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18 Oct 2010

Volume 97, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 162901 (2010); http://dx.doi.org/10.1063/1.3501139 (3 pages)

Wei-Feng Rao, Ke-Wei Xiao, Tian-Le Cheng, Jie E. Zhou, and Yu U. Wang
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Tailoring GaAs terahertz radiative properties with surface phonons polaritons

S. Vassant, F. Marquier, J. J. Greffet, F. Pardo, and J. L. Pelouard

Appl. Phys. Lett. 97, 161101 (2010); http://dx.doi.org/10.1063/1.3497645 (3 pages) | Cited 1 time

Online Publication Date: 18 October 2010

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Absorption of visible and infrared radiation by gratings due to the resonant excitation of surface waves is a well-known phenomenon. In this paper, we study the resonant absorption of terahertz (THz) radiation due to the excitation of surface phonon polaritons on a grating ruled on a GaAs substrate. We report the design and fabrication of such a grating. Reflectivity measurements clearly show the excitation of surface phonon polariton. Numerical simulations indicate that the radiative properties depend critically on the surface profile. We finally discuss potential applications to THz thermal emission.
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81.05.Ea III-V semiconductors
78.70.Gq Microwave and radio-frequency interactions
78.68.+m Optical properties of surfaces
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)
79.40.+z Thermionic emission

Visible-blind deep-ultraviolet Schottky photodetector with a photocurrent gain based on individual Zn2GeO4 nanowire

Chun Li, Yoshio Bando, Meiyong Liao, Yasuo Koide, and Dmitri Golberg

Appl. Phys. Lett. 97, 161102 (2010); http://dx.doi.org/10.1063/1.3491212 (3 pages) | Cited 2 times

Online Publication Date: 18 October 2010

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We report on the visible-blind deep-ultraviolet (DUV) photodetectors with metal-semiconductor-metal (MSM) Schottky contacts based on individual Zn2GeO4 nanowire single-crystals. At an 8 V bias voltage, the device shows an extremely low dark current (<0.1 pA), a responsivity of 38.3 A/W (corresponding gain ∼ 200), a high DUV-to-visible discrimination ratio up to ∼ 104, and a relatively fast response time upon 245 nm DUV illumination. By analyzing the light-intensity-dependent photocurrent generation and carrier transport, the photogenerated holes trapped in Schottky barrier and shrinking of depletion region under DUV illumination at the metal/Zn2GeO4 interface are proposed for the carrier injection and the photocurrent gain.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Three-dimensional localization precision of the double-helix point spread function versus astigmatism and biplane

Majid Badieirostami, Matthew D. Lew, Michael A. Thompson, and W. E. Moerner

Appl. Phys. Lett. 97, 161103 (2010); http://dx.doi.org/10.1063/1.3499652 (3 pages) | Cited 1 time

Online Publication Date: 18 October 2010

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Wide-field microscopy with a double-helix point spread function (DH-PSF) provides three-dimensional (3D) position information beyond the optical diffraction limit. We compare the theoretical localization precision for an unbiased estimator of the DH-PSF to that for 3D localization by astigmatic and biplane imaging using Fisher information analysis including pixelation and varying levels of background. The DH-PSF results in almost constant localization precision in all three dimensions for a 2 μm thick depth of field while astigmatism and biplane improve the axial localization precision over smaller axial ranges. For high signal-to-background ratio, the DH-PSF on average achieves better localization precision.
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42.30.Lr Modulation and optical transfer functions
42.15.Fr Aberrations
07.60.Pb Conventional optical microscopes

Efficiency limiting processes in 1.55 μm InAs/InP-based quantum dots lasers

Sayid A. Sayid, Igor P. Marko, Stephen J. Sweeney, Pedro Barrios, and Philip J. Poole

Appl. Phys. Lett. 97, 161104 (2010); http://dx.doi.org/10.1063/1.3504253 (3 pages) | Cited 2 times

Online Publication Date: 18 October 2010

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The threshold current density, Jth, and its radiative component, Jrad, in 1.55 μm InAs/InP (100) quantum dot lasers are measured as a function of temperature and hydrostatic pressure. We find that Jrad is relatively temperature insensitive. However, Jth increases significantly with temperature leading to a characteristic temperature T0 = 72 K over the range 220–290 K. Nonradiative recombination accounts for up to 94% of Jth at T = 293 K. Jth decreases with increasing pressure by 35% over 8 kbar causing an increase in T0 from 72 to 88 K. The results indicate that nonradiative Auger recombination determines temperature behavior of these devices and T0 value.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Terahertz heterodyne spectrometer using a quantum cascade laser

