LATTICE IMAGES OF DISLOCATIONS IN GERMANIUM

HAL Id: jpa-00219018

https://hal.archives-ouvertes.fr/jpa-00219018

Submitted on 1 Jan 1979

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished 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.

LATTICE IMAGES OF DISLOCATIONS IN GERMANIUM

A. Bourret, J. Desseaux

To cite this version:

A. Bourret, J. Desseaux. LATTICE IMAGES OF DISLOCATIONS IN GERMANIUM. Journal de

Physique Colloques, 1979, 40 (C6), pp.C6-7-C6-9. �10.1051/jphyscol:1979602�. �jpa-00219018�

JOURNAL

ColZoque C6, suppZhent

n06, tone 40, j u i n 1979, page C6-7

L A T T I C E IMAGES OF DISLOCATIONS I N GERNANIUPl

A. B o u r r e t and J. Desseaux

Centre d'e'tudes NucZe'aires de GrenobZe, De'partement de Recherche FondmentaZe, S e c t i o n de Physique du SoZide 85 X , 38041 Grenoble Cedex, France.

Resume.- Des s o u s - j o i n t s de f l e x i o n p u r e dans l e germanium o n t e t 6 observes p a r microscopic e l e c t r o - n i q u e a h a u t e r 6 s o l u t i o n . Ces j o i n t s c o n t i e n n e n t des d i s l o c a t i o n s c o i n s non d i s s o c i e e s e t des d i s l o - c a t i o n s d i s s o c i e e s en p a r t i e l l e s . Une e n e r g i e de f a u t e i n t r i n s s q u e r e l a t i v e m e n t e l e v e e e s t d e d u i t e s i l ' o n suppose que l e s p a r t i e l l e s ne t o u r n e n t pas d u r a n t l ' a m i n c i s s e m e n t . Cependant aucune preuve expe- r i m e n t a l e ne p e u t encore 6 t r e f o u r n i e ii l ' a p p u i de c e t t e hypothese.

A b s t r a c t . - Pure t i l t s u b g r a i n boundaries i n germanium have been s t u d i e d by h i g h r e s o l u t i o n e l e c t r o n microscopy. They c o n t a i n m a i n l y u n d i s s o c i a t e d edge d i s l o c a t i o n and two types o f s p l i t d i s l o c a t i o n s . A r e l a t i v e l y h i g h i n t r i n s i c s t a c k i n g f a u l t energy i s deduced by supposing t h a t no r o t a t i o n o f p a r t i a l s o c c u r s d u r i n g t h i n n i n g . No e x p e r i m e n t a l p r o o f has y e t been o b t a i n e d t o s u p p o r t t h i s h y p o t h e s i s .

1. I n t r o d u c t i o n . - U n t i l r e c e n t l y i t was supposed t o due t o s p l i t t i n g and s t a b i l i z a t i o n o f unusual d e f e c t s be v e r y d i f f i c u l t t o i n t e r p r e t t h e l a t t i c e images of by mutual i n t e r a c t i o n i n t h e g r a i n boundary p l a n e . d i s l o c a t i o n s as o b t a i n e d by e l e c t r o n microscopy. HOW- Three main types o f d i s l o c a t i o n s w i l l be discussed e v e r a new development o f t h i s t e c h n i q u e has begun here.

due t o a b e t t e r u n d e r s t a n d i n g o f imaging c o n d i t i o n s and a good c o n t r o l o f t h e d e f e c t geometry. The ima- g i n g mode ( a x i a l i l l u m i n a t i o n ) as a p p l i e d down t o a 3 p e r i o d i c i t y g i v e an image d i r e c t l y r e l a t e d t o t h e p r o j e c t e d s t r u c t u r e o f t h e o b j e c t i n g i v e n c o n d i t i o n s o f t h i c k n e s s and o f d e f o c u s s i n g d i s t a n c e ( t h i s i s s p e c i a l l y t r u e w i t h h i g h v o l t a g e i n s t r u m e n t ) . F o r d i s l o c a t i o n s o r any l i n e a r d e f e c t , an e a s y - t o - r e a d image i s o b t a i n a b l e when t h e d i s l o c a t i o n i s s t r i c l y seen end-on. The small a n g l e g r a i n boundary produced i n a b i c r y s t a l i s composed o f d i s l o c a t i o n s whose Burgers v e c t o r and d i r e c t i o n a r e easy t o c o n t r o l .

