碳酸酯类电解液中纳米银电极界面过程的原位拉曼光谱研究

锂电池体系中负极表面固态电解质界面相(SEI)对锂电池性能起到至关重要的作用。然而,SEI结构和化学组成复杂,其形成机理至今仍未完全阐明,阻碍了锂电池的发展和应用。本文从方法学角度出发,采用表面增强拉曼光谱(SERS)“借力”策略,通过优化银纳米粒子的结构并借助其外来表面局域等离激元共振作用,开展以EC-DMC为溶剂的碳酸酯类电解液体系中SEI成膜过程的原位研究。为了确保可靠的原位SERS测试,我们设计了一种三电极体系气密拉曼电池。我们利用原位SERS方法,在纳米银电极上获得了SEI成膜过程的组成和结构信息。研究表明,SEI随电位变化呈现出双层结构,其中内层由薄且致密的无机组分构成,外层由疏松的有机组分构成。同时,研究发现LEMC是EC还原的主要成分,而不是LEDC,且金属锂参与的化学反应在形成稳定SEI中的起到关键作用。此外,锂发生沉积后,由于锂与银的合金效应导致其介电常数发生变化,从而削无法进一步增强SEI的拉曼信号。本文为深入理解负极表面SEI的形成及演变过程提供依据,并为今后开展锂电池体系相关界面过程的原位研究提供借鉴。

Efficient plasmon-enhanced perovskite solar cells by molecularly isolated gold nanorods

Perovskite solar cells(PSCs)are becoming a promising candidate for next-generation photovoltaic cells due to their attractive power conversion efficiency(PCE).Plasmonic enhancement is regarded as an optical tuning approach for further improving the PCE of single-junction PSCs toward Shockley-Queisser limit.Herein,we introduce molecularly isolated gold nanorods(Au NRs),bearing relatively stronger scattering ability and localized surface plasmonic resonance(LSPR)effect,in the rear side of perovskites in PSCs,for promoting light harvesting and for electrical enhancement.Owing to the larger refractive index and better matched energy level alignment,the 4-mercaptobenzoic acid molecules coated on Au NRs prove to play important dual roles:isolating the metallic Au NRs from contacting with perovskite,and facilitating more efficient charge separation and transport across the interface under the synergetic LSPR effect of Au NRs.Our work highlights the capability of the plasmonic approach by nanorods and by molecular isolation,extending nanoparticle-based plasmonic approaches,toward highly efficient plasmon-enhanced PSCs.

Nanobridged rhombic antennas supporting both dipolar and high-order plasmonic modes with spatially superimposed hotspots in the mid-infrared

Mid-infrared antennas(MIRAs)support highly-efficient optical resonance in the infrared,enabling multiple applications,such as surface-enhanced infrared absorption(SEIRA)spectroscopy and ultrasensitive mid-infrared detection.However,most MIRAs such as dipolar-antenna structures support only narrow-band dipolar-mode resonances while high-order modes are usually too weak to be observed,severely limiting other useful applications that broadband resonances make possible.In this study,we report a multiscale nanobridged rhombic antenna(NBRA)that supports two dominant reson-ances in the MIR,including a charge-transfer plasmon(CTP)band and a bridged dipolar plasmon(BDP)band which looks like a quadruple resonance.These assignments are evidenced by scattering-type scanning near-field optical micro-scopy(s-SNOM)imaging and electromagnetic simulations.The high-order mode only occurs with nanometer-sized bridge(nanobridge)linked to the one end of the rhombic arm which mainly acts as the inductance and the resistance by the circuit analysis.Moreover,the main hotspots associated with the two resonant bands are spatially superimposed,en-abling boosting up the local field for both bands by multiscale coupling.With large field enhancements,multiband detec-tion with high sensitivity to a monolayer of molecules is achieved when using SEIRA.Our work provides a new strategy possible to activate high-order modes for designing multiband MIRAs with both nanobridges and nanogaps for such MIR applications as multiband SEIRAs,IR detectors,and beam-shaping of quantum cascade lasers in the future.

