Investigation of Photonic Band Gap in Si-Based One-Dimensional Photonic Crystal

A one-dimensional silicon based photonic crystal with nonlinear defect layers is examined. The linear and nonlinear optical properties are analyzed. The transmission spectrum was obtained by applying the optical transfer matrix formalism to the photonic crystal. The various transmittance peaks obtained with the defect layers are investigated. The nature of the transmittance peak is analyzed with the number of defect layers.

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures （CCSs） in two-dimensional （2D） photonic crystals （PCs） are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain （FDTD） method, and the results show that within a very short coupling distance of about 3λ, where ）, is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.

大带隙2维正方晶格光子晶体的优化设计

为了研究2维正方晶格光子晶体的完全带隙特性,采用平面波展开方法模拟了两种结构2维光子晶体,在固定光子晶体周期常数a的前提下,研究了2维正方晶格光子晶体的完全禁带随柱半径和折射率的变化规律。结果表明,以空气为背景的锗介质柱组成的光子晶体,随着半径的增大,完全带隙宽度先增大后减小最后消失,填充比为38.3%时,同时增大介质柱的介电常数,在介质柱折射率为4.2处,完全带隙最大,带宽是0.02754(ωa/(2πc));以锗为背景的空气柱组成的光子晶体,光子禁带对应的无量纲频率随半径的增大而增大,填充比为48.3%时,同时增大背景介质的介电常数,出现多个完全带隙,在背景折射率为6.2处,完全禁带最大,带宽为0.02922(ωa/(2πc))。光子晶体带隙的频谱响应也表明了完全带隙的范围。这为大带隙2维正方晶格光子晶体的设计和制备提供了依据。

正方介质柱二维光子晶体传输特性FDTD数值研究

把时域有限差分方法用于二维正方介质柱组成光子晶体传输函数理论研究,计算了若干情况下二维光子晶体的透射率即光传输函数随频率的变化。计算结果表明:对于一定的入射方向,某些频率的光不能在光子晶体中传播即出现所谓的禁带,禁带的宽度、频率范围与晶格结构、柱体截面大小及放置方位有关。

Controlled 2D growth of organic semiconductor crystals by suppressing “coffee-ring” effect

Owing to enhanced charge transport efficiency arising from the ultrathin nature,two-dimensional(2D)organic semiconductor single crystals(OSSCs)are emerging as a fascinating platform for high-performance organic field-effect transistors(OFETs).However,ucoffee-ring"effect induced by an evaporation-induced convective flow near the contact line hinders the large-area growth of 2D OSSCs through a solution process.Here,we develop a new strategy of suppressing the"coffee-ring"effect by using an organic semiconductor:polymer blend solution.With the high-viscosity polymer in the organic solution,the evaporation-induced flow is remarkably weakened,ensuring the uniform molecule spreading for the 2D growth of the OSSCs.As an example,wafer-scale growth of crystalline film consisting of few-layered 2,7-didecylbenzothienobenzothiophene(C10-BTBT)crystals was successfully accomplished via blade coating.OFETs based on the crystalline film exhibited a maximum hole mobility up to 12.6 cm^2·V^-1·s^-1,along with an average hole mobility as high as 8.2 cm^2·V^-1·s^-1.Our work provides a promising strategy for the large-area growth of 2D OSSCs toward high-performance organic electronics.

Deep Learning Accelerates the Discovery of Two- Dimensional Catalysts for Hydrogen Evolution Reaction

Two-dimensional materials with active sites are expected to replace platinum as large-scale hydrogen production catalysts.However,the rapid discovery of excellent two-dimensional hydrogen evolution reaction catalysts is seriously hindered due to the long experiment cycle and the huge cost of high-throughput calculations of adsorption energies.Considering that the traditional regression models cannot consider all the potential sites on the surface of catalysts,we use a deep learning method with crystal graph convolutional neural networks to accelerate the discovery of high-performance two-dimensional hydrogen evolution reaction catalysts from two-dimensional materials database,with the prediction accuracy as high as 95.2%.The proposed method considers all active sites,screens out 38 high performance catalysts from 6,531 two-dimensional materials,predicts their adsorption energies at different active sites,and determines the potential strongest adsorption sites.The prediction accuracy of the two-dimensional hydrogen evolution reaction catalysts screening strategy proposed in this work is at the density-functional-theory level,but the prediction speed is 10.19 years ahead of the high-throughput screening,demonstrating the capability of crystal graph convolutional neural networks-deep learning method for efficiently discovering high-performance new structures over a wide catalytic materials space.

