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Shake-up satellite structure of transition metal auger spectra: L2,3M4,5M4,5 spectra of the 4d metals
Journal of Electron Spectroscopy and Related Phenomena, 68 (1994) 329-334 036%2048/94/$07.00 0 1994 - Elsevier Science B.V. All rights reserved
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Shake-up Satellite Structure of Transition Metal Auger Spectra: L2,3M4,5M,,5 Spectra of the 4d Metals G.G. Klelman. R. Landers and S.G.C. de Castro Instituto de Fisica “Gleb Wataghin” Universidade Estadual de Campinas, Unicamp 13083-970, Campinas, sab Paulo, BRA!% Core hole Auger spectra of transition and noble metals have been relatively little studied because they are usually very broad, and hecause they provide little direct valence band information. Narrow and simple Lz,M4,,M,,, spectra of the 4d metals have been recently reported, however. Study of spectral peak energies has produced considerable information regarding ground and excited state electronic structure of these metals. Comparison of the spectra with atomic theoretical ones indicates that, whereas the LzJM4,,M,,, spectra of In, Sn and Sb manifest atomic nature, in such open shell metals as Ag and Pd, these spectra evince intrinsic satellite structures below those of the Auger transitions proper. The L2 and L, satellites, in contrast to those of the 3d LMM spectra, have the same form (within experimental error) and do not seem to involve L,L,X Caster-Kronig transitions, most of which are energetically forbidden. On the basis of the experimental systematics of the 4d spectra and the interpretation of 3d LMM spectra, we have identified these satellites as arising from shake-up involving spectator valence band holes. To our knowledge, such shake-up features have not been directly observed before in transition metals. 1. INTRODUCTION Analyses of X-ray Excited Auger Electron Spectra (XAES) of purely core level transitions (i.e., ijk transitions) in noble and transition metals and their alloys are usually hampered because of the considerable breadth of the ijk spectra which results from the superposition of contributions from various terms [1,2]. In recent work [3-81, we demonstrated that, in contrast to the broad spectra of the L2,3M2,3M2,3transitions in the 3d series [l], and the N6 704 j04 5 transitions in Tl, Pb and Bi [Z], the high e&rgy’LMM aud LMN spectra in the 4d metals are narrow and simple in form, although weak [4,7,8]. These spectra were analyzed to infer a number of results regarding valence as well as core states [3-81. In particular, in a recent paper [4], which we denote as I, we reported the experimental L2M4,5M4,5and L,M4,5M,,5 Auger spectra of In, Sn, and Sb and compared them with the results of atomic calculations using the jj-intermediate
SSDZ0368-2048(94)02130-R
coupling scheme ]2] for the initial-and final-states. As in other treatments [ 1,2], satisfactory agreement between theory and experiment was reached when the problem was considered atomic in nature 141. Since the 4d bands are full in the metals considered in I, it is interesting to investigate the form of the L&I45M,,5 spectra in metals for which there are holes in the initial-state d-band. In this paper, we report the results of such a study for the series Ag, Pd, and Rh, which runs the gamut from (almost) full to partially empty 46 bands. The forms of the main spectra agree with the results of jj-intermediate coupling calculations [9,10], as in I. There appear, however, anomaIous loss structures at lower kinetic energies whose origins seem different from any yet reported. In other work [9,10], we identify these loss spectra as arising from d-band spectator vacancy satellites and show that this model is consistent with all the aspects of the data. Caster-Kronig processes present in the Cu L2,3M4,5M4,5Auger spectra ate apparently absent here.
