refractive index dielectric (e.g., silicon (Si), germanium and gallium phosphide, etc.) nanostructures have emerged. [1-4] The low loss feature [5-8] together with the unique optical responses associated with the electric and magnetic multipole resonances provides an additional degree of freedom for light manipulation. [1-3,9-11] Recently, in addition to the electric and magnetic multipole moments, toroidal multipole moments, which are derived by multipolar decomposition of induced currents in dielectric resonators, have been attracting significant attention. [12] The lowest order toroidal multipole, i.e., the toroidal dipole (TD), is a current loop along a meridian of a torus in a dielectric resonator. The TD mode has the far-field radiation pattern identical to that of the electric dipole (ED) mode, and thus the destructive interference of the two modes produces a non-radiating state. [12,13] The state is called "anapole." The radiation-less anapole state can be realized in a simple dielectric nanodisk (ND) structure when the diameter-to-height ratio is higher than ≈5. [12] At the anapole state, electromagnetic fields are confined inside a ND, [14] which are utilized for the enhancement of the nonlinear optical responses, [15-19] the emission rate by the Purcell effect, [20] the Raman scattering, [21] and the photocatalytic activity. [22] TD moments exist not only in an isolated dielectric nanostructure, but also in coupled dielectric nanostructures like oligomers [23,24] and two dimensional arrays. [25-28] Basharin et al. suggested the existence of TD resonances in cluster arrays of subwavelength high-index dielectric cylinders in the terahertz frequency region. [25] Liu et al. theoretically demonstrated a high Q-factor response and resultant strong field confinement by TD resonances in square arrays of silicon split nanodisks. [26] Luo et al. proposed a metasurface consisting of two silicon split-ring resonators and theoretically demonstrated a high-Q TD resonance in the near-IR region. [27] These researches indicate that compared to TD resonances of isolated nanostructure, those of coupled nanostructures have higher degree of freedom in designing TD mode-related optical responses. However, experimental studies on TD responses of coupled dielectric nanostructures are still limited [29,30] and the application for the control of light-matter interactions has never been reported. In this work, we propose a two-dimensional hexagonal array of very thin (20-50 nm in thicknesses) circular Si NDs as the metasurface supporting coupled TD modes. We first calculate

Unraveling the charge transfer across a heterointerface is crucial for cutting-edge optoelectronic applications, including photodetectors, solar photovoltaics, light-emitting diodes, and so on. The incorporation of perovskite nanocrystals (NCs) into optoelectronics is limited primarily because of the presence of grain boundaries, carrier trapping, and ion migration, which restricts charge/energy transfer. Combining perovskite NCs with two-dimensional (2D) materials is a powerful approach to enhance energy harvesting and transport at the 0D-2D heterointerface. A simple sonication method was adopted to integrate zero-dimensional (0D) mixed halide perovskite CsPbBr2I NCs and topological 2D Bi2Se3 nanosheets (NSs) to realize a nanohybrid system. A series of optical signatures such as Raman shift, quenching of photoluminescence (PL), and shortened fluorescence lifetime in the nanohybrid clearly substantiate the interfacial charge transfer dynamics. Cyclic voltammetry and Kelvin probe force microscopy analysis and the optical studies established the type-I band alignment between perovskite NCs and Bi2Se3 NSs. The charge transfer dynamics of the nanohybrid was confirmed from the dramatic quenching of the PL intensity of CsPbBr2I NCs and an associated increase in the NIR PL as well as visible PL intensities of the Bi2Se3 NSs owing to increased carrier density caused by charge transfer. Furthermore, improved photoresponse performance of the hybrid system demonstrates the role of interfacial carrier transfer in 2D-0D nanohybrids, suppressing the radiative recombination in the light-harvesting perovskite NCs. The nanohybrid-based photodetector exhibits a high spectral responsivity of 14.4 A/W, a spectral detectivity of 0.4 × 1012 Jones, and a fast growth/decay time of 82 μs/24 μs. These results will stimulate further exploration of topological 2D materials/halide perovskite-based novel hybrid functional devices for photodetection, light-harvesting, and light-emitting applications.

Efficient excitation of a triplet (T1) state of a molecule has far‐reaching effects on photochemical reaction and energy conversion systems. Because the optical transition from a ground singlet (S0) to a T1 state is spin‐forbidden, a T1 state is generated via intersystem crossing (ISC) from an excited singlet (S1) state. Although the excitation efficiency of a T1 state can be increased by enhancing ISC utilizing a heavy atom effect, energy loss during S1→T1 relaxation is inevitable. Here, a general approach to directly excite a T1 state from a ground S0 state via magnetic dipole transition, which is boosted by enhanced magnetic field induced by a dielectric metasurface, is proposed. As a dielectric metasurface, a hexagonal array of silicon (Si) nanodisks is employed; the nanodisk array induces a strongly enhanced magnetic field on the surface due to the toroidal dipole (TD) resonance. A proof‐of‐concept experiment is performed using ruthenium (Ru) complexes placed on a metasurface and demonstrates that the phosphorescence is 35‐fold enhanced on a metasurface when the TD resonance is tuned to the wavelength of the direct S0→T1 transition. These results indicate that photon energy necessary to excite the T1 state can be reduced by more than 400 meV compared to the process involving the ISC. By combining optical measurements with numerical simulations, the mechanism of the phosphorescence enhancement is quantitatively discussed.

Arsenic ions have been implanted in (100)Si at an incident energy of 1 MeV to a dose of 1×1015/cm2. Rutherford backscattering measurements with a 1.5-MeV He-ion beam have shown that a buried amorphous layer is formed in the Si substrate which is implanted at a low ion-beam current of 0.8 μA and that considerable annealing occurs when implantation is carried out at a high ion-beam current of 2 μA. The implantation-induced amorphous layer recrystallizes after annealing above 550 °C, but a high density of lattice defects still remains in the substrate even after annealing at 1000 °C. Defect observations using a cross-sectional transmission electron microscope have revealed that those defects are located at the two depths corresponding to the initial transition regions where the crystallinity is changed from the amorphous to nonamorphized states in the substrate. In addition, secondary defects also exist in a particular region inside the initial buried amorphous layer. The recrystallization of the buried amorphous layer during post-implant annealing is initiated not only from the deeper part of the substrate but also from the nonamorphized surface layer. From a series of isothermal annealing studies, it has been shown that the recrystallization rates at 550 °C are 140 and 180 Å/min on the frontside and backside of the buried amorphous layer, respectively. Electrical profile measurements, using the differential Hall method, have shown that a highly doped, buried conductive layer with a peak carrier concentration of around 2×1019/cm3 can be formed by annealing above 800 °C.

A hexagonal array of low-aspect-ratio silicon nanodisks is formed on a silicon thin film and the optical absorption and photocurrent properties are studied. Numerical simulations reveal that the nanodisk array possesses the toroidal dipole modes that tightly confine incoming light in a silicon region below the nanodisks. The field confinement brings about narrow-band absorption when the extinction coefficient (κ) is very small, for example, κ = 10–2∼10–3. This suggests that defect-related sub-band gap absorption of silicon can be enhanced by utilizing the modes. Transmittance spectra of fabricated devices reveal that narrow dips assigned to the toroidal dipole resonances appear in the sub-band gap region. At the resonance wavelengths, the photocurrent is substantially enhanced; the enhancement factor reaches 30-fold. The observed narrow-band photodetection can be used as a current-detection-type refractive index sensor operating in the near-infrared range.