光诱导转化法制备片状三角形银纳米粒子的表面增强喇曼散射

采用柠檬酸三钠化学还原法制备球形Ag纳米粒子溶胶,并用高压球形氙灯对球形Ag纳米粒子溶胶进行光诱导实验.利用透射电子显微镜、紫外-可见吸收光谱研究了不同光照时间下的银胶纳米粒子的光谱特性和表面形貌,并以结晶紫为探针分子测量了银胶纳米粒子的表面增强喇曼散射光谱.实验结果表明:随着光照时间的增多,Ag纳米粒子溶胶颜色变化显著;紫外-可见吸收光谱吸收峰从单一峰渐渐显示出多个峰;透射电子显微镜图显示Ag纳米粒子由球形逐渐转变成片状三角形银纳米粒子、截角的片状三角形银纳米粒子;表面增强喇曼散射的增强效应随着光照时间的变化先逐渐增大,然后逐渐减小.     

电阻热蒸发镀膜与电子束蒸发镀膜对纳米球刻蚀方法制备二维银纳米阵列结构的影响

在使用纳米球刻蚀法制备二维银纳米点阵的过程中,使用不同的镀膜方法在同样的模板上得到了不同形貌的银纳米阵列结构.使用电阻热蒸发镀膜方法获得了六角排列的银纳米三角形阵列结构,使用电子束蒸发镀膜方法则获得了六角排列的银纳米环阵列结构.研究表明,沉积纳米粒子的粒径、表面纳米曲率效应和热能是形成不同结构形貌的纳米阵列结构的关键因素. 关键词： 银纳米阵列 电阻热蒸发 电子束蒸发 纳米球刻蚀     

三角形金属纳米粒子的光力特性研究

基于麦克斯韦应力张量理论,对多边形金纳米粒子在聚焦场下的光力特性进行了研究。以三角形金纳米粒子为例,从粒子在聚集场中的受力情况出发,分别研究了具有圆对称能量分布的聚焦场和具有三角形能量分布的聚焦场对三角形金纳米粒子的捕获特性。研究结果表明,当使用圆对称聚焦场时,可对边长为50～350 nm的三角形金纳米粒子实现稳定捕获;当使用三角形聚焦场时,在粒子以和聚焦场形状匹配的角度进入聚焦场的情况下,可对边长为100～350 nm的三角形金纳米粒子实现稳定捕获。将圆对称聚焦场和三角形聚焦场对三角形金纳米粒子的捕获特性进行比较,发现三角形聚焦场在x方向的捕获力要强于圆对称聚焦场;而在y方向,三角形聚焦场对粒子的捕获范围要大于圆对称聚焦场。该工作研究了三角形的金属纳米粒子在不同形状聚焦场下的光力捕获特性,为基于非球形金属粒子的光学操纵在拉曼光谱超分辨成像、粒子微加工等领域的应用奠定了理论基础。     

银纳米粒子阵列的自组装及其表面增强拉曼光谱应用

在以聚赖氨酸为表面耦联层分子的玻片基底制备了银纳米粒子阵列。ＳＥＭ表征结果表明,银粒子以亚单层的形式排列在基底表面。比较银溶胶和纳米粒子阵列的紫外可见光谱可见聚赖氨酸耦联层对银纳米粒子的粒径具有一定的选择性,甲基紫精在银纳米粒子阵列上的表面增强ＦＴ拉曼光谱表明在近红外区拉曼散射的表面增强主要来自于化学增强效应。     

Au/Au同质结的高压水热合成及其光学性能研究

本文通过水热法合成了Au和Au/Au同质结纳米粒子,并用透射电子显微镜(TEM)和紫外可见吸收(UV-vis)光谱对所合成的单分散Au纳米粒子和Au/Au同质结纳米粒子进行了表征。我们的研究发现,十六烷基三甲基溴化铵(CTAB)在Au/Au同质结纳米粒子的合成中起着非常重要的作用,改变CTAB的加入量,Au纳米粒子由单分散Au纳米粒子变成Au/Au同质结纳米粒子。     

片状三角形银纳米颗粒的自组织行为与光学特性

用化学方法制备了一种规则的片状三角形银纳米颗粒，边长为100±10nm，厚度约为30nm.紫外可见光谱分析表明了三角形银纳米颗粒形貌的完整性.颗粒表面修饰的有机分子，使三角形银纳米颗粒在碳膜上自组织形成二维单层膜，在硅片上形成高取向银膜，该银膜对吡啶分子具有很强的表面增强拉曼散射效应，增强因子可达108.     

