1981 Nobel Prizes in Physics Kai Siegbahn J.M. Thomas, Cambridge (Department of Physica/ Chemistry)
Robinson, in an elegant publication in quantitative chemical analyses could be Kai Siegbahn was born in 1918 in Lund and following his Bachaloria, studied physics mathe 1925, described how he recorded, photo undertaken. Band structures of solids matics and chemistry at Uppsala, graduating in graphically, the X-ray induced photoelec could be recorded more straightforwardly Stockholm. From 1942 until 1951 he was at the tron spectrum of gold. Although several than hitherto. Chemical shift information Nobel Institute for Physics and then Professor of subshells in the M and N shells of gold relating to "characteristic" binding Physics at the Royal Institute of Technology, could be identified in the photometric energies of certain electron energy levels Stockholm. Since 1954 he has been Professor recording of his photographic plate, the were shown to be dependent upon atomic and Head of the Physics Department at the Uni resolution was insufficient to distinguish all environment and charge density, both of versity of Uppsala. He is an Individual Member subshells and a true line spectrum was not which could, therefore, be probed using of the European Physical Society. obtained. This was the beginning of elec this new spectroscopic tool. Auger elec It is commonplace to remark that che tron spectroscopy. But its potential re trons, and Auger transitions, could be im mists invariably take advantage of, and mained untapped, its promise unfulfilled, mediately identified, and in favourable cir rejoice in, the discoveries of the physicist: for more than thirty years; and it is con cumstances, especially for free molecules this thought springs to mind with the an ceivable that this branch of high energy [see Siegbahn K. et al. ESCA Applied to nouncement of the 1981 Nobel prizewin spectroscopy would still be lying dormant Free Molecules, (North-Holland, Amster ners in physics, especially in regard to the had not Kai Siegbahn initiated, in 1951, a dam-London) 1969], vibrational fine struc sustained contributions of Kai Siegbahn. research programme aimed at the very high ture of Auger electron lines could be cha To appreciate fully the pleasure that resolution study of the energy spectrum of racterized, and the direct consequence of chemists derive from Siegbahn's award, it electrons expelled by X-rays. phenomena such as autoionization, elec is instructive to recall that seminal era — When the fruits of Siegbahn's labours tron-energy-loss, shake-off and shake-up the first few decades of this century — first appeared in the late sixties, their im ascertained. when both the fundamentals of quantum pact, especially upon physical chemists Siegbahn's work fired the imagination of mechanics and developments pertaining to and chemical physicists, was immediate a whole generation of scientists. His work X-rays occupied the thoughts of many phy and compelling. It has been argued that the has demonstrated how a concern for accu sical scientists. publication of "ESCA — Atomic Molecular racy and meticulous attention to experi Well before Manne Siegbahn (father of and Solid State Structure Studied by mental detail coupled to a broad vision and Kai) was awarded his Nobel Prize in 1924, Means of Electron Spectroscopy" [(Sieg scientific sure-footedness can open up new the Braggs and others had divined what bahn K. et ai.), Nova Acta Regiae, Soc. chapters in scientific endeavour. could be accomplished by X-ray diffrac Sci. Uppsaliensis Ser IV, Vol. 20 (1967)] Many of the new techniques and experi tion. So remarkable have been the achiev- marked a turning point, not only in the ments currently appearing in the fields of ments of X-ray crystallography in subse course of spectroscopy, but also in the ac surface, semiconductor and polymer quent years, there is a tendency amongst tivities and aspirations of many experimen science can trace their lineage to chemists and biologists to talk of "X-ray tally and theoretically oriented scientists. Siegbahn's pioneering work. It was not un spectrograms" when what is really meant The excitement that it caused has been til 1970, for example — and not until are "X-ray diffractograms". The subcons likened to that aroused amongst chemists Siegbahn's experiments using multilayers cious belief, one supposes, is that the by Pauling's Fischer-Baker Lectures "The of a-iodostearic and DL-a-bromostearic X-ray region of the electromagnetic spec Nature of the Chemical Bond", and acids had been fully appreciated — that trum yields its information upon structure amongst physicists by Mott and Gurney's monolayer amounts of adsorbed species on spectroscopically, just as do the UV visible, "Electronic Processes in lonic Crystals". single-crystal solid surfaces were first IR and microwave regions. Manne ESCA — Electron Spectroscopy for Che detected by electron spectroscopy. Nowa Siegbahn and others, notably Skinner, had mical Analysis — as the book was first days, less than a hundredth of a monolayer however, demonstrated what genuine designated, overwhelmed the reader by its of adsorbed species on a crystal of area less X-ray spectroscopy entailed and what it precision, breadth, execution and promise. than 1 cm2 may be detected in this way, could achieve. For many decades, X-ray In the preface, Siegbahn et al. soberly an and, with the aid of angle-resolved measu spectroscopy was the principal technique nounced that the work they had commen rements, the symmetry properties of or for experimentally determining the band ced in the early fifties on electron spec bitals or adatom sites may also be ascer structures of solids, as well as for establi troscopy was (in 1967) "ready for a more tained. With the advent of synchrotron shing the quantitative values of the elec general use". "The energies that can be radiation many of the experiments adum tron energy levels of atoms and molecules. measured by our present equipment range brated and already executed by Siegbahn When X-rays impinge upon matter, not from 1 MeV down to 0.01 eV, i.e. 26 oc and his contemporaries in electron spec only may they be diffracted or absorbed, taves". In the body of their text, they pro troscopy can be extended in directions they may also liberate electrons, the kinetic ceeded from one coruscating example to which require no further elaboration here. energies of which are equal to the dif another to demonstrate how high energy ference between the energy of the incom photoelectron spectroscopy could be utiliz REFERENCES ing photon and the binding energy of the ed to great advantage. The presence of any emitted electron. Robinson1, 2), de Broglie3) 1. Robinson H. and Rawlinson W.F., Phil. element from lithium to plutonium could be Mag., 28 (1914) 277. and Wiliams4), as well as others, had turn detected by its characteristic electron 2. Robinson H., Phil. Mag., 50 (1925) 241. ed their attention to this phenomenon of spectroscopic fingerprint. From a 3. De Broglie M., Compt. Rendus, 172 (1921) X-ray induced photoelectric emission in the knowledge of photo-electric cross-sections 274. second and third decades of this century. and escape depths (for solid samples) 4. Williams E. J., Nature, 121 (1928) 134.
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