  The recent progress in high-resolution transmission electron microscopy
(HRTEM) has given rise to the possibility of in situ observations of
nanostructure transformations and chemical reactions induced by electron
irradiation. In this article we briefly summarise experimental observations and
discuss in detail atomistic modelling of irradiation-induced processes in
HRTEM, as well as mechanisms of such processes recognised due to modelling.
Accurate molecular dynamics (MD) techniques based on first principles or
tight-binding models are employed in the analysis of single irradiation-induced
events, and classical MD simulations are combined with a kinetic Monte Carlo
algorithm to simulate continuous irradiation of nanomaterials. It has been
shown that sulphur-terminated graphene nanoribbons are formed inside carbon
nanotubes as a result of an irradiation-selective chemical reaction. The
process of fullerene formation in HRTEM during continuous electron irradiation
of a small graphene flake has been simulated, and mechanisms driving this
transformation analysed.
