Mass measurements based on nanomechanical devices: differential measurements

In the last few years, there has been a strong interest in implementing nano-mechanical devices as mass sensors. Regarding this application, an important question to address is to know to what extent the observed frequency shift is exclusively due to the targeted mass loading. For this purpose, we present a device, a polysilicon double cantilever, with an innovative design that allows the direct determination of the measurement uncertainty. Two almost identical nanomechanical resonators are simultaneously operated: one serves as sensor and the other as reference. In this way, rapid and reliable measurements in air are made possible. In first experimental measurements, some masses in the order of 300 fg, locally deposited by focused ion beam, have been measured with an uncertainty of 30 fg. These results are corroborated by the determination of the deposits size based on SEM images.