In situ water radiolysis in a scanning electron microscope and observation of micro- and nanobubbles formation

Abstract

Nanobubble formation by radiolysis of water has been observed in a transmission electron microscope using very high electron dose ratios. Here, surface micro- and nanobubbles were formed in situ in a conventional scanning electron microscope at relatively low magnifications of ∼1000. Bubble formation was observed at a low dose ratio of 1.3 × 1011 electrons/cm2 s, which is 5-7 orders of magnitude smaller than in previous studies using transmission electron microscopes. Our observations suggest that the pressure in the liquid cell is one of the important factors for the formation of bubbles. The contact angles obtained by direct observation of 69 bubbles were 50°-90°, with an average of 69°. These angles are much larger than those of the bubbles previously observed using an atomic force microscope. Despite the large contact angles (and large Laplace pressures), the micro- and nanobubble lifetimes were at least three days. Scanning electron microscopy shows potential as an important analytical tool for micro- and nanobubbles.