Professur Analytik an Festkörperoberflächen
Room temperature STM image:

Few coronene molecules (bright spots) are 
deposited on a clean Ag(111) single crystal surface.

Each molecule is surrounded by a standing wave 
pattern, created by scattering of surface electrons.

Average of the tunneling current vs. distance 
to the center of the molecule 
(numbering refers to the left image)

 
Closed layer of coronene molecules on Ag(111)

The molecules arrange in a hexagonal dense packing, which is also confirmed by LEED measurements.

Due to thermal drift and piezo hysteresis the molecular arrangement appears  somewhat asymmetric, 
indicated by the white hexagon in the image.
Close up of the image above:
By quantitative LEED analysis we know the 
unit cell vectors of the coronene adlayer. 

These vectors were used for distortion 
correction of the image above. 

Furthermore a correlation averaging with a close 
up was applied for noise reduction of the image.

Each single molecule appears brighter 
(higher tunneling current) on the right side.

Based on earlier NEXAFS measurements 
we believe the reason to be a tilt of the 
molecular plane against the substrate

M. Lackinger, S. Griessl, W.M. Heckl and M. Hietschold,
“Coronene on Ag(111) investigated by LEED and STM in UHV”,
J. Phys.Chem. B 106, 4482-4485 (2002)

M.Lackinger, 2002