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Top 20 Most Read Articles
August 2012
The 20 articles with the most full-text downloads during the month, in descending order.
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Luminescence decay in disordered low‐dimensional semiconductors Appl. Phys. Lett. 60, 2672 (1992); http://dx.doi.org/10.1063/1.106891 (3 pages)
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The luminescence decay of excitons in disordered low‐dimensional semiconductors with quantum confinement is shown experimentally to be characterized by a nonexponential profile and an absence of spectral diffusion. We are able to describe this luminescence as a hopping‐assisted recombination using the correlation function approach to nondispersive transport developed by H. Scher, M. F. Shlesinger, and J. T. Bendler [Phys. Today 41, 26 (1991)]. We suggest a simple derivation of analytical functions which accurately describe the anomalous luminescence decays of disordered II‐VI superlattices and of porous silicon, and show that this model includes exponential and Kohlrausch [Pogg. Ann. Phys. 119, 352 (1863)] (stretched‐exponential) relaxations as special cases. |
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Transparent superhydrophobic/superhydrophilic coatings for self-cleaning and anti-fogging Appl. Phys. Lett. 101, 033701 (2012); http://dx.doi.org/10.1063/1.4737167 (4 pages) Online Publication Date: 16 July 2012
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The high transparent superhydrophobic surface covered with hollow spheres has been fabricated through a carbon template route. The as-prepared coating without treating with low surface energy materials showed superhdrophilic and anti-fogging properties while displayed superhydrophobic characteristics after surface modification. Furthermore, such superhydrophilic/superhydrophobic glasses both exhibited a relatively high transmittance, and it is also demonstrated that the thickness of coating affects the transmittance and wettability from a control experiment. For comparison, we studied the anti-fogging properties of the transparent superhydrophobic, superhydrophilic, and the ordinary glass, showing absolutely different fogging characteristics.
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Appl. Phys. Lett. 101, 042410 (2012); http://dx.doi.org/10.1063/1.4738887 (3 pages) Online Publication Date: 25 July 2012
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We studied the propagation of spin waves in a Ni81Fe19 micro-waveguide comprising a smooth, S-shaped bend using Brillouin light scattering microscopy. A direct current flowing through a gold wire underneath the Ni81Fe19 provides a local magnetic field, which maintains a transverse magnetization around the bend of the waveguide. It is demonstrated that spin-wave propagation inside the bend can be realized in contrast to the case of an externally applied magnetic field, which generates strong inhomogeneities in the internal effective field distribution, preventing any spin-wave propagation across the bend.
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Taking whispering gallery-mode single virus detection and sizing to the limit Appl. Phys. Lett. 101, 043704 (2012); http://dx.doi.org/10.1063/1.4739473 (4 pages) Online Publication Date: 27 July 2012
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We report the label-free detection and sizing by a microcavity of the smallest individual RNA virus, MS2, with a mass only ∼1% of InfluenzaA (6 vs. 512 ag). Although detection of such a small bio-nano-particle has been beyond the reach of a bare spherical microcavity, it was accomplished with ease (S/N = 8, Q = 4 × 105) using a single dipole stimulated plasmonic-nanoshell as a microcavity wavelength shift enhancer, providing an enhancement of ∼70×, in agreement with theory. Unique wavelength shift statistics are recorded consistent with an ultra-uniform genetically programmed substance that is drawn to the plasmonic hot spots by light-forces.
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Demonstration of nonlinear magnetoelectric coupling in metamaterials Appl. Phys. Lett. 101, 051103 (2012); http://dx.doi.org/10.1063/1.4738774 (4 pages) Online Publication Date: 30 July 2012
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We demonstrate nonlinear magnetoelectric coupling in a varactor-loaded metamaterial at microwave frequencies. The nonlinear magnetoelectric coupling takes the form of second-harmonic generation in which incident magnetic fields at frequency ω drive an electric polarization at frequency 2ω. The magnitudes and phases of the generated signals from two nonlinear metamaterials are measured, verifying the dominant nonlinear process in each sample. We expect the metamaterial design employed in this letter to form the prototype for future investigations into nonlinear magnetoelectric coupling.
