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Top 20 Most Read Articles
September 2010
The 20 articles with the most full-text downloads during the month, in descending order.
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A morphotropic phase boundary system based on polarization rotation and polarization extension Appl. Phys. Lett. 97, 062906 (2010); http://dx.doi.org/10.1063/1.3479479 (3 pages) Online Publication Date: 10 August 2010
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Many ferroelectric solid solutions exhibit enhanced electromechanical properties at the morphotropic boundary separating two phases with different orientations of polarization. The mechanism of properties enhancement is associated with easy paths for polarization rotation in anisotropically flattened free energy profile. Another mechanism of properties enhancement related to free energy flattening is polarization extension. It is best known at temperature-driven ferroelectric-paraelectric phase transitions and may lead to exceedingly large properties. Its disadvantage is temperature instability of the enhancement. In this paper a temperature-composition phase diagram is proposed that exhibits compositionally driven-phase transitions with easy paths for both polarization rotation and polarization extension.
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Strongly coupled single quantum dot in a photonic crystal waveguide cavity Appl. Phys. Lett. 97, 111101 (2010); http://dx.doi.org/10.1063/1.3487937 (3 pages) Online Publication Date: 13 September 2010
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Cavities embedded in photonic crystal waveguides offer a promising route toward large scale integration of coupled resonators for quantum electrodynamics applications. In this letter, we demonstrate a strongly coupled system formed by a single quantum dot and such a photonic crystal cavity. The resonance originating from the cavity is clearly identified from the photoluminescence mapping of the out-of-plane scattered signal along the photonic crystal waveguide. The quantum dot exciton is tuned toward the cavity mode by temperature control. A vacuum Rabi splitting of ∼ 140 μeV is observed at resonance.
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A frequency-addressed plasmonic switch based on dual-frequency liquid crystals Appl. Phys. Lett. 97, 091101 (2010); http://dx.doi.org/10.1063/1.3483156 (3 pages) Online Publication Date: 30 August 2010
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A frequency-addressed plasmonic switch was demonstrated by embedding a uniform gold nanodisk array into dual-frequency liquid crystals (DFLCs). The optical properties of the hybrid system were characterized by extinction spectra of localized surface plasmon resonances (LSPRs). The LSPR peak was tuned using a frequency-dependent electric field. A ∼ 4 nm blueshift was observed for frequencies below 15 kHz, and a 23 nm redshift was observed for frequencies above 15 kHz. The switching time for the system was ∼ 40 ms. This DFLC-based active plasmonic system demonstrates an excellent, reversible, frequency-dependent switching behavior and could be used in future integrated nanophotonic circuits.
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Appl. Phys. Lett. 84, 3459 (2004); http://dx.doi.org/10.1063/1.1737072 (3 pages) Online Publication Date: 20 April 2004
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Electroluminescent devices combining two families of PbS colloidal quantum dots to achieve spectrally tailored two-color emission are reported. Depending on device structure selected—the use of two separated layers versus a mixture of nanocrystals—the structures demonstrated light emission either in two infrared frequency peaks corresponding to the spectral region 1.1–1.6 μm or in a wide band spanning this same spectral region. Separated-layer devices exhibit wide tunability in the relative intensity of the two peaks by varying excitation conditions. Replacing oleate with octodecylamine ligands increases the internal electroluminescence efficiency to 3.1%. © 2004 American Institute of Physics. |
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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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Can silicon behave like graphene? A first-principles study Appl. Phys. Lett. 97, 112106 (2010); http://dx.doi.org/10.1063/1.3489937 (3 pages) Online Publication Date: 15 September 2010
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The electronic properties of two-dimensional hexagonal silicon (silicene) are investigated using first-principles simulations. Though silicene is predicted to be a gapless semiconductor, due to the sp2-hybridization of its atomic orbitals, the weak overlapping between 3pz orbitals of neighbor Si atoms leads to a very reactive surface, resulting in a more energetically stable semiconducting surface upon the adsorption of foreign chemical species. It is predicted that silicene inserted into a graphitelike lattice, like ultrathin AlN stacks, preserves its sp2-hydridization, and hence its graphenelike electronic properties.
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Are Al2O3 and MgO tunnel barriers suitable for spin injection in graphene? Appl. Phys. Lett. 97, 092502 (2010); http://dx.doi.org/10.1063/1.3476339 (3 pages) Online Publication Date: 31 August 2010
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We report on the structural impact on graphene and multi-layers graphene of the growth by sputtering of tunnel barriers. Sputtered Al2O3 and MgO barriers were chosen for their well-known efficiency as spin injectors in spintronics devices. The impact of the growth on the structure of graphene and up to 4-layer flakes was analyzed by Raman spectroscopy. This study reveals that for Al2O3 growth, the impact is moderate for a monolayer and decreases sharply for bilayers and above. In the case of MgO all the flakes underwent a strong amorphization. Moreover, this reveals that while single layer graphene is believed to offer the best spin transport properties, the better robustness of multilayer graphene may ultimately make it a better choice for spintronics devices.