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In this paper, we emphasize the systematic behavior of the experimental data, and show to what extent we can reach model independent conclusions by considering these systematics within the context of the interpretations of the Cu I?,3Mq,5Mq,5 satellites. In Sec. 2, we report the experimentalresults, in Sec. 3, we discuss them and, in Sec. 4, we present the conclusions. Throughout, we draw freely on theoreticalresults reported in I. 2. EXPERNMENTALRESULTS The sample preparation and experimental procedures are reported elsewhere [3-8,11-141.In Figs. 1 to 3, we present, respectively, the Lz3M,5M,,5 Auger spectra of Ag, Pd., and Rh exbted with bremsstrahlung [15,16]. In each figure, the raw L,M,,,M,,, and L$,,$I, 5 spectral dam are represented by dots and t&d lines, respectively, and have been plotted on the same energy and intensity scales for ease of comparison; the absolute energies of the main (*G,) peaks are given in the figure captions [8]. An
important point for our future argumentationis that the ratio between the areas of the background subtracted L, and h spectra is around 2.2, which is quite close to the statistical ratio of 2, considering the uncertainties involved in measuring the areas and defining the background, which we determine from the Shirley method [ 171 (the background determination is discussed further in refs. 9 and 10). In each figure, the L, - and L,M, 5M,,, spectra exhibit structure to the left of the main peak (the “loss” region) which are remarkably similar and several peaks to the right of the main peak (the “atomic” region) of quite different shape. The relative energies of the atomic peaks agree with final-state term splittings calculated in the intermediate coupling (IC) scheme 1181. As pointed out in I, the LS coupling scheme is inadequate in these cases. The results of the calculations of the multiplet energies treating the final-state in the IC coupling scheme are presented elsewhere [9,10]. The transition rates were also calculated in the jj-IC intermediate coupling approximation
The L2M4,5M4,5(solid line) and L M,,5M,,, (dots) Auger spectra of Ag as a function of kinetic energy. The absolute energies of the main (9C,) peaks are, respectively, 2749.4eV and 2577.0 eV for the L, and L, spectra. The spectra have been plotted on the same energy and intensity scales to illustrate the difference in form of the atomic multiplet structure and the similarity of the loss structure in both spectra. Fig. 1
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[4,0,10]. The results of these atomic calculations are in quite good agreement with experiment for energies at and above that of the main peak [9,lo]. The theoretical spectra reproduce the shape and relative intensities of all the atomic experimental peaks [9,10], as in the case of the corresponding In, Sn and Sb spectra 141.The atomic calculations, however, are inadequate for describing the loss structures for kinetic energies below that of the main peak [9,10]. In contrast to the In, Sn and Sb spectra in I, the positions of the loss structure on the low kinetic energy sides of the spectra in Figs. 1 - 3 do not agree with the energies of plasmon losses f19,20]. Comparison with the Ag and Pd hM4,,M,,S spectra in AgPd alloys [9,10] indicates that the Ag and Pd loss structures have neither any effect on any of the other XPS and XAES lines, nor any mutual influence of one on the other in the pure metals and alloys studied, so that it is reasonable to consider the loss structure as intrinsic to the L,M,,5M4, transition iu the whole series. In the alloys stu&e~ the similarities between the L, and L,M,,,M,,5 illustrated in Figs. 1-3 are also observed [9,10].
The loss features of the b,3M4,5MIS spectra which we report here bear certain similarities to those associated with the corresponding spectra of the 3d metals, which have heen the subject of a great deal of attention[1,21-321.Examination of the similarities, as well as the differences, between the 4d and the 3d &,3M4,5M4,5spectra facilitates interpretation of the former. In particular, the satellites of the Cu L2.3M4,5M4,5 Auger spectra, which have been the most studied [1,21,23-26,28-323,seem to arise from 3d (i.e., M4,5) spectator vacancies produced before the Auger process. The b satellite seems mainly to originate in a L,L3M,,5 Caster-Kronig (CK) transition preceding the L3M,5M4,5 recombination; a substantial fraction of the ‘initial L,M4,5 states, however, seem to be produced directly in the photoemission process [29] (i.e., shake-up and shake-oft?. The L, satellite, on the other hand, seems to be consistently explained by the combination of an initial-state shake-up process and a L,bM,,, CK trausition preceding the L2M4,5M4,5 process [32]. The salient features of the Cu satellites are the following: (a) Thepositionsof the L, and L, satellites
3. DISCUSSION
20.0
E~&Y bv) Fig. 2 The L,M4,5M4,,(solid line) and L,M,,,M,,, (dots) Auger spectra of Pd as a function of kinetic energy. The absolute energies of the main (lGq) peaks are, respectively, 2625.7 eV and 2469.1 eV for the L, and L, spectra. The spectra have been plotted on the same energy and intensity scales to illustrate the difference in form of the atomic muitiplet structure and the similarity of the loss structure in both spectra.
