between Al0.14Ga0.86N barrier and GaN well layers in SLs sample. Strain relaxation was observed in the SLs sample with AlN interlayer by x-ray diffraction reciprocal space mapping method. The measured hole concentration of SLs sample with AlN interlayer at room temperature was over 1.6×1018 cm−3 but that was only 6.6×1016 cm−3 obtained in SLs sample without AlN interlayer. Variable temperature Hall-effect measurement showed that the acceptor activation energy decreased from 150 to 70 meV after inserting the AlN layer, which indicated that the strain modulation of SLs induced by AlN interlayer was beneficial to the Mg acceptor activation and hole concentration enhancement.
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73.21.Cd Superlattices
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.72.uj III-V and II-VI semiconductors
73.61.Ey III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.My Galvanomagnetic and other magnetotransport effects

Interface roughness transport in terahertz quantum cascade detectors

Emmanuel Lhuillier, Isabelle Ribet-Mohamed, Emmanuel Rosencher, Gilles Patriarche, Amandine Buffaz, Vincent Berger, and Mathieu Carras

Appl. Phys. Lett. 96, 061111 (2010); http://dx.doi.org/10.1063/1.3310022 (3 pages) | Cited 3 times

Online Publication Date: 11 February 2010

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Infrared detectors based on a quantum cascade have been proposed to suppress the dark current which is a limiting factor in quantum well infrared photodetectors. Those detectors have been mainly designed for the midinfrared wavelength. Operating in the terahertz range involves a complete change of regime of transport since the photon energy is lower than the optical phonon energy. Thanks to a two dimensional model of transport, we have identified interface roughness as the key interaction in such a structure. Interface parameters, evaluated by scanning transmission electron microscopy, are used to study their influence on the resistance of the device.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
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Breakdown probability of neon under the influence of field electron emission and surface charges on the cathode surface

V. Lj. Marković, S. R. Gocić, and S. N. Stamenković

Appl. Phys. Lett. 96, 061501 (2010); http://dx.doi.org/10.1063/1.3310020 (3 pages) | Cited 2 times

Online Publication Date: 8 February 2010

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Improved relations are suggested to determine of the breakdown probability in neon under the influence of field electron emission and surface charges on the gold plated cathode surfaces. The influence of field electron emission from a vacuum deposited gold layer is confirmed by the Fowler–Nordheim plot based on an analysis of the breakdown time delay dependence on the voltage math(U). Surface regions with a reduced conductivity on a hard galvanic layer of gold caused by diffusion of nickel atoms from a nickel sublayer are confirmed by scanning electron microscopy and energy dispersive x-ray spectrum.
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51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
68.35.Fx Diffusion; interface formation
79.70.+q Field emission, ionization, evaporation, and desorption

High current diffuse dielectric barrier discharge in atmospheric pressure air for the deposition of thin silica-like films

S. A. Starostin, P. Antony Premkumar, M. Creatore, H. de Vries, R. M. J. Paffen, and M. C. M. van de Sanden

Appl. Phys. Lett. 96, 061502 (2010); http://dx.doi.org/10.1063/1.3310024 (3 pages) | Cited 14 times

Online Publication Date: 9 February 2010

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The diffuse dielectric barrier discharge in atmospheric pressure air was applied for the thin film deposition on polymeric web in industrially relevant roll-to-roll configuration. The silica-like film deposition was performed using the admixture of hexamethyldisiloxane precursor to air flow. Fast discharge imaging at 2 μs exposure time confirms plasma uniformity in a single current pulse time scale. Morphology and composition analyses indicate that the process results in ultrasmooth films (roughness comparable to initial substrate roughness) and shows the possibility to synthesize carbon-free layers.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.J- Morphology of films
68.55.A- Nucleation and growth
82.80.-d Chemical analysis and related physical methods of analysis
77.55.D- High-permittivity gate dielectric films

Low-pressure indium-halide discharges for fluorescent illumination applications

Daiyu Hayashi, Rainer Hilbig, Achim Körber, Stefan Schwan, Robert Scholl, Martin Boerger, and Maria Huppertz

Appl. Phys. Lett. 96, 061503 (2010); http://dx.doi.org/10.1063/1.3318252 (2 pages) | Cited 4 times

