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Top 20 Most Read Articles
November 2012
The 20 articles with the most full-text downloads during the month, in descending order.
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Growth and ferromagnetic resonance properties of nanometer-thick yttrium iron garnet films Appl. Phys. Lett. 101, 152405 (2012); http://dx.doi.org/10.1063/1.4759039 (5 pages) Online Publication Date: 11 October 2012
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Growth of nm-thick yttrium iron garnet films and ferromagnetic resonance (FMR) linewidth properties in the films are reported. The films were grown on gadolinium gallium garnet substrates by pulsed laser deposition (PLD). Films in the 5–35 nm thickness range showed a (111) orientation and a surface roughness between 0.1 and 0.3 nm. The 10 nm films showed a 10 GHz FMR linewidth of about 6 Oe and a damping constant of 3.2 × 10−4. The FMR linewidth increases with both the surface roughness and the surface Fe deficiency. Thicker films exhibit a smaller FMR linewidth and a lower damping constant.
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Vacuum nanoelectronics: Back to the future?—Gate insulated nanoscale vacuum channel transistor Appl. Phys. Lett. 100, 213505 (2012); http://dx.doi.org/10.1063/1.4717751 (4 pages) Online Publication Date: 23 May 2012
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A gate-insulated vacuum channel transistor was fabricated using standard silicon semiconductor processing. Advantages of the vacuum tube and transistor are combined here by nanofabrication. A photoresist ashing technique enabled the nanogap separation of the emitter and the collector, thus allowing operation at less than 10 V. A cut-off frequency fT of 0.46 THz has been obtained. The nanoscale vacuum tubes can provide high frequency/power output while satisfying the metrics of lightness, cost, lifetime, and stability at harsh conditions, and the operation voltage can be decreased comparable to the modern semiconductor devices.
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Appl. Phys. Lett. 101, 132105 (2012); http://dx.doi.org/10.1063/1.4754078 (4 pages) Online Publication Date: 26 September 2012
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The coupling of CdTe/ZnTe quantum dot (QD) emission to micropillar cavity eigenmodes in the weak coupling regime is demonstrated. We analyze photoluminescence spectra of QDs embedded in monolithic micropillar cavities based on Bragg mirrors which contain MgSe/ZnTe/MgTe superlattices as low-index material. The pillar emission shows pronounced cavity eigenmodes, and their spectral shape is in good agreement with simulations. QD emission in resonance with the cavity mode is shown to be efficiently guided toward the detector, and an experimental Purcell enhancement by a factor of 5.7 is determined, confirming theoretical expectations.
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Monolithic polymer microlens arrays with antireflective nanostructures Appl. Phys. Lett. 101, 203102 (2012); http://dx.doi.org/10.1063/1.4747717 (4 pages) Online Publication Date: 12 November 2012
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This work reports a novel method for fabricating monolithic polymer microlens arrays with antireflective nanostructures (AR-MLAs) at wafer level. The antireflective nanostructures (ARS) were fabricated by etching the curved surface of polymer microlens with a metal annealed nanoisland mask. The effective refractive index of ARS was controlled with the etch profile of nanostructures to reduce the mismatch in refractive indices at air-lens interface. The reflectance of AR-MLAs decreases below 4% from 490 nm to 630 nm in wavelength. The lens transmission significantly increases by 67% across the visible spectrum by minimizing the reflection and absorption, compared to that of MLAs without ARS.
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Electron transport properties of carbon nanotube–graphene contacts Appl. Phys. Lett. 101, 153501 (2012); http://dx.doi.org/10.1063/1.4756693 (3 pages) Online Publication Date: 8 October 2012
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The properties of carbon nanotube-graphene junctions are investigated with first-principles electronic structure and electron transport calculations. Contact properties are found to be key factors in determining the performance of nanotube based electronic devices. In a typical single-walled carbon nanotube-metal junction, there is a p-type Schottky barrier of up to ∼ 0.4 eV which depends on the nanotube diameter. Calculations of the Schottky barrier height in carbon nanotube-graphene contacts indicate that low barriers of 0.09 eV and 0.04 eV are present in nanotube-graphene contacts ((8,0) and (10,0) nanotubes, respectively). Junctions with a finite contact region are investigated with simulations of the current-voltage characteristics. The results suggest the suitability of the junctions for applications and provide insight to explain recent experimental findings.
