ANALYSIS OF FIELD EMITTER SURFACES BY VERY HIGH RESOLUTION AUGER ELECTRON SPECTROSCOPY

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ANALYSIS OF FIELD EMITTER SURFACES BY VERY HIGH RESOLUTION AUGER ELECTRON

SPECTROSCOPY

M. Mundschau, R. Vanselow

To cite this version:

M. Mundschau, R. Vanselow. ANALYSIS OF FIELD EMITTER SURFACES BY VERY HIGH

RESOLUTION AUGER ELECTRON SPECTROSCOPY. Journal de Physique Colloques, 1986, 47

(C7), pp.C7-121-C7-126. �10.1051/jphyscol:1986722�. �jpa-00225915�

ANALYSIS O F F I E L D EMITTER SURFACES BY VERY H I G H RESOLUTION AUGER ELECTRON SPECTROSCOPY

M. MUNDSCHAU and R . VANSELOW

Department of Chemistry and Laboratory for Surface Studies, University of Wisconsin-Milwaukee, Milwaukee, W I 53201, U.S.A.

A b s t r a c t

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I m p u r i t y s e g r e g a t i o n o n P t was s t u d i e d u s i n g v e r y h i g h r e s o l u t i o n

p-

Auger e l e c t r o n s p e c t r o s c o p y a n a l y s i s o f a n n e a l e d f i e l d e m i t t e r s u r f a c e s . U s i n g e l e m e n t a l a n a l y s i s o b t a i n e d from t h e Auger s t u d i e s t o complement i n f o r m a t i o n o b t a i n e d from f i e l d e m i s s i o n m i c r o s c o p y s t u d i e s , t h e l a t e r a l d i s t r i b u t i o n o f s e g r e g a t e d s u r r a c e i m p u r i t i e s was d e t e r m i n e d a t t h e s u b - m i c r o n l e v e l .

I

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INTRODUCTION

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Very h i g h r e s o l u t i o n Auger e l e c t r o n s p e c t r o s c o p y (AES) c a n p r o v i d e e l e m e n t a l a n a l y - s i s o f f i e l d e m i t t e r s u r f a c e s . Such a n a l y s e s , p e r f o r m e d i n c o n j u n c t i o n w i t h FEH s t u d i e s , a l l o w s u r f a c e s e g r e g a t i o n o f i m p u r i t i e s t o b e i n v e s t i g a t e d a t t h e s u b - m i c r o n l e v e l . T h i s p a p e r d e s c r i b e s AES a n a l y s e s o f f i e l d e m i t t e r s u r f a c e s a n d i t s a p p l i c a t i o n s t o t h e s t u d y o f s u r f a c e s e g r e g a t i o n . S p e c i f i c a l l y , t h e s u r f a c e s o f P t f i e l d e m i t t e r s a r e examined. The r e l a t i v e l y h i g h a n n e a l i n g t e m p e r a t u r e s w h i c h a r e r e q u i r e d f o r t h e s t u d y o f s u r f a c e s e g r e g a t i o n u s u a l l y d u l l e m i t L e r s t o s u c h a n e x t e n t t h a t f i e l d d e s o r p t i o n t e c h n i q u e s a r e n o t a p p l i c a b l e . T h u s , t h e r e i s a need f o r e l e m e n t a l a n a l y s i s o n w e l l a n n e a l e d e m i t t e r s , w h i c h c a n e x c e e d o n e m i c r o n i n d i a m e t e r .

I t h a s l o n g b e e n known t o f i e l d e m i s s i o n m i c r o s c o p i s t s t h a t a n i m p u r i t y r i n g s t r u c t u r e o f h i g h t h e r m a l s t a b i l i t y c a n form a b o u t t h e P t { 1 0 0 } a r e a s 1e.g. 1-71.

T h i s I 1 0 0 1 r i n g s t r u c t u r e p e r s i s t s t o a b o v e 1 5 0 0 K 1 8 1 . I t b r o a d e n s when t h e s a m p l e i s h e a t e d t o t e m p e r a t u r e s b e t w e e n 8 7 0 K a n d 1 2 5 0 K a n d is r e d u c e d t o i t s h i g h t e m p e r a t u r e s i z e by h e a t i n g a b o v e 1 2 5 0 K 191.

