银纳米粒子修饰三维碳纳米管阵列SERS实验

为了使表面增强拉曼散射(SERS)基底的三维聚焦体积内包含更多的“热点”,能吸附更多探针分子和金属纳米颗粒,以便获得更强的拉曼光谱信号,提出了银纳米粒子修饰垂直排列的碳纳米管阵列三维复合结构作为SERS基底,并对其进行了实验研究。利用化学气相沉积(CVD)方法制备了垂直排列的碳纳米管阵列;采用磁控溅射镀膜方法先在碳纳米管阵列上形成一层银膜,再通过设置不同的高温退火温度,使不同粒径的银纳米粒子沉积在垂直有序排列碳纳米管阵列的表面和外壁。SEM结果表明：在有序碳纳米管阵列的表面和外壁都均匀地负载了大量银纳米粒子,并且银纳米颗粒的粒径、形貌及颗粒间的间距随退火温度的不同而不同。采用罗丹明6G(R6G)分子作为探针分子,拉曼实验结果表明：R6G浓度越高,拉曼强度越强,但是R6G浓度的增加与拉曼强度增强并不呈线性变化;退火温度为450 ℃,银纳米颗粒平均粒径在100～120 nm左右,退火温度为400 ℃,银纳米颗粒平均粒径在70 nm左右,退火温度为450 ℃的拉曼信号强度优于退火温度400和350 ℃。     

光源的偏振态对动态光散射颗粒测量结果的影响

研究了在动态光散射纳米颗粒测量中,光源的偏振态对测量结果的影响。采用了粒径为100nm、体积浓度为0.5%的标准颗粒作为样品,使He-Ne激光通过起偏器得到0°～180°方向的偏振光,测量了散射光强、偏振度和粒径测量值的变化,计算了相应的粒径均值偏差和标准差,并将这一结果与无偏振He-Ne激光入射进行了比较。结果表明,当入射光为线偏振光时,偏振方向垂直于散射面时测量效果最好;另一方面,由于颗粒系散射迭加造成的散射光偏振度降低,使线偏振光源与无偏振光源产生的散射光偏振度无明显差别,证明在测量中可以使用无偏振He-Ne激光代替。     

飞秒激光诱导硒化锌晶体表面自组织生长纳米结构

 以250 kHz高重复频率钛宝石飞秒激光聚焦到硒化锌晶体表面,利用扫描电子显微镜观测飞秒激光辐照后晶体的表面结构。发现线偏振激光辐照的区域形成了自组织周期性纳米结构,其周期为160 nm左右,并且可以通过改变激光的偏振方向调节纳米光栅结构的取向;当晶体相对于激光光束以10 mm/s速度移动,经激光扫描后,在晶体表面形成了长程类布拉格光栅。当飞秒激光光束为圆偏振光时,辐照区域形成均匀的纳米颗粒。     

银纳米颗粒对Tm3+/Yb3+共掺铋锗酸盐玻璃上转换发光性能的影响

利用传统熔融淬冷法制备了系列Tm3+/Yb3+共掺复合银纳米颗粒铋锗酸盐玻璃样品.测试得到表征银纳米颗粒存在的表面等离子体共振(SPR)峰位于556～581 nm,透射电镜图像中观察到均匀分布的Ag纳米颗粒,尺寸约为5～25 nm.通过测试玻璃样品在400～900 nm波段的上转换光谱,对铥镱共掺复合银纳米颗粒铋锗酸盐...     

局域表面等离激元诱导的三次谐波增强效应

本文研究了二维金三角形纳米颗粒阵列的三次谐波非线性光学效应. 金三 角纳米颗粒阵列是基于微球刻印技术制成. 采用反射式光学系统, 观察到该纳米结构在光谱分辨的飞秒激光照射下产生明显的三次谐波. 研究表明, 当激光抽运频率接近金纳米颗粒的局域表面等离激元共振位置时, 三次谐波信号得到增强; 三次谐波辐射方向满足动量匹配条件. 关键词： 微球刻印 三次谐波产生 表面等离激元     

多偏振飞秒激光制备彩色铁

采用四个不同偏振方向的线偏振和圆偏振态飞秒激光扫描处理金属铁表面来制备不同的彩色铁。从不同角度观察被处理区域时,线偏振扫描处理的彩色区域呈现不同的色彩,而圆偏振扫描处理的区域没有明显的颜色变化。扫描电子显微镜图片显示,线偏振激光扫描处理金属铁表面形成了nm量级的激光诱导周期表面结构,其方向始终与激光偏振方向垂直;圆偏振激光扫描处理金属铁表面形成的条纹结构不明显且有大量的纳米颗粒结构。     

