ANALYTICAL LOW VOLTAGE SEM IN UHV FOR SOLID SURFACE

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ANALYTICAL LOW VOLTAGE SEM IN UHV FOR SOLID SURFACE

T. Ichinokawa, H. Ampo, S. Kinoshita

To cite this version:

T. Ichinokawa, H. Ampo, S. Kinoshita. ANALYTICAL LOW VOLTAGE SEM IN UHV FOR SOLID SURFACE. Journal de Physique Colloques, 1984, 45 (C2), pp.C2-301-C2-306.

�10.1051/jphyscol:1984267�. �jpa-00223981�

Colloque C2, supplement au n02, Tome 45, fgvrier 1984 page C2-301

A N A L Y T I C A L LOW VOLTAGE SEM I N UHV FOR S O L I D SURFACE

T . Ichinokawa, H. Ampo and S . Kinoshita

Department of Applied Physics, Waseda University ^3-4-1, Ohkubo, Shinjuku-ku, Tokyo 160, Japan

Resum& - La c o n c e p t i o n e t l e s performances d ' u n SEM f o n c t i o n - n a n t s o u s u l t r a v i d e avec un canon

&mission de champ s o n t p r & s e n t d e s . D e s B t u d e s du n e t t o y a g e p a r r e c u i t d ' u n e s u r f a c e S i ( 1 1 i ) , d e s p r o c e s s u s de n u c l e a t i o n d e Au e t Ag s u r S i ( l l l ) , de

s u r S i ( l l O ) , i l l u s t r e n t l ' i n t 6 r E t d e l a mdthode.

A b s t r a c t - Design and performance of t h e U*-SEM w i t h a F i e l d e m i s s i o n gun a r e d e s c r i b e d . The a p p l i c a t i o n s of it t d t h e c l e a n i n g p r o c e s s of ~ i ( l l 1 ) s u r f a c e by a n n e a l i n g , n u c l e a t i o n p r o c e s s of Au and Ag on t h e S i ( l l 1 ) and k i n e t i c s of f o r m a t i o n of N i d i f f u s i o n l a y e r on t h e S i ( l 1 0 ) a r e demonstrated.

I-INTRODUCT I O N

Recent t e c h n i q u e s of s u r f a c e a n a l y s i s have been developed r a p i d l y . However, almost s u r f a c e a n a l y s e s were performed i n a l a t e r a l - a r e a l a r g e r t h a n

m m 4 and s t u d i e d a v e r a g i n g p r o p e r t i e s on t h e s u r f a c e .

On t h e o t h e r hand, it h a s been found t h a t s o l i d s u r f a c e s a r e n o t always homogeneous even i n monocrystal and l o c a l p r o p e r t i e s on t h e s u r f a c e p l a y a n i m p o r t a n t r o l e i n t h e s u r f a c e phenomena. From t h i s a s p e c t , m i c r o a n a l y s e s and imaging of s o l i d s u r f a c e by a u l t r a h i g h vacuum s c a n n i n g e l e c t r o n microscope (UHV-SEM) combined w i t h v a r i o u s k i n d s of e l e c t r o n s p e c t r o s c o p i e s and e l e c t r o n d i f f r a c t i o n a r e impor-

% a n t f o r c l e a n and w e l l d e f i n e d s u r f a c e s prepared i n t h e u l t r a h i g h vacuum. P r e p a r a t i o n s , e.g. s u r f a c e c l e a n i n g , e v a p o r a t i o n , a d s o r p t i o n , chemical r e a c t i o n , d e s o r p t i o n by specimen h e a t i n g a r e i n d e s p e n s a b l e f o r s u r f a c e a n a l y s e s .

I n t h e p r e s e n t a p e r , d e s i g n and performance t h e UHV-SEM w i t h t h e f i e l d e m i s s i o n gun i n a vacuum of

1PP6 Torr i n t h e specimen chamber, which has been c o n s t r u c t e d r e c e n t l y f o r s u r f a c e m i c r o a n a l y s e s , a r e d e s c r i b e d and some a p p l i c a t i o n s of t h e i n s t r u m e n t on S i s u r f a c e s a r e demonstrated w i t h composite r e s u l t s of Auger e l e c t r o n s p e c t r o s c o p y

(AES), e l e c t r o n l o s s s p e c t r o s c o p y (ELS), low energy e l e c t r o n d i f f r a c - t i o n ( ~ E E D ) and work f u n c t i o n measurements.

