Volume 103, Issue 25, 16 December 2013
- 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:
In order to assess the role of cytoskeletal structure in modulating cell surface topography during cell transformation, we investigated cytoskeletal organization of Madin-Darby canine kidney (MDCK) epithelial cells at different thermal gradients. Specifically, we examined actin polymerization as a function of temperature in a controlled thermal environment. After applying an increase in temperature of 5 °C, we observed fewer actin filaments in the network, as these molecular polymers depolymerized. Partial stress fibers of MDCK cells could be rearranged, but some of them were disrupted irreversibly after a second thermal treatment, and MDCK cells underwent apoptosis at higher temperatures as well.
- PHOTONICS AND OPTOELECTRONICS
103(2013); http://dx.doi.org/10.1063/1.4851115View Description Hide Description
We report on a multimodal analysis of photonic crystal L3 cavities milled in lithium niobate free-standing membranes. The classical L3 cavity geometry is compared to an L3 cavity containing a second lattice superimposed on the primary one. Those two different geometries are investigated in terms of vertical radiation and quality (Q) factor for each mode of the cavities. Depending on the cavity geometry, some modes undergo an enhancement of their vertical radiation into small angles while other modes experience a higher Q factor. Experimental characterizations are corroborated by three-dimensional finite difference time domain simulations.
103(2013); http://dx.doi.org/10.1063/1.4850522View Description Hide Description
We suggest a concept of a tunable graphene-based terahertz (THz) surface emitting laser with diffusion pumping. We employ significant difference in the electronic energy gap of graphene and a typical wide-gap semiconductor, and demonstrate that carriers generated in the semiconductor can be efficiently captured by graphene resulting in population inversion and corresponding THz lasing from graphene. We develop design principles for such a laser and estimate its performance. We predict up to 50 W/cm2 terahertz power output for 100 kW/cm2 pump power at frequency around 10 THz at room temperature.
103(2013); http://dx.doi.org/10.1063/1.4851118View Description Hide Description
Terahertz generation by femtosecond laser pulses with tilted intensity front in room-temperature and cryogenically cooled LiNbO3 crystals was investigated. The role of the interaction length and pump pulse duration was studied for weak and strong laser pump. It was shown that the optical-to-terahertz conversion efficiency is saturated as a result of the Kerr self-phase modulation of the optical pump.
103(2013); http://dx.doi.org/10.1063/1.4852035View Description Hide Description
Conversion of fs supercontinuum to the ultraviolet (UV) range from 260 to 305 nm in nonlinear photonic crystal of strontium tetraborate is obtained. Spectral shape of generated UV radiation is governed by the shape of supercontinuum spectrum, focusing conditions and phase mismatch in the material of nonlinear photonic crystal. Maximum integral UV power of 2.6 μW was obtained in the case of weaker focusing, and peaks with the spectral width 1–3 nm dominate in the spectrum. Using tight focusing, broadband radiation in the range 265–300 nm was obtained.
Manipulating terahertz electromagnetic induced transparency through parallel plate waveguide cavities103(2013); http://dx.doi.org/10.1063/1.4852115View Description Hide Description
To mechanically manipulate of electromagnetic induced transparency (EIT) in terahertz asymmetric parallel-plate waveguide cavities, the influence of waveguide spacing on the transmission response has been studied experimentally. After setting the appropriate shifting length between two cavities, we found with mechanically increasing the waveguide spacing, the symmetric resonance shows degeneracy when its wavelength is smaller than the waveguide spacing. An on-to-off modulation for symmetric resonance appeared in EIT can be observed with destructive interference broken. This control mechanism of EIT will open a door to design the tunable EIT devices.
103(2013); http://dx.doi.org/10.1063/1.4852775View Description Hide Description
We report the experimental realization of a high-Q slot photonic crystal cavity in Silicon-On-Insulator (SOI) configuration infiltrated by a liquid. Loaded Q-factor of 23 000 is measured at telecom wavelength. The intrinsic quality factor inferred from the transmission spectrum is higher than 200 000, which represents a record value for slot photonic crystal cavities on SOI, whereas the maximum of intensity of the cavity is roughly equal to 20% of the light transmitted in the waveguide. This result makes filled slot photonic crystal cavities very promising for silicon-based light emission and ultrafast nonlinear optics.
103(2013); http://dx.doi.org/10.1063/1.4835115View Description Hide Description
The polarization properties of a GaN nanowire laser are studied experimentally by direct analysis of the nanowire's end-facet emission. Linear and elliptical light polarizations are measured at different pumping strengths. Switching between these two polarization states is also observed as the optical excitation is increased. We attribute this polarization switching to a change in the transverse modes due to their different cavity losses.
