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Top 20 Most Read Articles
April 2007
The 20 articles with the most full-text downloads during the month, in descending order.
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Coupling between long range surface plasmon polariton mode and dielectric waveguide mode Appl. Phys. Lett. 90, 141101 (2007); http://dx.doi.org/10.1063/1.2719169 (3 pages) Online Publication Date: 3 April 2007
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Coupling of TM mode between long range surface plasmon polariton (LRSPP) mode and conventional dielectric waveguide mode is demonstrated numerically with finite element method. The characteristics of a hybrid coupler, which consists of the LRSPP waveguide and conventional single mode dielectric waveguide, are analyzed. The high efficient coupling shows a possible route for integrating the SPP device and conventional dielectric optical devices together and a method to excite LRSPP mode with dielectric waveguide. Because the coupling just occurs on TM mode, this kind of the hybrid coupler can be used as polarization mode splitter and combiner.
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Layer-by-layer photonic crystal fabricated by low-temperature atomic layer deposition Appl. Phys. Lett. 90, 151101 (2007); http://dx.doi.org/10.1063/1.2720752 (3 pages) Online Publication Date: 9 April 2007
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Layer-by-layer three-dimensional photonic crystals are fabricated by low-temperature atomic layer deposition of titanium dioxide on a polymer template created by soft lithography. With a highly conformal layer of titanium dioxide, a significantly enhanced photonic band gap effect appears at 3.1 μm in transmittance and reflectance. From optical investigations of systematically shifted structures, the robust nature of the photonic band gap with respect to structural fluctuations is confirmed experimentally. With angle-resolved Fourier-transform spectroscopy, the authors also demonstrate that the fabricated photonic crystal can be a diffraction-free device as the photonic band gap exists over the diffracting regime.
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Excitonic ultraviolet lasing in ZnO-based light emitting devices Appl. Phys. Lett. 90, 131115 (2007); http://dx.doi.org/10.1063/1.2718516 (3 pages) Online Publication Date: 30 March 2007
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The authors have fabricated ultraviolet (UV) laser diodes based on ZnO/BeZnO films. The devices have p-n heterojunction structures with a multiple quantum well (MQW) active layer sandwiched between guide-confinement layers. The MQW active layer comprises undoped ZnO and BeZnO, while the two guide-confinement layers were As-doped p-type ZnO/BeZnO and Ga-doped n-type BeZnO/ZnO films, respectively. The exciton binding energy in the MQW region is exceptionally large (263 meV). Exciton-related lasing was observed by optically pumping the MQWs. ZnO/BeZnO-based diodes showed laser action by current injection at room temperature. The lasing mechanism is inelastic exciton-exciton collision.
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Multiple plasmon resonances from gold nanostructures Appl. Phys. Lett. 90, 143105 (2007); http://dx.doi.org/10.1063/1.2719161 (3 pages) Online Publication Date: 3 April 2007
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Understanding and controlling plasmon resonances from metallic nanoscale structures have been the focus of much attention recently, with applications including local surface plasmon resonance sensing, surface enhanced Raman spectroscopy, and negative refractive index materials. In this letter the authors demonstrate the fabrication of uniform arrays of split rings from gold and show that such structures are capable of supporting multiple plasmon resonances. The authors show that up to five plasmon resonances can be identified and use finite difference time domain modeling and absorption spectroscopy to fully characterize and identify each resonance. The implications of higher order surface plasmon resonances for sensing are discussed.
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Dynamics of quantum dot photonic crystal lasers Appl. Phys. Lett. 90, 151102 (2007); http://dx.doi.org/10.1063/1.2720753 (3 pages) Online Publication Date: 9 April 2007
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Quantum dot photonic crystal membrane lasers were fabricated and the large-signal modulation characteristics were studied. The authors find that the modulation characteristics of quantum dot lasers can be significantly improved using cavities with large spontaneous emission coupling factor. Their experiments show, and simulations confirm, that the modulation rate is limited by the rate of carrier capture into the dots to around 30 GHz in their present system.
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Chip cooling with integrated carbon nanotube microfin architectures Appl. Phys. Lett. 90, 123105 (2007); http://dx.doi.org/10.1063/1.2714281 (3 pages) Online Publication Date: 20 March 2007
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Efficient cooling of silicon chips using microfin structures made of aligned multiwalled carbon nanotube arrays is achieved. The tiny cooling elements mounted on the back side of the chips enable power dissipation from the heated chips on the level of modern electronics demands. The nanotube fins are mechanically superior compared to other materials being ten times lighter, flexible, and stiff at the same time. These properties accompanied with the relative simplicity of the fabrication makes the nanotube structures strong candidates for future on-chip thermal management applications.