I1 - DESIGN OF ANALYTICAL UHV-FE-SEM

A

schematic diagram of t h e UHV-FE-SEM combined w i t h t h e s u r f a c e a n a l y t i c a l i n s t r u m e n t is shown i n Fig.1.

The i n s t r u m e n t is composed of two h i g h vacuum c h a m b e r ~ ~ o f which vacuum i s high- e r t h a n 2

10- . One chamber at- tached by a UHY-%?;EM, c y l i n d r i c a l m i r - r o r a n a l y s e r ( C M A ) , LEED o p t i c s and a n

i o n gun i s used f o r s u r f a c e microanaly- sis and s u r f a c e imaging. S i g n a l s of Auger e l e c t r o n , energy l o s s e d e l e c t r o n , d i f f r a c t e d e l e c t r o n i n LEED, specimen absorped c u r r e n t , secondary e l e c t r o n and b a c k s c a t t e r e d e l e c t r o n a r e a v a i l a b l e t o form c h a r a c t e r i s t i c images on s o l i d s u r f a c e . The a c c e l e r a t i n g v o l t a g e of UHV-FE-SEM is v a r i a b l e from lOOeV t o 3 0

keV and t h e s p a t i a l r e s o l u t i o n of t h e Fig.1 Diagram of UHV-PE-SEM s e c o n d a r y e l e c t r o n images a t t a i n s t o used i n t h e experiment.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984267

C2-302 JOURNAL DE PHYSIQUE

16094 a t 2OOeV and 20A a t 3OkeV i n a primary e l e c t r o n c u r r e n t of 8

10- A. The o p t i c a l column of t h e UHV-FE-SEM i s c o n s i s t e d of a u s u a l B u t t l e r e l e c t r o s t a t i c l e n s and two magnetic l e n s e s and t h e working d i s t a n c e is v a r i a b l e from s e v e r a l mm(hi h r e s o l u t i o n specimen p o s i t i o n

)

t o 35mm ( a n a l y t i c a l specimen p o s i t i o n 7 . The specimen m a n i p u l a t o r w i t h X, Y and Z t r a n s l a t i o n s , two a x i a l r o t a t i o n s and s l i g h t i n c l i n a - t i o n around t h e o t h e r a x i s i s mounted and t h e sample i s h e a t e d by d i r e c t e l e c t r i c c u r r e n t t h r o u g h t h e specimen w i t h measuring specimen t e m p e r a t u r e by a thermocouple.

Another chamber i s a v a i l a b l e f o r specimen p r e p a r a t i o n and macroscopic s u r f a c e a n a l y s e s and equiped by a same specimen m a n i p u l a t o r w i t h t h e specimen h e a t i n g s t a g e , a c l e a v a g e equipment, a n i o n gun, a n evapo- r a t i o n c e l l , AES-IiEED o p t i c s , a quadrapole mass s p e c t r o m e t e r , X-ray and W s o u r c e s and g a s i n l e t f o r s u r f a c e a n a l y s e s b SIMS, AES, LEED, XPS , UPS and t h e e l e c t r o n s t i m u l a t e d desorption(ESD5.

Both chambers a r e bakable up t o 200°C and connected by a g a t e v a l v e . The sample i s p u t i n t o a pre-vacuum chamber f o r sample exchange w i t h an a i r - l o c k system and t r a n s f e r e d t o t h e sample s t a g e s of t h e b o t h m a n i p u l a t o r s by a t r a n s f e r system w i t h magnetic coupling. The o u t of view is shown i n Fig.2.