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Network analyzer measurements of spin transfer torques in magnetic tunnel junctions Appl. Phys. Lett. 101, 022417 (2012); http://dx.doi.org/10.1063/1.4737017 (4 pages) Online Publication Date: 13 July 2012
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We demonstrate a simple network-analyzer technique to make quantitative measurements of the bias dependence of spin torque in a magnetic tunnel junction. We apply a microwave current to exert an oscillating spin torque near the ferromagnetic resonance frequency of the tunnel junction’s free layer. This produces an oscillating resistance that, together with an applied direct current, generates a microwave signal that we measure with the network analyzer. An analysis of the resonant response yields the strength and direction of the spin torque at non-zero bias. We compare to measurements of the spin torque vector by time-domain spin-torque ferromagnetic resonance.
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Appl. Phys. Lett. 101, 033508 (2012); http://dx.doi.org/10.1063/1.4737904 (4 pages) Online Publication Date: 18 July 2012
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The degradation of AlGaN/GaN high electron mobility transistors after off-state stress is studied by means of electroluminescence (EL) analysis, gate leakage current (Ig) monitoring, and atomic force microscopy (AFM) mapping of the semiconductor surface. It is found that the degradation of Ig upon stress is due to the combined effect of the individual defects underlying each of the EL spots, which contribute a few μA each to the total Ig. After removal of contacts and passivation, a direct one-to-one correspondence between EL spots and pits on the semiconductor surface is found. Reverse bias, conducting-tip AFM imaging showed that these surface pits do indeed act as leakage paths. Thus, the direct relationship between EL hot spots, surface pits, and gate current leakage is demonstrated. Discussion on the morphology of the surface pits and their possible origin is also provided.
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Micro-textured conductive polymer/silicon heterojunction photovoltaic devices with high efficiency Appl. Phys. Lett. 101, 033301 (2012); http://dx.doi.org/10.1063/1.4734240 (5 pages) Online Publication Date: 16 July 2012
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In this work, hybrid heterojunction solar cells are demonstrated based on a conjugate polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) directly spun-cast on micro-textured n-type crystalline silicon wafers. The fabrication conditions suggest that the organic coverage on the micro-textured surface is excellent and key to achieve high efficiency, leading to an average power conversion efficiency of 9.84%. A one-dimensional drift-diffusion model is then developed based on fitting the device characteristics with experimentally determined PEDOT:PSS parameters and projects an ultimate efficiency above 20% for organic/inorganic hybrid photovoltaics. The simulation results reveal the impacts of defect densities, back surface recombination, doping concentration, and band alignment.
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Low mode volume slotted photonic crystal single nanobeam cavity Appl. Phys. Lett. 101, 071104 (2012); http://dx.doi.org/10.1063/1.4742749 (4 pages) Online Publication Date: 13 August 2012
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We present and experimentally demonstrate a slotted photonic crystal single nanobeam cavity in silicon. The slot geometry is exploited to achieve ultra-small effective mode volumes, ∼0.025(λ/n)3, more than an order of magnitude smaller than traditional nanobeam cavities. A continuous slot and a tapered photonic crystal design are implemented to achieve experimental quality factors near 104. This device structure offers a unique platform for achieving enhanced light-matter interactions and could be used to benefit a variety of applications including non-linear optics, cavity quantum electro-dynamics, sensing, optical modulation, and nano-optomechanics.
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Coupled plasmonic modes in organic planar microcavities Appl. Phys. Lett. 100, 253301 (2012); http://dx.doi.org/10.1063/1.4729820 (4 pages) Online Publication Date: 20 June 2012
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We report on the nature of the resonant modes in organic planar microcavities featuring semi-transparent metallic layers. We theoretically demonstrate that symmetric microcavities support a total of four modes originating from the coupling of surface plasmon polaritons. For red top-emitting organic light-emitting diodes with one semi-transparent metallic electrode, we identify three coupled plasmonic modes and calculate a light outcoupling efficiency close to 34% when assuming emitters with isotropic transition dipole moment. This value is estimated to increase to 50% in the case the dipole moment is purely horizontal.
