esem

Environmental scanning electron microscope (ESEM) is a type of scanning electron microscope that can image specimens in a gaseous environment, enabling observation of hydrated, non-conductive, and beam-sensitive samples without the need for extensive dehydration or conductive coating. The technology emerged in the late 1980s and has since become widely used in science and industry.

Principle of operation: The instrument uses differential pumping to keep the electron column at high vacuum while the specimen chamber operates at a higher pressure with gas such as water vapor. The gas is ionized by the primary beam, and secondary electrons are detected with sensors designed to function in gas. This arrangement reduces charging, enhances surface imaging of insulating materials, and permits imaging of wet or fragile samples.

Applications: ESEM is applied in materials science, geology, biology, polymers, and forensic science. It supports imaging of hydrated tissues, minerals with adsorbed moisture, emulsions, fossils, pollen, seeds, and foods. Some systems also offer in-situ capabilities such as controlled humidity, heating, or gas exposure during observation.

Limitations: Compared with conventional high-vacuum SEM, ESEM can exhibit lower spatial resolution and higher background noise due to gas scattering. The imaging conditions can be sensitive to gas composition and pressure, and not all samples are compatible with the gas environment. The technology requires specialized hardware and maintenance compared with standard SEM.