U s i n g AES a n a l y s i s a n d FEM o b s e r v a t i o n s , t h e i m p u r i t y r e s p o n s i b l e f o r t h e s t a b l e { l o 0 1 r i n g s t r u c t u r e c o u l d b e d i s t i n g u i s h e d from t h e i m p u r i t i e s w h i c h c a u s e t h e r i n g t o b r o a d e n .

Not a l l f i e l t l e m i t t e r s a m p l e s w e r e c m t a m i n a t e d w i t h t h e i m p u r i t y which p r o d u c e s t h e { l o 0 1 r i n g s t r u c t u r e . I n some c a s e s i m p u r i t i e s w e r e f o u n d t o s t a b i l i z e non- e q u i l i b r i u m ' 0 1 2 ) p l a n e s / 9 , 1 0 / . T h e s e i m p u r i t i e s w e r e a l s o i d e n t i f i e d by v e r y h i g h r e s o l u t i o n AES. The t y p e o f i m p u r i t y p r e s e n t was found t o v a r y w i t h t h e m a n u f a c t u r e r o f t h e P t w i r e 191.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986722

C7-122 JOURNAL

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PHYSIQUE

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EXPERIMENTAL

2 . 1

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F i e l d Emission Microscopy

The e x p e r i m e n t a l a p p a r a t u s is d e s c r i b e d i n d e t a i l e l s e w h e r e 181. The FEM s t a t i o n employed s t a n d a r d UHV components. A l i q u i d n i t r o g e n c o o l e d z e o l i t e s o r p t i o n pump p r o v i d e d a rough vacuum. A 20 11s i o n pump a c h i e v e d a b a s e p r e s s u r e i n t h e low 1 0 - l o t o upper 1 0 - l 1 T o r r r a n g e t o

lo-'

P a s c a l ) a f t e r bakeout f o r 24 h a t 650 K.

The e m i t t e r s , e m i t t e r h e a t i n g l o o p s and e l e c t r o d e d e g a s s i n g w i r e s were p r e p a r e d from 0.0005" (0.127 mm) d i a m e t e r w i r e s (Sigmund Cohn Corp. (SCC) o r M a t e r i a l

Research Corp. (MRC) 99.999% p u r e ) and were e l e c t r o l y t i c a l l y e t c h e d a t room tempera- t u r e i n a 20% by w e i g h t aqueous s o l u t i o n of KCN / 8 / .

2.2

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Auger Microprobe

D i r e c t AES a n a l y s i s of t h e a p e x r e g i o n s of f i e l d e m i t t e r s was o b t a i n e d u s i n g a P h y s i c a l E l e c t r o n i c s v e r y h i g h r e s o l u t i o n s c a n n i n g Auger microprobe (Model 595).

Base p r e s s u r e s i n t h e same r a n g e a s i n t h e FEM were a c h i e v e d a f t e r baking o v e r n i g h t . The i n s t r u m e n t was c a p a b l e o f p e r f o r m i n g Auger l i n e s c a n s and s c a n n i n g Auger maps.

Average s e n s i t i v i t y of 0.001 of a monolayer was claimed by t h e m a n u f a c t u r e r f o r r o u t i n e a n a l y s i s . UHV-SEM c a p a b i l i t i e s w i t h a working m a g n i f i c a t i o n of 100,000 X were claimed by t h e m a n u f a c t u r e r . The minimum beam d i a m e t e r was 500

2.

A 3.5 nA c u r r e n t was used i n t h e a n a l y s i s of t h e e m i t t e r a p i c e s .

