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nanotimes
10-02 :: February 2010
News in Brief
within the Cluster of Excellence “Nanosystems Initia- responds to the state with the lowest energy. “In the
tive Munich” (NIM). The problem was tackled using end, we were able to show that the molecular geo-
an approach from statistical physics known as Monte metry and a few salient features encode the structu-
Carlo method, which allows one to conduct a detail- ral motifs observed,” explains theorist Franosch.
ed computer simulation on the statistics of molecular
interactions. The structural motifs so generated were “We plan to extend the approach to other types of
compared with experimental high-resolution images surface symmetries, but the model already provides
of molecular patterns obtained by STM. an important theoretical tool, because it helps us to
forecast the type of surface pattern that a given func-
Marta Balbás Gambra, a doctoral student, began tional molecule will form. This means that the design
each simulation with a mathematical representation of molecules can be optimized during the synthetic
of a collection of hundreds of randomly oriented phase, so as to obtain surfaces with the desired cha-
particles of defined conformation. These schematic racteristics”, says Hermann.
molecules were then perturbed by – computationally
– adding energy, causing the population to adopt The physicists in the group, who come from different
a new configuration. Using this simulation strategy, scientific backgrounds and were able to pool their
one can generate a greater variety of patterns than expertise for this project, envisage multiple potential
are found naturally, and many of these corresponded applications for their model in molecular electronics,
closely to the real molecular patterns revealed by sensor technology, catalysis and photovoltaics.
STM.
C. Rohr, M. Balbs Gambra, K. Gruber, E. C. Constable, E.
“In one case we actually predicted a pattern that was Frey, T. Franosch and B. A. Hermann: Molecular Jigsaw:
only later verified with STM,” reports doctoral stu- Pattern Diversity Encoded by Elementary Geometrical Fea-
dent Carsten Rohr. tures, In: Nano Letters, February 16, 2010, DOI: 10.1021/
nl903225j:
According to the laws of thermodynamics, physical

http://dx.doi.org/10.1021/nl903225j
systems tend to adopt the state with the most favou-
rable (i.e. lowest) energy. Experimental tests showed

http://www.wmi.badw-muenchen.de/spm/
that different molecular configurations interconvert
until an arrangement predominates that is reminis-
cent of tyre tracks. And indeed, the Monte Carlo
approach had predicted that this arrangement cor-