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to their respective main peaks are approximately the same, and agree with calculations of the energy of the L,M,,5 + M,,M,,,M,,, transition corresponding to MdJ spectator holes [%I; (b) The ratio of the intensities of the L, aud b main peaks is much more than 2, the ratio of initial-state multiplicities: part of the L, intensity is transferred to the L, satellite through the L2L3M4,5 CK process mentioned above [29];(cc)The double-peak structure of the b satellite seems to be caused by multiplet s@itting of the 3d Btal-state caused by strong spin-orbit coupling of the three M4,5holes [26], as reflected in optical data [33]; and (d) The ratios of the satellite to main spectrum intensities of both the L, and L, spectra are about the same for photon energies below the L, threshold [28]: since the CK process can be thought of as takiug holes from the main L2 line and donatiug them to the L, satellite, and since the b satellite has au unusually long lifetime [26,29], interpretation of these satellite lineshapes is complicated. relative
Cormsponding to points (a) to (d) above, we note that, for the L,,,M,,,M,,, spectra reported here: (1) In each figure, the L, and h losses are displaced the same amount relative to their respective main peaks, suggesting the validity of
the spectator vacancy mode1 - the most likely candidate being a NJ5 vacancy; (2) The ratio of the 5 and L, intensities is within ten percent of the statistical ratio (i.e., 2): this would suggest that L,L,X CK processes contribute little; (3) The shape of the loss structures in Figs. 1 to 3 would not seem to be atuibutable to multiplet splitting of the fmal-state with the spectator vacaucy, since both losses have approximately the same shape, whereas the corresponding atomic spectra have vacancies quite differentforms:indeedspectator consistent with the relative positions (in particular, N4,5vacancies) would not be expected to greatly modify the multiplet splitting of the Mq,5M4,5 hole state; (4) The ratios of loss to main spectrum intensities is very similar for both the L, and L, spectra, as in the case of Cu: the apparent absence of CK processes in the 4d metals, however, suggests that the same mechanism is responsible for both spectra.
In analogy with Cu, the only spectator vacancy state consistent with calculations of the energy [9,10] which could possibly produce the losses closest to the main peak is that corresponding to a 4d (i.e., N4,5) band hole [34]: consistent with this interpretation is the approximation of the satellite tothemainpeakaswepassfromAgtoRhinFigs.
Energy(4 Fig. 3 The bM&Q5 Isolid line) and L M+,5M4,5(dots) Auger spectra of Rh as a function of kinetic energy. The absolute energies of the main (9G4) peaks are, respectively, 2501.2 eV and 2358.9 eV for the L, and L, spectra, The spectra have been plotted on the same energy and intensity scales to illustrate tie difference in form of the atomic multiplet structure and the similarity of the loss structure in both spectra.