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Voltage modulation of a vertical cavity transistor laser via intra-cavity photon-assisted tunneling Appl. Phys. Lett. 101, 081102 (2012); http://dx.doi.org/10.1063/1.4745791 (3 pages) Online Publication Date: 20 August 2012
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We report the direct voltage modulated operation of a vertical cavity transistor laser via intra-cavity coherent signal photon-assisted tunneling. The reversed-bias base/collector junction of the transistor laser provides high input impedance for effective high speed direct voltage modulation. The optical L-VCE characteristics show that the emission intensity saturates and then decreases in laser intensity to half amplitude and broadens when VCE is switched from 3 to 6 V owing to intra-cavity photon-assisted tunneling at the base/collector junction. Correspondingly, the collector IC-VCE characteristics exhibit increased current at higher VCE.
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Highly compliant transparent electrodes Appl. Phys. Lett. 101, 061101 (2012); http://dx.doi.org/10.1063/1.4742889 (4 pages) Online Publication Date: 6 August 2012
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Adaptive optical devices based on electric field induced deformation of dielectric elastomers require transparent and highly compliant electrodes to conform to large shape changes. Electrical, optical, and actuation properties of acrylic elastomer electrodes fabricated with single-walled carbon nanotubes (SWCNTs) and silver nanowires (AgNWs) have been evaluated. Based on these properties, a figure of merit is introduced for evaluating the overall performance of deformable transparent electrodes. This clearly indicates that SWCNTs outperform AgNWs. Under optimal conditions, optical transparency as high as 91% at 190% maximum actuation strain is readily achievable using SWCNT electrodes.
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Appl. Phys. Lett. 101, 061102 (2012); http://dx.doi.org/10.1063/1.4742892 (4 pages) Online Publication Date: 6 August 2012
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InGaN-based vertical structure light emitting diodes (VLEDs) with multi-layer graphene transparent electrodes with higher optical output have been fabricated and tested. High temperature annealing introduced inter-diffusion of metal atoms and Ga atoms and generated the partially sandwiched graphene structure, which contributed to the performance improvement of VLEDs.
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Detection of domain wall eigenfrequency in infinity-shaped magnetic nanostructures Appl. Phys. Lett. 101, 062401 (2012); http://dx.doi.org/10.1063/1.4730997 (4 pages) Online Publication Date: 6 August 2012
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The dynamics of a magnetic infinity-shaped nanostructure has been experimentally studied by two different techniques such as the sinusoidal resonance excitation and the damped short pulse excitation to measure the eigenfrequency of domain walls. Direct observation of the magnetic domain wall nucleation has been measured in the frequency domain. Electrical measurements of the domain wall dynamics in the frequency domain reveal the existence of multi-eigenmodes for large excitation amplitudes. The time-resolved measurements show that the frequency of the damped gyration is similar to that of the frequency domain and indicate coexistence of spin wave excitations.
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Appl. Phys. Lett. 101, 074102 (2012); http://dx.doi.org/10.1063/1.4746247 (4 pages) Online Publication Date: 14 August 2012
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This paper presents a method to manipulate cells in a microfluidic chip without contact. A local streamline is generated when high-frequency oscillation of the microtool is induced in a microfluidic chip. The streamline can be controlled by tuning the oscillation parameters of the tool, such as the amplitude and phase of the oscillation. Cells then flow in the microchannel in accordance with the streamline, and their position, posture, and trajectories are controlled. Bovine oocyte manipulations, which were attraction, repulsion, and rotation, were conducted to demonstrate the capability of the proposed method without any contact by the oscillation tool.
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Tandem organic photovoltaics using both solution and vacuum deposited small molecules Appl. Phys. Lett. 101, 063303 (2012); http://dx.doi.org/10.1063/1.4742921 (4 pages) Online Publication Date: 7 August 2012
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We demonstrate a tandem organic photovoltaic cell incorporating solution- and vacuum-deposited small molecules as the active layers. A blue and green-absorbing boron subphthalocyanine chloride:C70 graded heterojunction (HJ) sub-cell is combined with a green and red-absorbing functionalized squaraine/C70 bilayer HJ sub-cell, resulting in a tandem cell with a wavelength response from 350 nm to 800 nm. The efficiency of the cells depends on process conditions such as solvent annealing, resulting in nanocrystalline morphology that leads to improved charge and exciton transport compared with un-annealed cells. The incorporation of C70 in both sub-cells leads to an increase of short-circuit current by at least 30% compared to analogous cells using C60. The optimized power conversion efficiency of the tandem cell is 6.6% ± 0.1%, with an open-circuit voltage of 1.97 ± 0.1 V under simulated 1 sun, AM 1.5G illumination. The tandem cell voltage is equal to the sum of the constituent sub-cells, indicating that the transparent, Ag nanoparticle/MoO3 compound charge recombination layer interposed between the cells is nearly lossless.
