不同Ag壳厚度Au@Ag纳米粒子的调控制备表征及表面增强拉曼光谱的效应

采用化学还原法制备了以Au为核、包覆Ag的双金属核壳Au@Ag纳米粒子,并成功地用于表面增强拉曼光谱(SERS)分析测试。通过改变制备液中Ag/Au的量比来调控Ag壳包覆厚度。采用透射电子显微镜(TEM)和紫外-可见光谱仪(UV-Vis)对Au@Ag纳米粒子的构貌进行表征。TEM显示明显存在核壳结构,且Ag壳层随Ag/Au的量比的增加而逐渐变厚;UV-Vis表明随着Ag/Au的量比的增加,Au@Ag纳米粒子出现了Au核与Ag壳吸收峰的2个等离子体共振峰,同时伴随着Au峰的蓝移和Ag峰的红移。以双甲脒为分析物,考察了不同Ag/Au的量比时的Au@Ag纳米粒子的SERS活性。结果表明,SERS活性随Ag/Au的量比的增加先增大后减小,在6∶5时其SERS增强效应最佳,此时Ag壳厚度约为6 nm。以对巯基苯胺(4-ATP)、结晶紫(CV)和双甲脒为分析测试对象,对比了Au@Ag、Ag、Au 3种基底的SERS活性。结果表明,所制备的Au@Ag纳米粒子的SERS活性要明显优于单纯的Au、Ag纳米粒子。     

Au/Ag合金溶胶与HCuCl4反应过程的紫外光谱研究

采用柠檬酸根为保护剂,通过水合肼还原的方法,在水相中合成了Au/Ag合金纳米粒子,UV-Vis光谱中只观察到一个位于单金属Ag和Au之间的等离子体共振峰,并且合金溶胶的最大吸收峰随着溶胶中Au的物质的量分数变化呈线性变化.通过紫外-可见吸收光谱研究了不同组分的溶胶与HCuCl4溶液的反应过程.结果显示,溶胶的紫外-可见吸收峰随着HCuCl4的加入量的改变而呈规律性变化,其中有一紫外吸收峰随着HCuCl4的加入而呈线性变化的区间,分析后认为这一过程为合金的去合金过程.     

Au-Ag合金纳米球壳的折射率传感特性分析与优化

基于Au纳米颗粒的稳定性、无毒性、生物相容性和Ag纳米颗粒优异的消光特性,Au-Ag合金纳米颗粒在生物传感中存在着潜在的应用价值。为了能找到传感性能更好的合金纳米颗粒,本文利用双层球Mie散射理论和介电函数尺寸修正模型定量研究了Au-Ag合金纳米球壳的尺寸参数对折射率灵敏度、半峰宽和品质因子的影响,获得了最佳品质因子和对应的优化尺寸。同时,本文研究了Au摩尔分数对最佳品质因子和优化尺寸的影响。结果发现,当Au摩尔分数x为0.5时,Au-Ag@SiO_2(Au-Ag@Vacuum)合金纳米球壳的最大品质因子为2.09(2.20),对应的内核半径和外壳厚度分别为22.3 nm(23.6 nm)和8.7 nm(6.9 nm)。当Au摩尔分数小于0.25时,Au-Ag合金纳米球壳的品质因子优于Au纳米球壳。随着Au摩尔分数的减小,品质因子增大,甚至是Au纳米球壳的2～3倍。此研究为Au-Ag合金纳米球壳在生物传感领域中的有效应用提供了理论指导。     

Ag-Au合金/SiO2复合薄膜的制备与表征

以AgNO3,HAuCl4和正硅酸乙酯为主要原料,利用溶胶-凝胶法和旋涂技术,通过热处理和紫外光辐射还原得到了不同nAg/nAu(1∶0,2∶1,1∶2,0∶1)的Ag-Au合金/SiO2复合薄膜.从扫描电子显微镜和X射线衍射谱的结果可以看出得到的薄膜均匀性好,复合薄膜中合金颗粒的尺寸为10 nm左右.利用紫外-可见分光光谱仪研究了复合薄膜的光吸收性能,结果表明,随着nAg/nAu的降低,吸收峰的位置也由最初的Ag纳米粒子的等离子共振吸收峰430 nm附近,逐渐红移到Au纳米粒子的等离子共振吸收峰605和880 nm附近.从光吸收谱可以看出,nAg∶nAu＝2∶1和1∶2的两个样品分别在515,730 nm附近和550,730 nm附近出现表面等离子共振吸收峰.这表明Au-Ag合金固溶体的形成.     

