碘分子双色激光感生光栅光谱

用Ｎｄ：ＹＡＧ激光倍频光分成强度大致相等的两束激光作为泵浦光，以２．７３°交叉于碘分子样品室中，两束泵渝光发生干涉在碘分子中选择激发形成了空间正弦分布的激发态分子光栅和基态耗尽型光栅。另一束窄线宽染料激光作为探索光射入到激光感生光栅上，沿着布拉格衍射的方向接收信号光。扫描探索光的波长，分别在５５５．９～５７０．６ｎｍ，５７６．３～５８７．２ｎｍ和６０５．０～６０５．６ｎｍ的波段内共获得１２９根与碘分子Ｂ－Ｘ态振转能级双共振的双色激光感生光栅光谱谱线。     

利用纳米门电极增强拉曼散射

为了更好地了解表面增强拉曼光谱(SERS)的机制,并进一步提高增强因子,研制了具有高稳定性的纳米劈裂装置及芯片。结合纳米劈裂技术及SERS技术,在拉曼光谱测量的同时能非常精确地操纵两纳米电极间的距离以观察相应拉曼光谱强度的变化。发现拉曼光谱强度依赖于纳米电极的间距以及激光的偏振化方向。在利用两纳米电极作为增强体的基础上引入了纳米门电极,并观察偏置电压下的门电极对拉曼光谱信号的影响。实验结果表明,拉曼光谱信号的强度强烈地依赖于纳米门电极上所施加的偏置电压。实验为增强拉曼信号提供了新的方法,同时为拉曼光谱增强机制的理论研究提供了参考数据。     

纳米金修饰碳纳米管阵列结构的表面增强拉曼散射

研究了纳米金粒子修饰碳纳米管阵列结构的表面增强拉曼散射性能.通过FDTD理论模拟仿真了不同粒径纳米金颗粒的场强分布;并采用化学还原的方法制备出直径分别为20、40和60 nm三种不同粒径的金颗粒,然后将纳米金粒子修饰到有序定向的碳纳米管阵列表面,并将该结构作为表面增强拉曼基底.FDTD软件仿真结果表明,60 nm粒径的纳米金颗粒周围场强分布最强,是入射场场强的15倍.同时将罗丹明6G溶液用于测试几组不同尺寸的金颗粒对拉曼散射光强的影响,发现60 nm金颗粒对R6G拉曼信号增强最大.FDTD理论模拟仿真和罗丹明6G溶液实验测试结果表明:金颗粒尺寸在20～60 nm内,颗粒尺寸越大,拉曼散射光的光强越大.     

利用偏振拉曼散射测定LB膜中分子取向的理论

在理论上导出了LB膜中拉曼散射强度和光的入射角、散射角及其分子有序排列方向角之间的关系,由此提出一种采用测定拉曼散射光强度的角分布来确定LB膜中分子有序排列的方向角的新方法。     

碳纳米管和金属纳米粒子复合结构的拉曼光谱特性

提出了一种基于碳纳米管和金属纳米粒子的表面增强拉曼基底,并进行了实验研究。采用化学方法制备了单壁和多壁碳纳米管薄膜;利用离子溅射方法在碳纳米管薄膜上形成Au纳米粒子,构成基于碳纳米管和金属纳米粒子复合结构的表面增强拉曼散射基底。对此样品进行了扫描电子显微镜(SEM),反射谱、拉曼谱等表征测试。研究表明,该基底由于碳纳米管极大的比表面积,可吸附更多的金属纳米粒子,增强拉曼散射信号强度。     

静压下GaAs_(1-x)P_x混晶的喇曼散射

在77K下和0—60kbar静压范围内测量了GaAs_(1-x)P_x(0.76 ≤x≤1)混晶的喇曼散射谱。得到了这些混晶的类GaP的LO模的压力系数。发现在所研究的x范围内GaAs_(1-x)P_x混晶的类GaP的LO模的压力行为与Gap的LO模基本相同。利用测得的压力系数计算了类GaP的LO模的模式Gruneisen参数。     

