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Top 20 Most Read Articles
September 2006
The 20 articles with the most full-text downloads during the month, in descending order.
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Appl. Phys. Lett. 89, 093120 (2006); http://dx.doi.org/10.1063/1.2339286 (3 pages) Online Publication Date: 31 August 2006
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The authors have demonstrated a surface plasmon device composed of a resonant optical antenna integrated on the facet of a commercial diode laser, termed a plasmonic laser antenna. This device generates enhanced and spatially confined optical near fields. Spot sizes of a few tens of nanometers have been measured at a wavelength ∼ 0.8 μm. This device can be implemented in a wide variety of semiconductor lasers emitting in spectral regions ranging from the visible to the far infrared, including quantum cascade lasers. It is potentially useful in many applications including near-field optical microscopes, optical data storage, and heat-assisted magnetic recording.
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Plasmonic coupling between a metallic nanosphere and a thin metallic wire Appl. Phys. Lett. 89, 103101 (2006); http://dx.doi.org/10.1063/1.2345352 (3 pages) Online Publication Date: 5 September 2006
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Using the plasmon hybridization method the authors examine light-induced coupling between the localized plasmons of a metallic nanosphere and the propagating plasmons of an infinite metallic wire. The plasmon resonances of the coupled system are found to be shifted in frequency relative to the plasmonic structure of the isolated nanoparticles. The magnitude of the shifts depends on the polarization of the incident light and the system geometry. In the limit of a thin wire, it is shown that the nanosphere can serve as an efficient nanoantenna which can couple incident electromagnetic radiation into low-energy propagating wire plasmons.
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Fairly pure ultraviolet electroluminescence from ZnO-based light-emitting devices Appl. Phys. Lett. 89, 111112 (2006); http://dx.doi.org/10.1063/1.2352722 (3 pages) Online Publication Date: 13 September 2006
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Fairly pure ultraviolet (UV) electroluminescence (EL) was realized on a ZnO-based metal-insulator (SiOx,x ⩽ 2)-semiconductor structure on a silicon substrate, which was easily fabricated by the reactive direct current sputtering and electron beam evaporation. The UV EL originated from the near-band-edge (NBE) emission of ZnO was achieved at room temperature when the device was under sufficient forward bias with the negative voltage applied on the silicon substrate. Moreover, the intermediate SiOx layer should be thick enough to confine the electrons in the conduction band of ZnO beneath the ZnO/SiOx interface, which is critical for generation of NBE emission from ZnO.
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Pressure-induced structural transformations in cadmium selenide nanorods Appl. Phys. Lett. 89, 093101 (2006); http://dx.doi.org/10.1063/1.2338808 (3 pages) Online Publication Date: 28 August 2006
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Pressure induced structural transformations in cadmium selenide (CdSe) nanorods are studied using parallel molecular dynamics. Nanorods (4.4 nm in diameter and 4.4 to 53 nm in length) are embedded in a liquid and subjected to pressure. Reversible structural transformations are observed from wurtzite to a single domain rocksalt crystal phase. The simulation results reveal a decrease in transformation pressure with rod length. The transformation mechanism involves atomic shifts within the (0001) plane of the wurtzite structure and is similar to the one observed in electronic structure calculations of pressure-induced structural transformation in bulk CdSe.
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Coupled-cavity two-dimensional photonic crystal waveguide ring laser Appl. Phys. Lett. 89, 101102 (2006); http://dx.doi.org/10.1063/1.2345374 (3 pages) Online Publication Date: 5 September 2006
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Coupled-cavity hexagonal ringlike photonic crystal lasers are fabricated as a class of single mode photonic crystal laser light sources. The structures are formed by placing one missing hole nanocavity (H1 type) between each two segments at 60° that form the hexagonal ringlike photonic crystal laser. The H1 cavities act as a mode filter, clamping the frequency of emission of the laser device. The emission frequency in these rings with cavities varies as the filling factor is changed, allowing the tuning of the laser emission. Stable single mode lasing occurs with side mode suppression greater than 20 dB. This kind of devices may be used as an efficient selective filter of modes and may have important applications in future photonic devices for optical communications and optical sensing.
