Thin Films and Surfaces

Thin films and surface science were the fields of scientific interest in the four periods of the scientific life of Ernst Bauer: Munich, Germany (1951-1958), China Lake, California (1958-1969), Clausthal,Germany (1969-1996) and Tempe, Arizona (since 1996).

Ernst Bauer started his scientific career in Munich with the study of the growth and structure of antireflection layers with electron microscopy and electron diffraction. His Ph.D. thesis was concerned with the structure and growth of thin evaporated layers of ionic materials and was the first extensive study of epitaxial and fiber orientation growth combining electron microscopy and electron diffraction. This experimental work stimulated a basic contribution to the theory of epitaxy. He derived in 1958 a classification of the basic thin film growth modes, which he called Volmer-Weber, Stranski-Krastanov and Frank-van der Merwe mechanisms. His thermodynamic criterion and terminology are used worldwide today. In the same year Ernst Bauer's book on "Electron diffraction: theory, practice and application" appeared.

Soon after his arrival in the Michelson Laboratory in China Lake surface science was born and he was involved early in it in order to understand thin film phenomena. In this period he started in situ thin film growth studies by conventional electron microscopy, UHV reflection electron diffraction, LEED and Auger electron spectroscopy. The difficulties encountered in the interpretation of the low energy electron diffraction (LEED) patterns reported by L. Germer in 1960 stimulated the invention in 1962 of the low-energy electron microscope (LEEM), which uses diffracted electrons for imaging. He was one of the first to recognize the importance of exchange, polarization, multiple scattering, and of the energy dependence of inelastic scattering of very slow electrons in LEED studies of surface, and he took them into account theoretically. The importance of adsorption on the initial growth of thin films led him also to adsorption studies. In these early years of UHV technique and surface science much of the work went into technological and methodological development.  

Thanks to excellent co-workers and strong financial support in his third scientific period in Technical University Clausthal Ernst Bauer could build up a broadly based surface science group encompassing a large variety of electron and ion beam techniques as well as optical methods. The quantitative interpretation of thermal desorption spectra was developed with the goal to obtain information on the interactions in adsorption layers. Work function measurements were developed and used for the determination of the thermodynamic properties of two-dimensional systems with attractive lateral interactions. For the study of two-dimensional systems with repulsive or oscillatory interactions, his group developed LEED-diffractometry that allows the determination of critical exponents in chemisorbed layers with an accuracy comparable to that achieved with x-rays in physisorbed layers. He developed electron stimulated desorption (ESD) and static SIMS for the study of adsorbed layers and ultrathin films on single crystal surfaces; alkali ion scattering (ISS) for structural analysis of surfaces; field ion microscopy (FIM) of single atoms and clusters; UHV-SEM studies of surface melting.  

In the fourth period at the Arizona State University his efforts concentrate on the further development of laterally resolved surface science methods and on their application to the study of the growth, structure and properties of thin films, in particular of ferromagnetic films and their magnetic structure as well as oxide surfaces. 

Ernst Bauer’s achievements in thin films research have been multiply honored: by the Medard Welch Award of the American Vacuum Society (1992) "for his contributions to the fundamental understanding of thin film nucleation and growth and for his invention, development and use of multiple surface characterization techniques to study those thin films"; by the Niedersachsenpreis for Science (1994) "for the development of LEEM and for his thin film research"; by Davisson-Germer Prize of the American Physical Society (2005) "for contributions to the science of thin-film nucleation and growth, and for the invention of Low Energy Electron Microscope" and by several more.

References:

E. Bauer: Epitaxy of metals on metals, Appl. Surf. Sci. 11/12 (1982) 479-494.

E. Bauer: Metals on Metals, in: Chemical Physics of Solid Surfaces and Heterogeneous Catalysis, eds. A. King and O.P. Woodruff, Vol. III B (Elsevier, Amsterdam 1984) p.1-57.

E. Bauer: Ultrathin metal films: from one to three dimensions, Ber. Bunsenges. Phys. Chem. 95 (1991) 1315-1325.

E. Bauer: The Many Facets of Metal Epitaxy, in: The Chemical Physics of Solid Surfaces, eds.   D.A.   King and D.P. Woodruff (Elsevier, Amsterdam 1997) Vol. 8, p. 46-65.

E. Bauer: Growth of Thin Films, J. Phys. Condens. Matter 11(1999) 9365-9385.

M.C. Tringides, M. Jalochowski and E. Bauer: Quantum size effects in metallic nanostructures, Physics Today 60 (2007) pp 50-54.

K.M. Man, A. Pavlovska, E. Bauer, A. Locatelli, T.O. Menteş, M.A. Niño, G.K.L. Wong, I.K. Sou, M.S. Altman: Growth and reaction of Fe on ZnS(100), J. Phys. Condens. Matter 26 (2014) 315006-1-11. doi:10.1088/0953-8984/26/27/315006

Y.R. Niu, K.L. Man, A. Pavlovska, E. Bauer and M.S. Altman: Fe on W(001) from continuous films to nanoparticles: growth and magnetic domain structure, Phys. Rev. B 95, 064404(2017)