Tunable Enhancement of Raman Scattering in Graphene‐Nanoparticle Hybrids

The realization of graphene‐gold‐nanoparticle (G‐AuNP) hybrids is presented here through a versatile electrochemical approach, which allows the continuous tuning of the size and density of the particles obtainable on the graphene surface. Raman scattering from graphene, which is significantly enhanced in such hybrids, is systematically investigated as a function of the size and density of particles at the same location. In agreement with theory, it is shown that the Raman enhancement is tunable by varying predominantly the density of the nanoparticles. Furthermore, it is observed that the increase in Raman cross‐section and the strength of Raman enhancement varies as a function of the frequency of the vibrational mode, which may be correlated with the plasmonic fingerprint of the deposited AuNPs. In addition to this electromagnetic enhancement, support is found for a chemical contribution through the occurrence of charge transfer from the AuNPs onto graphene. Finally, G‐AuNP hybrids can be efficiently utilized as SERS substrates for the detection of specifically bound non‐resonant molecules, whose vibrational modes can be unambiguously identified. With the possibility to tune the degree of Raman enhancement, this is a platform to design and engineer SERS substrates to optimize the detection of trace levels of analyte molecules.     

GdVO4晶体的受激拉曼散射

采用熔体提拉法生长出了高质量的a轴和c轴GdVO4单晶。测量了GdVO4晶体的室温透过光谱,结果表明GdVO4晶体的短波透过截止边为338 nm,长波透过截止边大于3000 nm,透过范围覆盖紫外、可见、近红外和部分中红外波段,因此可以在较宽波长范围内实现拉曼激光频移。研究了GdVO4晶体在532 nm和355 nm皮秒激光脉冲抽运下的受激拉曼散射(SRS)。采用腔外单次通过方式,获得了3级斯托克斯线(557.98 nm,586.86 nm,618.92 nm)和1级反斯托克斯线(508.01 nm),得到GdVO4晶体一级斯托克斯拉曼散射的稳态增益系数为26.6±0.2 cm/GW,二级斯托克斯拉曼散射的稳态增益系数为14.0±0.2 cm/GW,受激拉曼散射的整体转换效率达到43%。报道了GdVO4晶体355 nm激发的受激拉曼散射,观察到2级斯托克斯谱线(365.9 nm,378.1 nm),在此条件下测得一级斯托克斯谱线的拉曼增益高达114±9 cm/GW。     

基于表面增强拉曼光谱的结肠癌组织免疫分析

通过表面增强拉曼散射(SERS)标记抗体检测结肠癌组织切片上癌胚抗原(CEA)的表达,探讨SERS标记免疫检测技术用于临床分析结肠癌组织切片中蛋白质表达的可行性。采用种子生长法合成Ag壳Au核复合纳米粒子,将4-巯基苯甲酸(4-MBA)作为标记分子吸附于纳米粒子表面,制备出SERS探针;再将这种探针与CEA单克隆抗体相结合形成SERS免疫探针;最后通过SERS标记的抗体与结肠癌组织切片上相应的抗原发生特异性结合,对滴加探针的组织切片进行SERS检测和成像。结肠癌腺上皮出现很强的SERS信号,而除了少数非特异性吸附产生的信号之外,间质及正常上皮中几乎不出现SERS信号。通过SERS成像可以清晰地看到结肠癌腺上皮显示红色,表明结肠癌腺上皮高表达CEA,而间质及正常上皮几乎显示黑色和深蓝色,只有极个别点为红色,表明间质及正常上皮基本不表达CEA。研究表明,SERS标记抗体检测分析技术具有高灵敏度和高特异性,有望应用于结肠癌组织切片中蛋白质表达的分析,成为结肠癌辅助诊断的一种重要方法。     

Surface‐Enhanced Raman Scattering Using Microstructured Optical Fiber Substrates

Microstructured optical fibers (MOFs) represent a promising platform technology for fully integrated next generation surface enhanced Raman scattering (SERS) sensors and plasmonic devices. In this paper we demonstrate silver nanoparticle substrates for SERS detection within MOF templates with exceptional temporal and mechanical stability, using organometallic precursors and a high‐pressure chemical deposition technique. These 3D substrates offer significant benefits over conventional planar detection geometries, with the long electromagnetic interaction lengths of the optical guided fiber modes exciting multiple plasmon resonances along the fiber. The large Raman response detected when analyte molecules are infiltrated within the structures can be directly related to the deposition profile of the nanoparticles within the MOFs via electrical characterization.     