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High-brightness organic light-emitting diodes based on a simplified hybrid structure Appl. Phys. Lett. 101, 053306 (2012); http://dx.doi.org/10.1063/1.4740272 (4 pages) Online Publication Date: 1 August 2012
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High-brightness green phosphorescent hybrid inorganic-organic light-emitting diodes (HyLEDs) based on a simplified WO3/organic layer structure have been demonstrated. The WO3 layer greatly improved hole injection and enabled facile hole transport, leading to balanced charge injection and significant performance enhancement. The HyLEDs reached a luminance of 104 cd/m2 at 7.3 V. At this brightness level, their current efficiency was 55.2 cd/A, 57% higher than that of all-organic LEDs with a N,N-bis-(1-naphthyl)-N,N’-diphenyl-1,1′-biphenyl-4,4′-diamine hole transport layer. The HyLEDs also exhibited markedly improved reliability under constant-current stressing due to the stable indium-tin-oxide/WO3 interface.
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Phase separation of co-evaporated ZnPc:C60 blend film for highly efficient organic photovoltaics Appl. Phys. Lett. 100, 233302 (2012); http://dx.doi.org/10.1063/1.4726118 (5 pages) Online Publication Date: 5 June 2012
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We demonstrate phase separation of co-evaporated zinc phthalocyanine (ZnPc) and fullerene (C60) for efficient organic photovoltaic cells. With introducing a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) film and a crystalline copper iodide film on indium tin oxide, 20-nm-thick ZnPc film adopts a lying-down crystalline geometry with grain sizes of about 50 nm. This surface distributed with strong interaction areas and weak interaction areas enables the selective growth of ZnPc and C60 molecules during following co-evaporation, which not only results in a phase separation but also improve the crystalline growth of C60. This blend film greatly enhances the efficiencies in photocurrent generation and carrier transport, resulting in a high power conversion efficiency of 4.56% under 1 sun.
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Polarization conversion with elliptical patch nanoantennas Appl. Phys. Lett. 101, 023101 (2012); http://dx.doi.org/10.1063/1.4731792 (4 pages) Online Publication Date: 9 July 2012
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In this paper, we demonstrate arrays of optical patch nanoantennas can convert light polarization through reflection. By breaking the azimuthal symmetry, elliptical plasmonic patch nanoantennas exhibit both even and odd cavity modes, which can be expressed by Mathieu functions. It is shown that by properly orienting the incident polarization, a linearly polarized light in resonance with one cavity mode can be converted into an elliptical or circular polarization after reflection. Since the major cavity modes can be excited at all incident angles, the polarization conversion by these elliptical patch nanoantennas can be realized with wide range of incident angles.
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Appl. Phys. Lett. 101, 063306 (2012); http://dx.doi.org/10.1063/1.4745507 (4 pages) Online Publication Date: 9 August 2012
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High-efficiency single-layer (SL) white organic light-emitting devices (WOLEDs) with a bipolar transport host were fabricated. The SL WOLEDs were achieved by combining blue and orange emission. Compared with the corresponding multilayer WOLEDs, the SL WOLEDs alleviated the efficiency roll-off without compromise of current efficiency due to the broader exciton formation zone and balance of carrier injection and transport. For example, The power efficiency of the SL WOLED based on Iridium (III) bis(4-phenylthieno[3,2-c]pyridinato-N,C2′) acetylacetonate orange emission could reach 20.9 lm/W at 1000 cd/m2, which also could reach 14.5 lm/W at a very high brightness of 5000 cd/m2.
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