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30 Jan 2012

Volume 100, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 053101 (2012); http://dx.doi.org/10.1063/1.3679127 (3 pages)

Shinya Kano, Yasuyuki Yamada, Kentaro Tanaka, and Yutaka Majima
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Distributed Bragg reflectors based on diluted boron-based BAlN alloys for deep ultraviolet optoelectronic applications

M. Abid, T. Moudakir, G. Orsal, S. Gautier, A. En Naciri, Z. Djebbour, J.-H. Ryou, G. Patriarche, L. Largeau, H. J. Kim, Z. Lochner, K. Pantzas, D. Alamarguy, F. Jomard, R. D. Dupuis, et al.

Appl. Phys. Lett. 100, 051101 (2012); http://dx.doi.org/10.1063/1.3679703 (4 pages) | Cited 2 times

Online Publication Date: 30 January 2012

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Highly reflective deep UV distributed Bragg reflectors (DBRs) based on the BAlN material system have been grown by metalorganic vapour phase epitaxy on AlN template substrates. These structures make use of the transparency of BAlN in the deep UV and the high refractive index contrast between BAlN and AlN, which has been demonstrated to exceed 0.27 at 280 nm. 18-pair BAlN/AlN DBRs showed experimental peak reflectivity of 82% at 311 nm and a stop-bandwidth of 20 nm. At 282 nm, a 24-pair BAlN/AlN DBR structure is demonstrated with experimental peak reflectivity of 60% and stop-bandwidth of 16 nm.
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42.79.Bh Lenses, prisms and mirrors
42.82.-m Integrated optics
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Comparison of scanning tunneling microscope-light emission and photoluminescence from porphyrin films using ultra-high vacuum scanning tunneling microscopy

Ryusuke Nishitani, Hongwen Liu, and Hiroshi Iwasaki

Appl. Phys. Lett. 100, 051102 (2012); http://dx.doi.org/10.1063/1.3680597 (4 pages) | Cited 1 time

Online Publication Date: 30 January 2012

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In order to study the interaction between molecules and photon fields, including plasmonic and external laser fields, we have carried out in situ measurements of photoluminescence (PL) from porphyrin molecules on Au substrates with and without a scanning tunneling microscope (STM) tip. Measurements were performed in a ultra-high vacuum scanning tunneling microscope chamber during irradiation by a He-Cd laser with incident power varying in the 10−3 to 10−7 W range. At an incident power of around 10−7 W, the spectra depend strongly on the presence of STM tip, which is associated with STM light emission from molecules. We estimated the ratio of quantum efficiency of scanning tunneling microscope-induced light emission (STML) from molecules to PL on the basis of the STML/PL intensity ratio observed experimentally at a laser power of 7.5 × 10−8 W, with the use of a 40 μm laser beam diameter and an effective area of 2 nm for STML. The estimated quantum efficiency for an electron in STML is roughly 1010 times larger than that for one photon of PL. This anomalous enhancement will be discussed on the basis of plasmon-enhanced light emission from molecules in a STM nano-cavity.
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78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials

Speed enhancement of multi-particle chain in a traveling standing wave

Martin Šiler, Tomáš Čižmár, and Pavel Zemánek

Appl. Phys. Lett. 100, 051103 (2012); http://dx.doi.org/10.1063/1.3680234 (3 pages) | Cited 1 time

Online Publication Date: 31 January 2012

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A moving array of optical traps created by interference of two counter-propagating evanescent waves has been used for delivery of particle chains up to 18 micro-particles long immersed in water. The particles were optically self-arranged into a linear chain with well-separated distances between them. We observed a significant increase in the delivery speed of the whole structure as the number of particles in the chain increased. This could provide faster sample delivery in microfluidic systems. We quantified the contributions to the speed enhancement caused by the optical and hydrodynamic interactions between the particles.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
07.10.Cm Micromechanical devices and systems

Transmission enhancement in a non-adiabatic tapered nano-aperture waveguide

Yongzhu Chen, Xiangsheng Xie, Yongyao Li, and Jianying Zhou

Appl. Phys. Lett. 100, 051104 (2012); http://dx.doi.org/10.1063/1.3681135 (4 pages)

Online Publication Date: 31 January 2012

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Transmission enhancement via transverse mode control through an aluminum hollow tapered waveguide with a sub-100 nm aperture is simulated with optical wavefront modulations via a binary optical element. Efficient delivery of an input field by exciting the fundamental propagating mode near the apex is realized, giving rise to a significant transmission enhancement through the nano-tip.
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42.79.Gn Optical waveguides and couplers
02.70.Bf Finite-difference methods

