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28 May 2012

Volume 100, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 222402 (2012); http://dx.doi.org/10.1063/1.3700809 (4 pages)

Felix Balhorn, Simon Jeni, Wolfgang Hansen, Detlef Heitmann, and Stefan Mendach
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Metamaterial near-field sensor for deep-subwavelength thickness measurements and sensitive refractometry in the terahertz frequency range

Benjamin Reinhard, Klemens M. Schmitt, Viktoria Wollrab, Jens Neu, René Beigang, and Marco Rahm

Appl. Phys. Lett. 100, 221101 (2012); http://dx.doi.org/10.1063/1.4722801 (4 pages) | Cited 3 times

Online Publication Date: 29 May 2012

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We present a metamaterial-based terahertz (THz) sensor for thickness measurements of subwavelength-thin materials and refractometry of liquids and liquid mixtures. The sensor operates in reflection geometry and exploits the frequency shift of a sharp Fano resonance minimum in the presence of dielectric materials. We obtained a minimum thickness resolution of 12.5 nm (1/16 000 times the wavelength of the THz radiation) and a refractive index sensitivity of 0.43 THz per refractive index unit. We support the experimental results by an analytical model that describes the dependence of the resonance frequency on the sample material thickness and the refractive index.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.60.Hv Refractometers and reflectometers
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Near infrared two-photon self-confinement in photopolymers for light induced self-written waveguides fabrication

Alberto Barsella, Honorat Dorkenoo, and Loïc Mager

Appl. Phys. Lett. 100, 221102 (2012); http://dx.doi.org/10.1063/1.4722925 (3 pages) | Cited 1 time

Online Publication Date: 29 May 2012

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We present the fabrication of single mode light induced self-written waveguides using two-photon absorption in photopolymers. The measurements are compared to the finite element method simulation of the propagation and demonstrate that two-photon process leads to the confinement of light.
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42.70.Jk Polymers and organics
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers

Cherenkov high-order harmonic generation by multistep cascading in χ(2) nonlinear photonic crystal

Ning An, Huaijin Ren, Yuanlin Zheng, Xuewei Deng, and Xianfeng Chen

Appl. Phys. Lett. 100, 221103 (2012); http://dx.doi.org/10.1063/1.4722931 (4 pages) | Cited 2 times

Online Publication Date: 29 May 2012

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We propose a scheme for efficient Cherenkov high-order harmonic generation. Second to fifth order harmonic wave are observed in a single periodically poled ferroelectric crystal in our experiment. The noncollinear high-order harmonic generation is produced via enhanced Cherenkov second harmonic cascaded with successive multistep sum-frequency generation with simultaneously longitudinal phase-matching. The emission angle and power dependencies are analyzed in detail experimentally, which coincide with theoretical predictions.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Qs Photonic bandgap materials
41.60.Bq Cherenkov radiation

Transistor laser optical and electrical linearity enhancement with collector current feedback

H. W. Then, F. Tan, M. Feng, and N. Holonyak, Jr.

Appl. Phys. Lett. 100, 221104 (2012); http://dx.doi.org/10.1063/1.4723874 (3 pages)

Online Publication Date: 29 May 2012

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The three-port quantum well (QW) transistor laser (TL) is shown to provide a unique solution for generating ultra-linear electro-optical signals. With a simple collector current feedback loop, the 3rd order intermodulation distortion in the electrical and optical output signals of the transistor laser can be suppressed by as much 18.2 dB and 8.4 dB, respectively. These results show that the TL can be used for direct electro-optical feedback linearization, because of the base QW carrier-photon interaction, without incurring signal losses at multiple stages of auxiliary external electro-optical conversion circuitry.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
78.20.Jq Electro-optical effects

Temperature dependent distinct coupling and dispersions of heavy- and light-hole excitonic polaritons in ZnO

C. C. Zheng, S. J. Xu, J. Q. Ning, Y. N. Chen, F. Zhang, and C. M. Che

Appl. Phys. Lett. 100, 221105 (2012); http://dx.doi.org/10.1063/1.4722933 (4 pages) | Cited 3 times

