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5 Jul 2010

Volume 97, Issue 1, Articles (01xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 013301 (2010); http://dx.doi.org/10.1063/1.3458867 (3 pages)

M. Uno, Y. Hirose, T. Uemura, K. Takimiya, Y. Nakazawa, and J. Takeya
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Exciton and electron-hole plasma lasing in ZnO dodecagonal whispering-gallery-mode microcavities at room temperature

J. Dai, C. X. Xu, P. Wu, J. Y. Guo, Z. H. Li, and Z. L. Shi

Appl. Phys. Lett. 97, 011101 (2010); http://dx.doi.org/10.1063/1.3460281 (3 pages) | Cited 15 times

Online Publication Date: 6 July 2010

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Dodecagonal ZnO microrods were fabricated by vapor transport method. A dodecagonal ZnO microrod with diameter of 6.35 μm was employed as a whispering gallery mode microcavity, the low threshold exciton lasing was stimulated. In another smaller microrod, the electron-hole plasma lasing was observed under intense excitation as the carrier density was larger than the Mott transition density. The interference condition in the dodecagonal cavity was deduced, and the mode structures were investigated. Compared to the hexagonal microcavity with same diameter, the dodecagonal microcavity has higher lasing performance.
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72.30.+q High-frequency effects; plasma effects
71.35.Ee Electron-hole drops and electron-hole plasma
42.55.Sa Microcavity and microdisk lasers

Optically induced fast wavelength modulation in a quantum cascade laser

Gang Chen, Rainer Martini, Seong-wook Park, Clyde G. Bethea, I.-Chun A. Chen, P. D. Grant, R. Dudek, and H. C. Liu

Appl. Phys. Lett. 97, 011102 (2010); http://dx.doi.org/10.1063/1.3457871 (3 pages) | Cited 4 times

Online Publication Date: 7 July 2010

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An optically induced fast wavelength shift is demonstrated in a standard middle infrared (MIR) quantum cascade laser (QCL) by illuminating the front facet with a femtosecond (fs) near infrared (NIR) laser, allowing fast optical frequency modulation (FM) for free space optical communication (FSOC) and FM spectroscopy. Using an etalon as a narrow band-pass wavelength filter, the wavelength modulation (WM) was clearly observed at frequencies up to 1.67 GHz. This approach can also be used for wavelength conversion and might be extended to QCLs operating in different wavelength regions.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking

InGaN/GaN self-organized quantum dot green light emitting diodes with reduced efficiency droop

Meng Zhang, Pallab Bhattacharya, and Wei Guo

Appl. Phys. Lett. 97, 011103 (2010); http://dx.doi.org/10.1063/1.3460921 (3 pages) | Cited 21 times

Online Publication Date: 7 July 2010

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High density (2–5×1010 cm−2) self-organized InGaN/GaN quantum dots were grown by plasma-assisted molecular beam epitaxy. Room temperature photoluminescence shows that the quantum dots have strong emission ranging from 430 to 524 nm. The internal quantum efficiency of dots emitting at 500 nm was determined to be 32% by temperature dependent photoluminescence measurements. A recombination lifetime of 0.57 ns is derived from time resolved photoluminescence measurements. These superior optical properties are attributed to a small piezoelectric field in the quantum dots. Light emitting diodes fabricated with the InGaN/GaN quantum dots and emitting at λ = 524 nm demonstrate a small blueshift with current injection and reduced efficiency droop.
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81.07.Ta Quantum dots
82.53.Kp Coherent spectroscopy of atoms and molecules
81.40.Tv Optical and dielectric properties related to treatment conditions

Long exciton spin relaxation in coupled quantum wells

K. Kowalik-Seidl, X. P. Vögele, B. N. Rimpfl, S. Manus, J. P. Kotthaus, D. Schuh, W. Wegscheider, and A. W. Holleitner

Appl. Phys. Lett. 97, 011104 (2010); http://dx.doi.org/10.1063/1.3458703 (3 pages)

Online Publication Date: 8 July 2010

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Spatially indirect excitons in a coupled quantum well structure were studied by means of polarization and time-resolved photoluminescence. A strong degree of circular polarization (>50%) in emission was achieved when the excitation energy was tuned into resonance with the direct exciton state. The indirect transition remained polarized several tens of nanoseconds after the pumping laser pulse, demonstrating directly a very long relaxation time of exciton spin. The observed spin relaxation time exceeds the radiative lifetime of the indirect excitons.
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78.67.De Quantum wells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.-m Photoluminescence, properties and materials
71.35.-y Excitons and related phenomena