Online Publication Date: 11 February 2010

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Low-pressure gas discharges of molecular radiators were studied for fluorescent lighting applications with a goal of reducing the energy loss due to the large Stokes shift in phosphors of conventional mercury-based fluorescent lamp technology. Indium halides (InCl, InBr, and InI) were chosen as the molecular radiators that generate ultraviolet to blue light emissions. The electrical characteristics and optical emission intensities were measured in discharges containing gaseous indium halides (InCl, InBr, and InI) as molecular radiators. The low-pressure discharges in indium halide vapor showed potential as a highly efficient gas discharge system for fluorescent lighting application.
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42.72.Bj Visible and ultraviolet sources
52.80.-s Electric discharges
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Temperature-dependent shear band dynamics in a Zr-based bulk metallic glass

David Klaumünzer, Robert Maaß, Florian H. Dalla Torre, and Jörg F. Löffler

Appl. Phys. Lett. 96, 061901 (2010); http://dx.doi.org/10.1063/1.3309686 (3 pages) | Cited 16 times

Online Publication Date: 8 February 2010

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Flow serrations recorded during inhomogeneous deformation of Zr52.5Ti5Cu17.9Ni14.6Al10 (Vit105) were studied during compression testing at temperatures between −40 and 60 °C. The shear band velocities determined exhibit a pronounced temperature dependence covering nearly two orders of magnitude. The velocities follow an Arrhenius-type behavior with an associated activation energy of 0.3±0.05 eV. The results demonstrate a thermally activated mechanism of shear band propagation, which is similar to the behavior of other, nonmetallic amorphous materials.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.05.Kf Glasses (including metallic glasses)

Thermoreflectance characterization of band-edge excitonic transitions in CuAlS2 ultraviolet solar-cell material

Ching-Hwa Ho

Appl. Phys. Lett. 96, 061902 (2010); http://dx.doi.org/10.1063/1.3303826 (3 pages) | Cited 8 times

Online Publication Date: 8 February 2010

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Near band edge transitions of CuAlS2 chalcopyrite crystals have been characterized using temperature-dependent thermoreflectance (TR) spectroscopy in the temperature range between 30 and 340 K. A lot of interband transition features of EAn = 2, EAn = 3, EBn = 2, EC, ED, EE, and EF were detected in the low-temperature TR spectrum of 3–6 eV at 30 K. Transition energies of the TR features of CuAlS2 are analyzed. Transition origins of the features are evaluated. Optical-electric conversion behavior of CuAlS2 was evaluated by photoconductivity (PC) measurement at 300 K. The PC spectrum reveals that the maximum photoresponse occurs near the energy positions of EAn = 2, EAn = 3, and EBn = 2 features. The features are the fundamental band edge excitons which dominate photoelectric conversion behavior of CuAlS2 ultraviolet solar-energy material.
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78.20.nb Photothermal effects
78.40.Fy Semiconductors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.50.Pz Photoconduction and photovoltaic effects
88.40.H- Solar cells (photovoltaics)

Statistical composition-structure-property correlation and glass-forming ability based on the full icosahedra in Cu–Zr metallic glasses

Z. D. Sha, Y. P. Feng, and Y. Li

Appl. Phys. Lett. 96, 061903 (2010); http://dx.doi.org/10.1063/1.3310278 (3 pages) | Cited 17 times

Online Publication Date: 8 February 2010

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Using the large-scale atomic/molecular massively parallel simulator, fraction of the Cu-centered 〈0,0,12,0〉 full icosahedra (fico) is obtained from a statistical analysis over a broad compositional range with high resolution in the Cu–Zr binary system. Weak but significant peaks are observed at certain compositions which coincide with good glass formers. This correlation implies that the change in fico is a fundamental structural factor in determining the ease of glass formation. In this regard, fico can be an indicator of glass-forming ability. Our work provides further understanding on the atomic structure of the Cu–Zr system and its effect on glass formation.
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61.43.Fs Glasses
61.43.Bn Structural modeling: serial-addition models, computer simulation

Effects of additional Ce3+ doping on the luminescence of Li2SrSiO4:Eu2+ yellow phosphor

Tae-Gon Kim, Hyo-Sug Lee, Chun Che Lin, Taehyung Kim, Ru-Shi Liu, Ting-Shan Chan, and Seoung-Jae Im

