Volume 100, Issue 21, 21 May 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:
Transdermal delivery of nanocarriers provides an alternative pathway to transporttherapeutic agents, alleviating pain, improving compliance of patients, and increasing overall effectiveness of delivery. In this work, enhancement of transdermal delivery of fluorescent nanoparticles and sulforhodamine B with assistance of oleic acid was visualized utilizing multiphoton microscopy (MPM) and analyzed quantitatively using multi-photon excitation-induced fluorescent signals. Results of MPM imaging and MPM intensity-based spatial depth-dependent analysis showed that oleic acid is effective in facilitating transdermal delivery of nanoparticles.
- PHOTONICS AND OPTOELECTRONICS
100(2012); http://dx.doi.org/10.1063/1.4720094View Description Hide Description
We demonstrate the feasibility of the InAs/GaSb/AlSb type-II superlatticephotodiodes operating at the short wavelength infrared regime below 3 μm. An n-i-p type-II InAs/GaSb/AlSb photodiode was grown with a designed cut-off wavelength of 2 μm on a GaSb substrate. At 150 K, the photodiode exhibited a dark current density of 5.6 × 10−8 A/cm2 and a front-side-illuminated quantum efficiency of 40.3%, providing an associated shot noise detectivity of 1.0 × 1013 Jones. The uncooled photodiode showed a dark current density of 2.2 × 10−3 A/cm2 and a quantum efficiency of 41.5%, resulting in a detectivity of 1.7 × 1010 Jones.
Terahertz time-domain spectroscopy of anisotropic complex conductivity tensors in silicon nanowire films100(2012); http://dx.doi.org/10.1063/1.4721490View Description Hide Description
The effective complex conductivitytensor of a highly anisotropic, vertically aligned siliconnanowire film was measured by terahertz time-domain spectroscopy. The siliconnanowires were fabricated on a p-type silicon substrate by metal-assisted chemical etching, which resulted in a film with uniaxially anisotropic optical properties. The measured terahertz transverse and longitudinal conductivity values were in excellent agreement with the results of calculations based on the Drude-Smith and Lorentz models, respectively.
100(2012); http://dx.doi.org/10.1063/1.4719077View Description Hide Description
The initial proposal for scalable optical quantum computing required single photon sources, linear optical elements such as beamsplitters and phaseshifters, and photon detection. Here, we demonstrate a two qubit gate using indistinguishable photons from a quantum dot in a pillar microcavity. As the emitter, the optical circuitry, and the detectors are all semiconductor, this is a promising approach towards creating a fully integrated device for scalable quantum computing.
100(2012); http://dx.doi.org/10.1063/1.4720179View Description Hide Description
Many applications require a low-cost and large-scale mode of flexible electronics with reasonably high photoresponse that can be detected without high precision measurement systems. We demonstrate a very easy to fabricate ZnOUV sensor, made on common pencil drawn circuit over a paper. ZnO nanocrystals were extracted in a high throughput via a simple and green route. This sensor is well capable of detecting UV light and demonstrates features comparable to those of made with complex and expensive techniques.
Partial rectification of the plasmon-induced electrical tunnel current in discontinuous thin gold film at optical frequency100(2012); http://dx.doi.org/10.1063/1.4720513View Description Hide Description
The effect of plasmonoscillations, induced by pulsed laserirradiation, on the DC tunnel current between islands in a discontinuous thin goldfilm is studied. The tunnel current is found to be strongly enhanced by partial rectification of the plasmon-induced AC tunnel currents flowing between adjacent gold islands. The DC tunnel current enhancement is found to increase approximately linearly with the laser intensity and the applied DC bias voltage. The experimental data can be well described by an electron tunnelling model which takes the plasmon-induced AC voltage into account. Thermal heating seems not to contribute to the tunnel current enhancement.
100(2012); http://dx.doi.org/10.1063/1.4722917View Description Hide Description
In this paper, we present experimental demonstration of a resonant-cavity-enhanced mid-infrared photodetector monolithically fabricated on a silicon substrate. Dual-band detection at 1.6 μm and 3.7 μm is achieved within a single detector pixel without cryogenic cooling, by using thermally evaporated nanocrystalline PbTe as the photoconductive absorbers. Excellent agreement between theory and experiment is confirmed. The pixel design can potentially be further extended to realizing multispectral detection.
- SURFACES AND INTERFACES
100(2012); http://dx.doi.org/10.1063/1.4720402View Description Hide Description
We theoretically investigate the role of the dielectric mismatch between materials on the energy levels and recombination energies of a core-shell nanowire. Our results demonstrate that when the dielectric constant of the core material is lower than that of the shell material, the self-image potential pushes the charge carriers towards the core-shell interface in such a way that the ideal confinement model is no longer suitable. The effects of this interfacial confinement on the electronic properties of such wires, as well as on its response to applied magnetic fields, are discussed.
