Local Elasticity and Lubrication Measurements Using Atomic Force and Friction Force Microscopy at Ultrasonic Frequencies

We have modified and Atomic Force Microscope (AFM) that allow the detection of cantilever bending as well as torsional vibrationsat ultrasonic frequencies. Oscillatingeither probe tip of 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 of 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