A common tool for uncommon measurements: Adventures in atomic force microscopy

Many people are familiar with the atomic force microscope, but fewer have experience using its capabilities to do more than image the topography of a sample, usually in air. In this talk, I’ll present three different subfields of research that all involve the atomic force microscope. The “force curve” enables the measurement of mechanical properties, including Young’s modulus and adhesion. Normally, the tip is brought into contact with a surface, and the force required to push into the sample is measured. We have used the AFM to image natively adhered bacteria to surfaces in fluid and perform force curves on individual bacteria. We have also grown the biofilm on a cantilever and brought it into contact with different surfaces, to study the early stages of adhesion. Magnetic force microscopy (MFM) may be a familiar technique that can reveal the magnetic state of nanostructures. In rings of the correct size, there is a vortex state in which all moments lie circumferentially in plane, creating a closed-flux state that does not have any MFM contrast in a perfectly symmetric ring. It is challenging to experimentally control the clockwise or counterclockwise circulation of this vortex state with a uniform external applied field. Instead, we pass a current through a solid platinum AFM tip in order to create a local circular Oersted field to probe the magnetic behavior of rings and discs. Finally, I’ll present our current efforts using Kelvin probe force microscopy (KPFM) to image real-time charge motion in organic semiconductors. All of this work was completed in my lab at Mount Holyoke College, where I have mentored 50 undergraduate women over the past thirteen years.