Bremsstrahlung-induced Auger peaks

Journal of Electron Spectroscopy and Related Phenomena, 18 (1980) 355-358 0 Elsevler Sclentlfic Pubhshmg Company, Amsterdam - Printed m The Netherlands

Data bank

BREMSSTRAHLUNG-INDUCED

AUGER PEAKS

J E CASTLE and R H WEST Department of Metallurgy, Unrverslty of Surrey, Guddford, Surrey GU2 5XH (Gt Brztam) (Received

11 September

1979)

In a recent paper [l] published by the authors, the use of the Auger peaks excited by the Bremsstrahlung radiation from a conventional alummxum or magnesium X-ray source was described A special study has been made of the Bremsstrahlung-induced KLL Auger peak from silicon Not only 1s s&con an essential element m most minerals, but zts compounds are also vital m many mdustnal processes from catalysis to electronics The surface rnformatlon avalable from conventional &con XPS 1s limited, because only the Zp and 2s core-level peaks are observed and both are relatively weak and at the low bmdmg-energy end of the spectrum Another problem associated with msulatmg samples, including all silicates, is that sample chargmg causes the ejected photoelectrons to be retarded by an undefined amount The subsequent peak shift due to chargmg destroys useful chemical mformatlon As described m the authors’ paper, the use of the KLL Auger peak, induced by Bremsstrahlung radiation, overcomes this chargmg problem The posltlons of the KLL Auger and 2p core-level peaks for each element can be combined (as m Fig 1) to form an Auger parameter (x’ thus (Y* = E, (KLL)+E,(2p)- hv or a” = E,(KLL)- E,(2p) This parameter 1s independent of sample chargmg but strongly dependent on molecular and crystallme structure Table 1 summanzes peak-posltlon data for a wide variety of morganlc slhcon compounds The Auger parameters for the &con m these compounds vary by nearly 5eV, decreasing from the carbide to the oxide v&h an

356 SI (2p)

ow

1651

I

1601

I

I

I

I

I

I

1551

1501

1451

1401

1351

1301

Kmetlc energy (eV)

Fig 1 High kmetwenergy minium X-rays

region of photoelectron

spectrum of silicon irradiated by alu-

TABLE 1 PEAK POSITIONS AND AUGER POUNDS Sample silicon slllcon carbide slhcon mtrlde slllcon dioxide zinc silicate silica gel

Formula Sl SIC

S13 N4 SlOz

Zn S103 SIOz xHz 0 l

PARAMETERS

(Y& FOR A VARIETY

OF Sl COM-

S12p BE (eV)

Sl KLL KE (eV)

4, (ev)

99 103 102 102 108 107

1616 1610 1611 1609 1603 1604

462 460 460 458 458 457

6 9 0 6 1 0

4 2 7 6 7 3

4 5 1 6 2 7

associated increase m the electronegatlvlty of the nelghbourmg atoms around each atom of s&con The lowest values of a& will be expected for fluoroslhcon compounds In a previous study [2] , it was found that hydration of a s&ate structure reduces its slhcon Auger parameter, and this can be seen by comparmg the value for silica with that for s&a gel the latter 1s nearly 1 eV below the former Table 2 lists peak-poatlon data from a wide range of slhcate minerals As each slhcon ion m the lattice IS always surrounded by four oxygen ions as nearest nelghbours, these will strongly screen the slhcon Despite this, measurable differences m the slhcon Auger parameter are found from these minerals, even those from the same group, such as lepldohte and blotlte Agam, hydration of a silicate structure causes a reduction m cw,*, this can be

I F L L L L L L F L R F

almandme anorthlte talc blotlte bentomte pyrophylhte lepldohte muscovlte mlcroclme kaolin& beryl stllblte Ca[ti2Si,Gls]‘7H20

~2Be3[S16%11

~2(S1205WHk

K[A

K~2(Sl3WOlOW-U2 Sl3Osl

K(L~,A~)~(S~,A~)~G~O(GH)~

~2S14010(OW2

Mg,Sl401o(GW2 KtMgFe)s (SQ WAO VW2 AlzMg[% 010 lW% KWJaWbO

Fe3Ah WA 13 1

W&S1208

Formula

a& FOR A VARIETY

- -a Key to slhcate class F, framework, L, layer, R, ring, I, island

Classa

Mineral

PEAK POSITIONS AND AUGER PARAMETERS

TABLE 2

2 8 6 3 7 0 9 5 2 7 0 8

1607 1607 1606 1607 1607 1606 1606 1606 1606 1606 1607 1606

105 104 105 104 105 106 105 105 105 105 104 104

2 5 7 85 4 1 1 5 75 2 7 9

Si KLL (eV)

SI 2p (eV)

OF SILICATES

458 458 458 458 458 458 458 458 458 458 458 458

8 7 7 55 5 5 4 4 35 3 1 1

a& (eV)

seen between anorthlte and stllblte Generally greater vmatlon 1s found among the framework than among the layered slhcates, and this may be due to the more open structure and so less oxygen screening of the slhcon m the framework structures The data @ven here show the use of the Bremsstrahlung-induced Auger peak m the case of s&con m slhcates The authors are convinced that this effect could have many beneficial apphcatlons m industry, especially since It can be obtamed using exlstmg equipment

REFERENCES 1 2

J E Castle and R H West, J Electron Spectrosc Relat Phenom , 16 (1979) 195 J E Castle, L B Hazel1 and R H West , J Electron Spectrosc Relat Phenom , 16 (1979) 97