Zeng Jianhua, Chen Lei, Dai Qiaofeng, Lan Sheng, Tie Shaolong
Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices, School of Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou 510006, P. R. China.
School of Chemistry and Environment, South China Normal University, Guangzhou 510006, P. R. China.
Nanoscale. 2016 Jan 21;8(3):1572-9. doi: 10.1039/c5nr06105a.
We proposed a scheme in which normal Raman scattering is coupled with hyper-Raman scattering for generating a strong anti-Stokes hyper-Raman scattering in nanomaterials by using femtosecond laser pulses. The proposal was experimentally demonstrated by using a single-layer MoS2 on a SiO2/Si substrate, a 17 nm-thick MoS2 on an Au/SiO2 substrate and a 9 nm-thick MoS2 on a SiO2-SnO2/Ag/SiO2 substrate which were confirmed to be highly efficient for second harmonic generation. A strong anti-Stokes hyper-Raman scattering was also observed in other nanomaterials possessing large second-order susceptibilities, such as silicon quantum dots self-assembled into "coffee" rings and tubular Cu-doped ZnO nanorods. In all the cases, many Raman inactive vibration modes were clearly revealed in the anti-Stokes hyper-Raman scattering. Apart from the strong anti-Stokes hyper-Raman scattering, Stokes hyper-Raman scattering with small Raman shifts was detected during the ablation process of thick MoS2 layers. It was also observed by slightly defocusing the excitation light. The detection of anti-Stokes hyper-Raman scattering may serve as a new technique for studying the Raman inactive vibration modes in nanomaterials.
我们提出了一种方案，即通过飞秒激光脉冲，使正常拉曼散射与超拉曼散射耦合，从而在纳米材料中产生强反斯托克斯超拉曼散射。通过在SiO₂/Si衬底上使用单层MoS₂、在Au/SiO₂衬底上使用17nm厚的MoS₂以及在SiO₂-SnO₂/Ag/SiO₂衬底上使用9nm厚的MoS₂对该方案进行了实验验证，这些材料被证实对二次谐波产生具有高效性。在其他具有大二阶极化率的纳米材料中也观察到了强反斯托克斯超拉曼散射，例如自组装成“咖啡”环的硅量子点和管状铜掺杂氧化锌纳米棒。在所有情况下，许多拉曼非活性振动模式在反斯托克斯超拉曼散射中都清晰可见。除了强反斯托克斯超拉曼散射外，在厚MoS₂层的烧蚀过程中还检测到了具有小拉曼位移的斯托克斯超拉曼散射。通过稍微使激发光散焦也观察到了这一现象。反斯托克斯超拉曼散射的检测可作为研究纳米材料中拉曼非活性振动模式的一种新技术。
