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Top 20 Most Read Articles
January 2011
The 20 articles with the most full-text downloads during the month, in descending order.
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The origin of oxygen in oxide thin films: Role of the substrate Appl. Phys. Lett. 97, 192107 (2010); http://dx.doi.org/10.1063/1.3515849 (3 pages) Online Publication Date: 11 November 2010
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During the growth of oxide thin films by pulsed laser deposition, a strong oxygen substrate-to-film transfer has been experimentally observed for SrTiO3 and LaAlO3 thin films epitaxially grown on 18O exchanged SrTiO3 and LaAlO3 substrates by secondary ion mass spectrometry depth profiling. This oxygen transfer effect can seriously change the respective thin film properties. Taking the oxygen substrate contribution to the overall oxygen balance into account, original ways to design material properties of oxide thin films can be envisioned like a controlled charge carrier doping of SrTiO3 thin films.
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High internal and external quantum efficiency InGaN/GaN solar cells Appl. Phys. Lett. 98, 021102 (2011); http://dx.doi.org/10.1063/1.3540501 (3 pages) Online Publication Date: 10 January 2011
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High internal and external quantum efficiency GaN/InGaN solar cells are demonstrated. The internal quantum efficiency was assessed through the combination of absorption and external quantum efficiency measurements. The measured internal quantum efficiency, as high as 97%, revealed an efficient conversion of absorbed photons into electrons and holes and an efficient transport of these carriers outside the device. Improved light incoupling into the solar cells was achieved by texturing the surface. A peak external quantum efficiency of 72%, a fill factor of 79%, a short-circuit current density of 1.06 mA/cm2, and an open circuit voltage of 1.89 V were achieved under 1 sun air-mass 1.5 global spectrum illumination conditions.
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Frost formation and ice adhesion on superhydrophobic surfaces Appl. Phys. Lett. 97, 234102 (2010); http://dx.doi.org/10.1063/1.3524513 (3 pages) Online Publication Date: 7 December 2010
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We study frost formation and its impact on icephobic properties of superhydrophobic surfaces. Using an environmental scanning electron microscope, we show that frost nucleation occurs indiscriminately on superhydrophobic textures without any particular spatial preference. Ice adhesion measurements on superhydrophobic surfaces susceptible to frost formation show increased adhesion over smooth surfaces with a strong linear trend with the total surface area. These studies indicate that frost formation significantly compromises the icephobic properties of superhydrophobic surfaces and poses serious limitations to the use of superhydrophobic surfaces as icephobic surface treatments for both on-ground and in-flight applications.
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Localization of surface plasmon polaritons in hexagonal arrays of Moiré cavities Appl. Phys. Lett. 98, 031101 (2011); http://dx.doi.org/10.1063/1.3529469 (3 pages) Online Publication Date: 18 January 2011
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In view of the progress on the confinement of light, we report on the dispersion characteristics of surface plasmon polaritons (SPPs) on two-dimensional Moiré surfaces in the visible part of the electromagnetic spectrum. Polarization dependent spectroscopic reflection measurements show omnidirectional confinement of SPPs. The resonance wavelength of SPP cavity modes can be adjusted by tuning the propagation direction of SPPs. The results may have an impact on the control of spontaneous emission and absorption with applications in light emitting diodes and solar cells, as well as in quantum electrodynamics experiments.
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Surface-plasmon-induced light absorption on a rough silver surface Appl. Phys. Lett. 98, 011109 (2011); http://dx.doi.org/10.1063/1.3537812 (3 pages) Online Publication Date: 5 January 2011
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We investigate light absorption in metal films, silver and aluminum, with different surface roughness. Measurements using an integrating sphere show that the reflectance in silver decreases significantly with increasing surface roughness whereas the reflectance in aluminum is almost constant. The experimental results agree well with numerical simulations in which the surface roughness of metal is described properly. In particular, the simulations demonstrate that the absorption by surface-plasmon-polaritons excited on a rough silver surface causes the surface-dependent reflectance in silver. This study suggests a convenient and feasible rule to rationally design a backside metal reflector toward high-efficiency light-emitting diodes and photovoltaics.