苯硫酚吸附在新型Ag-Au合金纳米粒子上的表面增强拉曼光谱研究

以柠檬酸钠同时还原制备的Ag-Au合金纳米粒子为种子,用盐酸羟胺进一步使其生长得到粒径为40～60 nm的新型Ag-Au合金纳米粒子,采用UV-Vis光谱和TEM对纳米种子和再生长后的纳米粒子分别进行表征。两种粒子的UV-Vis光谱均只观察到一个等离子体共振峰,其频率随金的摩尔分数(x_Au)增加而红移,且TEM图像表明这两种粒子的颜色均一,因此判断这两种粒子均为合金结构。以苯硫酚为探针分子,研究了该新型合金纳米粒子的表面增强拉曼光谱(SERS),结果表明吸附了苯硫酚的合金纳米粒子的紫外最大吸收峰红移,并在近红外区出现聚集体的吸收峰。在632.8 nm波长激发下,由于表面等离子体共振效应Au上的SERS信号最强,而合金纳米粒子上的SERS信号随x_Au增大而增强。     

Ag-AAO纳米有序阵列复合结构等离子共振吸收特性研究

研究了Ag-AAO纳米有序阵列复合结构的等离子共振吸收特性。结果显示,Ag表面等离子共振吸收峰位于λ=352-377nm范围内,且可通过控制Ag纳米粒子的长径比使其吸收特性发生改变。若长径比增加,吸收峰位蓝移,强度增大,峰形变锐;反之,若长径比减少,吸收峰位红移,强度减弱,峰形逐渐宽化;运用麦克斯韦-加尼特（M-G）理论模拟的计算结果与实验规律基本相符,并较好地阐释了Ag表面等离子共振吸收峰的频移与其纳米粒子长径比之间的一些依赖关系。     

Ag-Au二元纳米微粒吸收谱的计算

纳米微粒的光学性能与其表面等离子体共振关系密切.本文利用推广的Mie理论计算研究了Au-Ag体系单质、合金以及核壳结构纳米颗粒的消光、吸收和散射的性能(包括壳核结构Ag-Au微粒在紫外-可见光的吸收性能),计算结果与实验值相符合得很好.研究表明,随着粒径的增加,微粒表面等离子体共振偶极吸收峰出现红移,波峰位置与纳米微粒的尺寸具有线性关系.壳核结构中,粒径与核壳比决定了整个微粒的吸收性能.进一步研究表明,当Au壳层较薄时,可以获得具有可调光学性能的壳核纳米结构;而当Au壳层较厚时,其光学性能与同尺寸单质Au微粒一致.通过计算分析,本文还将Mie理论推广到具有空腔结构并且壳层厚度达到一定值的纳米微粒.另外,研究发现合金结构纳米微粒的吸收峰位置与合金成分有着线性关系.本研究表明,人们可以通过控制纳米微粒的尺寸、形貌和结构,调节其表面等离子体共振峰位,这大大拓展了纳米微粒的应用范围.     

Ag-Au合金/SiO$lt;sub$gt;2$lt;/sub$gt;复合薄膜的制备与表征

以AgNO₃,HAuCl₄和正硅酸乙酯为主要原料,利用溶胶-凝胶法和旋涂技术,通过热处理和紫外光辐射还原得到了不同n_Ag/n_Au（1∶0,2∶1,1∶2,0∶1）的Ag-Au合金/SiO₂复合薄膜.从扫描电子显微镜和X射线衍射谱的结果可以看出得到的薄膜均匀性好,复合薄膜中合金颗粒的尺寸为10 nm左右.利用紫外-可见分光光谱仪研究了复合薄膜的光吸收性能,结果表明,随着n_Ag/n_Au的降低,吸收峰的位置也由最初的Ag纳米粒子的等离子共振吸收峰430 nm附近,逐渐红移到Au纳米粒子的等离子共振吸收峰605和880 nm附近.从光吸收谱可以看出,n_Ag∶n_Au＝2∶1和1∶2的两个样品分别在515,730 nm附近和550,730 nm附近出现表面等离子共振吸收峰.这表明Au-Ag合金固溶体的形成. 关键词： 2')" href="#">Ag-Au合金/SiO₂ 紫外辐射 光吸收性能     