The Auger e l e c t r o n e n e r g y a n a l y z e r was of t h e c y l i n d r i c a l m i r r o r t y p e . A LaB6 t h e r m i o n i c l f i e l d e m i s s i o n gun was c o a x i a l l y mounted i n t h e c e n t e r of t h e c y l i n d r i c a l m i r r o r a n a l y z e r a s was a c h a n n e l t r o n d e t e c t o r . The geometry allowed c o l l e c t i o n of e l e c t r o n s from t h e e n t i r e cone o f e l e c t r o n e m i s s i o n . A combination of a r e l a t i v e l y l a r g e e l e c t r o n c o l l e c t i o n e f f i c i e n c y and c h a n n e l t r o n a m p l i f i c a t i o n a l l o w e d d a t a t o be a c q u i r e d d i r e c t l y i n t h e N(E) mode (number of e l e c t r o n s , N , v s . e l e c t r o n e n e r g y , E) r a t h e r t h a n t h e dN/dE mode t y p i c a l f o r many AES i n s t r u m e n t s of t h e c y l i n d r i c a l m i r r o r a n a l y z e r t y p e , o r t h e d 2 ~ / d ~ ' mode t y p i c a l f o r r e t a r d i n g g r i d a n a l y z e r s o f t e n found i n LEED i n s t r u m e n t s . Data c o u l d be c o n v e r t e d i n t o t h e more f a m i l a r d e r i v a - t i v e modes from t h e N(E) mode u s i n g s o f t w a r e developed by t h e m a n u f a c t u r e r which p l o t t e d (N2-N1)/(E2-El) v s . E.

A s p e c i a l sample c a r o u s e l was d e s i g n e d t o h o l d up t o t h r e e f i e l d e m i t t e r e l e c t r o d e a s s e m b l i e s / 8 / . The c a r o u s e l allowed i n d i v i d u a l r e s i s t a n c e h e a t i n g of t h e samples a s w e l l a s r e s i s t a n c e h e a t i n g of d e g a s s i n g w i r e s . The c o n s t r u c t i o n o f a sample c a r o u s e l which p e r m i t s t h e h e a t i n g o f t h e e m i t t e r s i n UHV and which a l s o a l l o w s d e g a s s i n g of t h e e l e c t r o d e a s s e m b l i e s i s e s s e n t i a l i f meaningful d a t a a r e t o be c o l l e c t e d from f i e l d e m i t t e r s u r f a c e s . Analyses showed t h a t unheated e m i t t e r s were c o n t a m i n ~ t e d w i t h r e s i d u a l e t c h i n g a g e n t s , i m p u r i t i e s from t h e atmosphere and i m - p u r i t i e s a d s o r b e d d u r i n g t h e bakeout of t h e system / 8 , 1 1 / . These i m p u r i t i e s c o u l d be removed by s l o w g e n t l e h e a t i n g 18,111.

3 . EXPERIMENTAL RESULTS

F i g u r e l a i s a s t e r e o g r a p h i c p r o j e c t i o n o f a [ l l l ] o r i e n t e d f c c c r y s t a l . F i g u r e l b i s a FEM image o f a P t sample (SCC P t ) f l a s h e d t o 1700 K and quenched. The c h a r a c - t e r i s t i c r i n g s t r u c t u r e s a r e s e e n a b o u t t h e { l o o ) . F i g u r e l c i s t h e image t a k e n a f t e r h e a t i n g t h e e m i t t e r of l b t o 870 K f o r 200 s. The broadened { l o o } i m p u r i t y s t r u c t u r e s a r e s e e n . F i g u r e I d i s t h e image t a k e n a f t e r h e a t i n g MRC P t t o 870 K f o r 200 s. No 1100) r i n g s t r u c t u r e appeared. I n s t e a d , n o n - e q u i l i b r i u m {012} p l a n e s a r e s e e n . P l a t i n u m e m i t t e r s p r e p a r e d from w i r e s of b o t h companies were g i v e n iden- t i c a l p r e t r e a t m e n t .

F i g u r e 2 i s a UHV-SEM image o f a P t e m i t t e r a c e x (SCC P t ) , t a k e n i n t h e Auger i n s t r u m e n t , a f t e r t h e e m i t t e r was h e a t e d 200 s a t 870 K ( t h e same c o n d i t i o n which produced t h e broadened I1003 r i n g s t r u c t u r e of F i g . l b ) . By u s i n g maximum c o n t r a s t , t h e I1003 broadened i m p u r i t y s t r u c t u r e became v i s i b l e .

beam was t h e n r a s t e r e d o v e r t h e i m p u r i t y s t r u c t u r e .

