Volume 101, Issue 12, 17 September 2012
- photonics and optoelectronics
- surfaces and interfaces
- structural, mechanical, optical, and thermodynamic properties of advanced materials
- magnetics and spintronics
- superconductivity and superconducting electronics
- dielectrics, ferroelectrics, and multiferroics
- nanoscale science and technology
- organic electronics and photonics
- device physics
- biophysics and bio-inspired systems
- energy conversion and storage
- interdisciplinary and general physics
Index of content:
Ga-rich CuIn(1−x)GaxSe2 (CIGS) quantum dots(QDs) with a wide bandgap of 1.58 eV were utilized in dye-sensitized solar cells for energy harvesting. Ga-rich CIGS QDs at TiO2 photoanodes afford the recombination reduction and thus suppress the dark current, leading to the increase of short-circuit current from 14.47 to 15.27 mA·cm−2 and open-circuit voltage from 751 to 762 mV. This is due to well-adjusted conduction band minimum of Ga-rich CIGS QDs between that of TiO2 and excited state oxidation potential of N719, enhancing the photoelectron collection and suppressing electron back-transfer from TiO2 to oxidizedredox species in the electrolyte.
- PHOTONICS AND OPTOELECTRONICS
101(2012); http://dx.doi.org/10.1063/1.4752746View Description Hide Description
We fabricated polygonal silicatoroidal microcavities to achieve stable mechanical coupling with an evanescent coupler such as a tapered fiber. The octagonal cavity was fabricated by using a combination of isotropic etching,anisotropicetching, and laser reflow. It offers both high and low coupling efficiencies with the cavity mode even when the coupler is in contact with the cavity, which makes the device more practically because of easy alignment. A numerical simulation showed that an octagonal silicatoroidal microcavity had an optical quality factor of 8.8 × 106.
101(2012); http://dx.doi.org/10.1063/1.4753806View Description Hide Description
The Purcell factor (PF) of the propagating surface plasmonpolariton (SPP) mode on metallic grating is evaluated with full integration formula of Fermi's golden rule, while both spontaneous emissionlinewidth of single quantum dot and the spectrum broadening of photonic density of state (DOS) due to the propagation loss of SPP mode are involved. It is found that the PF would be degraded by taking account of the emission linewidth. For emitters with narrow linewidth, the DOS broadening is dominant while it would be helpful to some degree for wide-linewidth emitters.
Longitudinal computer-generated holograms for digital frequency control in electronically tunable terahertz lasers101(2012); http://dx.doi.org/10.1063/1.4753814View Description Hide Description
Longitudinal computer-generated holograms (LCGHs) can be used for the inverse design of aperiodic photonic lattices for customizable frequency control of light propagation. A one-dimensional binary LCGH, designed to harness the coarse gain tuning of a terahertz (THz) quantum cascade laser(QCL) operating at around 2.9 THz, is patterned directly by ion milling into the surface plasmon-based waveguides of pre-characterized QCLs. The initial multi-mode emission is suppressed in favour of electronically controlled, discretely tunable single-mode lasing spanning over 160 GHz. Side-mode suppression ratios of over 20 dB are also demonstrated in these tunable THz LCGH-QCLs.
Ordered ZnO nanorods-based heterojunction light-emitting diodes with graphene current spreading layer101(2012); http://dx.doi.org/10.1063/1.4753926View Description Hide Description
Ordered ZnO nanorods-based heterojunction light-emitting diodes(LEDs) have been fabricated by adopting few-layer graphene as a current spreading layer. The strong emission at low currents infers the high interfacial quality between GaN and ordered ZnOnanorods, and the current spreading effect resulting from graphene. The improved electroluminescence performance was achieved compared to the ZnO nanorods-based LED with a conventional indium-tin-oxide electrode, which can be attributed to the stable, reliable, and low resistance ohmic-contacts between graphene and ZnOnanorods, as well as the high transmittance of graphene. These results demonstrate feasibility of using graphene as electrodes for high-efficiency ZnO nanorods-based LEDs.
101(2012); http://dx.doi.org/10.1063/1.4753948View Description Hide Description
We report on the design, fabrication, and characterization of silicon-on-insulator rib and strip waveguides at wavelengths longer than 3.7 . Propagation losses of dB/cm at 3.73 and dB/cm at 3.8 have been measured for rib waveguides, whilst submicron strip waveguides exhibited propagation losses of dB/cm at the wavelength of 3.74 . A multimode interference (MMI) splitter and racetrack resonators based on submicron strip waveguides are also examined. Optical losses of dB/MMI and a racetrack resonator Q-value of 8.2 k are obtained at 3.74 .
