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Top 20 Most Read Articles
February 2007
The 20 articles with the most full-text downloads during the month, in descending order.
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“Plug and play” single-photon sources Appl. Phys. Lett. 90, 061103 (2007); http://dx.doi.org/10.1063/1.2437727 (3 pages) Online Publication Date: 5 February 2007
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The authors report a “plug and play” source of single photons, with full integration to a single-mode optical fiber. One end of the fiber is attached to the top of an InGaAs/GaAs quantum dot wafer. The other end is connected via a wavelength-division multiplexing system to two separate fibers: one for carrying excitation light and the other for emitted light. A
Hanbury-Brown and Twiss [Nature (London) 77, 27 (1956)]
measurement was performed on the emission from single excitons recombining in the quantum dots. A second-order correlation function at zero time delay of approximately 0.01 indicates a nearly ideal source of single photons. The maximum variation of peak position over 24 days is less than 0.1 nm.
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Ultrawide band quantum dot light emitting device by postfabrication laser annealing Appl. Phys. Lett. 90, 061101 (2007); http://dx.doi.org/10.1063/1.2458515 (3 pages) Online Publication Date: 5 February 2007
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An ultrawide band quantum dot (QD) light emitting device (LED) with bandwidth of 360 nm covering 1284–1644 nm spectral range has been demonstrated by postfabrication laser-irradiation technique. The integrated light output of the QD LED was found to increase by four times after laser annealing, attributed to the improved homogeneity of the QDs and enhanced lateral electrical and optical confinements at the active region after intermixing. Large wavelength blueshift of 315 nm has been obtained at the laser annealed region and an overall increase in bandwidth of 22% has been obtained in the QD LED after postfabrication laser annealing.
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Appl. Phys. Lett. 90, 052503 (2007); http://dx.doi.org/10.1063/1.2436715 (3 pages) Online Publication Date: 29 January 2007
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The spin-valve phototransistor is a semiconductor-ferromagnetic metal multilayer-semiconductor transistor operated by photoexciting hot electrons in the emitter semiconductor into a Schottky collector. This device uses an ultra-high vacuum-bonded float zone Si/multilayer/n-InP structure. To distinguish the emitter interband-excited component of collector current from base/collector internal photoemission, a lock-in spectroscopy sensitive only to the magnetocurrent is used. The experimental results indicate a pathway to improve the magnetocurrent of a related device, the spin-valve photodiode, by increasing the fraction of hot electron current that travels through both layers of the ferromagnetic spin valve and demonstrate that hot electrons photogenerated in one semiconductor can be collected by another through a thin ferromagnetic multilayer.
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High-frequency electrical properties of individual and bundled carbon nanotubes Appl. Phys. Lett. 90, 063106 (2007); http://dx.doi.org/10.1063/1.2437724 (3 pages) Online Publication Date: 6 February 2007
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Bundles of single wall carbon nanotubes have been proposed as an interconnect that could potentially replace copper in state-of-the-art ultralarge-scale-integrated circuits if theoretically predicted inductance, resistance, and capacitance scale with the number of carbon nanotubes within the bundle. The authors report direct measurement of the kinetic inductance of individual single wall carbon nanotubes and measurement of the high-frequency impedance of bundles showing that the bundle inductance scales with the number of individual carbon nanotubes.
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Microcontact insertion printing Appl. Phys. Lett. 90, 063114 (2007); http://dx.doi.org/10.1063/1.2457525 (3 pages) Online Publication Date: 9 February 2007
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The authors describe a chemical patterning technique, “microcontact insertion printing,” that utilizes conventional microcontact printing to pattern isolated molecules diluted within a preexisting self-assembled monolayer. By modifying the preexisting monolayer quality, the stamping duration, and/or the concentration of the patterned molecule, they can influence the extent of molecular exchange and precisely control the molecular composition of patterned self-assembled monolayers. This simple methodology can be used to fabricate complex patterns via multiple stamping steps and has applications ranging from bioselective surfaces to molecular-scale electronic components.