111 - PBRFORMANCX OF UHV-FE-SEM

It w a s s u g g e s t e d by t h e p r e s e n t a u t h o r s / l/ t h a t t h e primary energy of UW-SEM w a s p r e f e r a b l e t o o p e r a t e i n t h e low energy r a n g e from lOOeV t o s e v e r a l keV f o r sen- s i t i v e o b s e r v a t i o n s of t h e s u r f a c e and h i g h r e s o l u t i o n e l e c t r o n s p e c t r o s c o p i e s . The FE gun has a h i g h b r i g h t n e s s , because it i s s u i t a b l e t o g e t a h i g h r e s o l u t i o n i n t h e low a c c e l e r a t i n g v o l t a g e .

modi- f i e d H i t a c h i 5-800 e l e c t r o n o p t i c a l column was a t t a c h e d and t h e maximum t o t a l beam

c u r r e n t w a s 100p.A. The e l e c t r o n probe Fig.2 Out of view of t h e c u r r e n t - q n t h e spfcimen is o p e r a t e d b e t - UHV-FE-SEM

ween 1 0 t o 10-

depending on t h e probe s i z e . The s p a t i a l

r e s o l u t i o n a t v a r i o u s a c c e l e r a t i n g v o l t a g e w a s measured by t e s t -

i n g specimens of magn- e t i c t a p e and l a t e x p a r t i c l e s e v a p o r a t e d by gold as shown i n Fig.?.

The s p a t i a l r e s o l u t i o n and a v a i l a b l e magnifi- c a t i o n a r e shown i n F i g . 4 as a f u n c t i o n of t h e primary energy. The r e s o l u t i o n of 1600 A

h a s been a t t a i n e d a t the primary e l e c t r o p energy E =250eV and 20A a t E

= P 3 0 k e ~ w i t h a p ~ p t e P c u r r e n t of 8 x 1 0 A.

The d i s t u r b a n c e i n g e t - t i n g a h i g h r e s o l u t i o n was v i b r a t i o n s of t h e

specimen p u t on t h e

manipulator. Thus, it

needs that the specimen Fig.3 Micrographs t a k e n a t ( a ) E =30keV,

s t a g e i s pushed a g a i n s t 0,8keV, ( c ) 0,5keV and ( d ) 0 , 2 5 k 8 ~ .

of t h e c a n t i l e v e r manipulator.

I V -

APPLICATIONS OF UHV-FE-SEM TO SOLID SURFACE

( 1 ) Cleaning p r o c e s s of ~ i ( l l 1 ) s u r f a c e by a n n e a l i n g

The c l e a n i n g p r o c e s s of ~ i ( l l 1 ) s u r f a c e by a n n f a l i n g up t o 1200" i n t h e vacuum of 2X 10- T o r r w a s observed bv t h e UHV-FE-SEM a t E =2keV w i t h t h e secon&ary e l e c t r o n

d e t e z t i o n and is shown i n Fig.5.

S i ( l l i ) s u r f a c e had been c h e m i c a l l y e t c h e d

by a CP-4 s o l u t i o n of a n e t c h i n g a g e n t and

p u t i n t o t h e h i g h vacuum. The s u r f a c e was Fig.4 S p a t i a l r e s o l u t i o n observed w i t h a n n e a l i n g a t v a r i o u s tempera- and s u i t a b l e magnifica- t u r e s . Etched s u r f a c e w a s contaminated by t i o n a g a i n s t t h e primary carbon and oxygen, t h e r e f o r e a S i c l a y e r energy

grew on t h e s u r f a c e i n t e m p e r a t u r e s h i g h e r t h a n 8 0 0 " ~ as shown i n Fig.5. The S i c l a y e r was removed by t h e r m a l e t c h i n g i n t e m p e r a t u r e up t o 1 2 0 0 ' ~ and a c l e a n s u r f a c e w i t h a num- b e r of s t e p s i n d i s t a n c e of s e v e r a l ,urn a r e appeared as shown i n ~ i g . 5 ( d ) . However, f o r t h e S i ( l l 1 ) s u r f a c e covered by a n oxide l a y e of t h i c k n e s s of s e v e r a l monolayers formed by a s o l v e n t of

0 :H 0(3 :1:1) a t 90-100"

C f o r 1 0 minutes, g h e & s u r f a c e of t h e

7 s t r u c t u r e w i t h o u t s t e p was o b t a i n e d by a n n e a l i n g a t 8 0 o 0 c / 2 / . The 7

s t r u c t u r e of t h e c l e a n s u r f a c e s formed by b o t h methods shows t h e same LEED and RHEED p a t t e r n s a s shown i n Fig.6.