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Photonic non-volatile memories using phase change materials Appl. Phys. Lett. 101, 171101 (2012); http://dx.doi.org/10.1063/1.4758996 (4 pages) Online Publication Date: 22 October 2012
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We propose an all-photonic, non-volatile memory, and processing element based on phase-change thin-films deposited onto nanophotonic waveguides. Using photonic microring resonators partially covered with Ge2Sb2Te5 (GST) multi-level memory operation in integrated photonic circuits can be achieved. GST provides a dramatic change in refractive index upon transition from the amorphous to crystalline state, which is exploited to reversibly control both the extinction ratio and resonance wavelength of the microcavity with an additional gating port in analogy to optical transistors. Our analysis shows excellent sensitivity to the degree of crystallization inside the GST, thus providing the basis for non-von Neumann neuromorphic computing.
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The origin of broad distribution of breakdown times in polycrystalline thin film dielectrics Appl. Phys. Lett. 101, 153511 (2012); http://dx.doi.org/10.1063/1.4758684 (5 pages) Online Publication Date: 12 October 2012
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The distribution of breakdown times of thin film dielectrics, stressed in a constant voltage mode, is generally interpreted in terms of percolation theory of dielectric breakdown. The percolation model suggests that relative distribution of failure times (normalized to the mean) should narrow down considerably for thicker dielectrics. Explicitly contradicting this prediction, we find a larger distribution of failure times even for relatively thick polycrystalline oxides. We use atomic force microscopy and conductive AFM measurements to confirm that breakdown in these films are primarily localized in the grain boundaries, decorated with large number of pre-existing defects. The classical percolation model—adapted to this specific situation of spatially localized trap generation—offers an intuitive explanation of the breadth of the failure time distribution in thick polycrystalline dielectric. The theory offers an opportunity to optimize the intrinsic trade-off between variability and reliability in polycrystalline films.
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A little ribbing: Flux starvation engineering for rippled indium tin oxide nanotree branches Appl. Phys. Lett. 101, 193101 (2012); http://dx.doi.org/10.1063/1.4764508 (4 pages) Online Publication Date: 5 November 2012
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Combining vapour-liquid-solid growth with glancing angle deposition (VLS-GLAD) facilitates fabrication of branched nanowires not possible with either technique alone. Indium tin oxide (ITO) nanostructures grown by VLS-GLAD produce extremely porous nanotree structures, where periodic branch diameter oscillations are sometimes observed. We explain this rippled branch growth with a simple model linking the physics governing branch growth to the process variables controlled in VLS-GLAD. The model is verified by inducing specific, aperiodic ripples onto growing ITO branches through macroscopic vapour flux control and manipulation of local shadowing.
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Nanoantenna-like properties of sea-urchin shaped ZnO as a nanolight filter Appl. Phys. Lett. 101, 133101 (2012); http://dx.doi.org/10.1063/1.4752467 (5 pages) Online Publication Date: 24 September 2012
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A light scattering peak of ZnO rods is presented at 543.2 nm. The radiation peaks of ZnO nanospines correspond to 496.6 nm and 630.6 nm due to the breaking of the symmetry of the ZnO rods. The radiation peaks of sea-urchin shaped ZnO was observed and confirmed by utilizing the dipole approximation. Sea-urchin shaped ZnO can tune and then filter different frequencies of light by utilizing incident light to illuminate at the different positions of sea-urchin shaped ZnO which works like a nanolight filter device and has potential applications in photonic computers, bio-light emission device, and solar cells.