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Blue lasing at room temperature in high quality factor GaN/AlInN microdisks with InGaN quantum wells Appl. Phys. Lett. 90, 061106 (2007); http://dx.doi.org/10.1063/1.2460234 (3 pages) Online Publication Date: 6 February 2007
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The authors report on the achievement of optically pumped III-V nitride blue microdisk lasers operating at room temperature. Controlled wet chemical etching of an AlInN interlayer lattice matched to GaN allows forming inverted cone pedestals. Whispering gallery modes are observed in the photoluminescence spectra of InGaN/GaN quantum wells embedded in the GaN microdisks. Typical quality factors of several thousands are found (Q>4000). Laser action at ∼ 420 nm is achieved under pulsed excitation at room temperature for a peak power density of 400 kW/cm2. The lasing emission linewidth is down to 0.033 nm.
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Organic nanochannel field-effect transistor with organic conductive wires Appl. Phys. Lett. 90, 062101 (2007); http://dx.doi.org/10.1063/1.2454286 (3 pages) Online Publication Date: 5 February 2007
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The authors fabricated an organic nanochannel field-effect transistor (FET) that is self-wired with highly conductive organic conductors. The advantages of the transistor are a short channel (approximately 400 nm in length) and spontaneous formation of an active layer of the FET. Further, in principle, the carrier-injection barrier is absent at the interface of the organic metal and organic semiconductor. Thus, the transistor is highly conductive despite the narrow cross section of the channel. The FET characteristics of the nanochannel transistor exhibit the n-channel enhancement mode behavior.
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Room temperature ferromagnetism in Zn1−xCuxO thin films Appl. Phys. Lett. 90, 062504 (2007); http://dx.doi.org/10.1063/1.2450652 (3 pages) Online Publication Date: 5 February 2007
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Here the authors report systematic studies on the epitaxial growth and properties of Zn1−xCuxO (x = 0.02–0.1) thin films deposited onto sapphire c-plane single crystals using pulsed-laser deposition. X-ray diffraction and high resolution transmission electron microscopy (HRTEM) were employed to study the epitaxial relations of Zn1−xCuxO with the substrate, and x-ray photoelectron spectroscopy was used to establish the bonding characteristics and oxidation states of copper inside the ZnO host. Room temperature ferromagnetism was observed in the Zn1−xCuxO films with magnetic moment per Cu atom decreasing with an increasing Cu content. The presence of any magnetic phase was ruled out using HRTEM. Thus, the ferromagnetism was attributed to Cu ions substituted into the ZnO lattice.
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Midinfrared metamaterials fabricated by nanoimprint lithography Appl. Phys. Lett. 90, 063107 (2007); http://dx.doi.org/10.1063/1.2450651 (3 pages) Online Publication Date: 6 February 2007
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A metamaterial comprising an ordered array of four metallic L-shaped components designed to operate in the mid-IR frequency regime has been fabricated and characterized. The fourfold rotational symmetry of the unit cell should suppress the undesirable bianisotropy observed for split-ring resonators. Nanoimprint lithography was used to demonstrate scalability for mass production. A dipole plasmon resonance with a negative permittivity and a magnetic resonance with a negative permeability were observed at wavelengths of 3.7 and 5.25 μm, respectively, in agreement with theoretical predictions.
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Fabrication of high-Q chalcogenide photonic crystal resonators by e-beam lithography Appl. Phys. Lett. 90, 071102 (2007); http://dx.doi.org/10.1063/1.2476416 (3 pages) Online Publication Date: 12 February 2007
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The authors report design, fabrication, and characterization of photonic crystal nanocavities in nonlinear chalcogenide glass using e-beam lithography and chemically assisted ion beam etching. The design indicated that three-hole missing cavities with simultaneously modified side hole position and radii showed the maximum quality factor of 14 000, which was insensitive to the fabrication error of side holes. The fabricated cavities presented coupling dips of −2.6 dB at the wavelength of 1550 nm and quality factors up to 10 000 when excited with the evanescent field from a tapered optical fiber.
