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The Auger electron spectrum of technetium
Surface Science 128 (1983) L187-L189 North-Holland Publishing Company
SURFACE
SCIENCE
Ll87
LETTERS
THE AUGER ELECTRON
SPECTRUM
OF TECHNETIUM
F.P. LARKINS
Received 9 February 1983
In a recent Letter Chen et al. [1] have reported experimental results for the Auger electron spectrum of the technetium isotope i;Tc. A table of experimental Auger transition energies was reported but only five of the nineteen groups of lines were positively identified. In this Letter twelve of the remaining fourteen groups are identified mainly on the basis of semiempirical Auger electron calculations by Larkins [2] and the L-shell Auger transition probability data of Chen et al. [3]. Other groups of Auger lines not observed in the low resolution spectrum ]I], but which have energies and some line strength in the region investigated are also included in the present analysis. The Auger electron energy for the w, - X,Ykzs+‘LJ process has been determined within an intermediate coupling model for a wide range of elements and transition processes [2,4] using the expression
E(y - X/Y& 2s+‘L,)=&;
-&;
,
-
G’y- vp-k)
=+'LJ
where
+ K(
X,Y'),
(1)
Gt. is the binding energy of an electron in a selected subshell w,; 2s-)+ ‘L, is the interaction energy of a pair of holes in the orbitals X, and (x/yk) Y, of an atom in the “+iLJ multiplet state; K( X,Y,) is an adiabatic correction term that accounts for the lowering of the energy of the final state resulting from relaxation of the atomic orbitals due to the altered atomic environment. The following binding energies have been used for the subshells of technetium required in this work [5]: GL, = 2793.2 eV, G,, = 2676.9 eV, &,, = 544.0 eV, s MZ= 444.9 eV, G,, = 425.0 eV, EM1 = 256.4 eV, FM, = 252.9 eV, &;N, = 68.0 values for the binding eV, SN,, = 38.9 eV and GN,, = 2.0 eV. If improved energies should become available then the semiempirical Auger electron energies are readily adjusted using eq. (1) for the new values. The accuracy of the calculated line energies is therefore directly linked to the reliability of the experimental binding energies used. Within an intermediate coupling framework there are several multiplet lines possible. While these are listed in the original tables [2], for the present analysis it is sufficient, recognising the low resolution of the experimental data, to take 0039-6028/83/0000-00/$03.00
0 1983 North-Holland
LIX8 Table I Semiempirical
F. P. Larkins / Auger electron spectrum of technetrum
and experimental
Transition
Theory n)
N, -%P,, N,,-N,,N,, N, -N,,% Me -N,N, M,,-N,Nx M,,-Nd2~ W5 -N,N,, Me,-%N,, Me-N,,b Lx-M,M, Lx-M,M, L, -M,M, L,-M,M, L, -M,M,
- 28 - 35 - 64 108;; 142:; 171;; 183;: 214;: 254,: 1688;:f 1759 1773 1782;: 1802;: 1804::’ 1852,: 1875
L,-M,M, L,-M,M,, L,-M,M>
‘) Numbers in superscripts coupling, from ref. 121. h, From ref. [I].
Auger line energies Experiment
h,
31+1 60+
I
134+ 166* 17912 207i2 246+2
I 1
for i:Tc
(in eV)
Transition
Theory
L,-M,M, L,-M,M, L3-M,M,, Lz-M,M,s b -M3M,, L, --M2M,, L, -M,Nu Lz-M,M,, b%,b,
1898;; 1918;: 1949,; 1968;: 1973;;o 2065;; 2085 - ’ 2089;;’ I 2139;;’ 2184,: 2201- ’ 2204;: 225s ;i’ 2289 *, 23M);: 2320,: 2374,: 2459;: 2490;:
L,-M,%, L, -MIND
L, -M,% L, -M&L
1788k3 >
L-MP, L, -M,N,, Lz -M,N,, L, -%,%I L, -b,N, Lz-MGN,,
181313
and subscripts
represent
range
of multiplet
values
Experiment
1909+5 19S8rt 5 198455 2075 + 5 2138i_S
2275 + 5
2385 + 5 2435 + 5
in intermediate
aj average [6]. The results obtained are presented in table 1, While in principle there are many lines possible, only those lines in the energy ranges investigated experimentally It] with an estimate transition probability of at least 1% of the strongest series of lines, the L3-M,,M,, series, on the basis of the data presented by Chen et al. [3] for zirconium have been listed. This analysis takes no account of variations in the relative initial hole state populations due to differing subshell ionisation cross-sections and internal hole redistributions, but it is adequate for the present purposes. The extent of multiplet splitting around thejj average value listed in table 1 is indicated by the superscript and subscript values. The resolution associated with the derivative spectrum is not sufficient to resolve such fine structure. The Auger lines at 31 and 60 eV are due to N-NN super Coster-Kronig transitions. While not calculated in this study, there should also be L,-L,N Coster-Kronig lines at - 40 eV (L2-L3N,), - 80 eV (L,-L,N,,) and - 114 eV (L,-L,N,,), but only the weakest of this series at 43 eV has been observed. The origin of the Auger line observed at 14 eV is less clear. The only possible super Coster-Kronig transition. process in technetium is the M,-M,,M4s
