用并行扫描方法开展的表面等离激元电子能谱成像

本文报道了高定向热解石墨上银纳米结构表面等离激元的电子能谱成像研究. 本文利用现有扫描探针电子能谱仪的角度色散特性,发展了一种多道测量模式. 通过沿一个方向扫描,可以并行获得银纳米结构表面等离激元电子能谱的二维分布. 实验确定的能谱成像空间分辨为80 nm左右.     

激光诱导Ni等离子体特性的研究

以Nd·YAG激光器的二倍频输出作为激发源,获得了激光诱导Ni等离子体的发射光谱,基于发射光谱,对等离子体电子激发温度和电子密度进行了测量,其典型值分别为3 714 K,4.67×1016 cm-3。测量了等离子体电子激发温度和电子密度的空间分布,发现沿垂直于激光传播方向的径向,随到中心点距离的增加,等离子体辐射的强度减小,但线型和线宽不变,表明等离子体电子激发温度和电子密度沿径向均匀分布。沿激光传播方向,随到样品表面距离的增加,等离子体辐射强度、电子激发温度和电子密度先增加后降低,在距样品表面1.5 mm处,达到最大值。采用激光诱导击穿光谱技术进行相关探测时,收集距离样品表面1.5 mm处的发射谱,有利于提高探测灵敏度。     

介观尺寸原子链中的等离激元：紧束缚模型

本文运用紧束缚模型对介观尺寸原子链的等离激发进行了系统的研究, 通过量子响 应理论和相无规近似得到了等离激元的本征频率方程, 通过该方程计算了系统中等离子体的激发能量, 并分别对体系的本征振荡以及外电场作用在原子链上发生共振的情况进行了研究. 结果表明, 体系在外场作用下发生共振时, 偶极矩的峰值与等离子体的激发态相对应, 说明外场此时激发了等离激元; 体系处在共振情况下, 电荷振荡的幅度远远大于非共振的情况, 相对来说体系的电荷虚部的共振更为明显. 对于体系的本征等离振荡频率, 同等长度时等离子体的激发能量总是大于同级的单电子激发能量; 等离激元的能谱与原子链的长度和电子密度以及系统的库仑关联强度都有很大关系; 在原子链长度保持不变的情况下, 等离子体的激发能量随电子数目的变化以半满为中心呈对称关系. 关键词： 纳米结构 一维原子链 等离激元     

偏压在隧道效应中的作用

从隧道扫描势垒模型出发。用量子力学导出隧道电流与针尖间的偏压、间距及它们的逸出功之间的关系,并从能带模型的角度导出样品与针尖的间距不变时,隧道电流与偏压成正比关系．指出偏压的作用主要是提高针尖上电子的能量,使针尖上的电子比样品上的电子更容易穿过势垒,从而形成隧道电流．     

典型金属纳米结构的电子能量损失谱研究

利用格林函数推导出金属纳米结构电子能量损失谱的计算公式,基于时域有限差分方法对几种典型的结构进行建模仿真,数值模拟运动电荷和结构的距离、液晶环境材料对电子能量损失谱的调节作用.仿真结果表明:当增加电子与纳米结构的距离时,电子能量损失谱谱峰降低;当添加液晶材料或各向同性衬底材料时,电子能量损失谱的峰值发生明显红移,但液晶的光轴倾角改变对峰值的调制作用有限.通过计算电子能量损失谱研究金属纳米结构表面等离子激元共振特性,为高度复杂的等离子体激元纳米结构的设计提供了理论基础.     

