Seedless synthesis of gold nanorods by using hydrogen peroxide as a weak reducing agent

Abstract

A new seedless wet chemistry synthesis of gold nanorods by using hydrogen peroxide as the weak reducing agent is reported. A reduced concentration of hexadecyltrimethylammonium bromide is used in our experiment, and the synthesized gold nanorods exhibit tunable longitudinal surface plasmon resonance peaks ranging from 725 to 945?nm. The influence on gold nanorods growth by adjusting the amounts of sodium hydroxide, silver nitrate, sodium borohydride, and hexadecyltrimethylammonium bromide were investigated by the visible-near infrared spectroscopy. Under the proper experimental parameters, the longitudinal surface plasmon resonance peaks can be tuned by varying the hydrogen peroxide amounts. Furthermore, it can be seen that the redshift of the longitudinal absorption peak of the prepared gold nanorods with increasing hydrogen peroxide amount is consistent with the increase tendency of the length-to-width aspect ratio obtained from the transmission electron microscopy images. The method provides a facile pathway to prepare gold nanorods with tunable longitudinal surface plasmon resonance peaks, which have potential applications in biomedicine and nanophotonics.     

Surface plasmon tunneling through a touching gold nanocylinder array on a thin gold film

The optical property of a structure composed of a touching gold nanocylinder array on a thin gold film is investigated using finite-difference time-domain (FDTD) method. It is discovered that the transmission behavior can be tuned by tuning the geometry of the structure. As the film thickness increases, the transmission mode associated with the localized surface plasmon resonance blue shifts accompanied with a decrease of magnitude and full width at half maximum, and a second transmission appear due to the interaction of the plasmons on the cylinder with their images induced on the film. The localized waveguide resonance diminishes but the second resonance peak is intensified and broadened noticeably with the separation of the cylinder array and film increase. The cylinder radius size influences the localized surface plasmon resonance mode obviously. These results may be helpful for the design of a novel optical device.     

The effect of the Kerr nonlinearity on the transmission through the nanoslit gold film

This paper has made a theoretical study of enhanced transmission through a gold grating with arrays of subwavelength slits filled with nonlinear Kerr medium. The results of the research are based on rigorous finite-difference time domain calculations. The resonance transmission peaks in the investigated wavelength range are produced as a result of the surface plasmon resonance collaborated with the localized waveguide resonance. The paper also gives a detailed analysis of the influence exerted by various fa...     

Enhanced optical transmission through double-layer gold slit arrays

We investigate the relationship between the transmission and the layer distance of double-layer gold slit arrays by using the finite-difference time-domain method.The results show that the transmission properties can be influenced strongly by layer distance.We attribute the two types of resonant modes to surface plasmon resonance and the localised waveguide resonance.We find that the localised waveguide transmission peak redshifts and becomes broader with increasing layer distance D.We also describe and explain the splitting,shift,and degeneration of the surface plasmon resonant transmission peak theoretically.In addition,to clarify the physical mechanism of the transmission behaviours,we analyse the distributions of electric field and total energy for the three transmission peaks with distance D=45 nm for the double-layer system.Light transporting behaviours are mostly concentrated in the region of the slits as well as the interspaces of the two layers,and for different resonant wavelengths the electric field and energy distributions are different.It is expected that the results obtained here will be helpful for designing subwavelength metallic grating devices.     

金纳米球壳表面等离激元共振波长调谐特性研究

理论研究了金纳米球壳的几何结构参数, 及物理参量对局 域表面等离激元共振波长调谐特性的影响. 结果表明, 随着壳层厚度的增大, 球壳消光共振峰先蓝移后红移, 高阶峰转向时对应的壳层厚度比低阶峰大, 且该厚度与球壳内径的比值随内径尺寸的增大而减小, 随内核材料或外界环境介电常数的增大而增大, 散射共振峰也有类似的移动规律. 利用电子杂化效应和相位延迟效应对该现象进行了理论解释.     