Contributions of atomic diffusion and plastic deformation to the plasma surface activation assisted diffusion bonding of zirconium-based bulk metallic glass100(2012); http://dx.doi.org/10.1063/1.4721665View Description Hide Description
A mathematical model was established to estimate the contributions of atomic diffusion and plastic deformation to the diffusion bonding of zirconium-based bulk metallic glasses. Additionally, the surface state was introduced into the model since oxide film is the main barrier to atomic bonding across interface. The model calculation displayed that the contribution of plastic deformation to void closure was six orders of magnitude higher than atomic diffusion. The joints with ion etching before bonding were achieved to verify the model. The experimental strength of joints had a sound fit with the theoretical strength calculated by the model.
- STRUCTURAL, MECHANICAL, OPTICAL, AND THERMODYNAMIC PROPERTIES OF ADVANCED MATERIALS
100(2012); http://dx.doi.org/10.1063/1.4720181View Description Hide Description
Cylindrical actuators are made with dielectricelastomer sheets stiffened with fibers in the hoop direction. When a voltage is applied through the thickness of the sheets, large actuation strains are achievable in the axial direction, with or without pre-straining and mechanical loading. For example, actuation strains of 35.8% for a cylinder with a prestrain of 40%, and 28.6% for a cylinder without pre-strain have been achieved without any optimization. Furthermore, the actuation strain is independent of the aspect ratio of the cylinder, so that both large strains and large displacements are readily actuated by using long cylinders.
Ultrafast optical response originating from carrier-transport processes in undoped GaAs/n-type GaAs epitaxial structures100(2012); http://dx.doi.org/10.1063/1.4720157View Description Hide Description
We have investigated ultrafast optical responses of undoped GaAs/n-type GaAs (i-GaAs/n-GaAs) epitaxial structures at room temperature using a reflection-type pump-probe technique. The built-in electric field in the i-GaAs layer is controlled by its thickness. It is found that the decay time of a photoexcitation-induced reflectivity change in a sub-picosecond range decreases with an increase in the built-in electric field strength. The observed optical response is related to the transport process of photogenerated carriers from the i-GaAs layer to the n-GaAs layer. The shortest response time about 60 fs demonstrates that the i-GaAs/n-GaAs structure is useful for ultrafast optical applications.
100(2012); http://dx.doi.org/10.1063/1.4720169View Description Hide Description
The mechanical properties of ZnO were examined using nanoindentation and microcompression. The modulus, hardness, onset of yielding, and shear strength of the as-grown wafer measured by nanoindentation are 140, 7.1, 12, and 3.6 GPa. The onset of shearing (3.6 GPa) corresponds to the theoretical shear strength. Young’s modulus and yield strength measured from micropillar samples were 123 and 3 GPa. The primary slip plane forms an acute angle of 62° with respect to the basal planes, indicting it is pyramidal. Thermal annealing does not affect the residual stresses but can reduce the defect concentration, thus improves the ZnO luminescent properties.
Electrostatically driven collapsible Au thin films assembled using transfer printing for thermal switching100(2012); http://dx.doi.org/10.1063/1.4720397View Description Hide Description
We report deterministic assembly of 100 nm thick suspended goldfilms using transfer printing that are mechanically collapsible. We demonstrate the latter using electrostatic force to establish and break physical contact between the film and a silicon dioxide substrate in a reversible and repeatable manner. Modeling the thermal conductance at the interface between the suspended film and the substrate, we show that the fabricated structure behaves as a thermal switch. The on-state corresponds to the collapsed film and the off-state to the fully suspended film. The on- to off-state ratio for thermal conductance exceeds 106 in theory.
Time resolved pump-probe scattering in MnAs/GaAs(001): A look into the dynamics of α-β stripe domains100(2012); http://dx.doi.org/10.1063/1.4720398View Description Hide Description
Scattering of 130 nm radiation with 100 fs pulse length was used to monitor the α/β-striped microstructure in MnAs/GaAs(001), after a 390 nm 5 mJcm−2 pump pulse. A strong reduction of the Bragg peak intensity, corresponding to a widening of the β-stripes, takes place with a characteristic time of 15 ps. These results are relevant within the context of using MnAs/GaAs(001) as a template for the growth of ferromagnetic films, whose magnetization direction can be controlled by modifying the template temperature.
