Open discussion of papers by Rohrer, Becker, and Hansma

National Bureau of Standards, Gaithers- burg, MD): I would like to ask Heinrich Rohrer if he could- he had just very briefly showed us something that looked like magnetic information in one of his pictures-give us a few more seconds of discussion of what that was and how it works.DR. ROHRER: That was a tunneling experiment, not an atomic-force experiment, and the tip, as I said, was a film of cobalt/chromium.This experiment is a combination of force mapping and tunneling; you do it at the same time.The magnetic forces act on the film from which you tunnel.When the tip comes close to a domain wall or something like that, it is deflected in one way or another.We do not know the structure of the tip in this case, but we simply correct the deflections by moving the tip closer or further away until we have the originally set tunnel current.This is the combination of, let's say, force mapping with the tunneling microscope.The tip itself plays the role of the soft level in the atomic force microscope.If you are just interested in rough features, I think that this is a very convenient way of magnetic imaging.It is a very simple experiment with a very simple instrument.CYNTHIA FRIEND (Harvard University, Cambridge, MA): This I would like to direct to Dr. Rohrer and Dr. Hansma.You discussed diffusion of oxygen atoms on nickel, but I wonder if you could comment more generally if you see diffusion induced on surfaces of atoms and possibly small molecules, and if you can bracket a range in which you think you could possibly image molecules like smaller adsorbates.DR. ROHRER: You mean image when they diffuse under the tip or . . .?DR.FRIEND: In other words, do they diffuse?Let's say you wanted to look at CO on some transition metal, for example.Can you image it without inducing diffusion, and are there