Silicon nanowire resonators for aerosol nanoparticle mass sensing

In this work, silicon nanowire-based resonators were fabricated and employed to sense aerosol nanoparticles (NPs) by measuring resonant frequency shifts induced by the mass of stuck NPs. The fabrication of silicon nanowire (SiNW) arrays was performed utilizing inductively coupled plasma (ICP) cryogenic dry etching and multiple thermal oxidations. The SiNWs were coated with gold for contacting to the home-built electrostatic NP sampler to collect the flowing NPs. A piezoelectric shear actuator mounted in the frequency measurement system was used to excite the SiNW sensors into resonance. Tested in a TiO2 aerosol sampling with a total concentration of ~8500 particle/cm³, the sensor displayed its feasibility as a nanobalance to detect aerosol NPs in the femtogram scale with a mass sensitivity of 7.1 Hz/fg and a mass resolution of 31.6 fg. To extend the operating life of the sensor, an ultrasonic removal method was used to detach the adhered NPs.