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Top 20 Most Read Articles
April 2009
The 20 articles with the most full-text downloads during the month, in descending order.
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Semiconductor lasers with integrated plasmonic polarizers Appl. Phys. Lett. 94, 151101 (2009); http://dx.doi.org/10.1063/1.3093476 (3 pages) Online Publication Date: 13 April 2009
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The authors reported the plasmonic control of semiconductor laser polarization by means of metallic gratings and subwavelength apertures patterned on the laser emission facet. An integrated plasmonic polarizer can project the polarization of a semiconductor laser onto other directions. By designing a facet with two orthogonal grating-aperture structures, a polarization state consisting of a superposition of a linearly and right-circularly polarized light was demonstrated in a quantum cascade laser; a first step toward a circularly polarized laser.
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Optical properties of rolled-up tubular microcavities from shaped nanomembranes Appl. Phys. Lett. 94, 141901 (2009); http://dx.doi.org/10.1063/1.3111813 (3 pages) Online Publication Date: 6 April 2009
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Tubular optical microcavities have been fabricated by releasing prestressed SiO/SiO2 bilayer nanomembranes from polymer sacrificial layers, and their geometrical structure is well controlled by defining the shape of nanomembranes via photolithography. Optical measurements at room temperature demonstrate that resonant modes of microtubular cavities rolled up from circular shapes can be tuned in peak energy and relative intensity along the tube axes compared to those from square patterns. The resonant modes shift to higher energy with decreasing number of tube wall rotations and thickness, which fits well to finite-difference time-domain simulations. Polarization resolved measurements of the resonant modes indicate that their polarization axes are parallel to the tube axis, independent of the polarization of the excitation laser.
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Counting graphene layers on glass via optical reflection microscopy Appl. Phys. Lett. 94, 143101 (2009); http://dx.doi.org/10.1063/1.3115026 (3 pages) Online Publication Date: 6 April 2009
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We show that optical reflection microscopy is a reliable method to simultaneously locate and count graphene layers deposited on bulk, transparent substrates such as soda-lime glass. The visible contrast in optical reflection versus graphene layer number is resolvable on bulk substrates. A simple Fresnel theory based on the universal optical conductance of graphene layers accurately models optical reflection images taken at a wavelength of 550±5 nm. We directly count one to nine layers of graphene using reflection microscopy.
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Giant enhancement of top emission from ZnO thin film by nanopatterned Pt Appl. Phys. Lett. 94, 151102 (2009); http://dx.doi.org/10.1063/1.3116617 (3 pages) Online Publication Date: 13 April 2009
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The authors report the enhancement of the bandgap emission from ZnO thin films by surface modification and surface plasmon cross-coupling. 12-fold and twofold enhancements of bandgap emission from the metal side of ZnO film were observed by sputtering Pt nanopattern and Pt film onto ZnO film, respectively. Time-resolved photoluminescence indicates that the decay time is slowed down by Pt capping, contrary to common observations. The “abnormal” phenomena are interpreted by considering both the surface modification and surface plasmon coupling.
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Near-field imaging of coupled photonic-crystal microcavities Appl. Phys. Lett. 94, 151103 (2009); http://dx.doi.org/10.1063/1.3107269 (3 pages) Online Publication Date: 14 April 2009
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We report by means of near-field microscopy on the coupling between two adjacent photonic crystal microcavities. Clear-cut experimental evidence of the spatial delocalization of coupled-cavity optical modes is obtained by imaging the electromagnetic local density of states. We also demonstrate that it is possible to design photonic structures with selective coupling between different modes having orthogonal spatial extensions
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A subwavelength near-infrared negative index material Appl. Phys. Lett. 94, 131107 (2009); http://dx.doi.org/10.1063/1.3110957 (3 pages) Online Publication Date: 2 April 2009
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A single layer of a subwavelength negative index material (NIM) operating at a wavelength of 1 μm is demonstrated. The geometrical parameters of the nanostructure are determined by characterizing its optical transmission spectrum. We show through photonic band calculations that these parameters give rise to a negative index in a corresponding bulk NIM. The fabrication inaccuracies in the dielectric spacer thickness that are likely to be introduced in a prism composed of multiple layers of this structure are shown through full-wave simulations to be within a range that preserves its negative refractive behavior.
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Scanning tunneling microscopy on epitaxial bilayer graphene on ruthenium (0001) Appl. Phys. Lett. 94, 133101 (2009); http://dx.doi.org/10.1063/1.3106057 (3 pages) Online Publication Date: 30 March 2009
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The atomic structure of epitaxial single and bilayer graphene on Ru(0001) was studied by scanning tunneling microscopy (STM). High-resolution imaging of the surface of single layer graphene shows a moiré with pronounced buckling and broken A/B carbon sublayer symmetry due to a strong interaction with the metal substrate. The top sheet of bilayer graphene is largely unperturbed by residual interactions with the substrate. Screened from the metal substrate, it shows the hallmarks of freestanding monolayer graphene: a honeycomb structure with equivalent carbon sublattices imaged in STM and a linear dispersion of π-bands near the Dirac point.