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High-quality-factor photonic crystal heterostructure laser Appl. Phys. Lett. 89, 101104 (2006); http://dx.doi.org/10.1063/1.2345912 (3 pages) Online Publication Date: 5 September 2006
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A high-quality-factor (Q) photonic crystal heterostructure laser was designed and characterized. Good agreement was obtained between the experimental lasing data and three-dimensional finite-difference time-domain numerical predictions.
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Growth of epitaxial p-type ZnO thin films by codoping of Ga and N Appl. Phys. Lett. 89, 112103 (2006); http://dx.doi.org/10.1063/1.2338527 (3 pages) Online Publication Date: 11 September 2006
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Codoping of Ga and N was utilized to realize p-type conduction in ZnO films using rf magnetron sputtering. The films obtained at 550 °C on sapphire showed resistivity and hole concentrations of 38 Ω cm and 3.9×1017 cm−3, respectively. ZnO films also showed a p-type behavior on p-Si with better electrical properties. ZnO homojunctions synthesized by in situ deposition of Ga–N codoped p-ZnO layer on Ga doped n-ZnO layer showed clear p-n diode characteristics. Low temperature photoluminescence spectra of codoped films also revealed a dominant peak at 3.12 eV. The codoped films showed a dense columnar structure with a c-axis preferred orientation.
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Electrically controlled surface plasmon resonance frequency of gold nanorods Appl. Phys. Lett. 89, 103107 (2006); http://dx.doi.org/10.1063/1.2335812 (3 pages) Online Publication Date: 6 September 2006
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We have presented the voltage-controlled tuning of plasmonic response of absorption spectra of gold nanorods in liquid crystals. We observe that gold nanorods can be aligned along the rubbed polyimide substrate before applying external voltage. It is found that the transverse mode of gold nanorods shows a blueshift or a redshift when rotating the analyzer parallel or perpendicular to the rubbing direction, respectively, while all longitudinal modes display a redshift behavior. This work offers an easy way to tune the transverse and longitudinal modes of gold nanorods simultaneously, which makes it feasible to establish the color tunable devices.
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Appl. Phys. Lett. 89, 111104 (2006); http://dx.doi.org/10.1063/1.2353804 (3 pages) Online Publication Date: 11 September 2006
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The authors experimentally demonstrate a far-field holography for the realization of Ag nanoparticles-embedded periodic and quasiperiodic microstructures with feature sizes beyond the diffraction limit. Periodic cylindrical nanoshell arrays with about 240 nm hole diameter and 12-fold symmetry quasiperiodic structures with 220 nm feature sizes are achieved, respectively, by using a 632.8 nm laser beam. Our results imply that conventional far-field optical technology is capable of fabricating nanostructures in modern micromanufacture.
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Deep acceptor states in ZnO single crystals Appl. Phys. Lett. 89, 092122 (2006); http://dx.doi.org/10.1063/1.2335798 (3 pages) Online Publication Date: 1 September 2006
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The authors report the observation of both acceptor- and donorlike defects in ZnO by deep level transient spectroscopy. The observation is facilitated by using a p-n junction allowing the injection of holes and electrons. The junction is realized by implanting a n-conducting ZnO wafer grown by pressurized melt growth with nitrogen ions. The authors found the commonly observed donorlike defects E1 and E3 and two acceptorlike defects A2 and A3, as well as a broad acceptorlike defect band. The thermal activation energies of A2 and A3, were determined to be about 150 and 280 meV, respectively.