Y. Ren, J. N. Hovenier, R. Higgins, J. R. Gao, T. M. Klapwijk, S. C. Shi, A. Bell, B. Klein, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno

Appl. Phys. Lett. 97, 161105 (2010); http://dx.doi.org/10.1063/1.3502479 (3 pages) | Cited 3 times

Online Publication Date: 19 October 2010

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A terahertz (THz) heterodyne spectrometer is demonstrated based on a quantum cascade laser (QCL) as a local oscillator (LO) and an NbN hot electron bolometer as a mixer, and it is used to measure high-resolution molecular spectral lines of methanol (CH3OH) between 2.913–2.918 THz. The spectral lines are taken from a gas cell containing methanol gas and using a single-mode QCL at 2.9156 THz as an LO, which is operated in the free running mode. By increasing the pressure of the gas, line broadening and saturation are observed. The measured spectra showed good agreement with a theoretical model.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
33.20.Bx Radio-frequency and microwave spectra

Ultrafast optical imaging by molecular wakes

Jian Wu, Peifen Lu, Jia Liu, Hao Li, Haifeng Pan, and Heping Zeng

Appl. Phys. Lett. 97, 161106 (2010); http://dx.doi.org/10.1063/1.3505138 (3 pages) | Cited 1 time

Online Publication Date: 20 October 2010

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Ultrafast optical imaging is demonstrated by ultrashort laser pulse induced impulsive molecular alignment, involving optical image storage in the created molecular wakes followed by periodic readout and display. For diatomic molecules in air, both raised and intagliated monochromatic images are demonstrated, which is field-free, periodically achievable, and works as an ultrafast buffer memory for the imprinted optical images. Analogous to the holographic imaging, the phase information of a three-dimensional object can be revealed at various time delays.
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42.79.Vb Optical storage systems, optical disks
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.30.-d Imaging and optical processing
51.70.+f Optical and dielectric properties

Optical generation of terahertz and second-harmonic light in plasma-activated silicon nanophotonic structures

M. Wächter, C. Matheisen, M. Waldow, T. Wahlbrink, J. Bolten, M. Nagel, and H. Kurz

Appl. Phys. Lett. 97, 161107 (2010); http://dx.doi.org/10.1063/1.3503586 (3 pages)

Online Publication Date: 20 October 2010

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Plasma-activated silicon structures exhibit symmetry broken surfaces through chemical surface modification leading to a considerable second-order nonlinear optical response. This nonlinear response is demonstrated in second-harmonic and difference frequency generation measurements including the generation of terahertz radiation in silicon photonic nanowires using telecom wavelength excitation pulses.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.-e Optical elements, devices, and systems
81.65.-b Surface treatments

Nanoslot laser

Shota Kita, Shoji Hachuda, Kengo Nozaki, and Toshihiko Baba

Appl. Phys. Lett. 97, 161108 (2010); http://dx.doi.org/10.1063/1.3505139 (3 pages) | Cited 3 times

Online Publication Date: 21 October 2010

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We propose and demonstrate photonic crystal nanolaser with a nanoslot. Using high-aspect etching process, we succeed in fabricating a 30-nm-wide nanoslot device and room temperature lasing in both air and liquids. As an index sensor, it exhibits a high sensitivity of 410 nm per refractive index unit, as well as low temperature dependence in water. These behaviors and theoretical analysis suggest that the mode is strongly localized in the nanoslot. This device will be effective for enhancing light-matter interaction in cavity quantum electro dynamics, nonlinear optics, and biosensing.
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42.55.-f Lasers

Terahertz generation and power limits in In0.53Ga0.47As photomixer coupled to transverse-electromagnetic-horn antenna driven at 1.55 μm wavelengths

J. Mangeney, F. Meng, D. Gacemi, E. Peytavit, J. F. Lampin, and T. Akalin

Appl. Phys. Lett. 97, 161109 (2010); http://dx.doi.org/10.1063/1.3505341 (3 pages) | Cited 2 times

