EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Microcantilevers are already successfully implemented in mass sensing devices, offering a sensitivity down to the range of few picograms. While for mass sensing applications the frequency shift is used, the corresponding quality factor additionally depends on the ambient medium and scales inversely with the pressure. However, the sensing range of commercial microcantilevers is restricted, which limits the field of application. To expand the pressure range, the size of the cantilevers has to be further reduced: A beam with a thickness in the nm range would shift and additionally broaden the measurable regime to higher pressure values. Therefore, a precise characterization of the vibrational properties of nanowires is required, which is the fundament for further research on next-generation sensing devices. We present a correlative electron and light microscopic approach to characterize the sensing properties of single nanowires in dependence of the gas atmosphere and pressure level. The high vacuum in SEM/TEM enables the characterization of the intrinsic properties, which is directly related to the microstructure and surface quality. Moreover, in situ techniques can already be used during the growth process, where single crystalline defect-free nanowires are obtained. To analyze the damping effect caused by the interaction of the gas molecules with the nanowire, the in situ resonance measurements have to be performed within the molecular flow regime (~50mbar-200mbar). For this purpose, single nanowires are mounted in a compact gas chamber underneath the light microscope, which allows to observe the changing resonance behavior in dependence of the applied gas atmosphere (He, N2, Air, Ar) and pressure level. By using the resonance vibration, we demonstrate the pressure sensing capability of a single nanowire. Moreover, the damping behavior is used to examine the molar mass of the surrounding atmosphere. Together this shows that single nanowires can be utilized as versatile nanoscale gas sensors.