4. DISCUSSION

p--

As d e m o n s t r a t e d i n F i g . 3 , Auger e l e c t r o n s p e c t r a c a n b e o b t a i n e d from s u b - m i c r o n s i z e s t r u c t u r e s on f i e l d e m i t t e r s u r f a c e s . A l l o f t h e m a j o r P t s i g n a l s ( a s i n d i - c a t e d i n s t a n d a r d AES h a n d b o o k s 1 1 2 1 ) a r e s e e n . However, r e s o l u t i o n i n t h e Auger i n s t r u m e n t was n o t a d e q u a t e t o p e r f o r m Auger maps o r e v e n Auger l i n e s c a n s o f t h e P t { 1 0 0 } i m p u r i t y s t r u c t u r e . U s i n g t h e Auger m i c r o p r o b e a l o n e , t h e l o c a t i o n o f t h e i m p u r i t i e s r e s p o n s i b l e f o r t h e s t a b l e ( 1 0 0 ) r i n g s t r u c t u r e c o u l d n o t b e r e s o l v e d from t h e l o c a t i o n o f t h e i m p u r i t i e s w h i c h c a u s e t h e r i n g s t r u c t u r e t o b r o a d e n . However, by a c q u i r i n g a s p e c t r u m a f t e r f l a s h i n g t h e s a m p l e t o t e m p e r a t u r e s a b o v e 1 2 5 0 K , o n l y a P s i g n a l c o u l d be d e t e c t e d . Upon h e a t i n g t o 8 7 0 K , C, S i and S s i g n a l s , i n a d d i t i o n t o t h e P s i g n a 1 , w e r e d e t e c t e d . Upon s u b s e q u e n t r e f l a s h i n g , o n l y t h e P s i g n a l p e r s i s t e d . I n t h i s manner, u s i n g t h e h i g h r e s o l u t i o n i n f o r m a t i o n o b t a i n e d w i t h t h e FEM, i t was c o n c l u d e d t h a t P was r e s p o n s i b l e f o r t h e s t a b l e P t { 1 0 0 } r i n g s t r u c t u r e , a n d t h a t C , S i a n d S c a u s e d t h e r i n g t o b r o a d e n .

The AES m i c r o p r o b e and t h e FEN complement o n e a n o t h e r . The AES p r o v i d e s e l e m e n t a l a n a l y s i s , w h e r e a s t h e FEM a l l o w s t h e s p a t i a l d i s t r i b u t i o n o f t h e e l e m e n t s t o b e d e t e r m i n e d a t r e s o l u t i o n s beyond t h e c a p a b i l i t i e s o f p r e s e n t Auger m i c r o p r o b e s . On P t emitters p r e p a r e d f r o m MRC w i r e , no P s i g n a l was s e e n a n d n o { l o o } r i n g a p p e a r e d . Upon h e a t i n g t o 8 7 0 K , t h e t e m p e r a t u r e a t w h i c h t h e { 0 1 2 1 p l a n e s a p p e a r e d , a S i s i g n a l was s e e n . R e s o l u t i o n a n d c o n t r a s t i n t h e AES i n s t r u m e n t w e r e n o t a d e q u a t e , however, t o image t h e { D l 2 1 p l a n e s . As a c r o s s c h e c k , S i was v a p o r d e p o s i t e d o n t o SCC P t i n t h e FEM. A f t e r h e a t i n g t o 8 8 0 K , ( 0 1 2 ) p l a n e s a p p e a r e d / 8 , 1 0 / . L i k e w i s e , when P was d e p o s i t e d o n t o MRC P t , s t a b l e { l o o } r i n g s t r u c t u r e s w e r e formed upon a n n e a l i n g 1 8 , 1 3 1 . T h u s , t h e a c c u r a c y o f t h e AES a n a l y s i s c o u l d b e v e r i f i e d .

D e t a i l s o f t h e AES a n a l y s e s a r e g i v e n e l s e w h e r e / 8 , 9 , 1 1 / . I t m i g h t b e r e m a r k e d t h a t P, S i , S a n d C are common i m p u r i t i e s i n P t and a r e o f t e n f o u n d o n P t s u r f a c e s a n d i n i n t e r f a c e s 1 1 4 1 . The p h o s p h i d e , P t P 2 , i s known t o b e s t a b l e t o 1 6 7 0 K ( 1 a t m ) 1151.

