Chemical Analyses and Studies of Electronic Structure of Solids by Electron Energy Loss Spectroscopy with an Electron Microscope [and Discussion]
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
5 9 ] Printed in Great Britain C h e m ic a l a n a ly se s a n d stu d ies o f e le c tro n ic s tr u c tu r e o f solids b y e le c tro n e n e rg y loss sp e c tro sc o p y w ith a n e le c tro n m ic ro sc o p e B y J . M . T homas, F .R .S ., T . G. S p a r r o w , M . K . U pp al and B. G. W illiams Department o f Physical C h e m i s t r y , University o f , Lensfield Cambridge CB2 1 U.K. [Plates 1 and 2] Both the thickness and the com position of a specim en can be deduced from plasm on
... duced from plasm on spectroscopy, w hich is readily recorded w ith an electron m icroscope to w hich has been attach ed an electron spectrom eter o f resolution 1-3 eV. T his is illustrated in the study o f alkali m etals and sp m etals such as m agnesium and alum inium , w hich are produced by decom posing tern ary or binary hydrides (for exam ple, N aA lH 4 or M g H 2). But oth er m aterials, including silicon, are also am enable to studies of this kind. T h e elem ental com position, electronic structure and inter-atom ic distances o f a sam ple can be derived from the core-electron (K , L, M edge) loss peaks and their fine structure. A nd from the near-edge energy loss structure, and in p a rtic u la r from the 'w hite lin e ' intensity ratios (for exam ple, L 2/ L 3), the n u m b er of d-electrons an d hence the oxidation state of transition elem ents in com pounds o f first-row transitionm etal series m ay be determ ined. In the region beyond the near-edge structure, extended electron energy loss fine structure (e.x.e.l.f.s.) is observed and this m ay be used to ob tain inform ation ab o u t the local co-ordination of different atom s in the sam ple. Finally, by m onitoring the D oppler broadening of the scattered electrons liberated from the sam ple as a consequence of the ' electron * equivalent of the Com pton-process, we can probe the electronic properties of the solid in m om entum space. This reveals the n a tu re of the bonding in simple solids; and, in particu lar, reveals w hether an am orphous sam ple of carbon is m ore nearly g raphitic or ad am an tin e.