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1 to 3. All other states result in values of relative satellite positions which are much too large [9,10,20].Indeed, calculated sateRite positions are in reasonableagreement with experiment [9,10]. Lineshapes resulting from this picture are also consistent with the data [9,10]. In contrast to the case of Cu, where the satellite multiplet splitting arises from the strong spin-orbit interaction of the three M4,5 final-state holes, the proposed N4,5 spectator holes in the 4d metals interact only weakly with the M,,5 core holes because of the different atomic shells involved. The multiplet splitting resulting from the interaction of the three holes, therefore, is little different from that of the two M,,, holes, except for intrinsic broadening arising partly from the small extra multiplet splitting produced by the N4,5hole and partly from the width of the 4d-band. We expect, therefore, the satellite lineshapes to be essentially broadened images of the main, atomic spectra shown on the right side of the main peaks in Figs. 1 to 3. From the cousidcrations presented here, it appears that bL,X CK processes contribute little to the 46 spectrh in contrast with the situation in Cu, for example. In fact, the data seems to oblige us to interpret the loss features of the 4d L2,3M,,,M,5 spectra as arising from shake-up satellites a&mg from d-band valence holes. The probability of shake-up processes in photoemission increases with increasing photon energy [35]. Loss structure resulting from incomplete relaxation of the photoexcited state were observed previously in plasmon gain satellites of the KLL spectra of Na and Mg [3$j and shake-up satellites of the KLV spectra of Mg [36] and Al [37]. Since we use bremsstrahlung as the exciting radiation, the high photon energies involved may explain why shake-up processes are strong in the spectra in Figs. 1 to 3; of course, this requires that the d-baud spectator holes be sufficientIy long lived to survive until the Auger decay occurs [38]. What is not clear at present is why the L&,X CK processes are so weak. It should be noted that, from rough measurements of experimental peak areas, there appear to be L,L,,,X CK processes involved 19,101.The observed ratios of L, and L, intensities indicate, however, that CK process must have
approximately equal probability for both the L, and L2 spectra. 4. CONCLUSIONS We report the results of measurements of the L,,,M,,,M,,, spectra of Ag. Pd, and Rh. The atomic portion of the spectra agree with intermediate coupling calculations of multiplet splitting and relative intensities. The loss structures observed seem to be intrinsic and not attributable to plasmon losses. They are consistent with a model in which d-band spectator holes are responsible for the loss structure. LzL3X Costcrtionig processes do not appear to be involved to any significant extent. We would like to thank R.C.G. Vi&s for technical assistance and F. Alvarez for editorial assistance. This work was supported by CNPq, FAPESP,and FINEP of Brazil. REFERENCES 1. E. Antonides, EC. Janse, G.A. Sawatzky,Phy. Rev. B 15 (1977) 1669. 2. J.F. McGilp, P. Weigbtman, E.J. McGuire, I. Phys, c 10 (1977)3445. 3. G.G. Kleinian, R. Landers, S.G.C. de Castro, and P.A.P. Nascente, Phys. Rev. B 45 (1992) 13899;Surf. Sci. 287/288(1993)798. 4. G.G. Kleintan, R. Landers, P.A.P. Nascente and S.G.C. de Castro, Phys. Rev. B 46 (1992) 1970. 5. G.G.KIeiman, R. Landers, S.G.C. de Castro, and P.A.P. Nascente, Phys. Rev. B 44 (1991) 3383. 6. G.G. KIeiman, R. Landers, S.G.C. de Castro, and P.A.P. Nascente, J. Vat. Sci. Tech. A 10 (1992)2839. 7. G.G. Kleiman, R. Lauders, P.A.P. Nascente, and S.G,C. de Castro, Wys. Rev. B 46 (1992) 4405; Surf. Sci. 287/288 (1993)794. 8. R. Landers, P.A.P. Nascente, S.G.C. de Castro, and G.G. Kleiman, J. Phys.: Condens. Matter 4 (1992)5881; Surf. Sci. 287/288(1993) 802. 9. G.G. Kleiman, R. Landers, and S.G.C. de Castro (unpublished). 10.R. Landers, S.G.C. de Castro, andG.G. Kleiman (unpublished).
