Mechanical properties of atomic force microscopy probes with deposited thin films

• Diamond like carbon and fluorocarbon thin films have been deposited on commercial AFM probes.
• Thermal noise measurements showed changes of force constant and resonance frequency of the AFM probe cantilevers.
• A theoretical model accounting for the effect of thin film deposition on the AFM cantilever properties is proposed.
• Changes of the cantilever mechanical properties are used to determine the elasticity and density of the deposited films.

Deposition of thin films on atomic force microscopy (AFM) probes is a common technique that is used to either improve the light reflectance of the back side of the probe cantilevers or to modify the surface properties of the probe tips. However, this technique also affects the force constant and resonance frequency of the AFM cantilevers. The present work investigates theoretically this effect in the approximation of very thin films. The cantilever force constant changes due to the contribution of bending moment of the elastic force in the deposited film, while the resonant frequency changes due to the film contributions to the bending force and inertia of the cantilever. It is found that the relative variations of cantilever force constant and resonance frequency depend on the film to cantilever thickness, density and elasticity modulus ratios. This theoretical prediction is confirmed by the experimental investigations on mechanical properties of silicon cantilevers covered by diamond like carbon (DLC) and fluorocarbon thin films obtained by high power impulse magnetron sputtering depositions. Moreover, the effect of film depositions on the cantilever mechanical properties is used to determine the elasticity modulus and mass density of the deposited thin films.