Site:University of Karlsruhe (Universität Karlsruhe)
Institut für Physikalische Chemie und Elektrochemie
Lehrstuhl II Kaiserstrasse 12,
D-76128 Karlsruhe, Germany
Tel: (49) 721-608 2094; Fax: (49) 721-608 7232
http://www.chemie.uni-karlsruhe.de

Date of Visit: 14 October 1997

WTEC: D. Cox (report author)

Hosts:

BACKGROUND

The University of Karlsruhe has a strong effort in nanoscale science and technology. The effort encompasses several research groups in both the Chemistry and Physics Departments, as well as collaborative efforts with the Forschungzentrum Karlsruhe (FzK). The effort has both a strong experimental component and a strong theoretical component.

At present the formal structure is best exemplified by the two Sonderforschungbereiche (SFB) programs at the University. The earliest one SFB-195 was started in 1992 and has a focus on electron localization. The present coordinator of SFB-195 is Prof. H. von Löhneysen, a professor in the Physics Department. Beginning in 1998 Prof. Dr. Manfred Kappes in the chemistry department will assume the role of coordinator. The focus of the program is electron localization in macroscopic and microscopic systems, including clusters and cluster complexes. This is a multidisciplinary effort encompassing many research groups at Karlsruhe. Some of the groups participating in this program are those of

The total effort is estimated at about 70-90 researchers, including postdoctoral and PhD students.

In addition to SFB-195, the Karlsruhe group has received approval for a second SFB commencing January 1998. This new SFB will obtain funds, initially ~ DM 2 million/year for three years, to pursue research on carbon materials. Again a strong multidisiplinary approach is evident, with groups from Physics, Chemistry and Engineering contributing. The goal of the new effort will be to understand carbon-fiber-reinforced materials. The approach will be multifaceted with studies of carbon deposition from the gas phase, chemical vapor infiltration and chemical synthesis of carbon structures including materials aspects of carbon nanotubes and fullerenes, gas phase kinetics and surface radical interaction on carbon surfaces to understand the fundamental growth mechanisms, and solid state physics of nanotubes and carbon materials for potential nanoelectronic properties. Some of the groups involved include those of Kappes, Fenske, Hippler, Hüttinger, Ahlrichs, and von Löhneysen at the University, and Rietschel at the FzK.

RESEARCH AND DEVELOPMENT HIGHLIGHTS

The WTEC team held individual discussions with Prof. Kappes, Prof. Fenske, and Prof. von Löhneysen, and visited the laboratories of Professors Kappes and von Löhneysen. It is clear from the discussions that nanoscale science is a high priority area in Karlsruhe, both at the university and at the FzK (Prof. Dr. H. Gleiter). As examples of efforts in this area, the research activities in the three groups we visited are summarized below.

Research in Prof. Kappes' Group

At the present time Prof. Dr. Kappes has a group of 12, consisting of 1 postdoc and 11 PhD students. The main focus of the research is to understand several fundamental physical, chemical, and electronic properties of metal and carbon (fullerene) clusters using spectroscopic and beam techniques. Efforts are focused on

  1. photodissociation probes of mass selected transition metal clusters and derivatives
  2. studies of charge separation and chemi-ionization processes in thermal energy collisions of alkali clusters with various molecules (e.g., O29, Cl29, C60...)
  3. isolation and characterization of larger fullerenes, endohedral metallofullerenes, and fullerene derivatives
  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 ligand-stabilized 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 (PEt2Ph)x. As an example, molecular clusters with cores of Cu20Se13, Cu44Se22, up to Cu70Se35, have been synthesized and characterized. The structures of the clusters smaller than Cu70Se35 are found to be spherical, whereas the structure of Cu70Se35 is pyramidal. The color of the material depends on the cluster's size. For nanoscale technology, the Cu70Se35 is found to be metastable. It decomposes under vacuum into smaller Cu2xSex clusters. When a sheet is coated with Cu70Se35, a nearly uniform coating of smaller clusters of Cu2xSex (quantum dots) is formed, thus creating a 2-D array of quantum dots. The next step ¾ not a trivial one ¾ 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.

Research in Prof. von Löhneysen's Group

Prof. H. von Löhneysen in the Physics Department has a fairly large group of 20, with 5 postdocs and 15 PhD students. He has a well-funded operation and commented that funding in Germany may still be better than in the United States. However, he also felt that too much time has to be spent to get funding. He commented that the University of Karlsruhe strongly supports nanotechnology. He has strong interests and efforts in electron beam lithography, break junctions, metallic nanostructures, low temperature physics investigating nanostructures and thin films, metal insulator transitions, and magnetism/superconductivity. Research on break junctions is directed towards fabricating and characterizing nanometer structures with few atom contacts. Contacts are broken and then brought back together in a controlled fashion so that current voltage characteristics can be probed. A tour of his laboratories confirmed that support for equipment is certainly adequate, with strong capabilities in e-beam lithography, UHV STM, and 20 mK dilution refrigeration for low temperature physics studies.

Prof. H. von Löhneysen also outlined some of the other efforts in the Physics Department with some emphasis on nanoscale science. Prof. T. Schimmel uses STM treatments of surfaces to micromill and manipulate nanometer structures on surfaces, such as fabrication of small junctions. Prof. P. Wölfle carries out theoretical studies of phase coherence, and Prof. G. Scöhn is developing the theory for a single-electron current standard.


Published: September 1999; WTEC Hyper-Librarian