玻璃基底上不规则银纳米结构的生长及其光学性质的研究

以经过硅烷化后玻璃片为基底，之后吸附金纳米种子，采用柠檬酸钠为还原剂，在荧光灯照射条件下还原硝酸银，制备出基底表面具有银纳米粒子聚集结构的材料。采用透射电镜、扫描电镜和紫外可见分光光度计对产物的形貌和性质进行了表征，并考察银纳米粒子的形貌对其薄膜基底SERS活性的影响。结果表明：随着光照时间增加至16 h，金种子长大为平均粒径110 nm的不规则状多晶银纳米粒子，且出现双层粒子堆积。基底上纳米粒子的吸收光谱上出现了由银粒子的表面等离子体激元偶极子耦合引发的强烈吸收峰：随着光照时间的变化，耦合峰在600～813 nm波段内移动。光照时间为12 h后得到的SERS活性基底具有最强的SERS信号。     

金银纳米粒子的电化学性质及联苯胺的SERS研究

采用柠檬酸钠还原氯金酸,硼氢化钠还原硝酸银分别制备了较小粒径的金、银纳米粒子。运用紫外可见吸收光谱(UV-Vis)、扫描电子显微镜(SEM)、循环伏安法(CV)对金、银纳米粒子进行了表征。结果表明：所得金、银纳米粒子粒径分别约为16和10 nm,并能以亚单层形式组装于导电玻璃(ITO)表面;CV图显示金、银纳米粒子分别有一对不对称的氧化还原峰,而且纳米粒子的浓度对其氧化还原电位存在一定的影响。采用自组装方法,以联苯胺为偶联分子, 在粗糙金基底表面构筑了金/银纳米粒子的双层有序结构。表面增强拉曼光谱研究表明, 在有序金银纳米粒子组装体中偶联分子的拉曼散射得到了增强。     

银和去合金银-金纳米粒子的SERS活性研究

用乙二醇还原硝酸银,聚乙烯吡咯烷酮作表面活性剂合成了大量的银纳米颗粒。银纳米颗粒和HAuCl4发生置换反应后形成去合金银-金纳米粒子。以吡啶和SCN-作为探针分子研究了它们的SERS活性。结果表明,当探针分子吸附于银纳米颗粒和去合金银-金纳米粒子上时,探针分子的特征振动峰强度增强、频率发生位移。SERS可表征纳米粒子物理和化学性质的变化。     

一种新型银溶胶的制备、表征及其SERS活性的研究

报道了用一种化学还原方法制备银溶胶的新方法。用紫外-可见光谱和透射电镜研究银纳米粒子的形成过程,粒子形状及粒径分布。结果表明,在反应初期形成球形和棒状两种形状的银纳米粒子,随着反应的进行,大部分的棒状粒子逐渐变为球形粒子,最终棒状粒子少于银纳米粒子总数的3%。因此,最终得到了一种形状均一的,平均粒径为17nm银纳米粒子。同时也用紫外-可见光谱研究了Cl-的加入对这种银纳米粒子光谱性质的影响,结果表明Cl-加速了银纳米粒子的聚集。这种银溶胶有着较高的SERS活性。     

硼酸盐玻璃中Eu掺杂对Ag纳米颗粒的析出机制及其发光性质研究

采用高温熔融法制备了Eu-Ag共掺的硼酸盐玻璃,利用吸收光谱和发射光谱等研究了玻璃中网络形成体B₂O₃含量变化和Eu离子共掺对于Ag在基质中赋存状态的影响。在Eu-Ag共掺玻璃的吸收光谱中发现,随着B₂O₃含量的增加,Ag纳米颗粒在4 10 nm附近的宽带吸收强度逐渐下降;玻璃在340 nm光源激发下,位于350～600 nm的蓝绿光区出现一个Ag分子团簇的宽带发光,且其发光强度随B₂O₃含量的增加逐渐增强。在Eu或Ag单掺的玻璃中可分别观测到微弱的Eu3+或Ag分子团簇的本征发射,而Eu-Ag共掺样品中Eu3+和Ag分子团簇的发光都得到了显著的增强。并且Eu离子浓度的增加促进了Ag纳米颗粒在410 nm附近的宽带吸收。对Eu离子的添加促进Ag纳米颗粒析出的机理进行了讨论。同时,由于Eu3+的5D₀→7F_J的电子跃迁发射为橙红光,Ag纳米团簇可发射蓝绿光甚至黄光,因此通过玻璃结构的调控和Eu离子掺杂浓度的调节可以实现玻璃的白光发射,这有望成为潜在的白光LED用玻璃照明材料。     

