Professor Wiedemeier attended the University of MŸnster, Germany, where he received his D.Sc. degree in 1960. He joined Rensselaer's faculty in 1964. He is a scientific adviser for NASA, and a visiting research professor at the Max-Planck Institute, Stuttgart. For his crystal growth experiments in space, Dr. Wiedemeier received the National Aeronautics and Space Administration Medal for Exceptional Scientific Achievement in 1974. He is a principal investigator on the U.S.-European Spacelab-Shuttle Program.

Solid State and High Temperature Chemistry

Our research activities in solid state and high temperature chemistry are mainly concerned with the synthesis and crystal growth of technologically useful inorganic materials. This approach involves structural characterization of the solids as well as thermodynamic, kinetic, and transport studies of the processes relevant to synthesis and crystal growth.

Crystal Growth of Electronic Materials on Earth and in Space

Advanced technology is critically dependent on electronic materials in form of high quality single crystals. The growth of single crystals from the vapor phase is widely used for basic research and for technological applications. Our crystal growth studies of various binary and ternary materials on earth led to the prediction that structurally improved crystals could be grown in the low gravity environment of space. Our crystal growth experiments on Skylab, Apollo-Soyuz, and various Shuttle missions have confirmed our predictions, and also led to the discovery of unexpected mass transport phenomena. These investigations will be continued on future U.S.-European Spacelab Flights.

Thermodynamic and Kinetic Studies of Reactions

Sublimation, transport, and condensation reactions are basic phenomena that occur on a large scale in nature and that are technologically used for a wide range of processes. A thorough understanding of the thermodynamic and kinetic properties of such reactions provides the basis for the modification and reproducibility improvement of relevant processes. An important example is vapor phase crystal growth. Our thermochemical investigations of sublimation and condensation reactions led to the further improvement of theoretical models for crystal growth and for related processes. These results are of direct practical relevance.

Structural and Defect Studies on Solids

The properties of materials are based on their crystallographic structure and defects. This is of critical importance for the performance of electronic materials. In our investigations of the structure and defects of crystals, a wide range of advanced characterization techniques and facilities is employed. The recent development of a dynamic microbalance technique in our laboratory led to the first, direct, in-situ determination of the vacancy concentration and of the energy of vacancy formation in infra-red detector materials. This represents significant advancement in the understanding of the electronic properties of such materials.

"Growth of Hg_1-xCd_xTe Epitaxial Layers on (100) CdTe by Chemical Vapor Transport under Normal and Reduced Gravity Conditions", J. Crystal Growth, 146, 610 (1995) (with Y. R. Ge, M. A. Hutchins and Y. G. Sha).

"The Temperature-Composition Phase Diagram and the Miscibility Gap of
Hg_1-xCd_xTe Solid Solutions by Dynamic Mass-Loss Measurements", J. Electronic Materials, 24, 405 (1995) (with K. T. Chen).

"Defects in CdTe Single Crystals Grown by Very Fast Vapor Growth Technique", J. Electronic Materials, 24, 1007 (1995) (with G. H. Wu).

"The Temperature-Composition Phase Equilibria in the HgTe-HgI₂ Pseudobinary System", Z. Anorg. Allg. Chem., 622, 1150 (1996) (with M. A. Hutchins)

“The Synthesis and Crystal Structure of Hg₃TeI₄”, Z. Anorg. Allg. Chem., 623, 1843 (1997) (with M. A. Hutchins; Y. Grin, C. Feldmann, and H. G. von Schnering, (Max-Planck-Institut, Stuttgart, Germany)).

“Effects of Microgravity on Hg_1-xCd_xTe /(100) CdTe Epitaxy by CVT under Transient Growth Conditions”, J. Crystal Growth, 187,72 (1998) (with
Yu-Ru Ge and Mark A. Hutchins).

"Transient Behavior of Hg_1-xCd_xTe Film Growth on 30 Off-(100) CdTe Substrates by Chemical Vapor Transport", J. Electronic Materials, 27, 891 (1998) (with
Yu-Ru Ge).

"Transient Behavior of Hg_1-xCd_xTe Film Growth on (111) B CdTe Substrates by Chemical Vapor Transport", J. Electronic Materials, 28, 91 (1999) (with Y. R. Ge).

“Cd_xHg_1-xTe/CdTe Heteroepitaxy in a Microgravity Environment”, Encyclopedia of Materials: Science and Technology, pp. 1033 – 1039, Elsevier Science Ltd., Amsterdam, Oxford, 2001.

“The Temperature - Composition Phase Equilibria in the Hg_0.8Cd_0.2Te – HgI₂ System”, Z. Anorg. Allg. Chem., 628, 1489 (2002) (with M. A. Hutchins).