I n a d d i t i o n , P t P 2 i s e x t r e m e l y i n e r t c h e m i c a l l y 1161. P h o s p h o r u s i s a l s o o n e o f t h e most t e n a c i o u s p o i s o n s o f P t c a t a l y s t s 1 1 3 1 . T h u s , t h e p e r s i s t e n c e o f P o n P t e m i t -

t e r s i s c o n s i s t e n t w i t h known Pt-P c h e m i s t r y .

I n o r d e r t o o b t a i n r e a s o n a b l e AES s i g n a l s f r o m t h e s u b - m i c r o n s i z e s u r f a c e f e a t u r e s o n f i e l d e m i t t e r s , o n e m u s t u s e e i t h e r r e l a t i v e l y h i g h e l e c t r o n beam d e n s i t i e s f o r s h o r t p e r i o d s o f t i m e , o r u s e l o w beam d e n s i t i e s f o r l o n g e r p e r i o d s o f t i m e . I n e i t h e r c a s e o n e must be a w a r e o f e l e c t r o n beam e f f e c t s o n t h e s a m p l e . The e l e c t r o n beam c a n c o m p l e t e l y a l t e r t h e c h e m i c a l c o m p o s i t i o n o f a s u r f a c e . C h e m i c a l compounds c a n b e c r a c k e d by t h e e l e c t r o n beam, a n d some e l e m e n t s o r m o l e c u l e s c a n b e d e s o r b e d . F o r t h i s r e a s o n i t i s more d e s i r a b l e t o u s e a n e l e c t r o n beam power d e n s i t y a s l o w a s p o s s i b l e a n d t o i n c r e a s e t h e c o l l e c t i o n t i m e . The s p e c t r u m o f F i g . 3 was c o l l e c t e d w i t h i n 1 h. Long c o l l e c t i o n t i m e s i n c r e a s e t h e p r o b a b i l i t y o f c o n t a m i n a t i o n f r o m

t h e g a s p h a s e . However, c o n t r o l e x p e r i m e n t s a r e e a s i l y p e r f o r m e d by a n a l y z i n g sam- p l e s w h i c h h a v e b e e n e x p o s e d f o r e x t e n d e d p e r i o d s o f t i m e t o t h e r e s i d u a l g a s . ( I n t h e P t a n a l y s i s o n l y a s l i g h t i n c r e a s e i n oxygen s i g n a l was s e e n a f t e r o v e r n i g h t e x p o s u r e t o t h e r e s i d u a l g a s 181.

Wide s c a n a n a l y s e s ( 0 . 1 mm x 0 . 1 mm) o f t h e e m i t t e r s h a n k s a n d h e a t i n g l o o p s w e r e p e r f o r m e d a s e s s e n t i a l c o n t r o l s t o f u r t h e r m i n i m i z e t h e p r o b a b i l i t y o f e l e c t r o n s t i m u l a t e d d e s o r p t i o n o f s u r f a c e i m p u r i t i e s .

A p p a r e n t l y , t h e r e a r e two d i s t i n c t { l o o } r i n g s t r u c t u r e s o n P t w h i c h a r e s t a b l e t o h i g h t e m p e r a t u r e s . One, w h i c h c a n b e removed ( w i t h d i f f i c u l t y ) by f l a s h i n g t o h i g h t e m p e r a t u r e s , i s a t t r i b u t e d t o p h o s p h i d e f o r m a t i o n . A c c o r d i n g t o l i t e r a t u r e re- p o r t s , upon a n n e a l i n g i n t h e p r e s e n c e o f o x y g e n , a n o t h e r s i m i l a r r i n g s t r u c t u r e

