| Biography: Siegfried Hofmann
Siegfried Hofmann received a Ph.D. in Physics from the Technical University in Munich, Germany in 1968 and joined the Max-Planck-Institute for Metals Research in Stuttgart, where he established the first research laboratory on Applied Surface and Interface Analysis in Materials Science in Germany in 1972. Systematic work on depth profiling of bilayer and multilayer structures in nanometer dimensions resulted in an improved knowledge of the optimum experimental conditions for acquisition and interpretation of sputter depth profiles. With various coworkers, he showed the important influence of surface roughness on depth resolution using Ni/Cr multilayers and developed a generalized model of oxide sputtering that took account of cation mass and surface bonding. These fundamental studies promoted the development and effective utilization of standard reference materials for depth profiling (Ta2O5 by NPL, Ni/Cr by NIST).
In 1986 he was appointed to adjunct Professor of Physics at the University of Hohenheim-Stuttgart.
Beginning in the early 1990's, Siegfried performed sputter depth profiling measurements with high depth resolution on GaAs/AlAs superlattice planar nanostructures used in optoelectronics, and Si/Ge multilayer structures. The measurements led to the development of a completely new model of quantitative depth profiling, the so-called MRI model based on the separate contributions of ion-induced atomic Mixing, surface Roughness, and the Information depth for the detected Auger electrons. Comparisons of measured depth profiles with simulations from the MRI model led to more detailed insights into compositional variations in the vicinity of interfaces. These successes motivated him to develop software so that other scientists could conveniently apply the MRI model to sputter depth profiling applications in their own laboratories. This software is now incorporated in the COMPRO package that is available without charge from the web site of the Surface Analysis Society of Japan. The MRI software was developed while Siegfried was a research director at the National Research Institute of Metals (now NIMS) in Tsukuba, Japan, and was recognized by a prize from the Japanese Minister of Science and Technology in 1998. The MRI model has been further refined and applied in recent work.
Another important area of Siegfried's research has been the study of surface and interfacial segregation. An early detailed study of the kinetics of surface segregation of Sn on Cu showed the power of this new approach for determining bulk diffusion coefficients. Grain-boundary segregation was studied in later papers, particularly in Fe (Si,P,C) bicrystals, and resulted in considerable progress in the understanding of competitive segregation for multicomponent systems and to a predictive model based on the newly established linear relation between enthalpy and entropy of grain-boundary segregation. His outstanding accomplishments in this area were recognized by the award of the Ernst Mach Medal of Merit in the Physical Sciences by the Czech Academy of Sciences in 2003.
Finally, Siegfried has utilized X-ray photoelectron spectroscopy to investigate corrosion, passivation, and pitting corrosion in stainless steels. This work led to a new interpretation of the formation of passive layers by preferential dissolution of iron in iron-chromium alloys.
Siegfried is the author or co-author of about 300 publications, including nine review papers and book chapters on sputter depth profiling, six on surface and interface segregation, and one on characterization of coatings. Many of these publications are based on work performed jointly with other scientists, in particular with his most outstanding former doctorate students Anton Zalar (Ljubljana), Jose Maria Sanz (Madrid), Joachim Steffen (Mannheim) and Pavel Lejcek
(Prague) who are still cooperating with him. His publications have had significant impacts, with over 3500 citations. The Institute of Scientific Information (ISI) selected Siegfried in 2002 as one of only 250 "highly cited authors" in Materials Science (http://highlycited.com). In 2005 he became "Fellow of AVS".
Siegfried has served the larger scientific community as a member of many program committees for major meetings (including AVS National Symposia and the International Conference on Metallurgical Coatings and Thin Films), co-editor for the ICMCTF Proceedings, member of international groups (VAMAS, ISO/TC 201), chairman of the large international ECASIA conference in 1987, and member of editorial boards for six journals, amongst others. He is presently serving as an advisor for the newly created "International Center for Young Scientists" at the National Institute for Materials Science in Tsukuba, Japan.