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11. G.G. Kleimau, J.Phys.: Condens. Matter 5(1993) 1. 12. G.G. Kleimau, R. Landers, S.G.C. &Castro and J.D. Rogers, Phys. Rev. B 44 (1991)8529. 13. T.D. Thomas and P. Weight-man,Phys. Rev. B 33 (1986)5406. 14. P.A.P. Nascente, S.G.C. de Castro, R. Landers and G.G. Kleiman, Phjs. Rev. B 43 (1991) 4659. 15. CD. Wagner, J.A. Taylor, J. Electron Spec. 20 (1980)83. 16. V.S. Suudaram,J.D. Rogers, R. Landers, J. Vat. Sci. Technol. A 19 (1981) 117. 17. D.A. Shirley, Phys, Rev. B 5 (1972)4709. 18.E.U. Condon and G.H. Shortley, The Theory of Atomic Spectra, Cambridge University, London, 1963. 19. AC. Parry-Jones,P. Weightman, P.T. Andrews,J. Phys. C 12 (1979) 1587. 20. R.A. Pollak, L. Ley, F.R. McFeely, S.P. Kowalczk,D.A. Shirley, 3. Electron Spectrosc. 3 (1974)381. 21. E.D. Roberts, P. Weightman and C.E. Johnson, J. Phys. C 8 (1975)L301. 22. E. Antonides and G.A. Sawatzky, J. Phys. C 9 (1976)L547. 23, E. Antonides, E.C. Janse and G.A. Sawatzky, Phys. Rev. B 15 (1977)4596. 24. H.W. Haak, G.A. Sawatzky and T.D. Thomas, Phys. Rev. Lett. 41 (1978) 1825. 25. P. Weightman and P.T. Andrew&5. Phys. C 12 (1979)943. 26. N. Martenssonand 3. Johansson,Phys. Rev. B 28 (1983)3733. 27. N. Martensson, R. Nyholm and B. Johansson, Phys. Rev. B 30 (1984)2245. 28. D.D. !bma, C. Carbone, P. Sen, R. Ciiino and W. Gudat, Phys. Rev. Lett. 63 (1989)656. 29. N. Wassdahl, J.-E. Rubensson, G. Bray, P. Glans, P. Bleckert, R. Nyholm, S. Cramm, N. Martensson and J. Nordgren, Phys. Rev. L&t. 64 (1990)2807. 30. J.C. Fuggle and G.A. Sawatzky, Phys. Rev. Lett, 66 (1991)966. 31. D.D. Sarma, C. Carbone, P. Sen, R. Ciiino and W. Gudat, Phys. Rev. L&t. 66 (1991)967. 32. S.M. Thurgate and J. Neale, Surf. Sci. Lett. 256 (1991)L605.
33. C.E. Moore, Atomic Energy Levels, Natl. Bur. Stand. (U.S.), Cii. No. 467 (U.S. GPO, Washington,DC., 19581,Vol. II. 34. N. Martensson and R. Nyhohn, Phys. Rev. B 24 (1981)7121. 35. J.C. Fuggle, R. Lasser, 0. Gunnarsson and K. Schonhammer, Phys. Rev. Lett. 44 (1980) 1090. 36. M. Davies, D.R Jeunison and P. Weightman, I. Phys, C 17 (1984)L107. 37. P.H. Haunab aud P. Weightmau, J. Phys. C 18 (1985)L239. 38. G.G. Kleimau, Appl. Surf. Sci. 11/12 (1982) 730.