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Appl. Phys. Lett. 97, 091102 (2010); http://dx.doi.org/10.1063/1.3485064 (3 pages) Online Publication Date: 30 August 2010
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The authors report on high transverse magnetic (TM)-mode responsivity in a waveguided germanium Schottky-barrier metal-semiconductor-metal photodetector on silicon-on-insulator substrate for operating wavelength at 1550 nm. The employed aluminum interdigitated electrodes act as a one-dimensional rectangular grating above the depletion layer. By means of properly designed finger dimensions, surface plasmon polariton resonances can be excited at the interface of metal and silicon interfacial layer due to grating coupling. The resulting strong field intensities reach into active region, enabling high absorption under TM injection. At a voltage of 1 V, the TM-mode photocurrent is measured over three times than that of transverse electric mode, in spite of the relatively larger TM insertion loss in the silicon waveguide.
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Electromechanical probing of ionic currents in energy storage materials Appl. Phys. Lett. 96, 222906 (2010); http://dx.doi.org/10.1063/1.3446838 (3 pages) Online Publication Date: 4 June 2010
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The electrochemical processes in energy storage materials are generally linked with changes of molar volume of the host compound. Here, the frequency dependent strain response of one-dimensional electrochemically active system to periodic electric bias is analyzed. The sensitivity and resolution of electrochemical strain measurements are compared to the current-based electrochemical impedance spectroscopy. The resolution and detection limits of interferometric and atomic force microscopy based systems for probing electrochemical reactions on the nanoscale are analyzed.
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Optical constants of graphene measured by spectroscopic ellipsometry Appl. Phys. Lett. 97, 091904 (2010); http://dx.doi.org/10.1063/1.3475393 (3 pages) Online Publication Date: 31 August 2010
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A mechanically exfoliated graphene flake ( ∼ 150×380 μm2) on a silicon wafer with 98 nm silicon dioxide on top was scanned with a spectroscopic ellipsometer with a focused spot ( ∼ 100×55 μm2) at an angle of 55°. The spectroscopic ellipsometric data were analyzed with an optical model in which the optical constants were parameterized by B-splines. This parameterization is the key for the simultaneous accurate determination of the optical constants in the wavelength range 210–1000 nm and the thickness of graphene, which was found to be 3.4 Å.
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Appl. Phys. Lett. 97, 093301 (2010); http://dx.doi.org/10.1063/1.3486180 (3 pages) Online Publication Date: 1 September 2010
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This paper presents the effects of the work function of an indium tin oxide (ITO) gate electrode on the electrical characteristics of two pentacene-based field-effect devices—metal-insulator-semiconductor (MIS) capacitors and field-effect transistors (FETs). The ITO work function was varied by employing base and acid treatments. Flat-band voltage shifts of the MIS capacitors were found to result from the shift in the work function. The current onset and threshold voltage of the FETs were also found to be influenced by the work function. These results demonstrate the correlation of the flat-band conditions of pentacene-based field-effect devices with the gate electrode work function.
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InGaN/GaN nanorod array white light-emitting diode Appl. Phys. Lett. 97, 073101 (2010); http://dx.doi.org/10.1063/1.3478515 (3 pages) Online Publication Date: 16 August 2010
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Conventional InGaN/GaN light-emitting diodes based on planar quantum well structures do not allow for efficient long-wavelength operation beyond the blue region due to a strong quantum confined Stark effect in lattice-mismatched polar InGaN quantum wells. Here we overcome the limitation by using self-assembled GaN nanorod arrays as strain-free growth templates for thick InGaN nanodisks. In combination with enhanced carrier localization and high crystalline quality, this approach allows us to realize full-color InGaN nanodisk emitters. By tailoring the numbers, positions, and thicknesses of polychromatic nanodisk ensembles embedded vertically in the GaN nanorod p-n junction, we are able to demonstrate natural white (color temperature ∼ 6000 K) electroluminescence from InGaN/GaN nanorod arrays.
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Analytical technique for subwavelength far field imaging Appl. Phys. Lett. 97, 101103 (2010); http://dx.doi.org/10.1063/1.3487779 (3 pages) Online Publication Date: 7 September 2010
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We develop an analytical technique for retrieving the size and shape of subwavelength objects using far-field measurements. The approach relies on subwavelength diffraction gratings scattering evanescent information into the far field along with a numerical algorithm that is capable of deconvoluting this information based on the far-field intensity measurements. Several examples are presented, demonstrating resolution on the order of λ0/20. The developed method can be used at any frequency range, and may become a practical alternative to scanning near-field microscopy.