Online Publication Date: 21 October 2010

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We report continuous wave generation at frequencies up to 2 THz using ion-irradiated In0.53Ga0.47As photomixers coupled to transverse-electromagnetic-horn antennae driven at ∼ 1.55 μm wavelength. Output powers up to 0.1 μW at 700 GHz have been achieved. The dependence of the output power on incident optical power and the bias voltage is analyzed in the both regimes of Ohmic transport and recombination-limited transport. The fundamental limitations of the performance of the photomixer devices based on photoconductive phenomenon in recombination-limited transport are analyzed.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
72.40.+w Photoconduction and photovoltaic effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Surface plasmon coupling to nanoscale Schottky-type electrical detectors

Thomas Dufaux, Jens Dorfmüller, Ralf Vogelgesang, Marko Burghard, and Klaus Kern

Appl. Phys. Lett. 97, 161110 (2010); http://dx.doi.org/10.1063/1.3503534 (3 pages)

Online Publication Date: 21 October 2010

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We have investigated the near-field coupling of surface plasmons to a titanium/CdS nanowire interface for two different device configurations. A bare aluminum grating on an underlying aluminum layer exhibited the expected stronger electrical signal for perpendicular versus parallel light polarization. An opposite intensity ratio was detected when the grating and the Schottky contact are connected via an aluminum–silica–aluminum sandwich structure. Based upon finite difference time domain device simulations, the enhanced coupling for parallel polarization is attributed to the emergence of a transversal electric wave within the metal–insulator–metal structure.
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73.21.Hb Quantum wires
73.30.+y Surface double layers, Schottky barriers, and work functions
81.07.Vb Quantum wires
81.05.Dz II-VI semiconductors
78.67.Lt Quantum wires

Optically-addressed two-terminal multicolor photodetector

E. H. Steenbergen, M. J. DiNezza, W. H. G. Dettlaff, S. H. Lim, and Y.-H. Zhang

Appl. Phys. Lett. 97, 161111 (2010); http://dx.doi.org/10.1063/1.3505137 (3 pages) | Cited 1 time

Online Publication Date: 22 October 2010

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A two-terminal multicolor photodetector that is most advantageous for greater than two bands is proposed. This two-terminal design is particularly significant for focal plane arrays as it maximizes the fill factor and simplifies the readout integrated circuits. Individual color detection is realized with appropriate optical biasing. This concept is demonstrated experimentally using a three-color photodetector and biasing light emitting diodes. The measured linear dynamic range is greater than four orders of magnitude, making it a practical device for a broad range of applications.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Jb Light-emitting devices
42.79.Pw Imaging detectors and sensors
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Mode-coupling Cerenkov sum-frequency-generation in a multimode planar waveguide

Changdong Chen, Jie Su, Yong Zhang, Ping Xu, Xiaopeng Hu, Gang Zhao, Yanhua Liu, Xinjie Lv, and Shining Zhu

Appl. Phys. Lett. 97, 161112 (2010); http://dx.doi.org/10.1063/1.3505359 (3 pages) | Cited 2 times

Online Publication Date: 22 October 2010

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We present experimental and theoretical studies of the mode-coupling Cerenkov sum-frequency radiations in a multimode LiNbO3 planar waveguide. The radiations result from the coupling of different guided modes of the fundamental wave, which have the same optical frequencies but different propagation constants. At the same time, scattering-involved Cerenkov sum-frequency-generation was also observed and discussed. Our theoretical predictions are in well accordance with the experimental results.
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42.82.Et Waveguides, couplers, and arrays
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Nv Optical frequency converters
41.60.Bq Cherenkov radiation
42.79.Gn Optical waveguides and couplers

Deep-ultraviolet photodetectors from epitaxially grown NixMg1−xO

J. W. Mares, R. C. Boutwell, M. Wei, A. Scheurer, and W. V. Schoenfeld

Appl. Phys. Lett. 97, 161113 (2010); http://dx.doi.org/10.1063/1.3503634 (3 pages) | Cited 3 times

Online Publication Date: 22 October 2010

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Deep-ultraviolet (DUV) photodetectors were fabricated from high quality NixMg1−xO epitaxially grown by plasma-assisted molecular beam epitaxy on an approximately lattice matched MgO 〈100〉 substrate. A mid-range Ni composition (x = 0.54) NixMg1−xO film was grown for DUV (λpeak<300 nm) photoresponse and the film was characterized by reflected high-energy electron diffraction, Rutherford backscattering spectroscopy, x-ray diffraction, and optical transmission measurements. Photoconductive detectors were then fabricated by deposition of symmetric interdigitated contacts (10 nm Pt/150 nm Au) with contact separations of 5, 10, and 15 μm. The detectors exhibited peak responsivities in the DUV (λpeak ≈ 250 nm) as high as 12 mA/W, low dark currents (Idark<25 nA), and DUV:visible rejection ratio of approximately 800:1.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
78.66.Li Other semiconductors
52.77.-j Plasma applications
81.05.Hd Other semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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Breakdown temperature of electrons in SF6 gas

