  Employing electrons for direct control of nanoscale reaction is highly
desirable since it provides fabrication of nanostructures with different
properties at atomic resolution and with flexibility of dimension and location.
Here, applying in situ transmission electron microscopy, we show the reversible
oxidation and reduction kinetics in Ag, well controlled by changing the dose
rate of electron beam. Aberration-corrected high-resolution transmission
electron microscopy observation reveals that O atoms are preferably inserted
and extracted along the {111} close-packed planes of Ag, leading to the
nucleation and decomposition of nanoscale Ag2O islands on the Ag substrate. By
controlling electron beam size and dose rate, we demonstrated fabrication of an
array of 3 nm Ag2O nanodots in an Ag matrix. Our results open up a new pathway
to manipulate atomistic reaction with electron beam towards the precise
fabrication of nanostructures for device applications.