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Polarization dependent two-photon properties in an organic crystal Appl. Phys. Lett. 97, 101101 (2010); http://dx.doi.org/10.1063/1.3486683 (3 pages) Online Publication Date: 7 September 2010
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The dependence of the fluorescence on the excitation beam polarization under two-photon excitation was studied in a 1,4-bis(R-cyano-4-diphenylaminostyryl)-2,5-diphenylbenzene organic crystal. The crystal shows strong response to the polarization, especially when the pump intensity was increased. The polarization plays an important role on the threshold of amplified spontaneous emission (ASE) and the ΔGASE under two-photon excitation (TPE). Moreover, the polarization distribution between the TPE (800 nm) and one-photon excitation (400 nm) are very different. The former generates a cos4 θ distribution, while the later gives rise to cos2 θ distribution in different orientation.
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Appl. Phys. Lett. 97, 092103 (2010); http://dx.doi.org/10.1063/1.3484152 (3 pages) Online Publication Date: 31 August 2010
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We report on the formation of low-resistance Ohmic contacts to N-face n-GaN for high-power vertical light-emitting diodes using an Al–Ga solid solution (50 nm)/Ti(30 nm)/Al(200 nm) scheme and compare them with Ti(30 nm)/Al(200 nm) contacts. The Al–Ga solid solution layer is introduced to minimize the formation of Ga vacancies near the N-face n-GaN surface. It is shown that, unlike the Ti/Al contacts, the Al–Ga solid solution/Ti/Al contacts exhibit Ohmic behavior with a resistivity of 4.1×10−4 Ω cm2, even after annealing at 250 °C. X-ray photoemission spectroscopy and secondary ion mass spectrometry examinations are performed to understand the temperature dependence of the electrical properties.
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Detection of bio-organism simulants using random binding on a defect-free photonic crystal Appl. Phys. Lett. 97, 113701 (2010); http://dx.doi.org/10.1063/1.3487998 (3 pages) Online Publication Date: 13 September 2010
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The defect-free photonic crystal (PC) slab geometry was explored for size-selective detection of bio-organism simulants. Through feedback between finite-difference time-domain simulations and experiments, we generated a conservative limit of detection estimate for randomized pore filling of a two-dimensional PC slab, and predict that random binding affords the label-free PC-based optical detection of low numbers (of the order of 10) of biological particles.
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Biologically inspired humidity sensor based on three-dimensional photonic crystals Appl. Phys. Lett. 97, 103701 (2010); http://dx.doi.org/10.1063/1.3486115 (3 pages) Online Publication Date: 7 September 2010
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This letter presents a biomimetic humidity sensor inspired by the humidity-dependent color change observed in the cuticle of the Hercules beetle. A thin-film-type humidity sensor with nanoporous structures (three-dimensional photonic crystals) mimicking the spongy multilayer in the beetles was designed and fabricated using the colloidal templating method and a hydrophilic surface treatment. The visible color of the fabricated humidity sensor changes from blue-green to red as the environmental humidity increases. The wavelength of reflected light that is predicted by Bragg’s equation considering the effect of water absorption shows a good agreement with experimental results.
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Appl. Phys. Lett. 97, 101901 (2010); http://dx.doi.org/10.1063/1.3485084 (3 pages) Online Publication Date: 7 September 2010
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We observe iridescence in the form of spectrally dispersed white light reflected from the structured sidewalls of vertically aligned carbon nanotube forests. The iridescence is a result of diffraction from a self-assembled periodic rippling pattern on the forest sidewalls that acts as a reflection grating. We measure the grating spacing via white light and laser diffraction experiments and see good agreement with the spacing of the rippling pattern as measured via scanning electron microscopy. The periodic rippling pattern self-assembles during chemical vapor deposition growth of the forests.
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Appl. Phys. Lett. 97, 093110 (2010); http://dx.doi.org/10.1063/1.3488001 (3 pages) Online Publication Date: 3 September 2010
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In this study, we demonstrate GaN light-emitting diodes (LEDs) with antireflective subwavelength structures (SWS) for enhanced light extraction efficiency. To eliminate the internal Fresnel reflection, SWS were fabricated on an indium-tin-oxide (ITO) surface using an overall dry etch process of Ag nanoparticles. The average size of the Ag nanoparticles was carefully chosen by theoretical calculation of the reflective diffraction efficiency using a rigorous coupled-wave analysis (RCWA) method. Improvement in light output power of ∼ 30.2% was achieved for the fabricated ITO SWS LEDs compared to conventional LEDs, with no significant increase in the forward voltage.
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