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Scalable implementation of strongly coupled cavity-quantum dot devices Appl. Phys. Lett. 94, 121102 (2009); http://dx.doi.org/10.1063/1.3100781 (3 pages) Online Publication Date: 23 March 2009
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Using low temperature in situ optical lithography, we fabricate pillar microcavities with quality factors around 2×104. Each pillar embeds a spatially and spectrally resonant single InGaAs quantum dot (QD). Light-matter strong coupling regime is reached for 100% of the fabricated pillars for which the resonance can be tuned through temperature. This is a demonstration of scalable and deterministic implementation of strongly coupled cavity-QD devices.
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Magnetism and band gap narrowing in Cu-doped ZnO Appl. Phys. Lett. 94, 142502 (2009); http://dx.doi.org/10.1063/1.3112603 (3 pages) Online Publication Date: 6 April 2009
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First-principles calculations based on density functional theory are performed to study the magnetic, electronic, and optical properties of ZnO doped with 6.25%, 12.5%, and 18.75% of Cu. The Cu dopants are found spin polarized, and a net magnetic moment of 0.57μB is found for Cu at a composition of 6.25%. The calculations confirm an appreciable band gap reduction in ZnO in agreement with recent experimental results. The analysis of the partial density of states reveals that ferromagnetism and narrowing of ZnO band gap are due principally to the strong p-d mixing of O and Cu.
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Appl. Phys. Lett. 94, 132505 (2009); http://dx.doi.org/10.1063/1.3110963 (3 pages) Online Publication Date: 2 April 2009
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We report on the electrical field control of ferromagnetism (FM) at room temperature in III-N dilute magnetic semiconductor (DMS) films. A GaMnN layer was grown on top of an n-GaN substrate and found to be almost always paramagnetic. However, when grown on a p-type GaN layer, a strong saturation magnetization (Ms) was observed. This FM in GaMnN can be controlled by depletion of the holes in the GaMnN/p-GaN/n-GaN multilayer structures. We have demonstrated the dependence of the FM on the thickness of the p-GaN in this heterostructure and on the applied bias to the GaN p-n junction. The Ms was measured by an alternating gradient magnetometer (AGM) and a strong correlation between the hole concentration near the GaMnN/p-GaN interface and the magnetic properties of the DMS was observed. At room temperature an anomalous Hall effect was measured for zero bias and an ordinary Hall effect for reverse bias in a fully depleted p-GaN layer. This is in close agreement with the AGM measurement results.
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High output power density from GaN-based two-dimensional nanorod light-emitting diode arrays Appl. Phys. Lett. 94, 141111 (2009); http://dx.doi.org/10.1063/1.3119192 (3 pages) Online Publication Date: 10 April 2009
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Here we propose and realize a scheme for making a direct contact to a two-dimensional nanorod light-emitting diode (LED) array using the oblique-angle deposition approach. And, more importantly, we demonstrate highly efficient electrical carrier injection into the nanorods. As a result, we show that at a 20 mA dc current injection, the light output power density of our nanorod LED array is 3700 mW cm−2. More general, this contact scheme will pave the ways for making direct contacts to other kinds of nanoscale optoelectronic devices.
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Low voltage efficient simple p-i-n type electrophosphorescent green organic light-emitting devices Appl. Phys. Lett. 94, 133303 (2009); http://dx.doi.org/10.1063/1.3114378 (3 pages) Online Publication Date: 2 April 2009
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We present simple p-i-n structures with double-emitting and mixed-emitting layers for highly efficient phosphorescent green devices. Using a wide band-gap hole transporting material of 4,4′4″-tris(N-carbazolyl)-triphenylamine and a wide band-gap electron transporting material of bis[2-(2-hydroxyphenyl)-pyridine]beryllium, the bilayered p-i-n structure with no heterointerface barriers has been realized. A very low onset voltage value of 2.4 V corresponding to the energy of 2.4 eV of green electroluminescence, which is close to the photon energy of dopant emitting molecules (2.3–2.4 eV), is achieved in this simple p-i-n device configuration. Maximum current- and power-efficiency values of 53.3 cd/A and 61.4 lm/W and low rolloff of current efficiency (6%) are demonstrated in the simple p-i-n green phosphorescent devices, promising for the practical and economical high brightness applications.
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Poly(3-hexylthiophene)/ZnO hybrid pn junctions for microelectronics applications Appl. Phys. Lett. 94, 143501 (2009); http://dx.doi.org/10.1063/1.3114442 (3 pages) Online Publication Date: 6 April 2009
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Hybrid poly(3-hexylthiophene)/ZnO devices are investigated as rectifying heterojunctions for microelectronics applications. A low-temperature atomic layer deposition of ZnO on top of poly(3-hexylthiophene) allows the fabrication of diodes featuring a rectification ratio of nearly 105 at ±4 V and a current density of 104 A/cm2. Electrical characteristics are discussed taking into account the chemical structure of the stack and the energy band diagram.
