An advanced theoretical approach to study super-multiperiod superlattices:theory vs experiments

A new theoretical method to study super-multiperiod superlattices has been developed.The method combines the precision of the 8-band kp-method with the flexibility of the shooting method and the Monte Carlo approach.This method was applied to examine the finest quality samples of super-multiperiod Al_(0.3)Ga_(0.7)As/GaAs superlattices grown by molecular beam epitaxy.The express photoreflectance spectroscopy method was utilized to validate the proposed theoretical method.For the first time,the accurate theoretical analysis of the energy band diagram of super-multiperiod superlattices with experimental verification has been conducted.The proposed approach highly accurately determines transition peak positions and enables the calculation of the energy band diagram,transition energies,relaxation rates,and gain estimation.It has achieved a remarkably low 5%error compared to the commonly used method,which typically results in a 25%error,and allowed to recover the superlattice parameters.The retrieved intrinsic parameters of the samples aligned with XRD data and growth parameters.The proposed method also accurately predicted the escape of the second energy level for quantum well thicknesses less than 5 nm,as was observed in photoreflectance experiments.The new designs of THz light-emitting devices operating at room temperature were suggested by the developed method.

Luminescence enhancement of rare earth ions by metal nanostructures

Well-ordered metal structures, i.e. arrays of nanosized tips on silver surface for studies of the luminescence enhancement of absorbed media with rare earth ions were used. These arrays were prepared by the metal evaporation on track membranes. Calculations of reso- nanee frequencies of tips regarded as semispheroids were done taking into account the interaction between dipoles of tips. They were used to discuss experimental results for media with Eu（NO3）3·6H2O salt basing on data for bulk silver dielectric function.

Evidence of Electronic Phase Separation in the Strongly Correlated Semiconductor YbB_(12)

We investigate high-quality single-domain crystals of YbB_(12)using the precise x-ray diffraction technique in combination with the low-temperature polarized THz–infrared spectroscopy and accurate magnetotransport measurements.It is shown for the first time that this archetypal strongly correlated system with a metal-insulator transition to a mysterious dielectric ground state with a metal Fermi surface[Science 362,65(2018)and ibid 362,32(2018)]is actually a heterogeneous compound in the regime of electronic phase separation.Changes in the configuration of the discovered dynamic charge stripes are proposed upon cooling.As a result,a conclusion is drawn in favor of a crossover between different patterns of the filamentary electronic structure penetrating the semiconducting matrix of YbB_(12).We argue that the discovery of stripes in YbB_(12)is fundamental,elucidating the nature of exotic dielectric state in Kondo insulators.

Unlocking the out-of-plane dimension for photonic bound states in the continuum to achieve maximum optical chirality

The realization of lossless metasurfaces with true chirality crucially requires the fabrication of three-dimensional structures,constraining experimental feasibility and hampering practical implementations.Even though the threedimensional assembly of metallic nanostructures has been demonstrated previously,the resulting plasmonic resonances suffer from high intrinsic and radiative losses.The concept of photonic bound states in the continuum(BICs)is instrumental for tailoring radiative losses in diverse geometries,especially when implemented using lossless dielectrics,but applications have so far been limited to planar structures.Here,we introduce a novel nanofabrication approach to unlock the height of individual resonators within all-dielectric metasurfaces as an accessible parameter for the efficient control of resonance features and nanophotonic functionalities.In particular,we realize out-of-plane symmetry breaking in quasi-BIC metasurfaces and leverage this design degree of freedom to demonstrate an optical all-dielectric quasi-BIC metasurface with maximum intrinsic chirality that responds selectively to light of a particular circular polarization depending on the structural handedness.Our experimental results not only open a new paradigm for all-dielectric BICs and chiral nanophotonics,but also promise advances in the realization of efficient generation of optical angular momentum,holographic metasurfaces,and parity-time symmetry-broken optical systems.

Modularized sulfur storage achieved by 100% space utilization host for high performance lithium-sulfur batteries

Popularization of lithium-sulfur batteries(LSBs) is still hindered by shuttle effect and volume expansion.Herein, a new modularized sulfur storage strategy is proposed to solve above problems and accomplished via employing 100% space utilization host material of cobalt loaded carbon nanoparticles derived from ZIF-67. The modular dispersed storage of sulfur not only greatly increases the proportion of active sulfur,but also inhibits the occurrence of volume expansion. Meanwhile, 100% space utilization host material can greatly improve the conductivity of the cathode, provide a larger electrolyte wetting interface and effectively suppress the shuttle effect. Moreover, loaded cobalt particles have high catalytic activity for electrochemical reaction and can effectively improve the redox kinetics. The cell with new cathode host material carbonized at 650 ℃(ZIF-67(650 ℃)) exhibits superior rate performance and can maintain a high specific capacity of 950 m Ah/g after 100 cycles at 0.2 C, showing a good cycle stability.

Investigation of natural contamination layer growth on optical substrates

The surface contamination layer on mirrors can cause significant degradation of the optical performance, which is widely observed in applications, particularly in the fabrication of X-ray focusing telescopes. In this paper, we study the natural contamination layer arising from adsorption precipitation of hydrocarbons or other organic and water molecules in the absence of any external factor. Temporal evolution of the layer formed on super-smooth fused silica, borosilicate glass, and silicon substrates is studied by X-ray reflectometry, atomic force microscopy, and transmission electron microscopy for a one-year period after surface cleaning. The general characteristics of adhesion layer growth are established and discussed. The reconstructed dielectric constant profiles demonstrate that an increase in the adhesion layer thickness, deposited mass and density over time obeys power laws with extremely small exponents. Therefore, the adhesion layer growth is rapid immediately after surface cleaning, with a - 1 nm thick layer formed within the first day on all three substrates studied, while the layer density is low （- 1 g/cm^3）. The layer growth on the fused silica and silicon substrates became very slow in the succeeding days, with only a 1.4-1.5 nm thick layer and 1.2-1.3 g/cm^3 density after one year of storage in air. At the same time, the adhesion layer growth on the glass substrate showed unexpected acceleration about two months after cleaning, so that the layer thickness reached - 2.2 nm after one year of storage. The reason for this effect, which is connected with leaching of the glass, is discussed briefly.

Domain formation on the nonpolar lithium niobate surfaces under electron-beam irradiation:A review

In this review,our recent results on the electron-beam domain writing(EBDW)on the nonpolar surfaces of LiNbO_(3) crystals of different compositions are presented.Under EB irradiation of the nonpolar surfaces,domains nucleated in irradiation points grow frontally along the polar Z-direction in a thin(of microns in thickness)surface layer;the driving force is the tangential component of space-charge fields induced by EB in irradiation points.This geometry of the experiment provides a possibility of three-dimensional(3D)characterization of domain patterns using the combination of atomic force microscopy(AFM)and second harmonic generation(SHG)confocal microscopy methods.The obtained results permitted us to relate the main characteristics of domain formation(the domain sizes and velocity Vf of the frontal motion)to the irradiation conditions(the accelerating voltage U of scanning electron microscopy(SEM),EB current I,the inserted charge Q).The domain depth Td is controlled by U via the electron penetration depth;the domain length Ld increases linearly with Q owing to the domain frontal growth by the viscous friction law.The electron emission coefficient
affects the domain formation due to the fundamental dependence of
on U.In the framework of current approach to EB charging of insulators,the effect of an enhanced conductance on EBDW characteristics is analyzed.The difference between EBDW characteristics observed in varied LiNbO_(3) compositions is discussed in the framework of the intrinsic defect structure of LiNbO_(3).The obtained results extend the possibility of EBDW application to a wider range of crystals.