时间：5月21日 下午3:00
地点：近代物理系210会议室
题目：Scanning near-field optical microscopy with new probes and feedback modes
报告人:Anton Smirnov 瑞士联邦理工学院（洛桑）
摘要：Fluorescence Resonance Energy Transfer (FRET) is one of the most promising ways to improve the spatial resolution of the SNOM. The idea is to use a donor (acceptor) nanoparticle/molecule as local fluorescence center attached to the tip and measure the fluorescence induced by it in the sample (or vice versa) due to the FRET. Ca. ten years ago, this idea has been realized at the single molecule level with CdSe nanocrystals and appropriate dye molecules. Despite the high spatial resolution (better than 20 nm) attained in this experiment, it remains an isolated one, and this is for a valid reason: albeit rather large, the photostability of dye molecules and semiconductor nanocrystals still enables to use a single fluorescence center exploiting for imaging only a few minutes at best. Fluorescent centers with high photostability should be used to overcome this problem. Earlier, claimed to be very photostable and bright NV color centers in nanodiamond crystals were proposed. This talk will show that such system is not suitable to realize single fluorescent center FRET SNOM method. The alternative is also proposed.
The common problem of most aperture SNOMs is the fragility of the tip. The use of plastic fibers to solve this problem will be demonstrated. These fibers look very promising for use as SNOM probes as one can anticipate much less fragility (compare glass and plastic) and greater ease of tip preparation. For such a preparation, hazardous treating with hydrofluoric acid, which remains the most popular approach to prepare SNOM probes from the glass fibers, can be avoided entirely.
Also the realization of a new approach to decrease the forces between the tip and sample will be discussed: bent sharpened glass optical fibers with carefully controlled sizes of the bent part and the radius of the curvature of the bending were prepared and experimentally exploited as SNOM probes. Detailed analysis of fiber vibration modes shows that realization of truly tapping mode of the probe dithering require an extreme caution. In case of using the second resonance mode, probes vibrate mostly in shear-force mode unless the bending radius is rather small (ca. 0.3 mm) and the probe’s tip is short. Otherwise, the shear force character of the dithering persists.
Biography: Anton Smirnov 2015年硕士毕业于俄罗斯Lomonosov Moscow State University，同年赴瑞士联邦理工学院（洛桑）（EPFL） Laboratory of Physics of Living Matter攻读博士学位，预期2019年5月底答辩。 主要研究方向是扫描光学近场原子力显微镜(SNOM）及其在生物学上的应用。 Anton在低温及室温SNOM仪器搭建与创新上做了一系列的工作。