C7-124 JOURNAL DE _PHYSIQUE

i s formed 14-61. T h i s [ l o o } r i n g s t r u c t u r e a p p a r e n t l y c a n n o t b e removed e v e n a f t e r f l a s h i n g t o n e a r t h e m e l t i n g p o i n t o f P t . A r e f r a c t o r y non-Pt o x i d e was s u s p e c t e d 14-61. The Auger a n a l y s e s p e r f o r m e d i n t h e p r e s e n t e x p e r i m e n t s f a i l e d t o d e t e c t o x y g e n o n t h e s u r f a c e s o f t h e P t e m i t t e r s . No oxygen was d e t e c t e d i n w i d e s c a n a n a l y s e s o f t h e e m i t t e r s h a n k s o r h e a t i n g l o o p s , w h i c h would m i n i m i z e t h e c h a n c e t h a t o x y g e n , i f i t w e r e p r e s e n t , was d e s o r b e d by t h e e l e c t r o n beam. I n s t u d i e s o f t h e s o c a l l e d "anomalous P t o x i d e " /1.7,18/, w h i c h i s now i n t e r p r e t e d a s b e i n g a r e f r a c t o r y non-Pt o x i d e , l a r g e oxygen Auger s i g n a l s p e r s i s t . T h i s f i n d i n g i m p l i e s t h a t o x y g e n , i f p r e s e n t , i s n o t d e s o r b e d by t h e e l e c t r o n beam t o s u c h a n e x t e n t t h a t i t s Auger s i g n a l c a n n o l o n g e r b e d e t e c t e d . T h u s , i t was c o n c l u d e d t h a t t h e P t ( 1 0 0 ) r i n g s t r u c t u r e s s e e n i n t h e p r e s e n t e x p e r i m e n t s a r e d u e t o f o r m a t i o n o f p h o s p h i d e a n d n o t d u e t o a r e f r a c t o r y o x i d e . l i i o o f t h e s u s p e c t e d "anomalous P t o x i d e s " , S i 0 2 and A1203, a r e a p p a r e n t l y not t h e c a u s e of t h e { 1 0 0 } r i n g s t a b i l i z e d by oxygen. I n s t u d i e s o f S i 0 2 o n P t , S i 0 2 i s removc!d f r o m t h e s u r f a c e a t t e m p e r z t u r e s w e l l b e l o w t h o s e employed i n t h e f i e l d e m i s s i o n s t u d i e s

/ l a / .

A l s o , on P t s a m p l e s c o n t a m i n a t e d by S i , no s t a b l e { l o o ] r i n g s w e r e formed 1 8 1 . D e p o s i t i o n o f aluminum o x i d e on P t a l s o f a i l e d t o p r o d u c e r i n g s a b o u t t h e Pt!100} 181. P o s s i b l y CaO i s r e s p o n s i b l e f o r t h e s t a b i l i z a t i o n o f t h e P t { 1 0 0 ) r i n g by o x y g e n . C a l c i u m was s e e n o n SCC P t s a m p l e s 1 8 , 1 1 1 , a l t h o u g h t h e o x i d e h a s y e t t o b e d e t e c t e d o n P t f i e l d e m i t t e r s u r f a c e s . SUMMARY

By p r o v i d i n g e l e m e n t a l i d e n t i f i c a t i o n , v e r y h i g h r e s o l u t i o n AES a n a l y s i s o f s u r f a c e s o f f i e l d e m i t t e r s c a n complement i n f o r m a t i o n o b t a i n e d w i t h t h e YEM. One c a n s t u d y , f o r e x a m p l e , a t what t e m p e r a t u r e s s u r f a c e s e g r e g a t i o n o c c u r s and i n what c r y s t a l l o - g r a p h i c a r e a s t h e i m p u r i t i e s a d s o r b . The d i s t r i b u t i o n o f i m p u r i t i e s c a n be d e t e r - mined a t t h e sub-micron l e v e l . Such i n f o r m a t i o n i s d i f f i c u l t t o o b t a i n by o t h e r t e c h n i q u e s o f UHV s u r f a c e s c i e n c e .

ACKNOWLEDGMENTS

We t h a n k Dr. C . J . L a p e y r e f o r u s e of t h e h i g h r e s o l u t i o n AES a t CRISS, Bozeman, Montana (NSF Grant-CIIE 7916134) a n d M r . M . J a e h n i g f o r h i s a s s i s t a n c e .