F.P. Lmkins / Auger electron specirwn of technetium
LIXY
however most lines in this series are predicted to be near the limit for energetically favourable processes. The M,-NN lines have previously been discussed [I], but the M,-NN processes are also in the same energy range and have considerable intensities. It should also be noted that for these processes the extent of multiplet splitting is much greater than the uncertainty quoted for the experimental values. The strongest of the L,,- MM line series are listed in table 1. The calculations are sufficiently accurate, despite possible uncertainties in binding energies, to confidently assign the observed line energies to particular Auger processes. The other L,,- MM processes listed while having lower transition probabilities should be observable with higher analyser resolution. At the highest kinetic energies investigated there is also a series of weak L,,-NN Auger lines. It is possible, using the data listed in ref. [2] to provide a similar detailed analysis of the Auger structure for other period-5 transition metals beyond that previously given by Haas et al. [7] using a simplified model.
References [1] [t] (31 [4] [5] [6] [7]
T.P. Chen, E.L. Wolf and A.L. Giorgi, Surface Sci. I22 (1982) L613. F.P. Larkins, At. Data Nucl. Data Tables 20 (1977) 311. M.H. Chen, B. Crasemann and H. Marks, At. Data Nucl. Data Tables 24 (1979) 13. F.P. Larkins, J. Phys. B9 (1976) 47. K.D. Sevier, Low Energy Electron Spectroscopy (Wiley-Interscience, New York, 1972). F.P. Larkins, J. Phys. B9 (1976) 37. T.W. Haas, J.T. Grant and G.J. Wololey, Phys. Rev. Bl (1970) 1449.
SURFACE
SCIENCE
Ll87
LETTERS
THE AUGER ELECTRON
SPECTRUM
OF TECHNETIUM
F.P. LARKINS
Received 9 February 1983
In a recent Letter Chen et al. [1] have reported experimental results for the Auger electron spectrum of the technetium isotope i;Tc. A table of experimental Auger transition energies was reported but only five of the nineteen groups of lines were positively identified. In this Letter twelve of the remaining fourteen groups are identified mainly on the basis of semiempirical Auger electron calculations by Larkins [2] and the L-shell Auger transition probability data of Chen et al. [3]. Other groups of Auger lines not observed in the low resolution spectrum ]I], but which have energies and some line strength in the region investigated are also included in the present analysis. The Auger electron energy for the w, - X,Ykzs+‘LJ process has been determined within an intermediate coupling model for a wide range of elements and transition processes [2,4] using the expression
E(y - X/Y& 2s+‘L,)=&;
-&;
,
-
G’y- vp-k)
=+'LJ
where
+ K(
X,Y'),
(1)
Gt. is the binding energy of an electron in a selected subshell w,; 2s-)+ ‘L, is the interaction energy of a pair of holes in the orbitals X, and (x/yk) Y, of an atom in the “+iLJ multiplet state; K( X,Y,) is an adiabatic correction term that accounts for the lowering of the energy of the final state resulting from relaxation of the atomic orbitals due to the altered atomic environment. The following binding energies have been used for the subshells of technetium required in this work [5]: GL, = 2793.2 eV, G,, = 2676.9 eV, &,, = 544.0 eV, s MZ= 444.9 eV, G,, = 425.0 eV, EM1 = 256.4 eV, FM, = 252.9 eV, &;N, = 68.0 values for the binding eV, SN,, = 38.9 eV and GN,, = 2.0 eV. If improved energies should become available then the semiempirical Auger electron energies are readily adjusted using eq. (1) for the new values. The accuracy of the calculated line energies is therefore directly linked to the reliability of the experimental binding energies used. Within an intermediate coupling framework there are several multiplet lines possible. While these are listed in the original tables [2], for the present analysis it is sufficient, recognising the low resolution of the experimental data, to take 0039-6028/83/0000-00/$03.00
0 1983 North-Holland
LIX8 Table I Semiempirical
F. P. Larkins / Auger electron spectrum of technetrum
and experimental
Transition
Theory n)
N, -%P,, N,,-N,,N,, N, -N,,% Me -N,N, M,,-N,Nx M,,-Nd2~ W5 -N,N,, Me,-%N,, Me-N,,b Lx-M,M, Lx-M,M, L, -M,M, L,-M,M, L, -M,M,
- 28 - 35 - 64 108;; 142:; 171;; 183;: 214;: 254,: 1688;:f 1759 1773 1782;: 1802;: 1804::’ 1852,: 1875
L,-M,M, L,-M,M,, L,-M,M>
‘) Numbers in superscripts coupling, from ref. 121. h, From ref. [I].