( 2 ) N u c l e a t i o n p r o c e s s of Au and Ag on S i (111) s u r f a c e

Formations of m e t a l and s i l i c i d e t h i n f i l m s on S i s u r f a c e a r e n o t only i n t e r e s t i n g on t h e k i n e t i c s a t t h e s u r f a c e and i n t e r f a c e , b u t a l s o i m p o r t a n t i n t h e semiconductor i n d u s t r y . When gold i s evaporated i n t h e ~ i ( l l 1 ) c l e a n s u r f a c e i n a t h i c k n e s s of a b o u t 1 0 monolayer, a homogeneous s i l i c i d e l a y e r of AuSi is! form- ed on t h e s u r f a c e a t room t e m p e r a t u r e by i n t e r m i x i n g of Au and S i atoms t h r o u g h a n i n t e r f a c e . The e f f e c t c a n be checked by s p l i t t i n g t h e S i LVV Auger peak (92eV) i n t o two peaks (92eV and 93eV). By a n n e a l i n g up t o 3 0 0 " ~ , s e m i - s p h e r i c a l small i s l a n d s l e s s t h a n s e v e r a l um i n d i a m e t e r a r e n u c l e a t e d on t h e s u r f a c e as shown i n Fig.7, and t h e s i z e and d i s t r i b u t i o n depend on t h e s u r f a c e conta- m i n a t i o n and s t e p s . The n u c l e a t e d i s l a n d s a r e amorophus ( n o t e p i t a x i a l l y grown) and have a composition of s i l i c i d e . The i s l a n d s r e d u c e t h e i r d i a m e t e r and d i s a p p e a r by h e a t i n g up t o 9 0 0 " ~ . By h e a t i n g up t o 90O0C, t h e S i

s u b s t r a t e forms a G x . 6 s t r u c t u r e i n a cover- Fig.5 Cleaning p r o c e s s a g e of Au one monolayer and by h e a t i n g f o r of s i ( l l 1 ) s u r f a c e by

s e v e r a l minutes a t 9 0 0 ' ~ t h e s u r f a c e s t r u c t - a n n e a l i n g .

u r e changes t o a 5 x 1 w i t h a coverage of

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DE PHYSIQUE

approximately 0.5 monolayer. By l o n g h e a t i n g a t 9 0 0 " ~ ~ t h e 5

1 s t r u c t u r e d i s a p p e a r s and t h e n t h e 7 X7 s t r u c t u r e of t h e c l e a n s u r f a c e a p p e a r s . Each s u r f a c e s t r u c t u r e of t h e S i ( l l 1 )

~ ~ 6 x 6 , ~ i ( 1 l l ) A u 5

1 and S i ( 1 1 1 ) 7 X 7 t r a n s - forms t o t h e 1 X 1 s t r u c t u r e a t 730eC, 8 0 0 ~ ~ and 840°C, r e s p e c t i v e l y .

On t h e o t h e r hand, Ag e v a p o r a t e d f i l m of a b o u t 1 0 monolayer t h i c k n e s s does n o t form a homogen- eous s i l i c i d e and i s grown by monolayer i n t h e t h i c k n e s s l e s s t h a n one monolayer and by i s l a n d i n t h i c k e r t h a n one monolayer ( S t r a n s k i - K r a s t a - nov t y p e growth)/3/. By h e a t i n g up t o 400°C, i s l a n d s of f l a t polyhedron p a r a l l e l t o t h e s u r f a c e a r e grown as shown i n Fig.8. The is- l a n d s a r e pure s i l v e r and e p i t a x i a l l y grown on t h e s u b s t r a t e . The s i l v e r i s l a n d s e v a p o r a t e d i n t e m p e r a t u r e s h i g h e r t h a n 600°C and t h e s u b s t - r a t e covered by Ag one monolayer had aoxc

s t r u c t u r e . Furthermore, 0.5 monolayer Ag sub- s t r a t e had a 6

s t r u c t u r e . A f t e r t h e h e a t i n g f o r s e v e r a l minutes a t t e m p e r a t u r e h i g h e r t h a n 600"C, t h e S i ( 1 1 1 ) 7 ~ 7 c l e a n s u r f a c e appeared.