Online Publication Date: 30 May 2012

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Distinct coupling behavior of heavy- and light-hole excitonic polaritons in ZnO was unveiled by investigating the optical reflectance spectra of a high quality ZnO single crystal as a function of temperature both experimentally and theoretically. A resonance like coupling region was found at a temperature of around 50 K at which several relevant physical quantities such as the transverse exciton transition energy, polarizability, and damping parameters of the two kinds of excitonic polaritons were revealed to overturn. Calculated dispersions correctly reflect the nature of coupled photon and exciton and reproduce the spectral structures of the interacting polaritons.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.40.Fy Semiconductors
71.35.-y Excitons and related phenomena
71.20.Nr Semiconductor compounds
61.66.Fn Inorganic compounds

Spatio-temporal mapping of ablated species in ultrafast laser-produced graphite plasmas

K. F. Al-Shboul, S. S. Harilal, and A. Hassanein

Appl. Phys. Lett. 100, 221106 (2012); http://dx.doi.org/10.1063/1.4722939 (4 pages) | Cited 5 times

Online Publication Date: 30 May 2012

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We studied the spatial and temporal distributions of ionic, neutral, and molecular species generated by femtosecond laser produced plasma under varying ambient nitrogen gas pressures. Plasmas were generated by irradiating planar graphite targets using 40 fs pulses of 800 nm radiation from a Ti:Sapphire laser. The results show that in the presence of an ambient gas, the molecular species spatial extension and lifetime are directly correlated to the evolution of excited ions. The present studies also provide valuable insights into the evolution history of various species and their excitation during ultrafast laser ablation.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Nature of optical transitions involving cation vacancies and complexes in AlN and AlGaN

A. Sedhain, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 100, 221107 (2012); http://dx.doi.org/10.1063/1.4723693 (4 pages)

Online Publication Date: 30 May 2012

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Photoluminescence spectroscopy was employed to probe the nature of optical transitions involving Al vacancy (VAl) and vacancy-oxygen complex (VAl-ON) in AlN. An emission line near 2 eV due to the recombination between the 2− charge state of (VAl-ON)2−/1−, and the valence band was directly observed under a below bandgap excitation scheme. This photoluminescence (PL) band was further resolved into two emission lines at 1.9 and 2.1 eV, due to the anisotropic binding energies of VAl-ON complex caused by two different bonding configurations–the substitutional ON sits along c-axis or sits on one of the three equivalent tetrahedral positions. Moreover, under an above bandgap excitation scheme, a donor-acceptor pair like transition involving shallow donors and (VAl-ON)2−/1− deep acceptors, which is the “yellow-luminescence” band counterpart in AlN, was also seen to split into two emission lines at 3.884 and 4.026 eV for the same physical reason. Together with previous results, a more complete picture for the optical transitions involving cation vacancy related deep centers in AlGaN alloy system has been constructed.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
61.72.jd Vacancies
71.20.Ps Other inorganic compounds

Enhanced optical limiting in nanosized mixed zinc ferrites

Panit Chantharasupawong, Reji Philip, Tamio Endo, and Jayan Thomas

Appl. Phys. Lett. 100, 221108 (2012); http://dx.doi.org/10.1063/1.4724194 (4 pages) | Cited 3 times

Online Publication Date: 30 May 2012

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Optical limiting performance of zinc ferrite, nickel zinc ferrite, and copper zinc ferrite nanoparticles is investigated at 532 nm using 5 nanosecond laser pulses. Enhanced optical limiting is observed in the mixed zinc ferrites, which is attributed to the relative longevity of self-trapped charge transfer states. Samples exhibit absorption saturation followed by a rapid onset of optical limiting as the input fluence is increased. This is advantageous in applications where detector sensitivity should be retained at the maximum value until the input fluence approaches the detector damage regime. The Z-scan results are compared to those measured in C60.
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42.79.-e Optical elements, devices, and systems
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Mechanism of electron acceleration by chirped laser pulse

X. Y. Wu, P. X. Wang, and S. Kawata

Appl. Phys. Lett. 100, 221109 (2012); http://dx.doi.org/10.1063/1.4723847 (4 pages) | Cited 2 times

Online Publication Date: 31 May 2012

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We studied the mechanism of electron acceleration by a chirped laser pulse. We found that, because of the chirp effect, a region exists where the laser wave phase experienced by the electron varies slowly, so that the electron can be accelerated for a long time. The mechanism of chirped laser acceleration is different to that of the capture and acceleration scenario, although both of them have a main acceleration stage in which the electrons are trapped for long periods.
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41.75.Fr Electron and positron beams
42.62.-b Laser applications
42.60.Fc Modulation, tuning, and mode locking