Characterization of sensing capability of optofluidic ring resonator biosensors

Hao Li and Xudong Fan

Appl. Phys. Lett. 97, 011105 (2010); http://dx.doi.org/10.1063/1.3462296 (3 pages) | Cited 17 times

Online Publication Date: 9 July 2010

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The sensing capability of the capillary-based optofluidic ring resonator in bulk refractive index (RI) detection and label-free small molecule detection is investigated. In bulk RI detection, a sensitivity of 570 nm/refractive index units (RIU) is achieved with a Q-factor of 1.2×105. A change of 2.8×10−7 RIU is observed with the noise equivalent detection limit (NEDL) of 3.8×10−8 RIU. In small molecule detection, 10 nM biotin is detected with surface mass density of 1.6 pg/mm2. The NEDL is approximately 0.14 pg/mm2. These results set the benchmark for ring resonator sensing performance and compare very favorably with those obtained with other label-free optical sensors.
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87.80.-y Biophysical techniques (research methods)
87.15.-v Biomolecules: structure and physical properties
07.60.Hv Refractometers and reflectometers
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Polarization based control of optical hysteresis in coupled GaAs microdisks

S. N. Ghosh, B. B. Buckley, C. G. L. Ferri, X. Li, F. M. Mendoza, Y. K. Verma, N. Samarth, D. D. Awschalom, and S. Ghosh

Appl. Phys. Lett. 97, 011106 (2010); http://dx.doi.org/10.1063/1.3462309 (3 pages)

Online Publication Date: 9 July 2010

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Optical microresonators crafted from semiconducting materials are powerful systems for both understanding and harnessing the interactions between light and matter. We report an all-optical method of controlling the hysteretic emission of evanescently coupled GaAs microdisk pairs. Under partial excitation, the coupled lasing emission demonstrates optical bistability caused by saturable absorption. We observe that the presence of hysteresis can be modulated by the polarization state of the incident excitation. This optical control is an important functionality which, if extended to a large array, could lead to the creation of optical flip-flop and gated logic devices with multinode capabilities.
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42.55.Sa Microcavity and microdisk lasers
42.60.Fc Modulation, tuning, and mode locking
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Laser initiated thermal tuning of a cholesteric liquid crystal

Lalgudi V. Natarajan, Timothy J. White, Jeremy M. Wofford, Vincent P. Tondiglia, Richard L. Sutherland, Stephen A. Siwecki, and Timothy J. Bunning

Appl. Phys. Lett. 97, 011107 (2010); http://dx.doi.org/10.1063/1.3459957 (3 pages) | Cited 3 times

Online Publication Date: 9 July 2010

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We report on the large wavelength range and light-initiated thermal tuning of the reflection of a liquid crystal (LC) formulation (S811/ZLI-2806) near a smectic (SmA) to cholesteric (CLC) phase transition enabled by the use of a high order parameter heat transfer dye (anthraquinone, AQ). Upon irradiation with a 647 nm Krypton ion (Kr+) laser line, absorption by AQ generates heat that is transferred to the surrounding LC host. In the S811/ZLI-2806 formulation examined here, the optically generated increase in temperature serves to transition the phase from SmA to CLC. As has been documented, the SmA→CLC transition is typified by a pitch contraction that blueshifts the position of the CLC reflection, in this case a shift from 2500 to 700 nm that can occur in less than 100 s. The tuning range and speed are dependent on the laser power and the amount of dye in the cell.
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64.70.mj Experimental studies of liquid crystal transitions
78.15.+e Optical properties of fluid materials, supercritical fluids and liquid crystals
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
61.30.-v Liquid crystals
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.20.nb Photothermal effects

Interacting waves on chains of split-ring resonators in the presence of retardation

V. Lomanets, O. Zhuromskyy, G. Onishchukov, O. Sydoruk, E. Tatartschuk, E. Shamonina, G. Leuchs, and U. Peschel

Appl. Phys. Lett. 97, 011108 (2010); http://dx.doi.org/10.1063/1.3462314 (3 pages) | Cited 1 time

