Element discrimination in a hexagonal boron nitride nanosheet by aberration corrected transmission electron microscopy

Boron nitride nanosheets prepared by an exfoliation technique were observed by aberration
corrected transmission electron microscopy at 300 kV acceleration voltage. Single boron and nitrogen atoms in a monolayer region were imaged with different image contrast; a boron atom gave 16% less contrast than a nitrogen atom. The number of atoms at each hexagonal ring site was determined by the image intensity that changed discretely with a 0.25 - 0.30 intensity difference. A double BN sheet was found to have a boron vacancy layer, and a triple BN layer has also a boron deficient layer on the incident surface resulting from the electron beam thinning process. The high sensitivity for atomic species was achieved by the high resolution and a small information limit due to the use of a cold field emission electron source.