Graphene-coated conductive probes with enhanced sensitivity for nanoIR spectroscopy

Nano-infrared(nanoIR)probes play a crucial role as nano-mechanical sensors and antennas for light absorption and emission,and their testing performance is critically dependent on their optical properties and structural stability.Graphene-coated dielectric probes are highly attractive for enhancing light–matter interactions and integrating IR photonics,providing a broadband optical response and strong electromagnetic field.However,achieving continuous single-layer graphene growth on non-planar and non-single crystalline dielectrics is a significant challenge due to the low surface energy of the dielectric and the large difference in size between the probe tip,cantilever,and substrate.Herein,we present a novel method for the growth of high-quality and continuous graphene with good conductivity on non-planar and amorphous dielectric probe surfaces using manganese oxide powder-assisted short time heating chemical vapor deposition.The resulting graphene-coated dielectric probes exhibit an average IR reflectance of only 5%in the mid-IR band,significantly outperforming probes without continuous graphene coating.Such probes can not only effectively transduce the local photothermal sample expansion caused by the absorption of IR laser pulses,but also effectively scatter near-field light,which is 25 times stronger than the commercial metal-coated probes,and have advantages in the application of nanoIR sensing based on atomic force microscope-based infrared(AFM-IR)spectroscopy and infrared scattering scanning near field optical microscopy(IR s-SNOM)principles.Furthermore,our graphene growth method provides a solution for growing high-quality graphene on the surfaces of non-planar dielectric materials required for integrated circuits and other fields.

Advances of surface-enhanced Raman and IR spectroscopies: from nano/microstructures to macro-optical design

Raman and infrared(IR)spectroscopy are powerful analytical techniques,but have intrinsically low detection sensitivity.There have been three major steps(i)to advance the optical system of the light excitation,collection,and detection since 1920s,(ii)to utilize nanostructure-based surface-enhanced Raman scattering(SERS)and surface-enhanced infrared absorption(SEIRA)since 1990s,and(iii)to rationally couple(i)and(ii)for maximizing the total detection sensitivity since 2010s.After surveying the history of SERS and SEIRA,we outline the principle of plasmonics and the different mechanisms of SERS and SEIRA.We describe various interactions of light with nano/microstructures,localized surface plasmon,surface plasmon polariton,and lightning-rod effect.Their coupling effects can significantly increase the surface sensitivity by designing nanoparticle–nanoparticle and nanoparticle–substrate configuration.As the nano/microstructures have specific optical near-field and far-field behaviors,we focus on how to systematically design the macro-optical systems to maximize the excitation efficiency and detection sensitivity.We enumerate the key optical designs in particular ATR-based operation modes of directional excitation and emission from visible to IR spectral region.We also present some latest advancements on scanning-probe microscopy-based nanoscale spectroscopy.Finally,prospects and further developments of this field are given with emphasis on emerging techniques and methodologies.

Quantification of electron accumulation at grain boundaries in perovskite polycrystalline films by correlative infrared-spectroscopic nanoimaging and Kelvin probe force microscopy

Organic–inorganic halide perovskites are emerging materials for photovoltaic applications with certified power conversion efficiencies(PCEs)over 25%.Generally,the microstructures of the perovskite materials are critical to the performances of PCEs.However,the role of the nanometer-sized grain boundaries(GBs)that universally existing in polycrystalline perovskite films could be benign or detrimental to solar cell performance,still remains controversial.Thus,nanometer-resolved quantification of charge carrier distribution to elucidate the role of GBs is highly desirable.Here,we employ correlative infrared-spectroscopic nanoimaging by the scattering-type scanning near-field optical microscopy with 20 nm spatial resolution and Kelvin probe force microscopy to quantify the density of electrons accumulated at the GBs in perovskite polycrystalline thin films.It is found that the electron accumulations are enhanced at the GBs and the electron density is increased from 6×10^(19) cm^(−3 )in the dark to 8×10^(19) cm^(−3 ) under 10 min illumination with 532 nm light.Our results reveal that the electron accumulations are enhanced at the GBs especially under light illumination,featuring downward band bending toward the GBs,which would assist in electron-hole separation and thus be benign to the solar cell performance.

Probing surface structure on two-dimensional metal-organic layers to understand suppressed interlayer packing

Two-dimensional metal-organic layers(MOLs)from alternatively connected benzene-tribenzoate ligands and Zr6(μ3-O)_(4)(μ3-OH)_(4) or Hf6(μ3-O)_(4)(μ3-OH)_(4) secondary building units can be prepared in gram scale via solvothermal synthesis.However,the reason why the monolayers did not pack to form thick crystals is unknown.Here we investigated the surface structure of the MOLs by a combination of sum-frequency generation spectroscopy,nanoscale infrared microscopy,atomic force microscopy,aberration-corrected transmission electron microscopy,and compositional analysis.We found a partial coverage of the monolayer surface by dangling tricarboxylate ligands,which prevent packing of the monolayers.This finding illustrates low-density surface modification as a strategy to prepare new two-dimensional materials with a high percentage of exposed surface.