  We report on a nanomechanical engineering method to monitor matter growth in
real time via e-beam electromechanical coupling. This method relies on the
exceptional mass sensing capabilities of nanomechanical resonators. Focused
electron beam induced deposition (FEBID) is employed to selectively grow
platinum particles at the free end of singly clamped nanotube cantilevers. The
electron beam has two functions: it allows both to grow material on the
nanotube and to track in real time the deposited mass by probing the
noise-driven mechanical resonance of the nanotube. On the one hand, this
detection method is highly effective as it can resolve mass deposition with a
resolution in the zeptogram range; on the other hand, this method is simple to
use and readily available to a wide range of potential users, since it can be
operated in existing commercial FEBID systems without making any modification.
The presented method allows to engineer hybrid nanomechanical resonators with
precisely tailored functionality. It also appears as a new tool for studying
growth dynamics of ultra-thin nanostructures, opening new opportunities for
investigating so far out-of-reach physics of FEBID and related methods.