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Blue light emitting diodes based on fluorescent CdSe/ZnS nanocrystals Appl. Phys. Lett. 90, 051106 (2007); http://dx.doi.org/10.1063/1.2426899 (3 pages) Online Publication Date: 30 January 2007
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The authors report on the blue electroluminescence from CdSe/ZnS core/shell nanocrystals prepared from ultrasmall, magic size CdSe clusters that have a diameter of less than 2 nm. The light emitting device consists of an active layer of nanocrystals blended with 4,4′,N,N′- diphenylcarbazole and an evaporated electron transporting/hole blocking layer made of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline. A blue, stable electroluminescence at 485 nm from the hybrid device was observed, in good agreement with the photoluminescence spectra of a solid film of the same nanocrystals used for the device.
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Metal-enhanced fluorescence: Surface plasmons can radiate a fluorophore’s structured emission Appl. Phys. Lett. 90, 053107 (2007); http://dx.doi.org/10.1063/1.2435661 (3 pages) Online Publication Date: 31 January 2007
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In this letter, the authors report the observation of metal-enhanced structured fluorescence emission. Perylene in close proximity to silver island films (SiFs) enhances the structured fluorescence emission intensity. In this regard, an approximately two-fold higher perylene fluorescence intensity was observed from SiFs as compared to a glass control sample, containing no silver nanoparticles. The findings strongly suggest that surface plasmons can radiate a fluorophore’s vibrational structure. This observation is helpful in the authors’ understanding, not only for studying the interactions between plasmons and lumophores but also for their laboratories’ continued efforts to develop a unified plasmon-lumophore theory.
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Fiber-based architectures for organic photovoltaics Appl. Phys. Lett. 90, 063501 (2007); http://dx.doi.org/10.1063/1.2435988 (3 pages) Online Publication Date: 5 February 2007
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Using poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 bulk-heterojunction blends as the absorbing material, organic photovoltaic devices have been fabricated onto multimode optical fibers. The behavior of the short circuit current density, filling factor, and open circuit voltage as the angle of the incident light onto the cleaved fiber face is varied suggests that the evanescent field at the interface between the fiber and the transparent contact may play a role in coupling light from the fiber into the device. Further, optical loss into the device increases as the fiber diameter decreases.
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High speed silicon photonic crystal waveguide modulator for low voltage operation Appl. Phys. Lett. 90, 071105 (2007); http://dx.doi.org/10.1063/1.2475580 (3 pages) Online Publication Date: 12 February 2007
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A high speed compact silicon modulator is experimentally demonstrated to work at a low driving voltage desirable for on-chip applications. As carrier injection is the only practical option for optical modulation in silicon, a lower limit of current density ( ∼ 104 A/cm2) exists for achieving gigahertz modulation in the p-i-n diode configuration. Exploiting the slow group velocity of light in photonic crystal waveguides, the interaction length of this Mach-Zehnder interferometer-type silicon modulator is reduced significantly compared to conventional modulators. The required high current density is achieved with a low voltage (2 V) by scaling down the interaction length to 80 μm.
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Photovoltaic effects on the organic ambipolar field-effect transistors Appl. Phys. Lett. 90, 063511 (2007); http://dx.doi.org/10.1063/1.2457801 (3 pages) Online Publication Date: 8 February 2007
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An organic multifunctional device, which can function as an ambipolar field-effect transistor (FET) and a photovoltaic (PV) cell, has been demonstrated using a phase separated mixture of poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester. The gold (Au) electrode used for hole injection in the FET mode (source) acts as the anode in PV cell mode, and the aluminum (Al) electrode for electron injection in the FET mode (drain) acts as the cathode in PV cell mode. The device exhibits clear PV phenomena under illumination at zero gate bias with a power conversion efficiency of 0.6% as well as the properties of an ambipolar FET when the gate bias is applied.