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Ultra-thin perfect absorber employing a tunable phase change material Appl. Phys. Lett. 101, 221101 (2012); http://dx.doi.org/10.1063/1.4767646 (5 pages) Online Publication Date: 26 November 2012
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We show that perfect absorption can be achieved in a system comprising a single lossy dielectric layer of thickness much smaller than the incident wavelength on an opaque substrate by utilizing the nontrivial phase shifts at interfaces between lossy media. This design is implemented with an ultra-thin (∼λ/65) vanadium dioxide (VO2) layer on sapphire, temperature tuned in the vicinity of the VO2 insulator-to-metal phase transition, leading to 99.75% absorption at λ = 11.6 μm. The structural simplicity and large tuning range (from ∼80% to 0.25% in reflectivity) are promising for thermal emitters, modulators, and bolometers.
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One electron-based smallest flexible logic cell Appl. Phys. Lett. 101, 183101 (2012); http://dx.doi.org/10.1063/1.4761935 (4 pages) Online Publication Date: 29 October 2012
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A one electron-based operating half-adder, the smallest arithmetic block, has been implemented on silicon-on-insulator structure whose basic element is a nanoscale single-electron transistor (SET) with two symmetrical side-wall gates. Grayscale contour plots of the resulting cell output voltages exhibit the Coulomb blockade-induced periodic alternating high/low features. Their voltage transfer characteristics display typical Sum and Carry-Out functions for binary, multi-valued (MV), and binary-MV mixed input voltages. Moreover, the half-adder function converts into a subtraction mode by adjusting control gates of the SET element. This flexible multi-valued cell provides an arithmetic block for the SET MV logic family of high density integration, operating with ultra-low power.
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Broadband super-Planckian thermal emission from hyperbolic metamaterials Appl. Phys. Lett. 101, 131106 (2012); http://dx.doi.org/10.1063/1.4754616 (5 pages) Online Publication Date: 24 September 2012
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We develop the fluctuational electrodynamics of metamaterials with hyperbolic dispersion and show the existence of broadband thermal emission beyond the black body limit in the near field. This arises due to the thermal excitation of unique bulk metamaterial modes, which do not occur in conventional media. We consider a practical realization of the hyperbolic metamaterial and estimate that the effect will be observable using the characteristic dispersion (topological transitions) of the metamaterial states. Our work paves the way for engineering the near-field thermal emission using metamaterials.
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Coupled plasmonic modes in organic planar microcavities Appl. Phys. Lett. 100, 253301 (2012); http://dx.doi.org/10.1063/1.4729820 (4 pages) Online Publication Date: 20 June 2012
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We report on the nature of the resonant modes in organic planar microcavities featuring semi-transparent metallic layers. We theoretically demonstrate that symmetric microcavities support a total of four modes originating from the coupling of surface plasmon polaritons. For red top-emitting organic light-emitting diodes with one semi-transparent metallic electrode, we identify three coupled plasmonic modes and calculate a light outcoupling efficiency close to 34% when assuming emitters with isotropic transition dipole moment. This value is estimated to increase to 50% in the case the dipole moment is purely horizontal.
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Noise spectroscopy as an equilibrium analysis tool for highly sensitive electrical biosensing Appl. Phys. Lett. 101, 093704 (2012); http://dx.doi.org/10.1063/1.4748931 (5 pages) Online Publication Date: 28 August 2012
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We demonstrate an approach for highly sensitive bio-detection based on silicon nanowire field-effect transistors by employing low frequency noise spectroscopy analysis. The inverse of noise amplitude of the device exhibits an enhanced gate coupling effect in strong inversion regime when measured in buffer solution than that in air. The approach was further validated by the detection of cardiac troponin I of 0.23 ng/ml in fetal bovine serum, in which 2 orders of change in noise amplitude was characterized. The selectivity of the proposed approach was also assessed by the addition of 10 μg/ml bovine serum albumin solution.
