Rowland Institute
at Harvard

 

 

Atomic Force Microscopy | Torsional Harmonic Cantilever

Atomic Force Microscopy

Atomic force microscope (AFM) has been the workhorse of nanotechnology as it allows to image samples with nanoscale spatial resolution. Biological molecules, carbon nanotubes, semiconductor devices, cells, viruses, and many more materials can be investigated with this microscope. (Learn More about AFM)

The most common operation mode of AFMs is the tapping mode. The animation to the right is illustrating the basic operation mechanism. Here the force sensing cantilever is vibrated on resonance. When the cantilever is scanned across the surface, vibration amplitude changes in response to the bumps and grooves on the surface. A feedback loop keeps the vibration amplitude constant by controlling the separation between the base height of the cantilever and the sample,. Then, the feedback signal corresponds to the topographical map of the surface.

 

One of the biggest goals in imaging nanoscale objects is to achieve the ability to identify chemical composition and material properties. Such an ability will not only improve our understanding of novel materials, but also provide new types of biological and chemical sensors. Our goal is to use the platform of the tapping-mode imaging to measure mechanical properties of the surfaces at the molecular scale. The animation above shows time variation of tip position (top right row), interaction forces (middle row), and the harmonic content of the interaction forces (bottom). There are two different materials on the surface; green (stiff) and gray (compliant). If you look at the tip sample force waveform, you can see that it is changing from one material to the other. We have developed special AFM cantilevers to measure these forces and extract quantitative information about material properties. We use this technique on a variety of biological and materials science related problems. Check our cantilever page to learn more about these special cantilevers.