Recombination mechanisms and band alignment of GaAs1−xBix/GaAs light emitting diodes

N. Hossain, I. P. Marko, S. R. Jin, K. Hild, S. J. Sweeney, R. B. Lewis, D. A. Beaton, and T. Tiedje

Appl. Phys. Lett. 100, 051105 (2012); http://dx.doi.org/10.1063/1.3681139 (3 pages) | Cited 5 times

Online Publication Date: 31 January 2012

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We investigate the temperature and pressure dependence of the light-current characteristics and electroluminescence spectra of GaAs1−xBix/GaAs light emitting diodes. The temperature dependence of the emission wavelength shows a relatively low temperature coefficient of emission peak shift of 0.19 ± 0.01 nm/K. A strong decrease in emission efficiency with increasing temperature implies that non-radiative recombination plays an important role on the performance of these devices. The pressure coefficient of the GaAs0.986Bi0.014 bandgap is measured to be 11.8 ± 0.3 meV/kbar. The electroluminescence intensity from GaAsBi is found to decrease with increasing pressure accompanied by an increase in luminescence from the GaAs cladding layers suggesting the presence of carrier leakage in the devices.
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85.60.Jb Light-emitting devices

Gas refractometry using a hollow-core photonic bandgap fiber in a Mach-Zehnder-type interferometer

I. Shavrin, S. Novotny, A. Shevchenko, and H. Ludvigsen

Appl. Phys. Lett. 100, 051106 (2012); http://dx.doi.org/10.1063/1.3681171 (3 pages) | Cited 3 times

Online Publication Date: 31 January 2012

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We present the design of a fiber-optic gas refractometer that enables spectrally resolved measurements of both real and imaginary parts of the complex refractive index. The proposed concept is based on a Mach-Zehnder-type interferometer with a hollow-core photonic bandgap fiber in one of the interferometer’s arms. The fiber is used simultaneously as an optical waveguide and an analyte containing cell. We demonstrate the performance of the device by measuring the complete complex refractive index of an air-acetylene gas mixture within the optical C-band. The introduced concept leads towards versatile applications in optics as well as atomic and molecular physics.
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07.60.Hv Refractometers and reflectometers
07.60.Ly Interferometers
42.79.Gn Optical waveguides and couplers

Optical detection of melting point depression for silver nanoparticles via in situ real time spectroscopic ellipsometry

S. A. Little, T. Begou, R. W. Collins, and S. Marsillac

Appl. Phys. Lett. 100, 051107 (2012); http://dx.doi.org/10.1063/1.3681367 (4 pages) | Cited 4 times

Online Publication Date: 1 February 2012

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Silver nanoparticle films were deposited by sputtering at room temperature and were annealed while monitoring by real time spectroscopic ellipsometry (SE). The nanoparticle dielectric functions (0.75 eV–6.5 eV) obtained by SE were modeled using Lorentz and generalized oscillators for the nanoparticle plasmon polariton (NPP) and interband transitions, respectively. The nanoparticle melting point could be identified from variations in the oscillator parameters during annealing, and this identification was further confirmed after cooling through significant, irreversible changes in these parameters relative to the as-deposited film. The variation in melting point with physical thickness, and thus average nanoparticle diameter, as measured by SE enables calculation of the surface energy density.
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64.70.dj Melting of specific substances
68.35.Md Surface thermodynamics, surface energies
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Bz Metals and metallic alloys
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.40.Gh Other heat and thermomechanical treatments

Experimental generation of a radially polarized beam with controllable spatial coherence

Fei Wang, Yangjian Cai, Yiming Dong, and Olga Korotkova

Appl. Phys. Lett. 100, 051108 (2012); http://dx.doi.org/10.1063/1.3681802 (4 pages) | Cited 5 times

Online Publication Date: 1 February 2012

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We have experimentally generated a radially polarized (RP) beam with controllable state of spatial coherence by using a rotating ground-glass plate and a radial polarization converter. Furthermore, experimental and theoretical analysis of the focusing properties of a partially coherent RP beam is carried out. Our results show that we can shape the beam profile of the focused RP beam by varying its initial spatial coherence, which is useful for material thermal processing and particle trapping. The experimental results are in complete agreement with the theoretical predictions.
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42.70.Ce Glasses, quartz

Temperature dependence of the intraexcitonic AC Stark effect in semiconductor quantum wells

