Professur Analytik an Festkörperoberflächen
STM at low temperatures (»20K):

Coronene tends to form islands on a graphite surface. 

These islands are randomly distributed with apparent 
heights between 1.5 nm and 2.5nm. 

At room temperature the coronene clusters are 
mobile on the surface and can be pinned by 
defects, like the step edge running from A to B.

Changes of the effective tip length due to collection 
or deposition of molecular clusters lead to 
abrupt changes of substrate (=background) height.

An example is marked with white arrows in the image.
Zoom beneath the islands:

All islands lie on a closed monolayer of coronene molecules according to the Stranski-Krastanov growth mode. 

The molecules arrange in a hexagonal pattern.

A formation of seven single molecules is marked in the image by the white circles.

The internal structure of each single molecule 
shows seven bright spots, representing 
the p-electron clouds. 

Interaction with the substrate leads to a modulation of 
these spots - because of the commensurability of the coronene layer - in the same way for each molecule. 

This leads to a brightest spot (marked by the arrow) 
always on the same position within the molecule.

M. Lackinger, S. Griessl, W.M. Heckl and M. Hietschold,
“STM and STS of Coronene on HOPG(0001) in UHV –Adsorption of the smallest possible Graphite flakes on Graphite”,
Analytical and Bioanalytical Chemistry, submitted (2001).

M.Lackinger, 2002