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Appendix B. Site Reports—Europe 217
4. cluster ion-surface scattering including the determination of
fragmentation, delayed ionization, and neutralization rates upon
collisions to obtain activation energies
5. probes of cluster ion penetration into HOPG, including tailoring of
surface morphologies by controlled etching of nanometer-sized impact
defects
The laboratory is well equipped, having several molecular/ion beam
systems, many different laser systems for spectroscopic and particle
generation, ultrahigh vacuum (UHV) STM for surface studies, Ti-Sapphire
laser-based Raman spectrometer, HPLCs for fullerene extraction, and
purification, among other equipment.
In addition to its experimental effort, the Kappes group collaborates with
the theory group of Prof. Ahlrichs. Each PhD student may be expected to
spend about one-quarter of his/her time performing theoretical studies,
perhaps calculating electronic spectra of fullerenes, alkali clusters or
transition metal clusters, properties of isomeric structures, and/or model
spectra, e.g., IR or Raman, for many of the new neutral and ionic species
being studied.
Research in Prof. Fenske’s Group
Prof. Fenske’s group consists of about 15 PhD students and has
historically focused on synthesis and structure/X-ray, primarily of new metal
calcogenide molecular clusters. In addition to the effort on synthesis, more
recent studies are now directed to probing the stability of the ligandstabilized
clusters, via ligand alteration and cluster size and composition.
One goal is to synthesize molecular clusters of well-defined size and
geometry in order to investigate quantum confinement in such species.
Recent successes are in the area of copper selenium molecular clusters
stabilized by the protective ligand field of (PEt 2 Ph) x . As an example,
molecular clusters with cores of Cu 20 Se 13 , Cu 44 Se 22 , up to Cu 70 Se 35 , have
been synthesized and characterized. The structures of the clusters smaller
than Cu 70 Se 35 are found to be spherical, whereas the structure of Cu 70 Se 35 is
pyramidal. The color of the material depends on the cluster’s size. For
nanoscale technology, the Cu 70 Se 35 is found to be metastable. It decomposes
under vacuum into smaller Cu 2x Se x clusters. When a sheet is coated with
Cu 70 Se 35 , a nearly uniform coating of smaller clusters of Cu 2x Se x (quantum
dots) is formed, thus creating a 2-D array of quantum dots. The next step—
not a trivial one—will be to form interconnects. One thought is to use
graphite surfaces using the beam techniques developed by Prof. Kappes.
The semiconducting cluster complexes can then stick to the graphite surface
at the defect site.