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Appl. Phys. Lett. 89, 091116 (2006); http://dx.doi.org/10.1063/1.2338773 (3 pages) Online Publication Date: 31 August 2006
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The authors demonstrate, using finite-difference time-domain modeling, an enhancement in the extraction efficiency of flip-chip GaN light-emitting diodes (LEDs) using photonic crystals. The authors compare the extraction efficiencies of four configurations of a flip-chip GaN LED: with and without photonic crystal (PhC) layers, with a perfect reflecting mirror, and a bottom PhC reflector on GaN in combination with a top PhC extractor on sapphire. The authors show that, by using a photonic crystal layer as a bottom reflector, they can enhance the extraction efficiency similar to that of a mirror, yet the PhC reflector has the advantage that the metallic mirror loss can be avoided.
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Control of p- and n-type conductivities in Li-doped ZnO thin films Appl. Phys. Lett. 89, 112113 (2006); http://dx.doi.org/10.1063/1.2354034 (3 pages) Online Publication Date: 12 September 2006
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Li-doped ZnO films were prepared by pulsed laser deposition. The carrier type could be controlled by adjusting the growth conditions. In an ionized oxygen atmosphere, p-type ZnO was achieved, with the hole concentration of 6.04×1017 cm−3 at an optimal Li content of 0.6 at. %, whereas ZnO exhibited n-type conductivity in a conventional O2 growth atmosphere. At a Li content of more than 1.2 at. % only high-resistivity ZnO was obtained. The amount of Li introduced into ZnO and the relative concentrations of such defects as Li substitutions and interstitials could play an important role in determining the conductivity of films.
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Appl. Phys. Lett. 89, 123107 (2006); http://dx.doi.org/10.1063/1.2354427 (3 pages) Online Publication Date: 19 September 2006
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For the case of hexagonal ZnO waveguides the Helmholtz equation is solved numerically taking into account the anisotropy of both index of refraction and gain, as well as the material dispersion. The intensity distribution of all waveguide modes, their energy dependence, and the confinement as a function of the nanorod diameter are discussed. The authors apply these model calculations to determine the coupling of nanorod lasers in dense arrays and to optimize the geometry of nanorods for single mode lasing.
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Coupling of waveguide and surface modes in enhanced transmission through stacking gratings Appl. Phys. Lett. 89, 091101 (2006); http://dx.doi.org/10.1063/1.2338796 (3 pages) Online Publication Date: 28 August 2006
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The physics of enhanced transmission through two metallic gratings stacked one on top of another with a lateral shift is studied. Full electromagnetic calculations via the method of rigorous coupled-wave analysis show that enhanced transmission may result even when the slits in one grating are covered by the other. Despite the channel of waveguide mode is blocked, the coupling of strongly excited surface modes in one grating to the waveguide mode in another leads to an enhanced transmission which could even be larger than that in the case of two stacking gratings unshifted with respect to one another.
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Compact Mach-Zehnder acousto-optic modulator Appl. Phys. Lett. 89, 121104 (2006); http://dx.doi.org/10.1063/1.2354411 (3 pages) Online Publication Date: 19 September 2006
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The authors demonstrate a compact optical waveguide modulator based on a Mach-Zehnder interferometer driven by surface acoustic waves. The modulator was monolithically fabricated on GaAs with an active region length of approximately 15 μm. It yields peak-to-peak modulation exceeding 90% of the average transmission and operation in the gigahertz frequency range.
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Au-assisted growth approach for vertically aligned ZnO nanowires on Si substrate Appl. Phys. Lett. 89, 113112 (2006); http://dx.doi.org/10.1063/1.2207832 (3 pages) Online Publication Date: 13 September 2006
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We have described a Au-assisted approach for growth of vertically aligned ZnO nanowires on Si substrate by metal-organic chemical vapor deposition. By employing an annealed Au/Si substrate, on which Au nanoislands are homogeneously distributed, vertically aligned ZnO nanowires on a Si substrate are resulted. Photoluminescence measurement shows that the near-band emission intensity of these ZnO nanowires is significantly improved compared with the ZnO film grown directly on a Si substrate. Extensive characterization by transmission electron microscopy has been made and the growth mechanism of these ZnO nanowires is discussed.
