MEMS and NEMS (Micro and Nano Electro-Mechanical Systems) presently undergo a wide development within the framework of the Nanomechanics. The efficient operation of these MEMS / NEMS requires the control and knowledge of fundamental interactions between surfaces separated by distances of the order of 100 nm to 1 micron. At this scale, dominant forces can have different origins (van der Waals, Casimir effect, electrostatic, magnetic...). This thesis presents an experimental study by AFM of the electrostatic and Van der Waals/Casimir interactions between a microsphere and a metallic surface. First, characterisation of the sensors that is based on a microsphere glued onto a cantilever beam is presented. Sensitivity of our measurements determined by noise analysis is shown to provide us with a resolution in the subpiconewton range. In static mode (i.e. cantilever deflection measurement), we have precisely measured capacitive forces of the order of few dozens of piconewton in the 100 to 500 nanometer range. We have also measured and quantified the cantilever deflection effects on the determination of the sphere-surface distance. By dynamic measurements (cantilever as an oscillator at resonance), we studied the coupling between the oscillator mechanically or thermally excited and a surface under the influence of Casimir effect. Finally, dynamic mode measurements allowed us to study dissipation mechanisms associated to long range interactions. For example, we have observed the damping induced by electromechanical coupling.