Photonic crystal tunable slow light device integrated with multi-heaters

Norihiro Ishikura, Ryo Hosoi, Ryo Hayakawa, Takemasa Tamanuki, Mizuki Shinkawa, and Toshihiko Baba

Appl. Phys. Lett. 100, 221110 (2012); http://dx.doi.org/10.1063/1.4724191 (3 pages) | Cited 2 times

Online Publication Date: 31 May 2012

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We fabricated photonic crystal slow light waveguides integrated with multi-heaters, using CMOS-compatible process. By optimizing heating powers and adjusting the index distribution, a clear delay peak was observed, which suggests that the fabrication errors were compensated for completely. When a linear index chirp was added to this condition, the delay was tuned by 54 ps. When a quadratic chirp was added, arbitrary group delay dispersion was generated at wavelengths around 1550 nm within a 3 nm bandwidth. The continuously tunable range was from −32 to 54 ps/nm/mm. Using this as a dispersion compensator, we compressed pre-chirped pico-second pulses.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials
42.82.Cr Fabrication techniques; lithography, pattern transfer

Surface plasmon polariton-controlled tunable quantum-dot emission

R. J. Moerland, H. T. Rekola, G. Sharma, A.-P. Eskelinen, A. I. Väkeväinen, and P. Törmä

Appl. Phys. Lett. 100, 221111 (2012); http://dx.doi.org/10.1063/1.4724327 (4 pages) | Cited 2 times

Online Publication Date: 1 June 2012

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The unique properties of surface plasmon polaritons, such as strong field confinement and local field enhancement effects, make them ideal candidates to enhance and shape the emission of luminescent nanoparticles. Of these nanoparticles, quantum dots are highly versatile, suitable for vastly different applications due to their size and material tunability. In many cases however, the emission wavelength of the quantum dots is fixed after manufacturing, allowing no control over the in situ emission properties. Here, we show fully optical, in situ tunability of the emission wavelength of quantum dots, with shifts of over 30 nm, employing surface plasmon polaritons to control the emission wavelength.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.22.Lp Collective excitations
73.21.La Quantum dots
78.55.-m Photoluminescence, properties and materials
78.67.Hc Quantum dots
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Crystalline order of polymer nanoparticles over large areas at solid/liquid interfaces

M. S. Hellsing, V. Kapaklis, A. R. Rennie, A. V. Hughes, and L. Porcar

Appl. Phys. Lett. 100, 221601 (2012); http://dx.doi.org/10.1063/1.4723634 (4 pages)

Online Publication Date: 29 May 2012

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We report on the formation of large two-dimensional domains (about 20 cm2) of oriented and ordered structures of polystyrene particles dispersed in water at a solid/liquid interface. Gentle flow of the dispersed sample into the holder at a shear strain rate of about 0.1 s−1 caused particles at the air/latex meniscus to self-assemble in a regular structure on both solid silica or alumina surfaces. Scattering experiments show that the particle separation at the surface was the same as in the bulk and determined by repulsion arising from the charges on the particles. Close-packed planes formed parallel to the interface.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.41.+e Polymers, elastomers, and plastics
81.16.Dn Self-assembly

Electrophoretic motion of a charged water droplet near an oil-air interface

Dong Woog Lee, Do Jin Im, and In Seok Kang

Appl. Phys. Lett. 100, 221602 (2012); http://dx.doi.org/10.1063/1.4723633 (4 pages) | Cited 4 times

Online Publication Date: 30 May 2012

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The trajectory of a charged droplet near an oil-air interface is investigated. When a charged droplet is translated in oil by electrophoresis, the droplet follows a straight line between two electrodes. However, if an oil-air interface is close to a droplet, the droplet follows an upwardly concave parabolic pathway. By using the leaky dielectric model, we have verified that this phenomenon is caused by the distorted electric field due to the difference in permittivities. Furthermore, it is enhanced by the accumulated free charges on the oil-air interface due to the difference in the electric conductivities of oil and air. Finally, we suggest a complementary arrangement of electrodes for realizing a straight pathway of the droplet near the interface.
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82.45.-h Electrochemistry and electrophoresis
47.65.-d Magnetohydrodynamics and electrohydrodynamics
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
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Polarization-tunable polariton excitation in a compound plasmonic crystal

Lin Zhou, Xia-Mei Tang, Cheng-Ping Huang, Yi Zhang, and Yong-Yuan Zhu

Appl. Phys. Lett. 100, 221901 (2012); http://dx.doi.org/10.1063/1.4722937 (4 pages)