Han S. Uhm, Eun H. Choi, Guangsup Cho, and Han-Yong Ryu

Appl. Phys. Lett. 97, 161501 (2010); http://dx.doi.org/10.1063/1.3502476 (3 pages) | Cited 1 time

Online Publication Date: 18 October 2010

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The breakdown temperature Tb of electrons in SF6 gas is obtained by expressing the ionization and attachment coefficients of the gas in terms of the electron temperature Te assuming that the electron energy in the gas is in a Maxwellian distribution. The sparking criterion of the SF6 gas was obtained in terms of the gas pressure p and the anode-cathode distance d. It was found that the breakdown temperature Tb of electrons in SF6 in a high-pressure gas characterized by pd⪢0.001 is 4.9 eV, which is independent of the parameter pd. Here, pd is in units of atm cm.
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51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
52.80.-s Electric discharges
34.80.Gs Molecular excitation and ionization

Microplasma-induced surface engineering of silicon nanocrystals in colloidal dispersion

V. Švrček, D. Mariotti, and M. Kondo

Appl. Phys. Lett. 97, 161502 (2010); http://dx.doi.org/10.1063/1.3505329 (3 pages) | Cited 1 time

Online Publication Date: 22 October 2010

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We report on an atmospheric-pressure dc microplasma that can be used to passivate silicon nanocrystals (SiNCs) in ethanol and that stabilizes their optoelectronic properties. We show that microplasma processing enhances the SiNCs photoluminescence intensity by factor of more than ten times and ∼ 80 nm redshift of its maximum. The microplasma induces the replacement of hydrogen terminations with hydroxyl-/organic-based bonds. The resulting surface characteristics are responsible for the formation of conductive and stable SiNCs self-organized assemblies extending over 0.5 mm after dewetting on a substrate.
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81.05.Cy Elemental semiconductors
81.65.Rv Passivation
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.Ap Elemental semiconductors
73.63.-b Electronic transport in nanoscale materials and structures
72.40.+w Photoconduction and photovoltaic effects
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The role of Bi3+ ions in magneto-optic Ce and Bi comodified epitaxial iron garnet films

Jae-Yeol Hwang, Marcello Ferrera, Luca Razzari, Alain Pignolet, and Roberto Morandotti

Appl. Phys. Lett. 97, 161901 (2010); http://dx.doi.org/10.1063/1.3502477 (3 pages) | Cited 3 times

Online Publication Date: 18 October 2010

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Epitaxial Ce and Bi comodified iron garnet and Ce-modified yttrium iron garnet thin films were grown on (100)-oriented Gd3Ga5O12 substrates by pulsed laser deposition, in order to investigate the role of Bi3+ ions and their contribution to the structural, chemical, and magneto-optical properties. Both films showed a strong Faraday rotation of 0.65 deg/μm and 0.52 deg/μm at 1.55 μm, respectively. The valence state of the Ce ions was significantly changed by the substitution with Bi3+, which in turn was demonstrated to lead to an increase in the concentration of Ce3+ as well as to the decrease in the lattice mismatch.
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78.20.Ls Magneto-optical effects
75.70.Ak Magnetic properties of monolayers and thin films
68.55.at Other materials
81.15.Fg Pulsed laser ablation deposition
61.66.Fn Inorganic compounds

Observation of dodecagon-shape V-defects in GaN/AlInN multiple quantum wells

Lin Zhou, Martha R. McCartney, David J. Smith, Anas Mouti, E. Feltin, J. F. Carlin, and N. Grandjean

Appl. Phys. Lett. 97, 161902 (2010); http://dx.doi.org/10.1063/1.3502483 (3 pages) | Cited 3 times