Structural and spectroscopic studies of thin film of silver nanoparticles

We report the deposition of thin film of silver (Ag) nanoparticles by wet chemical method. The as-synthesized Ag nanoparticles have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray energy dispersive spectroscopy (EDS), field emission transmission electron microscopy (FETEM) and high-resolution TEM (HRTEM), UV-vis spectroscopy and thermogravimetric-differential thermal analysis (TG-DTA) respectively. FESEM image indicates that the silver film prepared on the quartz substrate is smooth and dense. XRD pattern reveals the face-centered cubic (fcc) structure of silver nanoparticles. EDS spectrum indicates that samples are nearly stoichiometric. From TEM analysis, it is found that the size of high purity Ag nanoparticles is ranging from 10 to 20 nm with slight agglomeration. Absorption in UV-vis region by these nanoparticles is characterized by the features reported in the literature, namely, a possible Plasmon peak at ∼403 nm. Optical absorbance spectra analysis reveals that the Ag film has an indirect band structure with bandgap energy 3.88 eV. TGA/DTA studies revealed that a considerable weight loss occurs between 175 and 275 °C; and the reaction is exothermic.     

Silver nanoplates: controlled preparation, self-assembly, and applications in surface-enhanced Raman scattering

Silver nanoplates were prepared in a dual reduction system with NaBH₄ and sodium citrate both as reducing agents. And then the as-prepared nanoplates could be growing up through multistage growth methodology. The average edge length of Ag nanoplates can be tailored from 40 nm to 260 nm without changing their shape, crystallinity, and the average thickness. Furthermore, the effectiveness of these silver nanoplates as substrates prepared by the silanization self-assembly method toward surface-enhanced Raman scattering (SERS) detection was evaluated by using 4-aminothiophenol (4-ATP) and rhodamine 6G (R6G) as probe molecules. It was found that the enhancement ability of the silver nanoplates film is remarkable lower than that of the spherical silver nanoparticle film. The reason is attributed to the electromagnetic mechanism and chemical mechanism. This work will be of great significance in understanding the SERS enhancement mechanism and in the fabrication of nanoparticle films for biosensing.     

SERS study on surface chain geometry of atactic poly (methyl methacrylate) film and nanosphere

The surface chain geometry of atactic poly (methyl methacrylate) (a‐PMMA) film and nanosphere (NS) was revealed by surface‐enhanced Raman scattering (SERS) spectra. The Ag nanoparticles and nanoplates were prepared by electrochemical deposition and chemical synthesis for SERS substrates. The experimental results suggested that the molecular chain axis of a‐PMMA film adopted a trans‐conformation on bonding to Ag surface ascribed to the short‐range chemical (CHEM) effect according to the SERS selection rules. However, for the well‐coated monolayer of a‐PMMA NSs, the α‐CH₃ in polymer chains stood vertically to the Ag surface due to the giant local electromagnetic effect, then the chain conformation presented in the interface between a‐PMMA NSs and Ag metal was adopted the opposite orientation compared with a‐PMMA film. The Raman enhancement of the Ag nanoparticles was more prominent than that of the Ag nanoplates due to the free energies of face‐centered cubic crystal faces in nanoparticles, but the single crystals with (111) plane of Ag nanoplates could improve the stability of SERS signals when the annealed temperature was above T_g of a‐PMMA NSs. The present work can provide some useful information of surface chain geometry and conformation of NSs for designing various materials with well‐defined structure via a‐PMMA NSs template. Copyright © 2013 John Wiley & Sons, Ltd.     

Laser sintering of silver nanoparticle thin films: microstructure and optical properties

We present a method for the sintering of silver (Ag) nanoparticle thin films by millisecond pulsed laser irradiation. The microstructure of sintered thin films and sintering behaviors of nanoparticles were systematically investigated in this paper. Absorption spectra of sintered thin films showed blue-shifted surface plasmon resonances (SPR) from 500 nm to 480 nm and red-shifted from 480 nm to 550 nm when laser power was varied from 100 W to 140 W and from 140 W to 200 W, respectively. This indicates a new technique to control light absorption through joining nanoparticles with laser sintering. According to theoretical calculations based on a heat diffusion model, the melting temperature of these Ag nanoparticles was estimated to be 440 °C during laser irradiation.     