Germanium b i c r y s t a l s w i t h a [ I 0 1 1 1 common a x i s have been b y t h e C z o c h r a l s k i method i n a g r a - p h i t e c r u c i b l e under a p u r e argon atmosphere. The germanium has a 40 Rcm r e s i s t i v i t y and i s p-type.

M e t a l l i c i m p u r i t i e s as measured b y a c t i v a t i o n ana- l y s i s a r e o f t h e o r d e r o f ppm. The oxygen and carbon c o n t e n t has n o t y e t been measured

techniques a r e b e i n g developed t o measure these s i n c e t h e carbon whose s e g r e g a t i o n i s i m p o r t a n t , may i n f l u e n c e d i s l o - c a t i o n s p l i t t i n g .

T h i s paper r e p o r t s t h e r e s u l t s a c t u a l l y o b t a i - ned about t h e s t r u c t u r a l aspects o f d i s l o c a t i o n s i n s u b g r a i n boundary, and s t r e s s e s t h e problems w h i c h remain unsolved.

2. D i s l o c a t i o n s t r u c t u r e i n subgrain.- The s u b g r a i n boundary s t r u c t u r e has shown a g r e a t c o m p l e x i t y i n t h e d i s l o c a t i o n arrangement /1/ ( F i g . 1 ) p o s s i b l y

F i g . 1

P a r t o f a p u r e t i l t 0 1 1 7 g r a i n boundary i n germanium ( t i l t a n g l e : 2 ' 6 when viewed end-on a l o n g t h e [ O l l l common a x i s . D i s l o c a t i o n c o r e s appear as b l a c k d o t s and s t a c k i n g f a u l t as s t r a i g h t segments j o i n i n g cores. Three t y p e s o f d i s l o c a t i o n a r e r e c o g n i z a b l e

( A ) , non d i s s o c i a t e d d i s l o c a t i o n ; (B) , d i s l o c a t i o n s p l i t i n t o p a r t i a l s p e r p e n d i c u l a r t o t h e g r a i n boundary p l a n e ; ( C ) , t h r e e grouped d i s l o c a t i o n s s e p e r a t e d by s t a c k i n g f a u l t s . B r i g h t f i e l d multibeam imaging mode, E

100 keV.

2.1. ~ ~ y ~ - ~ d q ~ - d ~ ~ ~ ~ c ~ ~ ~ ~ ~ n ~ ~ i g ~ - ~ - ~ j . - T h i s d i s - l o c a t i o n has a Burgers v e c t o r 1/2 1 0 i l ~ . I t i s

Lomer d i s l o c a t i o n as i t s d i r e c t i o n c o n t a i n s two {I111 p l a n e s . The g l i d e p l a n e i s (100) and t h e r e f o r e t h i s t y p e o f d i s l o c a t i o n cannot be produced i n t h e e a r l y stages o f p l a s t i c d e f o r m a t i o n .

The h i g h r e s o l u t i o n image t a k e n a t 500 keV shows c l e a r l y t h a t no d i s s o c i a t i o n occurs ; f u r t h e r m o r e a r e g i o n o f h i g h c o n t r a s t occurs i n t h e d i s l o c a t i o n core. E l a s t i c i t y t h e o r y would p r e d i c t a d i s s o c i a t e d

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979602

C6-8

DE PHYSIQUE

form w i t h a s e s s i b l e c o n f i g u r a t i o n f o r t h i s d i s l o c a - 2.2. ~~0_-d_j~lo_c_fit_i~n_-[FjgII2-~).- Imaging t h i s d i s - t i o n . The expected r e ? c t i o n scheme i s : l o c a t i o n b y two d i f f e r e n t (1111 a t o m i c planes, one

1 [ O T ~ J

k ^{[ZTI] +} [ o T ~ ] + k ^[?ill e x t r a h a l f p l a n e i s v i s i b l e on o n l y one s e t w i t h a d i s t i n c t s t a c k i n g f a u l t and no d i s c o n t i n u i t y on t h e

F i g . 2

High r e s o l u t i o n images o f d i f f e r e n t t y p e o f d e f e c t s i n germanium : (A), edge d i s l o c a t i o n ; (B) 60" d i s l o c a t i o n s p l i t i n t o two Shockley p a r t i a l s b o a r d i n g an i n t r i n s i c f a u l t ; ( C ) , t h r e e i d e n t i c a l l y grouped Frank d i s l o c a t i o n s s e p a r a t e d by an i n t r i n s i c and an e x t r i n s i c s t a c k i n g f a u l t . (A) and ( C ) t a k e n a t 500 keV

( B ) t a k e n a t 100 keV. A x i a l i l l u m i n a t i o n , 5 beam imaging c o n d i t i o n s i n c l u d i n g f o u r (111) d i - f r a c t i o n spots.

