High-Tech Corp, Japan). The liquid sample holder was mounted onto the SEM stage and the detector terminal was connected to a pre-amplifier under the holder. The SE-ADM images (1280 × 1020 pixels) were captured at 100,000-120,000× magnification with a scanning time of 40 s, a working distance of 7 mm, an EB acceleration voltage of 4 kV and a current of 1-5 pA.