Performance and polarization effects in () long wavelength light emitting diodes grown on stress relaxed InGaN buffer layers101(2012); http://dx.doi.org/10.1063/1.4753949View Description Hide Description
Long wavelength (525–575 nm) () light emitting diodes were grown pseudomorphically on stress relaxed InGaNbuffer layers. Basal plane dislocation glide led to the formation of misfit dislocations confined to the bottom of the InGaNbuffer layer. This provided one-dimensional plastic relaxation in the film interior, including the device active region. The change of the stress state of the quantum well due to one-dimensional plastic relaxation altered the valence bandstructure, which produced a significant shift in polarization of emitted light. Devices grown on relaxed buffers demonstrated equivalent output power compared to those for control samples without relaxation.
101(2012); http://dx.doi.org/10.1063/1.4751034View Description Hide Description
Broadband wavelength tunability over 136 nm (between 1182.5 nm and 1319 nm) of picosecond pulses in passive mode-locked regime is demonstrated in a multi-section quantum-dot laser in external cavity configuration at room temperature. The maximum peak power of 870 mW with 15 ps pulse duration was achieved at 1226 nm wavelength.
101(2012); http://dx.doi.org/10.1063/1.4753795View Description Hide Description
The horizontal and vertical polarizations of the terahertz radiation emitted from a small-gap dipole photo-conductive antenna are characterised using a single detector and a homemade thin-film wire grid polarizer. The two polarizations are seen to be temporally distinct. In addition, the dependence of the position of the excitation spot on the dipole with the polarity of the horizontal polarization is studied where a reversal in the horizontal polarization is observed between the two edges of the antennaanode.
101(2012); http://dx.doi.org/10.1063/1.4753805View Description Hide Description
Recent electrochemical experiments on gold-based photonic metamaterials have shown a sizable reversible tuning and modulation of plasmonic resonances. Here, we study the mechanism of the electrochemical modulation by measuring the change of the resonance transmittance and resonance frequency during underpotential deposition of Pb,Cu, and electrosorption of OH. The electric resistance change of the resonators is identified as decisive for the resonance transmittance change, while the space-charge layer at the metal surface shifts the resonance frequency.
High-power tunable two-wavelength generation in a two chip co-linear T-cavity vertical external-cavity surface-emitting laser101(2012); http://dx.doi.org/10.1063/1.4754295View Description Hide Description
We report the design and experimental results of a two chip co-linear T-cavity vertical external cavitysurface emitting laser (VECSEL) capable of generating two continuously tunable orthogonally polarized lasing wavelengths. A polarizing beamsplitter is used to overlap two VECSEL cavities thus generating high-power intra-cavity two-wavelength generation ideal for type-II nonlinear frequency conversion. Nearly equal power at each wavelength with a combined dual-wavelength CW output power in excess of 13 W was observed. In a high Q cavity, the wavelength separation was tuned from 35 nm to 52 nm by using birefringent filters in regions where each wavelength lases independently of the other.
101(2012); http://dx.doi.org/10.1063/1.4754572View Description Hide Description
A two-dimensional surface lattice of cylindrical topology obtained via perturbing the inner surface of a cylinder is considered. Periodic perturbations of the surface lead to observation of high-impedance, dielectric-like media and resonant coupling of surface and non-propagating volume fields. This allows synthesis of tailored-for-purpose “coating” material with dispersion suitable, for instance, to mediate a Cherenkov type interaction. An analytical model of the lattice is discussed and coupled-wave equations are derived. Variations of the lattice dispersive properties with variation of parameters are shown, illustrating the tailoring of the structure's electromagnetic properties. Experimental results are presented showing agreement with the theoretical model.
101(2012); http://dx.doi.org/10.1063/1.4754137View Description Hide Description
Coupling is a critical issue for most plasmonicnanostructures. However, the coupling efficiency for many nanoplasmonic architectures is relatively weak due to the lack of theoretical optimization approaches. Consequently, it is essential to address the understanding of the mechanism and improvement of the coupling efficiency through nanoplasmonic structures. In this letter, we provide a theoretical analysis to quantitatively predict the coupling efficiency from infinite-length and finite-length nanoslits to planar metal-insulator-metal (MIM) waveguidestructures, both analytically and numerically. This design principle will be useful for the development of MIM plasmonic networks to bridge the gap between photonics, optoelectronics, and nanoelectronics.
101(2012); http://dx.doi.org/10.1063/1.4754139View Description Hide Description
Merging of electronics and photonics at subwavelength dimensions could potentially allow development of ultracompact electro-optic modulators and active optical interconnects. Here, we introduce a field-effect active plasmonicmodulator where the metallic ring serves as both a photonic resonator and a field electrode. By exploiting the simultaneous electronic and photonic functionalities of our plasmonic device, we show devices offering significantly improved modulation depths (as high as ∼10.85 dB) compared to active dielectric micro-ring resonators. Device concepts introduced in this work are applicable in realization of various integrated components and could play an important role in development of active plasmonic circuits.
