Book of Abstracts Book of Abstracts - Universität Konstanz

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126
Phase Changes in Clusters: Targets for Experiments
R. Stephen Berry 1 , and Ana Proykova 2
1 Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago,
Illinois 60637, USA
2 University of Sofia, Faculty of Physics, 5 James Bourchier Blvd, Sofia 1126, Bulgaria
It is now well established that some clusters exhibit the finite-system counterparts of firstorder
transitions, and that these differ from bulk phase transitions insofar as clusters may exist
in two or more phases in observable amounts, in thermal equilibrium. It is also apparent from
simulations that bulk second-order transitions may have small-system analogues that have either
one or two local free-energy minima, corresponding to second-order-like or first-order-like
behavior. These findings raise several questions that await experimental study. One is the
observation of sharp upper or (more likely) lower temperature bounds for the local stability of
the unfavored phase. A second is the possibility of observing and distinguishing between cases
in which phases persist long enough to exhibit well-defined, measurable characteristics and
cases in which the dynamic equilibrium between the phases is so labile that no well-defined
distinguishable phases can be observed. Still a third challenge is the possibility of observing
phase changes or phase coexistence that look first-order-like in small clusters but become
second-order in the large-system limit. With this challenge is the alternative of true secondorder-like
behavior in which multiple phases do not coexist because the free energy has only a
single minimum. All of these are experimental investigations that will almost certainly require
monodisperse cluster samples, because the phase behavior of small clusters is highly variable
and not at all monotonic with cluster size.