基于二维光子晶体的双谐振腔6通道WDM设计

针对全光通信网络容量和频谱效率问题,文章提出了一种基于二维(2-D)光子晶体点缺陷谐振腔与线缺陷波导耦合特性的双谐振腔6通道波分复用器(WDM)。运用2-D时域有限差分法进行性能参数分析,考虑相对折射率的影响,选择双谐振腔和单个直波导耦合的方式,实现了1 451、1 487、1 557、1 658、1 440和1 604 nm 6波长的波分复用。实验结果表明,该WDM具有高达218 nm的光谱覆盖范围,各通道的传输效率均高于91%,插入损耗均小于0.43 dB,通道间串扰均小于-9.2 dB,且大小也只有13.56μm×19.21μm,对光通信系统中粗波分复用非常有用,对于密集波分复用也有参考意义。

Holographic fabrication of octagon graded photonic supercrystal and potential applications in topological photonics

Novel optical properties in graded photonic super-crystals can be further explored if new types of graded photonic super-crystals are fabricated.In this paper,we report holographic fabrication of graded photonic super-crystal with eight graded lattice clusters surrounding the central non-gradient lattices through pixel-by-pixel phase engineering in a spatial light modulator.The prospect of applications of octagon graded photonic super-crystal in topological photonics is discussed through photonic band gap engineering and coupled ring resonators.

Enhanced absorption of solar cell made of photonic crystal by geometrical .design

In this paper, via numerical simulation we designed the geometry of solar cell made by onedimensional （1D） and two-dimensional （2D） photonic crystals with two kinds of materiel （silicon （Si） and hydrogenated amorphous silicon （a-Si：H）） in order to enhance its absorption. The absorption characteristics of light in the solar cell structures are simulated by using finite-difference time-domain （FDTD） method. The calculation results show that the enhancement of absorption in patterned structure is apparent comparing to the unpatterned one, which proves the ability of the structure to produce photonic crystal solar cell. We found solar cell geometries as a 2D photonic crystal enable to increase the absorption between 380 and 750 nm.

two-dimensional material functional devices enabled by direct laser fabrication

During the past decades,atomically thin,two-dimensional（2D）layered materials have attracted tremen-dous research interest on both fundamental properties and practical applications because of their extraordinary mechanical,thermal,electrical and optical properties,which are distinct from their counterparts in the bulk format.Various fabrication methods,such as soft-lithography,screen-printing,colloidal-templating and chemical/dry etching have been developed to fabricate micro/ nanostructures in 2D materials.Direct laser fabrication with the advantages of unique three-dimensional（3D）processing capability,arbitrary-shape designability and high fabrication accuracy up to tens of nanometers,which is far beyond the optical diffraction limit,has been widely studied and applied in the fabrication of various micro/ nanostructures of 2D materials for functional devices.This timely review summarizes the laser-matter interaction on 2D materials and the significant advances on laser-assisted 2D materials fabrication toward diverse functional photonics,optoelectronics,and electrochemical energy storage devices.The perspectives and challenges in designing and improving laser fabricated 2D materials devices are discussed as well.

Synthetic Two-dimensional Organic Structures

Synthetic two-dimensional（2 D） polymers have totally different topology structures compared with traditional linear or branched polymers. The peculiar 2 D structures bring superior properties. Although, from linear to 2 D polymers, the study of these new materials is still in its infancy, they already show potential applications especially in optoelectronics, membranes, energy storage and catalysis, etc. In this review, we summarize the recent progress of the 2 D materials from three respects：（1） Chemistry—different types of polymerization reactions or supramolecular assembly to construct the 2 D networks were described;（2） Preparation methods—surface science, crystal engineering approaches and solution synthesis were introduced;（3） Functionalization and some early applications.

