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Top 20 Most Read Articles
June 2010
The 20 articles with the most full-text downloads during the month, in descending order.
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Three-dimensional imaging of pore structures inside low-κ dielectrics Appl. Phys. Lett. 96, 223108 (2010); http://dx.doi.org/10.1063/1.3442496 (3 pages) Online Publication Date: 2 June 2010
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The three-dimensional reconstruction of a porous low-dielectric constant film (κ = 2.5), resolving pores as small as 1 nm, was achieved using annular dark-field scanning transmission electron tomography, enabling quantitative measurements of the pore morphologies and size distribution. Most large pores were elliptical. Together with log-normal pore-size distribution, this suggests pore coalescence during the material’s growth. Ellipsometric porosimetry indicates a high degree of interconnectivity between pores. Tomography shows the material exhibits little large-scale pore connectivity, thus placing an upper limit on the size of the interconnections at below 1 nm. Systematic errors in the tomographic and ellipsometric size distributions appear to be largely complementary.
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Appl. Phys. Lett. 96, 231104 (2010); http://dx.doi.org/10.1063/1.3443734 (3 pages) Online Publication Date: 7 June 2010
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A novel technology for controlling the In composition of InGaN quantum wells on the same wafer was developed, which paved the way for the monolithic integration of three-primary-color nano-light-emitting diodes. In the experiment, InGaN/GaN multiple quantum well nanocolumn arrays with nanocolumn diameters from 137 to 270 nm were prepared on the same substrate with the Ti-mask selective area growth by rf-plasma-assisted molecular beam epitaxy. The emission color changed from blue to red (from 479 to 632 nm in wavelength) with increasing nanocolumn diameter. The emission color change mechanism was clearly explained by the beam shadow effect of the neighboring nanocolumns.
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Optically pumped ultraviolet lasing from nitride nanopillars at room temperature Appl. Phys. Lett. 96, 241101 (2010); http://dx.doi.org/10.1063/1.3449576 (3 pages) Online Publication Date: 14 June 2010
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A vertical cavity structure composing of an in situ grown bottom AlxGa1−xN/AlyGa1−yN distributed Bragg reflector and a top SiO2/HfO2 dielectric mirror for ultraviolet (UV) emission has been demonstrated. Close-packed nanopillars with diameters of around 500 nm have been achieved by the route of nanosphere lithography combined with inductively-coupled plasma etching. Optically-pumped UV lasing at a wavelength of 343.7 nm (3.608 eV) was observed at room temperature, with a threshold excitation density of 0.52 MW/cm2. The mechanism of the lasing action is discussed in detail. Our investigation indicates promising possibilities in nitride-based resonant cavity devices, particularly toward realizing the UV nitride-based vertical-cavity surface-emitting laser.
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Nonuniformity of a planar polarizer for spin-transfer-induced vortex oscillations at zero field Appl. Phys. Lett. 96, 212507 (2010); http://dx.doi.org/10.1063/1.3441405 (3 pages) Online Publication Date: 28 May 2010
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We discuss a possible mechanism of the spin-transfer-induced oscillations of a vortex in the free layer of spin-valve nanostructures, in which the polarizer layer has a planar magnetization. We demonstrate that if such planar polarizer is essentially nonuniform, steady gyrotropic vortex motion with large amplitude can be excited. The best excitation efficiency is obtained for a circular magnetization distribution in the polarizer. In this configuration, the conditions for the onset of the oscillations depend on the vortex chirality but not on the direction of its core.
