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Top 20 Most Read Articles
September 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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C60-based hot-electron magnetic tunnel transistor Appl. Phys. Lett. 101, 102404 (2012); http://dx.doi.org/10.1063/1.4751030 (4 pages) Online Publication Date: 4 September 2012
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A C60-based magnetic tunnel transistor is presented. The device is based on the collection of spin-filtered hot-electrons at a metal/C60 interface, and it allows an accurate measurement of the energy level alignment at such interface. A 89% change in the collected current under the application of a magnetic field demonstrates that these devices can be used as sensitive magnetic field sensors compatible with soft electronics.
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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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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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Appl. Phys. Lett. 101, 122403 (2012); http://dx.doi.org/10.1063/1.4753816 (3 pages) Online Publication Date: 18 September 2012
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The electric field-induced ∼180° magnetization reversal is realized for a sputtered CoFeB/MgO-based magnetic tunnel junction with perpendicular magnetic easy axis in a static external magnetic field. Application of bias voltage with nanoseconds duration results in a temporal change of magnetic easy axis in the free layer CoFeB to in-plane, which induces precessional motion of magnetization in the free layer. The magnetization reversal takes place when the bias voltage pulse duration is adjusted to a half period of the precession. We show that the back and forth magnetization reversal can be observed by using successive application of half-period voltage pulses.
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Appl. Phys. Lett. 101, 093306 (2012); http://dx.doi.org/10.1063/1.4749285 (4 pages) Online Publication Date: 30 August 2012
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We have designed and synthesized a high-efficiency purely organic luminescent material, 2,4-bis{3-(9 H-carbazol-9-yl)-9 H-carbazol-9-yl}-6-phenyl-1,3,5-triazine (CC2TA) comprising the bicarbazole donor and phenyltriazine acceptor units, which is capable of emitting thermally activated delayed fluorescence. The molecular design of CC2TA allows spatial separation of HOMO and LUMO on the donor and acceptor fragments, respectively, leading to an exceptionally small singlet–triplet exchange energy (ΔEST = 0.06 eV) together with a high triplet energy. Furthermore, a high external electroluminescence quantum efficiency as high as 11% ± 1% has been achieved in the sky-blue organic light-emitting diodes employing CC2TA as an emitter.
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Wireless power transfer to a cardiac implant Appl. Phys. Lett. 101, 073701 (2012); http://dx.doi.org/10.1063/1.4745600 (4 pages) Online Publication Date: 13 August 2012
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We analyze wireless power transfer between a source and a weakly coupled implant on the heart. Numerical studies show that mid-field wireless powering achieves much higher power transfer efficiency than traditional inductively coupled systems. With proper system design, power sufficient to operate typical cardiac implants can be received by millimeter-sized coils.
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Anomalous temperature dependence of photoluminescence in self-assembled InGaN quantum dots Appl. Phys. Lett. 101, 131101 (2012); http://dx.doi.org/10.1063/1.4754533 (5 pages) Online Publication Date: 24 September 2012
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Self-assembled InGaN quantum dots (QDs) were fabricated by metal-organic chemical vapor deposition. Abnormal temperature dependence of photoluminescence (PL) was observed. The integrated PL intensity of QDs sample shows a dramatic increase in a temperature range from 160 K to 215 K and reaches the maximum value at 215 K instead of 10 K as usual. To interpret this phenomenon, a theoretic model of temperature induced carrier redistribution mechanism is designed using rate equation, which fits closely with the experimental result. It is concluded that carriers’ redistribution from shallow QDs or wetting layer to deep QDs gives rise to the unique behavior for InGaN QDs structure.
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Holographic microrefractometer Appl. Phys. Lett. 101, 091102 (2012); http://dx.doi.org/10.1063/1.4747168 (3 pages) Online Publication Date: 27 August 2012
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In-line holographic microscopy of micrometer-scale colloidal spheres yields heterodyne scattering patterns that may be interpreted with Lorenz-Mie theory to obtain precise time-resolved information on the refractive index of the suspending medium. We demonstrate this approach to spatially resolved refractometry with measurements on calibrated refractive index standards and use it to monitor chemical concentration in a microfluidic channel. Using commercially available colloidal spheres as probe particles and a standard video camera for detection yields values for the fluid’s refractive index at the position of each probe particle in each holographic snapshot with a demonstrated resolution of 2×10−3 refractive index units (RIU) and a potential resolution surpassing 10−4 RIU. The combination of spatial resolution, temporal resolution, multi-point in situ access, and technical simplicity recommends this technique for cost-effective lab-on-a-chip applications.
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Uniform and refreshable liquid electroluminescent device with a back side reservoir Appl. Phys. Lett. 101, 113302 (2012); http://dx.doi.org/10.1063/1.4749791 (4 pages) Online Publication Date: 10 September 2012
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We fabricated a refreshable organic light-emitting diode with a liquid emitting layer. This device has a mesh-structured cathode and a liquid reservoir in the back side of the cathode for easy convection of the liquid emitter. The small uniform gap between the electrodes was fabricated by means of micro-electro-mechanical systems (MEMS) processing. Although the device luminance decreased because of decomposition of the liquid emitters under the drive current, the decreased emission was quickly recovered to the initial state by convectional replacement of the decomposed emitters with fresh emitters through the holes of the mesh cathode.
