A high-stiffness axial resonant probe for atomic force microscopy

A high-stiffness, (>500 N/m) resonant atomic force microscope probe was constructed to allow force measurements in the presence of large force gradients. The probe employs a piezoresistively detected, electrostatically driven resonant beam sensor oriented perpendicularly to the sample surface. This probe is distinguished from shear force microscopy and noncontact atomic force microscopy in that the design allows for a stationary probe tip for improved spatial resolution and measures forces rather than force gradients. Measured results show a force resolution of 9 nN in a 1-kHz bandwidth in air with an oscillation amplitude of 36 nm and a resonance quality of 20. In a 1-mtorr vacuum the force resolution in the same bandwidth improves to 200 pN with a resonance quality of 450 and oscillation amplitude of 53 nm. This resolution is limited by white noise of the piezoresistor, and scales as expected with amplitude and resonance quality