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Surface plasmon polariton mediated photoluminescence from excitons in silicon nanocrystals Appl. Phys. Lett. 89, 101907 (2006); http://dx.doi.org/10.1063/1.2345261 (3 pages) Online Publication Date: 6 September 2006
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Surface plasmon polaritons (SPPs) of a metal film can efficiently be excited when a light emitter is placed nearby. The excited SPPs are converted to photons by compensating for the momentum mismatch. The authors study SPP-mediated emission from excitons in Si nanocrystals (Si-nc’s) by placing an organic grating on a thin Au film placed near Si-nc’s. The dispersion relation is obtained from angle-resolved photoluminescence measurements, and all the observed modes are well explained by model calculation. The results indicate that excitons in Si-nc’s can efficiently excite SPPs in thin metal films and directed photoluminescence can be realized.
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Appl. Phys. Lett. 89, 093103 (2006); http://dx.doi.org/10.1063/1.2336629 (3 pages) Online Publication Date: 28 August 2006
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An engineered enhancement in short-circuit current density and energy conversion efficiency in amorphous silicon p-i-n solar cells is achieved via improved transmission of electromagnetic radiation arising from forward scattering by surface plasmon polariton modes in Au nanoparticles deposited above the amorphous silicon film. For a Au nanoparticle density of ∼ 3.7×108 cm−2, an 8.1% increase in short-circuit current density and an 8.3% increase in energy conversion efficiency are observed. Finite-element electromagnetic simulations confirm the expected increase in transmission of electromagnetic radiation at visible wavelengths, and suggest that substantially larger improvements should be attainable for higher nanoparticle densities.
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Formation of p-type MgZnO by nitrogen doping Appl. Phys. Lett. 89, 102104 (2006); http://dx.doi.org/10.1063/1.2345846 (3 pages) Online Publication Date: 5 September 2006
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A wurtzite N-doped MgZnO film with 20 at. % Mg (MgZnO:N) was grown by plasma-assisted molecular beam epitaxy on c-plane sapphire using radical NO as oxygen source and nitrogen dopant. The as-grown MgZnO:N film behaves n-type conduction at room temperature, but transforms into p-type conduction after annealed for 1 h at 600 °C in an O2 flow. The p-type MgZnO:N has a hole concentration of 6.1×1017 cm−3 and a mobility of 6.42 cm2/V s. X-ray photoelectron spectroscopy measurement indicates that substitution of N for O site is in forms of N atom (N)O and N molecule (N2)O for the as-grown MgZnO:N, but almost only in a form of (N)O for the annealed MgZnO:N. The mechanism of the conduction-type transition induced by annealing is discussed in the present work.
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Ferromagnetic ZnO bicrystal nanobelts fabricated in low temperature Appl. Phys. Lett. 89, 093117 (2006); http://dx.doi.org/10.1063/1.2339048 (3 pages) Online Publication Date: 30 August 2006
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Zinc oxide bicrystal nanobelts were fabricated via a vapor phase transport of a powder mixture of Zn, BiI3, and MnCl2∙H2O at temperatures as low as 300 °C. The bicrystal nanobelts, growing along the [01
 3] direction, have the widths of 40–150 nm and lengths of tens of microns. The energy dispersive x-ray spectroscopy result verifies that the bicrystal nanobelts contain higher concentration of both Bi and Mn along the grain boundary. The investigation of the growth mechanism proposes that MnBi may induce the formation of bicrystal nanobelts. Photoluminescence spectra show that the ultraviolet emission of the bicrystal nanobelts has a blueshift of 18 meV as compared to Bi–ZnO nanowires at 10 K. The bicrystal nanobelts also exhibit ferromagnetism at room temperature. |
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