Online Publication Date: 29 May 2012

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Propagation of an electromagnetic (EM) wave through a compound plasmonic crystal composed of perpendicularly arranged gold nanorod pairs has been studied. Because of the strong coupling between the EM wave and vibrations of free electrons inside nanorod pairs, the polarization-tunable polariton stop band as well as pronounced polarization conversion can be achieved in the compound plasmonic crystal. A theory based on Huang-Kun-like equations is presented to reveal the mechanism, which agrees well with the simulations. Our results may shed light on the structure design and physical understandings on the anisotropic metamaterials.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
78.66.Bz Metals and metallic alloys

Correlating whisker growth and grain structure on Sn-Cu samples by real-time scanning electron microscopy and backscattering diffraction characterization

Fei Pei, Nitin Jadhav, and Eric Chason

Appl. Phys. Lett. 100, 221902 (2012); http://dx.doi.org/10.1063/1.4721661 (4 pages) | Cited 4 times

Online Publication Date: 29 May 2012

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Whiskers/hillocks grow out of Pb-free Sn coatings used in electronics manufacturing. To determine which grains form whiskers/hillocks, we use scanning electron microscopy and backscattering diffraction to simultaneously monitor the surface morphology and grain structure. To reduce surface roughness, we developed a “peel-off” method to prepare ultra-flat samples that were measured repeatedly while whiskers/hillocks formed. We find grains that form into whiskers/hillocks are present in the as-deposited film (i.e., not re-nucleated) and many have horizontal grain boundaries beneath them. Grain rotation during whisker/hillock formation means that measurements performed after the features grow do not indicate their initial grain orientations.
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68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
79.20.Kz Other electron-impact emission phenomena
81.05.Bx Metals, semimetals, and alloys
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.A- Nucleation and growth

Realizing almost perfect bending waveguides with anisotropic epsilon-near-zero metamaterials

Jie Luo, Ping Xu, Huanyang Chen, Bo Hou, Lei Gao, and Yun Lai

Appl. Phys. Lett. 100, 221903 (2012); http://dx.doi.org/10.1063/1.4723844 (5 pages) | Cited 9 times

Online Publication Date: 31 May 2012

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We study metamaterials with an anisotropic permittivity tensor in which one component is near zero. We find that such an anisotropic metamaterial can be used to control wave propagation and construct almost perfect bending waveguides with a high transmission rate (>95%). This interesting effect originates in the power flow redistribution by the surface waves on the input and output interfaces, which smoothly matches with the propagating modes inside the metamaterial waveguide. We also find that waves in such anisotropic epsilon-near-zero materials can be reflected by small-sized perfect magnetic conductor defects. Numerical calculations have been performed to confirm the above effects.
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42.79.Gn Optical waveguides and couplers
42.70.-a Optical materials
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Lutetium-doped EuO films grown by molecular-beam epitaxy

A. Melville, T. Mairoser, A. Schmehl, D. E. Shai, E. J. Monkman, J. W. Harter, T. Heeg, B. Holländer, J. Schubert, K. M. Shen, J. Mannhart, and D. G. Schlom

Appl. Phys. Lett. 100, 222101 (2012); http://dx.doi.org/10.1063/1.4723570 (4 pages) | Cited 3 times

Online Publication Date: 29 May 2012

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The effect of lutetium doping on the structural, electronic, and magnetic properties of epitaxial EuO thin films grown by reactive molecular-beam epitaxy is experimentally investigated. The behavior of Lu-doped EuO is contrasted with doping by lanthanum and gadolinium. All three dopants are found to behave similarly despite differences in electronic configuration and ionic size. Andreev reflection measurements on Lu-doped EuO reveal a spin-polarization of 96% in the conduction band, despite non-magnetic carriers introduced by 5% lutetium doping.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.at Other materials
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
78.20.Ls Magneto-optical effects
78.66.Nk Insulators

Upper limit of two-dimensional hole gas mobility in strained Ge/SiGe heterostructures

T. Tanaka, Y. Hoshi, K. Sawano, N. Usami, Y. Shiraki, and K. M. Itoh

Appl. Phys. Lett. 100, 222102 (2012); http://dx.doi.org/10.1063/1.4723690 (4 pages) | Cited 1 time

