具有双共振吸收峰的Au纳米粒子制备及其拉曼表征

表面增强拉曼散射(SERS)很大程度的弥补了拉曼散射强度弱的缺点,迅速成为科研工作者们的研究热点,在食品安全、环境污染、毒品以及爆炸物检测等领域应用广泛。纳米技术的发展使得目前对于SERS的研究主要集中于金属纳米颗粒基底的制备,金属纳米粒子的种类、尺寸及形貌对SERS增强和吸收峰峰位均有影响,要获得好的增强效果,需要对金属纳米结构进行工艺优化。特别是,需要结合金属纳米粒子的结构和激励光波长,以期获得更好的增强效果。为了研究SERS增强和吸收峰之间的关系,开展了具有双共振吸收峰的金属纳米粒子的研究。首先利用FDTD Solutions仿真建模,主要针对金纳米颗粒直径、金纳米棒长径比及分布状态对共振吸收峰进行仿真,得到金纳米球理论直径在50 nm左右,金纳米棒理论长径比在3.5~4.5左右时,吸收峰分别分布在532及785 nm附近,符合多波段激励光拉曼增强条件;对于激励光偏振方向,其沿金纳米棒长轴方向偏振时吸收峰位于785 nm附近,沿金纳米球短轴方向偏振时吸收峰位于532 nm附近。然后采用种子生长法,制备了可用于多种波长激励光的双吸收峰表面增强拉曼散射基底。通过改变硝酸银用量(5,10,20,30和40 μL)、盐酸用量(0.1和0.2 mL)以及其生长时间(15,17,21和23 h)等多种工艺参数来控制金纳米棒含量,得到了同时含有金纳米球及金纳米棒的双吸收共振峰金纳米粒子。最后用该样品作为基底,罗丹明6G(R6G)作为探针分子,分别测试其在532,633和785 nm激励光入射时的SERS表征,对分析物R6G最低检测浓度均达到了10-7 mol·L-1,增强因子达到了~105,满足了多波段SERS检测的需要。     

银胶体系中皮考酸的原位变温表面增强拉曼散射研究

研究了温度对皮考酸(2-吡啶羧酸)分子在银胶体系中表面增强拉曼散射(SERS)谱的影响。变温范围在22℃～80℃时,皮考酸吸附在银纳米颗粒表面的SERS谱是可逆的,说明银胶体系在此温度范围内是一种稳定的SERS活性基底。银胶与皮考酸的混合液在持续加热的过程中,SERS谱的整体强度增强,但各谱峰的相对强度变化不大,分析认为在22℃～80℃范围内,皮考酸分子在银纳米颗粒表面的吸附方式基本不变,一直以羧基和N原子上的孤对电子共同作用侧立吸附在银纳米颗粒表面,文中还解释了SERS强度整体增强的原因。     

电解法制备纳米溴化银溶胶及其SERS活性研究

将一定量的十六烷基三甲基溴化铵溶于500 mL去离子水中作为电解液,用直径为1.0 cm、长为10.0 cm银棒分别作为阴及阳电极,加上7 V直流电压,通电 3 h,用电解方法得到了乳白色的纳米溴化银溶胶。用吸收光谱、对该进行研究。其吸收峰为292.5 nm, 透射式电镜表明纳米溴化银粒径分布在一个较大的范围,既有大小不一的球形粒子,也有大小不一的椭球形粒子,部分粒子产生了凝聚。为测试该纳米溴化银溶胶是否具有表面增强拉曼散射(SERS)活性,选用了阳离子型分子甲基橙(Methyl orange)、中性分子苏丹红(Sudan red)及吡啶(Pyridine)作为测试分子,用二次去离子水配成适当浓度后,与纳米溴化银溶胶按1∶1的比例混合后,置入毛细管样品池中用Renishaw 2000测定,激发波长514.5 nm。结果发现电解法制备的纳米溴化银对这三种分子都具有较强的SERS活性,甲基橙中明显增强的峰是1 123,1 146,1 392,1 448,1 594 cm-1;苏丹红中明显增强的峰是1 141,1 179,1 433,1 590 cm-1;吡啶中明显增强的峰是1 003,1 034,1 121 cm-1。值得注意的是在该方法制备的纳米溴化银上,得到了在常规方法制备的黄银胶、灰银胶上得不到的甲基橙分子的SERS谱,对可能的原因进行了讨论。     