多偏振飞秒激光制备彩色铁

采用四个不同偏振方向的线偏振和圆偏振态飞秒激光扫描处理金属铁表面来制备不同的彩色铁。从不同角度观察被处理区域时,线偏振扫描处理的彩色区域呈现不同的色彩, 而圆偏振扫描处理的区域没有明显的颜色变化。扫描电子显微镜图片显示,线偏振激光扫描处理金属铁表面形成了nm量级的激光诱导周期表面结构,其方向始终与激光偏振方向垂直;圆偏振激光扫描处理金属铁表面形成的条纹结构不明显且有大量的纳米颗粒结构。     

一维氧化锌柱阵列空间取向激发的荧光光谱研究

用两步气相沉积-氧化法制备了具有高度一致指向性的一维纤锌矿六方结构的氧化锌单晶柱阵列,探测它的不同空间取向激发条件下的荧光光谱。结果表明,一维阵列样品在不同空间取向的激发光照射下,其荧光光谱有明显变化。当低功率355 nm激光对一维方向进行横向激发时,激子发光的相对强度较大;当用1 064 nm 激光取向激发时,发射光谱的差异更明显。除了荧光光谱的发射峰强弱发生变化外,在一维横向激发时上转换发射光谱产生了新的发射峰,表明在不同的取向激发下一维阵列样品对激发光的吸收有明显变化。由此产生的荧光发射的差异非常明显,表明一维氧化锌柱阵列对能量吸收、能量传递等有很强的方向性。上转换偏振光谱表明,当偏振光的振动方向与阵列的一维方向平行时,发射光谱中400 nm的发光峰强度比偏振方向与一维方向垂直时要大,表明偏振方向对一维阵列的空间取向激发荧光光谱是有影响的。在讨论阵列发光性质如发光光谱,发射强度的时候,必须明确激发光的强度、取向以及激发光的偏振方向。     

飞秒激光辐射诱导金属表面微纳结构研究

通过1 kHz的飞秒脉冲(脉宽130 fs,中心波长800 nm)对厚度为60 μm的不锈钢65Mn表面进行飞秒微加工,通过拟合得到65Mn的消融阈值为0.5 J·cm-2。研究了飞秒激光作用下表面形成的多种微结构,其中包括纳米孔及纳米柱状物。同时讨论了激光能量和作用脉冲个数对微结构形成的影响。随着周期波纹结构的形成,发现在各种能量和脉冲个数条件下,周期结构的周期约为入射脉冲的波长。相同的激光功率下,在不同加工速度和加工次数下对不锈钢进行表面微加工,得到了规则的圆孔阵列结构。     

飞秒激光烧蚀氟化钙晶体表面特性

采用飞秒激光对氟化钙晶体表面进行加工。通过调控激光参数,采用静止聚焦和动态扫描两种方式在晶体表面加工出一系列微结构(烧蚀孔和烧蚀线)。分别对两种加工方式烧蚀后的氟化钙晶体表面微结构进行系统研究,包括参数依赖关系、材料表面烧蚀阈值等。计算结果表明:在静止聚焦情况下,累积因子为0.0033;在动态扫描情况下,当扫描方向与激光偏振方向垂直或平行时,累积因子分别为0.0043和0.0052。飞秒激光加工过程中的脉冲累积效应能够对晶体的烧蚀产生重要影响。     

Formation mechanisms of uniform arrays of periodic nanoparticles and nanoripples on 6H-SiC crystal surface induced by femtosecond laser ablation

Uniform arrays of periodic nanoparticles with 80-nm period are formed on 6H-SiC crystal irradiated by circularly polarized 400-nm femtosecond laser pulses. In order to understand the formation mechanism, the morphology evolvement as a function of laser pulse energy and number is studied. Periodic nanoripples are also formed on the sample surface irradiated by linearly polarized 400-, 510- and 800-nm femtosecond laser pulses. All these results support well the mechanism that second-harmonic generation plays an important role in the formation of periodic nanostructures. PACS 79.20.Ds; 42.62.Cf; 61.80.Ba; 81.05.Cy; 78.30.Am     

Femtosecond pulse laser-induced self-organized nanostructures on the surface of ZnO crystal

This paper reports self-organized nanostructures observed on the surface of ZnO crystal after irradiation by a focused beam of a femtosecond Ti：sapphire laser with a repetition rate of 250kHz. For a linearly polarized femtosecond laser, the periodic nanograting structure on the ablation crater surface was promoted. The period of self-organization structures is about 180 nm. The grating orientation is adjusted by the laser polarization direction. A long range Bragglike grating is formed by moving the sample at a speed of 10μm/s. For a circularly polarized laser beam, uniform spherical nanoparticles were formed as a result of Coulomb explosion during the interaction of near-infrared laser with ZnO crystal.     

