Site: Stuttgart, Germany
Date: Monday, 13 October 1997
WTEC: C. Koch (report author)
University of Ulm
Max Planck Institutes
A group of scientists from or near Stuttgart were invited to a roundtable discussion of their various research projects on nanoscale technology and materials. Names of attendees, their affiliations, and addresses are included above. The highlights of these presentations are given below, by institution.
Tel: (49) 711-689 0; Fax: (49) 711-689 1010
Professor v. Klitzing described research on functional nanodevices at the Max Planck Institute (MPI). He also discussed the broader view of work on nanotechnology in Germany, particularly on III-V quantum structure devices. Summaries of work on this subject, financial supporters, and details of technical progress are summarized in III-V-Elektronik Mesoskopische Bauelemente (in German). There is broad cooperation between universities and industry on this project. Professor v. Klitzing briefly described some of his own research, including MBE growth and etching system for study of GaAs/AlAs/ AlGaAs:15/AlAs:6/GaAs and quantum dot lasers GaInP and InP. The ultimate single-electron tunneling transistor - which is being addressed at many laboratories is the goal of much of the research.
The electronic properties of clusters are studied, e.g., gold clusters with well-defined number of atoms as contacts and islands for charge transfer. Some examples of low-dimensional electronic systems prepared by the chemistry department of the MPI FKF Stuttgart are "0-dimensional" CS11O3, "one-dimensional" Na5Ba3N, and "two-dimensional" Ba2N crystals. Prof. v. Klitzing is skeptical about the ultimate use of nano-semiconductor systems, such as quantum dots, for applications in mainstream microelectronics.
Dr. Billas in the group of Prof. Dr. T.P. Martin described the group's work on clusters studied by means of time-of-flight mass spectrometry. Much of the work deals with metal-covered C60 or C70 molecules. C60 is an ideal template for growing shells of metal atoms. Several systems include alkali metal, alkaline earth metal, and transition-metal-covered fullerenes. Fabrication of new exotic magnetic nanostructures is part of an interregional research project "magnetic nanostructures," which includes researchers from adjacent regions of France and Germany partially funded by regional governments. The project collaborators are listed below:
France: Rhône-Alpes region:
Germany: Baden-Würtemberg region:
The research of this program includes fabrication and stabilization of nanosize magnetic structures (magnetic dots and clusters) and their characterization by time-of-flight mass spectroscopy, TEM and HRTEM, XRD, and absorption techniques, Rutherford Backscattering, and XPS. Magnetic properties are measured by magnetic force microscopy, magnetometry (microSQUIDs), magnetotransport measurements, and ultrafast magnetooptical measurements.
Dr. Wagner is staff scientist at the Max-Planck Institut für Metallforschung leading the "Thin Film Synthesis and Processing" group. His current research uses STM, TEM, coupled with standard surface analysis techniques, to characterize metal and ceramic films, multilayers, and alloy films with defined chemical composition grown by MBE and sputter deposition on a variety of substrates. The main thrust of his group is to investigate physico-chemical mechanisms of thin film growth like solid state reactions, nucleation processes, and interface formation during film deposition. The following thin film systems are under investigation:
Metal/Ceramic Nb, Cu/Al2O3 Al, Ag/MgAl2O4 Si, Pd, Cu/SrTiO3
Ceramic/Ceramic Ti2O3/Al2O3 ZrO2/Al2O3 TiO2/Al2O3
In addition, special thin film systems are grown to study their mechanical properties (e.g., alloy films), thermal stability (grain growth, stability of boundaries), atomistic structure, and bonding interfaces.
The main thrust of Prof. Rühle's group is use of state-of-the-art analytical tools to study materials and thin film microstructures and interfaces. One major goal of the research is to correlate chemical composition and microstructure of materials to their macroscopic properties. In this context, it is of fundamental interest to quantitatively investigate and model the growth, atomistic structure, and bonding at interfaces of both real materials and model systems. Such model systems are fabricated by different techniques, like ultra high vacuum diffusion boding and molecular beam epitaxy. Major research activities are concentrated on electron microscopy and interfacial research. Analysis is carried out with tools such as HRTEM, analytical electron microscopy (AEM), and surface science techniques. Interfaces of these material systems have been studied both experimentally and theoretically: grain boundaries in metals, intermetallic and complex oxides, and metal/ceramic phase boundaries, including the following:
metal/metal: NiAl/NiAl Cu/Cu
metal/ceramic Nb, Cu/Al2O3 Al, Ag/MgAl2O4 Pd, Cu/SrTiO3
ceramic/ceramic Al2O3/Al2O3 SrTiO3/SrTiO3
Major research interests include those listed below:
Dr. Redlich is also in Prof. Rühle's institute. His research interests are in the field of carbon nanofibers. Institute researchers use arc-discharge methods to synthesize their carbon nanotubes. They are also studying chemically modified C nanotubes. Using BC4N as an anode they obtain a new material. They use HRTEM and EELS to characterize their materials. The interdisciplinary approach to these studies is emphasized with collaborations with experts in synthesis and characterization within MPI, Germany, and the United States.