Online Publication Date: 30 May 2012

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High two-dimensional hole gas (2DHG) mobility (μ2DHG>10000cm2/Vs at T<100K) strained Ge/Si1−xGex structures with x = 0.5 and 0.65 were fabricated, and temperature dependence of their 2DHG mobility was obtained experimentally by the mobility spectrum analysis of the conductivity under magnetic fields. The theoretically calculated 2DHG mobility was compared to experimental data to determine the effective deformation potentials for scattering by acoustic and optical phonons. Using empirically confirmed parameters, the upper theoretical limit of room temperature 2DHG mobility μ2DHG in strained Ge as a function of strain was calculated. The possibility to achieve μ2DHG>5000cm2/Vs at room temperature is presented.
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81.05.Cy Elemental semiconductors
81.05.Hd Other semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.10.Di Scattering by phonons, magnons, and other nonlocalized excitations

On conversion of luminescence into absorption and the van Roosbroeck-Shockley relation

Rupak Bhattacharya, Bipul Pal, and Bhavtosh Bansal

Appl. Phys. Lett. 100, 222103 (2012); http://dx.doi.org/10.1063/1.4721495 (3 pages)

Online Publication Date: 30 May 2012

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The problem of conversion of experimentally measured luminescence spectrum into the absorption cross section is revisited. The common practice of using the van Roosbroeck-Shockley (or Kubo-Martin-Schwinger or Kennard-Stepanov) relation in this context is incorrect because luminescence from semiconductors is essentially all due to the spontaneous emission component of the recombination of carriers distributed far-from-equilibrium. A simple, physically consistent, and practical prescription for converting the luminescence spectra into absorption is presented and its relation to the so-called nonequilibrium generalization of the van Roosbroeck-Shockley relationship is discussed.
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78.55.Cr III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

GaAsSb bandgap, surface fermi level, and surface state density studied by photoreflectance modulation spectroscopy

J. S. Hwang, J. T. Tsai, I. C. Su, H. C. Lin, Y. T. Lu, P. C. Chiu, and J. I. Chyi

Appl. Phys. Lett. 100, 222104 (2012); http://dx.doi.org/10.1063/1.4724097 (4 pages) | Cited 1 time

Online Publication Date: 30 May 2012

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The bandgap, surface Fermi level, and surface state density of a series of GaAs1−xSbx surface intrinsic-n+ structures with GaAs as substrate are determined for various Sb mole fractions x by the photoreflectance modulation spectroscopy. The dependence of the bandgap on the mole composition x is in good agreement with previous measurements as well as predictions calculated using the dielectric model of Van Vechten and Bergstresser in Phys. Rev. B 1, 3551 (1970). For a particular composition x, the surface Fermi level is always strongly pinned within the bandgap of GaAs1−xSbx and we find its variation with composition x is well described by a function EF = 0.70 − 0.192 x for 0 ≦ x ≦ 0.35, a result which is notably different from that reported by Chouaib et al. [Appl. Phys. Lett. 93, 041913 (2008)]. Our results suggest that the surface Fermi level is pinned at the midgap of GaAs and near the valence band of the GaSb.
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71.20.Nr Semiconductor compounds
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.20.At Surface states, band structure, electron density of states
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Spinel oxides: Δ1 spin-filter barrier for a class of magnetic tunnel junctions

Jia Zhang, X.-G. Zhang, and X. F. Han

Appl. Phys. Lett. 100, 222401 (2012); http://dx.doi.org/10.1063/1.4722804 (4 pages) | Cited 3 times

Online Publication Date: 29 May 2012

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The orbital composition of the electrode wave functions and the complex bands within the barrier band gap are two important factors in deciding the spin-filter effect. This is illustrated in a class of spinel oxides, including MgAl2O4, ZnAl2O4, SiMg2O4, and SiZn2O4. Through first-principles calculations of the complex bands and electron transmission along the [001] direction, they are shown to have the same Δ1 spin-filter effect as MgO due to the combination of both factors. Due to better lattice match with typical bcc magnetic electrodes than MgO, these materials provide a broad spectrum of candidate materials for magnetic tunnel junctions.
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73.40.Rw Metal-insulator-metal structures
71.15.-m Methods of electronic structure calculations

Axial and azimuthal spin-wave eigenmodes in rolled-up permalloy stripes

Felix Balhorn, Simon Jeni, Wolfgang Hansen, Detlef Heitmann, and Stefan Mendach

Appl. Phys. Lett. 100, 222402 (2012); http://dx.doi.org/10.1063/1.3700809 (4 pages)

