Observation of wet specimens sensitive to evaporation using scanning electron microscopy.

Noriyuki Inoue,Mitsuo Suga,Toshiaki Suzuki,Osamu Takai,Yoshikazu Nemoto,Yoshiko Takashima

doi:10.1093/jmicro/dfy041

Noriyuki Inoue, Mitsuo Suga + Show 4 more

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https://doi.org/10.1093/jmicro/dfy041

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Abstract

Wet specimens are notoriously difficult to image in scanning electron microscopes (SEM) owing to evaporation from the required vacuum of the specimen chamber. Traditionally, this issue has been addressed by increasing the specimen chamber pressure. Unfortunately, observation under high specimen chamber pressure cannot prevent the initial evaporation effects. The wet cover method, where the original surface water is retained (and, therefore, considered wet), provides a way to introduce and subsequently image specimens that are sensitive to evaporation within a SEM, while preventing evaporation-related damage, and to observe interesting specimen-water interactions.

Highlights

An electron microscope is an indispensable tool for observing small objects
Scanning electron microscopy (SEM) requires the specimen to be in vacuum, since electrons do not propagate in atmosphere or liquid, which is a major disadvantage in case of specimens composed of materials containing relatively low boiling points such as water or other biological fluids, often resulting in the destruction of the specimens
Without the wet cover, the water droplet gradually became smaller during evacuation, and the volume became 30% of the initial value, when the specimen chamber pressure reached 700 Pa and the evacuation was switched from Fig. 3 (a) to (b) (~85 s after the start of evacuation)

Summary

Introduction

An electron microscope is an indispensable tool for observing small objects. Scanning electron microscopy (SEM) requires the specimen to be in vacuum, since electrons do not propagate in atmosphere or liquid, which is a major disadvantage in case of specimens composed of materials containing relatively low boiling points such as water or other biological fluids, often resulting in the destruction of the specimens. Abrams and McBain reported one such environmental cell for transmission electron microscopy (TEM) [1] Using this structure, observation of a wet specimen was achieved by introducing water vapor from the outside to the specimen [2]. Observation of a wet specimen was achieved by introducing water vapor from the outside to the specimen [2] Progress in this technology has been remarkable in recent years owing to the development of micro electron mechanical system (MEMS) technology [3,4]. Among various methods for observing wet specimens, environmental SEM has been widely used for various types of specimens, including cultured cells, particles in liquid, and water droplets [19], as the surface and cross-section of wet specimens are observed stereoscopically.

Methods

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Concluding remarks