Volume 95, Issue 7, 17 August 2009
- lasers, optics, and optoelectronics
- structural, mechanical, thermodynamic, and optical properties of condensed matter
- electronic transport and semiconductors
- magnetism and superconductivity
- dielectrics and ferroelectricity
- nanoscale science and design
- organic electronics and photonics
- device physics
- biophysics and bio-inspired systems
- interdisciplinary and general physics
Index of content:
We report an electrical scheme to detect specific DNA. Engineered hairpin probe DNA are immobilized on a silicon chip between gold nanoelectrodes. Hybridization of target DNA to the hairpin melts the stem nucleotides.Goldnanoparticle-conjugated universal reporter sequence detects the open hairpins by annealing to the exposed stem nucleotides. The goldnanoparticles increase charge conduction between the electrodes. Specifically, we report on a hairpin probe designed to detect a medically relevant mutant form of the oncogene. Direct current measurements show three orders of magnitude increase in conductivity for as low as of target molecules.
- LASERS, OPTICS, AND OPTOELECTRONICS
95(2009); http://dx.doi.org/10.1063/1.3206666View Description Hide Description
High crystalline -plane GaNepitaxial layers with smooth surface morphology were grown on -plane sapphire substrate by metalorganic chemical vapor deposition. The full width at half maximum of x-ray rocking curve was measured as 407 arc sec along -axis direction, and the root mean square roughness was 1.23 nm. Nonpolar -plane InGaN/GaN light emitting diodes were subsequently grown on -plane GaN template, and the optical output power of 0.72 mW was obtained at drive current of 20 mA (3.36 V) and 2.84 mW at 100 mA (4.62 V) with the peak emission wavelength of 477 nm.
95(2009); http://dx.doi.org/10.1063/1.3206738View Description Hide Description
This letter provides an experimental demonstration of extraordinary transmission in a closed waveguide system loaded with an electrically small diaphragm. This is a situation where the standard surface plasmonpolariton (SPP) theory does not apply. The theoretical explanation is then based on the concept of impedance matching. This concept has previously been applied by some of the authors to account for enhanced transmission in situations where surface plasmontheory can be used: periodic arrays of small holes or slits in flat metal screens. The experiment in this letter supports the impedance matching model, valid for when SPPs are present or not.
95(2009); http://dx.doi.org/10.1063/1.3206739View Description Hide Description
We demonstrate direct green laser operation from InGaN based diodes at wavelengths as long as 515.9 nm with 50 mW output power in pulse operation. A factor of defect reduction for the In-rich InGaN quantum wells based on improvements of the epitaxialgrowth process and design of the active layers on -plane GaN-substrates makes it possible to demonstrate laser operation at room temperature. Micrometer-scale photoluminescence mappings and electro-optical measurements confirm the reduction of nonradiative defects in the emitting layers. The broad-area gain-guided laser structures were driven in pulse operation to minimize thermal effects and to accurately measure the laser temperature dependence. The threshold current density was and the fitted slope efficiency had a value of for an optical output up to 50 mW.
95(2009); http://dx.doi.org/10.1063/1.3207823View Description Hide Description
We report that metalthin films can be directly photoetched by a pulsed neodymiumdoped yttrium aluminum garnet laser beam irradiating the filmsurface. This process utilizes a laser-induced thermoelastic force, which plays a role to detach the film from the underlying layer. High-fidelity patterns at the micrometer scales have been fabricated using a spatially modulated laser beam. A zinc-tin-oxide thin film transistor with photoetched Al source and drain electrodes exhibited an on/off ratio higher than and a very low off-current level. This indicates that the metallic layer is completely etched out by this process, making an additional cleaning or etching step unnecessary.
Plasmonic light enhancement in the near-field of metallic nanospheroids for application in intermediate band solar cells95(2009); http://dx.doi.org/10.1063/1.3205470View Description Hide Description
In order to enhance infrared light absorption in sub-bandgap transitions in an intermediate band solar cell, the scattered near-field potential from uncoated and coated metallic nanoparticles with a spheroidal shape is calculated with the electrostatic model. The absorption enhancement produced at the surface plasmon frequency of the nanoparticles can be of several orders of magnitude in some cases.
