STUDY OF CHEMICAL COMPOSITION AND ELECTRONIC STRUCTURE OF HIGH-MELTING COMPOUNDS OF ZIRCONIUM BY ELECTRONIC AES

(1)

HAL Id: jpa-00223994

https://hal.archives-ouvertes.fr/jpa-00223994

Submitted on 1 Jan 1984

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

STUDY OF CHEMICAL COMPOSITION AND ELECTRONIC STRUCTURE OF HIGH-MELTING COMPOUNDS OF ZIRCONIUM BY ELECTRONIC

AES

I. Brytov, A. Wander, V. Neshpor

To cite this version:

I. Brytov, A. Wander, V. Neshpor. STUDY OF CHEMICAL COMPOSITION AND ELECTRONIC STRUCTURE OF HIGH-MELTING COMPOUNDS OF ZIRCONIUM BY ELECTRONIC AES.

Journal de Physique Colloques, 1984, 45 (C2), pp.C2-353-C2-356. �10.1051/jphyscol:1984280�. �jpa- 00223994�

(2)

STUDY OF CHEMICAL COMPOSITION AND ELECTRONIC STRUCTURE OF HIGH-MELTING COMPOUNDS OF ZIRCONIUM BY ELECTRONIC AES

I . A . B r y t o v , A . S . Wander and V.S. Neshpor VNIINauchprybor, Leningrad, U.S.S.R.

Rgsurn6 - Les changements de composition et de strucbure Blec- tronique des couches superficielles de carbures Z r C x et des nitrures ZrNy dans les domaines d'existence (0,51 < x < 1,0, 0,766 y( l,O),produitsparchauffage sous bombardement Blectro- nique dans une gamrne de tempsratures de 300 K(Th(2300 K sont 6tudigs par spectromgtrie drBlectrons Auger.

Abstract - Changes in chemical composition and electronic structure of surface layers of ZrCx and ZrNy i n areas of homogeneity (0.51 < xC1.0, 0.765 y s I .0) under the action of

sample heating by electron bombardment within the temperature range 300 K dThC 2300 K have been studied using layer-by- layer analysis of sample surface by AES.

Till now study of zirconium nitrides and carbides have been performed in the main using X-ray methods which do not permit to obtain information about composition and electronic structure of surface layers of these materials, Not numerous papers on investigation of zirconium carbide using AES /I ,2/ gave authors the possibility to carry out semiquautitative analysis of surface elemental composition of stoichiometric ZrC and its change in the course of interaction with oxygen and oxygen-bearing gases. Information obtained from non- differentiated Auger-spectra may be used only indirectly for analysis;

of chemical state of surface atoms because these spectra are low see sitive to the change of fine structure of Auger-llnes comprising valence band, There &re available very few papers on study of non-stoichiometric carbides and nitrides of Zr using AES.

We performed analysis of samples of carbide ZrC, and nitride ZrN, i n areas of homogeneity ( 0.51 < x 61 .O and 0.76-2 y& 1 .o) using A ~ S method in a mode of differentiated Auger-spectra within the tempera-

ture range from 300 up to 2300 K when heating samples by electron bombardment in a vacuum of 10-9 torr.

Analysis of samples was performed for lines of W-series of Zr and KLL-series of C, N and 0. Fig. 1 shows Auger-spectra of polycrystal- line stoichiometric samples of Zrl *0 and ZrN1 .0 cleaned with heating up to Th = 2300 K (curves 1 aad 4) as well as spectra of these saqika which were after cleaning during 13 hrs in a vacuum chamber under the pressure of residual gases p=10-5 torr (curves 2 and 5). Curve 3 corresponds to ZrC, -o sample heated up to ThtllOO H at p=10'5 torr.

15N23N05-line which-is a single line in metallic Zr is splitted

& b&h-compounds into two lines, splitting value A E being 3 eV ~ ~

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984280

(3)

C2-354 JOURNAL DE PHYSIQUE

f o r c a r b i d e and 5 eV f o r n i t r i d e . Surfaces of Z r C and Z r f l a f t e r in+*

a c t i o n with r e s i d u a l gases gave s i m i l a r s p e c t r a (curves 3 and 5) d i f - f e r i n g from s p e c t r a of pure samples by even l a r g e r s p l i t t i n g value

a E45=7eV.

0) ...

...

0) 6) :::::'.:. a , . . . .. ."". ." , ^, _....... ^--a.- ^N

...

I

I . . . ! -c

. . 1:

-... ... ^{' , r}^I... .-0

...

.... ^I ⁾ . ^Ar

.. ^J... 81 ! ...

.. :...:. ..I ...

1 't .,.. ^::..r

I ..:: ^f!?..^.+... ...

..I: a::: ... ¹ ....