Appl. Phys. Lett. 96, 061904 (2010); http://dx.doi.org/10.1063/1.3308486 (3 pages) | Cited 14 times

Online Publication Date: 9 February 2010

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Additional Ce3+ doping improves the luminescence of Li2SrSiO4:Eu2+, a yellow phosphor for ultraviolet or blue light-emitting diodes. By examining the photoluminescence of Li2SrSiO4:Eu2+, Li2SrSiO4:Ce3+, and Li2SrSiO4:Ce3+,Eu2+, it was confirmed that the energy transfer from Ce3+ to Eu2+ ions contributes little to the enhanced luminescence of Li2SrSiO4:Ce3+,Eu2+. Alternatively, we suggested that Ce3+ ions could stabilize the Li vacancies, inhibit the oxidization of Eu2+ to Eu3+, and consequently increase emission intensity, based on the characterizations with decay time and synchrotron light source x-ray absorption measurements. The proposed argument was validated with first principle calculations of the defect formation energies.
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78.55.Hx Other solid inorganic materials
61.72.up Other materials
85.60.Jb Light-emitting devices

Optical and electro-optic anisotropy of epitaxial Ba0.7Sr0.3TiO3 thin films

D. Y. Wang, S. Li, H. L. W Chan, and C. L. Choy

Appl. Phys. Lett. 96, 061905 (2010); http://dx.doi.org/10.1063/1.3302453 (3 pages) | Cited 6 times

Online Publication Date: 9 February 2010

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The anisotropic optical and electro-optic properties of ferroelectric Ba0.7Sr0.3TiO3 thin films, deposited on highly transparent single-crystal MgO (001), (011), and (111) substrates using pulsed laser deposition, were investigated. The experimental results show a strong correlation between optical, electro-optic properties, and the orientation of Ba0.7Sr0.3TiO3 thin films. The linear electro-optic coefficient rc of the (001), (011), and (111)-oriented Ba0.7Sr0.3TiO3 thin films are 99.1, 15.7, and 87.8 pm/V, respectively. Such a correlation may be attributed to the orientation dependent distribution and magnitude of spontaneous polarization.
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77.55.Px Epitaxial and superlattice films
78.66.Nk Insulators
78.20.Jq Electro-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity

Identification of extremely radiative nature of AlN by time-resolved photoluminescence

T. Onuma, K. Hazu, A. Uedono, T. Sota, and S. F. Chichibu

Appl. Phys. Lett. 96, 061906 (2010); http://dx.doi.org/10.1063/1.3284653 (3 pages) | Cited 6 times

Online Publication Date: 9 February 2010

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Extremely radiative nature of high-quality AlN single crystalline epilayers was identified by means of far ultraviolet time-resolved photoluminescence using a frequency-quadrupled femtosecond Al2O3:Ti laser. The gross radiative lifetimes of a free excitonic polariton emission as short as 10 ps at 7 K and 180 ps at 300 K were revealed, which are the shortest ever reported for bulk semiconductor materials.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena
78.47.jd Time resolved luminescence
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Effect of Mg doping on enhancement of terahertz emission from InN with different lattice polarities

X. Q. Wang, G. Z. Zhao, Q. Zhang, Y. Ishitani, A. Yoshikawa, and B. Shen

Appl. Phys. Lett. 96, 061907 (2010); http://dx.doi.org/10.1063/1.3303983 (3 pages) | Cited 10 times

Online Publication Date: 9 February 2010

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Effect of Mg doping on terahertz (THz) emission from InN with different lattice polarities was studied. Strong enhancement of THz emission was observed from InN with appropriate Mg-concentrations (1018 cm−3), which is independent of lattice polarity. The buried p-type layers show stronger THz emission than the n-type ones. The dominant mechanism for THz emission was found to be photo-Dember effect and the emission intensity was inversely proportional to the conductivity, which is beneficial to investigate THz emission from InN since the conductivity can be more accurately measured than the carrier concentration and mobility due to the electron accumulation on surface.
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61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.sd Impurity concentration
73.61.Ey III-V semiconductors
73.50.Pz Photoconduction and photovoltaic effects
73.50.Dn Low-field transport and mobility; piezoresistance

