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Molecular Vista | VP, Engineering and Technology

Dr. Thomas Albrecht

AFM in the Early Years:  From Foil and Diamond to Microcantilevers, and from Tunneling to Optical Sensing

 

 

 

Abstract

The Atomic Force Microscope, in its infancy, was quite different than the commercially available tools now commonly in use.  Gerd Binnig, Christoph Gerber, and Cal Quate created the first AFM at Stanford out of spare STM parts, plenty of double-stick tape, and a hand-made metal foil cantilever with a diamond shard as the tip.  Tunneling detection was used to sense the motion of the back of the cantilever using a common tungsten STM tip.  Although tunneling detection had excellent displacement sensitivity, it soon became apparent that significant forces act between the tip and cantilever, particularly in air, which compromise the ability of the AFM to work with very small forces.  Optical sensing methods such as the optical lever or interferometer were superior and eventually replaced tunneling entirely.  Binnig and Quate recognized immediately that minimizing the size and mass of the force-sensing cantilever in the AFM would offer significant advantages in speed and sensitivity.  As the first graduate student for AFM, I was assigned to work in Stanford's microelectronics lab to create microcantilevers, a successful project which (along with a similar project at IBM in Germany) set the direction for AFM cantilevers still in use today.  Cantilevers from Stanford were used by various groups around the world, and microcantilevers were eventually made commercially by many companies.  I will also discuss early AFM results from Stanford using tunneling detection, including the first demonstration of sensing atomic corrugations on electrically insulating layered materials.  Although this demonstration is no longer viewed as a true atomic resolution, it launched AFM on an eventually successful quest to demonstrate the same level of resolution as STM.  I will also touch on later developments such as FM detection in vacuum for AFM, and the pursuit of my current company Molecular Vista — the combination of IR spectroscopy with AFM to achieve mechanically-detected IR absorption spectroscopy with nm-scale spatial resolution.

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