..4. .*-.:~*.,,%,,*...*,.,s,%

%B4 ... ^L..:..8) . . . . ..,.. ...

... ...

. _.. ^.:: ^!

,Y;

..

1 .;zS .

1. ..I..

::I." '... ...

.. ^J. % w . + * s ~ w w ~

, . , ' I

-

- 1 - r n v ^TfHHH)

UO 300 500 00 150 0 10 20

Fig, 1 - Auger-spectra of ZrCm Pig. 4 - P r o f i l e s of Auger-line and ZrN,,

.

^{1 , 4}correspond t o ZrC,, i n t e n s i t i e s d i s t r i b u t i o n i n depth and ZrN,., , r e s p e c t i v e l y a f t e r he- of Z r N samples. a ) Y=1.0;6) Y=

a t i n g up t o 1000 K and t h e f o l - 0.85; 8) Y=0.76. The following lowing i o n bombardment; 2,5 cor- l i n e s a r e taken f o r t h e elements:

respond t o Z r C g o and Z r N o a f t e r Z r

-

^{92 eV,} ^Ar^-215 eV, C - ^Z72eV,

13 h r s of s t a y a t p=lO - 4 t o r r ; N - 381 eV, 0 - ^{509 eV.}

3 corresponds t o Z r C L o a f t e r h e a t i n g up t o Th = 1100 K a t p = 10-5 t o r r during 10 min.

There i s a l s o observed d i f f e r e n c e i n e n e r g e t i c p o s i t i o n of o t h e r l i n e s of MNN-series of Z r and s h i f t towards t h e lower k i n e t i c ener- g i e s of e l e c t r o n s i s i n c r e a s e d with t h e i n c r e a s e of e l e c t r o n e g a t i v i t y of m e t a l l o i d atoms in Z r X (X = C , N, 0 ) . I n samples of non-stoichiometric c a r b i d e s and n i t r i d e s a value of Y A E does not change ~ ~ in p r a c t i c e with t h e change of concentration of - m e t a l l o i d s t r u c t u r a l va- cancies in c r y s t a l l a t t i c e . A t t h e same time t h e r e d i s t r i b u t i o n of peak i n t e n s i t i e s i n metal doublet t a k e s place. I n Fig. 2 t h e r e a r e shown s p e c t r a of ZrC, samples with t h e s u r f a c e cleaned by i o n bom- --

bardment. Nearing t h e l o w e r boundary of t h e homogeneity a r e a of car- b i d e a h e i g h t of long-wave peak i s reduced as compared with a height of short-wave one. The s i t u a t i o n i s s i m i l a r f o r Z r N samples.

Y

Note, t h a t K I ~ ~ L ~ ~ - l i n e of mete,lloid i n compounds under study i s a l s o s p l i t t e d and splitting value i s c l o s e t o a value of A E45 i n corres- ponding M5N23N45 - spectrum of Z r .

Successive h e a t i n g of samples from room temperature up t o 2300 K shows t h a t a f t e r c l e a n i n g t h e s u r f a c e from contaminations and oxygen ( a t Th = 1200 K f o r ZrNg and 1600 K f o r ZrCx) t h e r e a r e no changes

(4)

r e l a t i o n between l i n e i n t e n s i t i e s connected with t h e l o s s of metal- l o i d atoms in s u r f a c e l a y e r s . I n Fig. 3 t h e r e a r e shown Auger-spect- r a of ZrC, heated up t o Th=1800 K. Comparing Fig. 2 and Fig. 3 one can s e e a change of r e l a t i o n between short- and long-wave peaks a f t e r t h e h e a t i n g and t h i s change i s t h e h i g h e s t f o r ZrCo.6 sample.

Fig. 2 - Spectra of ZrCx samples Fig, 3 - Spectra of Z r C x samples subjected t o i o n i c bombardment. heated up t o Th = 1800 K.

1 - ^X=l^,O, ²- ^X=008,3 - ^X-0.7, ¹- ^{X=I.O, 2}- ^X=0.8, ³ - ^X=0.7,

4 - ^X=0.6; ^a)- survey s p e c t r a , 4 - X=0.6; a ) - survey s p e c t r a , 6 ) -

6 ) - MNN-serles of Z r . fV1NN-series of Z r .

Layer-by-layer a n a l y s i s of Z r X y samples shows t h a t t h e a r e a of chan- ged composition ( r e l a t i v e t o t h e volume one) n e a r t h e s u r f a c e i s of 50 A and i t i s t h e wider t h e more i s t h e concentration of metal- l o i d v a c a c i e s i n a sample volume. For n i t r i d e t h i s a r e a i s approxi- mately twice a s wide a s f o r carbide. A s i l l u s t r a t i o n i n Fig, 4 t h e r e a r e shown i n t e n s i t y p r o f i l e s of Auger-lines of Z r N samples of v a r i - ous composition. D i s t r i b u t i o n p r o f i l e s of 0 , A r and Z r f o r ZrC, Y samp l e a change Fn a s i m i l a r way. Behaviour of d i s t r i b u t i o n p r o f i l e of t h e main m e t a l l o i d in Z r X samples i s i d e n t i c a l .

