A hydrogen sensor based on plasmonic metasurfaces is demonstrated to exhibit the industry-required 10 s reaction time and sensitivity. It consists of a layer of either Y or WO 3 sandwiched between a top Pd nanodisk and a Au mirror at the base. The phase change layer (Y, WO 3 ) reacts with hydrogen, and the corresponding change of the refractive index (permittivity) is detected by the spectral shift of the resonance dip in reflectance at the IR spectral window. This direct reflectance readout of the permittivity change due to hydrogen uptake is fast and is facilitated by radiation field enhancement extending into the phase change volume. Numerical modeling was used to elucidate the effects that real and imaginary parts of the refractive index exert on the spectral shifts of resonance. The mechanism of sensor performance is outlined, and a possibility to tune its spectral range of operation by the diameter of the Pd nanodisk and thickness of the phase change material makes this design applicable to other molecular detection applications including surfaceenhanced IR absorption.
We investigated the quantum confined Stark effect in GaAs quantum wires formed in a V-groove structure, demonstrating observation of a blueshift of the photoluminescence peak with the increase of electric fields at 50 K. This blueshift is attributed to the fact that the change in enhanced binding energy of excitons due to the electric field is larger than that in quantized energy levels of electrons and holes. Time-resolved photoluminescence was also measured. The photoluminescence decay time is decreased in small quantum wires of 8 nm width with the increase of electric fields, while the decay time is increased in the quantum wires with a size of 35 nm. These results indicate that the escaping of carriers is more dominant in smaller structures than reduction of the oscillator strength due to the electric fields.
An InGaAs/InAlAs five-layer asymmetric coupled quantum well (FACQW) exhibiting a giant electrorefractive index change was proposed and has been studied theoretically and experimentally. Giant electrorefractive sensitivity |d
n/d
F| (4.4×10-4 cm/kV) at a wavelength range with a width of over 100 nm can be expected at an electric field of approximately F=-30 to -60 kV/cm. The FACQW structure was successfully fabricated using molecular beam epitaxy (MBE). The results of photoabsorption current measurements are consistent with the theory. The giant electrorefractive index change of the FACQW is very promising for realizing low-voltage and high-speed compact Mach–Zehnder modulators and switches.
A strained InGaAs quantum wire laser with a vertical microcavity structure was fabricated for the first time. In this laser structure, quantum wires with a lateral width of about 10 nm were grown by a selective metalorganic chemical vapor deposition technique. The length of the microcavity was 4λ(λ=883 nm), with AlAs/AlGaAs distributed Bragg reflectors. The cavity effect was demonstrated by the measurement of photoluminescence with and without the cavity. Lasing oscillation was observed at 77 K by optical pumping.
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