Number 195 (Story #2), September 20, 1994 by Phillip F. Schewe and Ben Stein A MAGNETIC FORCE MICROSCOPE (MFM) produces images of a superconductor's surface through the detection of the force between a magnetic cantilever-mounted probe tip and the sample, which tries to repel magnetic fields. The MFM technique can attain a spatial resolution of 20 nm, which is not as good as is possible with a scanning tunneling microscope (STM). However, since it senses a much larger volume of the sample at any one moment, MFM is not nearly as sensitive as STM to surface cleanliness or order. This might make MFM a better tool than STM for characterizing superconductor surfaces. The MFM can also image non- superconductor materials. As a demonstration, a team of scientists at the University of Texas and Park Scientific Instruments (Sunnyvale, CA) has used their MFM device to image magnetic structures in VHS tape at room temperature, at 77 K, and at 6 K. (C.W. Yuan et al., Applied Physics Letters, 5 Sept. 1994.)