银纳米有序阵列SERS活性基底的制备及在膀胱肿瘤细胞检测中的应用

以多孔阳极氧化铝(porous anodic alumina,PAA)膜为模板,采用真空电子束蒸镀技术,分别在PAA多孔层以及阻挡层表面形成了银纳米孔和银纳米帽有序阵列表面增强拉曼散射(surface-enhancedRaman scattering,SERS)活性基底,并以膀胱肿瘤细胞作为分子探针,测试和分析了这两种SERS活性基底的表面增强拉曼光谱的特性。结果表明,两种SERS活性基底对膀胱肿瘤细胞的拉曼散射信号均有很好的增强作用。银纳米帽有序阵列SERS活性基底不仅具有较高的SERS增强和荧光猝灭效应,而且不存在与PAA膜中草酸根杂质相关的干扰峰,可获得膀胱肿瘤细胞拉曼散射光谱的更多细节信息。     

全息干版银膜的制备、表征及其SERS活性的研究

报道了一种新的制备SERS基底的方法。通过对全息干版进行曝光、显影和定影,获得了具有良好稳定性的固体银膜。用紫外-可见光谱测量其表面等离子体共振吸收,发现其吸收谱线在420 nm处存在银粒子的特征吸收峰,且吸收峰具有较窄的半峰宽,这表明采用该方法制备的银膜表面分布着大小均一的银粒子。用扫描电子显微镜对其表面粒子形貌进行表征,发现银粒子分布均匀且平均粒径为100 nm左右。同时以结晶紫为探针分子测量了该银膜的表面增强拉曼光谱,结果表明该银膜具有良好的表面增强拉曼散射活性。采用这种方法制备的银膜稳定性好且易于保存,在常温下空气中放置数月,仍能保持原有的表面增强拉曼散射活性。     

激光刻蚀银胶的制备及其SERS应用

激光刻蚀技术制备金属胶体是一种新兴的表面增强拉曼散射(SERS)活性衬底制备方法,本文利用激光刻蚀技术制备了'化学纯'银胶,并通过透射电镜、吸收光谱、表面增强拉曼散射光谱等手段对其进行研究,结果表明:银胶的等离子体共振吸收峰位于396nm;银粒子分布比较均匀,多数为球形颗粒,颗粒大小在20nm左右,并且有很好的分散性;吡啶的SERS谱分析显示此银胶具有很好的增强效果。     

动态多级周期纳米棒阵列及其SERS研究

具有"热点"结构的有序纳米图案由于其高灵敏度和高重复性可以作为表面增强拉曼散射(SERS)基底。基于多级周期阳极氧化铝模板独特的三维孔道,以聚合物复制其多级结构,得到具有一定长径比的纳米棒阵列,并蒸镀贵金属银获得SERS活性。通过精确调控多级周期纳米棒阵列周期内和周期间纳米棒的间距,使纳米棒在等离子体驱动过程中以周期为单位转变为"闭合"状态,从而实现动态响应过程并获得高效SERS活性位点。该动态响应基底有望进一步发展为智能等离激元器件。     

人血红细胞在纳米银膜上的表面增强拉曼光谱研究

将硝酸银和聚乙烯醇加入去离子水中混合后作为电解液,以紫外光激发,用银棒电解得到纳米银膜。用扫描电镜观测纳米银的形貌,发现银膜上的颗粒是紧靠在一起的。以该纳米银膜为基底,用便携式拉曼光谱仪对4个正常人和7个白血病人的血红细胞样品进行了表面增强拉曼散射(SERS)光谱的检测。实验中发现,该纳米银膜对人血红细胞的拉曼散射光谱具有较好的增强的效果和较好的重复性。比较正常人与白血病人血红细胞的SERS谱,存在明显的差别,7个白血病人血红细胞样品在1385 cm-1(吡咯四分之一环伸缩振动)处SERS峰消失,在1425 cm-1处的谱线(CαCm的对称伸缩振动)变宽和变强,对可能的原因进行了分析。     

银纳米阵列直径对SERS增强效果的影响

采用电化学沉积法分别在不同孔径的阳极氧化铝(AAO)模板上沉积一系列直径不同,排列规则的银纳米阵列。以对氨基苯甲酸(PABA)和三聚氰胺两种分子分别作为探针分子, 研究了银纳米阵列的直径大小对其表面增强拉曼散射(SERS)效果的影响。结果表明, 在波长为514.5 nm的激光激发下, 探针分子的SERS信号强度随银纳米阵列直径的改变而明显变化, 并在银纳米阵列直径约为53 nm时, SERS强度达到最大。利用电磁增强机制对此实验结果进行了分析和解释。     

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。     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.