Frequency-modulated atomic force spectroscopy on NiAl(110) partially covered with a thin alumina film

Force spectroscopy has been performed using a low-temperature scanning tunneling microscope (STM) and atomic force microscope (AFM) with small amplitude frequency modulation (FM). Frequency shift versus distance curves acquired on NiAl(110) are compared to measurements performed on a thin alumina film. Interaction force and energy are determined from the frequency shift. Due to the high stability of small amplitude frequency modulation in combination with a stiff force sensor, it is possible to observe clear differences in the interaction potential between the metal and oxide surface. The setup also allows us to gain specific information in the repulsive regime of the contact formation, where elastic and plastic stages have been identified.