Direct visualization of phase-matched efficient second harmonic and broadband sum frequency generation in hybrid plasmonic nanostructures

Second harmonic generation and sum frequency generation(SHG and SFG)provide effective means to realize coherent light at desired frequencies when lasing is not easily achievable.They have found applications from sensing to quantum optics and are of particular interest for integrated photonics at communication wavelengths.Decreasing the footprints of nonlinear components while maintaining their high up-conversion efficiency remains a challenge in the miniaturization of integrated photonics.Here we explore lithographically defined AlGaInP nano(micro)structures/Al_(2)O_(3)/Ag as a versatile platform to achieve efficient SHG/SFG in both waveguide and resonant cavity configurations in both narrow-and broadband infrared(IR)wavelength regimes(1300-1600 nm).The effective excitation of highly confined hybrid plasmonic modes at fundamental wavelengths allows efficient SHG/SFG to be achieved in a waveguide of a cross-section of 113 nm×250 nm,with a mode area on the deep subwavelength scale(λ2/135)at fundamental wavelengths.Remarkably,we demonstrate direct visualization of SHG/SFG phase-matching evolution in the waveguides.This together with mode analysis highlights the origin of the improved SHG/SFG efficiency.We also demonstrate strongly enhanced SFG with a broadband IR source by exploiting multiple coherent SFG processes on 1μm diameter AlGaInP disks/Al_(2)O_(3)/Ag with a conversion efficiency of 14.8%MW^(−1) which is five times the SHG value using the narrowband IR source.In both configurations,the hybrid plasmonic structures exhibit>1000 enhancement in the nonlinear conversion efficiency compared to their photonic counterparts.Our results manifest the potential of developing such nanoscale hybrid plasmonic devices for state-of-the-art on-chip nonlinear optics applications.

Modulating vectored non-covalent interactions for layered assembly with engineerable properties

Vectored non-covalent interactions—mainly hydrogen bonding and aromatic interactions—extensively contribute to(bio)-organic self-assembling processes and significantly impact the physicochemical properties of the associated superstructures.However,vectored non-covalent interaction-driven assembly occursmainly along one-dimensional(1D)or three-dimensional(3D)directions,and a two-dimensional(2D)orientation,especially that of multilayered,graphene-like assembly,has been reported less.In this present research,by introducing amino,hydroxyl,and phenyl moieties to the triazine skeleton,supramolecular layered assembly is achieved by vectored non-covalent interactions.The planar hydrogen bonding network results in high stability,with a thermal sustainability of up to about 330°C and a Young’s modulus of up to about 40 GPa.Upon introducing wrinkles by biased hydrogen bonding or aromatic interactions to disturb the planar organization,the stability attenuates.However,the intertwined aromatic interactions prompt a red edge excitation shift effect inside the assemblies,inducing broad-spectrum fluorescence covering nearly the entire visible light region(400–650 nm).We show that bionic,superhydrophobic,pillar-like arrays with contact angles of up to about 170°can be engineered by aromatic interactions using a physical vapor deposition approach,which cannot be realized through hydrogen bonding.Our findings show the feasibility of 2D assembly with engineerable properties by modulating vectored non-covalent interactions.

基于半导体纳米材料的偏振光发射:从材料到发光二极管

由于偏光片、彩色滤光片和液晶层等结构的损耗,基于背光源技术的液晶显示器的整体效率不足5%.自发射发光二极管(LED)不但具有巨大的市场潜力,而且能够满足未来显示的需求,迎来了巨大的发展机遇.更重要的是,由于避免了偏光片造成的光损失,偏振LED可以提高背景光利用效率.因此,亟需寻找有效的方法组装高质量的各向异性纳米材料薄膜,从而制备出具有高偏振度和高外量子效率的偏振LED.本文介绍了一些半导体纳米材料的光电特性及其在偏振LED中的潜在应用.综述了在偏振光发射领域从材料到薄膜,再到LED的研究进展;总结和比较了构建偏振光发射薄膜和LED的不同组装策略;最后,讨论了当前面临的挑战,并对偏振LED的潜在商业应用价值进行了展望.我们希望这篇综述能够对偏振LED当前研究进展进行有价值的总结,并对其未来发展激发一些新的、切实可行的想法.

Ferroelectricity in biological building blocks:Slipping on a banana peel?

Ferroelectricity in biological system has been anticipated both theoretically and experimentally over the past few decades.Claims of ferroelectricity in biological systems have given rise to confusion and methodological controversy.Over the years,a“loop”of induced polarization in response to a varying applied electrical field and a consequent polarization reversal has prompted many researchers to claim ferroelectricity in biological structures and their building blocks.Other observers were skeptical about the methodology adopted in generating the data and questioned the validity of the claimed ferroelectricity as such,“loop”can also be obtained from linear capacitors.In a paper with somewhat tongue-in-cheek title,Jim Scott showed that ordinary banana peels could exhibit closed loops of electrical charge which closely resemble and thus could be misinterpreted as ferroelectric hysteresis loops in barium sodium niobate,BNN paraphrasing it as“banana”.In this paper,we critically review ferroelectricity in biological system and argue that knowing the molecular and crystalline structure of biological building blocks and experimenting on such building blocks may be the way forward in revealing the“true”nature of ferroelectricity in biological systems.