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.
103(2013); http://dx.doi.org/10.1063/1.4855055View Description Hide Description
ZnO-based photo-thin film transistors with enhanced photoresponse were developed using transparent conductive oxide contacts. Changing the electrode from opaque Mo to transparent In-Zn-O increases the photocurrent by five orders of magnitude. By changing the opacity of each source and drain electrode, we could observe how the photoresponse is affected. We deduce that the photocurrent generation mechanism is based on an energy band change due to the photon irradiation. More importantly, we reveal that the photocurrent is determined by the energy barrier of injected electrons at the interface between the source electrode and the active layer.
103(2013); http://dx.doi.org/10.1063/1.4852017View Description Hide Description
We demonstrate an atom chip trapping system that allows the placement and high-resolution imaging of ultracold atoms within microns from any ≲100 μm-thin, UHV-compatible material, while also allowing sample exchange with minimal experimental downtime. The sample is not connected to the atom chip, allowing rapid exchange without perturbing the atom chip or laser cooling apparatus. Exchange of the sample and retrapping of atoms has been performed within a week turnaround, limited only by chamber baking. Moreover, the decoupling of sample and atom chip provides the ability to independently tune the sample temperature and its position with respect to the trapped ultracold gas, which itself may remain in the focus of a high-resolution imaging system. As a first demonstration of this system, we have confined a 700-nK cloud of 8 × 104 87Rb atoms within 100 μm of a gold-mirrored 100-μm-thick silicon substrate. The substrate was cooled to 35 K without use of a heat shield, while the atom chip, 120 μm away, remained at room temperature. Atoms may be imaged and retrapped every 16 s, allowing rapid data collection.
Far off-resonant coupling between photonic crystal microcavity and single quantum dot with resonant excitation103(2013); http://dx.doi.org/10.1063/1.4852555View Description Hide Description
In this paper, we experimentally demonstrate that with sub-nanowatt coherent s-shell excitation of a single InAs quantum dot, off-resonant coupling of 4.1 nm is possible between L3 photonic crystal microcavity and the quantum dot at 50 K. This resonant excitation reduces strongly the effect of surrounding charges to quantum dot, multiexciton complexes and pure dephasing. It seems that this far off-resonant coupling is the result of increased number of acoustical phonons due to high operating temperature of 50 K. The 4.1 nm detuning is the largest amount for this kind of coupling.
Terahertz generation and detection with InGaAs-based large-area photoconductive devices excited at 1.55 μm103(2013); http://dx.doi.org/10.1063/1.4855616View Description Hide Description
We report on scalable large-area terahertz emitters and detectors based on In0.53Ga0.47As/In0.52Al0.48As heterostructures for excitation with 1.55 μm radiation. Different geometries involving three different electrode gap sizes are compared with respect to terahertz (THz) emission, bias field distribution, and Joule heating. The field distribution becomes more favorable for THz emission as gap size increases, while Joule heating exhibits the opposite dependence. Devices with three different gap sizes, namely 3 μm, 5 μm, and 7.5 μm, have been investigated experimentally, the emitter with a gap size of 7.5 μm showed the best performance. The scalable devices are furthermore employed as detectors. The scalable electrode geometry enables spatially integrated detection, which is attractive for specific applications, e.g., where an unfocused THz beam has to be used.
103(2013); http://dx.doi.org/10.1063/1.4851095View Description Hide Description
We report on the demonstration of correlated photon pair generation in a quasi-phase-matched superlattice GaAs/AlGaAs waveguide using a continuous-wave pump. Our photon pair source has a low noise level and achieves a high coincidence-to-accidental ratio greater than 100, which is the highest value reported in III–V chips so far. This correlated photon pair source has the potential to be monolithically integrated with on-chip pump laser sources fabricated on the same superlattice wafer structure, enabling direct correlated/entangled photon pair production from a compact electrically powered chip.
103(2013); http://dx.doi.org/10.1063/1.4852715View Description Hide Description
A frequency selective metasurface capable of sorting photons in the near-infrared spectral range is designed, fabricated, and characterized. The metasurface, a periodic array of dielectric cylindrical cavities in a gold film, localizes and transmits light of two spectral frequency bands into spatially separated cavities, resulting in near-field light splitting. The design and fabrication methodologies of the metasurface are discussed. The transmittance and photon sorting properties of the designed structure is simulated numerically and the measured transmission is presented.
- 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.