The UHV-SEM combined w i t h AES and LEED i s a u s e f u l i n s t r u m e n t f o r a n a l y s i s of k i n e t i c s of f i l m formation.

V- KINETICS OF FORMATION OF NICKEL DIFFUSION LAYER BY

TREATMENTS ON SILICON(110) It w a s r e p o r t e d / 4 / t h a t S i ( l 1 0 ) c l e a n s u r f a c e showed v a r i o u s k i n d s of r e c o n s t r u c t e d s t r u c - t u r e s , e.g. 4X 5, 2 x 1 , 5 x 1 , "Xn and i n i t i a l /4/. However, t h e r e s u l t i n t h e p r e s e n t e x p e r i - ment by U S , LEED, ELS showed t h a t t h e S i ( l 1 0 ) c l e a n s u r f a c e had only a s i n g l e r e c o n s t r u c t e d s t r u c t u r e of a "16

2" (correspond t o

s t r u c t u r e ) a t room t e m p e r a t u r e and i t transformed r e v e r s i b l y t o t h e 1 x 1 i n a t e m p e r a t u r e r a n g e from 700°C t o 740°C. Other 4 x 5 , 2 x 1 and 5 x 1 s t r u c t u r e s were observed when t h e s u r f a c e w a s contaminated by

and t h e n annealed a t temp- e r a t u r e s h i g h e r t h a n 800°C i n t h e u l t r a h i g h vacuum. N i c o n t a m i n a t i o n w a s occured by p i c k i n g up t h e specimen w i t h a p i n c e t t made by s t a i n - l e s s s t e e l o r by t o u c h i n g t h e specimen w i t h m a t e r i a l s i n c l u d i n g N i . The N i c o n t a m i n a t i o n on a l o c a l i z e d a r e a s p r e a d o v e r t h e s u r f a c e by s u r f a c e d i f f u s i o n w i t h a n n e a l i n g up t o 800*

C, whereas C r and Fe c o n t a m i n a t i o n s d i f f u s e d i n t o b u l k and were n o t d e t e c t a b l e on t h e s u r f - a c e by AES. T h i s f a c t i n d i c a t e s t h a t t h e s u r f - a c e d i f f u s i o n c o e f f i c i e n t of N i on t h e S i s u r f a c e i s c o n s i d e r a b l y l a r g e t h a n t h a t of bulk The d i f f u s i o n l a y e r c o n t a i n i n g

a t t h e

s u r f a c e was s t u d i e d by Auger e l e c t r o n s p e c t r o - scopy by u s i n g N i L M M t r a n s i t i o n s w i t h e l e v a t - i n g t e m p e r a t u r e . The

Auger y i e l d s d e c r e a s e r a p i d l y w i t h i n c r e a s i n g t e m p e r a t u r e i n a r a n g e h i g h e r t h a n 60ooC as shown i n Fig.9. I n Fig.9, t h e s o l i d curve I shows t h e N i Auger y i e l d s measured as t e m p e r a t u r e i n c r e a s e s , while s o l i d c u r v e I1 is measured a f t e r 20 minutes k e p t i n each temperature. These phenomena mean t h a t

Fig. 6 LEED and RHEED p a t t e r n s of ~ i ( l l 1 )

