Solar cells and optical detection devices often incorporate antireflective surfaces to reduce undesired reflection and enhance optical absorption. This letter reports a “black silicon” structure of antireflective porous silicon fabricated by using electrochemical etching. The sample has a gradient-index multilayer structure, i.e., the refraction indices of the structure increase from the top (near the air) to the bottom (near the Si substrate). Reflectance below 5% is obtained over a broad wave number range $(3000–28000{\mathrm{cm}}^{-1})$ and the depression mechanism of the optical reflectance is analyzed by simulating the structure with the transfer matrix method. The simulated result fits the measured spectra well.

In an assembly of double-layered metallic U-shaped resonators with two resonant frequencies ${\omega }_H$ and ${\omega }_L$, the effective induced electric and magnetic dipoles, which originate from the specific distribution of induced surface electric current upon the illumination of incident light, are collinear at the same frequency. Consequently, for left circularly polarized incident light, negative refractive index occurs at ${\omega }_H$, whereas for right circularly polarized incident light it occurs at ${\omega }_L$. We suggest that this design provides a new example to apply chiral structures to tune the electromagnetic properties, and could be enlightening in exploring chiral metamaterials.

Fourier transform infrared (FTIR) spectrometer is a powerful tool for studying the photoluminescence (PL) properties of semiconductors, due to its well-known multiplexing and throughput advantages. However, it suffers from internal He–Ne laser disturbance in near-infrared and∕or environmental background thermal emission in mid- and far-infrared spectral regions. In this work, a modulated PL technique is developed based on step-scan (SS)-FTIR spectrometer. Theoretical analysis is conducted, and applications of the technique are given as examples in the PL study of mid-infrared HgCdTe thin films and near-infrared $\mathrm{Ga}\mathrm{In}\mathrm{P}∕\mathrm{Al}\mathrm{Ga}\mathrm{In}\mathrm{P}$ multiple quantum wells, respectively. The results indicate that the He–Ne laser and∕or thermal emission disturbance can be reduced at least $1∕1000$ and∕or even $1∕10000$ , respectively, by the modulated SS-FTIR PL technique, and hence a rather smooth PL spectrum can be obtained even under room temperature for HgCdTe thin films. A brief comparison is given of this technique with previously reported phase-sensitive modulation methods based on conventional rapid-scan (RS)-FTIR spectrometer, and the advantages of this technique over the former RS- FTIR-based ones are emphasized.

We report in this Letter that when radiation is incident on a metal surface perforated with an array of ring-shaped subwavelength apertures, the phase difference between the propagating surface Bloch wave and the localized surface wave can be tailored by the geometrical parameters of the array so as to affect the shape of the transmission spectrum. Above the resonant frequency of the aperture, interference between the two kinds of surface waves leads to a minimum in the transmission spectrum, whereas below it, the interference leads to a maximum. We suggest that this feature provides flexibility in engineering surface-wave-based all-optical devices.

A model for lattice thermal conductivity in a semiconductor nanowire with a rectangular cross section is investigated. It is based on solving the equations of phonon radiative transfer taking into account interface scattering and modification of the acoustic phonon dispersion. From the numerical calculations, we predict a decrease by an order of magnitude of the lattice thermal conductivity of a 10-nm-thick and 20-nm-wide rectangular nanowire. The interface scattering and phonon confinement play important roles in the reduction of lattice thermal conductivity. The nanowire lattice thermal conductivity is found to decrease with increasing temperature at moderate and high temperatures. It is shown that the phonon confinement becomes more important than interface scattering in the highly specular scattering case. The effect of interface roughness scattering and phonon confinement on the lattice thermal conductance in a rectangular wire at low temperature is also examined. We calculate the contribution to the lattice thermal conductance due to the longitudinal mode for the catenoid contact. It is found that phonon confinement leads to a significant decrease of the lattice thermal conductance at sufficiently low temperatures $\text{(T<0.1}\mathrm{K}\mathrm{).}$