金纳米薄膜的荧光光谱特性

采用电化学方法制备了胶体盒纳米球状颗粒,并利用自组装方法在石英玻璃村底上镀制了金纳米薄膜。在室温下测得其紫外-可见吸收光谱和荧光发射光谱。在吸收光谱中观察到两个吸收峰,其中610nm、处的吸收峰来源于凝聚金纳米颗粒纵向的表面等离子体共振。在荧光发射光谱中也观察到与纵向表面等离子体共振有关的长波段的发射峰。增加激励光强度或增加薄膜中金粒子散密度都将导致新荧光发射峰的产生．这表明金纳米薄膜中存在循环多重散射,并由此引发了荧光发射峰数目和强度的变化。     

金纳米球壳对的局域表面等离激元共振特性分析

应用有限元方法, 研究金纳米球壳对的几何结构参数及物理参量对其表面等离激元共振的散射及消光光谱的影响, 并根据等离激元杂化理论进行了理论分析. 结果表明, 随着金壳厚度的增加, 金纳米球壳对的散射及消光共振峰先发生蓝移而后红移, 而随着金纳米球壳间隙的减小, 或者随着金纳米球壳的内核尺寸或内核介质折射率的增大, 散射及消光共振峰均发生红移; 随着金壳厚度或内核尺寸减小, 或者随着内核介质折射率增大, 金纳米球壳对的散射与消光共振强度减弱, 而随着金壳间隙的减小, 金纳米球壳对的散射共振强度先增强后减弱, 而消光共振强度逐渐增强, 数值模拟与理论分析一致.     

Structural and photoluminescence properties of silicon nanocrystals embedded in SiC matrix prepared by magnetron sputtering

Si nanocrystals (NCs) embedded in an SiC matrix were prepared by the deposition of Si-rich Si_1?xC_x/SiC nanomultilayer films using magnetron sputtering, subsequently followed by thermal annealing in the range of 800～1200 °C. As the annealing temperature increases to 1000 °C, Si NCs begin to form and SiC NCs also start to emerge at the annealing temperature of 1200 °C. With the increase of annealing temperature, two photoluminescence (PL) peaks have an obvious redshift. The intensity of the low-energy PL peak around 669～742 nm gradually lowers, however the intensity of high-energy PL peak around 601～632 nm enhances. The low-energy PL peak might attribute to dangling bonds in amorphous Si (a-Si) sublayers, and the redshift of this peak might be related to the passivation of Si dangling bonds. Whereas the origin of the high-energy PL peak may be the emergence of Si NCs, the redshift of this peak correlates with the change in the size of Si NCs.     

Enhanced optical transmission of non-coaxial double-layer gold nano-slit with slanted sidewall arrays

We present the numerical investigation of the optical transmission through the non-coaxial double-layer gold nano-slit with slanted sidewall arrays by using the finite-difference time-domain (FDTD) method. It is found that there mainly exist three resonant peaks in the transmission spectra and the transmission behaviors are strongly dependent on the lateral displacement, the slit widths, the layer separation and the thickness of the film. Based on the field distribution, we show that the two short wavelength transmission peaks are characterized as the surface plasmon resonance, while the long wavelength transmission peak is characterized as the localized waveguide resonance.     

Investigation on the transmission of subwavelength metallic cavity arrays

Numerical investigation of the optical transmission through the one-dimensional subwavelength metallic cavity arrays (SMCA) is presented. Based on the finite-difference time-domain technique, we discuss the influence of the structural parameters on the transmission spectrum. The transmission peaks are attributed to the Fabry-Perot resonance; and the transmission dips are attributed to the surface plasmon resonance. For the SMCA with two cavities in one unit, the redshift of the transmission peak with increasing the distance between the two cavities originates from the depression of the coupling strength. These results obtained here will be helpful to design the plasmonic frequency-selecting device.     