Micro‐Raman Scattering Imaging of Langmuir–Blodgett Surface Relief Gratings

Surface relief gratings (SRGs) recorded on Langmuir–Blodgett (LB) films of an azobenzene homopolymer were visualized using micro‐Raman imaging. Raman scattering (RS) was achieved using the 780 nm laser line while pre‐resonance Raman scattering (pre‐RRS) and resonance Raman scattering were achieved using the 633 and 514.5 nm laser lines, respectively. Pre‐surface‐enhanced resonance Raman scattering (pre‐SERRS) and surface‐enhanced resonance Raman scattering (SERRS) were collected for the LB films covered with a 6 nm thick silver island film. The SRG could be chemically identified by the spatial variation in the Raman signal scattered by the film due to a concentration gradient. The pre‐SERRS provided signals of the same intensity along and across the grooves, indicating that the molecular architecture at the SRG surface is the same at the peaks as in the valleys.     

Probing Individual Layers in Functional Oxide Multilayers by Wavelength‐Dependent Raman Scattering

The integration of functional oxides on silicon requires the use of complex heterostructures involving oxides of which the structure and properties strongly depend on the strain state and strain‐mediated interface coupling. The experimental observation of strain‐related effects of the individual components remains challenging. Here, a Raman scattering investigation of complex multilayer BaTiO₃/LaNiO₃/CeO₂/YSZ thin‐film structures on silicon is reported. It is shown that the Raman signature of the multilayers differs significantly for three different laser wavelengths (633, 442, and 325 nm). The results demonstrate that Raman scattering at various wavelengths allows both the identification of the individual layers of functional oxide multilayers and monitoring of their strain state. It is shown that all of the layers are strained with respect to the bulk reference samples, and that strain induces a new crystal structure in the embedded LaNiO₃. Based on this, it is demonstrated that Raman scattering at various wavelengths offers a well‐adapted, non‐destructive probe for the investigation of strain and structure changes, even in complex thin‐film heterostructures.     

Fabrication of a Macroporous Microwell Array for Surface‐Enhanced Raman Scattering

Here, a colloidal templating procedure for generating high‐density arrays of gold macroporous microwells, which act as discrete sites for surface‐enhanced Raman scattering (SERS), is reported. Development of such a novel array with discrete macroporous sites requires multiple fabrication steps. First, selective wet‐chemical etching of the distal face of a coherent optical fiber bundle produces a microwell array. The microwells are then selectively filled with a macroporous structure by electroless template synthesis using self‐assembled nanospheres. The fabricated arrays are structured at both the micrometer and nanometer scale on etched imaging bundles. Confocal Raman microscopy is used to detect a benzenethiol monolayer adsorbed on the macroporous gold and to map the spatial distribution of the SERS signal. The Raman enhancement factor of the modified wells is investigated and an average enhancement factor of 4 × 10⁴ is measured. This demonstrates that such nanostructured wells can enhance the local electromagnetic field and lead to a platform of ordered SERS‐active micrometer‐sized spots defined by the initial shape of the etched optical fibers. Since the fabrication steps keep the initial architecture of the optical fiber bundle, such ordered SERS‐active platforms fabricated onto an imaging waveguide open new applications in remote SERS imaging, plasmonic devices, and integrated electro‐optical sensor arrays.     

