Oct 13, 2009
Thermal noise highlights viscoelasticity in micro-cantilever
Researchers based at the Université de Lyon, France, have discovered an unexpected 1/f like thermal noise spectrum below the first resonance of an AFM cantilever thanks to the low detection noise of their homemade interferometric AFM deflection sensor.
The fluctuation-dissipation theorem links the observed behaviour to a frequency independent dissipation process: the stiffness of the cantilever has a small constant imaginary part that describes the inner dissipation processes (as opposed to viscous damping by the surrounding atmosphere, which is roughly proportional to velocity, and thus frequency).
To go further than the simple observation, Ludovic Bellon and his team reconstructed the full mechanical response of the cantilever from Kramers-Kronig relations to end up with a phenomenological description of this viscoelasticity, which is shown to arise from the presence of a metallic coating on the micro-lever.
The result could lead to improved coating procedures and would also suit the study of cantilever-based chemical or biological sensors.
The researchers presented their work in the journal Nanotechnology.
About the author
Ludovic Bellon is a CNRS researcher and P. Paolino is his PhD student in the physics laboratory of the ENS de Lyon, Université de Lyon. Based on their homemade enhanced force resolution AFM, the group is currently exploring applications of thermal noise in the area of nano-physics.