透射共振对二次谐波产生的增强

为了提高二次谐波产生转换效率,本文提出将一维周期光学超晶格两端贴上未被极化的厚度可以改变的非线性介质层,通过调整附加介质层的厚度来调制基频波的场,从而观察二次谐波产生转换效率的变化情况.结果表明:基频渡场可以很大程度地调制二次谐波产生;随着能量的增加,二次谐波产生转换效率增加,随着能量的减小,二次谐波产生转换效率减小;...     

Investigation of the surface properties of gold nanowire arrays

Gold nanowire arrays with diameters ranging from 45 to 200 nm were obtained via electrochemical deposition within the ion-track templates. The morphology of gold nanowires was imaged by scanning electron microscopy (SEM). The surface properties were investigated by surface plasmon resonance (SPR) and X-ray photoelectron spectroscopy (XPS). The SPR peaks were observed as the gold nanowire arrays embedded in the templates and their intensity decreased after the sample exposed to the air for a certain time due to the formation of chemisorbed oxygen on nanowire surface. The positive binding energy shifts in Au core level was found when the gold nanowire arrays embodied in template and the initial- and finial-state effects were introduced to explain this phenomenon.     

Linear and nonlinear optical properties of strained GaN/AlN quantum dots: Effects of impurities,radii of QDs,and the incident optical intensity

The linear and nonlinear optical properties of cylinder GaN/AlN quantum dots with strain effects and impurity are investigated by taking into account the effects of the deformation potential and piezoelectric potential on the conduction band edge. The results are presented as a function of photon energies and QD radii. The optical absorption spectrum and refractive index changes have a blueshift in the presence of the impurity. With increasing distance of the impurity’s position along the growth direction, the peak values of the refractive index changes decrease and shift to higher photon energy. When the sizes of the QDs increase, redshift effects are observed and the relative amplitudes diminish. It can be found that the nonlinear effect becomes obvious with increase of the incident optical intensity. Then there is a “hole-burning” in the absorption coefficient spectra and two new peaks will appear in the total refractive index change spectrum when the optical intensity becomes larger enough. Finally it can be concluded that the intensity of the incident light and the position of the impurity play an important role in the linear and nonlinear optical properties.     

双稳态结构中的1/2次谐波共振及其对隔振特性的影响

以典型的双稳态系统——屈曲梁结构为例,基于等效模型,结合解析、数值和实验手段,研究了双稳态结构中的1/2次谐波共振特性、演化过程、参数调节规律及其对隔振特性的影响.研究发现,当非线性刚度系数或激励幅值增加到一定程度时,系统会在一定带宽下产生显著的1/2次谐波共振;随着激励幅值增加,阻尼系统的1/2次谐波遵循“产生-增强-衰退-消失”的过程,该过程对峰值频率和峰值传递率有重要影响;适当提高非线性强度能有效改善双稳态结构隔振特性.针对双稳态屈曲梁结构开展的实验验证了1/2次谐波特性和隔振特性变化规律.     

Transmission and reflection spectra of a photonic crystal with a Raman defects

Features of Raman gain of probe radiation in three-level atoms placed in a defect of a one-dimensional photonic crystal in the presence of laser radiation (pump) at an adjacent high-frequency transition have been theoretically investigated. It has been shown that there is a pump intensity range where narrow peaks (resonances) simultaneously appear in the transmission and reflection spectra of the probe field. Beyond this region, the peak in the transmission spectrum is transformed to a narrow dip. The spectral position of these peaks is determined by the Raman resonance and the transmittance and reflectance can be larger than unity at pump intensities from several microwatts per square centimeter to several tens of milliwatts per square centimeter. The nature of narrow peaks is due to a sharp dispersion of a nonlinear refractive index near the Raman resonance; this dispersion is responsible for a strong decrease in the group velocity of probe radiation. The proposed scheme makes it possible to obtain controlled ultranarrow resonances in the transmission and reflection spectra of the photonic crystal.     