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Lithography-free fabrication of graphene devices Appl. Phys. Lett. 90, 143518 (2007); http://dx.doi.org/10.1063/1.2719607 (3 pages) Online Publication Date: 6 April 2007
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We have developed a lithography-free, all-dry process for fabricating graphene devices using an ultrathin quartz filament as a shadow mask. This technique, which is free of the possible contamination of graphene during lithographic process, is simple to implement, versatile, and capable of achieving high throughput. We prepared devices for electrical transport as well as planar tunnel junction studies of n-layer graphene (nLG), with n = 1,2,3, and higher using this technique. We observed possible weak localization behavior and an apparent reduction of density of states near the Fermi energy in nLG.
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32 TW atmospheric white-light laser Appl. Phys. Lett. 90, 151106 (2007); http://dx.doi.org/10.1063/1.2722564 (3 pages) Online Publication Date: 10 April 2007
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Ultrahigh power laser pulses delivered by the Alisé beamline (26 J, 32 TW pulses) have been sent vertically into the atmosphere. The highly nonlinear propagation of the beam in the air gives rise to more than 400 self-guided filaments. This extremely powerful bundle of laser filaments generates a supercontinuum propagating up to the stratosphere, beyond 20 km. This constitutes the highest power “atmospheric white-light laser” to date.
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Appl. Phys. Lett. 90, 143104 (2007); http://dx.doi.org/10.1063/1.2719035 (3 pages) Online Publication Date: 3 April 2007
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Composite media comprised of a host with amplification and high aspect ratio metallic spheroids exhibit a dielectric resonance which is accompanied by both a gigantic index of refraction and large collective gain. Expressions for the complex index of refraction near this dielectric anomaly are derived for the case of oriented spheroids in an amplifying host. The large index of refraction and gain can be used to satisfy the laser cavity resonance condition in nanoscale subwavelength structures with EH11 transverse modes allowing for the future miniaturization of laser devices.
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Vertical surround-gated silicon nanowire impact ionization field-effect transistors Appl. Phys. Lett. 90, 142110 (2007); http://dx.doi.org/10.1063/1.2720640 (3 pages) Online Publication Date: 5 April 2007
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One of the fundamental limits in the scaling of metal oxide semiconductor field-effect transistor technology is the room-temperature (RT) limit of ∼ 60 mV/decade in the inverse subthreshold slope. Here, the authors demonstrate vertical integration of a single surround-gated silicon nanowire field-effect transistor with an inverse subthreshold slope as low as 6 mV/decade at RT that spans four orders of magnitude in current. Operation of the device is based on avalanche breakdown in a partially gated vertical nanowire, epitaxially grown using the vapor-liquid-solid method. Low-power logic based on impact ionization field-effect transistors in combination with a vertical architecture is very promising for future high-performance ultrahigh-density circuits.
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Magnetic properties of n-type Cu-doped ZnO thin films Appl. Phys. Lett. 90, 142502 (2007); http://dx.doi.org/10.1063/1.2719034 (3 pages) Online Publication Date: 2 April 2007
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A series of n-type Zn1−xCuxO (x = 0.02, 0.06, 0.10, and 0.12) films was prepared using direct current reactive magnetron sputtering. Magnetic measurements indicate that all the films are ferromagnetic at room temperature and the moment per Cu ion decreases with increasing copper concentration and nitrogen doping. The observed magnetic moment was 1.8 μB/Cu for Zn0.98Cu0.02O film and the transition temperature of about 350 K decreased to 320 K due to nitrogen doping. It can be concluded that itinerant electrons play an important role in ferromagnetism. The resistivity increased with increasing copper concentration and nitrogen doping. The anomalous Hall effect has been found for ferromagnetic materials.
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Spatial refractive index sensor using whispering gallery modes in an optically trapped microsphere Appl. Phys. Lett. 90, 161101 (2007); http://dx.doi.org/10.1063/1.2722695 (3 pages) Online Publication Date: 16 April 2007
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The authors propose the use of an optically trapped, dye doped polystyrene microsphere for spatial probing of the refractive index at any position in a fluid. Using the dye embedded in the microsphere as an internal broadband excitation source the authors eliminated the need for a tunable excitation source. They measured the full width at half maximum and frequency spacing of the transverse electric and transverse magnetic resonances as a function of the refractive index of the immersion fluid. The authors achieved a sensitivity of 5×10−4 in refractive index, even when the exact size of the microsphere was not known.
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ZnO nanowires and nanobelts: Shape selection and thermodynamic modeling Appl. Phys. Lett. 90, 143116 (2007); http://dx.doi.org/10.1063/1.2720715 (3 pages) Online Publication Date: 6 April 2007
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The authors show that, during a steady-state vapor phase growth of ZnO nanomaterials, indium doping causes the structural change from usual [0001]-axial short nanowires to [11
 0]-axial nanobelts of much larger aspect ratio. They used an analytical thermodynamic model based on geometric summation of the Gibbs free energy to predict the dimension dependence of the nanowires and nanobelts for both pure and In-doped ZnO. The calculation result agrees with the experiment observation that in situ indium doping influences the nucleation and supports the dominating growth of a-axial nanobelts over c-axial nanowires. |
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Roles of donor and acceptor nanodomains in 6% efficient thermally annealed polymer photovoltaics Appl. Phys. Lett. 90, 163511 (2007); http://dx.doi.org/10.1063/1.2730756 (3 pages) Online Publication Date: 19 April 2007
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The authors have fabricated thin film polymer photovoltaics using 1-(3-methoxycarbonyl)propyl-1-phenyl-(6,6)C61 within regioregular poly(3-hexylthiophene) bulk heterojunction absorbing layers. Using thermal annealing at temperatures approaching the glass transition temperature, they have examined the formation of nanodomains within the matrix. These domains modify charge transport pathways in such a way as to allow for the efficient use of thicker absorbing layers. This results in a nearly 20% gain in overall performance for this polymer system with external power efficiencies exceeding 6%.