Albert-Einstein-Allee 45, D-89081 Ulm, Germany
Dr. Unger is in the Department of Optoelectronics of the University of Ulm (K.J. Ebeling, Director). Research topics in the university include vertical cavity surface emitting lasers (VCSELs), Gbit data transmission using VCSELs, high-power semiconductor lasers, and nitride-based semiconductors (for LEDs, lasers). The funding of this research comes from the German Ministry of Education, Science, Research, and Technology (BMBF), Baden-Württemberg, German Research Society (DFG), the European Union, and industry (Siemens, Daimler-Benz, Telekom). The equipment used includes MBE (for GaAs, AlGaAs, InGaAs), GSMBE (for InP, GaInAsP, AlGaInP) and MOVPE (and GSMBE) for GaN, InGaN, and AlGaN. Lithography is both optical and e-beam, and dry etching is by RIE, CAIBE. Nanotechnology studies include epitaxial growth (quantum wells, nanometer accuracy, nanometer reproducibility) and lithography and dry etching (holograms, waveguides, and laser mirrors). No structures have nanometer-scale dimensions, but they do have nanometer-scale definition, accuracy, and side wall roughness.
Dr. Fecht is in the Faculty of Engineering, Department of Electronic Materials/Materials Science. Dr. Fecht has a number of basic research and applied research projects, many of which involve nanoscale science and technology. The per-year funding level is about $1.2 million. Eight projects are of particular interest for nanostructured materials research:
Dr. Behm is in the Faculty of Sciences, Department of Organic Chemistry and Catalysis. He described the fabrication of nanostructures by scanning probes. These included semiconductor materials where, e.g., scanning tunneling microscopy was used for direct local deposition of Si or Si-Hx species from a SiH4 precursor gas on the Si(111)-(7x7) surface. Direct writing of nanostructures with lateral dimensions down to 40 nm is accomplished; similarly, nanofabrication of small Cu clusters on Au (111) electrodes is accomplished with the STM. Work is also carried out on the chemical properties of defined multicomponent particles of interest for catalysis. It is suggested that bimetallic catalysts may have a future, compared to single-component monolayers, which are too expensive. About 80% of this research is directed toward fuel cell catalysis. These programs are funded by government (BMBF, DFG, EU) and industry.
Center for Solar Energy and Hydrogen Research, Baden-Württemberg, Department of Electrochemical Material Research and Development
The major function of the Center for Solar Energy and Hydrogen Research is to characterize materials - some of which may be nanostructured - for batteries, supercapacitors, fuel cells (direct methanol), and hydrogen storage (fuel cell, carbon nc materials). The center obtains its materials from others, since it does not make materials. At this time it is not possible to predict whether nanostructured materials will be useful in the above applications.
Dr. Franke is in the Central Institute for Biomedical Technology, Department of Biomaterials. Dr. Franke described several interesting studies related to the interfaces between biomaterials and tissues. One study (funded by BMBF) involves the tribology of implants under load. The wear particles of the implant can be in the size range of nm to mm and lead to inflammation of the tissue and subsequent loosening of the implant. Nanostructures may be important in filtering devices, sensors, and artificial organs. Specificity - specific reactions by receptors - is important in organisms, while biomaterials typically react by nonspecific reactions. Placement of receptor-like molecules on biomaterials by nanomanipulation methods should open new opportunities. In general, there appear to be many new exciting research possibilities in the fields of wear, mechanical, and chemical properties of nc biomaterials.
Dr. Lojkowski is in the Department of Electronic Materials/Materials Science as visiting scientist from the Polish Academy of Sciences, High Pressure Research Center in Warsaw, Poland (a Center of Excellence). His major research interests at Ulm involve characterization of nc powder and high pressure sintering. In terms of characterization of nanomaterials, X-ray diffraction analysis is the methodology used. Ab initio calculations are made of diffraction spectra for model structures and compared with the experimental data. Information about size, shape, strain, and polytype-structure of the nanopowders is obtained.
Studies of the sintering of nc SiC and nc diamond are carried out at pressures up to 40 GPa and temperatures up to 2000°C. In situ X-ray diffraction studies are made under pressure to determine the processes taking place during sintering.
Dr. Spatz is in the Faculty of Sciences, Department of Organic Chemistry/Macromolecular Chemistry (director, Dr. Marten Möller). He described his department's research on using diblock copolymers in ultrathin films for patterning. The phase organization of the diblock copolymers into micelles can be arranged in various ways on substrates. The distance between clusters can be about 10 nm and modified by changing the molecular weights. The chemical inhomogeneity of the diblock copolymers films can be used to deposit metals locally on either block "A" or "B." This can provide masks on the nanometer scale with the limit so far of about 30 nm. Another method to approach limits of 1 nm uses the addition of metal compounds in solution to the core of a copolymer, then reduces the metal compound to the metal. An example is Au nanoparticles about 6 nm in diameter with the distance between them controlled by the polymer. Oxygen plasmas can be used to remove the polymer with the metal particles remaining in place. The particle size can be reduced with lower molecular weight polymers. Precise islands 5-20 nm and 10-200 nm apart can make high density quantum dot arrays, 1,000 dots/mm2.
Prof. Dr. Kappes briefly described the scope of their work related to nanostructures. This includes studies of fullerenes, electronic structure of clusters, and use of clusters as projectiles to make well-defined defects on substrate surfaces. The details of the work in Prof. Dr. Kappes' laboratory are given in the report of the site visit to Karlsruhe (Appendix B).
Dr. Trapp provided an industrial perspective on work on carbon nanofibers as part of a large, $1 billion per year, carbon company business. The present cost is about $30/lb. The carbon nanofibers may be used in composites (for automotive, electronics applications), electrochemistry for electrodes, etc., and hydrogen storage. An industrial concern with carbon nanofibers is potential or possible health/environmental problems. This is a major obstacle to commercialization.