Fig.7 I s l a n d growth of Au on t h e S i ( l l 1 ) s u r f a c e

Fig.8 I s l a n d growth

of Ag on t h e ~ i ( l l 1 )

s u r f a c e

temperature. On t h e o t h e r hand, by r a p i d c o o l i n g from h e a t i n g temperature ( a

c o o l i n g speed being s e v e r a l seconds t o 2

300°C b s w i t c h i n g o f f t h e h e a t i n g

c u r r e n t g , t h e N i Auger y i e l d s a t room temperature depended on t h e h e a t i n g

temperature as shown by broken curve i n Fig.9. A s s e e n from Fig.9? t h e N i Auger ;

y i e l d r e t u r n s t o t h e i n i t l a l v a l u e before t h e h e a t t r e a t m e n t f o r t h e case

of t h e r a p i d c o o l i n g from temperatures

Tcwrrolurc("C) ¹⁰⁰⁰

higher t h a n 800°C. However, t h e Auger

y i e l d of specimen cooled r a p i d l y from Fig.9 Variation of surface temperatures between 600°C and 8 0 0 ' ~ Ni concentration with h e a t shows t h e minimum y i e l d a t approximate- treatments f o r s i ( 1 1 0 ) l y 700°C. Auger e l e c t r o n y i e l d depends

on time kept i n t h e temperature a s shownTable

~ ~ and con- i ~ k ~ ~ ~ ~

by Curve II i n Fig.9. These phenomena c e n t r a t i o n of

d i f f u s i o n a r e explained by t h e d e c r e a s i n g of t h e

f o r

surface d i f f u s i o n c o e f f i c i e n t i n t h e s u r f ace on ~ i ( l 1 0 ) s e g r e g a t i o n with d e c r e a s i n g temperature.

Therefore, t h e t h i c k n e s s of t h e s u r f a c e d i f f u s i o n l a y e r a t room temperature depends on t h e h e a t t r e a t m e n t and i n -

c r e a s e s by t h e r a p i d c o o l i n g f$om temp-

e r a t u r e s between 6 0 0 " ~ and 800 C. The v a r i o u s s u r f a c e s t r u c t u r e s of t h e 4

5 , 2

and 5

l appear depending uniquely

on t h e N i c o n c e n t r a t i o n a s shown i n Fig.

9. The s u r f a c e s e g r e g a t i o n of N i by

r a p i d c o o l i n g i s a t t r i b u t a b l e t o lower- i n g of a s u r f a c e f r e e energy on account of t h e N i s u r f a c e s e g r e g a t i o n . Thus, we

can f i n d t h a t v a r i o u s s u r f a c e s t r u c t u r e s ~ ~

phase b l transitions ~ of observed up t o t h e p r e s e n t f o r S i ( l 1 0 ) r e c o n s t r u c t e d s t r u c t u r e s ofi a r e caused by t h e d i f f e r e n c e of t h e s e v e r a l c r y s t a l planes f o r S i s u r f a c e N i c o n c e n t r a t i o n by h e a t t r e a t -

ments. I n Auger e l e c t r o n spectroscopy, two peaks of d i f f e r e n t t r a n s i t i o n s on a r e l e v a n t element a r e measurable, hence t h e d e p t h of t h e d i f f u s i o n l a y e r s can be estimated from t h e Auger y i e l d r a t i o between d i f f e r e n t e n e r g i e s t a k i n g ac- count of t h e escape depth. Assuming homogeneous d i f f u s i o n l a y e r s , we can e s t i m a t e t h e i r t h i c k n e s s and concent- r a t i o n f o r d i f f e r e n t s u r f a c e s t r u c t u r e s a s shown i n Table 1. We should n o t i c e

h e r e t h a t a N i contaminated l a y e r is

h a r d l y removed by t h e h e a t t r e a t m e n t and has d i f f e r e n t p r o p e r t i e s a t t h e s u r f ace from o t h e r elements.

S i s u r f a c e have v a r i o u s r e c o n s t r u c t e d s t r u c t u r e s depending on t h e c r y s t a l planes and t h e y transform a t temperatures a s shown i n Table 2.