I n f a c t t h i s r e a c t i o n i s n o t e x p e r i m e n t a l l y observed.

From t h i s o b s e r v a t i o n i t can be i n f e r r e d t h a t a shu- f f l e s e t w i t h no broken bonds /2/ i s t h e s t a b l e f o r m o f t h i s d i s l o c a t i o n . As a m a t t e r o f f a c t any d i s s o - c i a t i o n o f t h e s h u f f l e s e t ( F i g . 3 ) would produce broken bonds and consequently a h i g h energy c o r e s i - t u a t i o n which would c o u n t e r b a l a n c e t h e d e c r e a s i n g e l a s t i c energy term. Furthermore t h e presence o f a seven r i n g and a f i v e r i n g i n t h i s t y p e o f s t r u c t u r e c o u l d produce a b r i g h t f o t i n t h e empty t u n n e l and a d a r k a r e a i n t h e compact r e g i o n as observed expe- r i m e n t a l l y

however t h i s d i r e c t i d e n t i f i c a t i o n a l - though a l r e a d y suggested by K r i v a n e k /3/ must be checked b y image matching. I t i s w o r t h n o t i n g t h a t s i m i l a r non d i s s o c i a t e d edge d i s l o c a t i o n s have been o b t a i n e d i n w u r t z i t e s t r u c t u r e /4/.

a h c

F i g . 3 : D i f f e r e n t a t o m i c models o f t h e c o r e o f an edge d i s l o c a t i o n a l o n g Loll]. a ) s h u f f l e c o n f i g u r a - t i o n , b ) i f d i s s o c i a t e d w i t h two i n t r i n s i c f a u l t s , t h e number o f open bonds i s 2, c ) i f d i s s o c i a t e d w i t h two e x t r i n s i c f a u l t s t h e number o f open bonds i s 6.

I n f a c t o n l y t h e c o n f i g u r a t i o n a ) i s observed

o t h e r s e t . Thus t h e Burgers v e c t o r must be o f t h e t y p e 1/2 <101> and t h e s e d i s l o c a t i o n s a r e o f 60" type.

They a r e d i s s o c i a t e d i n t o two p a r t i a l s g i v i n g an edge Shockley d i s l o c a t i o n and a 30" Schockley d i s l o c a t i o n . The two p a r t i a l s a r e v i s i b l e even a t medium range r e - s o l u t i o n when observed end-on w i t h b r i g h t f i e l d m u l t i - beam c o n d i t i o n ( F i g . 4 a ) . The s t a c k i n g f a u l t c h a r a c t e r i s always i n t r i n s i c . T h i s c h a r a c t e r i s determined e i t h e r f r o m t h e h i g h r e s o l u t i o n image, t h e 30° d i s l o - c a t i o n g i v i n g r i s e t o a smooth d i s c o n t i n u i t y i n con- t r a s t t o t h e edge p a r t i a l , o r f r o m weak beam images o b t a i n e d a f t e r a l a r g e specimen t i l t .

F i g . 4 : T e s t i n g t h e p a r a l l e l i s m o f 60' d i s l o c a t i o n i n r e s p e c t t o t h e roll] d i r e c t i o n .

a ) B r i g h t f i e l d m u l i i b e a m imaging i n a 800 A t h i c k r e g i o n

t h e two d a r k p o i n t s i n d i c a t e a v e r y small r o t a t i o n o f t h e p a r t i a l s when viewed a l o n g t h e 5 0 1 1 ~ d i r e c t i o n :

b B r i g h t f i e l d m u l t i b e a m i m a g i n g a f t e r a 3" r o t a - t i o n o f t h e specimen away f r o m t h e [ O l l l d i r e c t i o n . The s t a c k i n a f a u l t i s v i s i b l e and i s ~ r o . i e c t e d as a lozenge-shape (B) whose edges a r e s l i g h t j y r o t a t e d i n r e s p e c t t o t h e edge d i s l o c a t i o n (A). The r o t a t i o n a n g l e i s now measurable and i s a p p r o x i m a t e l y +lo