The influence of Ni additions on the relative stability of η and η′ Cu6Sn5

U. Schwingenschlögl, C. Di Paola, K. Nogita, and C. M. Gourlay

Appl. Phys. Lett. 96, 061908 (2010); http://dx.doi.org/10.1063/1.3310019 (3 pages) | Cited 14 times

Online Publication Date: 9 February 2010

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We investigate how 5 at. % Ni influences the relative stability of η and η′ Cu6Sn5. Synchrotron x-ray diffraction shows that, while Cu6Sn5 exists as η′ at 25 and 150 °C and transforms to η on heating to 200 °C, Cu5.5Ni0.5Sn5 is best fit to η throughout 25–200 °C. Our first principles calculations predict that η′ is stable at T = 0 K in both Cu6Sn5 and Cu5.5Ni0.5Sn5, but that the energy difference is substantially reduced from 1.21 to 0.90 eV per 22 atom cell by the Ni addition. This effect is attributed to Ni developing distinct bonding to both Cu and Sn in the η phase.
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61.66.Dk Alloys

Optical band-gap determination of nanostructured WO3 film

P. P. González-Borrero, F. Sato, A. N. Medina, M. L. Baesso, A. C. Bento, G. Baldissera, C. Persson, G. A. Niklasson, C. G. Granqvist, and A. Ferreira da Silva

Appl. Phys. Lett. 96, 061909 (2010); http://dx.doi.org/10.1063/1.3313945 (3 pages) | Cited 10 times

Online Publication Date: 9 February 2010

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The optical band-gap energy of a nanostructured tungsten trioxide film is determined using the photoacoustic spectroscopy method under continuous light excitation. The mechanism of the photoacoustic signal generation is discussed. The band-gap energy is also computed by other methods. The absorption coefficient as well as the band-gap energy of three different crystal structures of tungsten trioxide is calculated by a first-principles Green’s function approach using the projector augmented wave method. The theoretical study indicates that the cubic crystal structure shows good agreement with the experimental data.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.66.-w Optical properties of specific thin films
73.22.-f Electronic structure of nanoscale materials and related systems
71.20.-b Electron density of states and band structure of crystalline solids
07.60.Rd Visible and ultraviolet spectrometers
42.25.Bs Wave propagation, transmission and absorption

Monte Carlo modeling of the fiber curliness effect on percolation of conductive composites

H. M. Ma, X.-L. Gao, and T. Benson Tolle

Appl. Phys. Lett. 96, 061910 (2010); http://dx.doi.org/10.1063/1.3309590 (3 pages) | Cited 7 times

Online Publication Date: 10 February 2010

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A three-dimensional (3D) Monte Carlo model is developed to study the fiber curliness effect on the percolation threshold of a composite filled with electrically conductive curved fibers. These fibers are simulated as zigzag-shaped fibers that are randomly positioned in the composite, forming a 3D random network. The simulation results show that the fiber curliness can significantly affect the percolation threshold: the more curved the fibers, the higher the threshold. The results also reveal an exponential relationship between the threshold and the fiber aspect ratio: the higher the aspect ratio, the lower the threshold. These predicted trends agree well with existing experimental and simulation results based on straight fibers or curved fibers with simpler shapes.
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64.60.ah Percolation
61.43.Bn Structural modeling: serial-addition models, computer simulation

Spontaneous and electric field induced quadratic optical nonlinearity in ferroelectric crystals AgNa(NO2)2

A. V. Kityk, R. Czaplicki, A. Klöpperpieper, A. S. Andrushchak, and B. Sahraoui

Appl. Phys. Lett. 96, 061911 (2010); http://dx.doi.org/10.1063/1.3315941 (3 pages) | Cited 1 time

Online Publication Date: 11 February 2010

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We demonstrate the second harmonic generation (SHG) in ferroelectric AgNa(NO2)2 crystals resulting from the spontaneous and electric field induced polarizations. Relatively high effective nonlinear optic (NLO) susceptibility is combined in this crystals with the existing several phase matching geometries of NLO interaction. Anomalously large response of SHG with respect to an applied electric field has been found in the vicinity of the paraelectric-to-ferroelectric phase transition. The behavior of NLO properties in the ferroelectric phase and especially in the region of the Curie point is discussed within the phenomenological theory.
Show PACS
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.An Optical susceptibility, hyperpolarizability
77.80.B- Phase transitions and Curie point
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
42.70.Mp Nonlinear optical crystals
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