Temperature dependence of the energy gap and spin-orbit splitting in a narrow-gap InGaAsSb solid solution100(2012); http://dx.doi.org/10.1063/1.4720515View Description Hide Description
Temperature dependence of the energy gap and the spin-orbit split off transition in a thick layer of narrow-gap InGaAsSb material with high In content has been determined by a combination of photoluminescence and photoreflectance. The respective temperature coefficients have been found to be equal for both the transitions and determined to be α = −0.41 meV/K. For the investigated In0.86Ga0.14As0.83Sb0.17 alloy, the separation energy of the split-off band has been obtained to be Δso = 0.460 eV and experimentally evidenced to be independent on temperature, which opens broad application prospects for these multinary (multicomponent) narrow gap compounds and their heterostructures.
100(2012); http://dx.doi.org/10.1063/1.4721660View Description Hide Description
We fabricate and study quantum dot structures incorporating quasi-one-dimensional excited states. The structures are realized by graded bandgap GaAs/AlGaAs quantum wires self-formed inside inverted tetrahedral pyramids. The ground state transitions exhibit typical characteristics of fully confined excitons, including single photon emission. Efficient carrier thermalization and relaxation, as well as correlated photon emission is observed also among the excited states, indicating the formation of quasi-one-dimensional multi-exciton states. These structures offer interesting possibilities for collecting and directing charge carriers towards heterostructured potential traps.
Parametric optomechanical oscillations in two-dimensional slot-type high-Q photonic crystal cavities100(2012); http://dx.doi.org/10.1063/1.4719107View Description Hide Description
We experimentally demonstrate an optomechanical cavity based on an air-slot photonic crystalcavity with optical quality factor Qo = 4.2 × 104 and a small modal volume of 0.05 cubic wavelengths. The optical mode is coupled with the in-plane mechanical modes with frequencies up to hundreds of MHz. The fundamental mechanical mode shows a frequency of 65 MHz and a mechanical quality factor of 376. The optical spring effect, optical damping, and amplification are observed with a large experimental optomechanical coupling rate gom /2π of 154 GHz/nm, corresponding to a vacuum optomechanical coupling rate g */2π of 707 kHz. With sub-mW or less input power levels, the cavity exhibits strong parametric oscillations. The phase noise of the photonic crystal optomechanical oscillator is also measured.
100(2012); http://dx.doi.org/10.1063/1.4722789View Description Hide Description
A digital holographic interferometry was applied to analyze the morphology transformation of the magnetorheological elastomer, and both the contraction and stretch deformation were observed under applying an external magnetic field on the sample. Both isolated particles and grouped particles were observed in the magnetorheological elastomer sample, and these two kinds of particles resulted in the concave-convex deformation of the sample. The deformation of magnetorheological elastomer was calculated by using a 2D finite element model, and the results agreed well with the experimental analysis.
100(2012); http://dx.doi.org/10.1063/1.4720167View Description Hide Description
Ultraviolet-visible absorption spectra of nanoscaled EuS thin films reveal a blue shift of the energy between the top-valence and bottom-conduction bands. This band-gap tuning changes smoothly with decreasing film thickness and becomes significant below the exciton Bohr diameter ∼3.5 nm indicating strong quantum confinement effects. The results are reproduced in the framework of the potential morphing method in Hartree Fock approximation. The large values of the effective mass of the holes, due to localization of the EuS f-states, limit the blue shift to about 0.35 eV. This controllable band-gap tuning of magnetic semiconductor EuS renders it useful for merging spintronics and optoelectronics.
100(2012); http://dx.doi.org/10.1063/1.4720180View Description Hide Description
An ordered L10structure has been formed in near-stoichiometric Fe-Au alloy nanoparticles. The L10structure with a = 0.367 nm and c = 0.360 nm was observed in nanoclusters with diameters below 10 nm after slow cooling from 600 °C. The stable L10structure formed from a parent fcc solid solution phase observed in the as-formed clusters. The fcc phase has a lattice parameter of 0.417 nm, significantly expanded compared to both Au and γ-Fe. The saturation magnetization and coercivity of both fcc and L10structures were much lower than expected considering Fe dilution effects suggesting competing ferromagnetic and anti-ferromagnetic ordering.
100(2012); http://dx.doi.org/10.1063/1.4722786View Description Hide Description
Molecular dynamics (MD) simulations were employed to study the mechanical response of various bicrystal graphene consisting of symmetric tilt boundary subject to uniaxial tensile loading at room temperature. We found that the strength of zigzag-oriented graphene increases slightly with mis-orientation angle, while the strength of armchair-oriented graphene deceases slightly with mis-orientation angle. Given that the difference in strength is small, one might conclude that the dependence of strength of graphene sheet containing grain boundaries upon tilt mis-orientation angle is rather weak. The origin for such weak dependence is believed to be that these grain boundaries all consisting of pentagon-heptagon pairs do not resemble nano-cracks, which result in rather heterogeneous stress field around the crack tip and therefore stress gradient plays an important role.