High confidence level calibration for AFM based fracture testing of nanobeams

Abstract

When designing micro- or nanoelectromechanical systems, (MEMS and NEMS), it is important to consider whether structural elements will withstand loads experienced during operation. Fracture behavior at length scales present in MEMS and NEMS is much different than at macro- and mesoscopic scales. Due to a smaller probability of crystal defects and a high surface to volume ratio, fracture is controlled by surface characteristics rather than volumetric ones. Prior measurements using doubly clamped Si beams loaded with an atomic force microscope (AFM) showed that fracture of Si nanobeams is highly affected by surface roughness (Alan T et al., Appl Phys Lett 89:091901, 2006) and oxidation (Alan T et al., Appl Phys Lett 89:231905, 2006). In experiments of this type, calibration of the system, particularly the AFM cantilever stiffness, is critical to the accuracy of both the force and displacement results. A new set of experiments are underway in which the tests are performed by adapting a direct, traceable method for calibrating the AFM cantilever stiffness (Ying ZC et al., Rev Sci Instrum 78:063708,2007). The improved calibration should not only improve the accuracy of the strength results but will allow linear stiffness measurements of the sample to be used to back out sample thickness, a key parameter in interpretation of the data. © The Society for Experimental Mechanics, Inc. 2013.