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Organic electroluminescent diodes Appl. Phys. Lett. 51, 913 (1987); http://dx.doi.org/10.1063/1.98799 (3 pages)
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A novel electroluminescent device is constructed using organic materials as the emitting elements. The diode has a double‐layer structure of organic thin films, prepared by vapor deposition. Efficient injection of holes and electrons is provided from an indium‐tin‐oxide anode and an alloyed Mg:Ag cathode. Electron‐hole recombination and green electroluminescent emission are confined near the organic interface region. High external quantum efficiency (1% photon/electron), luminous efficiency (1.5 lm/W), and brightness (>1000 cd/m2) are achievable at a driving voltage below 10 V. |
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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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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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Degradation induced decrease of the radiative quantum efficiency in organic light-emitting diodes Appl. Phys. Lett. 101, 103301 (2012); http://dx.doi.org/10.1063/1.4749815 (4 pages) Online Publication Date: 4 September 2012
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The efficiency decrease during electrical operation of organic light-emitting diodes is a crucial issue for both applied and fundamental research. In order to investigate degradation processes, we have performed an efficiency analysis for phosphorescent state-of-the-art devices in the pristine state and after an accelerated aging process at high current density resulting in a luminance drop to less than 60% of the initial value. This loss in efficiency can be explained by a decrease of the radiative quantum efficiency of the light-emitting guest/host system from 70% to 40%, while other factors determining the efficiency are not affected.
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On-chip fabrication of ultrasensitive NO2 sensors based on silicon nanowires Appl. Phys. Lett. 101, 103101 (2012); http://dx.doi.org/10.1063/1.4748099 (5 pages) Online Publication Date: 4 September 2012
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We report a very simple, robust, and reliable on-chip fabrication method of a chemoresistive sensor based on silicon nanowires (NWs). Our method permits the use of nanowires without the need of their removal and transfer to a support different from the growth substrate. Our method, completely based on the silicon technology platform, exploits nanowires directly grown onto a selected area, over and between pre-patterned, interdigitated electrodes defined on oxidized silicon. The fabricated sensor is capable to detect NO2 down to a few ppb levels operating at room temperature. The sensor characteristics benefit of the presence of self-welded nanowires.
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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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Appl. Phys. Lett. 101, 121104 (2012); http://dx.doi.org/10.1063/1.4753926 (4 pages) Online Publication Date: 18 September 2012
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Ordered ZnO nanorods-based heterojunction light-emitting diodes (LEDs) have been fabricated by adopting few-layer graphene as a current spreading layer. The strong emission at low currents infers the high interfacial quality between GaN and ordered ZnO nanorods, and the current spreading effect resulting from graphene. The improved electroluminescence performance was achieved compared to the ZnO nanorods-based LED with a conventional indium-tin-oxide electrode, which can be attributed to the stable, reliable, and low resistance ohmic-contacts between graphene and ZnO nanorods, as well as the high transmittance of graphene. These results demonstrate feasibility of using graphene as electrodes for high-efficiency ZnO nanorods-based LEDs.
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Appl. Phys. Lett. 101, 113304 (2012); http://dx.doi.org/10.1063/1.4752445 (4 pages) Online Publication Date: 12 September 2012
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We demonstrate bilayer organic photovoltaic cells that incorporate a singlet exciton fission sensitizer layer to increase the external quantum efficiency (EQE). This solar cell architecture is realized by pairing the singlet exciton donor layer tris[4-(5-phenylthiophen-2-yl)phenyl]amine (TPTPA) with the singlet exciton fission layer 5,6,11,12-tetraphenylnaphthacene (rubrene). The presence of the rubrene layer at the donor-acceptor interface allows for a singlet generated in TPTPA to undergo singlet exciton fission with a corresponding doubling in the TPTPA EQE from 12.8% to 27.6%. This scheme de-couples singlet exciton fission from photon absorption, exciton diffusion, and charge transport for very high EQE organic photovoltaic cells.
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Appl. Phys. Lett. 101, 103304 (2012); http://dx.doi.org/10.1063/1.4750141 (4 pages) Online Publication Date: 5 September 2012
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Two different types of inverted top-emitting blue electrophosphorescent organic light-emitting diodes (OLEDs) are demonstrated that differ only in the choice of high electron mobility transport layers. The electron transport layer consists of either 1,3,5-tri(p-pyrid-3-yl-phenyl)benzene (TpPyPB) or 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene) (TmPyPB). Devices with TpPyPB exhibit a current efficacy of 5.1 cd/A at 1259 cd/m2. OLEDs with TmPyPB show higher performance with a current efficacy of 33.6 cd/A at 1126 cd/m2. The difference in performance of OLEDs with TmPyPB is due to a combination of TmPyPB's higher triplet energy that decreases exciton transfer to the ETL and altered charge balance.
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Impact of spectral broadening on plasmonic enhancement with metallic gratings Appl. Phys. Lett. 101, 121102 (2012); http://dx.doi.org/10.1063/1.4753806 (4 pages) Online Publication Date: 17 September 2012
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The Purcell factor (PF) of the propagating surface plasmon polariton (SPP) mode on metallic grating is evaluated with full integration formula of Fermi's golden rule, while both spontaneous emission linewidth of single quantum dot and the spectrum broadening of photonic density of state (DOS) due to the propagation loss of SPP mode are involved. It is found that the PF would be degraded by taking account of the emission linewidth. For emitters with narrow linewidth, the DOS broadening is dominant while it would be helpful to some degree for wide-linewidth emitters.
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