Figure 2

(Color) Examples of nonperiodic features in STM images of hematite (001) surfaces. (A) A 60 × 60 nm image (in air), -500 mV, 726 pA, 300 pA z range (current contrast). This image shows a semiperiodic modulation of the terrace structure with a ~2 nm periodicity, as observed in Ref. 19, and which typically involves height differences between high and low points of about 0.1 nm. In Ref. 19 it was concluded that the higher parts of the modulation are domains of Fe termination. Atomic-scale structure can be discerned in some parts of the image. There are a few nonperiodic bumps on the terraces, but they are most common along the steps. (B) A 20 × 20 nm image (in air), -800 mV, 500 pA, z range 0.5 nm. In this image there is a highly periodic surface structure punctuated both by a few protruding "bumps" as well as slight depressions. Again, there are more of these features along the step.