固-液系统中表面增强喇曼散射强度I_(SERS)对浓度c的依赖关系及水杨酸分子的吸附等温特性研究

在恒定温度下,通过测量不同浓度溶液中吸附在Ag镜表面水杨酸分子(SA)的表面增强喇曼散射(SEKS)强度(I_(SERS),对固-液系统中吸附在Ag镜表面上SA分子的I_(SERS)对溶液浓度的依赖关系进行实验研究,并对I_(SERS)与吸附分子数N~s的关系进行分析讨论。实验研究和理论分析的结果表明:利用SERS技术通过测量I_(SERS)与溶液浓度c的依赖关系,可为固-液系统中分子在固体表面的吸附过程及吸附特性研究提供一个高灵敏度的、分子级水平的新手段。     

2-噻吩甲酸在Fe3O4@Ag基底上的吸附及表面增强拉曼光谱

采用共沉淀法合成Fe₃O₄纳米颗粒,再以柠檬酸三钠还原AgNO₃获得了具有SERS活性的Fe₃O₄@Ag磁性纳米复合材料。基于密度泛函理论(DFT)的量子化学计算方法和表面增强拉曼光谱(SERS)技术,从理论计算和实验测定表征探讨了2-噻吩甲酸(2-TCA)在Fe₃O₄@Ag表面的吸附行为和增强效应。结果表明:理论计算得到的拉曼光谱与实际测得的常规拉曼光谱基本一致,而在DFT理论计算中所键连的Ag原子数越多,与实测值就越接近。溶液的浓度和pH对拉曼增强效果有很大的影响,当溶液的pH=3且浓度为1×10^-4 mol·L^-1时有最大拉曼增强效应。峰强随2-TCA浓度的增加呈现先增大后减小的趋势,浓度过大会导致大量2-TCA分子吸附聚集在Ag表面形成局部"拥堵",阻碍了激发光尤其是光谱信号的散射通过,从而减弱了拉曼增强效应。pH的变化使溶液中2-TCA分子形态发生改变,结构形态不同,其在Ag表面的吸附方式也不同。中性C₄H₃SCOOH分子以环上S:形式垂直吸附键合在Ag表面,形成S—Ag配位键而产生SERS光谱。-1价C₄H₃SCOO^-离子以S—Ag配位和O—Ag共价"双键合"侧卧方式共同吸附在Ag表面而产生SERS光谱。在Ag表面,以单独S—Ag配位键吸附或键合的能力比S—Ag配位和O—Ag共价共同吸附方式要弱,但其产生的SERS信号更强,故2-TCA中性分子比2-TCA^-离子更有利于SERS的产生。随着pH值的增加,溶液中的2-TCA由中性分子逐渐转化为-1价的C₄H₃SCOO^-离子,因而在pH>3以后,拉曼增强效应逐步减弱。     

H原子在Al(111)和Ag(111)面上的吸附

本文用电荷自洽的EHT方法,研究了H原子在Al(111)和Ag(111)面上的吸附,结果指出:在Al(111)面上,H以原子状态吸附在某些对称位置上,它也能渗透到表面层中去,成为填隙原子;H₂分子在表面处发生解离吸附。在Ag(111)表面上,H原子有可能以分子状态吸附,H—H键平行于表面,这与高分辨率电子能量损失谱所得到的实验结果一致;但H₂分子在Ag(111)表面也可能发生解离吸附。 关键词：     

KDP晶体固-液界面吸附行为的分子模拟研究

通过构建晶体表面-KDP分子界面吸附结构模型, 采用分子动力学和密度泛函计算方法研究KDP分子在(001)和(010)面吸附的物理化学过程, 考察了温度对物理吸附行为的影响. 研究表明: KDP晶体表面的吸附过程和生长习性主要由化学吸附主导, 化学吸附能的计算表明[K-O₈]基元在(001)界面的结合能是(010)界面结合能的2.86倍; 在饱和温度附近, [H₂PO₄]^-阴离子在KDP界面的物理结合能随温度的变化呈现振荡特征, 溶液中有较多的离子团簇形成, 溶液变得很不稳定; 当温度从323 K降低至308 K时, 水分子在界面的结合能总体呈下降趋势, 而KDP分子在界面的吸附能总体呈上升趋势, 脱水过程是水分子和[H₂PO₄]^-阴离子在固液界面边界层竞争吸附的结果. 研究结果对确足晶体生长界面动力学过程发展和完善晶体生长理论有重要意义. 关键词： 分子动力学 双层结构模型 结合能     

