Study of the interfacial shear strength pressure dependence by modulated lateral force microscopy

By combining lateral contact stiffness and friction measurements versus loa d obtained by modulated lateral force microscopy (MUM), the shear strength dependence on contact pressure can be studied. The adjustment of the elasti city contact theories to the experimental data also allows one to study the variation law of the friction force. Measurements on silicon oxide, mica, carbon fibers, and epoxy in ambient air and under a vacuum are presented. T wo behaviors of the shear strength have been observed depending on the natu re of the contact between tip and sample and on the environmental condition s. The shear strength presents either a linear dependence with the contact pressure or stays constant, i.e. independent of the pressure. When it depen ds on the pressure, the friction force apparently is proportional to the lo ad; when it stays constant with varying pressure, the friction force is pro portional to the contact area.