Local elasticity and lubrication measurements using atomic force and friction force microscopy at ultrasonic frequencies

We have modified an Atomic Force Microscope (AFM) that allows the detection of cantilever bending as well as torsional vibrations at ultrasonic frequencies. Oscillating either probe tip or sample vertically modulates the normal force about the setpoint force, acting between tip and sample. When the tip contacts the sample, the surface resists the oscillation and deformation of the sample is dependent on the local stiffness or elasticity. For a constant normal force, a soft area deforms more than a hard area and thus the cantilever deflection is less over a soft area. The variations in cantilever vertical oscillation is a measure of relative elasticity of the sample. Elasticity maps with a lateral resolution of better than 100 nm have been taken on alumina-based ceramic composite, and on two metal particle (MP) recording tapes. By vibrating the sample laterally, the shear forces are modulated. Detecting and analyzing the cantilever torsional behavior, we are able to characterize friction and viscosity of thin films used for lubrication of magnetic disks.