Temperature dependent optical properties of (002) oriented ZnO thin film using surface plasmon resonance95(2009); http://dx.doi.org/10.1063/1.3206954View Description Hide Description
Temperature dependent optical properties of -axis oriented ZnOthin film were investigated using surface plasmon resonance (SPR) technique. SPR data for double layer (prism-Au-ZnO-air) and single layer (prism-Au-air) systems were taken over a temperature range (300–525 K). Dielectric constant at optical frequency and real part of refractive index of the ZnOfilm shows an increase with temperature. The bandgap of the oriented ZnOfilm was found to decrease with rise in temperature. The work indicates a promising application of the system as a temperature sensor and highlights an efficient scientific tool to study optical properties of thin film under varying ambient conditions.
95(2009); http://dx.doi.org/10.1063/1.3207826View Description Hide Description
Simultaneous two-level lasing, corresponding to ground level and excited level transitions in GaInAsSb/GaSb quantum well lasers under continuous wave operation is reported. The effect is attributed to a slowed-down intersubband relaxation in the quantum wells due to buildup of hot phonon population resulting in an incomplete clamping of the excited state population above the ground level lasing threshold.
95(2009); http://dx.doi.org/10.1063/1.3211129View Description Hide Description
We have studied two types of InGaN laser diodes emitting at 410 and 440 nm. Each device was characterized by measuring light-current characteristics in two geometries for which the light was collected: along the resonator and perpendicularly to the cavity. In the first configuration, the 410 nm device displays no reduction of differential efficiency while 440 nm laser shows evidence of droop. In the perpendicular configuration both devices show the pronounced droop. We associate the suppression of the droop for 410 nm laser in the “along cavity” configuration with the appearance of the stimulated recombination.
Effects of backward-propagating waves and lumped mirror losses on self-induced transparency modelocking in quantum cascade lasers95(2009); http://dx.doi.org/10.1063/1.3206741View Description Hide Description
Work to date on self-induced transparency modelocking in quantum cascade lasers(QCLs) has neglected backward-propagating waves and lumped mirror losses. In this work, we remove these unrealistic assumptions. The qualitative features of the modelocking are unaffected by this improvement in the model, but the parameter regime in which stable modelocked pulses may be found is reduced. This reduction is due to incomplete gain recovery near the edges of the QCL when pulses pass through after reflecting from the mirrors, coincident with the loss of pulse energy at the mirrors.Spatialhole burning is observed in parameter regimes in which continuous waves can grow, but it does not affect the stability of the modelocking.
95(2009); http://dx.doi.org/10.1063/1.3207832View Description Hide Description
For an aperture with transverse size , Fraunhofer region is named when the distance between the aperture and the detector is larger than , where is the wavelength of the illuminating light. For a lensless system, when both reference detector and the object are located in Fraunhofer region relative to the thermal source, we demonstrate that a ghost “pinhole” camera with magnification can be obtained by the second-order correlation of two light fields even if the test detector is a single pointlike detector. Effects determining the quality of ghost pinhole imaging and its potential applications are also discussed.
95(2009); http://dx.doi.org/10.1063/1.3211867View Description Hide Description
We experimentally demonstrate the trapped rainbow in tapered left-handed heterostructures (LHHs) at visible frequencies. The employed left-handed metamaterials (LHMs) are isotropic with the size of hundreds of square millimeter. Specifically, the LHMs sample at visible frequencies has a broad spectral range and low loss, making it an intrinsic optical response for the LHHs. It is found that the frequency components of the wave packet separate at positions with different guide thicknesses only if the inclination of tapered LHHs is greater than zero and smaller than the critical value.
95(2009); http://dx.doi.org/10.1063/1.3211875View Description Hide Description
We demonstrate numerically, using a modified total-field/scattered-field formalism, that metallic lenses, based on arrays of nanoscale slits with varying widths in a planar metallic film, can be used to focus light and compensate for various angles of incidence. These structures could be used as integrated microlenses to improve the efficiency of pixels in solid-state image sensors. Our design guidelines simultaneously accomplish a prism and focusing action. Our results also indicate the importance of the aperture effect for such far-field focusing devices.
95(2009); http://dx.doi.org/10.1063/1.3211956View Description Hide Description
In this letter, ring artifacts in two-dimensional (2D) tomographic slices are considered. For a parallel beam geometry we propose an interactive algorithm, which removes the artifacts while preserving fine image details. The algorithm comprises two stages and is based on a priori information about the true attenuation coefficient in some areas of a 2D slice. Even in the absence of any a priori information the initial stage of the algorithm can already provide good ring artifact suppression.
