Christian H. Schwalb, SCL Sensor.Tech. Fabrication GmbH, Vienna, Austria
Correlated AFM & SEM Microscopy of Nanostructured Materials
Written by Vineet Venugopal
Using two different kinds of imaging can give scientists a powerful combination of high specificity and detailed structural information, Nature wrote in a feature in 2013. Combining an atomic force microscope (AFM) and a scanning electron microscope (SEM) seems like the obvious next big merger. Both give complimentary information about the surface. While the SEM takes high resolution images, the AFM probes the surface with a sharp tip—yielding not just topographical information but also electro-chemical-mechanical properties. However, to determine the position of the tip, the AFM relies on a laser signal reflected off the back of the cantilever and onto a photodiode—a mechanical setup that is too cumbersome to be integrated with an electron microscope. Christian Schwalb and his team at SCL Sensor Tech, with other collaborators, have overcome this restriction by employing piezoresistive cantilevers that generate an electrical signal based on their deflection, overcoming the light sensor hurdle. They demonstrate that the noise level with their “AFSEM” is comparable to other AFMs if they use a smaller probe size. This is possibly because the sensitivity of the cantilever is proportional to the stiffness which is inversely proportional to size. Not using the laser system means that the AFSEM is instantly operational (like a Chromebook) with no lead time. The next step in this correlated microscopy is correlated analysis for which the group is collaborating with the Chinese Academy of Sciences to develop more intelligent probes. At this stage the AFSEM can work in the contact and AC modes.