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Low efficiency droop in blue-green m-plane InGaN/GaN light emitting diodes Appl. Phys. Lett. 96, 231101 (2010); http://dx.doi.org/10.1063/1.3449557 (3 pages) Online Publication Date: 7 June 2010
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We investigated the electroluminescence and relatively external quantum efficiency (EQE) of m-plane InGaN/GaN light emitting diodes (LEDs) emitting at 480 nm to elucidate the droop behaviors in nitride-based LEDs. With increasing the injection current density to 100 A/cm2, the m-plane LEDs exhibit only 13% efficiency droop, whereas conventional c-plane LEDs suffer from efficiency droop at very low injection current density and the EQE of c-plane LEDs decrease to as little as 50% of its maximum value. Our simulation models show that in m-plane LEDs the absence of polarization fields manifest not only the hole distribution more uniform among the wells but also the reduction in electron overflow out of electron blocking layer. These results suggest that the nonuniform distribution of holes and electron leakage current due to strong polarization fields are responsible for the relatively significant efficiency droop of conventional c-plane LEDs.
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Comment on “Guided modes in graphene waveguides” [ Appl. Phys. Lett. 94, 212105 (2009) ] Appl. Phys. Lett. 96, 186101 (2010); http://dx.doi.org/10.1063/1.3425716 (2 pages) Online Publication Date: 5 May 2010
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Appl. Phys. Lett. 96, 186102 (2010); http://dx.doi.org/10.1063/1.3425717 (2 pages) Online Publication Date: 5 May 2010
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Metal-cavity surface-emitting microlaser at room temperature Appl. Phys. Lett. 96, 251101 (2010); http://dx.doi.org/10.1063/1.3455316 (3 pages) Online Publication Date: 21 June 2010
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We propose and realize a substrate-free metal-cavity surface-emitting microlaser with both top and sidewall metal and a bottom distributed Bragg reflector as the cavity structure. The transfer-matrix method is used to design the laser structure based on the round-trip resonance condition inside the cavity. The laser is 2.0 μm in diameter and 2.5 μm in height, and operates at room temperature with continuous-wave mode. Flip-bonding the device to a silicon substrate with a conductive metal provides efficient heat removal. A high characteristic temperature about 425 K is observed from 10 to 27 °C.
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Optical gain in carbon nanotubes Appl. Phys. Lett. 96, 231105 (2010); http://dx.doi.org/10.1063/1.3443634 (3 pages) Online Publication Date: 8 June 2010
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Semiconducting single-wall carbon nanotubes (s-SWNTs) have proved to be promising material for nanophotonics and optoelectronics. Due to the possibility of tuning their direct band gap and controlling excitonic recombinations in the near-infrared wavelength range, s-SWNT can be used as efficient light emitters. We report the first experimental demonstration of room temperature intrinsic optical gain as high as 190 cm−1 at a wavelength of 1.3 μm in a thin film doped with s-SWNT. These results constitute a significant milestone toward the development of laser sources based on carbon nanotubes for future high performance integrated circuits.
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Appl. Phys. Lett. 96, 251103 (2010); http://dx.doi.org/10.1063/1.3454240 (3 pages) Online Publication Date: 22 June 2010
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We report the development of a GaN-based green light-emitting diode (LED) with a selective area photonic crystal (SPC) structure, which was formed outside the p-bonding electrode on p-GaN. As a result, the optical output power of LEDs with SPC was enhanced by 78% compared to that without PC. In addition, the forward voltage, series resistance, and leakage current of LEDs with SPC were remarkably improved. These results show that the light extraction efficiency of green LEDs can be greatly increased using the SPC structure, with no degradation of electrical properties.
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Appl. Phys. Lett. 96, 226101 (2010); http://dx.doi.org/10.1063/1.3442493 (1 page) Online Publication Date: 1 June 2010
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Scatterer induced mode splitting in poly(dimethylsiloxane) coated microresonators Appl. Phys. Lett. 96, 221101 (2010); http://dx.doi.org/10.1063/1.3435480 (3 pages) Online Publication Date: 1 June 2010
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We investigate scatterer induced mode splitting in a composite microtoroidal resonator (Q ∼ 106) fabricated by coating a silica microtoroid (Q ∼ 107) with a thin poly(dimethylsiloxane) layer. We show that the two split modes in both coated and uncoated silica microtoroids respond in the same way to the changes in the environmental temperature. This provides a self-referencing scheme which is robust to temperature perturbations. Together with the versatile functionalities of polymer materials, mode splitting in polymer and polymer coated microresonators offers an attractive sensing platform that is robust to thermal noise.