Online Publication Date: 29 May 2012

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We experimentally realized rolled-up permalloy stripes to form three-dimensional ring-like ferromagnetic structures. By means of microwave absorption spectroscopy, we find multiple resonances occurring above a demagnetization field threshold which depends on the ring’s axial width. Our experimental data can be well modeled by assuming both axial and azimuthal spin-wave confinement.
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75.30.Ds Spin waves
75.50.Bb Fe and its alloys
78.70.Gq Microwave and radio-frequency interactions
75.60.-d Domain effects, magnetization curves, and hysteresis

Enhancement of the magneto-optical properties in 2-dimensional bilayered magnetic anti-dot lattice

N. G. Deshpande, J. S. Hwang, K. W. Kim, J. Y. Rhee, Y. H. Kim, L. Y. Chen, and Y. P. Lee

Appl. Phys. Lett. 100, 222403 (2012); http://dx.doi.org/10.1063/1.4722926 (4 pages)

Online Publication Date: 29 May 2012

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The magneto-optical (MO) properties of two-dimensional bilayered magnetic anti-dot lattice (BMAL) structure, which consists of upper perforated “Co” layer over uniform “Ni” underlayer in square-lattice arrangement, were investigated. Enhancement in the MO activity was found in such structures. Nearly 4 times larger MO-Kerr activity was observed for the first-order diffracted beam as compared with that of the zeroth-order one. To understand the origin of the enhanced MO rotation, the magnetization-domain configuration was also investigated by field-dependent magnetic-force microscopy. Additionally, comparison between MO response and magnetization-domain configuration for the rhomboid BMAL structure was done, which allowed us to understand more clearly the enhancement of MO properties.
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78.20.Ls Magneto-optical effects
68.65.Hb Quantum dots (patterned in quantum wells)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
78.67.Hc Quantum dots
78.20.Ek Optical activity

Large magnetocaloric effect induced by intrinsic structural transition in Dy1−x HoxMnO3

Mingjie Shao, Shixun Cao, Shujuan Yuan, Jin Shang, Baojuan Kang, Bo Lu, and Jincang Zhang

Appl. Phys. Lett. 100, 222404 (2012); http://dx.doi.org/10.1063/1.4722930 (4 pages)

Online Publication Date: 29 May 2012

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We report the magnetic and magnetocaloric properties of Dy1−xHoxMnO3 (0 ≤ x ≤ 1). Large entropy change of 12.5 J/kg K and refrigeration capacity of 312 J/kg at 7 T for HoMnO3 is calculated based on isothermal magnetization measurements. The peak temperature of magnetic entropy change for all samples keeps the same 10.5 K, indicating that Ho3+ doping only affects the value of magnetic entropy. An unambiguous intrinsic structural transition near 7 K is first observed by strain measurement, which is believed as the origin of magnetic symmetry transition of Dy1−xHoxMnO3 and induces the magnetocaloric effect with the cooperation interaction between Dy3+/Ho3+and Mn3+ spins.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
61.72.up Other materials
65.40.gd Entropy

Stroboscopic imaging of an alternating magnetic field from a perpendicular magnetic recording head by frequency-modulated magnetic force microscopy

Zhenghua Li, Kodai Hatakeyama, Genta Egawa, Satoru Yoshimura, and Hitoshi Saito

Appl. Phys. Lett. 100, 222405 (2012); http://dx.doi.org/10.1063/1.4720508 (4 pages) | Cited 1 time

Online Publication Date: 29 May 2012

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The alternating current (ac) magnetic field from perpendicular magnetic recording head was imaged by using our developed frequency-modulated magnetic force microscopy (FM-MFM), which uses the frequency modulation of cantilever oscillation caused by applying ac magnetic field to a mechanically oscillated cantilever. The amplitude and phase signals (or orthogonal X and Y signals) of the ac magnetic field can be obtained separately by using the FM-MFM technique incorporated with a lock-in amplifier. A signal transformation technique to characterize the AC magnetic field source for frequency modulated magnetic force microscopy was proposed. Two-dimensional vector analysis together with the magnetization vector rotation of the perpendicular recording head was demonstrated using the FM-MFM method combined with the signal transformation algorithm. By taking advantage of this technique, the present method opens a possibility to stroboscopic analyze the AC magnetic field source and gives a very useful feedback for the development of advanced magnetic recording heads.
Show PACS
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
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