Dual-polarization multiplexing amorphous Si:H grating couplers for silicon photonic transmitters in the photonic BiCMOS backend of line

In this paper,we report on polarization combining two-dimensional grating couplers(2D GCs)on amorphous Si:H,fabricated in the backend of line of a photonic BiCMOS platform.The 2D GCs can be used as an interface of a hybrid silicon photonic coherent transmitter,which can be implemented on bulk Si wafers.The fabricated 2D GCs operate in the telecom C-band and show an experimental coupling efficiency of−5 dB with a wafer variation of±1.2 dB.Possibilities for efficiency enhancement and improved performance stability in future design generations are outlined and extension toward O-band devices is also investigated.

An optical slot-antenna-coupled cavity (SAC) framework towards tunable free-space graphene photonic surfaces

The optical conductivity of single layer graphene (SLG) can be significantly and reversibly modified when the Fermi level is tuned by electrical gating. However, so far this interesting property has rarely been applied to free-space two-dimensional (2D) photonic devices because the surface-incident absolute absorption of SLG is limited to 1%–2%. No significant change in either reflectance or transmittance would be observed even if SLG is made transparent upon gating. To achieve significantly enhanced surface-incident optical absorption in SLG in a device structure that also allows gating, here we embed SLG in an optical slot-antenna-coupled cavity (SAC) framework, simultaneously enhancing SLG absorption by up to 20 times and potentially enabling electrical gating of SLG as a step towards tunable 2D photonic surfaces. This framework synergistically integrates near-field enhancement induced by ultrahigh refractive index semimetal slot-antenna with broadband resonances in visible and infrared regimes, ~ 3 times more effective than a vertical cavity structure alone. An example of this framework consists of self-assembled, close-packed Sn nanodots separated by ~ 10 nm nanogaps on a SLG/SiO2/Al stack, which dramatically increases SLG optical absorption to 10%-25% at λ = 600–1,900 nm. The enhanced SLG absorption spectrum can also be controlled by the insulator thickness. For example, SLG embedded in this framework with a 150 nm-thick SiO2 insulating layer displays a distinctive red color in contrast to its surrounding regions without SLG on the same sample under white light illumination. This opens a potential path towards gate-tunable spectral reflectors. Overall, this work initiates a new approach towards tunable 2D photonic surfaces.

二维正方复式晶格的完全光子带隙

为产生光子晶体完全光子带隙 ,在二维正方晶格的介质柱中心构造一个空气柱孔缺陷 ,应用平面波展开的方法研究了光波在其中的传播规律 ,发现在特定的结构参数条件下 ,该结构产生了完全光子带隙 。

用转移矩阵法数值研究二维正方介质柱光子晶体的传输特性

利用转移矩阵方法对二维正方介质柱光子晶体的传输特性进行了研究,数值计算研究了不同晶格、同一晶格柱体截面面积不同、放置方位角不同时光子晶体的传输特性。数值结果表明光子禁带的宽度与中心频率和晶格结构有很大关系,正方晶格更易形成平坦光子禁带,柱体截面面积大,则形成的禁带较宽,在其他因素相同的条件下柱体放置的方位角对光子禁带有重要影响。数值研究表明在正方介质柱下设计宽平坦光子禁带时,可以首先考虑正方晶格结构,其次设法使柱体截面尽量大一些,最后可通过柱体放置方位角来微调光子禁带的宽度与中心频率以达到设计要求。

二维光子晶体偏振分束器的优化设计

为解决二维光子晶体在光束调整和光束偏转中的应用,采用有限时域差分法和完全匹配层吸收边界条件,通过在结构中引入消反层,从理论上实现基于二维光子晶体的偏振分束器。优化计算表明,通过随光频的改变调节消反层参数,可以实现TE模超过95%的光发生透射,TM模超过95%的光发生反射,从而使TM模与TE模分离。引入消反层的偏振分束器具有尺寸小、透射率高、分束角大和偏振分束率高等优点,在高密度集成光通信系统中有广泛的应用。