103(2013); http://dx.doi.org/10.1063/1.4851938View Description Hide Description
Plasmonic off-axis unidirectional beaming of luminescence is demonstrated using nitride semiconductor quantum wells. The underlying mechanism involves the near-field excitation of surface plasmon polaritons on an ultrathin metal film, which are then diffractively scattered by an adjacent periodic array of asymmetric metallic nanoparticles. By tailoring the nanoparticles shape, we show that forward scattering can be suppressed in favor of backward diffraction (or vice versa), thereby enabling unidirectional beaming at geometrically tunable oblique angles. These nanostructures can be used to control the output light directionality of arbitrary planar luminescent devices, with a spatial resolution that would be unattainable with bulk optics.
Large area, low capacitance, GaAs nanowire photodetector with a transparent Schottky collecting junction103(2013); http://dx.doi.org/10.1063/1.4852136View Description Hide Description
We present experimental results on a GaAs/Indium-Tin-Oxide Schottky-like heterojunction photodetector based on a nanowire device geometry. By distributing the active detecting area over an array of nanowires, it is possible to achieve large area detection with low capacitance. Devices with bare GaAs and passivated AlGaAs/GaAs nanowires are fabricated to compare the responsivity with and without surface passivation. We are able to achieve responsivity of >0.5A/W and Signal-Noise-Ratio in excess of 7 dB for 2 V applied reverse bias with passivated nanowire devices. Capacitance-voltage measurement yields <5 nF/cm2, which shows a strong possibility for high-speed applications with a broad area device.
Negative group velocity propagation in a highly nonlinear fiber embedded in a stimulated Brillouin scattering laser ring cavity103(2013); http://dx.doi.org/10.1063/1.4852735View Description Hide Description
Superluminal propagation at negative group velocity was demonstrated in a highly nonlinear fiber embedded in a stimulated Brillouin scattering laser ring cavity. A maximum advancement of 369 ns and strong Stokes lasing power of 482 mW were observed when the cavity was pumped with a 1 MHz sinusoidal wave modulated signal at the power level of 1 W. The frequency dependence of fast light in this fiber ring cavity was examined with modulation frequencies of 1 kHz to 15 MHz, a maximum fractional advancement of 0.54 was achieved at 10 kHz, and a maximum negative group index of −9480 was demonstrated at 1 kHz.
- SURFACES AND INTERFACES
103(2013); http://dx.doi.org/10.1063/1.4850525View Description Hide Description
We report enhanced life-time stability for the electron field emitters prepared by coating nanocrystalline diamond (NCD) on carbon nanotubes (CNTs). Upon overcoming the problem of poor stability in CNTs, the NCD-CNTs exhibit excellent life-time stability of 250 min tested at different applied voltages of 600 and 900 V. In contrast, the life-time stability of CNTs is only 33 min even at relatively low voltage of 360 V and starts arcing at 400 V. Hence, the NCD-CNTs with improved life-time stability have great potential for the applications as cathodes in flat panel displays and microplasma display devices.
103(2013); http://dx.doi.org/10.1063/1.4850520View Description Hide Description
Stability of oxide/semiconductor interfaces during device fabrication is critically important, particularly for adoption of new semiconductor channel materials, such as III-V compounds. Unintentional oxidation of an underlying In0.53Ga0.47As(100) surface through atomic layer deposited (ALD) Al2O3 layers of varying thickness is investigated. Oxygen annealing of 1 ∼ 2 nm thickness Al2O3 layers at 300 °C or higher and large-dose water vapor exposure during the ALD-Al2O3 process at 300 °C produces InGaAs surface oxidation. This subcutaneous oxidation of InGaAs increases the Al2O3/InGaAs interface defect density as observed in suppressed band-edge photoluminescence and in capacitance-voltage analysis, possibly by creating As dangling bonds at the InGaAs surface.
103(2013); http://dx.doi.org/10.1063/1.4850527View Description Hide Description
We have studied the influence of oxygen exposure at the prototypical interface between cobalt and the organic semiconductor tris(8-hydroxyquinoline)aluminum (III) (Alq3) by photoemission spectroscopy. We find that oxidation of the cobalt leads to a gradual suppression of hybrid interface states, to a progressive change in the work function and to a continuous energetic shift of the molecular orbitals towards higher binding energies. Based on these observations, we propose controlled oxidation of the ferromagnetic electrode as an easy and effective possibility to tune the performance of organic spintronics devices.
