Charge redistribution in electrochemically actuated mechanical sensors

Abstract

to real-life applications also requires the monitored mechanical effect to be highly specific. Moving towards more specificity in cantilever-based sensing, monitoring the mechanical response of electrochemically actuated microcantilevers is then thought to provide a fast, reliable and complementary experimental information to the longtime cantilever bending measurement for the detection of target molecules. Full-field measurements are therefore used to investigate the way the electro-elastic coupling is altered when a microcantilever undergoes decane-thiol adsorption. The proposed technique reveals that the latter results in a charge density redistribution along the cantilever in addition to the local surface passivation. Focusing on the cantilever tip displacement under electrochemical actuation, this redistribution partially compensates the electro-elastic coupling alteration due to the surface passivation, therefore possibly yielding an ambiguous detection result. This effect should be taken into account for the optimal design of specific electrochemically actuated mechanical sensors.

Effect of surface charge state on the surface stress of a microcantilever

“…Plugging equation (22) ( ) ( ) s = / Formula (29) or (30) is the well-known Stoney's equation [47], which is often used in the process of quantifying surface stress when the cantilever deformation is recorded by the laser-optical-lever technology. The equivalence of equations (28) and equations (29) or (30) indicates that our model (i.e. equation (28)) is actually an alternative version of Stoney's equation in terms of the film electrical properties, and the well-known old version in terms of the cantilever deformation actually conceals the film electrical properties, because the cantilever deformation is closely related to the film electrical properties.…”

“…However, there are few papers to quantify this electromechanical coupling effect. Amiot et al [28] used a full-field laser interference measurement to observe the relation between the cantilever displacement under potential actuation and the electromechanical coupling effect due to the surface passivation. Fritz et al [29] calculated the surface potential for a given change in surface charge density by the Grahame equation.…”

Adsorption induced surface-stress sensing signal originating from both vertical interface effects and intermolecular lateral interactions

“…Besides the above discussed factors, at the interface, the charge redistribution is believed to play an important role in the generation of surface-stress. 25,26,32 Godin et al used the charge redistribution to explain the independent surface-stress response of the molecular chain-length of self-assembled thiols on gold. 17 In addition to the molecule adsorption modifying the surface's local free energy, redistribution of the electronic structure of the substrate surface-atoms will change the surfacestress.…”

Electro-elastic coupling modelling from multiple wavelengths imaging microscopy

“…A lot of previous studies focus on redox reactions between electrolyte and solid electrode [9], but [10][11] report ways to identify adsorbed molecules without involvement of electrochemical reactions. However the exact mechanisms underlying the electro-elastic coupling when a molecule is adsorbed are described qualitatively and not quantitatively [10,12]. Multiple wavelengths imaging microscopy provide both the local surface electrical charge density and the deformation field by decoupling wavelength-dependent andindependent (ie kinematic) contributions to the collected intensity [13].…”