不同实验条件对激光诱导等离子体的影响机理研究

常温常压下,采用波长532 nm的Nd:YAG纳秒激光器激发诱导空气中的铝合金,由高分辨率的光谱仪和ICCD对等离子体发射光谱采集和实现光电转换。研究激光能量、ICCD门延迟和聚焦透镜到样品表面的距离(lens-to-sample distance,LTSD)对谱线信号强度和等离子体电子温度的影响,并分析了产生影响的物理机制。结果表明,固定ICCD门延迟和LTSD,随着激光能量的增大,谱线强度和电子温度均增大;计算结果表明,当激光能量从20 mJ增加到160 mJ时,原子谱线Al I 396.15 nm,Mg I 518.36 nm,离子谱线Mg II 279.54 nm谱线强度相较于20 mJ分别提高了12.83,6.45,10.56倍。固定激光能量和LTSD,ICCD门延迟在100~4000 ns范围内变化时,随着延迟的增加,谱线强度和等离子体电子温度均呈指数形式衰减。固定ICCD门延迟和激光能量,采用焦距为75 mm的聚焦透镜,研究了LTSD对等离子体参数的影响机理。结果表明,聚焦透镜到样品的距离对等离子体的谱线强度和电子温度有较大的影响。等离子体的特征谱线强度和等离子体的电子温度的变化规律基本一致,分别在聚焦透镜到样品表面的距离为73 mm和79 mm处取得峰值,并在73 mm处对应最大值。     

用扫描隧道显微镜测量局域功函数

用扫描隧道显微镜在Cu（111）-Au和Pt（111）-Ag表面上对局域功函数进行了测量．在扫描的同时通过测量隧道电流对针尖样品间距离变化的响应，可以在得到扫描隧道显微镜（STM）图的同时得到功函数图．用这种方法，成功地观察到Au，Ag覆盖层与Cu，Pt衬底间的功函数的差别．结果表明：Au覆盖层的功函数介于Cu（111）和Au（111）的功函数之间，这与其它方法的结果一致．在Pt（111）-Ag表面观察到了局域功函数随覆盖层厚度的变化．本工作表明：扫描隧道显微镜在研究功函数与表面结构的关系方面是十分有用的；用测量局域功函数的方法还可以区分表面不同种的物质 关键词：     

探针对表面等离子体共振的影响

采用时域有限差分方法(FDTD)对探针诱导表面等离子体共振耦合纳米光刻(PSPRN)技术中探针的引入对表面等离子体共振(SPR)产生的影响进行了模拟分析,以获得最佳的光刻实验条件。结果表明,高斯光束聚焦光斑越小,SPR场增强效应也越小。接触模式下,针尖曲率半径为10 nm的硅(Si),35 nm,100 nm的金(Au)探针,分别使SPR共振角变化了0,0.8°和1°。且对于Au探针,针尖曲率半径大的,针尖处的局域场增强效应要小。分析表明,采用针尖曲率半径为10 nm的Si或35 nm的Au探针,在合适的SPR膜层上通过调整光入射角度,很有可能实现50 nm的光刻记录点。     

纳腔等离激元对分子上和分子旁边的隧穿电子诱导发光的作用研究

本文使用含时量子主方程,从理论上计算了当分子或者等离激元分别被激发的情形下等离激元-分子耦合体系发光特性的时间和光谱演化,并在此基础上讨论了纳腔等离激元在扫描隧道显微镜（STM）诱导发光中发挥的不同作用.当STM针尖在分子上方,隧穿电子可以直接激发分子时,纳腔等离激元的主要作用是通过提高分子的辐射速率来增强其发光,此时耦合体系表现出具有分子特征的尖锐发光峰.另一方面,当STM针尖非常靠近分子边缘但没有载流子注入直接激发分子时,等离激元-分子之间的相干耦合会在这两个量子客体之间产生相消干涉,导致在分子激子能量附近出现法诺共振,使我们观察到具有法诺凹谷特征的等离激元发光光谱.     

纳腔等离激元对分子上和分子旁边的隧穿电子诱导发光的作用研究（英文）

本文使用含时量子主方程,从理论上计算了当分子或者等离激元分别被激发的情形下等离激元-分子耦合体系发光特性的时间和光谱演化,并在此基础上讨论了纳腔等离激元在扫描隧道显微镜(STM)诱导发光中发挥的不同作用.当STM针尖在分子上方,隧穿电子可以直接激发分子时,纳腔等离激元的主要作用是通过提高分子的辐射速率来增强其发光,此时耦合体系表现出具有分子特征的尖锐发光峰.另一方面,当STM针尖非常靠近分子边缘但没有载流子注入直接激发分子时,等离激元-分子之间的相干耦合会在这两个量子客体之间产生相消干涉,导致在分子激子能量附近出现法诺共振,使我们观察到具有法诺凹谷特征的等离激元发光光谱.     

