Ultrafast scanning electron microscopy images carrier dynamics and carrier induced surface voltages using a laser pump electron probe scheme, potentially surpassing all-optical techniques in probe resolution and surface sensitivity. Current implementations have left a four order of magnitude gap between optical pump and electron probe resolution, which particularly hampers spatial resolution in the investigation of carrier induced local surface photovoltages. Here, we present a system capable of focusing the laser using an inverted optical microscope built into an ultrafast scanning electron microscopy setup to enable high numerical aperture pulsed optical excitation in conjunction with ultrafast electron beam probing. We demonstrate an order of magnitude improvement in optical pump resolution, bringing this to sub-micrometer length scales. We further show that temporal laser pump resolution can be maintained inside the scanning electron microscope by pre-compensating dispersion induced by the components required to bring the beam into the vacuum chamber and to a tight focus. We illustrate our approach using molybdenum disulfide, a two-dimensional transition metal dichalcogenide, where we measure ultrafast carrier relaxation rates and induced negative surface potentials between different flakes selected with the scanning electron microscope as well as on defined positions within a single flake.

中文翻译：

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具有亚微米光泵分辨率的超快扫描电子显微镜

超快扫描电子显微镜使用激光泵电子探针方案对载流子动力学和载流子感应表面电压进行成像，可能在探针分辨率和表面灵敏度方面超越全光学技术。目前的实施在光泵和电子探针分辨率之间留下了四个数量级的差距，这特别妨碍了研究载流子引起的局部表面光电压的空间分辨率。在这里，我们提出了一个系统，该系统能够使用内置于超快扫描电子显微镜装置中的倒置光学显微镜聚焦激光，以实现高数值孔径脉冲光激发与超快电子束探测的结合。我们展示了光泵分辨率的数量级改进，使其达到亚微米长度尺度。我们进一步表明，通过预补偿将光束带入真空室并聚焦所需的组件引起的色散，可以在扫描电子显微镜内保持时间激光泵分辨率。我们使用二硫化钼（一种二维过渡金属二硫化物）来说明我们的方法，我们在其中测量超快载流子弛豫率和在用扫描电子显微镜选择的不同薄片之间以及在单个薄片内的定义位置上诱导的负表面电位。