局域表面等离激元对InGaN/GaN多量子阱发光效率的影响

Ag纳米粒子的形貌对InGaN/Ga N多量子阱(MQWs)的光致发光(PL)效率有着显著影响。本文采用离子束沉积(IBD)技术将Ag沉积在InGaN/Ga N MQWs上,然后通过快速热退火处理制备Ag纳米粒子。通过改变Ag的沉积时间获得了具有不同Ag纳米粒子形貌的样品。用原子力显微镜对各样品的Ag纳米粒子形貌和尺寸进行了表征,并且测试了吸收谱、室温和变温PL谱及时间分辨光致发光(TRPL)谱。结果表明:随着Ag沉积时间的延长,所得Ag纳米粒子粒径增大,粒子纵横比先增大后减小且吸收谱峰红移。由于不同形貌的Ag纳米粒子在入射光作用下产生的局域表面等离激元(LSPs)与MQWs中激子耦合强度不同,光发射能力也不同,与没有Ag纳米粒子的样品相比,沉积时间为15 s的样品室温PL积分强度被抑制6.74倍,沉积时间为25 s和35 s的样品室温PL积分强度分别增强1.55和1.72倍且峰位发生红移,沉积时间为45 s的样品室温PL积分强度基本没有变化。TRPL与变温PL的测试结果证明,室温PL积分强度的改变是由于LSPs与MQWs中的激子耦合作用引起的。纵横比大且吸收谱与MQWs的PL谱交叠大的Ag纳米粒子能够更好地增强InGaN/Ga N MQWs的发光。     

Au/SiO2纳米复合薄膜的微结构及光吸收特性研究

用多靶磁控溅射技术制备了Au/SiO2纳米多层薄膜.利用透射电子显微镜以及吸收光谱对Au/SiO2复合薄膜的微观结构、表面形貌及光学性能进行了表征和测试.研究结果表明:单层Au/SiO2薄膜中Au沉积时间小于10s时,分散在SiO2中的Au颗粒随Au的沉积时间的延长而增大;当沉积时间超过10s后,Au颗粒的尺寸几乎不随沉积时间变化,但Au颗粒的形状由网络状结构变为薄膜状结构.[Au(t1)SiO2(600)]×5多层薄膜在540-560nm波长附近有明显的表面等离子共振吸收峰,且吸收峰的强度随Au的沉积时间增加而增强.基于修正后的Maxwell-Garnett (M-G)有效媒质理论,讨论了金属颗粒的形状对等离子共振吸收峰的峰位和强度的影响.模拟的吸收光谱与实验吸收光谱形状、趋势及吸收峰位相符合.     

金银合金纳米粒子的合成及其SERS研究

采用柠檬酸三钠作为保护剂,通过水合肼还原的方法合成了不同组成的Au-Ag合金纳米粒子。UV-Vis光谱中只观察到一个位于单金属银和金之间的等离子体共振峰, 表明金银已形成合金。TEM显示合成的粒子非核壳结构,金银分布均匀, 合金粒径在25 nm左右。用吡啶为探针分子研究了合金的表面增强拉曼光谱(SERS), 结果表明吡啶在合金表面表现出了不同于纯金和纯银的行为。     

Surface characteristics of Ag‐doped Au nanoparticles probed by Raman scattering spectroscopy

We have examined the surface characteristics of Ag‐doped Au nanoparticles (below 5 mol% of Ag) by means of the surface‐enhanced Raman scattering (SERS) of 2,6‐dimethylphenylisocyanide (2,6‐DMPI) and 4‐nitrobenzenethiol (4‐NBT). When Ag was added to Au to form ∼35‐nm‐sized alloy nanoparticles, the surface plasmon resonance band was blue‐shifted linearly from 523 to 517 nm in proportion to the content of Ag up to 5%. In the SERS spectra of 2,6‐DMPI, the N‐C stretching peak also shifted almost linearly from 2184 to 2174 cm⁻¹ when the Ag content was 5 mol% or less; the peak then remained the same as that of the pure Ag film. The potential variation of the SERS spectrum of 2,6‐DMPI in an electrochemical environment, as well as the effect of organic vapor, also showed a similar tendency. From the SERS of 4‐NBT, we confirmed the occurrence of a surface‐induced photoreaction converting 4‐NBT to 4‐aminobenzenethiol, when Ag was added to Au to form alloy nanoparticles. The photoreaction induction ability also increased linearly with the Ag content, reaching a plateau level at 5 mol% of Ag. All these observations suggest that the surface content of Ag should increase almost linearly as a function of the overall mole fraction of Ag and, once the Au/Ag nanoparticles reach 5 mol% of Ag, their surfaces are fully covered with Ag, showing the same surface characteristics of pure Ag nanoparticles. Copyright © 2011 John Wiley & Sons, Ltd.     

