Photonic Excitation of a Micromechanical Cantilever in Electrostatic Fields

Abstract

We present a specific near-field configuration where an electrostatic force gradient is found to strongly enhance the optomechanical driving of an atomic force microscope cantilever sensor. It is shown that incident photons generate a photothermal effect which couples with electrostatic fields even at tip-surface separations as large as several wavelengths, dominating the cantilever dynamics. The effect is the result of resonant phenomena where the photothermal-induced parametric driving acts conjointly (or against, depending on electric field direction) with a photovoltage generation in the cantilever. The results are achieved experimentally in an atomic force microscope operating in vacuum and explained theoretically through numerical simulations of the equation of motion of the cantilever. Intrinsic electrostatic effects arising from electronic work-function difference of tip and surface are also highlighted. The findings are readily relevant for other opto-micromechanical systems where electrostatic force gradients can be implemented.

Near‐Field Nano‐Optical Imaging of van der Waals Materials

“…Accordingly, the measurement of the force gradient through heterodyne detection suppresses the contributions owing to the scattering force and the photothermal effect on the cantilever, where the laser excitation impacts the cantilever dynamics. [99][100][101][102][103] The PiFM signal also involves photothermal force originating from the sample expansion after optical absorption that is mediated by the noncontact vdW force, which is termed the thermally modulated vdW force. In addition, there is the thermally induced photoacoustic force due to acoustic wave propagation (in a nonvacuum medium) and the optomechanical damping caused by the vibrating cantilever.…”

Photothermal Plasmonic Actuation of Micromechanical Cantilever Beams

“…Note that the photothermal effects are large in coated cantilevers due to the bimorph effect [41,66]. This makes negligible the contribution of other photoinduced driving mechanisms, such as photovoltage [67] or radiation pressure [68] effects. The resulting equation of motion including the photothermal actuation and the surface forces can then be written as:…”

Detection of magnetic force fields at macroscopic distances with a micromechanical cantilever oscillator

“…In addition, the results can be of interest for direct excitation methods of micromechanical cantilevers, where a driving force is directly applied to the cantilever without acoustic transmission through additional components, methods particularly valuable when operating in liquids. Along with photothermal driving 43,44 , magnetic excitations of cantilevers are indeed possible by attaching a magnetic bead to the cantilever 45,46,47 or by coating the cantilever with a magnetic thin film 48 .…”