XPS intensity ratios for Fe, Ni, Pd and Cd metals

Journal of Electron Spectroscopy and Related Phenomena, 17 (1979) 275-278 0 Elsewer Sclentlfic Pubhshmg Company, Amsterdam - Prmted In The Netherlands

Data bank

XPS INTENSITY RATIOS FOR Fe, Nl, Pd AND Cd METALS

E SOBCZAK

and K PERSY *

Instztute of Physics. Polzsh Academy

of Scaences, Warsaw (Poland)

* Instztute of Technacal Physrcs, Techntcal Unwersrty, Vrenna (Austrra)

This communlcatlon presents the XPS lme mtenslty measurements for outer electron subshells m Fe, Nl, Pd and Cd metals for the photon energes of the Ka emlsslon lmes of magnesium at 1254eV and of alummum at 1487 eV usmg a GCA McPherson ESCA 36 spectrometer (without retardmg field), the angle between the mcommg photon and the outgomg electron IS 90°. Before photoemlsslon measurements the metal samples were etched by ion bombardment. The integral mtensltles I, and Ii of photoelectron lmes from z-th and I-th subshells were measured assummg a linear behavlour of the background. The mtenslty ratlo I, /I, of photoelectron lmes from the z-th and I-th subshells of the gwen atom can be wntten [ 1,2,3] as Ii r,=,

0,

. -.-.4 + 0, 4 + p,

AK

Rz

A,

R,

(1)

where o, 1s the total photolomzatlon cross-section of the z-th subshell, 0, 1s the asymmetry parameter, X, w the mean free path for melastlc scattenng of electrons wlvch 1s proportional todc , and R, 1sthe correction factor due to the energy w&h of the spectrometer sht bemg proportional to the kmetlc energy Ekin of the photoelectrons The expementally determined photolonlzatlon cross-section ratio 1s therefore even by

(2) The asymmetry parameter p = 2 for s-electrons at energres far from the threshold [ l] Although p IS not accurately known for the p- and d-subshells discussed here, typical values of 0 for large kmetlc energy are about 1 5 for p-subshells [ 1,4] and m the range 1 O-l 5 for d-subshells [ 1,51

276 TABLE

1

INTENSITY

RATIOS

FOR Fe AND Nl LEVELS

VB/3s

3Pi3s

I, l4 (aq).X,t (w?j)theoly expt /theory

TABLE 2 INTENSITY

RATIOS

(cq/~~j)~~~~ (~fbj)theQry expt /theory

VBI~P

Fe

Nl

Fe

Nl

Fe

Nl

31 32 2 48 13

29 30 2 74 11

0 95 10 0 37’ 27

13 14 0 65a 22

0 31 0 32 0 15a 21

0 44 0 45 0 24a 19

FOP Pd AND Cd LEVELS

3d/4s

414

AT Mg Kcu(1254 eV)

AT Mg Ka (1254 eV)

VB 14s

4PJ4S

VBI3d

VBI~P

Pd

Cd

Pd

Cd

Pd

Cd

Pd

Cd

Pd

Cd

37 64 326 2.0

36 68 363 19

36 3 6 323 11

33 3 4 332 10

56 6 1 243a 25

57 6 1 318* 19

16 16 075a 21

17 17 09Sa 17

0 16 0 095 O075a 12

0 16 009 0,090a 10

a The sum of (J&j and us=

In Tables 1 and 2 the expenmental XPS mtenslty ratios and the derived cross-sectlon ratros at Mg Kac are compared with the theoretlcal photoionlzation cross-section ratios gwen by Scofleld [S] . Analogous results obtamed at the Al Karphoton energy are shown m Tables 3 and 4. The expenmental results agree reasonably well with theory for ratios of p to s mner subshell photoemission as well as for ratios of d-core to d-valence band photoemission Larger discrepancies are revealed for the photoemlsslon of dcore and d-valence electrons relative s- and p-subshells The expernnental mtenslty ratios of d/s and d/p photoemlssron are about twme the theoretical ratios The expenmental errors due to the area peak measurements (about lo%), and the p correction (below 10%) are small compared to these dlscrepancles Multielectron effects are not expected to be so strong as to decrease by a factor of two the measured s- and p-subshell photoemlsslon Sohd state effects like hybndlzatron of s and d orbltals also can not be considered as reasons for the discrepancies, smce they should decrease the expernnental mtensity of the d-valence band compared to the photolonlzatlon crosssections for s and d outer subshells m free atoms. Therefore theoretical crosssections for s and p photoemisslon, which together are a small contnbutlon

277

TABLE 3 INTENSITY

RATIOS

FOR Fe AND Nl LEVELS VBJ3s

3P/3s

&II, (O;/OJ)expt (wq)thfmY expt /theory

AT Al KCU(1487 eV)

VBI3p

Fe

Nl

Fe

N1

Fe

Nl

26 27 2 24 12

31 32 2 48 13

0 66 0 73 0 2ga 26

10 11 0 51a 22

0 25 0 26 0 132a 20

0 32 0 33 0 205a 16

a The sum of o&j and 04~ TABLE

4

INTENSITY

RATIOS

FOR Pd AND

3dJ4s

IElI, (a$~,).,,~ (wJ~J)u-y expt /theory a The

SUIIl

Of

Cd LEVELS

AT Al Ka! (1487 eV)

VB/4s

4Pl4S

VBI3d

VW4p

Pd

Cd

Pd

Cd

Pd

Cd

Pd

Cd

Pd

Cd

30 49 268 18

32 56 292 19

38 40 315 13

37 39 3 25 12

43 47 207a 23

45 49 2 73a 18

11 11 0 66a 17

12 12 087a 14

0 14 0 10 0077’ 12

0 14 0 09 0093’ 10

u&j

and 0~

to the total atomic photolonlzatlon cross-section, seem to be 1 5-2 tnnes lower than the expenmental values The unique XPS mvestlgatlons [7] of Cd and Sr free atoms also show that the intensity ratios of Cd 3d5,* /Cd 3p3,2 and Sr 3d/Sr 3p3,* core subshells are about 1.5 tunes bigger than the theoretical values

ACKNOWLEDGEMENT

One of the authors (E S ) would hke to thank the Austrian Academy of Sciences for havmg gwen her an opportunity to perform measurements in Vienna.

REFERENCES 1 2

J W Cooper and S T Manson, Phys Rev, B L Henke, Phys Rev A, 6 (1972) 94

177 (1969) 157

278 3 4 5 6 7

V I Nefedov, N P Sergushm, I M Band and M B Trzhaskovskaya, J Electron Spectrosc Relat Phenom , 2 (1973) 383 S T Manson, J Electron Spectrosc Relat Phenom , 1 (1972) 413 M 0 Krause, Phys Rev, 177 (1969) 151 J H Scofleld, J Electron Spectrosc ReIat Phenom , 8 (1976) 129 W Mehlhorn, B Breuckmann and D Hausamann, Phys Scr , 16 (1977) 177

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