The changes of E I S s p e c t r a with t h e phase t r a n s i t i o n s were measured by

a t E t100eV. The r e s u l t s a r e shown i n Fig.10. Fig.10 shows t h a t

P

C2-306 JOURNAL

DE

S S and S peaks a t t r i b u t a b l e t o t h e

s%faZe stat2s of d a n g l i n g and back bonds,

E and E peaks a s s o c i a t e d w i t h t h e bulk i d t e r b a n g t r a n s i t i o n s and a bulk plasmon peak do n o t change a p p r e c i a b l y a c r o s s t h e phase t r a n s i t i o n s , however t h e s u r f a c e plasmon peak s h i f t s s e n s i t i v e l y by 1.6eV t o l. OeV depending on t h e phase t r a n s i t i o n s . On t h e o t h e r hand, t h e changes of t h e work f u n c t i o n d u r i n g t h e phase t r a n s i t i o n s were observed by LEED o p t i c s a t E =100eV w i t h a r e t a r d i n g p o t e n t i a l d i f f e r g n c e method.

The method is a s s o c i a t e d w i t h t h e measure- ments of a t h r e s h o l d p o t e n t i a l a t t h e

i n i t i a l r a i s i n g of t h e s e c o n d a r y e l e c t r o n

emission. The work f u n c t i o n changed by

0.25 t o 0.12eV towards t h e same d i r e c t i o n s

a s t h o s e of t h e s u r f a c e plasmon energy.

This f a c t s u g g e s t s t h a t t h e cause of t h e phase t r a n s i t i o n of t h e r e c o n s t r u c t e d

s t r u c t u r e s i s a t t r i b u t e d t o t h e c o l l e c t i v e

n a t u r e . The e l e c t r o n l o s s spectrum can be e x p r e s s e d by a l o s s f u n c t i o n which i s w r i t t e n by t h e d i e l e c t r i c f u n c t i o n , b u t t h e d i e l e c t r i c f u n c t i o n of r e c o n s t r u c t e d s t r u c t u r e s have n o t been c a l c u l a t e d y e t . The changes of t h e s u r f a c e plasmon and work f u n c t i o n seems t o be a t t r i b u t e d t o

t h e v a r i a t i o n of a c o l l e c t i v e e l e c t r o n

d e n s i t y o r a n e l e c t r o n d e n s i t y p r o f i l e

*

p e r p e n d i c u l a r t o t h e s u r f a c e , however t h e

q u a n t i t a t i v e c a l c u l a t i o n s of t h i s e f f e c t

has n o t been performed f o r r e c o n s t r u c t e d

s t r u c t u r e s .

CONCLUS I O N

7'0°C

3

The combination of t h e UHV-SEM w i t h a

s u r f a c e a n a l y t i c a l i n s t r u m e n t i s promis- 3

i n g f o r t h e s u r f a c e m i c r o a n a l y s i s . The gun combined w i t h %he AES, ELS and LEED low energy UHV-SEM w i t h f i e l d e m i s s i o n

P

i s e s p e c i a l l y i m p o r t a n t as a n a n a l y t i c a l

e l e c t r o n microscope f o r s o l i d s u r f a c e

as l i k e as t h e a n a l y t i c a l t r a n s m i s s i o n

e l e c t r o n microscope f o r t h i n specimens.

REFERENCES

I.T.Ichinokawa,T.Ishikawa, N.Awaya and A. Onoguchi, Scanning E l e c t r o n Microscopy

(SEM Inc., AMF OIHare, I L ) l ( 1 9 8 1 ) 271.

2 A h i a k a , K Nakagawa a n Y a k , 2nd I n t . Conf. MBE-CST (Tokyo) (1982) 3.J.A. Venables, A.P.Janssen, P.Akhter,

J.Derr i e n and C. J. Harland, J. Microscopy

118 (1980) 351.

4 x ~ o n a , - -- IBM J. Res. Develop. 2 (1965)

2 ' / 3 . E"eqi Loss ( CV )

B.Z. Olshnetsky and V.I.Mashanov, S u r f .

S c i . z (1981)414. F i g . 10 V a r i a t i o n of EL

s p e c t r a a c r o s s t h e phase

t r a n s i t i o n s f o r s e v e r a l

c r y s t a l p l a n e s of S i