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Appl. Phys. Lett. 101, 193307 (2012); http://dx.doi.org/10.1063/1.4766913 (4 pages) Online Publication Date: 9 November 2012
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Grain boundaries in organic thin film have been controlled by engineering the different growth conditions in such a way that it reduces the contact resistance and enhances the carrier mobility in p-type copper phthalocyanine and n-type copper hexadecafluoro phthalocyanine based organic thin film transistors. Reduced effect of grain boundary has been demonstrated by temperature dependence of charge carrier mobility and other transport parameters. A correlation has been established between contact resistance and certain thin film morphology, achieved by varying different growth conditions.
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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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A full free spectral range tuning of p-i-n doped gallium nitride microdisk cavity Appl. Phys. Lett. 101, 161105 (2012); http://dx.doi.org/10.1063/1.4744947 (4 pages) Online Publication Date: 15 October 2012
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Effective, permanent tuning of the whispering gallery modes (WGMs) of p-i-n doped GaN microdisk cavity with embedded InGaN quantum dots over one free spectral range is demonstrated by irradiating the microdisks with a ultraviolet laser (380 nm) in DI water. For incident laser powers between 150 and 960 nW, the tuning rate varies linearly. Etching of the top surface of the cavity is proposed as the driving force for the observed shift in WGMs and is supported by experiments. The tuning for GaN/InGaN microdisk cavities is an important step for deterministically realizing nanophotonic devices for studying cavity quantum electrodynamics.
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Appl. Phys. Lett. 101, 213101 (2012); http://dx.doi.org/10.1063/1.4767230 (3 pages) Online Publication Date: 19 November 2012
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The relationship between cutting forces and lattice orientations of monolayer graphene is investigated by using an atomic force microscopy (AFM) based nanorobot. In the beginning, the atomic resolution image of the graphene lattice is obtained by using an AFM. Then, graphene cutting experiments are performed with sample rotation method, which gets rid of the tip effect completely. The experimental results show that the cutting force along the armchair orientation is larger than the force along the zigzag orientation, and the cutting forces are almost identical every 60°, which corresponds well with the 60° symmetry in graphene honeycomb lattice structure. By using Poisson analysis method, the single cutting force along zigzag orientation is 3.9 nN, and the force along armchair is 20.5 nN. This work lays the experimental foundation to build a close-loop fabrication strategy with real-time force as a feedback sensor to control the cutting direction.
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Interference of surface plasmon polaritons excited at hole pairs in thin gold films Appl. Phys. Lett. 101, 201102 (2012); http://dx.doi.org/10.1063/1.4767523 (4 pages) Online Publication Date: 12 November 2012
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The excitation of surface plasmon polaritons by focusing a laser beam onto a hole pair in a thin gold film is studied both experimentally and theoretically. By means of leakage radiation microscopy we quantitatively measure the light-plasmon coupling efficiency as a function of the hole distance. We find a modulation of the coupling efficiency as a function of hole distance that strongly depends on the polarization direction of the incident light, in agreement with theoretical simulations.
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Homogeneous pinhole free 1 nm Al2O3 tunnel barriers on graphene Appl. Phys. Lett. 101, 203104 (2012); http://dx.doi.org/10.1063/1.4765348 (3 pages) Online Publication Date: 12 November 2012
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We report on the topographical and electrical characterisations of 1 nm thick Al2O3 dielectric films on graphene. The Al2O3 is grown by sputtering a 0.6 nm Al layer on graphene and subsequentially oxidizing it in an O2 atmosphere. The Al2O3 layer presents no pinholes and is homogeneous enough to act as a tunnel barrier. A resistance-area product in the mega-ohm micrometer-square range is found. Comparatively, the growth of Al2O3 by evaporation does not lead to well-wetted films on graphene. Application of this high quality sputtered tunnel barrier to efficient spin injection in graphene is discussed.
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