Observation of liquid contains samples using capsule-type holder in scanning electron microscope

抄録

The optical microscope is widely used for the observation of the structures in liquid samples. However, due to the limited resolution of optical microscopes, it is difficult to observe particles in a liquid when their size is smaller than 1 um. Especially, for samples containing nano-scale structures dispersed in a liquid, the resolution of an optical microscope is insufficient, making it necessary to employ a high-resolution scanning electron microscope (SEM) for observation. Nevertheless, SEM observation is conducted under vacuum conditions, requiring the liquid-dispersed samples to be dried. During the drying process, deformation and aggregation of the samples can occur, posing a challenge to preserve their original shape. Recently, we have tried to use capsule-type holder (Aquarius Starter Kit, FlowVIEW Tek) for observing structures in liquid. Because liquid samples can be sealed within the holder under atmospheric pressure conditions, it is possible to achieve in-situ observation of liquid samples through a silicon nitride membrane window with a thickness of 20 nm (according to the sample, 30 nm and 50 nm are also available). In contrast, this capsule-type holder is suitable for high-resolution observations as well. The cross-sectional schematic diagram of the holder is shown in Fig 1a [1-2]. In this study, we attempted to observe and analyze particles dispersed in a liquid using a FE-SEM (JSM-IT800<i>, JEOL Ltd.) employing this liquid-sample-dedicated holder. Moreover, in order to capture the dynamic changes of particles, a high responsibility detector (scintillator backscattered electron detector (SBED)) was used. As an example, we observed a liquid makeup primer emulsion. The SEM image (Fig 1b) shows that the dispersion state of particles contained within the makeup primer emulsion can be clearly confirmed. In addition, we also investigated the relationship between incident voltage and image formation, as well as the feasibility of Energy Dispersive X-ray Spectroscopy (EDS) analysis (JED-2300, JEOL Ltd.) during observations of liquid samples. Through the membrane window, elements present in the sample, from light elements (such as carbon, oxygen) to heavy elements, can all be detected by EDS analysis.

References

[1] E. J. Lang, N. M. Heckman, T. Clark, B. Derby, A. Barrios, A. Monterrosa, C. M. Barr, D. L. Buller, D. D. Stauffer, N. Li, B. L. Boyce, S. A. Briggs, K. Hattar, Nucl. Instrum. Methods Phys. Res., Sect. B 537, 29, (2023).

[2] N. Asano, J. Lu, S. Asahina, S. Takami, Nanomaterials, 11, 908, (2021).