M. Wagner, M. Teich, M. Helm, and D. Stehr

Appl. Phys. Lett. 100, 051109 (2012); http://dx.doi.org/10.1063/1.3681399 (3 pages)

Online Publication Date: 2 February 2012

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We have investigated the temperature-dependent, intraexcitonic AC Stark effect that manifests itself in a line splitting of the heavy-hole 1s exciton transition in a GaAs/AlGaAs multi quantum well when the 1s-2p intraexciton transition is driven by intense THz light. The observed wavelength-dependent splitting at Helium temperature can still be distinguished at elevated temperatures up to 200 K. Although the thermal energy exceeds the exciton binding energy by a factor of 1.7, thermal exciton ionization influences the coherent nonlinear effect only indirectly via thermal line broadening. With a threefold transmission change on ultrafast timescales in a region accessible to Peltier-cooling the scheme could be promising for optical modulators.
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78.67.De Quantum wells
71.35.Ee Electron-hole drops and electron-hole plasma
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.20.Jq Electro-optical effects
81.07.St Quantum wells
78.30.Fs III-V and II-VI semiconductors

Surface depletion mediated control of inter-sub-band absorption in GaAs/AlAs semiconductor quantum well systems

Walter R. Buchwald, Justin W. Cleary, and Joshua Hendrickson

Appl. Phys. Lett. 100, 051110 (2012); http://dx.doi.org/10.1063/1.3680232 (3 pages)

Online Publication Date: 2 February 2012

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The modification of quantum well inter-sub-band absorption properties due to surface depletion induced band bending is reported. Fourier transform infrared spectroscopy measurements of a GaAs/AlAs multiple quantum well system reveal a reduction in the characteristic absorption resonance in correlation with wet chemical etching. High resolution transmission electron microscopy confirms the presence of the quantum wells after etching, suggesting the quantum wells are positioned within the surface depletion region of the structure. This method of inter-sub-band absorption modification could be used for the formation of quantum dots from a quantum well system with the precise, deterministic control of their location.
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73.21.Fg Quantum wells
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning

Standoff detection via single-beam spectral notch filtered pulses

Adi Natan, Jonathan M. Levitt, Leigh Graham, Ori Katz, and Yaron Silberberg

Appl. Phys. Lett. 100, 051111 (2012); http://dx.doi.org/10.1063/1.3681365 (3 pages)

Online Publication Date: 3 February 2012

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We demonstrate single-beam coherent anti-Stokes Raman spectroscopy (CARS), for detecting and identifying traces of solids, including minute amounts of explosives, from a standoff distance (>50 m) using intense femtosecond pulses. Until now, single-beam CARS methods relied on pulse-shapers in order to obtain vibrational spectra. Here, we present a simple and easy-to-implement detection scheme, using a commercially available notch filter that does not require the use of a pulse-shaper.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
06.60.Jn High-speed techniques (microsecond to femtosecond)

Fabrication of flower-like silver nanostructure on the Al substrate for surface enhanced fluorescence

Jun Dong (董军), Hairong Zheng (郑海荣), Xiaoqing Yan, Yu Sun, and Zhenglong Zhang

Appl. Phys. Lett. 100, 051112 (2012); http://dx.doi.org/10.1063/1.3681420 (3 pages) | Cited 3 times

Online Publication Date: 3 February 2012

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Surface-enhanced fluorescence (SEF) substrates consisting of flower-like nanostructure of electromagnetically coupled silver dendrites on Al surface were manufactured by modified galvanic displacement process between Ag ion and Al at room temperature. Substrate enhancement efficiency, which was evaluated from SEF intensities of the adsorbed Rhodamine 6 G(Rh6G), was found to increase rapidly with reaction time. The observation highlights the importance of strong coupling effects between nanobranches in SEF. The variation of SEF efficiency can be qualitatively explained with local surface plasmon resonance model of coupled silver nanostructures.
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81.05.Bx Metals, semimetals, and alloys
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
78.55.Hx Other solid inorganic materials
61.46.Hk Nanocrystals
81.16.-c Methods of micro- and nanofabrication and processing

A quantum model for light emission performance of carbon nanotube field effect transistor

M. R. Aziziyan, V. Ahmadi, and N. Moghadam

Appl. Phys. Lett. 100, 051113 (2012); http://dx.doi.org/10.1063/1.3681787 (3 pages) | Cited 1 time

