Manipulating the directional emission of monolayer semiconductors by dielectric nanoantenna arrays

Collective Mie resonances in silicon (Si) nanoparticle arrays (NPAs) feature low absorption losses and strong field enhancement extending to a large area. They provide a high-efficient scheme to manipulate the emission properties of monolayer semiconductors. However, the poor quality factor of the current reported Si NPA limits the performance of light-emitting devices. It is mainly due to the constituent materials of nanoparticles being amorphous or polycrystalline silicon, which have higher absorption coefficients in comparison with monocrystalline silicon (c-Si) among the visible band. This invited paper demonstrates a versatile technique to integrate the atomic layers onto the c-Si NPA. We show that our method can fully preserve the monolayer sample. We further investigate the directional emission tailored by the NPA with different diameters by combining back-focal-plane imaging and reciprocity simulations. The flexible tune of the geometry parameters of NPAs can offer many possibilities to control and manipulate the emission from monolayer semiconductors by engineering their photonic environments.

Light focusing by silicon nanosphere structures under conditions of magnetic dipole and quadrupole resonances

Metalens is a planar device for light focusing. In this work, we design and optimize c-Si nanosphere metalenses working on the magnetic dipole and quadrupole resonances of the c-Si nanoparticle. Resonant optical response of c-Si nanostructures is simulated by the multipole decomposition method along with the zero-order Born approximation. Limitations of this approach are investigated. The obtained results of optimization are verified by simulation via the T-matrix method.

Structure and Magnetic Properties Of Fe/Si Nanoparticles Prepared by High Energy Milling Process

The structure and magnetic properties of Fe/Si nanoparticle prepared by high energy milling process have been examined, focusing on the phase transition. Fe/Si nanoparticles were processed by high energy milling (HEM) for 10 hours to 50 hours with a weight per cent ratio of 9:1. Based on the X-ray diffraction (XRD) pattern, transmission electron microscope (TEM) observations, and vibrating sample magnetometer (VSM) analysis, the phase transition induced by HEM, were evidenced. The effect of structural state and the particle size on the magnetic properties such as magnetization was also studied. It was found that iron and iron oxides (-Fe2O3/ Fe3O4) phase were exhibited on all milled samples. The magnetization value of Fe/Si nanoparticles increased up to 20 hours with 142 emu/gr saturated magnetization and then decreased linearly with increasing milling time. Referring to the XRD result, this decline was initially caused by the iron oxide formation and magnetic interaction between iron and iron oxides nanoparticles. The phase and magnetic properties value changes related to the interaction mechanism between Fe atoms caused by interstitial occupied of Si atoms, particle size reduction, and oxidation process.

Study of Filtration in Polyethylene Fibers used in Masks for Protection Against SARS-CoV-2 via Luminescent Aerosolized Silicon Nanoparticles

Commercial polyethylene (PE) fiber-based masks are currently used as personal filters for protection against various microorganisms. Due to the coronavirus (SARS-CoV-2) pandemic of 2020, the use of masks has become the critical mechanism in reducing the spread. The PE mask filter uses a sieve (geometry) in a spider web fashion to filter out microorganisms using Van der Waals atomic forces. However, the non-geometrical part of the filtration process is not fully understood. In this work, we utilized luminescent ultra-small silicon nanoparticles, which are Si-H or/and Si-OH terminated to examine how the filter operates at a chemical level. The particles were sprayed onto the fiber network by an atomizer and we used scanning electron microscopy (SEM), optical microscope and fluorescence spectroscopy under UV radiation. The images and measurements clearly showed that the Si nanoparticles bonded to the PE fiber network. The results were analyzed in terms of chemical bonding between Si nanoparticle and fiber. Our findings suggest that the PE fibers could act as a chemical filter via hydrogen or hydrolysis–based bonding or via Si-C bonding, which is complementary to their physical filtration ability via the geometric sieve process. Moreover, the results indicate that the filter would be effective against the novel coronavirus, not only by the geometrical sieve but can be additionally enhanced as a chemical filter by allowing the amine, carboxyl and hydroxyl function groups of the virus to attach to fibers via C-N and C-O bonds.

Nucleation and growth of Si nanoparticles under different pulse repetition rates without the baffle for nanosecond pulsed laser-ablated deposition

In this article, Si nanoparticle (NP) films were prepared by pulsed laser ablation (PLA) in the argon atmosphere of 10 Pa at room temperature under different pulse repetition rates from 1 to 40 Hz without the baffle. Different from the conventional PLA method, the substrates were placed below and parallel to the ablated plume axis. The obtained films containing NPs were characterized by scanning electron microscopy and Raman spectrometer. The experimental results under constant laser fluence demonstrate the strong dependence of the mean size and the area number density of NPs on the repetition rate. Specifically, with the increase of pulse repetition rate, the mean size of the NPs in the film first decreases and reaches its minimum at 20 Hz, and then increases after 20 Hz, and decreases again till 40 Hz. The area number density shows the contrary trend versus mean size. The in situ diagnostic results of Langmuir probe denote the ablated Si ion density increases monotonously with the increase of repetition rate, while the temperature is almost constant. Combining with the nucleation probability, the growth/aggregation duration of NPs in the “nucleation region” and the effect of the baffle, the influence of pulse repetition rate on the formation of NPs is addressed. It is found that the repetition rate impacts the growth modes of NPs (i.e., growth and aggregation). 1–20, 20–30, and 30–40 Hz, respectively, correspond to growth-, aggregation-, and growth-controlled rate ranges without the baffle; however, 1–10, 10–20, and 20–40 Hz, respectively, correspond to growth-controlled, aggregation/growth-coexisted, and aggregation-controlled rate ranges with the baffle.