SPEES针尖参数对样品表面电子出射影响的模拟研究

报道了对扫描探针电子能谱仪（SPEES）中俄歇电子出射的理论模拟研究。 通过对俄歇电子在针尖电场作用下运动轨迹的模拟以及综合考虑从针尖场发射电子到俄歇电子出射全过程中各种因素的影响, 系统研究了针尖形状、 针尖偏压和针尖 样品距离对俄歇电子出射效率的影响, 以及出射俄歇电子束流密度在针尖电场区边缘处的分布。 研究结果为提高SPEES的收集效率、 空间分辨以及能量分辨提供了重要的参考数据。 The simulation of the Auger electron emissions in scanning probe electron energy spectrometer (SPEES) is reported. By simulating the trajectory of Auger electrons, we systematically investigate the dependence of the emission efficiency of Auger electrons on the shape of tip, the biasing voltage, and the distance between the tip and sample surface, as well as the intensity distributions of Auger electrons at the edge of tip sample region. The results will be the significant reference for improving the sensitivity, spatial and energy resolutions of SPEEs.     

Absorption Range and Energy Shift of Surface Plasmon in Au Monomer and Dimer

The resonance behaviors of local surface plasmon resonance in Au monomer and dimer are characterized systemically by electron energy loss spectroscopy in a scanning transmission electron microscope.The measured absorption range is about 20 nm larger than the physical size of the Au nanoparticles and the resonance peak energy shows a red shift when the electron beam passes off the nanoparticles.The Au dimer displays similar behaviors.Numerical simulation also reproduces those experimental results.     

Formation of nanostructures by an intense femtosecond pulse laser irradiating Au film on sapphire substrate

We investigate the morphology change of Au film on sapphire substrate by irradiating with a 1 kHz femtosecond pulse laser. Under observation of a scanning electron microscope, a textured nanostructure was formed in the exposed area on Au film due to laser ablation and subsequent stress relaxation. This process was strongly determined by the laser intensity profile and the dynamics of molten liquid. With the increasing of laser pulses number, the Au film was broken down and then a few polarization-dependent nanoripples arranged in the same direction appeared on the sapphire surface, which may result from a spatial modulation of energy due to the interference between the incident light and the excited surface plasmon polaritons. In addition, we used an energy dispersive spectrometer to analyze the chemical composition of nanoripples on the surface and in the ablated crater, respectively. The changes of O and Al elements implied that a complicated chemical transformation participated in the nanoripples formation process. We believe that present results are very useful for the analysis of the interaction between femtosecond laser and solids, especially the film material.     

半壳结构金纳米膜的局域表面等离子体共振效应

采用纳米模版印刷术和化学自组装技术制备了半壳结构的金粒子膜.利用场发射扫描电子显微镜和光谱仪等测试手段对样品的结构和光学性质进行了分析.研究发现，该结构的金膜所具有独特的局域表面等离子体共振效应取决于样品的粒子大小、间距等微观结构，且其峰值吸收波长对其周围环境介质的介电常数变化十分敏感.实验结果表明，粒子排列均匀的亚单层膜结构是控制光学性质稳定的关键. 关键词： 局域表面等离子体共振 半壳结构 纳米模版印刷术     

Determination of the thickness and density of the ion bombardment induced altered layer in SiC by means of reflection electron energy loss study

The steady state surfaces of ion bombarded 3C-, 4H- and 6H-SiC samples were studied by means of reflected electron energy loss spectroscopy (REELS). The REELS exhibit a well-defined loss peak in the region of about 20 eV. The position of the maximum of the loss peak depends on the bombarding ion energy (decreasing with increasing ion energy), and on the primary electron beam energy (increasing with increasing primary energy). This behavior can be explained if we suppose that the plasmon energy in the altered layer (produced by ion bombardment) is different from that of the unaltered bulk. In this case the measured loss peak is the sum of two overlapping plasmon peaks. With modeling the system as a homogeneous altered layer and a homogeneous unaltered substrate the plasmon energy in the altered layer was derived to be 19.8 eV. The large change of the plasmon energy with respect to the bulk value of 23 eV is explained by a thin low density overlayer on the surface of the sample produced by the ion bombardment.     