Online Publication Date: 3 February 2012

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We propose a full quantum model based on non-equilibrium Green function method to simulate short channel, ohmic-carbon nanotube field effect transistor as light emitter. We consider carrier annihilation using self-energy concept in non-ballistic regime, regarding current conservation. Using this model, we calculate radiative recombination rate and electroluminescence spectrum of device. Since, higher bias voltage causes higher carrier injection, we expect to observe more recombination rate by increasing drain or gate voltage. Variation of gate voltage can shift the electroluminescence peak due to slight band gap change. The device current confirms that the electrical and optical properties of device are correlated.
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85.30.Tv Field effect devices
85.35.Kt Nanotube devices
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Functional plasma polymers deposited in capacitively and inductively coupled plasmas

Dirk Hegemann, Enrico Körner, Shang Chen, Jan Benedikt, and Achim von Keudell

Appl. Phys. Lett. 100, 051601 (2012); http://dx.doi.org/10.1063/1.3681382 (3 pages) | Cited 1 time

Online Publication Date: 1 February 2012

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Capacitively and inductively coupled plasmas were investigated in order to deposit functional plasma polymers. Considering plasma chemical and surface processes, comparable films can be obtained with both plasma sources yielding distinctly higher deposition rates for ICP. While the gas phase processes scaled with the energy input into the plasma, the surface processes were controlled by the energy dissipated during film growth (ion bombardment).
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52.77.Dq Plasma-based ion implantation and deposition
61.80.Jh Ion radiation effects
82.35.-x Polymers: properties; reactions; polymerization
52.50.Dg Plasma sources

Cation stoichiometry optimization of SrTiO3 (110) thin films with atomic precision in homogeneous molecular beam epitaxy

Zhiming Wang, Jiagui Feng, Yang Yang, Yuan Yao, Lin Gu, Fang Yang, Qinlin Guo, and Jiandong Guo

Appl. Phys. Lett. 100, 051602 (2012); http://dx.doi.org/10.1063/1.3681796 (3 pages) | Cited 3 times

Online Publication Date: 2 February 2012

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We study the evolution of surface reconstructions on SrTiO3 (110) determined by cation concentration ratio and find it detectable by high energy electron diffraction (RHEED) even at high temperature up to 800 °C. The evaporation rate of Sr and Ti sources can be calibrated precisely by monitoring RHEED patterns in situ and in real time during the extended homogeneous oxide molecule beam epitaxy growth of SrTiO3 (110) film. High quality film is obtained with deviation of cation stoichiometry less than 0.5%.
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61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
68.35.bt Other materials
79.60.Dp Adsorbed layers and thin films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.47.Gh Oxide surfaces
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
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Calculation of self-diffusion coefficients in diamond

Baohua Zhang and Xiaoping Wu

Appl. Phys. Lett. 100, 051901 (2012); http://dx.doi.org/10.1063/1.3680600 (3 pages) | Cited 2 times

Online Publication Date: 30 January 2012

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In the light of recently reported pressure-volume-temperature relationships in diamond, we show that the self-diffusion coefficient of diamond as a function of temperature and pressure can be satisfactory reproduced in terms of the bulk elastic and expansivity data by means of a thermodynamical model that interconnects the parameters of point defects to the bulk properties. Our calculated self-diffusion coefficients are in good agreement with the experimental ones when the uncertainties are taken into account.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.72.jd Vacancies
62.20.D- Elasticity

Polarity-dependent photoemission spectra of wurtzite-type zinc oxide

Jesse Williams, Hideki Yoshikawa, Shigenori Ueda, Yoshiyuki Yamashita, Keisuke Kobayashi, Yutaka Adachi, Hajime Haneda, Takeshi Ohgaki, Hiroki Miyazaki, Takamasa Ishigaki, and Naoki Ohashi

Appl. Phys. Lett. 100, 051902 (2012); http://dx.doi.org/10.1063/1.3673553 (3 pages) | Cited 3 times

Online Publication Date: 1 February 2012

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The polar surfaces of wurtzite-type zinc oxide (ZnO) were characterized by x-ray photoemission spectroscopy to identify the origin of the polarity dependence of the valence band spectra. A characteristic sub-peak always appeared in the valence band spectra of the (0001) face regardless of the surface preparation conditions. It also appeared in the valence band spectra of the (10math2) face, but only when the photoelectron take-off angle was parallel to the c-axis of ZnO. Our analysis demonstrates that this take-off angle dependency originates not from the surface state, photoelectron diffraction, or the presence of surfactants but from the crystal polarity.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
71.20.Nr Semiconductor compounds
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
73.20.At Surface states, band structure, electron density of states