不同烧蚀条件下飞秒激光脉冲诱导ZnO纳米结构研究

烧蚀条件对飞秒激光脉冲诱导氧化锌纳米结构有重要影响.研究了800 nm,150 fs,250 kHz的飞秒激光脉冲分别在空气中,去离子水中以及无水乙醇中垂直聚焦于氧化锌晶体表面,诱导形成不同形态的纳米结构.实验结果表明,在空气中利用飞秒激光脉冲辐照样品表面,形成了周期为180 nm的纳米线;在去离子水中辐照诱导形成了由氧化锌纳米线聚集而成的"纳米球";在无水乙醇中形成出现分叉结构的纳米线.拉曼光谱分析辐照前后晶体晶相结果表明,形成的纳米结构相对于辐照前特征峰437 cm-1强度有所下降,在570 cm-1处的峰值则显著增强.分析了在各种烧蚀条件下诱导形成纳米结构的演化过程以及物理机理.     

Femtosecond pulse laser-induced self-organized nanogratings on the surface of a ZnSe crystal

Periodic nanostructures are observed on the surface of ZnSe after irradiation by a focused beam of a femtosecond Ti:sapphire laser, which are aligned perpendicular to the laser polarization direction. The period of self-organized grating structures is about 160 nm. The phenomenon is interpreted in terms of interference between the incident light field and the surface scattered wave of 800-nm laser pulses. With the laser polarization parallel to the moving direction we produce long-range Bragg-like gratings by slowly moving the crystal under a fixed laser focus. The nanograting orientation is adjusted by laser polarization and the accumulation effect. PACS 81.16.Rf; 78.67.-n; 33.80.Rv; 82.53.Mj; 81.16.-c     

Sub-100-nm laser-induced periodic surface structures upon irradiation of titanium by Ti:sapphire femtosecond laser pulses in air

The formation of laser-induced periodic surface structures (LIPSS) on titanium upon irradiation with linearly polarized femtosecond (fs) laser pulses (τ=30 fs, λ=790 nm) in an air environment is studied experimentally and theoretically. In the experiments, the dependence on the laser fluence and the number of laser pulses per irradiation spot has been analyzed. For a moderate number of laser pulses (N<1000) and at fluences between ～0.09 and ～0.35 J/cm², predominantly low-spatial-frequency-LIPSS with periods between 400 nm and 800 nm are observed perpendicular to the polarization. In a narrow fluence range between 0.05 and 0.09 J/cm², high-spatial-frequency-LIPSS with sub-100-nm spatial periods (～λ/10) can be generated with an orientation parallel to the polarization (N=50). These experimental results are complemented by calculations based on a theoretical LIPSS model and compared to the present literature.     

Self-organized periodic surface structures on ZnO induced by femtosecond laser

Self-organized periodic surface structures on ZnO have been observed after multiple linearly polarized femtosecond laser pulse irradiation. The observed self-organized structures are attributed to the second harmonics in the sample surface excited by the incident laser. The grating orientation could be adjusted by the laser polarization direction. We also find that fluences play an important role in the formation of self-organized nanostructures.     

Sub-wavelength surface structures on silicon irradiated by femtosecond laser pulses at 1300 and 2100 nm wavelengths

We present periodic ripples and arrays of protrusions formed on the surface of silicon after irradiation by low-fluence linearly polarized femtosecond laser pulses. Laser-induced periodic surface structures (LIPSS) are observed for irradiation at center wavelengths of 800, ∼ 1300, and ∼ 2100 nm, with the structure periods somewhat less than the incident wavelengths in air. Additionally, we observe structures with spatial periods substantially less than the incident laser wavelengths. These sub-wavelength periodic structures form only when the photon energy is less than the silicon bandgap energy. We discuss a number of factors which may contribute to the generation of this surface morphology.     

Femtosecond-laser-induced nanostructure formed on hard thin films of TiN and DLC

We report observation of nanostructures formed on thin TiN and DLC films that were irradiated by 800- and 267-nm, femtosecond (fs) Ti:sapphire laser pulses at an energy fluence slightly above the ablation threshold. On the ablated thin-film surfaces, the linearly polarized fs pulses produce arrays of fine periodic structures that are almost oriented to the direction perpendicular to the laser polarization, while the circularly polarized light forms fine-dot structures. The size of these surface structures is 1/10–1/5 of the laser wavelength and decreases with a decrease in the laser wavelength. Received: 3 September 2002 / Accepted: 4 September 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +81-778/62-3306, E-mail: yasuma@fukui-nct.ac.jp     

Effect of polarization on femtosecond laser pulses structuring silicon surface

Arrays of conical-like spikes can be formed on silicon surface after irradiated with femtosecond laser pulses in ambient of SF₆ or N₂. In this article, we report our observations on how the shape of the spikes formed on silicon surface varies with the polarization of laser beam. The experimental results show that, with circular polarized laser irradiation, the shape of the spikes is conical; however, with linearly polarized laser irradiation, the spikes show elliptic conical shape, and the long-axes are perpendicular to the direction of the polarization of laser beam. The asymmetric shape of spikes produced by linearly polarized laser beam can be explained by considering the polarization dependence of Fresnel-refraction.