Online Publication Date: 9 July 2010

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Wave propagation is studied experimentally in a one-dimensional periodic chain of magnetically coupled split-ring resonators with a spacing of about one tenth of the resonant wavelength. Retardation leads to a strong interaction between magnetoinductive and free-space waves. Two kinds of guided modes are observed: a slow backward wave which propagates far outside the light cone, and a fast forward wave close to the light cone. The two merge in a region of zero group velocity. The results are relevant for all one- and two-dimensional periodic systems interacting with waves of the surrounding space.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Experimental determination of the quadratic nonlinear magnetic susceptibility of a varactor-loaded split ring resonator metamaterial

Stéphane Larouche, Alec Rose, Ekaterina Poutrina, Da Huang, and David R. Smith

Appl. Phys. Lett. 97, 011109 (2010); http://dx.doi.org/10.1063/1.3460919 (3 pages) | Cited 6 times

Online Publication Date: 9 July 2010

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This letter presents a quantitative measurement of the second harmonic generated by a slab of varactor loaded split ring resonator metamaterial and the retrieval of the effective quadratic nonlinear magnetic susceptibility χm(2) using an approach based on transfer matrices. The retrieved value of χm(2) is in excellent agreement with that predicted by an analytical effective medium theory model.
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81.05.Xj Metamaterials for chiral, bianisotropic and other complex media
84.40.Az Waveguides, transmission lines, striplines
84.32.Tt Capacitors
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Removal of floating dust in glow discharge using plasma jet

C. M. Ticoş, I. Jepu, C. P. Lungu, P. Chiru, V. Zaroschi, and A. M. Lungu

Appl. Phys. Lett. 97, 011501 (2010); http://dx.doi.org/10.1063/1.3460293 (3 pages) | Cited 1 time

Online Publication Date: 6 July 2010

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Dust can be an inconvenient source of impurities in plasma processing reactors and in many cases it can cause damage to the plasma-treated surfaces. A technique for dust expulsion out of the trapping region in plasma is presented here, based on the wind force exerted on dust particles by a pulsed plasma jet. Its applicability is demonstrated by removing floating dust in the sheath of parallel-plate capacitive radio-frequency plasma.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.77.-j Plasma applications
52.80.Hc Glow; corona
52.25.Vy Impurities in plasmas

Evidence of atomic adsorption on TiO2 under plasma exposure and related C2H2 surface reactivity

O. Guaitella, C. Lazzaroni, D. Marinov, and A. Rousseau

Appl. Phys. Lett. 97, 011502 (2010); http://dx.doi.org/10.1063/1.3462295 (3 pages) | Cited 2 times

Online Publication Date: 8 July 2010

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Adsorption/reaction kinetics of C2H2 on the surface of plasma-treated SiO2 and TiO2 catalysts is studied. The catalysts are pretreated with a dc discharge in Ar, O2, N2, or air. Then 950 ppm of C2H2 in air is introduced in the closed-volume reactor. It is found that TiO2 pretreated with O2 or air plasma catalyzes C2H2 removal from the gas phase without any UV activation. During 10 min after introduction the loss of C2H2 in the whole reactor is about 5×1015 molecules. Comparison between different pretreatment procedures shows that weakly bonded oxygen atoms may remain on TiO2 long after plasma exposure.
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68.43.Mn Adsorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Enhancement of a laminar premixed methane/oxygen/nitrogen flame speed using femtosecond-laser-induced plasma

Xin Yu, Jiangbo Peng, Peng Yang, Rui Sun, Yachao Yi, Yongpeng Zhao, Deying Chen, and Junhua Yu

Appl. Phys. Lett. 97, 011503 (2010); http://dx.doi.org/10.1063/1.3457384 (3 pages) | Cited 1 time

Online Publication Date: 9 July 2010

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We first investigate the effects of femtosecond-laser-induced plasma on the flame speed of a laminar premixed methane/oxygen/nitrogen flame with a wide range of the equivalence ratios (0.8–1.05) at atmospheric pressure. It is experimentally found that the flame speed increases 20.5% at equivalence ratios 1.05. The self-emission spectra from the flame and the plasma are studied and an efficient production of active radicals under the action of femtosecond (fs)-laser pulses has been observed. Based on the experimental data obtained, the presence of oxygen atom and hydrocarbon radicals is suggested to be a key factor enhancing flame speed.
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47.70.Pq Flames; combustion
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
47.15.-x Laminar flows