Online Publication Date: 18 October 2010

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The microstructure of GaN(Si)/AlInN multiple quantum wells grown on GaN/Al2O3 (0001) templates by metalorganic vapor-phase epitaxy has been investigated using transmission electron microscopy and associated techniques. Dodecagon-shape V-defects with hexagonal apexes, which nucleate on screw-component threading dislocations, are observed at the film surface. The hexagonal apexes are bounded by {11math1} planes, whereas the dodecagons are bounded by {10math1} and {11math1} planes, where the {10math1} facets are generated from the edges between adjacent {11math1} planes. Indium segregation is observed along these edges. A possible reason for formation of these defects is briefly discussed.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
64.75.Bc Solubility
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.-a Thin film structure and morphology

The effect of excess atomic volume on He bubble formation at fcc–bcc interfaces

M. J. Demkowicz, D. Bhattacharyya, I. Usov, Y. Q. Wang, M. Nastasi, and A. Misra

Appl. Phys. Lett. 97, 161903 (2010); http://dx.doi.org/10.1063/1.3502594 (3 pages) | Cited 3 times

Online Publication Date: 18 October 2010

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Atomistic modeling shows that Cu–Nb and Cu–V interfaces contain high excess atomic volume due to constitutional vacancy concentrations of ∼ 5 at. % and ∼ 0.8 at. %., respectively. This finding is supported by experiments demonstrating that an approximately fivefold higher He concentration is required to observe He bubbles via through-focus transmission electron microscopy at Cu–Nb interfaces than in Cu–V interfaces. Interfaces with structures tailored to minimize precipitation and growth of He bubbles may be used to design damage-resistant composites for fusion reactors.
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61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.jd Vacancies
81.30.Mh Solid-phase precipitation

Contactless transport of acoustically levitated particles

Nada Bjelobrk, Daniele Foresti, Marko Dorrestijn, Majid Nabavi, and Dimos Poulikakos

Appl. Phys. Lett. 97, 161904 (2010); http://dx.doi.org/10.1063/1.3504191 (3 pages) | Cited 4 times

Online Publication Date: 18 October 2010

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We present herein a method for the acoustic translation of solid particles of waterlike density in air, by employing a single transducer and controlling the pressure field through regulation of the distance between the reflector and the radiating plate. The levitation and translation of polystyrene particles over a length of 37 mm (approximately 37 particle diameters) were experimentally demonstrated, numerically modeled, and explained. The results of the model show quantitatively how the acoustic pressure distribution inside the levitator chamber and the position of the potential nodes depend on the distance between reflector and radiating plate when the plate is driven in a flexural resonance mode. This phenomenon significantly extends the range of applications of acoustic levitation.
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43.25.Qp Radiation pressure
43.38.Ar Transducing principles, materials, and structures: general

Structural coherency of epitaxial graphene on 3C–SiC(111) epilayers on Si(111)

A. Ouerghi, R. Belkhou, M. Marangolo, M. G. Silly, S. El Moussaoui, M. Eddrief, L. Largeau, M. Portail, and F. Sirotti

Appl. Phys. Lett. 97, 161905 (2010); http://dx.doi.org/10.1063/1.3497287 (3 pages) | Cited 7 times

Online Publication Date: 18 October 2010

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Graphene has emerged as a promising nanoelectronic material in electronic devices applications and studying two-dimensional electron gases with relativistic dispersion near Dirac point. Nonetheless, the control of the preparation conditions for homogeneous large-area graphene layers is difficult. Here, we illustrate evidence for high structural and electronic quality epitaxial graphene on 3C–SiC(111). Morphology and electronic structure of the graphene layers have been analyzed with low energy electron microscopy and angle resolved photoemission spectroscopy. Using scanning tunneling microscopy and scanning transmission electron microscopy, we show that graphene exhibits remarkably continuity of step edges suggesting the possibility of growing large scale graphene layer.
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73.22.Pr Electronic structure of graphene
81.05.ue Graphene
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.55.ag Semiconductors

Non-melting super-resolution near-field apertures in Sb–Te alloys

R. E. Simpson, P. Fons, X. Wang, A. V. Kolobov, T. Fukaya, and J. Tominaga

Appl. Phys. Lett. 97, 161906 (2010); http://dx.doi.org/10.1063/1.3502593 (3 pages) | Cited 3 times

Online Publication Date: 19 October 2010

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The super-resolution near-field structure permits the formation of short-lived subdiffraction limit apertures that channel electromagnetic energy at the aperture boundary. This effect is commonly observed when a laser is focused onto a thin film of Sb based material. The aperture formation within Sb, Sb2Te3, Sb2Te, and SbTe is investigated by time resolved optical pump-probe techniques and found to occur without melting. Ab initio modeling has shown a threshold-like change in the optical properties below the melting temperature which leads to the formation of a near-field aperture. This threshold is shown to be a consequence of thermally induced misalignment of p-type bonding.
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42.79.Ag Apertures, collimators
42.70.-a Optical materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Interface chemistry and electronic structure of GaN/MgAl2O4 revealed by angle-resolved photoemission spectroscopy