Beam-scanning planar lens based on graphene

Hong Ju Xu, Wei Bing Lu, Yun Jiang, and Zheng Gao Dong

Appl. Phys. Lett. 100, 051903 (2012); http://dx.doi.org/10.1063/1.3681799 (4 pages) | Cited 8 times

Online Publication Date: 1 February 2012

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One of the most important advantages of graphene is the capability of dynamically tuning its conductivity by means of chemical doping or gate voltage. Based on this property, we propose a planar gradient index graphene-based lens transforming spherical waves of the transverse-magnetic (TM) surface plasmon polariton (SPP) wave to plane waves of the TM SPP wave with specific beam deflections. Using numerical simulations, it is confirmed that a single-atomic-layered graphene can be a platform for planar gradient-index lens, which can be applied to modulate the propagation of SPP waves.
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42.79.Bh Lenses, prisms and mirrors
42.79.Ls Scanners, image intensifiers, and image converters
78.67.Wj Optical properties of graphene

Time-of-flight-photoelectron emission microscopy on plasmonic structures using attosecond extreme ultraviolet pulses

S. H. Chew (周淑芬), F. Süßmann, C. Späth, A. Wirth, J. Schmidt, S. Zherebtsov, A. Guggenmos, A. Oelsner, N. Weber, J. Kapaldo, A. Gliserin, M. I. Stockman, M. F. Kling, and U. Kleineberg

Appl. Phys. Lett. 100, 051904 (2012); http://dx.doi.org/10.1063/1.3670324 (4 pages) | Cited 2 times

Online Publication Date: 2 February 2012

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We report on the imaging of plasmonic structures by time-of-flight-photoemission electron microscopy (ToF-PEEM) in combination with extreme ultraviolet (XUV) attosecond pulses from a high harmonic generation source. Characterization of lithographically fabricated Au structures using these ultrashort XUV pulses by ToF-PEEM shows a spatial resolution of ∼200 nm. Energy-filtered imaging of the secondary electrons resulting in reduced chromatic aberrations as well as microspectroscopic identification of core and valence band electronic states have been successfully proven. We also find that the fast valence band electrons are not influenced by space charge effects, which is essentially important for attosecond nanoplasmonic-field microscopy realization.
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79.20.Hx Electron impact: secondary emission
77.22.Jp Dielectric breakdown and space-charge effects
79.60.-i Photoemission and photoelectron spectra
73.22.Lp Collective excitations

Magnetic shape memory effect in orbital-spin-coupled system MnV2O4

Y. Nii, N. Abe, K. Taniguchi, and T. Arima

Appl. Phys. Lett. 100, 051905 (2012); http://dx.doi.org/10.1063/1.3681581 (3 pages)

Online Publication Date: 2 February 2012

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Magnetic-field(H)-induced shape memory effect without temperature variation is demonstrated by a combination of H-sweep and H-rotation in an orbital-spin-coupled spinel-type insulating system MnV2O4. A rotation of the direction of a magnetic field of 5 T in the low-temperature tetragonal phase gives rise to a large macroscopic strain up to 1%, which stems from a 90° rotation of tetragonal domains. The results show several possible ways of macroscopic shape control in this class of matter, and may open a possibility of high-speed actuators free from the eddy current.
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81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
81.30.Kf Martensitic transformations

Temperature dependent dynamics of ZnO nanoparticles probed by Raman scattering: A big divergence in the functional areas of nanoparticles and bulk materials

Harish Kumar Yadav, R. S. Katiyar, and Vinay Gupta

Appl. Phys. Lett. 100, 051906 (2012); http://dx.doi.org/10.1063/1.3681144 (5 pages)

Online Publication Date: 2 February 2012

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Temperature dependent Raman scattering of the E2(low) and E2(high) modes of ZnO nanoparticle powder samples has been investigated. The dynamics exhibited by the ZnO nanoparticles, the E2 modes, follow single crystal like behavior but with strong cubic or/and quadratic anharmonicity by supporting additional channels for immediate lattice relaxation. The strong anharmonic character associated with the E2 modes reflects enhanced thermal conductivity of the ZnO nanoparticles. An anomalous variation in linewidth of the E2(low) mode is observed and is attributed to the superposition of the large displacement field, associated with the surface atoms of the nanoparticles and the lattice mode.
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63.20.Ry Anharmonic lattice modes
78.30.Fs III-V and II-VI semiconductors
66.70.Df Metals, alloys, and semiconductors