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Appl. Phys. Lett. 90, 053506 (2007); http://dx.doi.org/10.1063/1.2436641 (3 pages) Online Publication Date: 1 February 2007
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n-type organic thin-film transistors based on a thiazolothiazole derivative were fabricated on a SiO2 gate insulator treated with n-alkyl self-assembled monolayers (SAMs), which were composed of various alkyl chain lengths. The field-effect electron mobility increased depending on the alkyl chain length of the SAMs. A long alkyl chain significantly improved the on current and electron mobility. The highest electron mobility of 1.2 cm2/V s and on/off ratio of 107 were achieved with an alkyl chain longer than that of tetradecyl-trichlorosilane. This result is attributed to the suppression of the influence of electron trap sites on the SiO2 gate insulator by employing the SAM with the long alkyl chain.
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Appl. Phys. Lett. 90, 052505 (2007); http://dx.doi.org/10.1063/1.2435606 (3 pages) Online Publication Date: 31 January 2007
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Ni-doped ZnO nanocrystals have been synthesized by a wet chemical reaction. The nanocrystals have been investigated carefully by high resolution transmission electron microscopy and all the particles are found to be the known wurtzite ZnO. X-ray photoelectron spectroscopy and Raman spectra results provide the evidence that Ni2+ is incorporated into the ZnO lattice at Zn2+ site. Magnetic property measurements reveal that the as-grown Zn1−xNixO nanocrystals exhibit room temperature ferromagnetic behaviors with saturation magnetization of 0.01 emu/g and Curie temperature above 340 K for Ni concentration of ∼ 1% in atomic ratio.
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Charge transfer effect in the polyaniline-gold nanoparticle memory system Appl. Phys. Lett. 90, 053101 (2007); http://dx.doi.org/10.1063/1.2434167 (3 pages) Online Publication Date: 29 January 2007
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A composite system comprised of polyaniline nanofibers bonded with gold nanoparticles is shown to possess a memory effect via a charge transfer mechanism. The charge transfer occurs between the imine nitrogen in the polyaniline and the gold nanoparticles as confirmed by x-ray photoelectron spectroscopy and Raman spectroscopy. This charge transfer enables a bistable electrical conductivity, allowing the material system to be used as a digital memory device. The charge transfer is further confirmed by the elimination of the conductance switching when the fully reduced form of polyaniline, leucoemeraldine, which possesses no imine nitrogens, is used in place of the emeraldine form.
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Wafer-bonded surface plasmon waveguides Appl. Phys. Lett. 90, 061108 (2007); http://dx.doi.org/10.1063/1.2468660 (3 pages) Online Publication Date: 7 February 2007
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Direct wafer bonding and thinning were explored as an approach for constructing long-range surface plasmon waveguides. The structures consist of a thin metal stripe deposited into a shallow trench etched into one of the claddings, to which another cladding of the same material is directly bonded. The approach was developed first using Pyrex wafers in order to assess feasibility and then using lithium niobate wafers. Optical and electro-optical measurements validate the approach.
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Efficient photonic crystal cavity-waveguide couplers Appl. Phys. Lett. 90, 073102 (2007); http://dx.doi.org/10.1063/1.2472534 (3 pages) Online Publication Date: 12 February 2007
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Coupling of photonic crystal (PC) linear three-hole defect cavities to PC waveguides is theoretically and experimentally investigated. The systems are designed to increase the overlap between the evanescent cavity field and the waveguide mode and to operate in the linear dispersion region of the waveguide. The simulations indicate increased coupling when the cavity is tilted by 60° with respect to the waveguide axis, which was also confirmed by experiments. Up to 90% coupling efficiency into the waveguide was obtained.
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