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A structure composed of a hexagonal array of Si nanodisks having toroidal dipole resonances and a reflecting mirror separated by a SiO2 spacer is proposed as a platform that exhibits narrow-band perfect absorption in the Si sub-bandgap wavelength range for a CMOS compatible Si based photodetector operating below the bandgap range. The numerical simulation reveals that the structure possesses Fabry–Pérot bound states in the continuum at proper spacer thicknesses due to the interference between the toroidal dipole and its image dipole. By slightly detuning the spacer thickness to meet the critical coupling condition, narrow-band perfect absorption appears despite assumption of a very small extinction coefficient (5 × 10−4). The wavelength of the perfect absorption is controlled in a wide range by the structural parameters of a Si nanodisk hexagonal array and is insensitive to the fluctuation of the extinction coefficient and the choice of a metallic mirror. In the structure, over 90% of incident power can be absorbed in the Si region. This suggests that the structure can be used as a narrow-band photodetector operating in the Si sub-bandgap wavelength range. We also evaluate the sensing performance of the proposed structure as an intensity based refractive index sensor operating in the near-infrared range. [ABSTRACT FROM AUTHOR]

Resonant excitation and manipulation of complex interactions among two or more resonances in high-index dielectric nanostructures provide great opportunities for engineering novel optical phenomena and applications. However, difficulties often arise when interpreting the observed spectra because of the overlap of the broad resonances contributed by many factors such as particle size, shape, and background index. Therefore, selective excitation of resonances that spectrally overlap with each other provides a gateway towards an improved understanding of the complex interactions. Here, we demonstrate selective excitation and enhancement of multipolar resonances of silicon nanospheres using cylindrical vector beams (CVBs) with different diameters of nanospheres and numerical apertures (NAs) of the excitations. By combining single particle spectroscopy and electrodynamic simulations, we show that the radially polarized beam can selectively excite the electric multipoles, whereas the azimuthally polarized beam can selectively excite the magnetic multipoles even though multipolar resonances are convoluted together due to their spectral overlap. Moreover, focusing the CVBs with high NA can lead to a dominant longitudinal polarization of the electric or magnetic field. We show that the enhanced longitudinal polarization with increasing NA of the radially and azimuthally polarized beams can selectively enhance the electric and magnetic multipolar resonances, respectively. Our approach can be used as a spectroscopy tool to enhance and identify multipolar resonances leading to a better understanding of light-matter interactions in other dielectric nanostructures as well as serve as a first step toward excitation of dark mode and Fano resonances in dielectric oligomers by breaking the symmetry of the nanostructures. [ABSTRACT FROM AUTHOR]

Nanoimprinting followed by metal deposition is a low-cost, high-throughput, and highly reproducible process for the fabrication of large-size plasmonic substrates required for commercial products. However, the plasmonic substrates prepared by the process usually have very broad surface plasmon resonances, which cannot be well reproduced by numerical simulations. The poor agreement between experiments and calculations has prevented the detailed analysis of the field enhancement behavior and the improvement of the performance as plasmonic substrates. In this work, we demonstrate that large-area plasmonic substrates with sharp surface plasmon resonances, which can be well reproduced by numerical simulations, are produced by sputter-deposition of gold (Au) on a commercially available nanoimprinted substrate. The good agreement between experiments and simulations allow us to identify the locations and field distributions of the hot spots. The angle dependence of specular reflectance and diffuse reflectance measurements in combination with numerical simulations reveal that a dipolelike bright mode and a higher-order dark mode exist at gaps between Au nanorods. Finally, we demonstrate the application of the developed plasmonic substrates for surface-enhanced fluorescence in sandwich immunoassays for the detection of influenza virus nucleoprotein. We show that the sharp resonance and the capability of precise tuning of the resonance wavelength significantly enhance the luminescence signal. [ABSTRACT FROM AUTHOR]