Pressure dependence of plasma structure in microwave gas breakdown at 110 GHz

Alan Cook, Michael Shapiro, and Richard Temkin

Appl. Phys. Lett. 97, 011504 (2010); http://dx.doi.org/10.1063/1.3462320 (3 pages) | Cited 10 times

Online Publication Date: 9 July 2010

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Recent studies of 110 GHz microwave discharges in air at atmospheric pressure have demonstrated formation of a large array of quarter-wavelength-spaced plasma filaments. Here we present measurements showing that as pressure is decreased from atmosphere to a few torr, the discharge transitions from a well-defined array to a smeared-out array and finally to a diffuse plasma. Despite the distinct nature of breakdown phenomena at high microwave frequencies, the pressure dependence of the breakdown threshold field is seen to follow a Paschen-type curve. Data for air and argon at 110 GHz are compared with previous low-frequency data.
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52.80.-s Electric discharges
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
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Electric field controlled Faraday rotation in an electro-optic/magneto-optic bilayer

Yu. S. Dadoenkova, I. L. Lyubchanskii, Y. P. Lee, and Th. Rasing

Appl. Phys. Lett. 97, 011901 (2010); http://dx.doi.org/10.1063/1.3456534 (3 pages) | Cited 2 times

Online Publication Date: 6 July 2010

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The Faraday rotation for light transmission through a bilayered structure composed of an electro-optic semiconductor film and a slab with high values of magneto-optic and magnetoelectric interactions is theoretically investigated. The influence of dispersion as well as an external electric field on the Faraday rotation is studied.
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78.66.Sq Composite materials
78.20.Ls Magneto-optical effects
78.20.Jq Electro-optical effects
77.55.Nv Multiferroic/magnetoelectric films
75.85.+t Magnetoelectric effects, multiferroics

Active waveguide effects from porous anodic alumina: An optical sensor proposition

F. Trivinho-Strixino, H. A. Guerreiro, C. S. Gomes, E. C. Pereira, and F. E. G. Guimarães

Appl. Phys. Lett. 97, 011902 (2010); http://dx.doi.org/10.1063/1.3447375 (3 pages) | Cited 1 time

Online Publication Date: 7 July 2010

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We present in this paper an active waveguide effect observed in porous anodic alumina (PA), which can be applied in optical sensors. The spectral position, shape, and polarization effect of the narrow waveguide modes is described. An analytical test with a commercial pesticide was performed.
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42.79.Gn Optical waveguides and couplers
78.60.-b Other luminescence and radiative recombination

Two-photon spectral hole burning spectroscopy of InAs/GaAs quantum dots

T. Moldaschl, W. Parz, T. Müller, S. Golka, G. Strasser, and K. Unterrainer

Appl. Phys. Lett. 97, 011903 (2010); http://dx.doi.org/10.1063/1.3460527 (3 pages)

Online Publication Date: 7 July 2010

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Femtosecond spectral hole burning experiments were performed on InAs/GaAs quantum dots to investigate the influence of high excitation intensities. The observation of additional spectral holes, as well as distinct absorption line broadening are both attributed to two-photon absorption processes. These spectral holes can be unambiguously assigned to degenerate two-photon biexciton creation, whereas the absorption line broadening is a direct result of Coulomb renormalization, initiated by carriers created through two-photon absorption in the surrounding GaAs crystal matrix and the InAs wetting layer.
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78.67.Hc Quantum dots
78.47.nd Hole burning spectroscopy
71.35.-y Excitons and related phenomena
82.53.Mj Femtosecond probing of semiconductor nanostructures

A high refractive index metamaterial at visible frequencies formed by stacked cut-wire plasmonic structures

Xingzhan Wei, Haofei Shi, Xiaochun Dong, Yueguang Lu, and Chunlei Du

Appl. Phys. Lett. 97, 011904 (2010); http://dx.doi.org/10.1063/1.3453477 (3 pages) | Cited 4 times

Online Publication Date: 8 July 2010

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A type of metamaterial composing of stacked cut-wire plasmonic structures has been designed, fabricated, and characterized. The excitation of electric resonance caused by the surface plasmons effect dominates the electric field states, so that the effective refractive index can behave as a dramatic increase at visible frequencies, which is intimately associated with the resonance strength and can be modulated by reasonably changing the structure geometries. The phenomenon has been demonstrated with the measured transmittances being in agreement with simulation results. And the effective parameters judged by Kramers–Kronig relations have been uniquely retrieved from the simulated transmission and reflection data.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Enhanced optical transmission through metal-dielectric multilayer gratings

