  Nanoelectromechanical systems (NEMSs) are emerging nanoscale elements at the
crossroads between mechanics, optics and electronics, with significant
potential for actuation and sensing applications. The reduction of dimensions
compared to their micronic counterparts brings new effects including
sensitivity to very low mass, resonant frequencies in the radiofrequency range,
mechanical non-linearities and observation of quantum mechanical effects. An
important issue of NEMS is the understanding of fundamental physical properties
conditioning dissipation mechanisms, known to limit mechanical quality factors
and to induce aging due to material degradation. There is a need for detection
methods tailored for these systems which allow probing motion and stress at the
nanometer scale. Here, we show a non-invasive local optical probe for the
quantitative measurement of motion and stress within a multilayer graphene NEMS
provided by a combination of Fizeau interferences, Raman spectroscopy and
electrostatically actuated mirror. Interferometry provides a calibrated
measurement of the motion, resulting from an actuation ranging from a
quasi-static load up to the mechanical resonance while Raman spectroscopy
allows a purely spectral detection of mechanical resonance at the nanoscale.
Such spectroscopic detection reveals the coupling between a strained
nano-resonator and the energy of an inelastically scattered photon, and thus
offers a new approach for optomechanics.