Alloy Engineering in Few‐Layer Manganese Phosphorus Trichalcogenides for Surface‐Enhanced Raman Scattering

Manganese phosphorus trichalcogenides are widely used in the field of photocatalysis and magnetic studies due to their broadband gaps. Herein, an alloy engineering method for the few‐layer manganese phosphorus trichalcogenides (MnPS_3–xSe_x, 0 ≤ x ≤ 3) in surface‐enhanced Raman scattering (SERS) is reported. A new strategy, with the coupling of exciton resonance (µ_ex) and photoinduced charge transfer (PICT), is applied to screen out materials for SERS enhancement. According to the calculation of density functional theory, the bandgap of manganese phosphorus trichalcogenides (MnPS₃) can be adjusted to match the band energy of Rhodamine 6G molecules by alloy engineering. Furthermore, a series of few‐layer MnPS_3–xSe_x (0 ≤ x ≤ 3) are fabricated to study the PICT‐induced SERS behavior under resonance excitation. The good performance with a detection limit down to 10^?9 m indicates that the synergistic resonances between µ_ex and PICT are crucial to the enhancement.     

An On‐Chip Break Junction System for Combined Single‐Molecule Conductance and Raman Spectroscopies

Systems that are capable of robustly reproducing single‐molecule junctions are an essential prerequisite for enabling the wide‐spread testing of molecular electronic properties, the eventual application of molecular electronic devices, and the development of single‐molecule based electrical and optical diagnostics. Here, a new approach is proposed for achieving a reliable single‐molecule break junction system by using a microelectromechanical system device on a chip. It is demonstrated that the platform can (i) provide subnanometer mechanical resolution over a wide temperature range (≈77–300 K), (ii) provide mechanical stability on par with scanning tunneling microscopy and mechanically controllable break junction systems, and (iii) operate in a variety of environmental conditions. Given these fundamental device performance properties, the electrical characteristics of two standard molecules (hexane‐dithiol and biphenyl‐dithiol) at the single‐molecule level, and their stability in the junction at both room and cryogenic temperatures (≈77 K) are studied. One of the possible distinctive applications of the system is demonstrated, i.e., observing real‐time Raman scattering in a single‐molecule junction. This approach may pave a way to achieving high‐throughput electrical characterization of single‐molecule devices and provide a reliable platform for the convenient characterization and practical application of single‐molecule electronic systems in the future.     

On‐Chain Fluorenone Defect Emission from Single Polyfluorene Molecules in the Absence of Intermolecular Interactions

The emission of semiconducting polyfluorenes is often accompanied by an undesired feature in the green spectral region. Whereas a number of previous investigations have argued in favor of a monomolecular origin of the emission species based on ketonic defects, recent experimental results suggested the necessity of excimer formation between individual fluorenone units. We provide a range of new evidence supporting the monomolecular origin of green band emission in polyfluorenes. Most importantly, we succeed in performing single‐molecule spectroscopy on fluorenone‐containing polyfluorene model compounds. Whereas most fluorenone‐containing molecules exhibit both blue backbone and green fluorenone emission independent of fluorenone concentration, it is the relative intensities of the two species which correlate strongly with the fluorenone concentration on the single‐molecule level. Furthermore, we consider a novel model compound with a bifacial arrangement of two fluorenone units. This compound does not provide any signatures of enhanced intramolecular excimer formation but does strongly indicate that concentration quenching effects occur once fluorenone units can interact electronically. The ability to detect on‐chain defect emission in a single polymer molecule demonstrates that photochemical reactions in conjugated polymers can be monitored by fluorescence spectroscopy down to the level of a few atoms, constituting an unprecedented degree of materials characterization.     

Plasmonic Self‐Propelled Nanomotors for Explosives Detection via Solution‐Based Surface Enhanced Raman Scattering

Nanomotors represent a class of artificial machines that span the chasm between molecular motors and bigger micromotors. Their importance lies in the fact that to effectively navigate and perform tasks in a biological environment without alerting the action of the immune system, the maximal size of the object has to be well below 200 nm. Fully nanosized gold/silver core/shell plasmonic nanomotors using the seeded growth wet chemical approach, which allows high scalability of synthesis of the nanomotors compared to planar substrate‐based methods, is presented. Using the nanoparticle tracking analysis, the catalysis driven enhanced diffusion of the plasmonic nanomotors in the presence of low concentrations of fuel is presented and shown that the prepared nanomotors are good candidates for a solution‐based surface‐enhanced Raman spectroscopy detection of picric acid, a typical explosive. In addition to the mentioned effects, ligand‐exchange is performed on the nanomotors to replace the surfactant with its thiolated analog, a combination which is already proven in literature to be stealthy to the immune response of the living organism.     

