Micro/nano resonant cantilevers with a laser deflection readout have been very popular in sensing applications over the past years. Despite the popularity, however, most of the research has been devoted to increasing the sensitivity, and very little attention has been focused on effects-induced errors. Among these effects, the surface effects and the so-called readout back-action are the two most influential causes of errors. In this paper, we investigate (1) the influence of the surface effects such as water adsorption, gas adsorption, and generally surface contaminations, and (2) the effect of the laser deflection detection, including power and positions of the laser, on the resonance frequency of silicon cantilevers. Our results show that both the surface contaminations and the laser back-action effects can significantly change the resonant response of the cantilevers. We conclude that the effects have to be taken into account, particularly in the case of ultra high sensitivity cantilevers.@en

Laser beam deflection is a well-known method commonly used in detecting resonance frequencies in atomic force microscopes and in mass/force sensing. The method focuses a laser spot on the surface of cantilevers to be measured, which might change the mechanical properties of the cantilevers and affect the measurement accuracy. In this work we showed that the joule heating of the laser, besides other extrinsic effects such as surface contamination, can cause a significant amount of shift in the resonator. The longer and softer the cantilever is, the more significant the effect. We suggest that the laser effects on the resonant response of sensors have to be taken into account.@en

Measuring frequency shift of a resonator to obtain information on mass and force is common in the fields of micro-electromechanical systems (MEMS). Typically on a cantilever structure, the method uses the spring-mass equation of the cantilever, together with the measured frequency shift, extracts the force parameters and makes a sensor. Although popular and widely accepted as a good method, we showed in our work that this method has a fundamental problems and may induce large errors if scaling the device into nanometer dimensions. The problem is mainly because the frequency shift method cannot decouple force change from stiffness change, therefore surface contaminations, adsorptions of the atmospheric elements can cause the cantilever to shift its resonance frequency without any external force interaction. We showed in this work the importance of the issue and experimentally measured the surface induced error; furthermore, the more sensitive the sensor, the more susceptible it may be to this fundamental issue of the frequency-shift method. We found out that by simply exposing the device to ambient environment is enough to cause a significant error in the measurement.@en