This study investigates the propagation dynamics of plasma streamers in a packed-bed dielectric barrier discharge using a 2D particle-in-cell/Monte Carlo collision model. To accurately simulate the high-intensity discharge and streamer propagation mechanism at atmospheric pressure, additional algorithms for particle merging and a new electron mechanism are incorporated into the traditional particle-in-cell/Monte Carlo collision model. To validate the accuracy of this improved model, qualitative comparisons are made with experimental measurements from the existing literature. The results show that the speed of streamer propagation and the distribution of plasma are strongly influenced by the dielectric constant of the packed pellet, which is commonly used as a catalyst. In cases with a moderate dielectric constant, the presence of a strong electric field between the pellet and dielectric layer on the electrode significantly enhances the discharge. This enables the streamer to propagate swiftly along the pellet surface and results in a wider spread of plasma. Conversely, a very high dielectric constant impedes streamer propagation and leads to localized discharge with high intensity. The improved model algorithms derived from this research offer valuable insights for simulating high-density plasma discharge and optimizing plasma processing applications.

This paper puts forward a subwavelength grating for highly sensitive refractive index (RI) sensing. The light-coupling condition of the grating covered by the liquid to be detected is sensitive to changes in RI of the liquid. The influence of the grating period and thickness on the coupling is studied. At the large angle of incidence, it is found that the effective RI of the grating slab is varied with the incidence angle, from which the coupling originating from the guided-mode resonance (GMR) impacted by such variation is revealed. Incidence angle is scanned at a fixed wavelength of 623.8 nm, and the calculated results indicate that the sensor sensitivity is mainly dependent on the period, while the resolution is controlled by the thickness. After the period and thickness have been optimized in sequence, an averaged sensitivity of 249.7°/RIU and resolution ranging from 0.1° to 0.3° are obtained; those of the grating sensor are better than those of the surface plasmon resonance (SPR) sensor, which has high sensitivity supported by a substrate with low RI.

An optical refractive index (RI) sensor, possessing excellent sensing characteristics in sensitivity, resolution and SNR, is proposed by using a composite subwavelength grating (CSG). The CSG has a sandwich structure: the interlayer is a low-RI grating layer (LRGL), and the two sides are arranged with a high-RI grating layer. The light-coupling condition of the CSG is sensitive to RI changes of the liquid sample. The calculated results indicate that the sensitivity mainly depends on the CSG period, and the resolution and SNR can be improved by regulating the thickness and position of the LRGL. By optimizing these parameters, finally, an averaged sensitivity of ∼273°/RIU and resolution ranging from 0.1° to 0.15° are given by this CSG, and there is a minimal reflectance of ∼1% adjacent to the resonant peak.

The miniaturization and integration of photonic devices are new requirements in the fast-growing optics field. In this paper, we focus on a feature-rich sub-wavelength nanograting-coated single-layer metal film. The numerical results show that the reflection behaviors of this proposed structure can realize bidirectional dual-channel ultra-narrowband polarized filtering and bidirectional wavelength-modulated sensing in a wide refractive index (RI) range from 1.0 to 1.4 for incident angle of 10° with transverse-magnetic (TM) polarized illumination at wavelengths between 550 nm to 1500 nm. Moreover, the bidirectional properties of filtering and sensing are not obviously decreased when increasing incident angle from 10° to 30°, and decreasing incident angle from 10° to 0°. The calculated RI sensitivity can be up to 592 nm/RIU with a high figure of merit (FOM) of 179.4 RIU⁻¹. More to the point, this nanograting has a simple structure and is less sensitive to the height and shape of grating ridge, which provides great convenience for the fabrication of devices. The other thing that is going on is that this structure can also realize synchronously tunable color filtering, including green to red, with high color purity in the visible band by choosing the period. The underlying physical mechanism is analyzed in detail, and is primarily attributed to surface plasmon polariton (SPP) resonance and dipole resonance at double plasmon resonance wavelengths. This work has tremendous potential in developing multipurpose and high-performance integrated optical devices such as spectral filters, colored displays and plasmon biomedical sensors.

A neutral h-BN/Fe/Al2O3/H2O2 composite slurry was developed to couple surface oxidation with interfacial friction regulation during chemical mechanical polishing (CMP) of Si-face 4H-SiC. In this system, Fe promoted H2O2-assisted surface oxidation, Al2O3 abrasives removed the generated oxide layer, and layered h-BN regulated slurry dispersion, wettability, and frictional contact at the polishing interface. Under optimized conditions containing 0.5 wt% h-BN, 0.5 wt% Fe, 1.0 wt% Al2O3, and 6 wt% H2O2 at pH 7.0, the material removal rate reached 546.6 nm/h and the surface roughness Ra decreased to 0.364 nm. XPS analysis indicated the formation of SiOx/Si-O-Si-related surface species in Fe-containing slurries, whereas zeta potential, contact angle, and friction measurements showed that h-BN improved dispersion stability and moderated locally excessive rigid contact. The enhanced CMP performance is therefore attributed to the coupling of Fe-assisted surface oxidation, Al2O3-assisted oxide-layer removal, and h-BN-mediated interfacial regulation rather than to a single chemical or mechanical effect.