Surface functionalization and monolayer formation on silicon resonant nanoballances

This work presents formation of molecular monolayers on silicon surfaces of micromechanical resonant devices and measurement of the mass of the deposited monolayer using such. Thermally actuated single crystalline silicon micromechanical resonators with resonant frequencies in the 20-30 MHz range were used as highly sensitive mass sensors. Monolayers of long chain amine molecules were formed by reacting the amine groups with epoxide groups covalently bonded to the silicon surfaces. As a result a consistent negative frequency shift of ~100ppm was measured for the resonators. Mass calculations based on the measured frequency shift show a 6.9% surface coverage for the monolayer. XPS surface analysis shows existence of nitrogen atoms on the resonator surface confirming that the measured frequency shifts are due to the addition of the amine molecules.