Atomic Force Microscope: Implementations

Abstract

Our version of the atomic force microscope (AFM), and variants which measure electric and magnetic force are described from an engineering viewpoint. Discussion centers on design and performance issues, with emphasis on application to magnetic recording. The basic force probe consists of an L-shaped wire cantilever, whose end is etched to a radius of less than 1000 A, mounted on a piezoelectric bimorph When the tip is held close to a sample, forces between tip and sample modify the dynamical properties of the resonant cantilever; the force gradient changes the effective spring constant, and thus the resonant frequency. Vibration of the tip is measured by heterodyne interferometry, a technique about as sensitive as tunnelling but easier to set up and insensitive to slow drifts. By driving the tip near resonance, the change in the resonance frequency is translated into an amplitude shift; force gradients of 10^-4N/m and force increments of 10^-13N have been measured in this way. This atomic force probe has achieved lateral resolutions of 50 A, and there seems to be no fundamental impediment to achieving atomic resolution. The magnetic force microscope (MFM) is very similar. It uses a steel wire tip to measure magnetic field or field gradient with a spatial resolution of better than 1000 Å. Data are shown, which demonstrate the usefulness of magnetic imaging for profiling the field patterns in recording heads and disk media.