Advances in ultra-low contact force nanometric surface metrology

This dissertation describes the theoretical design, practical construction and experimental use of a novel profiler intended to bridge the gap between atomic force microscopes (AFMs) and conventional stylus instruments. More specifically, it may be regarded as a hybrid instrument, combining the long-range of stylus instruments with the low contact force, high-speed operation of the AFM. The heart of the new instrument is a miniature capacitance-based force probe, constructed of glass and ceramic materials chosen primarily for thermal stability. This force probe can sense forces encompassing the range from atomic force levels (10¯7 N) to stylus instrument levels (10-⁴ N). Probes used in subsequent studies range from ISO standard spherical diamond styli (radii 2, 5 and 10 ᶙm) to 20 nm radius Berkovich diamond tips. A custom designed low excitation voltage, high frequency capacitance gage, used to monitor the sub-nanometer displacements of the force probe is presented. To measure surface profiles, the force probe is mounted on a PZT actuator and, much like an AFM, follows a contour of constant force under servo control. The specimen traverses underneath the force probe on an ultra-precision kinematic slideway using a flat glass datum surface and polymeric dry bearings. A novel, inexpensive laser interferometer used to monitor specimen position and control data acquisition of the profiler is described. In this manner, profiler repeatability is enhanced to the nanometer level in two axes. Profiler performance is tested for repeatability, noise force servo bandwidth and temperature stability. A force servo response bandwidth of 300 Hz was ascertained. This compares favorably with the sub- ten Hz responses of stylus instruments. A series of experiments designed to validate the high-speed performance of the profiler are presented. This high speed operation is some 10 to 100 times faster than conventional stylus instruments. Dynamic, non-linear interactions between the stylus tip and specimen are first derived and then examined experimentally. These dynamic interactions may eventually make it possible to measure specimen internal damping and interface stiffness or mechanical properties at the point contact level