UM-StL Scanned Tip & Electron Image Lab's
Feb'96 Image of the Month

For us "lateral displacement microscopy" refers to the study of images inferred by examining distortions BETWEEN PAIRS of scanned probe images, taken of the same surface with different scan directions. The distortions are calculated using algorithms similar to those used for quantifying height maps from stereopairs. The image contrast is PROPORTIONAL to coefficient of friction, rather than just affected by it, since the normal force terms which complicate lateral force microscope images cancel. For more on this, see "Lateral Displacement Microscopy of Holograms using Scanned Tip Image Pairs" by C. Shen and P. Fraundorf in Microscopy Society of America's Proceedings Microscopy 1993, San Francisco Press, p. 534-535.

We now predict that specimen hardness will play a role in SFM displacement, but not in air-STM displacement, images. As a challenge to those who might enjoy thinking about this, or better taking data along these lines, we've posted a couple of simulated images -- an SFM image of a cosine ripple i.e. cos[|r|], and an air-STM image of intergrown hemispherical bumps -- as our February '96 images. The SFM image is calculated assuming that the specimen deforms if the normal force of the tip exceeds a critical value. The question posed here: Can you tell us what that critical force was for this image, in units of the vertical force set point of the microscope?

Just something to think about, for those so inclined. No prizes for the correct answer, yet, except perhaps an opportunity for some interesting collaborations.{CS,PF}

Questions and proposed answers invited. Phil Fraundorf