G. He, T. Chikyow, and Shigefusa F. Chichibu

Appl. Phys. Lett. 97, 161907 (2010); http://dx.doi.org/10.1063/1.3505153 (3 pages) | Cited 1 time

Online Publication Date: 20 October 2010

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By modifying the MgAl2O4 substrate surface using chemical etching and thermal passivation, high-quality GaN films have been achieved on the MgAl2O4 (111) substrate via metalorganic chemical vapor deposition. The interface chemistry and electronic structure of GaN/MgAl2O4 interface have been investigated by angle-resolved photoemission spectroscopy. It has been noted that thermal passivation leads to the formation of Al2O3 buffered layer, which remains thermally stable during deposition and are primarily responsible for the epitaxial growth of GaN on MgAl2O4 (111) substrate.
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79.60.Jv Interfaces; heterostructures; nanostructures
79.60.Dp Adsorbed layers and thin films
68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Rv Passivation

The absorption coefficient of PbSe/CdSe core/shell colloidal quantum dots

Bram De Geyter and Zeger Hens

Appl. Phys. Lett. 97, 161908 (2010); http://dx.doi.org/10.1063/1.3499754 (3 pages)

Online Publication Date: 20 October 2010

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PbSe/CdSe core/shell colloidal quantum dots (QDs) are used as a model system to study the absorption coefficient of colloidal QD heterostructures, consisting of at least two semiconductor materials. We show that at energies far above the band gap (3.1 and 3.5 eV) the experimental intrinsic absorption coefficient is in excellent agreement with the Maxwell–Garnett effective medium theory for core/shell heterostructures and bulk values for the dielectric function. This allows for a straightforward measurement of the QD concentration from the absorbance spectrum. It also implies that basic optical measurements on core/shell heterostructures, such as measurements of the oscillator strength and photoluminescence lifetime, can be corrected for the local field reduction in QD heterostructures.
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78.67.Hc Quantum dots
78.55.Hx Other solid inorganic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)

Structure and stability of thin water films on quartz surfaces

Yun-Wen Chen and Hai-Ping Cheng

Appl. Phys. Lett. 97, 161909 (2010); http://dx.doi.org/10.1063/1.3504710 (3 pages) | Cited 1 time

Online Publication Date: 22 October 2010

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We investigated thin water films on quartz (0001) surfaces using first-principles density functional theory calculations. Interfacial structure and energetics were studied through a layer-by-layer deposition. From monolayer to multilayer, the low energy state configurations and adsorption sites show a transition due to formation of a highly stable bilayer membranelike structure. The water adsorption energy on a quartz surface coated by this membrane is of typical hydrogen bond strength for both dry and fully hydroxylated surfaces. The interactions between the surface and the water films are short-ranged due to shielding of the bilayer.
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68.43.Mn Adsorption kinetics
68.43.Bc Ab initio calculations of adsorbate structure and reactions
68.15.+e Liquid thin films
61.50.Lt Crystal binding; cohesive energy
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Diamagnetic shift of the A free exciton in CuGaSe2 single crystals

F. Luckert, M. V. Yakushev, C. Faugeras, A. V. Karotki, A. V. Mudryi, and R. W. Martin

Appl. Phys. Lett. 97, 162101 (2010); http://dx.doi.org/10.1063/1.3502608 (3 pages) | Cited 5 times

Online Publication Date: 18 October 2010

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Single crystals of CuGaSe2 were studied using magnetophotoluminescence in magnetic fields up to 20 T at 4.2 K. The rate of the diamagnetic shift in the A free exciton peak was determined to be 9.82×10−6 eV/T2. This rate was used to calculate the reduced mass as 0.115m0, the binding energy as 12.9 meV, the Bohr radius as 5.1 nm and an effective hole mass of 0.64m0 (m0 is the free electron mass) of the free A exciton using a low-field perturbation approach and the hydrogenic model.
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75.20.Ck Nonmetals
71.35.-y Excitons and related phenomena
78.55.Hx Other solid inorganic materials
71.15.Nc Total energy and cohesive energy calculations
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