The behavior of a rarefied gas between two parallel plates, each having its uniform temperature but having a square wave-like distribution of the accommodation coefficients, is numerically analyzed using the Direct Simulation Monte Carlo method. The gas temperature near the plate becomes close to the plate temperature only if the accommodation coefficient of the wall is large enough. A lower accommodation coefficient leads to the difference between the gas temperature and the adjacent wall. This temperature distribution induces a gas flow similar to the well-known thermal transpiration flow along the plate. When only one plate has a wave-like distribution of the accommodation coefficients, an array of vortical flow is induced between the plates. The magnitude of the vortex is linear to the difference in the accommodation coefficients. When both plates have a wave-like distribution of the accommodation coefficients, a one-way flow through the channel between the plates is induced. This flow depends on the phase difference of the discontinuity point. The size of one-way flow is nonlinear to the difference in accommodation coefficients. [ABSTRACT FROM AUTHOR]

The behavior of the rarefied gas in the thermal transpiration pump with the porous material is investigated numerically by the direct simulation Monte Carlo method. The mass flux achieved by the pump is analyzed for a wide range of Knudsen numbers and ratios of the pore length to the pore diameter. The results show that the thermal edge flows around the ends of the pore play an essential role in determining the maximum performance. The effect of the thermal edge flow leads to a qualitative difference in the driving mechanism from a similar thermal transpiration pump by Knudsen. The mass flow takes a maximum value at a considerably large Knudsen number when the pore length is much larger than the pore diameter. The numerical tests show that a larger mass flux is possible when the edge flow is suppressed. The mass flux is investigated for several values of accommodation coefficient and complex pore geometries. The present results show that only the latter leads to the reduction in the mass flux. The compression ratio, including the performance curve of the pump, is also analyzed for several cases. The results show that the small accommodation coefficient decreases the compression ratio of the pump. [ABSTRACT FROM AUTHOR]

Boron (B) doped Si nanocrystals (Si-ncs) dispersed in hydrofluoric (HF) acid solution are prepared by dissolving borosilicate films containing B-doped Si-ncs in HF solution. We find that the etching rate of B-doped Si-ncs is much smaller than that of undoped Si-ncs. The difference of the etching rate allows us to extract only doped Si-ncs in the mixture of doped and undoped Si-ncs and observe the photoluminescence (PL) due to the transition from the conduction band to the acceptor state. The PL was very broad with the maximum around 1.15 eV. From the analysis of the PL data obtained for the samples prepared under different conditions and different etching time, preferential doping sites of B atoms are estimated. The data suggests that B-doped Si-ncs consists of intrinsic cores and heavily B-doped shells. [ABSTRACT FROM AUTHOR]

Presents a study which investigated reactive ion etching of InP using a C[sub2]H[sub6]/hydrogen[sub2]/oxygen[sub2] mixture. Details on the dry etching technique of III-V compound semiconductors; Materials and methods; Overview of the scanning electron microscope photographs of InP substrate; Description of the mass spectra of the gases in the etching chamber.

Studies a rarefied gas between two coaxial circular cylinders made of the condensed phase of the gas, where each cylinder is kept at a uniform temperature and is rotating at a constant angular velocity around its axis. Analysis of the steady behavior of the gas on the basis of kinetic theory from the continuum to the Knudsen limit.

Studies steady evaporating flows from a cylindrical condensed phase into a vacuum, on the basis of kinetic theory. Problem and basic equation; Method of numerical solution; Free molecular and continuum solutions; Macroscopic variables; Mass and energy flows from the cylinder; Velocity distribution function; Effect of condensation factor.

Steady evaporating flows from a spherical condensed phase into a vacuum are considered. On the basis of the Boltzmann–Krook–Welander equation, the behavior of the gas (the velocity distribution function as well as the density, velocity, and temperature) from the sphere to downstream infinity is analyzed numerically in detail for the whole range of the Knudsen number. The discontinuity of the velocity distribution function in the gas, a typical behavior of the gas around a convex body, is analyzed accurately. It extends, with appreciable size, to downstream infinity not only for intermediate and large Knudsen numbers but also even for rather small Knudsen numbers. The flow is highly in nonequilibrium over the whole field except for very small Knudsen numbers. The velocity and temperature at downstream infinity take finite values, determined by the Knudsen number, except the temperature at zero Knudsen number. An analytic solution for small Knudsen numbers, especially the temperature at infinity (frozen temperature) is obtained with the aid of the asymptotic theory and the hypersonic expansion. [ABSTRACT FROM AUTHOR]