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Strong coupling in a quantum dot micropillar system under electrical current injection Appl. Phys. Lett. 96, 221102 (2010); http://dx.doi.org/10.1063/1.3442912 (3 pages) Online Publication Date: 1 June 2010
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Integrating In0.3Ga0.7As quantum dots (QDs) featuring a high oscillator strength into a high quality electrically contacted micropillar cavity enabled us to realize strong coupling under electrical carrier injection. In the micropillar cavity with a quality factor of 10 000 and a diameter of 1.9 μm, a vacuum Rabi splitting of 108 μeV was observed when an electrically excited QD exciton was tuned through resonance with the fundamental cavity mode by varying the temperature.
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Fast reset and suppressing spontaneous emission of a superconducting qubit Appl. Phys. Lett. 96, 203110 (2010); http://dx.doi.org/10.1063/1.3435463 (3 pages) Online Publication Date: 21 May 2010
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Spontaneous emission through a coupled cavity can be a significant decay channel for qubits in circuit quantum electrodynamics. We present a circuit design that effectively eliminates spontaneous emission due to the Purcell effect while maintaining strong coupling to a low-Q cavity. Excellent agreement over a wide range in frequency is found between measured qubit relaxation times and the predictions of a circuit model. Using fast (nanosecond time-scale) flux biasing of the qubit, we demonstrate in situ control of qubit lifetime over a factor of 50. We realize qubit reset with 99.9% fidelity in 120 ns.
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Appl. Phys. Lett. 96, 226102 (2010); http://dx.doi.org/10.1063/1.3442494 (1 page) Online Publication Date: 1 June 2010
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Theory of electroluminescence intensity and insights into recombination in thin film solar cells Appl. Phys. Lett. 96, 222102 (2010); http://dx.doi.org/10.1063/1.3443637 (3 pages) Online Publication Date: 1 June 2010
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Equations describing the electroluminescence (EL) intensity as a function of material properties are derived for thin film solar cells and experimentally validated using Cu(In,Ga)Se2 solar cells. EL intensity at constant voltage is controlled by the electronic properties of the neutral bulk even when the diode current is controlled by recombination in the space charge region. Using a combination of techniques, it is found that recombination in the quasineutral bulk does not correlate with recombination in the space charge region. Differences between EL measurements on thin film cells and crystalline silicon cells are discussed including the effects of secondary barriers.
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Appl. Phys. Lett. 96, 126101 (2010); http://dx.doi.org/10.1063/1.3372622 (1 page) Online Publication Date: 22 March 2010
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Rare frustration of optical supercontinuum generation Appl. Phys. Lett. 96, 151108 (2010); http://dx.doi.org/10.1063/1.3374860 (3 pages) Online Publication Date: 14 April 2010
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Recent work has shown that optical rogue waves, large bandwidth fluctuations following heavy-tailed statistics, can arise during spectral broadening by stochastic enhancement of nonlinearity. Here, we report the observation of a different form of extreme fluctuations in supercontinuum pulse trains: Pulses of unusually small spectral bandwidth following left-skewed heavy-tailed statistics. Displaying a pulse evolution strongly varying from that of large extremes in supercontinuum, these rogue events appear when spectral broadening is frustrated by competition between presolitonic features within the modulation-instability band. This suppression effect can also be externally induced with a weak control pulse.
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Appl. Phys. Lett. 96, 126102 (2010); http://dx.doi.org/10.1063/1.3357437 (2 pages) Online Publication Date: 23 March 2010
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Appl. Phys. Lett. 96, 216101 (2010); http://dx.doi.org/10.1063/1.3431743 (1 page) Online Publication Date: 24 May 2010
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