An Asymmetric Grating Refractive Index Sensor Generating Quasi-Bound States in the Continuum with High Figure of Merit and Temperature Self-Compensation

A subwavelength asymmetric grating refractive index (RI) sensor based on quasi-bound states in the continuum (q-BIC) with temperature self-compensation was proposed. The sensor structure consisted of a Prism / Asymmetric grating / Analytes, where the grating layers were periodically arranged asymmetric silicon (Si) and polydimethylsiloxane (PDMS). The asymmetry of the structure led to the fact that the tangential field component and the radiative field component in the grating layer were no longer in a fully decoupled state at the resonance position, creating two extremely narrow q-BIC resonance peaks, which gave the sensor a high Figure of Merit (FOM) and a low detection limit (DL). In addition, the thermo-optical coefficient of the materials made one of the resonance peaks more sensitive to temperature changes, realizing the temperature self-compensation of RI detection and thus improving the detection accuracy. From the results, reducing the asymmetry of the structure by modifying the parameters could theoretically make FOM > 5.1*106 RIU-1 and DL < 9.8*10-9 RIU. For the RI sensor with temperature self-compensation, FOM = 3057.85 RIU-1 and DL = 1.64*10-5 RIU for the RI, FOM = 0.88 °C-1 and DL = 0.057 °C for the temperature. These findings could effectively improve the temperature interference resistance of the sensor and thus the accuracy of trace substance detection.

Homo-composition and hetero-structure nanocomposite Pnma Bi2SeS2 - Pnnm Bi2SeS2 with high thermoelectric performance

Nanocomposite engineering decouples the transport of phonons and electrons. This usually involves the in-situ formation or ex-situ addition of nanoparticles to a material matrix with hetero-composition and hetero-structure (heC-heS) interfaces or hetero-composition and homo-structure (heC-hoS) interfaces. Herein, a quasi homo-composition and hetero-structure (hoC-heS) nanocomposite consisting of Pnma Bi2SeS2 - Pnnm Bi2SeS2 is obtained through a Br dopant-induced phase transition, providing a coherent interface between the Pnma matrix and Pnnm second phase due to the slight structural difference between the two phases. This hoC-heS nanocomposite demonstrates a significant reduction in lattice thermal conductivity (~0.40 W m−1 K−1) and an enhanced power factor (7.39 μW cm−1 K−2). Consequently, a record high figure-of-merit ZTmax = 1.12 (at 773 K) and a high average figure-of-merit ZTave = 0.72 (in the range of 323–773 K) are achieved. This work provides a general strategy for synergistically tuning electrical and thermal transport properties by designing hoC-heS nanocomposites through a dopant-induced phase transition.

Plasmon-induced transparency sensor for detection of minuscule refractive index changes in ultra-low index materials

Detection of low-index materials such as aerogels and also detection of refractive index variations in these materials is still a challenging task. Here, a high figure of merit (FOM) sensor based on plasmon-induced transparency (PIT) is proposed for the detection of aerogel refractive index changes. In the proposed PIT sensor, the transparency window in an opaque region arises from the coupling between surface plasmon polariton (SPP) mode and planar waveguide mode. By comprising sub-wavelength grating (SWG) in the planar waveguide region, the maximum of the electric field of waveguide occurs in a low index media. This facilitates detection of the aerogels when they are used as the low index material (sensing material). Application of the subwavelength grating waveguide also improves the sensitivity of the sensor by a factor of six compared to a conventional structure with a homogenous waveguide. The proposed structure has a quality factor of Q ≥ 1800, and a reflection of 86%, and can detect the refractive index changes as low as Δn = 0.002 (around n = 1.0). The lineshape, Q-factor, and resonant wavelength of the transparency spectrum can be controlled by tailoring the structural parameters. Our work also has potential application in switching, filtering, and spectral shaping.

Shedding Light on the Optical and Nonlinear Optical Properties of Super-Alkali Doped Borophene

The present investigation highlights the 2-dimentional design of several interesting super alkali doped borophene derivatives for efficient nonlinear optical (NLO). Borophene (B36) and super alkali units (Li3O) whose combining effects and resulting NLO responses have been evaluated by orienting super-alkali clusters at various sites such as a hub, rim, and bridged around the B36 molecule. The charge analysis is characterized by frontier and natural bond orbital analysis, narrowed HOMO-LUMO band gap, better intramolecular charge transfers. Molecular electrostatic potential surfaces demonstrate enhanced optoelectronic features of these complexes that are viable owing to Li3O adsorption. Singly doped and doubly doped complexes have been considered and their NLO properties have been calculated. Band gap energy reduces about three times when doped with two Li3O. A considerably high figure of merit, first hyperpolarizability (bo) values up to five digits 10611 a. u. for complex A proved that these systems can be utilized as promising candidates in various NLO applications.

South Korean Science and Technology Policy

The article analyzes the policy of South Korea in the field of science and technology, examines the main trends of the ROK’s science development, current state, key problems and prospects of the industry. The characteristics of the state scientific and technological policy and its main actors are presented. It is stated that at the beginning South Korea abundantly used adopt experience, foreign technologies and successfully got accepted them in production. The ROK succeeded to hold leading positions in the world innovation ratings through smart patent activity, essential investment and government policy. At the same time, the author predicts the necessity of tremendous efforts, includes but not limited to fi ancial injection for maintaining such high figure. The issue of not only human resources’ import but also keeping of South Korean skilled labor, the demand and competition for whom are ramping up dramatically, has still unresolved. The article focuses on the impact of the Covid-19 pandemic on the scientific policy and the development of innovations in the fight against such pandemics. It was revealed that research in the field of biotechnology and establishment of “smart” health care centers based on the innovations become a priority of science policy. It was noted that South Korea one of the first reaps the benefits of IT solution, which helps to prevent economics collapse and further viral shedding through the rapid digital technics’ implementing.