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Graphene synthesis by ion implantation Appl. Phys. Lett. 97, 183103 (2010); http://dx.doi.org/10.1063/1.3507287 (3 pages) Online Publication Date: 2 November 2010
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We demonstrate an ion implantation method for large-scale synthesis of high quality graphene films with controllable thickness. Thermally annealing polycrystalline nickel substrates that have been ion implanted with carbon atoms results in the surface growth of graphene films whose average thickness is controlled by implantation dose. The graphene film quality, as probed with Raman and electrical measurements, is comparable to previously reported synthesis methods. The implantation synthesis method can be generalized to a variety of metallic substrates and growth temperatures, since it does not require a decomposition of chemical precursors or a solvation of carbon into the substrate.
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Vertical cavity surface emitting laser action of an all monolithic ZnO-based microcavity Appl. Phys. Lett. 98, 011101 (2011); http://dx.doi.org/10.1063/1.3533800 (3 pages) Online Publication Date: 3 January 2011
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We report on room temperature laser action of an all monolithic ZnO-based vertical cavity surface emitting laser (VCSEL) under optical pumping. The VCSEL structure consists of a 2λ microcavity containing eight ZnO/Zn0.92Mg0.08O quantum wells embedded in epitaxially grown Zn0.92Mg0.08O/Zn0.65Mg0.35O distributed Bragg reflectors (DBRs). As a prerequisite, design and growth of high reflectivity DBRs based on ZnO and (Zn,Mg)O for optical devices operating in the ultraviolet and blue-green spectral ranges are discussed.
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Coupling of a surface plasmon with localized subwavelength microcavity modes Appl. Phys. Lett. 98, 021105 (2011); http://dx.doi.org/10.1063/1.3536504 (3 pages) Online Publication Date: 11 January 2011
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Midinfrared photonic modes of a periodically patterned metal-dielectric-metal structure have been investigated theoretically and experimentally. We have observed an anticrossing behavior between cavity modes localized in the double-metal regions and the surface plasmon polariton, signature of a hybridization between the two modes.
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Epitaxial growth and structural property of graphene on Pt(111) Appl. Phys. Lett. 98, 033101 (2011); http://dx.doi.org/10.1063/1.3543624 (3 pages) Online Publication Date: 18 January 2011
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We report on epitaxial growth of graphene on Pt(111) surface. It was found out that the proportion of different rotational domains varies with growth temperature and the graphene quality can be improved by adjusting both the growth temperature and ethylene exposure. Rippled and unrippled domains of high quality graphene are observed. The adhesive energy and electronic structure of two models, representing rippled and unrippled graphene, are obtained with density functional theory calculation, which shows that the interaction between graphene and Pt(111) surface is very weak and the electronic structure is nearly the same as that of a free standing graphene.
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Appl. Phys. Lett. 98, 023301 (2011); http://dx.doi.org/10.1063/1.3535603 (3 pages) Online Publication Date: 10 January 2011
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Organic solar cells were fabricated by inserting a thin rubrene fluorescent dye between pentacene and fullerene heterojunction with a multicharge separation (MCS) structure, which was adopted to inherently further improve maximum open circuit voltage and power conversion efficiency. The morphology of organic films showed that a more surface roughness of pentacene film could be beneficial for an effective MCS interface, exciton dissociation, and charge carrier transportation. Moreover, a slight improvement of short-circuit current density when adding a 1 or 2 nm rubrene layer was also analyzed in detail based on external quantum efficiency spectra and optical transfer matrix theory.
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Appl. Phys. Lett. 97, 261103 (2010); http://dx.doi.org/10.1063/1.3531753 (3 pages) Online Publication Date: 28 December 2010
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A graded-composition electron blocking layer (GEBL) with aluminum composition increasing along the [0001] direction was designed for c-plane InGaN/GaN light-emitting diodes (LEDs) by employing the band-engineering. The simulation results demonstrated that such GEBL can effectively enhance the capability of hole transportation across the EBL as well as the electron confinement. Consequently, the LED with GEBL grown by metal-organic chemical vapor deposition exhibited lower forward voltage and series resistance and much higher output power at high current density as compared to conventional LED. Meanwhile, the efficiency droop was reduced from 34% in conventional LED to only 4% from the maximum value at low injection current to 200 A/cm2.