Y

The s p l i t t i n g of M5N23N45 - l i n e of Z r i n compounds under study i s apparently connected with t h e s p l i t t i n g of d-band of Z r i n s t a t e s with t h e d i f f e r e n t symmetry of wave f u n c t i o n s which according t o cal- c u l a t i o n d a t a /3/ should be observed i n analyzed metal-like compounds.

A t t h e same time according t o c a l c u l a t i o n d a t a f o r s t o i c h i o m e t r i c Z r C 1 .0 and Z r N , .0 the d e n s i t i e s of d r - s t a t e s i n occupied p a r t of valence band a r e considerably higher than d e n s i t i e s of dE - s t a t e s n e a r Fermi l e v e l . There a r e always a l o t of open bonds on a s u r f a c e r e s u l t i n g i n r e d i s t r i b u t i o n of d e n s i t i e s of d r - and d& - s t a t e s which may be a reason of e q u a l i z a t i o n of Auger-peak h e i g h t s of M5N23N45-doublet of Z r a s compared with t h e expected from theory high d i f f e r e n c e of heights.

(5)

C2-356 JOURNAL DE PHYSIQUE

The s p l i t t i n g o f KL1L23-line o f non-metal i s a l s o in good agreement w i t h d a t a o f lmown c a l c u l a t i o n s /3/ where occupied 2 p - s t a t e s of non- m e t a l a r e s p l i t t e d . U n v a r i a b i l i t y of d o u b l e t shape in KLL-spectnun of m e t a l l o i d i s a p p a r e n t l y connected w i t h u n v a r i a b i l i t y of n e a r e s t environment o f X atoms by metal atoms (octahedron a e 6 X > i s always completed).

I n t e n s i t y d e c r e a s e o f long-wave peak connected w i t h Me-Me i n t e r a c - t i o n i s bound up w i t h t r a n s i t i o n of a p a r t o f d y - e l e c t r o n s o f me%&

t o d g - s t a t e s i n b r e a k i n g o f Me-X bonds. Such an e x p l a n a t i o n f o r a shape change of M5N23Na5-doublet of Z r i s n o t c o n t r a d i c t o r y t o

-< .-

r e s u l t s o f c a l c u l a t i o n of d e n s i t y histograms o f d - s t a t e s f o r n i t r i d e of i s o e l e c t r o n i c analogue o f Zr - ^TiN^/4/. The c & c u l a t i o n was p e r - formed t a k i n g i n t o account non-completeness of TiN6 octahedron f o r n i t r o g e n ,

Known a t p r e s e n t d a t a on work f u n c t i o n o f cathodes o f ZrX, compounds a r e i n good agreement with t h e d a t a o b t a i n e d i n t h e p>esent s t u d y on t h e s u r f a c e composition change. So d e c r e a s e o f 'p mrith i n c r e a s e o f temperature t a k e s p l a c e due t o t h e l o s s of m e t a l l o i d atoms by a s u r f a c e in c a s e o f non-congruent v a p o r i z a t i o n .

Thus t h e performed s t u d i e s show t h a t e l e c t r o n i c Auger-spectra o f s u r f a c e c o n t a i n v a l u a b l e i n f o m a t i o n about f e a t u r e s of v a l e n c e band s t r u c t u r e i n s u r f a c e l a y e r s o f analyzed compounds o f ZrX, type. The most i n t e r e s t i n g as we f e e l i s t h e f a c t t h a t t h e shape Gf Auger-

s p e c t r a comprising valence band may be used f o r e v a l u a t i o n of chemi- c a l bond type o f s u r f a c e atoms a s w e l l as f o r d e t e r m i n a t i o n of metd- l o i d c o n c e n t r a t i o n i n homogeneous i m p l a s t a t i o n phases of v a r i a b l e composition.

References

1. UTSKEVICH T.L., KAZANTSEV A.P., FTT 20 (1978) No. 11 3 3 6 5 .

2. MATSKEVICH T.L., KAZANTSEV A.P., Tezisy dokladov XVII v s e s o j u z n o i konf e r e n t s i i po emissionnoi e l e c t r o n i k e , Leningrad ( 1 978) 203.

3. ZHURAXOVSKII E.A., Electronnaya s t r u c t u r a tugoplavkikh soedinenii, Kiev, Naukova dumka (1 976) 383

4. SHINJO K., OHNISHI S., TSUKADA M., SUGANO S., J. Phys. C: S o l i d S t a t e Phys. PJ (1981) 5575.