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Shake-up Satellite Structure of Transition Metal Auger Spectra: L2,3M4,5M,,5 Spectra of the 4d Metals G.G. Klelman. R. Landers and S.G.C. de Castro Instituto de Fisica “Gleb Wataghin” Universidade Estadual de Campinas, Unicamp 13083-970, Campinas, sab Paulo, BRA!% Core hole Auger spectra of transition and noble metals have been relatively little studied because they are usually very broad, and hecause they provide little direct valence band information. Narrow and simple Lz,M4,,M,,, spectra of the 4d metals have been recently reported, however. Study of spectral peak energies has produced considerable information regarding ground and excited state electronic structure of these metals. Comparison of the spectra with atomic theoretical ones indicates that, whereas the LzJM4,,M,,, spectra of In, Sn and Sb manifest atomic nature, in such open shell metals as Ag and Pd, these spectra evince intrinsic satellite structures below those of the Auger transitions proper. The L2 and L, satellites, in contrast to those of the 3d LMM spectra, have the same form (within experimental error) and do not seem to involve L,L,X Caster-Kronig transitions, most of which are energetically forbidden. On the basis of the experimental systematics of the 4d spectra and the interpretation of 3d LMM spectra, we have identified these satellites as arising from shake-up involving spectator valence band holes. To our knowledge, such shake-up features have not been directly observed before in transition metals. 1. INTRODUCTION Analyses of X-ray Excited Auger Electron Spectra (XAES) of purely core level transitions (i.e., ijk transitions) in noble and transition metals and their alloys are usually hampered because of the considerable breadth of the ijk spectra which results from the superposition of contributions from various terms [1,2]. In recent work [3-81, we demonstrated that, in contrast to the broad spectra of the L2,3M2,3M2,3transitions in the 3d series [l], and the N6 704 j04 5 transitions in Tl, Pb and Bi [Z], the high e&rgy’LMM aud LMN spectra in the 4d metals are narrow and simple in form, although weak [4,7,8]. These spectra were analyzed to infer a number of results regarding valence as well as core states [3-81. In particular, in a recent paper [4], which we denote as I, we reported the experimental L2M4,5M4,5and L,M4,5M,,5 Auger spectra of In, Sn, and Sb and compared them with the results of atomic calculations using the jj-intermediate
SSDZ0368-2048(94)02130-R
coupling scheme ]2] for the initial-and final-states. As in other treatments [ 1,2], satisfactory agreement between theory and experiment was reached when the problem was considered atomic in nature 141. Since the 4d bands are full in the metals considered in I, it is interesting to investigate the form of the L&I45M,,5 spectra in metals for which there are holes in the initial-state d-band. In this paper, we report the results of such a study for the series Ag, Pd, and Rh, which runs the gamut from (almost) full to partially empty 46 bands. The forms of the main spectra agree with the results of jj-intermediate coupling calculations [9,10], as in I. There appear, however, anomaIous loss structures at lower kinetic energies whose origins seem different from any yet reported. In other work [9,10], we identify these loss spectra as arising from d-band spectator vacancy satellites and show that this model is consistent with all the aspects of the data. Caster-Kronig processes present in the Cu L2,3M4,5M4,5Auger spectra ate apparently absent here.
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In this paper, we emphasize the systematic behavior of the experimental data, and show to what extent we can reach model independent conclusions by considering these systematics within the context of the interpretations of the Cu I?,3Mq,5Mq,5 satellites. In Sec. 2, we report the experimentalresults, in Sec. 3, we discuss them and, in Sec. 4, we present the conclusions. Throughout, we draw freely on theoreticalresults reported in I. 2. EXPERNMENTALRESULTS The sample preparation and experimental procedures are reported elsewhere [3-8,11-141.In Figs. 1 to 3, we present, respectively, the Lz3M,5M,,5 Auger spectra of Ag, Pd., and Rh exbted with bremsstrahlung [15,16]. In each figure, the raw L,M,,,M,,, and L$,,$I, 5 spectral dam are represented by dots and t&d lines, respectively, and have been plotted on the same energy and intensity scales for ease of comparison; the absolute energies of the main (*G,) peaks are given in the figure captions [8]. An
