Photothermally driven AFM of soft matter samples

P. van Schendel, P. Frederix, H. Gunstheimer, E. Nelson, D. Ziegler, C. Bippes, J. Adams

Keywords: photothermal excitation, mass measurement, off-resonance imaging, mechanical properties


Since its invention in 1986, the atomic force microscope (AFM) has evolved into a multifunctional toolbox. Although there have been many developments towards improving the fundamental elements of an AFM – the scanner, controller, deflection detection system, and AFM cantilevers – most AFM systems still rely on a dither piezo to induce oscillation of the tip. In recent years, photothermal excitation – an intensity modulated light source directed onto the cantilever – has shown significant benefit over the standard dither piezo for clean and stable tip oscillation. Such improvement has enabled mass measurements of live cells with high temporal and sub-nanogram mass resolution. However, photothermal excitation also provides the ability to excite the AFM cantilever in new ways. Cantilever oscillations can be driven from high frequency all the way to static DC deflection. Taking advantage of this effect, WaveMode is an off-resonance imaging mode that uses photothermal excitation to overcome the speed limitations of conventional off-resonance imaging modes. Here, we will present an overview of new developments and advances in how a photothermal excitation can be used to investigate different properties of many different materials, such as soft biological samples, in greater detail. We will show that the effect of the second laser on the temperature of cantilever tip can be controlled, and will highlight examples of imaging applications, mechanical property measurements as well as cantilever-based mass measurements.