Anisotropic gold nanoparticles and gold plates biosynthesis using alfalfa extracts

Industrial and medical applications for gold nanoparticles are extensive, yet highly dependent on their chemical and structural properties. Thus, harnessing the size and shape of nanoparticles plays an important role in nanoscience and nanotechnology. Anisotropic polyhedra and nanoplates were biosynthesized via reduction of 3 mM AuCl₄ ⁻ solution at room temperature. Alfalfa biomass extracts prepared in water and in isopropanol separately were used as reducing agents at pH 3.5 and 3.0, respectively. Nanoparticles observed in the isopropanol extract presented a size range of 30–60 nm, and the morphologies present included 30 nm decahedra and 15 nm icosahedra. Gold nanoplates produced in the water extract were mainly triangular, ranging from 500 nm to 4 μm in size. The resulting nanoparticles and nanoplates can be potentially used in the study of their unique physical properties and for the mechanisms of formation using alfalfa biomass extracts.     

Fabrication and characterization of Bi2Te3 nanoplates via a simple solvothermal process

Bi₂Te₃ nanoplates have been successfully obtained by a novel solvothermal method in the presence of hexadecyltrimethylammonium bromide (CTAB). Various techniques such as X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), selected area electron diffraction (SAED), and Fourier transform infrared spectrometry (FT-IR) have been used to characterize the obtained products. The results show that the as-synthesized samples are rhombohedral-structured Bi₂Te₃ single-crystal nanoplates about 70–200 nm in diagonal and 30 nm in thickness, and the growth direction is perpendicular to c-axis. The existence of CTAB is vital to the formation of the plate-like morphology. In addition, the reaction solvents also have important influence on the shape-control of final products.     

Understanding the role of hexadecyltrimethylammonium bromide in the preparation of selenium nanoparticles: a spectroscopic approach

In this work, we report the size tunable synthesis of selenium (Se) nanoparticles with an average particle size ~16 nm by using hydrazine hydrate as the reducing agent. The solution of selenium dioxide was taken as the precursor and hexadecyltrimethylammonium bromide (CTAB) a cationic surfactant, which helps in providing sufficient stabilization to the Se nanoparticles. The synthesized Se nanoparticles were characterized by the UV–vis, X-ray diffraction (XRD), and transmission electron microscopic techniques, which demonstrated high stability of Se nanoparticles in aqueous media. The particle sizes estimated from the band gap values using effective mass approximation (EMA) agreed fairly well with those calculated from the XRD measurements. The concentration effects of Se and CTAB on the particle size have also been examined. The capping ability of the CTAB has been quantitatively evaluated from FTIR studies.     

Capping effect of CTAB on positively charged Ag nanoparticles

A facial synthesis process of silver nanoparticles (NPs) capped by cetyltrimethylammonium bromide (CTAB) is reported with exploration for the capping effect of CTAB on particles’ stability and surface properties in aqueous medium. Multidisciplinary approaches including electrophoresis, UV-visible absorption spectroscopy, Fourier-transformed infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), thermal gravimetric analysis (TGA) and small angle X-ray scattering (SAXS) are conducted to systematically investigate surface charge and the adsorbed CTAB layer structure on Ag clusters. Obtained results indicate that CTAB molecules bind strongly to silver surface via their headgroups and form a bilayer shell. Detailed analysis of SAXS and NMR data and discussion on the interaction between CTAB molecules and NPs’ surface, provide a clearer model of capped molecules on Ag clusters.     

Controlling SERS intensity by tuning the size and height of a silver nanoparticle array

It is demonstrated that the surface-enhanced Raman scattering (SERS) intensity of R6G molecules adsorbed on a Ag nanoparticle array can be controlled by tuning the size and height of the nanoparticles. A firm Ag nanoparticle array was fabricated on glass substrate by using nanosphere lithography (NSL) combined with reactive ion etching (RIE). Different sizes of Ag nanoparticles were fabricated with seed polystyrene nanospheres ranging from 430 nm to 820 nm in diameter. By depositing different thicknesses of Ag film and lifting off nanospheres from the surface of the substrate, the height of the Ag nanoparticles can be tuned. It is observed that the SERS enhancement factor will increase when the size of the Ag nanoparticles decreases and the deposition thickness of the Ag film increases. An enhancement factor as high as 2×10⁶ can be achieved when the size of the polystyrene nanospheres is 430 nm in diameter and the height of the Ag nanoparticles is 96 nm. By using a confocal Raman mapping technique, we also demonstrate that the intensity of Raman scattering is enhanced due to the local surface plasmon resonance (LSPR) occurring in the Ag nanoparticle array.