important point for our future argumentationis that the ratio between the areas of the background subtracted L, and h spectra is around 2.2, which is quite close to the statistical ratio of 2, considering the uncertainties involved in measuring the areas and defining the background, which we determine from the Shirley method [ 171 (the background determination is discussed further in refs. 9 and 10). In each figure, the L, - and L,M, 5M,,, spectra exhibit structure to the left of the main peak (the “loss” region) which are remarkably similar and several peaks to the right of the main peak (the “atomic” region) of quite different shape. The relative energies of the atomic peaks agree with final-state term splittings calculated in the intermediate coupling (IC) scheme 1181. As pointed out in I, the LS coupling scheme is inadequate in these cases. The results of the calculations of the multiplet energies treating the final-state in the IC coupling scheme are presented elsewhere [9,10]. The transition rates were also calculated in the jj-IC intermediate coupling approximation
The L2M4,5M4,5(solid line) and L M,,5M,,, (dots) Auger spectra of Ag as a function of kinetic energy. The absolute energies of the main (9C,) peaks are, respectively, 2749.4eV and 2577.0 eV for the L, and L, spectra. The spectra have been plotted on the same energy and intensity scales to illustrate the difference in form of the atomic multiplet structure and the similarity of the loss structure in both spectra. Fig. 1
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[4,0,10]. The results of these atomic calculations are in quite good agreement with experiment for energies at and above that of the main peak [9,lo]. The theoretical spectra reproduce the shape and relative intensities of all the atomic experimental peaks [9,10], as in the case of the corresponding In, Sn and Sb spectra 141.The atomic calculations, however, are inadequate for describing the loss structures for kinetic energies below that of the main peak [9,10]. In contrast to the In, Sn and Sb spectra in I, the positions of the loss structure on the low kinetic energy sides of the spectra in Figs. 1 - 3 do not agree with the energies of plasmon losses f19,20]. Comparison with the Ag and Pd hM4,,M,,S spectra in AgPd alloys [9,10] indicates that the Ag and Pd loss structures have neither any effect on any of the other XPS and XAES lines, nor any mutual influence of one on the other in the pure metals and alloys studied, so that it is reasonable to consider the loss structure as intrinsic to the L,M,,5M4, transition iu the whole series. In the alloys stu&e~ the similarities between the L, and L,M,,,M,,5 illustrated in Figs. 1-3 are also observed [9,10].
The loss features of the b,3M4,5MIS spectra which we report here bear certain similarities to those associated with the corresponding spectra of the 3d metals, which have heen the subject of a great deal of attention[1,21-321.Examination of the similarities, as well as the differences, between the 4d and the 3d &,3M4,5M4,5spectra facilitates interpretation of the former. In particular, the satellites of the Cu L2.3M4,5M4,5 Auger spectra, which have been the most studied [1,21,23-26,28-323,seem to arise from 3d (i.e., M4,5) spectator vacancies produced before the Auger process. The b satellite seems mainly to originate in a L,L3M,,5 Caster-Kronig (CK) transition preceding the L3M,5M4,5 recombination; a substantial fraction of the ‘initial L,M4,5 states, however, seem to be produced directly in the photoemission process [29] (i.e., shake-up and shake-oft?. The L, satellite, on the other hand, seems to be consistently explained by the combination of an initial-state shake-up process and a L,bM,,, CK trausition preceding the L2M4,5M4,5 process [32]. The salient features of the Cu satellites are the following: (a) Thepositionsof the L, and L, satellites
3. DISCUSSION
20.0
E~&Y bv) Fig. 2 The L,M4,5M4,,(solid line) and L,M,,,M,,, (dots) Auger spectra of Pd as a function of kinetic energy. The absolute energies of the main (lGq) peaks are, respectively, 2625.7 eV and 2469.1 eV for the L, and L, spectra. The spectra have been plotted on the same energy and intensity scales to illustrate the difference in form of the atomic muitiplet structure and the similarity of the loss structure in both spectra.