Strong interband transitions in InAs quantum dots solar cell

Jiang Wu, Y. F. M. Makableh, R. Vasan, M. O. Manasreh, B. Liang, C. J. Reyner, and D. L. Huffaker

Appl. Phys. Lett. 100, 051907 (2012); http://dx.doi.org/10.1063/1.3681360 (4 pages) | Cited 6 times

Online Publication Date: 3 February 2012

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Solar cells fabricated from a stack of ten periods of InAs quantum dots sandwiched in a GaAs p-n junction were fabricated and tested. The 300 K photoresponse spectrum exhibits two strong peaks and several weak peaks related to band-to-band transitions within the quantum dots. A few of these peaks were also observed in the photoluminescence and external quantum efficiency spectra. The power conversion efficiency was obtained from the current-voltage characteristics. Surface plasmon effect on the solar cell was investigated by coupling gold nanoparticles to the surface of the device using dithiol ligands with an enhancement on the order of 10%.
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88.40.jp Multijunction solar cells

Thermal conductivity and photoluminescence of light-emitting silicon nitride films

Amy Marconnet, Matt Panzer, Selçuk Yerci, Salvatore Minissale, X. Wang, X. Zhang, Luca Dal Negro, and K. E. Goodson

Appl. Phys. Lett. 100, 051908 (2012); http://dx.doi.org/10.1063/1.3682508 (4 pages)

Online Publication Date: 3 February 2012

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Silicon-rich and rare-earth-doped nitride materials are promising candidates for silicon-compatible photonic sources. This work investigates the thermal conductivity and photoluminescence (PL) of light emitting samples fabricated with a range of excess silicon concentrations and annealing temperatures using time-domain picosecond thermoreflectance and time-resolved photoluminescence. A direct correlation between the thermal conductivity and photoluminescence dynamics is demonstrated, as well as a significant reduction of thermal conductivity upon incorporation of erbium ions. These findings highlight the role of annealing and stoichiometry control in the optimization of light emitting microstructures suitable for the demonstration of efficient Si-compatible light sources based on the silicon nitride platform.
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66.70.Df Metals, alloys, and semiconductors
78.47.J- Ultrafast spectroscopy (<1 psec)
78.20.N- Thermo-optic effects
78.55.Hx Other solid inorganic materials
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
85.60.Jb Light-emitting devices

A transparent 90° polarization rotator by combining chirality and electromagnetic wave tunneling

Mehmet Mutlu and Ekmel Ozbay

Appl. Phys. Lett. 100, 051909 (2012); http://dx.doi.org/10.1063/1.3682591 (4 pages) | Cited 6 times

Online Publication Date: 3 February 2012

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A three-layer chiral metamaterial is constructed by using two layers of four mutually rotated resonators and a subwavelength mesh sandwiched symmetrically between these layers. The resulting structure is an ultrathin, transparent, and polarization angle independent 90° polarization rotator. Due to the electromagnetic tunneling effect exerted by the negative permittivity mesh, a cross-polarization conversion efficiency of 99% and 93% is achieved numerically and experimentally. The structure is modeled using the effective medium theory and then the transfer matrix method is applied to demonstrate the existence of the tunneling resonance theoretically.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.79.-e Optical elements, devices, and systems
81.05.Xj Metamaterials for chiral, bianisotropic and other complex media
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Fabrication and characterization of ambipolar devices on an undoped AlGaAs/GaAs heterostructure

J. C. H. Chen, D. Q. Wang, O. Klochan, A. P. Micolich, K. Das Gupta, F. Sfigakis, D. A. Ritchie, D. Reuter, A. D. Wieck, and A. R. Hamilton

Appl. Phys. Lett. 100, 052101 (2012); http://dx.doi.org/10.1063/1.3673837 (3 pages) | Cited 5 times

Online Publication Date: 30 January 2012

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We have fabricated AlGaAs/GaAs heterostructure devices in which the conduction channel can be populated with either electrons or holes simply by changing the polarity of a gate bias. The heterostructures are entirely undoped, and carriers are, instead, induced electrostatically. We use these devices to perform a direct comparison of the scattering mechanisms of two-dimensional electrons (μpeak = 4 × 106 cm2/Vs) and holes (μpeak = 0.8 × 106 cm2/Vs) in the same conduction channel with nominally identical disorder potentials. We find significant discrepancies between electron and hole scattering, with the hole mobility being considerably lower than expected from simple theory.
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85.30.-z Semiconductor devices
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