真空中固液界面的离子束分析研究

原位实时地高精度测量固液界面的元素或离子(电荷)组成和动态变化对于界面反应和相互作用研究非常重要,但是传统的高分辨离子束分析实验在真空环境中不能直接测量液体样品。本文研制了一种固体-液体界面探针,该探针使用氮化硅-铝纳米复合膜作为真空密封窗和电化学电极,利用复旦大学核微探针成功开展了真空中固体-液体界面探针0.01 mol/L氯化钡和1 mol/L氯化镧溶液样品固体-液体界面的卢瑟福背散射(RBS)分析和粒子激发X射线(PIXE)分析。实验结果表明,真空环境下,固液界面探针纳米薄窗可承受2 MeV He+离子注量为1.0×1018 ions/cm2的辐照。微区PIXE分析成功获得了固液界面探针结构的元素分布。通过对卢瑟福背散射能谱进行分析,获取了20 nm分辨的电极界面微米深溶液中的La, Cl元素浓度。在1 mol/L的LaCl3固液界面电极表面,负电压(–2.3 V)时电解质离子在电极表面高浓度聚集,正电压(+2.3 V)时电解质在电极表面呈低浓度分布,在约1 250 nm深处电解质溶液趋向于体浓度。     

2,3-二巯基丁二酸在银表面的电化学表面增强拉曼光谱及电还原特性

采用原位电化学表面增强拉曼光谱(EC-SERS)和电化学还原方法,研究了内消旋-2,3-二巯基丁二酸(DMSA)在活化的银电极上的吸附行为。通过模型分子DMSA进行结构优化的密度泛函理论计算,得到了理论拉曼光谱。在相同的DMSA自组装时间条件下,其在Ag电极表面的覆盖度倒数与溶液浓度倒数成线性关系,说明DMSA单分子层在活性Ag表面的化学吸附遵循Langmuir等温吸附模型。在酸性介质中,DMSA浸置自组装50 min后,SERS峰强趋于稳定,达到了该浓度下的动态吸附平衡。EC-SERS信号随施加电位的负移逐渐减弱至基本消失。通过计算探针分子DMSA在不同电位下的增强因子(EF),指出较负电位下存在着还原/脱附作用,使得Ag表面的拉曼活性降低,尤其在小于-0.4 V的还原电位时,增强因子显著减小。     

多重散射团簇方法对吸附系统SO2/Ag(110)的理论分析

利用多重散射团簇方法(MSC)对吸附系统SO₂/Ag(110)的S原子K边X射线吸收精细结构谱(NEXAFS)作了理论分析.研究表明,覆盖度为0.5时,吸附的SO₂的S—O键长比气体状态时增长了(0.014±0.006)nm,OSO键角减小了15°±5°;SO₂分子的S原子处于芯位,但两个O原子处于不对称的位置;分子平面与(110)的夹角约为52°,同时分子平面相对衬底表面法线有一小角度的倾斜.MSC计算证实了该吸附系统存在一介于π^{关键词： X射线吸收精细结构 2/Ag(110)')" href="#">吸附系统SO₂/Ag(110) 多重散射团簇方法}     