95(2009); http://dx.doi.org/10.1063/1.3211970View Description Hide Description
Hot phosphor acid etching is presented to form a roughened surface with dodecagonal pyramids on laser lift-off N face GaN grown by metalorganic chemical vapor deposition. A detailed analysis of time evolution of surface morphology is described as a function of etching temperature. The activation energy of the etching process is 1.25 eV, indicating the process is reaction-limited scheme. And it is found that the oblique angle between the facets and the base plane increases as the temperature increases. Thermodynamics and kinetics related factors of the formation mechanism of the dodecagonal pyramid are also discussed. The light output power of a vertical injection light-emitting-diode (LED) with proper roughened surface shows about 2.5 fold increase compared with that of LED without roughened surface.
- STRUCTURAL, MECHANICAL, THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER
95(2009); http://dx.doi.org/10.1063/1.3196430View Description Hide Description
Electroluminescence(EL) was observed on conventional cathodoluminescent (CL)phosphor with the incorporation of carbon nanotube(CNT) at ambient air. The role of CNT can be understood as enhancing the local electrical field, which allows electron injection to the active center of phosphor at relatively low operating voltages. In this EL device, the brightness of CLphosphor was significantly improved from no light emission in the case of no addition of CNT to with CNT at 10 kHz of ac 300 V.
95(2009); http://dx.doi.org/10.1063/1.3190198View Description Hide Description
The adhesive and cohesive properties of organosilicate thin films are remarkably insensitive to UV curing. We demonstrate how to maximize these properties with UV standing waves together with an optical spacer underlying layer. Using a simulation of the UV cure profile through the film thickness, we demonstrate how a UV transparent SiN optical spacer layer can be selected to maximize curing at both sides of the organosilicate film with marked increases in interfacial fracture energy. On the contrary, a UV absorbing SiCN underlying layer resulted in significantly reduced UV intensities and small improvements of the interfacial fracture energies.
95(2009); http://dx.doi.org/10.1063/1.3210791View Description Hide Description
The thermodynamics of hydrogen absorption in Pd-capped Mgfilms are strongly dependent on the magnesium thickness. In the present work, we suppress such dependency by inserting a thin Ti layer between Mg and Pd. By means of optical measurements, we show that the surface energy contribution to the destabilization of is negligible. The inserted Ti layer prevents Mg–Pd alloy formation at the Mg/Pd interface, leading to quasifree Mgfilms and enhancing the kinetics of hydrogen desorption. Our observations are important for the development of thin film devices.
95(2009); http://dx.doi.org/10.1063/1.3206931View Description Hide Description
We consider the relationship of nucleation tendency with crystallizing-phase structures in silicate glasses using glassy sanbornite that shows homogeneous nucleation resulting crystallization of and phases with a layered structure of a network modifier and a network former. This trend is also confirmed in other silicate glasses with homogeneous nucleation tendency, which has been assessed by Zanotto and other researchers. It is suggested that the structural dimension of the crystallizing phase governs the nucleation tendency in silicate glasses.
95(2009); http://dx.doi.org/10.1063/1.3204454View Description Hide Description
InAlN thin filmsgrown on (0001) templates by metal-organic vapor phase epitaxy were studied by transmission electron microscopy techniques. V-defects in the form of hexagonal inverted pyramids with sidewalls were observed on the films’ surfaces linked to the termination of threading dislocations. Their origin is explained by the different surface atom mobility of In and Al and the built-in strain relaxation. Indium segregation in the films is influenced by the formation of V-defects, the edges and the apexes of which function as paths of migrating indium atoms diffusing along nanopipes formed at the open-core threading dislocations.
95(2009); http://dx.doi.org/10.1063/1.3211112View Description Hide Description
Precompression treatments on bulk metallic glass rods with tapered ends induced controllable stress distributions and resulted in residual stress accompanied with a few tiny shear bands after unloading. The built-in stress state increased macroscopic plasticity dramatically and produced predictable distributions of shear bands in the cylindrical samples cut from the taper-ended samples. The macroscopic plasticity was interpreted in terms of the competition among different types of shear bands.