Steady evaporating flows from a cylindrical condensed phase in an infinite expanse of its vapor gas are investigated numerically on the basis of the Boltzmann–Krook–Welander equation. Not only the mass flow rate and the energy flow rate from the cylinder, but also the local variables of the gas over the whole flow field are obtained for a wide range of the Knudsen number and the pressure ratio, which is defined by the pressure at infinity divided by the saturation gas pressure at the temperature of the condensed phase. The acceleration of gas flows, especially to a supersonic flow, near the cylinder and the deceleration to the stationary state at infinity are clarified. The discontinuity of the velocity distribution function in the gas, a typical behavior of a gas around a convex body, is analyzed accurately with the difference scheme devised for this purpose, and its relation to the S layer [Phys. Fluids 16, 1422 (1973)] is discussed. [ABSTRACT FROM AUTHOR]

A semi-infinite expanse of a gas in contact with its plane condensed phase is considered. The steady gas flow condensing on or evaporating from the condensed phase is investigated numerically on the basis of the Boltzmann–Krook–Welander equation in the case where there is a gas motion along the condensed phase. First, it is shown by a time-dependent analysis that the steady evaporating flow is possible only when there is no gas motion along the condensed phase. Then, with the aid of time-dependent and time-independent analyses, the effect of gas motion along the condensed phase on the steady condensing flow is clarified. That is, the relation of the parameters at infinity and of the condensed phase that allows a steady flow, together with the accurate profiles of the steady solutions, is established. The present results of the half-space problem complete the boundary condition of the compressible Euler equation required in describing steady gas flows around the condensed phase of a smooth shape in the continuum flow limit. [ABSTRACT FROM AUTHOR]

Focuses on cylindrical Couette flows of a rarefied gas between concentric circular cylinders consisting of the condensed phase of the gas on the basis of kinetic theory. Behavior of the gas in the continuum limit; Asymptotic analysis of the Boltzmann equation; Definition of the Knudsen number of the system.

Demonstrates the unsuitability of the heat-condition equation for describing the temperature field of a gas in the continuum limit around bodies at rest in a closed domain or in an infinite domain without flow at infinity, where the flow vanishes in this limit. Application of the kinetic theory; Basic equation; Asymptotic analysis; Numerical examples.

We demonstrate a new gain switching mechanism in semiconductor lasers with an asymmetric double quantum well. The idea is to utilize overlap integral enhancement for coupled sublevels in the double quantum well at an applied forward voltage. Optical pulses of less than 10 ps full width at half maximum have been readily obtained with a moderate electrical excitation pulse height, 16.3 V (at a 50 Ω load) and bias current of 6% of the threshold. The advantages of the structure over a single quantum well for generating optical short pulses are shown experimentally. [ABSTRACT FROM AUTHOR]

A reactive ion etching method is applied to fabricate mirrors of 1.5 μm GaInAsP/InP mass transport lasers using a mixture of ethane and hydrogen as an etchant. Threshold currents as low as 35 mA are achieved for the 300-μm-long cavity lasers with one etched and one cleaved facet. The differential quantum efficiencies of the lasers with one dry etched facet and both dry etched facets are 13 and 9.5%, respectively. [ABSTRACT FROM AUTHOR]

A 1.5 μm GaInAsP/InP buried-heterostructure laser diode was fabricated by reactive ion etching using a mixture of ethane and hydrogen for the formation of mesa stripe. Blocking layers were regrown on the dry etched wafers by liquid phase epitaxy. Continuous-wave operation was obtained at room temperature. A threshold current as low as 15 mA was achieved, which is superior to that of the same structure laser diode fabricated by conventional chemical etching. [ABSTRACT FROM AUTHOR]

Corrects the errors published in a 1996 'Physics of Fluids' paper about the inappropriateness of the heat conduction equation for description of a temperature field of a stationary gas in the continuum limit. Asymptotic analysis; Numerical computation; Boltzmann equation.