咖啡酸分子表面增强拉曼光谱的理论与实验研究

咖啡酸（CA）是一种具有很高的医学价值的药物成分,在抗菌抗病毒方面应用广泛,尤其是咖啡酸及其衍生物在抗肿瘤方面有着巨大作用,现在对咖啡酸的相关研究越来越多,但大部分都是关于咖啡酸医学性质的研究,所以对咖啡酸分子的微观结构研究是非常有必要的。目前关于CA在Ag表面上的表面增强拉曼散射（SERS）光谱的理论与实验结合的研究尚未见报道,而对其振动光谱及表面增强机理的研究可以为咖啡酸的各种药学机理的研究提供一种科学的物理解释,所以有必要将密度泛函理论（DFT）方法与表面增强拉曼散射技术相结合,对咖啡酸在Ag纳米颗粒上的吸附性质及表面增强机理进行全面的研究,这对推进它们在医药学等领域的相关研究有着重要的参考价值。采用SERS与DFT技术对CA分子在Ag纳米颗粒表面上的表面增强拉曼光谱进行了研究。在实验方面,利用热还原反应原理,使用柠檬酸三钠和硝酸银在加热搅拌情况下制备Ag纳米颗粒,并使用激光共聚焦显微拉曼光谱仪测量了CA分子的常规拉曼散射（NRS）光谱及其表面增强拉曼散射（SERS）光谱。在理论计算方面,采用DFT的B3LYP方法,以6-31+G**和LANL2DZ分别作为C,H,O和Ag的计算基组来优化咖啡酸的分子构型,羟基与Ag₄的吸附构型,羧基与Ag₄的吸附构型,羟基与羧基共同与Ag₄吸附的构型,并以此为基础分析计算了CA分子的NRS光谱以及三种可能吸附模型的SERS光谱,并结合实验结果进行比较。同时对CA分子的振动模式进行了详细指认。根据实验数据和理论结果分析,在452 cm-1处的谱峰归属为环面外弯曲振动和O-H面外弯曲振动的耦合,这说明CA分子上的酚羟基是与Ag纳米颗粒表面作用的,不过相互作用较弱,推测CA分子平面可能与Ag基底表面不垂直;出现在1 338 cm-1处的谱峰归属于COO-伸缩振动,则可以说明CA分子上的羧基可能与Ag纳米颗粒垂直吸附。结果表明,CA分子是以羧基和酚羟基为吸附位吸附在Ag纳米颗粒表面上的。同时对CA分子的振动模式进行了详细指认。该工作对推进咖啡酸在生物医药等领域进一步的应用将起到重要作用。     

FeOx上AsH3吸附净化的密度泛函研究

基于密度泛函理论研究了AsH₃和O₂分子在α-Fe₂O₃(001)表面和FeO(100)表面的吸附及共吸附性质.结果表明：AsH₃和O₂分子在α-Fe₂O₃(001)表面最稳定的吸附构型都是Hollow吸附位点. AsH₃分子在FeO(100)表面最稳定的吸附位点为Top O吸附位点. O₂分子在FeO(100)表面最稳定的吸附位点为Hollow吸附位点. O₂分子在α-Fe₂O₃(001)和FeO(100)表面吸附后均被活化从而促进AsH₃分子的催化氧化. AsH₃分子在α-Fe₂O₃(001)表面最小的吸附能为-0.7991 eV,在FeO(100)表面最小的吸附能为-0.9117 eV.吸附值数据表明AsH     

硫代水杨酸在银表面的化学吸附及其表面增强拉曼光谱研究

采用电化学法对Ag电极粗糙活化,进而对含巯基基团的硫代水杨酸(TSA)进行表面增强拉曼光谱(SERS)研究。研究表明,溶液浓度与pH对增强效应影响显著,1×10-3 mol·L-1与pH 4分别为增强效应的最佳浓度与酸度。浓度增大由于空间位阻等因素影响而增强效应急速下降。由TSA化学吸附所产生的S—Ag峰位基本不随pH改变;但pH对峰强度有显著影响。经对TSA在不同pH下的分布和机理研究表明,TSA是通过中性C₆H₄(COOH)SH分子中的硫醇端基脱H后与活化的Ag表面进行吸附,形成S—Ag化学键而产生SERS光谱。在较强碱性条件下负一价的C₆H₄(COO-)SH 可能与OH- 形成竞争吸附而不易产生SERS;同时吸附基团巯基对羧基振动谱峰的变化以及对苯环共轭体系中的电子云分布有很大影响。     

Does the excitation of a plasmon resonance induce a strong chemical enhancement in SERS? On the relation between chemical interface damping and chemical enhancement in SERS

In this contribution, a fundamental new approach is made to explain high enhancement factors in surface-enhanced Raman spectroscopy (SERS) on the basis of chemical enhancement. Usually, high SERS enhancement factors are explained by electromagnetic enhancements due to the excitation of localized surface plasmon resonances and strong near field dipole–dipole coupling. However, very often the corresponding SERS spectra show clear signatures of a chemical enhancement. I propose that this contradiction is easily solved by taking chemical interface damping of the plasmon resonance into account. Chemical interface damping is caused by an electron transfer from the metallic structure into an adsorbate. However, this mechanism is also the basis for chemical enhancement in SERS, i.e., an electron transfers in the lowest unoccupied molecular orbital of the molecule and back to the metal. Hence, if a molecule causes a strong chemical interface damping, the excitation of plasmons is still the key factor for the SERS enhancement. But the reason for this enhancement might be not solely due to electromagnetic fields rather than by a chemical enhancement due to electron transfers from the metal to the molecules.     