有序金纳米颗粒阵列的制备及光吸收特性研究

采用纳米球刻蚀技术中漂移法在玻璃基片上制备较大 面积不同直径的聚苯乙烯小球掩模板, 采用磁控溅射技术在掩模板上沉积不同厚度的金薄膜, 去除聚苯乙烯小球后, 通过扫描电子显微镜观察到周期排列的三角状金纳米颗粒点阵. 通过紫外-可见分光光度计测试所制备样品的光吸收特性, 发现表面等离子体共振峰随粒径增大发生红移, 随金纳米颗粒高度增加发生蓝移. 基于Mie理论, 利用Matlab软件编程对不同粒径的金阵列光吸收特性进行理论模拟, 并与实验结果进行对比. 关键词： 纳米球刻蚀 金纳米颗粒阵列 表面等离子体共振     

Laser-assisted generation of gold nanoparticles and nanostructures in liquid and their plasmonic luminescence

Nanoparticles (NPs) and surface nanostructures (NS) are produced via laser ablation of a bulk gold target in liquid using second harmonics of 10 ps Nd:YAG laser (532 nm) with repetition rate of 50 kHz. The morphology and plasmon photoluminescence (PL) properties of obtained nanoscale objects are described. Transmission electron microscopy and field emission scanning electron microscopy are used for morphology characterization of NPs and NS, respectively. Plasmon PL of both gold NPs and NS is experimentally studied using the third harmonics of the Nd:YAG picosecond laser (355 nm) as a pump. The wavelength of intensity maximum of PL of Au NPs colloidal solution virtually coincides with the position of Au NPs plasmon absorption peak. Real-time excitation of both plasmon PL and Raman scattering of surrounding liquid by picosecond laser pulses in aqueous colloidal solution is also investigated. The efficient cross section of plasmon PL of Au NPs colloid is evaluated using Raman scattering of water as a comparative parameter. The results are in good agreement with values obtained in previous works. Plasmon PL from self-organized NS on the Au surface produced via laser ablation is observed for the first time. Its spectrum is compared to PL spectra of both aqueous colloidal solutions of NPs and of NPs deposited on a Si wafer. The obtained experimental data are discussed with reference to the band structure of bulk Au.     

Investigation of intrinsic plasmon energy losses associated with the Fe 1s core level in metallic iron

A recently developed Cu Kα₁ (hν = 8047.8 eV) X-ray source/ESCA300 electron spectrometer combination has been used to investigate the intrinsic plasmon energy losses associated with the Fe 1s core level (binding energy = 7111 eV) in metallic iron. The surface and bulk intrinsic plasmon energy losses were separated and it was found that using the theoretically calculated extrinsic energy loss cross-section to represent the bulk intrinsic energy loss cross-section gave an overall intrinsic loss probability which is approximately the same as if a Lorentzian type cross-section is used. However, this approach does not separate the surface and bulk intrinsic losses properly and is not a good approximation for peak shape analysis in the near peak region. A more realistic approximation is provided by using a Lorentzian type energy loss cross-section to represent the bulk intrinsic energy losses. It has also been shown that for the Fe 1s core level of metallic iron the probability that a photoelectron will suffer an intrinsic energy loss is higher at the surface than in the bulk. Also for this core level the excitation probability for the intrinsic plasmons is greater than that of the extrinsic plasmons. Hence ignoring the intrinsic plasmons would cause considerable error in peak shape analysis in the near peak region.