权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Local non-linear spectroscopy using electromagnetic enhancement effect of a metal tip apex

利用金属尖端电磁增强效应的局部非线性光谱

基本信息

批准号：
15204026
负责人：
USHIODA Sukekatsu
金额：
$ 30.37万
依托单位：
Japan Advanced Institute of Science and Technology (2004)Tohoku University (2003)
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

When a laser beam is shined at the tip-sample gap of a scanning funneling microscope (STM), the electromagnetic field is strongly enhanced immediately below the sharp tip apex. Using this phenomenon one can realize optical spectroscopy with very high special resolution beyond the optical diffraction limit. In this study we have constructed a tip-enhanced nonlinear spectroscopy system that consists of an ultra-high-vacuum low-temperature STM, a highly sensitive photon detection system, and a tunable laser system. As a first experiment, we have measured the tip-enhanced Raman spectra of single wall carbon nanotubes (SWNT) deposited on the Au(111) surface with excitation light of 785 nm. In this experiment we used Au tips, which are expected to show large electromagnetic enhancement. The Au tips were fabricated by electrochemical etching in a saturated aqueous solution of NaCl. By adjusting the temperature and pH of the electrolyte, we have succeeded in producing Au tips with the radii of curvature less than 50 nm. Using an Au tip we observed STM images of the sample until an individual SWNT bundle was found. Then the STM tip was fixed over the target SWNT bundle, and subsequently the Raman spectra were measured as a function of the tip-sample distance. The Raman intensity of the G-band (〜1590 cm^<-1>) of SWNT decreases rapidly as the tip-sample distance increases up to 〜10 nm. This result clearly shows the tip-enhanced scattering effect. Furthermore, we have observed optical second harmonic generation from Au nanowire arrays on faceted NaCl(110) substrates with wire widths from 40 to 60nm, in order to investigate the general local field near Au nanostructures. We have found that the amplitude of the incident field polarized perpendicular to the nanowire axes is considerably reduced by the de polarization field induced in the nanowires.

当激光照射在扫描漏斗显微镜(STM)的尖端-样品缝隙时，电磁场在尖端尖端下方被强烈增强。利用这一现象，可以实现超光学衍射极限的高分辨率光学光谱。在本研究中，我们构建了一个由超高真空低温扫描隧道显微镜、高灵敏度光子探测系统和可调谐激光系统组成的针尖增强型非线性光谱系统。作为第一个实验，我们测量了沉积在Au(111)表面的单壁碳纳米管(SWNT)在785 nm激发光下的尖端增强拉曼光谱。在这个实验中，我们使用了Au尖端，预计它将显示出很大的电磁增强。在饱和的氯化钠水溶液中通过电化学腐蚀的方法制备了Au针尖。通过调节电解液的温度和pH值，我们成功地制备出了曲率半径小于50 nm的Au尖端。使用Au针尖，我们观察了样品的STM图像，直到发现了单独的SWNT束。然后将STM针尖固定在目标单壁碳纳米管束上，随后测量了作为针尖-样品距离的函数的拉曼光谱。单壁碳纳米管的G带(~1590 cm~(-1)~gt；)的拉曼强度随针尖-样品距离增加到~10 nm而迅速减小。这一结果清楚地表明了尖端增强散射效应。此外，为了研究Au纳米结构附近的局域场，我们还观察到了Au纳米线阵列在线宽为40-60 nm的多面NaC l(110)衬底上产生的光学二次谐波。我们发现，在纳米线中诱导的退极化场使垂直于纳米线轴线极化的入射场的幅度大大降低。