Kai Manne Börje Siegbahn

We remember with deepest respect the memory of a very distinguished scientist, who was our colleague, Prof. Kai M. Siegbahn. He was born on 20th April 1918 in Lund, Sweden. He passed away on 20th July, 2007 at the age of 89 at his summer home in Angelholm, in southern Sweden. He became a Member of our Academy on 14th December 1985. Kai Siegbahn was the son of another great Swedish physicist, Manne Siegbahn, who won the Nobel Prize in 1924. Kai Siegbahn himself won the Nobel Prize in 1981; he received half the prize for the new approach to chemical analysis based on photoelectron spectroscopy; the other half was shared by Arther Schalow and Nicolaas Bloembergen for their contributions to laser spectroscopy. Both these areas owe their origin to the conceptual discoveries of Einstein, earlier in the century, of the photoelectric effect and of coherence. Kai Siegbahn always acknowledged his father’s influence on him; he remarked to the New York Times: ‘Conversations in early life with the Nobelist at the breakfast table gave him an advantage unanticipated at that time’. By winning a Nobel Prize that his father had also won earlier, Kai M. Siegbahn joined several other families in this respect: the Thompsons (J.J. and G.P.); the Braggs (William and Lawrence); the Curie family (Marie and Pierre Curie, Irene and Fredrick Joliot Curie); the Bohrs (Neils and Aage); and most recently the Kornbergs (Arthur & Roger). Kai M. Siegbahn was a student at Uppsala University (1936-1942). From 1942-1951, he carried out research in Stockholm; he took his Ph.D. in Physics from the University of Stockholm in 1944. Kai Siegbahn’s primary contribution was in the field of photo electron spectroscopy. He was the inventor of ESCA (Electron Spectroscopy for Chemical Analysis). This was essentially based on the bombardment of any given material with a beam of X-rays as a result of which electrons would be released. The energies of these electrons could be measured with a spectrometer and was characteristic of the electronic binding energies in the atoms from which they came; this was to some extent dependent on the chemical environment of the atom. As a result, one could reliably tell the composition of the material being tested. The photoelectric effect, which relates to the emission of electrons from a metal surface irradiated by photons had been explained by Einstein in 1905; and X-rays were used for such experiments in the second decade of the last century. But it was through the work of Kai Siegbahn and his collaborators, who developed sophisticated instruments for studying the energy spectrum of the emitted electrons, that it became the method it is today, for widest application for chemical analysis. ESCA was based on Kai Siegbahn’s deep understanding of nuclear spectroscopy. One should recall the classic works edited by him ‘Beta- and Gamma-Ray Spectroscopy’ (1955) and ‘Alpha-, Beta- and Gamma-Ray Spectroscopy’ (1965). Throughout the 1970s there were innumerable surveys on ESCA. They had their roots in his books ‘ESCA: Atomic, Molecular and Solid- State Structure Studied by Means of Electron Spectroscopy’ (1967) and ‘ESCA applied to Free Molecules’ (1969). He was editor for the journal ‘Nuclear Instruments and Methods in Physics Research’ since it started in 1957. The Nobel lecture that Kai M. Siegbahn gave on 8th December 1981, when he received the Nobel Prize, was on ‘Electron Spectroscopy for Atoms, Molecules and Condensed Matter’. ESCA is now used routinely for studies of surface reactions such as those that occur in corrosion and catalytic reactions; for testing the surfaces of semi conductors etc. These are vital in many process industries. Later Nobel Prizes have been awarded for a deep understanding of processes at surfaces. ESCA is an extremely sensitive technique, and particularly with the rapid development of computers, become fairly all-pervasive. Kai Siegbahn was deeply committed to science and its applications. He was a simple person and a good friend.

M.G.K. Menon