Copper Nanoparticles Grafted on a Silicon Wafer and Their Excellent Surface‐Enhanced Raman Scattering

Copper nanoparticles grafted on a silicon wafer are fabricated by reducing copper ions with silicon–hydrogen bonds and assembling them in situ on the Si wafer. The nanoparticles, with an average size of 20 nm, grow uniformly and densely on the Si wafer, and they are used as substrates for surface‐enhanced Raman scattering. These substrates exhibit excellent enhancement in the low concentration detection (1 × 10^?9 M ) of rhodamine 6G with an enhancement factor (EF) of 2.29 × 10⁷ and a relative standard deviation (RSD) of <20%. They are also employed to detect sudan‐I dye with distinguished sensitivity and uniformity. The results are interesting and significant because Cu substrates are otherwise thought to be poor. These effects might provide new ways to think about surface‐enhanced Raman scattering based on Cu substrates.     

High‐Density Hotspots Engineered by Naturally Piled‐Up Subwavelength Structures in Three‐Dimensional Copper Butterfly Wing Scales for Surface‐Enhanced Raman Scattering Detection

Very recently, wing scales of natural Lepidopterans (butterflies and moths) manifested themselves in providing excellent three dimensional (3D) hierarchical structures for surface‐enhanced Raman scattering (SERS) detection. But the origin of the observed enormous Raman enhancement of the analytes on 3D metallic replicas of butterfly wing scales has not been clarified yet, hindering a full utilization of this huge natural wealth with more than 175 000 3D morphologies. Herein, the 3D sub‐micrometer Cu structures replicated from butterfly wing scales are successfully tuned by modifying the Cu deposition time. An optimized Cu plating process (10 min in Cu deposition) yields replicas with the best conformal morphologies of original wing scales and in turn the best SERS performance. Simulation results show that the so‐called “rib‐structures” in Cu butterfly wing scales present naturally piled‐up hotspots where electromagnetic fields are substantially amplified, giving rise to a much higher hotspot density than in plain 2D Cu structures. Such a mechanism is further verified in several Cu replicas of scales from various butterfly species. This finding paves the way to the optimal scale candidates out of ca. 175 000 Lepidopteran species as bio‐templates to replicate for SERS applications, and thus helps bring affordable SERS substrates as consumables with high sensitivity, high reproducibility, and low cost to ordinary laboratories across the world.     

Arrays of Cone‐Shaped ZnO Nanorods Decorated with Ag Nanoparticles as 3D Surface‐Enhanced Raman Scattering Substrates for Rapid Detection of Trace Polychlorinated Biphenyls

A new, highly sensitive and uniform three‐dimensional (3D) hybrid surface‐enhanced Raman scattering (SERS) substrate has been achieved via simultaneously assembling small Ag nanoparticles (Ag‐NPs) and large Ag spheres onto the side surface and the top ends of large‐scale vertically aligned cone‐shaped ZnO nanorods (ZnO‐NRs), respectively. This 3D hybrid substrate manifests high SERS sensitivity to rhodamine and a detection limit as low as 10^?11 M to polychlorinated biphenyl (PCB) 77—a kind of persistent organic pollutants as global environmental hazard. Three kinds of inter‐Ag‐NP gaps in 3D geometry create a huge number of SERS “hot spots” that mainly contribute to the high SERS sensitivity. Moreover, the supporting chemical enhancement effect of ZnO‐NRs and the better enrichment effect ascribed to the large surface area of the substrate also help to achieve a lower detection limit. The arrays of cone‐shaped ZnO‐NRs decorated with Ag‐NPs on their side surface and large Ag spheres on the top ends have potentials in SERS‐based rapid detection of trace PCBs.