Professor Peter M. Hoffmann
At the core of our research is the development and application of novel Atomic Force Microscopy (AFM) techniques. AFM is a powerful tool for measuring and imaging forces at the atomic scale. It can be used in any environment, including liquids, and has applications in surface physics, nanotechnology, materials science, chemistry, and biology. However, not all AFM's are created equal, and in our laboratory we focus on the application and further development of a novel AFM technique, which is optimized for quantitative local measurements of nanomechanical phenomena. This is achieved by using a dynamic measurement method in which the cantilever is oscillated at ultra-small amplitudes of less than 1 Ångstrom and monitoring changes in this amplitude as the surface is approached or the lever is scanned across the surface. Such a small amplitude allows to perform linear and local measurements of force gradients and forces. To measure changes in such a tiny amplitude we use a highly sensitive, optical fiber interferometer mounted to a sub-micron resolution manipulator. The interferometer can achieve several 100 mV signal per 1 Ångstrom deflection and can measure amplitude changes that correspond to a few hundredth of the diameter of a single hydrogen atom. Using such a small amplitude enables us to completely map any interaction point-by-point and achieve atomic resolution force gradient images at fixed separations. While we operate one instrument in ultra-high vacuum (UHV) for atomic resolution work, our technique also works well in liquids. We have build new small-amplitude AFMs operating in liquids. Interactions we have measured include bonding between single atoms (in UHV) and ordering of water molecules in a confined geometry (in liquid). We can also measure currents, charges and fields at the molecular/ atomic scale as well as atomic scale energy dissipation and molecular shear forces in liquids. Current research includes forces, structure and dynamics in confined liquids and forces associated with in biological macromolecules such as lipids and proteins.
To learn more about this research, visit http://www.physics.wayne.edu/~hoffmann/