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to their respective main peaks are approximately the same, and agree with calculations of the energy of the L,M,,5 + M,,M,,,M,,, transition corresponding to MdJ spectator holes [%I; (b) The ratio of the intensities of the L, aud b main peaks is much more than 2, the ratio of initial-state multiplicities: part of the L, intensity is transferred to the L, satellite through the L2L3M4,5 CK process mentioned above [29];(cc)The double-peak structure of the b satellite seems to be caused by multiplet s@itting of the 3d Btal-state caused by strong spin-orbit coupling of the three M4,5holes [26], as reflected in optical data [33]; and (d) The ratios of the satellite to main spectrum intensities of both the L, and L, spectra are about the same for photon energies below the L, threshold [28]: since the CK process can be thought of as takiug holes from the main L2 line and donatiug them to the L, satellite, and since the b satellite has au unusually long lifetime [26,29], interpretation of these satellite lineshapes is complicated. relative
Cormsponding to points (a) to (d) above, we note that, for the L,,,M,,,M,,, spectra reported here: (1) In each figure, the L, and h losses are displaced the same amount relative to their respective main peaks, suggesting the validity of
the spectator vacancy mode1 - the most likely candidate being a NJ5 vacancy; (2) The ratio of the 5 and L, intensities is within ten percent of the statistical ratio (i.e., 2): this would suggest that L,L,X CK processes contribute little; (3) The shape of the loss structures in Figs. 1 to 3 would not seem to be atuibutable to multiplet splitting of the fmal-state with the spectator vacaucy, since both losses have approximately the same shape, whereas the corresponding atomic spectra have vacancies quite differentforms:indeedspectator consistent with the relative positions (in particular, N4,5vacancies) would not be expected to greatly modify the multiplet splitting of the Mq,5M4,5 hole state; (4) The ratios of loss to main spectrum intensities is very similar for both the L, and L, spectra, as in the case of Cu: the apparent absence of CK processes in the 4d metals, however, suggests that the same mechanism is responsible for both spectra.
In analogy with Cu, the only spectator vacancy state consistent with calculations of the energy [9,10] which could possibly produce the losses closest to the main peak is that corresponding to a 4d (i.e., N4,5) band hole [34]: consistent with this interpretation is the approximation of the satellite tothemainpeakaswepassfromAgtoRhinFigs.
Energy(4 Fig. 3 The bM&Q5 Isolid line) and L M+,5M4,5(dots) Auger spectra of Rh as a function of kinetic energy. The absolute energies of the main (9G4) peaks are, respectively, 2501.2 eV and 2358.9 eV for the L, and L, spectra, The spectra have been plotted on the same energy and intensity scales to illustrate tie difference in form of the atomic multiplet structure and the similarity of the loss structure in both spectra.
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1 to 3. All other states result in values of relative satellite positions which are much too large [9,10,20].Indeed, calculated sateRite positions are in reasonableagreement with experiment [9,10]. Lineshapes resulting from this picture are also consistent with the data [9,10]. In contrast to the case of Cu, where the satellite multiplet splitting arises from the strong spin-orbit interaction of the three M4,5 final-state holes, the proposed N4,5 spectator holes in the 4d metals interact only weakly with the M,,5 core holes because of the different atomic shells involved. The multiplet splitting resulting from the interaction of the three holes, therefore, is little different from that of the two M,,, holes, except for intrinsic broadening arising partly from the small extra multiplet splitting produced by the N4,5hole and partly from the width of the 4d-band. We expect, therefore, the satellite lineshapes to be essentially broadened images of the main, atomic spectra shown on the right side of the main peaks in Figs. 1 to 3. From the cousidcrations presented here, it appears that bL,X CK processes contribute little to the 46 spectrh in contrast with the situation in Cu, for example. In fact, the data seems to oblige us to interpret the loss features of the 4d L2,3M,,,M,5 spectra as arising from shake-up satellites a&mg from d-band valence holes. The probability of shake-up processes in photoemission increases with increasing photon energy [35]. Loss structure resulting from incomplete relaxation of the photoexcited state were observed previously in plasmon gain satellites of the KLL spectra of Na and Mg [3$j and shake-up satellites of the KLV spectra of Mg [36] and Al [37]. Since we use bremsstrahlung as the exciting radiation, the high photon energies involved may explain why shake-up processes are strong in the spectra in Figs. 1 to 3; of course, this requires that the d-baud spectator holes be sufficientIy long lived to survive until the Auger decay occurs [38]. What is not clear at present is why the L&,X CK processes are so weak. It should be noted that, from rough measurements of experimental peak areas, there appear to be L,L,,,X CK processes involved 19,101.The observed ratios of L, and L, intensities indicate, however, that CK process must have
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