Auger line energies Experiment
h,
31+1 60+
I
134+ 166* 17912 207i2 246+2
I 1
for i:Tc
(in eV)
Transition
Theory
L,-M,M, L,-M,M, L3-M,M,, Lz-M,M,s b -M3M,, L, --M2M,, L, -M,Nu Lz-M,M,, b%,b,
1898;; 1918;: 1949,; 1968;: 1973;;o 2065;; 2085 - ’ 2089;;’ I 2139;;’ 2184,: 2201- ’ 2204;: 225s ;i’ 2289 *, 23M);: 2320,: 2374,: 2459;: 2490;:
L,-M,%, L, -MIND
L, -M,% L, -M&L
1788k3 >
L-MP, L, -M,N,, Lz -M,N,, L, -%,%I L, -b,N, Lz-MGN,,
181313
and subscripts
represent
range
of multiplet
values
Experiment
1909+5 19S8rt 5 198455 2075 + 5 2138i_S
2275 + 5
2385 + 5 2435 + 5
in intermediate
aj average [6]. The results obtained are presented in table 1, While in principle there are many lines possible, only those lines in the energy ranges investigated experimentally It] with an estimate transition probability of at least 1% of the strongest series of lines, the L3-M,,M,, series, on the basis of the data presented by Chen et al. [3] for zirconium have been listed. This analysis takes no account of variations in the relative initial hole state populations due to differing subshell ionisation cross-sections and internal hole redistributions, but it is adequate for the present purposes. The extent of multiplet splitting around thejj average value listed in table 1 is indicated by the superscript and subscript values. The resolution associated with the derivative spectrum is not sufficient to resolve such fine structure. The Auger lines at 31 and 60 eV are due to N-NN super Coster-Kronig transitions. While not calculated in this study, there should also be L,-L,N Coster-Kronig lines at - 40 eV (L2-L3N,), - 80 eV (L,-L,N,,) and - 114 eV (L,-L,N,,), but only the weakest of this series at 43 eV has been observed. The origin of the Auger line observed at 14 eV is less clear. The only possible super Coster-Kronig transition. process in technetium is the M,-M,,M4s
F.P. Lmkins / Auger electron specirwn of technetium
LIXY
however most lines in this series are predicted to be near the limit for energetically favourable processes. The M,-NN lines have previously been discussed [I], but the M,-NN processes are also in the same energy range and have considerable intensities. It should also be noted that for these processes the extent of multiplet splitting is much greater than the uncertainty quoted for the experimental values. The strongest of the L,,- MM line series are listed in table 1. The calculations are sufficiently accurate, despite possible uncertainties in binding energies, to confidently assign the observed line energies to particular Auger processes. The other L,,- MM processes listed while having lower transition probabilities should be observable with higher analyser resolution. At the highest kinetic energies investigated there is also a series of weak L,,-NN Auger lines. It is possible, using the data listed in ref. [2] to provide a similar detailed analysis of the Auger structure for other period-5 transition metals beyond that previously given by Haas et al. [7] using a simplified model.
References [1] [t] (31 [4] [5] [6] [7]
T.P. Chen, E.L. Wolf and A.L. Giorgi, Surface Sci. I22 (1982) L613. F.P. Larkins, At. Data Nucl. Data Tables 20 (1977) 311. M.H. Chen, B. Crasemann and H. Marks, At. Data Nucl. Data Tables 24 (1979) 13. F.P. Larkins, J. Phys. B9 (1976) 47. K.D. Sevier, Low Energy Electron Spectroscopy (Wiley-Interscience, New York, 1972). F.P. Larkins, J. Phys. B9 (1976) 37. T.W. Haas, J.T. Grant and G.J. Wololey, Phys. Rev. Bl (1970) 1449.