Accuracy of the Tougaard method for quantitative surface analysis. Comparison of the Universal and REELS inelastic cross sections

Three tests have been performed to investigate whether cross sections determined experimentally from reflection electron energy loss spectroscopy (REELS) are more accurate than the Universal cross section for background correction of electron spectra. In the first test, the shape of background corrected spectra from a thin layer and from an infinitely thick layer of the same element were compared for the Ag3d, Au4d, and Yb4d peaks. It was found that the Universal cross section is more accurate than the experimentally determined REELS cross sections to determine consistently the peak shape of background corrected spectra. In the second test, the intensity ratio of the two components in the Au4d, Cu2p, Zn2p, and Yb4d doublets were compared to theoretical photoionization cross sections. For both the Universal and the REELS inelastic cross sections, the obtained intensity ratios agree well with theory. In the third test, we compare with theory the peak intensity ratios to Au4d of major peaks from Si, Cu, Ag, Yb, and Au obtained by using the Universal and the REELS cross sections for background correction. For the metals, the two cross sections give peak intensity ratios that are equally close to theory to within the expected uncertainties in the theoretical peak intensity ratios. However, for Ag with application of the Universal cross section the deviation from theory is slightly larger. For Si the REELS cross section is clearly most accurate.     

Optical characterization of the polymer embedded alloyed bimetallic nanoparticles

A theoretical approach for the calculation of the bimetallic nanoparticles absorption spectra has been developed as an extension of the Mie theory in which nanoparticle dielectric function is found by the weighted linear combination of the dielectric functions for particles made of the corresponding pure metals. In the frame work of the theoretical model an expression for the resonance light absorption frequency were derived taking into account the interband transitions in the dielectric functions. We propose a simple method for the on-line monitoring of the bimetallic nanoparticles composition based on the measurement of the absorption peak position. Elaborated theoretical approach was used to investigate the polymer embedded Ag/Au nanoparticles which were prepared by reducing gold and silver salts (HAuCl4 and AgNO3, respectively) by ethylene glycol in presence of poly(vinyl pyrrolidone) (PVP) at room temperature. Calculated absorption spectra for the Ag/Au nanoscopic systems showed good agreement with the experimental data. Temporal evolution of the Ag/Au nanoparticles has also been investigated by this approach.     

Ag离子注入非晶SiO2的光学吸收、拉曼谱和透射电镜研究

能量为200keV的Ag离子，以1×10¹⁶，5×10¹⁶，1×10¹⁷ cm^-2的剂量分别注入到非晶SiO₂玻璃，光学吸收谱显示：注入剂量为1×10¹⁶ cm^-2的样品的光吸收谱为洛伦兹曲线，与Mie理论模拟的曲线形状一致；注入剂量较大的5×10¹⁶，1×10¹⁷ cm^-2的谱线共振吸收增强，峰位红移并出现伴峰. 透射电镜观察分析表明，注入剂量不同的样品中形成的纳米颗粒的大小、形状、分布都不同，注入剂量较大的还会产生明显的表面溅射效应，这些因素都会影响共振吸收的峰形、峰位和峰强. 当注入剂量达到1×10¹⁷ cm^-2时，Ag纳米颗粒内部可能还形成了杂质团簇. 关键词： 离子注入 纳米颗粒 共振吸收 红移     

Synthesis of NiAu alloy and core–shell nanoparticles in water-in-oil microemulsions

NiAu alloy nanoparticles with various Ni/Au molar ratios were synthesized by the hydrazine reduction of nickel chloride and hydrogen tetrachloroaurate in the microemulsion system. They had a face-centered cubic structure and a mean diameter of 6–13 nm, decreasing with increasing Au content. As Au nanoparticles did, they showed a characteristic absorption peak at about 520 nm but the intensity decreased with increasing Ni content. Also, they were nearly superparamagnetic, although the magnetization decreased significantly with increasing Au content. Under an external magnetic field, they could be self-organized into the parallel lines. In addition, the core–shell nanoparticles, Ni₃Au₁@Au, were prepared by the Au coating on the surface of Ni₃Au₁ alloy nanoparticles. By increasing the hydrogen tetrachloroaurate concentration for Au coating, the thickness of Au shells could be raised and led to an enhanced and red-shifted surface plasmon absorption.     

Broadband tunable plasmonic substrate using self-assembled gold–silver alloy nanoparticles

In the present work, a facile approach of Au–Ag alloy NPs fabrication is proposed for plasmonic inclusion applicative studies. These hybrid NPs were prepared by the sequential deposition of Ag, Au layers on a glass substrate via RF-sputtering followed by high-temperature annealing. Compositional and size controllability of the NPs was attained by changing the ratio of nominal thicknesses of the respective Au, and Ag layers during the deposition. LSPR red (blue) peak shift occurs with increasing layer thickness Au (Ag) signifying the peak sensitivity. The influence of geometrical, compositional, and background media for achieving LSPR-sensitivity is examined and validated by FDTD simulation studies. With the agreeable peak shift tendencies, the proposed study of broadband tunable LSPR-sensitivity is expected to provide a framework for a wide range of plasmonic applications.