低温散射式近场光学显微镜的研发

Development of cryogenic scattering-type scanning near-field optical microscope

散射式扫描近场光学显微镜(s-SNOM)是现代光学技术的重要分支。s-SNOM突破了衍射极限,在红外和太赫兹波段实现了纳米尺度成像。目前市面上商用的s-SNOM大多适合在常温常压环境下使用。而很多具有新奇物性的材料需要低温的测试环境。本文作者设计并搭建了一套采用液氦杜瓦维持低温环境的超高真空近场光学显微镜。该系统基于原子力显微镜(AFM),可以同时获得样品的形貌和近场光学成像。自制的压电驱动电机用于探针、样品和抛物面镜的位移控制。作者用标准样品TGQ1评估了s-SNOM的性能,并对NdNiO_(3)薄膜的金属绝缘体相变(MIT)进行红外近场成像。测量结果展现了该系统在低温下的优异性能。低温s-SNOM技术能够为NdNiO_(3)等关联氧化物薄膜相变过程提供介观尺度的丰富信息。

Scattering-type scanning near-field optical microscope(s-SNOM) has become an important tool among the modern optical techniques in the past decades.s-SNOM exceeds the diffraction limitation and allows the nanoscale imaging over a broad spectral range from infrared to terahertz frequencies.Currently,most commercial s-SNOM’s are operated at room temperature and atmospheric pressure.However,cryogenic environment is needed for materials with novel physical properties.Here we designed an ultrahigh-vacuum(UHV) cryogenic s-SNOM equipped with liquid helium Dewar.The s-SNOM system allows for simultaneous AFM topography and near-field optical imaging based on the homemade AFM.The stages of tip,sample,and mirror are driven independently by homemade piezo positioners.The reliability of the s-SNOM is evaluated by standard test sample TGQ1,and further demonstrated by the infrared near-field imaging of MIT in NdNiO_(3)films.The corresponding measurements show the excellent result of our design s-SNOM under cryogenic environment.Cryogenic s-SNOM can provide valuable meso-scale information of phase transitions in more correlated oxides films.