Single Molecule STM Nanospectroscopy using Difference Frequency Generation at the Tunnel Gap

使用隧道间隙差频生成的单分子 STM 纳米光谱

基本信息

批准号：
14350017
负责人：
MAEDA Koji
金额：
$ 9.54万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-14350017/
关键词：
Scanning Tunneling Microscopy Infrared Absorption Molecular Vibrations Nonlinear Optics Nano Resolution Near Field Plasmon Micro Analysis 分析

项目摘要

We have developed a new scheme of single-molecule-resolved nanospectroscopy (STM-DFG) that uses an intense infrared light locally generated at the tunnel gap of tip and sample in a scanning tunneling microscope (STM). The achievements are as follows. (1)Measurements of optical field enhancement at STM probe tips : From a tunneling current arising from a rectification of optical field at the tunnel gap due to the nonlinear I-V relation, we have measured for graphite samples the optical field enhancement factors as large as 10^3 and 5×10^2 even for W tips and Pt-Ir tips, respectively. (2)Proving difference frequency generation at a tunneling gap : For the combination of C_<60> film sample and W tip that was illuminated with two laser lights from a Ti-sapphire laser (wavelength fixed) and a diode laser (wavelength swept), we have successfully acquired spectra in agreement with infrared absorption by C_<60> crystals. (3)Field enhancement effect in carbon nanotubes (CNT) : We have found a remarkable enhancement of Raman scattering from N-Dimethyl formamide (DMF) molecules only when the DMF contained CNT and the excitation light is resonant (633nm) with CNT, a signature of the expected field enhancement effect of CNT. (4)STM observations of optical field enhancement effect : Using Au nano-rods as a model sample, we have developed an STM technique to observe directly the optical enhancement taking place at individual particles by detecting the local rectified current. (5)Optimum conditions for STM-DFG : We have concluded that it is most efficient to more intensely focus the light beam, to use pulsed laser lights, to increase the set tunneling current, and to use special materials (Ag, Au, CNT) for STM tips.

我们已经开发了一种新方案，该方案是单分子分辨的纳米光谱镜（STM-DFG），该方案使用了在扫描隧道显微镜（STM）中局部生成的强烈红外光线。成就如下。（1）在STM探针提示处的光场增强的测量：由于非线性I-V关系而导致的隧道间隙的光场的隧道电流，我们已经测量了石墨样品的光场增强因子，分别为WISP和PT-ir，分别为10^3和5×10^2。（2）在隧道差距上证明差异频率产生：对于C_ <60>胶卷样品和W尖端的组合，这些胶片样品和W尖端用Ti-Sapphire激光器（波长固定）和二极管激光器（波长）（波长扫描）亮起的两个激光灯（我们）成功地获得了与c_ <60> Cyrys Cymer的基础相一致。（3）碳纳米管（CNT）的现场增强效应：我们发现，只有当DMF包含CNT和兴奋光是共振（633nm）时，N-二甲基甲酰胺（DMF）分子的拉曼散射仅显着增强。（4）光场增强效应的STM观察结果：使用AU纳米杆作为模型样品，我们开发了一种STM技术，可以直接观察单个颗粒通过检测局部整流电流的光学增强。（5）STM-DFG的最佳条件：我们得出的结论是，更有效地将光束聚焦，使用脉冲激光灯，增加固定隧道电流并使用特殊材料（AG，AU，CNT）来进行STM尖端，这是最有效的。