Direct laser writing of symmetry-broken nanocorrals and their applications in SERS spectroscopy

We propose a simple and fast approach to prepare surface-enhanced Raman scattering (SERS) substrates over a large area with high flexibility by using direct laser writing (DLW) technique. The proposal is demonstrated by the direct fabrication of an array and a complex of symmetry-broken nanocorrals with DLW followed by a metal deposition process. SERS measurements show significant SERS enhancement, which can be controlled through engineering the focused “hot spots” by changing the structural parameters. The experimental observations are further confirmed by our simulations with a finite-difference time-domain tool. The studies can be extended to versatile SERS substrates with arbitrary geometries.     

Surface plasmon resonance and surface-enhanced Raman scattering activity of SiO2–Au core-cap nanostructure arrays

SiO₂–Au core-cap nanostructure arrays were prepared by dip-coating technique combined with wet chemical reduction method. The surface morphologies, structures, and optical properties of the obtained samples were characterized by scanning electron microscopy, X-ray diffraction, and ultraviolet–visible spectrophotometer, respectively. The surface-enhanced Raman scattering (SERS) activity of SiO₂–Au core-cap nanostructure arrays substrates was investigated using leucine as probe molecule. And the relationship between the SERS effect and the surface plasmon resonance (SPR) peaks was discussed. High-quality, stable, and reproducible SERS spectra of leucine were successfully obtained. When the maximum SPR peak matched with the excitation wavelength, the substrate gave rise to the highest SERS enhancement. Furthermore, six different fluorescent dyes were also chosen as probe molecules. It was found that the substrate showed good Raman enhancement and highly efficient fluorescence quenching characteristic on these fluorescent dyes.     

SERS scaling rules

We demonstrate the qualitative analysis of surface-enhanced Raman scattering (SERS) intensity and optical extinction by experimentally and numerically. This analytical methods are well matched not only the simple square lattice array of nanostructures, but also the rectangular lattices. We also demonstrate SERS selectivity of modes controlling the optical extinction of excitation and scattering wavelength. Both square lattice and rectangular lattice have similar tendency, but the rectangular lattice structures have much higher selectivity of SERS modes.     

Investigation of the catalysis and SERS properties of flower-like and hierarchical silver microcrystals

Noble metal nano/microstructures have attracted considerable attention because of their unique properties and their various applications. Controlling the shape of noble metal nano/microstructures is a promising strategy to tailor their physical and chemical properties for various applications in fields such as biological labeling and imaging, catalysis, and sensing. Among various specific structures, flower-like and hierarchical silver nano/microstructures have attracted increasing interest because exploration of these novel nano/microstructures with unusual optical properties can provide new perspectives into the rational design of novel materials. It is significantly more challenging to develop facile and effective solution approaches for systematic manipulation of the shape of Ag nano/microstructures. In this article, we revisited the ascorbic acid reduction method to prepare flower-like silver microcrystal with plate petals and hierarchical Ag microcrystal on a large scale and in high purity. Ascorbic acid plays two roles of a reducing agent and a crystal growth regulator. Therefore, the molar ratio of ascorbic acid and silver nitrate is critical to the formation of Ag microcrystal. The controlling of the two different Ag microstructures can be achieved by adjusting the molar ratio of the reactants in aqueous medium at room temperature. The as-prepared Ag microcrystals were characterized by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. The flower-like Ag microcrystal with plate petals and hierarchical Ag microcrystal with nanoscale sharp tips and gaps could exhibit high catalytic activity and strong surface-enhanced Raman spectroscopy (SERS) activity due to the high surface area and the local electromagnetic field intensity enhancement, respectively. The potential application of the as-prepared Ag microcrystals in catalysis and SERS was investigated, which revealed that these two kinds of Ag microcrystals exhibit high catalytic activities to the NaBH₄-catalyzed reduction of 4-nitrophenol and significant SERS effect to 4-aminothiophenol molecular due to their nanoscale sharp tips and gaps. Therefore, the flower-like Ag microcrystal and hierarchical Ag microcrystal investigated here could be promising candidates for single particle catalyst and SERS.     