双层金属纳米光栅的TE偏振光异常透射特性

根据在亚波长金属光栅表面添加电介质会引起TE偏振光的透射异常性, 应用严格耦合波理论和时域有限差分方法, 研究了双层金属纳米光栅在TE偏振光入射时产生的异常透射现象. 利用等效折射率方法建立了双层金属光栅的等效模型, 得到了TE偏振光透射率与聚合物的折射率、厚度以及金属层厚度的变化关系. 确认了结构中聚合物是透射异常出现的必要条件, TE偏振光以波导电磁模式在其中传播, 并认为类Fabry-Perot腔谐振是透射峰值产生的主要原因.     

Transmission of light through coaxial and non-coaxial double-layer gold slit arrays

We investigate numerically the transmittance of light through gold double-layer structures with periodic coaxial and non-coaxial slits. We attribute the enhanced optical transmission to the surface plasmon resonance collaborating with the localized waveguide resonance. The transmission spectra and the surface electric fields are used to characterize the resonances of both types. For the coaxial system, with the increase of the slit width of the second layer, the resonance peak values of both types increase sharply at first until the two layers have the same slit width and then decrease dramatically; additionally, the center of the localized waveguide resonance peak shifts to shorter wavelength noticeably, but the surface plasmon peak center moves negligibly. As regards the non-coaxial structure, it shows a similar behavior of the localized waveguide resonance peak to that of the coaxial one; however, the surface plasmon resonance peak behaves in a different way. These results may be associated with the surface plasmon coupling modes and the Fabry–Perot cavity modes in the double-layer structure.     

THEORETICAL DEPENDENCE OF LONG WAVELENGTH PHOTOEMISSION UPON THE SIZE OF Ag NANOPARTICLES EMBEDDED IN BaO SEMICONDUCTOR THIN FILM

The dependence of long wavelength photoemission upon the size of Ag nanoparticles embedded in a BaO semiconductor is predicted and discussed theoretically. The calculated results show that the increase in the diameter of the Ag nanoparticle, in the range from 1.5 to 37.0nm, leads to the emergence of a roughly Gaussian form of the photoemission spectra and the peaks become markedly narrower. The results also show that the increase in the diameter of the Ag nanoparticle leads to the decrease of the long wavelength threshold. The incident light wavelength corresponding to the peak value of the photoemission gets bigger with the increase of the size of Ag nanoparticles, thus showing a redshift.     

两端对称负折射率缺陷复合光子晶体:多通道滤波和光开关

采用传输矩阵法对两端对称负折射率缺陷复合光子晶体结构[D(AB)mD]N的透射特性进行了研究.结果表明:当N=2时,该结构透射谱的禁带出现两个完全共振透射峰,当N增加时,每个共振透射峰又分裂为N-1条；当复合光子晶体的层数m逐渐增加时,透射峰的品质因子逐渐提高,且分裂的共振透射峰距离逐渐减少；既为该结构实现高品质的多通...     

Photoexcited Blueshift and Redshift Switchable Metamaterial Absorber at Terahertz Frequencies

We propose a design and numerical study of an optically blueshift and redshift switchable metamaterial(MM)absorber in the terahertz regime. The MM absorber comprises a periodic array of metallic split-ring resonators(SRRs) with semiconductor silicon embedded in the gaps of MM resonators. The absorptive frequencies of the MM can be shifted by applying an external pump power. The simulation results show that, for photoconductivity of silicon ranging between 1 S/m and 4000 S/m, the resonance peak of the absorption spectra shifts to higher frequencies, from 0.67 THz to 1.63 THz, with a resonance tuning range of 59%. As the conductivity of silicon increases, the resonance frequencies of the MM absorber are continuously tuned from 1.60 THz to 1.16 THz, a redshift tuning range of 28%. As the conductivity increases above 30000 S/m, the resonance frequencies tend to be stable while the absorption peak has a merely tiny variation. The optical-tuned absorber has potential applications as a terahertz modulator or switch.