103(2013); http://dx.doi.org/10.1063/1.4850532View Description Hide Description
We show that a flat surface of a polymer in rubber state illuminated with intense electromagnetic radiation is unstable with respect to periodic modulation. Initial periodic perturbation is amplified due to periodic thermal expansion of the material heated by radiation. Periodic heating is due to focusing-defocusing effects caused by the initial surface modulation. The surface modulation has a period longer than the excitation wavelength and does not require coherent light source. Therefore, it is not related to the well-known laser induced periodic structures on polymer surfaces but may contribute to their formation and to other phenomena of light-matter interaction.
103(2013); http://dx.doi.org/10.1063/1.4851239View Description Hide Description
Ultrathin (sub-monolayer to 12 monolayers) AlN nanosheets are grown epitaxially by plasma assisted molecular beam epitaxy on Ag(111) single crystals. Electron diffraction and scanning tunneling microscopy provide evidence that AlN on Ag adopts a graphite-like hexagonal structure with a larger lattice constant compared to bulk-like wurtzite AlN. This claim is further supported by ultraviolet photoelectron spectroscopy indicating a reduced energy bandgap as expected for hexagonal AlN.
103(2013); http://dx.doi.org/10.1063/1.4852015View Description Hide Description
Water on structured hydrophobic surfaces can be supported in a Wenzel or Cassie state, depending on surface chemistry and structure geometry. The Cassie state is often desirable for superhydrophobic materials as it features high contact angles and low contact angle hysteresis due to an air layer which separates most of the liquid from contact with the solid. We present evidence that multiple wetting states for water can also exist on multiscale structured surfaces with a layer of an immiscible liquid coating the surface and that a Cassie-like state can be achieved which results in enhancement of the surface properties.
- STRUCTURAL, MECHANICAL, OPTICAL, AND THERMODYNAMIC PROPERTIES OF ADVANCED MATERIALS
103(2013); http://dx.doi.org/10.1063/1.4850195View Description Hide Description
A unique type of heavy transition metal carbide Ru2C was synthesized experimentally at high pressure-high temperature and consequently quenched to ambient condition. The dynamical stability study reveals the instability at ambient condition. We have found that it can be stabilized from 30 to 110 GPa. The stronger 4d-2p hybridization and the formation of a cage like Fermi surface do impact the stability. The mixed bands primarily 2p characteristic weighted crossing the Fermi level form a Fermi surface piece at Gamma point under pressure. The clear change of topology of Fermi surface verifies the Lifshitz transition from ambient condition to high pressure.
103(2013); http://dx.doi.org/10.1063/1.4850196View Description Hide Description
The microwave properties of polymer-based glass fiber reinforced composites containing amorphous Fe77Si10B10C3 microwires in parallel and orthogonal arrays and their dependencies on external magnetic field have been investigated. Double-negative-index characteristics are confirmed for both wire arrays through the observed transmission window in the 1–7 GHz frequency band. The microwave interaction within inter-wire range is responsible for a multi-peak feature observed in the absorption spectra of the parallel wire array composite when the wire spacing is below 7 mm. We introduce the term of “effective diameter” associated with the microwire domain structure to remedy the discrepancy between the computed and experimentally observed plasma frequency.
Influence of c-axis orientation and scandium concentration on infrared active modes of magnetron sputtered ScxAl1−xN thin films103(2013); http://dx.doi.org/10.1063/1.4850735View Description Hide Description
Doping of wurtzite aluminium nitride (AlN) with scandium (Sc) significantly enhances the piezoelectric properties of AlN. ScxAl1−xN thin films with different Sc concentrations (x = 0 to 0.15) were deposited by DC reactive magnetron sputtering. Infrared (IR) absorbance spectroscopy was applied to investigate the Sc concentration dependent shift of the IR active modes E1(TO) and A1(TO). These results are compared to ab initio simulations, being in excellent agreement with the experimental findings. In addition, IR spectroscopy is established as an economical and fast method to distinguish between thin films with a high degree of c-axis orientation and those exhibiting mixed orientations.
103(2013); http://dx.doi.org/10.1063/1.4850877View Description Hide Description
In this Letter, we study the stability of the domain model for lithium intercalated graphite in stages III and II by means of Density Functional Theory and Kinetic Lattice Monte Carlo simulations. We find that the domain model is either thermodynamically or kinetically stable when compared to the standard model in stages III and II. The existence of domains in the intercalation sequence is well supported by recent high resolution transmission electron microscope observations in lithiated graphite. Moreover, we predict that such domain staging sequences leads to a wide range of diffusivity as reported in experiments.