101(2012); http://dx.doi.org/10.1063/1.4754148View Description Hide Description
We investigate the effect of angular tuning on coherently coupled optical parametric generation (OPG) in two-dimensional purely nonlinear lattices and demonstrate how it allows accessing both shared signal and shared idler regimes, resulting in twin-beam outputs in the mid- and near infrared, respectively. Furthermore, we present the results of a systematic spectral and angular mapping of the twin-beam OPG response in the near-infrared as a function of the pump incidence angle.
Athermal and tunable operations of 850 nm vertical cavity surface emitting lasers with thermally actuated T-shape membrane structure101(2012); http://dx.doi.org/10.1063/1.4753807View Description Hide Description
We demonstrate the athermal operation and the wavelength tuning of 850 nm GaAs-based vertical cavity surface emitting lasers with a thermally actuated cantilever structure. The thermal actuation of a top distributed Bragg reflector mirror enables us to compensate the temperature drift of lasing wavelengths. The temperature dependence of lasing wavelengths could be controlled from −0.011 nm/K to −0.18 nm/K by changing the cantilever length. In addition, a T-shape membrane structure was introduced for efficient electro-thermal tuning. A small temperature dependence of −0.011 nm/K and wavelength tuning of 4 nm were obtained.
- SURFACES AND INTERFACES
101(2012); http://dx.doi.org/10.1063/1.4753817View Description Hide Description
We employ resistance measurements and Raman spectroscopy to investigate the effects of UV ozone (UVO) exposure and Ar annealing on graphene-on-SiO2transistors. Shorter UVO exposures lead to oxygen adsorption and doping; longer exposures lead to significant defect generation and then to etching. Elevated-temperature Ar annealing following UVO exposure leads to local defect healing, as shown by the evolution of the characteristic Raman D- and G-peaks. In striking contrast, the overall graphenetransistor resistance increases significantly due to void formation. Density functional calculations show that carbon-oxygen reactions lead to efficient consumption and release of C atoms (as CO or CO2) under conditions of high surface oxygen concentration.
101(2012); http://dx.doi.org/10.1063/1.4754122View Description Hide Description
We investigated the preparation of single domain Ge(100):As surfaces in a metal-organic vapor phase epitaxy reactor. In situ reflection anisotropy spectra (RAS) of vicinal substrates change when arsenic is supplied either by tertiarybutylarsine or by background during annealing.Low energy electron diffraction shows mutually perpendicular orientations of dimers, scanning tunneling microscopy reveals distinct differences in the step structure, and x-ray photoelectron spectroscopy confirms differences in the As coverage of the Ge(100):As samples. Their RAS signals consist of contributions related to As dimer orientation and to step structure, enabling precise in situ control over preparation of single domain Ge(100):As surfaces.
101(2012); http://dx.doi.org/10.1063/1.4754140View Description Hide Description
Metallic surface is intrinsically hydrophilic due to its high surface energy. In this work, we present a different picture that highly hydrophobicmetallic coatings could be directly fabricated by thermal spraying of Fe-based amorphouspowders through the surface roughness control. These hydrophobiccoatings are amorphous, exhibiting super-high hardness and excellent corrosion resistance. With low surface energy modification, the coatings become superhydrophobic and exhibit clearly self-cleaning effect. The present work opens a window for the applications of the amorphouscoatings.
- STRUCTURAL, MECHANICAL, OPTICAL, AND THERMODYNAMIC PROPERTIES OF ADVANCED MATERIALS
101(2012); http://dx.doi.org/10.1063/1.4752747View Description Hide Description
By in situ uniaxial-tensile tests with dynamic and atomic scale observation, we report the quantitative investigation of strain-induced deformation-twinning process through incoherent twin boundary propagation in nanocrystallineAu. The consecutive and quantitative strain maps revealed that a strong compressive strain, up to 5.8%, was formed. A screw-rotation twinning mechanism by consecutive and collective screw-rotations of triple-partials along a  screw-axis is proposed. This twin generates a macro-strain of 0.707, same as the conventional shear twins, but in a helical manner.
Polarized and diameter-dependent Raman scattering from individual aluminum nitride nanowires: The antenna and cavity effects101(2012); http://dx.doi.org/10.1063/1.4753798View Description Hide Description
Raman scattering of individual aluminum nitride(AlN)nanowires is investigated systematically. The axial direction of single nanowire can be rapidly verified by polarized Raman scattering. The angular dependencies of E2(high) mode show strongly anisotropic behavior in smaller nanowires, which results from optical antenna effect. Raman enhancement (RE) per unit volume of E2(high) increases with decreasing diameter of nanowires. Compared to the thin film, ∼200-fold increase of RE is observed in AlNnanowires having diameter less than 50 nm, which is far beyond the quantum confinement regime. Such a large RE can be attributed to the effects of resonant cavity and stimulated Raman scattering.