Surface-enhanced Raman scattering (SERS)-based volatile organic compounds (VOCs) detection using plasmonic bimetallic nanogap substrate

In this paper, we present surface-enhanced Raman scattering (SERS)-based volatile organic compounds (VOCs) detection with bimetallic nanogap structure substrate. Deep UV photolithography at the wavelength of 250 nm is used to pattern circular shape nanostructures. The nanogap between adjacent circular patterns is 30 ± 5 nm. Silver (30 nm) and gold (15 nm) plasmonic active layers are deposited on the nanostructures subsequently. SERS measurements on different concentrations of acetone vapor ranged from 0.7, 1.5, 3.5, 10.3, 24.5 % and control have been performed with the substrate. The measurement results are found reproducible, and the detection limit is found to be 9.5 pg (acetone molecule). The detection sensitivity is 28.7 % higher than that of the recent reported leaning silicon nanopillar substrate. With further system miniaturization, the sensing technique can work as a portable SERS-based VOCs detection platform for point-of-care breath analysis, homeland security, chemical sensing and environmental monitoring.     

Combined taper-and-cylinder optical fiber probes for highly sensitive surface-enhanced Raman scattering

A combined taper-and-cylinder optical fiber fabricated by simple tube-etching and modified with silver nanoparticles is developed for surface-enhanced Raman scattering (SERS) sensing. It has the advantages of high light transmission efficiency and large interaction areas for light and silver nanoparticles. The detection of rhodamine 6G in remote mode indicates that the sensitivity could realize 10^?13 M. The fiber SERS probe with high flexibility and sensitivity shows great potential for molecule detection in various sensing applications.     

Platinum and palladium as substrates for surface enhanced Raman spectroscopy

Surface enhanced Raman scattering (SERS) has been observed from the electrogenerated I₂ and I^-₃ coadsorbed on Pt and Pd electrodes. Theoretical models on the SERS process that emphasize the important role of the optical properties of the metal substrate cannot be used to explain this observation. The electronic interaction between the adsorbate and the substrate is believed to be the most important mechanism for the observed SERS.     

Surface-enhanced Raman scattering of 4-mercaptobenzoic acid and hemoglobin adsorbed on self-assembled Ag monolayer films with different shapes

Polyvinylpyrrolidone (PVP)-protected silver nanostructures of various shapes, including nanocubes, nanospheres, and hybrid shapes with nanospheres and nanorods, on the surface of glass or Si substrates (PVP-Ag films) are prepared by using electrostatic self-assembly. With 4-mercaptobenzoic acid (4-MBA) as a probe molecule, it is demonstrated that the PVP-protected silver nanocubes films (PVP-Ag NCs) have better surface-enhanced Raman scattering (SERS) activity with an order of magnitude larger enhancement factors (EF) than the PVP-protected silver nanospheres films and the PVP-protected silver hybrid shapes films, which is confirmed by our numerical simulations. The EF of 4-MBA on the PVP-Ag NCs film are up to ~5.38 × 10⁶, and the detection limit is at least down to ~10^?8 M. The uniformity and reproducibility of the SERS signals on PVP-Ag NCs film are tested by point-to-point and batch-to-batch measurements. Meanwhile, the PVP-Ag films are also shown to be an excellent SERS substrate with good biocompatibility for hemoglobin detection. It is shown that the PVP-Ag NCs films can be used as excellent SERS substrate with good activity, uniformity, reproducibility, and biocompatibility and are promising for a myriad of chemical and biochemical sensing applications.     

On‐site detection of phosgene agents by surface‐enhanced Raman spectroscopy coupled with a chemical transformation approach

Phosgene and its analogs are greatly harmful to the public health, environmental safety and homeland security as widely used industrial substances with extremely high toxicity. In order to rapidly evaluate the emergency risk caused by these chemicals, a new highly sensitive method based on surface‐enhanced Raman spectroscopy (SERS) technique for measurement of phosgene agents was developed for the first time. Coupled with a chemical transformation approach, the highly toxic phosgene was conveniently converted to a SERS‐sensitive probe, i.e. iodine (I₂), with low toxicity or non‐toxicity. The characteristic SERS peak in 459 cm⁻¹ was used for quantitation and was presumed as a formation of triiodide anion (I₃⁻), which was induced in an iodide (I⁻)‐aggregation Au NPs system. The total measurement can be completed in ~20 min with the limits of detection of ~60 µg/l (phosgene) and ~30 µg/l (diphosgene), respectively, on a portable Raman spectrometer. This work is the first report of SERS measurement on phosgene and diphosgene in a quantitative level. This method is expected to meet the requirements of on‐site detection of phosgene agents, promote emergency responses and raise more opportunities for the portable SERS applications. Copyright © 2015 John Wiley & Sons, Ltd.