  The determination of the chemical content is crucial for the quality control
in high-precision device fabrication and advanced process development. For
reliable chemical composition characterization, certain interaction volume of
the target material is necessary for conventional techniques such as
energy-dispersive X-ray spectroscopy (EDX) and electron energy loss
spectroscopy (EELS). This remains however a challenge for nanostructures. We
hereby propose an alternative technique for measuring chemical composition of
nanostructures with limited volume. By measuring the differences in the optical
absorption of the nanostructure due to the differences in the chemical
composition with the resonance frequency detuning of a nanomechanical resonator
as well as the assistance of the analytical optical modelling, we demonstrate
the possibility of characterizing the carbon content in the direct-write
focused electron beam induced deposition (FEBID) gold nanostructures.
