His scientific interests have been in the area of surfaces and nanostructures. Utilizing his experience with synchrotron radiation he devised methods for mapping energy bands of solids and surfaces by angle-resolved photoemission. As complement he developed inverse photoemission with tunable photon energy for the study of unoccupied states. For identifying the bonding configurations at semiconductor surfaces/interfaces he took advantage of surface-sensitive core level spectroscopy with synchrotron radiation. Self-assembled nanostructures at surfaces have been a common thread throughout his career, such as magnetic quantum wells, atomic chains for the study of low-dimensional electrons, and an atomic scale memory for testing the limits of data storage. More recently, he ventured into the attachment of bio-molecules to surfaces and the design of new materials for solar cells. Since retiring he has shifted his focus toward new ideas for solving long-standing problems in physics. He has about 480 publications in refereed journals and was listed among the 100 most-cited physicists.