等离子体填充二维金属光子晶体色散特性研究

提出了等离子体填充的二维金属光子晶体模型,采用时域有限差分法研究了等离子体填充的二维正方晶格和三角晶格金属光子晶体的色散和带隙特性.对比分析了两种结构中等离子体密度对TM及TE模式传播特性的影响规律.研究发现,由于背景等离子体的引入,二维金属光子晶体的色散曲线明显往高频方向移动,等离子体密度的改变可同时控制TE和TM模的带隙位置和禁带宽度.这些特性使得二维等离子体金属光子晶体在设计可调谐光子晶体器件方面具有潜在的应用价值.

Metallic and ferromagnetic MoS2 nanobelts with vertically aligned edges

Edge effects are predicted to significantly impact the properties of low dimensional materials with layered structures. The synthesis of low dimensional materials with copious edges is desired for exploring the effects of edges on the band structure and properties of these materials. Here we developed an approach for synthesizing MoS2 nanobelts terminated with vertically aligned edges by sulfurizing hydrothermally synthesized MoO3 nanobelts in the gas phase through a kinetically driven process; we then investigated the electrical and magnetic properties of these metastable materials. These edge-terminated MoS2 nanobelts were found to be metallic and ferromagnetic, and thus dramatically different from the semiconducting and nonmagnetic two-dimensional （2D） and three-dimensional （3D） 2H-MoS2 materials. The transitions in electrical and magnetic properties elucidate the fact that edges can tune the properties of low dimensional materials. The unique structure and properties of this one-dimensional （1D） MoS2 material will enable its applications in electronics, spintronics, and catalysis.

Few-layered organic single-crystalline heterojunctions for high-performance phototransistors

Photogating and electrical gating are key physical mechanisms in organic phototransistors(OPTs).However,most OPTs are based on thick and polycrystalline films,which leads to substantially low efficiency of both photogating and electrical gating and thus reduced photoresponse.Herein,high-performance OPTs based on few-layered organic single-crystalline heterojunctions are proposed and the obstacle of thick and polycrystalline films for photodetection is overcome.Because of the molecular scale thickness of the type I organic single-crystalline heterojunctions in OPTs,both photogating and electrical gating are highly efficient.By synergy of efficient photogating and electrical gating,key figures of merit of OPTs reach the highest among those based on planar heterojunctions so far as we know.The production of few-layered organic single-crystalline heterojunctions will provide a new type of advanced materials for various applications.

Drawing highly ordered MXene fibers from dynamically aggregated hydrogels

Assembly of two-dimensional (2D) nanomaterials into well-organized architectures is pivotal for controlling their function and enhancing performance. As a promising class of 2D nanomaterials, MXenes have attracted significant interest for use in wearable electronics due to their unique electrical and mechanical properties. However, facile approaches for fabricating MXenes into macroscopic fibers with controllable structures are limited. In this study, we present a strategy for easily spinning MXene fibers by incorporating polyanions. The introduction of poly(acrylic acid) (PAA) into MXene colloids has been found to alter MXene aggregation behavior, resulting in a reduced concentration threshold for lyotropic liquid crystal phase. This modification also enhances the viscosity and shear sensitivity of MXene colloids. Consequently, we were able to draw continuous fibers directly from the gel of MXene aggregated with PAA. These fibers exhibit homogeneous diameter and high alignment of MXene nanosheets, attributed to the shear-induced long-range order of the liquid crystal phase. Furthermore, we demonstrate proof-of-concept applications of the ordered MXene fibers, including textile-based supercapacitor, sensor and electrical thermal management, highlighting their great potential applied in wearable electronics. This work provides a guideline for processing 2D materials into controllable hierarchical structures by regulating aggregation behavior through the addition of ionic polymers.