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Observation of whispering-gallery modes in Si microdisks at room temperature Appl. Phys. Lett. 90, 141102 (2007); http://dx.doi.org/10.1063/1.2719225 (3 pages) Online Publication Date: 3 April 2007
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Whispering-gallery modes are observed at room temperature in silicon microdisk resonators fabricated on silicon-on-insulator substrates. Sharp luminescent peaks originating from the crystalline silicon film, corresponding to the whispering-gallery modes, are observed to change in microdisks with different diameters. Over 30 times enhancement of the photoluminescence from bulk silicon is observed due to the microdisk.
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Enhanced light extraction of GaN-based light-emitting diodes by using textured n-type GaN layers Appl. Phys. Lett. 90, 161110 (2007); http://dx.doi.org/10.1063/1.2724903 (3 pages) Online Publication Date: 17 April 2007
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The authors report on the enhancement of the light extraction efficiency of GaN-based light-emitting diodes (LEDs) via the texturing of n-type layers. Compared with standard LEDs, LED fabricated with the textured n-type layers produced a significant improvement in the output power, depending on the reflectivity of the n electrode, the etch-pit size, and the chip dimension. The textured LEDs were found to yield the output power enhancement as high as 54%. However, it was also found that the electrical property of the textured LEDs can be degraded when the size of the etch pits is too large, indicating that a well-controlled texturing process is required for the realization of high-efficiency LEDs.
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Large-scale synthesis and optical behaviors of ZnO tetrapods Appl. Phys. Lett. 90, 153116 (2007); http://dx.doi.org/10.1063/1.2712512 (3 pages) Online Publication Date: 12 April 2007
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Zinc oxide tetrapods were synthesized on a large scale through thermal evaporation of zinc powder with a vapor transportation deposition method. Scanning electron microscope images gave clear evidences of twin planes at the junction of the tetrapods. Photoluminescence and waveguide behaviors of a single tetrapod were demonstrated with a near-field scanning optical microscope.
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Surface plasmon enhanced photoluminescence of conjugated polymers Appl. Phys. Lett. 90, 161107 (2007); http://dx.doi.org/10.1063/1.2721134 (3 pages) Online Publication Date: 17 April 2007
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To produce surface plasmons, silver nanostructures were fabricated using a thermal evaporation method and the surface plasmon wavelength was tuned via an annealing. These nanostructures were located between the indium tin oxide (ITO) and poly(3,4-ethylenedioxy thiophene)/poly(styrenesulfonate) for the coupling of the surface plasmon resonance with organic fluorophores. To prevent the quenching of emission, spacer was placed between the light emitting polymers and the ITO substrate. As a result, the authors were able to observe an increase in photoluminescence of conjugated polymers using the silver nanostructures.
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Magnetic alignment of ZnO nanowires for optoelectronic device applications Appl. Phys. Lett. 90, 133115 (2007); http://dx.doi.org/10.1063/1.2717575 (3 pages) Online Publication Date: 29 March 2007
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Ni caps on ZnO nanowires were synthesized to control the direction and position of these nanowires using magnetism. Vertically ordered ZnO nanowires were grown 15 μm in length by metal organic chemical vapor deposition and then ferromagnetic Ni was capped on top of the nanowires by sputtering. The synthesized nanowires were aligned at the edge of the magnetized Ni patterns by applying a magnetic field. The density of the aligned nanowires depended on the magnetic force of the Ni patterns. Nanowire-based ultraviolet sensors were demonstrated using the magnetic alignment method.
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Three-dimensional nanoscale subsurface optical imaging of silicon circuits Appl. Phys. Lett. 90, 131101 (2007); http://dx.doi.org/10.1063/1.2716344 (3 pages) Online Publication Date: 26 March 2007
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Three-dimensional subsurface imaging through the back side of a silicon flip chip is reported with a diffraction-limited lateral resolution of 166 nm and an axial performance capable of resolving features only 100 nm deep. This performance was achieved by implementing sample-scanned two-photon optical beam induced current microscopy using a silicon solid immersion lens and a peak detection algorithm. The excitation source was a 1530 nm erbium:fiber laser, and the lateral optical resolution obtained corresponds to 11% of the free-space wavelength.
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