Lin Zhou, Cheng-ping Huang, Shan Wu, Xiao-gang Yin, Yu-min Wang, Qian-jin Wang, and Yong-yuan Zhu

Appl. Phys. Lett. 97, 011905 (2010); http://dx.doi.org/10.1063/1.3458702 (3 pages) | Cited 3 times

Online Publication Date: 8 July 2010

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The optical transmission properties of metal-dielectric multilayer gratings have been investigated both experimentally and numerically. A remarkable transmission resonance, which makes a significant difference from that of traditional single/triple-layer analogs, has been reported. To understand its physical origin, a field-interference mechanism of dipole arrays induced by the lateral and vertical plasmon coupling has been suggested.
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42.25.Bs Wave propagation, transmission and absorption
42.79.Dj Gratings

High force sensitivity in Q-controlled phase-modulation atomic force microscopy

Naritaka Kobayashi, Yan Jun Li, Yoshitaka Naitoh, Masami Kageshima, and Yasuhiro Sugawara

Appl. Phys. Lett. 97, 011906 (2010); http://dx.doi.org/10.1063/1.3457431 (3 pages) | Cited 1 time

Online Publication Date: 9 July 2010

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We investigate the dependence of effective Q-factor on force sensitivity in Q-controlled phase-modulation atomic force microscopy. With Q-control, the phase noise density spectrum shows a characteristic dependence on modulation frequency (fm). The phase noise density spectrum is nearly constant in the low-fm region, whereas it decreases inverse-proportionally to fm in the high-fm region. Such a decrease enhances the force sensitivity. We demonstrate that force sensitivity can be markedly increased with Q-control to exceed the limit of force sensitivity without Q-control.
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68.37.Ps Atomic force microscopy (AFM)

Nonlinear optical conductance in a graphene pn junction in the terahertz regime

X. G. Xu, S. Sultan, C. Zhang, and J. C. Cao

Appl. Phys. Lett. 97, 011907 (2010); http://dx.doi.org/10.1063/1.3462972 (3 pages) | Cited 1 time

Online Publication Date: 9 July 2010

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We show that the optical responses of a graphene pn junction is dominated by nonlinear intraband and interband processes. At the experimentally relevant electric field intensity, nonlinear conductance is an order of magnitude larger than the linear conductance. Furthermore, the total conductance is negative in the terahertz to far infrared regime. The negative conductance provides a unique mechanism for photon generation in graphene and could be used for developing coherent terahertz radiation sources.
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78.67.Wj Optical properties of graphene
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Interfacial thermal conductance in spun-cast polymer films and polymer brushes

Mark D. Losego, Lionel Moh, Kevin A. Arpin, David G. Cahill, and Paul V. Braun

Appl. Phys. Lett. 97, 011908 (2010); http://dx.doi.org/10.1063/1.3458802 (3 pages) | Cited 9 times

Online Publication Date: 9 July 2010

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Interfaces between inorganic materials and anharmonic polymers have potentially intriguing thermal transport behavior. The low thermal conductivity of amorphous polymers limits significant interfacial effects to polymer film thicknesses of only a few nanometers. We use time-domain thermoreflectance to directly measure interfacial effects in the thermal conductance of spun-cast poly(methyl methacrylate) (PMMA) thin films and PMMA brushes “grafted-from” the substrate. PMMA brushes are expected to have polymer chains partially aligned perpendicular to the substrate, yet only a modest increase (13%) in thermal conductivity is observed over spun-cast layers.
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81.16.-c Methods of micro- and nanofabrication and processing
61.41.+e Polymers, elastomers, and plastics
81.20.-n Methods of materials synthesis and materials processing
78.20.N- Thermo-optic effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
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Ge quantum dot tunneling diode with room temperature negative differential resistance

M. Oehme, A. Karmous, M. Sarlija, J. Werner, E. Kasper, and J. Schulze

Appl. Phys. Lett. 97, 012101 (2010); http://dx.doi.org/10.1063/1.3462069 (3 pages) | Cited 6 times

