Understanding the Dynamic Response of Nanoelectromechanical Sensors to Ultra-High Purity Gases: Implications for Gas Sensing and Surface Chemistry Study*

Nanoelectromechanical sensors are exceptionally sensitive for gas detection and mass measurement. To detect gases effectively, it's crucial to comprehend the interaction between analytes and sensors, even in non-specific adsorption cases. This study investigates the impact of pulses of ultra-high purity (UHP) gases on nanoelectromechanical resonators. The study examines frequency shifts in uncoated microcantilevers, revealing three distinct temperature regimes. Above 200K, positive frequency shifts occur, while between 200K and 100K, temporary frequency dips are observed. Below 100K, a continuous negative frequency drift appears, along with negative frequency shifts upon gas introduction. These shifts result from the interplay of squeeze film damping and moisture adsorption on the cantilever, with the gases themselves (argon or helium) having a minimal role in the negative frequency shifts. The study elucidates these findings using analytical and finite element method (FEM) simulations, capturing the kinetics of adsorption-desorption processes under varying partial pressures and temperatures. This research provides a comprehensive understanding of how mechanical resonators respond to UHP gases and their impurities, with broad implications for gas sensing using mechanical resonators.