REFERENCES

A. Korb, i n E . W. Muller, E r g e b . N a t u r .

7

( 1 9 5 3 ) 290.

A . P. Komar and V . P. S a v c h e n k o , S o v i e t P h y s . - S o l i d S t a t e

4

( 1 9 6 2 ) 1 9 6 8 . R. Vanselow, MS T h e s i s , T e c h n i c a l U n i v e r s i t y B e r l i n ( 1 9 6 2 ) .

R. Vanselow, P h y s . S t a t . S o l .

4

( 1 9 6 4 ) 697.

R. Vanselow, P h y s . S t a t . S o l .

2

(1967) 69.

A. J . Melmed, J. Appl. P h y s .

36

(1965) 3691.

R. Lewis a n d R. Gomer, S u r f . S c i .

12

( 1 9 6 8 ) 1 5 7 .

M. Mundschau, " I m p u r i t y S e g r e g a t i o n and A d s o r p t i o n o f C a t a l y t i c S u p p o r t M a t e r i a l o n P l a t i n u m - I n v e s t i g a t i o n s by F i e l d E m i s s i o n M i c r o s c o p y , " Ph.D.

D i s s e r t a t i o n . Univ. o f Wisconsin-Milwaukee ( 1 9 8 6 ) . M. Mundschau and K. V a n s e l o w , S u r f . S c i . 1 5 5 ( 1 9 8 5 ) 1 2 1 . M. Mundschau a n d R . V a n s e l o w , P h y s . Rev. L e t t . 5 3 (1984) 1 0 8 4 . M. Mundschau a n d K. V a n s e l o w , S u r f . S c i .

157

(1?%5) 8 7 .

P. W. P a l m b e r g , G . E. R i a c h , R. E. Weber, a n d N. C. McDonald, "Handbook o f Auger E l e c t r o n S p e c t r o s c o p y , ' ' ( P h y s i c a l E l e c t r o n i c s I n d u s t r i e s I n c . , E d i n a , MN, 1 9 7 2 ) .

M. Mundschau a n d R . Vanselow, S u r f . S c i .

166

( 1 9 8 0 ) 1.131.

R. G . M u s k e t , W. McLean, C. A. C o l e m e n a r e s , D. M . M a r k o w s k i e c k i a n d W. J . S i e k h a u s , Appl. S u r f . S c i .

10

( 1 9 8 2 ) 1 4 3 .

W. B i l t z , F. Weibke, E. May and K. M e i s e l , Z . Anorg. Allgem. Chem.

223

( 1 9 3 5 ) 1 2 9 .

A. B a g h d a d i , A. F i n l e y , P. R u s s o , R . A r n o t t a n d A. Wold, J . L e s s Common M e t a l s

34

( 1 9 7 4 ) 31.

H. N i e h u s a n d G. Comsa, S u r f . S c i .

102

(1981) L14.

H. P. B o n z e l , A. M. F r a n k e n and G. P i r u g . S u r f . S c i .

104

( 1 9 8 1 ) 625.

c h a r a c t e r i s t i c { l o o ) r i n g s t r u c t u r e i s p r e s e n t . Phosphorus was t h e o n l y i m p u r i t y d e t e c t e d . ( c ) A f t e r h e a t i n g t h e e m i t t e r of F i g . l b t o 870 K f o r 200 s. The broadened {100] i m p u r i t y s t r u c t u r e s a r e s e e n . S i l i c o n , S and C , i n a d d i t i o n t o P a r e p r e s e n t . (d) Image a f t e r h e a t i n g MRC P t o t 870 K f o r 200 s . Non-equilibrium I0123 p l a n e s a r e s t a b i l i z e d by S i .

C7-126 JOURNAL DE PHYSIQUE

Fig. 2

-

^UHV-SEM image o f P t emitter apex taken a f t e r heating 200 s a t 870 K.

A broadened 100 impurity structure is seen. The i n s e r t shows a FEM imaqe o f

the impurity structure on another sample which was qiven an identical heat treatment.

Fig. 3

-

A q e r electron spectrum taken from the region o f the impurity structure imaged i n Fig. 2 .