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Appl. Phys. Lett. 97, 211111 (2010); http://dx.doi.org/10.1063/1.3518473 (3 pages) Online Publication Date: 24 November 2010
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We present the design and characterization of a single-photon avalanche diode (SPAD) fabricated with a standard 0.13 μm complementary metal-oxide-semiconductor process. We have developed a figure of merit for SPADs when these detectors are employed in high frame-rate fluorescent lifetime imaging microscopy, which allows us to specify an optimal bias point for the diode and compare our diode with other published devices. At its optimum bias point at room temperature, our SPAD achieves a photon detection probability of 29% while exhibiting a dark count rate of only 231 Hz and an impulse response of 198 ps.
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Appl. Phys. Lett. 98, 023303 (2011); http://dx.doi.org/10.1063/1.3541648 (3 pages) Online Publication Date: 11 January 2011
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A desirable vertical phase separation of a bulk-heterojunction was achieved by inserting a P3HT layer between the blend layer and the poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) layer. According to the high (PEDOT:PSS) and low (P3HT) surface energies of substrate, it might be possible to modulate the vertical phase separation in the bulk-heterojunction. The result of vertical phase separation was determined using time-of-flight secondary-ion mass spectroscopy analysis. A controlled thickness of 50 nm for the inserted P3HT layer prevented undesirable light absorption and the power conversion efficiency of this condition was increased by 44% compared to that of a reference device.
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Appl. Phys. Lett. 97, 201112 (2010); http://dx.doi.org/10.1063/1.3520139 (3 pages) Online Publication Date: 19 November 2010
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Two light-emitting diode samples are grown with InGaN and GaN underlying layers beneath the multiple quantum wells (MQWs), respectively. By measuring the carrier lifetime as a function of photon energy, it is found that the MQW with InGaN underlying layer has a higher degree of carrier localization. Comparison between the external quantum efficiency and injection current of these two samples reveals that efficiency droop at small injection current is attributed to the delocalization of carriers, while further droop at a higher injection current is due mostly to the carrier leakage demonstrated through temperature-dependent electroluminescence measurements.
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Design of subwavelength superscattering nanospheres Appl. Phys. Lett. 98, 043101 (2011); http://dx.doi.org/10.1063/1.3536475 (3 pages) Online Publication Date: 24 January 2011
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We design a subwavelength superscattering nanosphere with plasmonic-dielectric-plasmonic layer structure. We show that the scattering cross section of such a particle can be significantly enhanced by employing multiple resonances with different total angular momenta, and by ensuring that all these resonances have almost the same frequency and operate in the overcoupling region.
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Angular constraint on light-trapping absorption enhancement in solar cells Appl. Phys. Lett. 98, 011106 (2011); http://dx.doi.org/10.1063/1.3532099 (3 pages) Online Publication Date: 4 January 2011
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Light trapping for solar cells can reduce production cost and improve energy conversion efficiency. Understanding some of the basic theoretical constraints on light trapping is therefore of fundamental importance. Here, we develop a general angular constraint on the absorption enhancement in light trapping. We show that there is an upper limit for the angular integration of absorption enhancement factors. This limit is determined by the number of accessible resonances supported by an absorber.
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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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Kerr detection of acoustic spin transport in GaAs (110) quantum wells Appl. Phys. Lett. 97, 242110 (2010); http://dx.doi.org/10.1063/1.3524218 (3 pages) Online Publication Date: 16 December 2010
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Time-resolved Kerr reflectometry (TRKR) is used to investigate the long-range transport of spins by surface acoustic waves in undoped GaAs (110) quantum wells. TRKR measurements under an applied magnetic field demonstrate the coherent precession of the optically generated electron spin during acoustic transport over several micrometers and yield information about the relaxation processes for moving spins.
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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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Graphene quantum dots embedded in hexagonal boron nitride sheets Appl. Phys. Lett. 98, 013105 (2011); http://dx.doi.org/10.1063/1.3533804 (3 pages) Online Publication Date: 5 January 2011
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We have carried out first-principles calculations on electronic properties of graphene quantum dots embedded in hexagonal boron nitride monolayer sheets. The calculations with density functional theory show that the band gaps of quantum dots are determined by the quantum confinement effects and the hybridization of π orbitals from B, N, and C atoms. The energy states near the Fermi level are found to be strongly localized within and in the vicinity of the quantum dots.
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