Online Publication Date: 7 July 2010

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We present current density-voltage characteristics of Ge quantum dot p+-i-n+ tunneling diodes. The diode structure with Ge quantum dots embedded in the intrinsic region was grown by low temperature molecular beam epitaxy without any postgrowth annealing steps. The quantum dot diodes were fabricated using a low thermal budget fabrication process which preserves the Ge quantum structure. A negative differential resistance at room temperature of a Ge quantum dot tunneling diode was observed. A maximum peak to valley ratio of 1.6 at room temperature was achieved.
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85.30.Kk Junction diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
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Electron transport properties of InAs ultrathin films obtained by epitaxial lift-off and van der Waals bonding on flexible substrates

Hayato Takita, Norihiko Hashimoto, Cong Thanh Nguyen, Masahiro Kudo, Masashi Akabori, and Toshi-kazu Suzuki

Appl. Phys. Lett. 97, 012102 (2010); http://dx.doi.org/10.1063/1.3459137 (3 pages) | Cited 5 times

Online Publication Date: 7 July 2010

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We investigated InAs ultrathin films on flexible substrates. InAs layers grown on GaAs(001) are separated by epitaxial lift-off (ELO), followed by van der Waals bonding (VWB) on flexible substrates. We employed “normal” and “inverted” VWB; in the former, top and bottom sides are maintained during ELO and VWB, while inverted in the latter. From the InAs on flexible substrates, we fabricated Hall-bar devices with recess etch-thinning, using which electron transport properties depending on InAs layer thickness were characterized. For the inverted VWB, we observe very high electron mobilities of InAs ultrathin films, such as ∼ 10 000 cm2/V s for ∼ 100 nm thickness and ∼ 7000 cm2/V s for ∼ 20 nm. These carrier mobilities are highest not only for thin films on flexible substrates but also for InAs thin films; higher than those of InAs films grown on GaAs(111)A and membranes fabricated from them.
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73.61.Ey III-V semiconductors
68.55.ag Semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance

High temperature conductance characteristics of LaAlO3/SrTiO3-heterostructures under equilibrium oxygen atmospheres

F. Gunkel, S. Hoffmann-Eifert, R. Dittmann, S. B. Mi, C. L. Jia, P. Meuffels, and R. Waser

Appl. Phys. Lett. 97, 012103 (2010); http://dx.doi.org/10.1063/1.3457386 (3 pages) | Cited 3 times

Online Publication Date: 7 July 2010

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The interface conductance of LaAlO3/SrTiO3 heterostructures was investigated under high temperature oxygen equilibrium. The dependence of the heterostructure’s conductance on oxygen partial pressure (from 10−22 to 1 bar) and temperature (800 to 1100 K) was compared to the characteristic of SrTiO3 single crystals, which is described in terms of a defect chemistry model. Up to 950 K the equilibrated heterostructures reveal an additional influence of a metallic-like conduction path with a very slight dependence on the oxygen partial pressure. Donor-type interface states which may result from either lattice distortions or A-site cation intermixing during processing are discussed as a possible origin for the exceptional interface conduction of LaAlO3/SrTiO3 heterostructures.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Band-gap narrowing of TiO2 doped with Ce probed with x-ray absorption spectroscopy

S. W. Chen, J. M. Lee, K. T. Lu, C. W. Pao, J. F. Lee, T. S. Chan, and J. M. Chen

Appl. Phys. Lett. 97, 012104 (2010); http://dx.doi.org/10.1063/1.3460916 (3 pages) | Cited 10 times

Online Publication Date: 7 July 2010

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The electronic structure of TiO2 doped with Ce was investigated with x-ray absorption and photoluminescence (PL) spectra. Ce doping narrows the band gap of TiO2, as evidenced by a redshift in the absorption edge in the O K-edge spectrum and PL. Narrowing is ascribed to the formation of an impurity band, composed of Ce 4f (Ce3+/Ce4+) and oxygen defect states, that induces tailing of the conduction band. Band gap narrowing extends the photoactivity of TiO2 to visible light. The impurity band located below the minimum of the conduction band traps excited electrons and suppresses recombination, enhancing the photocatalytic activity.
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71.20.Ps Other inorganic compounds
78.55.Hx Other solid inorganic materials
78.70.Dm X-ray absorption spectra
61.72.up Other materials
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