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Vertical coupling between short range surface plasmon polariton mode and dielectric waveguide mode Appl. Phys. Lett. 94, 141104 (2009); http://dx.doi.org/10.1063/1.3111001 (3 pages) Online Publication Date: 7 April 2009
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Coupling performance between a short range surface plasmon polariton (SRSPP) mode and a conventional dielectric waveguide mode is demonstrated numerically. Simulation results show that the coupling length, as short as tens of microns, can be realized because the field of SRSPP extremely concentrates to the metal surface. SRSPP-based hybrid coupler provides not only an approach to realize highly compact functional devices, such as the TE-pass polarizer with high performance, but also an integratable route for efficiently exciting SRSPP mode, which is very useful in the SRSPP-based biosensor or SRSPP-assisted emission enhancement devices.
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Generation and transport of photoexcited electrons in single-crystal diamond Appl. Phys. Lett. 94, 152102 (2009); http://dx.doi.org/10.1063/1.3120225 (3 pages) Online Publication Date: 15 April 2009
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We report time-dependent photocurrent and transport measurements of sub-bandgap photoexcited carriers in nitrogen-rich (type Ib), single-crystal diamond. Transient carrier dynamics are characteristic of trapping conduction with long charge storage lifetimes of ∼ 3 hours. By measuring the photoexcited Hall effect, we confirm that the charge carriers are electrons and by varying the excitation energy we observe a strong turn-on in the photoconduction at ∼ 1.9 eV. These findings shed light on sub-bandgap states in nitrogen-doped single-crystal diamond.
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Plasmonic Bloch oscillations in chirped metal-dielectric structures Appl. Phys. Lett. 94, 161105 (2009); http://dx.doi.org/10.1063/1.3119666 (3 pages) Online Publication Date: 21 April 2009
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We study the propagation of plasmon polaritons in one-dimensional chirped metal-dielectric layered structures. We find an optical Wannier–Stark ladder in the mode spectrum and analyze Bloch oscillations associated with the coupling of surface plasmons localized at the metal-dielectric interfaces. For long structures, we find that the energy flow may dramatically change its direction, thus providing possibilities for the beam steering in the transmission band.
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Electrically pumped quantum post vertical cavity surface emitting lasers Appl. Phys. Lett. 94, 131104 (2009); http://dx.doi.org/10.1063/1.3112578 (3 pages) Online Publication Date: 1 April 2009
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We demonstrate low threshold electrically pumped lasing in oxide apertured vertical cavity surface emitting lasers with quantum posts (QPs) as the active medium. A lasing threshold current as low as 12 μA is achieved at 7 K and room temperature continuous wave lasing is also demonstrated in the cavities with quality factors of ∼ 10 000. At low temperature, the QP devices show remarkably lower lasing current thresholds compared to equivalent quantum dot devices.
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Appl. Phys. Lett. 94, 133302 (2009); http://dx.doi.org/10.1063/1.3110969 (3 pages) Online Publication Date: 1 April 2009
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We demonstrate a relative improvement in power conversion efficiency of polymer nanocomposite photovoltaic cells consisting of poly(3-hexylthiophene) (P3HT) functionalized CdSe nanocrystals. Thermal deprotection processing of the tert-buthoxycarbonyl moiety in the carbamate ligand surrounding the surface of CdSe nanocrystal significantly shortened the length of the ligand between nanocrystals and between the nanocrystal and the polymer matrix. The resulting device performance was investigated as a function of the composition ratio of P3HT/CdSe and the heating temperature. This simple and straightforward ligand deprotection strategy resulted in a significant increase in current density due to improvement of charge transport between the constituent materials.
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Crystal structure and optical properties of silver nanorings Appl. Phys. Lett. 94, 153102 (2009); http://dx.doi.org/10.1063/1.3117504 (3 pages) Online Publication Date: 14 April 2009
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We report the polyol synthesis and crystal structure characterization of silver nanorings, which have perfect circular shape, smooth surface, and elliptical wire cross-section. The characterization results show that the silver nanorings have well-defined crystal of singly twinned along the whole ring. The spatial distribution of the scattering of a silver nanoring with slanted incidence reveals the unique focus effect of the nanoring, and the focus scattering varies with the incident wavelength. The silver nanorings with perfect geometry and well-defined crystal have potential applications in nanoscaled photonics, plasmonic devices, and optical manipulation.
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Appl. Phys. Lett. 94, 143302 (2009); http://dx.doi.org/10.1063/1.3114379 (3 pages) Online Publication Date: 6 April 2009
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We demonstrate a cascade-energy-level alignment based organic photovoltaic cell by using stacking three materials with appropriate energy levels. A cell with a structure of ITO/4,4′,4″-tris[N,(3-methylphenyl)-N-phenylamino]-triphenylamine (m-MTDATA)/copper phthalocyanine (CuPc)/fullerene (C60)/4,4′-N,N′-dicarubreneazolebiphenyl (BCP)/LiF/Al was shown to have a power efficiency enhancement in more than 30% over that of a standard reference cell (ITO/CuPc/C60/BCP/LiF/Al), which has only one exciton-dissociation interface. The efficiency improvement was mainly ascribed to the ingenious cascade-energy-level alignment and the application of the bipolar carrier transporting property.
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