The s p l i t t i n g d i s t a n c e as deduced f r o m a t o m i c

0

p l a n e imaging g i v e s an apparent d i s t a n c e o f 3 1 A between p a r t i a l s . T h i s g i v e s an i n t r i n s i c s t a c k i n g f a u l t energy o f 100 ergs/cm2. T h i s r e l a t i v e l y h i g h e r v a l u e t h a n t h a t o b t a i n e d by weak beam /5/ can be a t t r i b u t e d t o d i f f e r e n t i m p u r i t y c o n t e n t o r t o t h e method o f measurement i t s e l f ( f o r d i s c u s s i o n o f t h e s u r f a c e e f f e c t see below).

I t has n o t y e t been p o s s i b l e t o d i s t i n g u i s h

t h e g l i d e s e t and t h e s h u f f l e s e t /6/ which m i g h t

appear on t h e edge p a r t i a l : however t h i s may be

p o s s i b l e i f t h e p a r t i a l s remain s t r i c l y p a r a l l e l

t o t h e C 0 1 1 ] d i r e c t i o n even i n a t h i n f o i l .

A . B o u r r e t and J. Desseaux C6-9

2.3. Gcoup-gf-Fygnk-dl~~~c_at_io_nssL~igL-2c). - One arrangement has been i s o l a t e d on f i g u r e 2c : i t i n - cludes t h r e e (111) a t o m i c p l a n e s which s t o p a t a Frank d i s l o c a t i o n g i v i n g s u c c e s s i v e l y an i n t r i n s i c and an e x t r i n s i c s t a c k i n g f a u l t . The s p l i t t i n g o c c u r s i n t h e g r a i n boundary p l a n e c o n t r a r y t o t h e 60" d i s - l o c a t i o n which s p l i t s p e r p e n d i c u l a r t o t h e g r a i n boun- d a r y plane. T h i s d i s l o c a t i o n arrangement i s e n t i r e l y edge i n c h a r a c t e r and c o m p l e t e l y s e s s i l e : i t accomo- dates m i s o r i e n t a t i o n between t h e two a d j a c e n t g r a i n s . The s p l i t t i n g d i s t a n c e between Frank p a r t i a l s i s n o t governed b y t h e s t a c k i n g f a u l t energy a n g l e o f m i s o r i e n t a t i o n ( 1 - 3 " ) , b u t r a t h e r by t h e d i s t a n c e between d e f e c t s .

Another g r o u p i n g n o t so f r e q u e n t l y encountered, r e s u l t s f r o m t h e f o l l o w i n g decomposition on two (111) planes :

p r o d u c i n g always an i n t r i n s i c f a u l t c u t t i n g an e x t r i n - s i c one a t an a c u t e angle.

These p e c u l i a r d i s l o c a t i o n g r o u p i n g s a r e proba- b l y s p e c i f i c t o t i l t s u b g r a i n boundary and have n e v e r been observed i n deformed m a t e r i a l . However t h e y g i v e an o p p o r t u n i t y t o produce c o n t r o l l e d i n t r i n s i c and e x t r i n s i c s t a c k i n g f a u l t s .

3. I n f l u e n c e o f t h e s u r f a c e of t h e f o i l . - The obser- v a t i o n o f l i n e a r d e f e c t s by h i g h r e s o l u t i o n m i c r o s - copy i s easy i f t h e l i n e s r u n s t r i c l y p a r a l l e l t o t h e o b s e r v a t i o n d i r e c t i o n . I n o r d e r t o f u l f i l t h i s r e q u i - rement t h e <011> d i r e c t i o n seems t o be t h e most appro- p r i a t e as even d u r i n g t h i n n i n g t h e d i s l o c a t i o n s would have a tendancy t o s t a y and l i e a l o n g throughs o f t h e P e i e r l s p o t e n t i a l . However t h i s assumption must be checked c a r e f u l l y . F o r t h e d e f e c t whose c h a r a c t e r i s e s s e n t i a l l y s e s s i l e i t i s l i k e l y t h a t no r o t a t i o n d u r i n g t h i n n i n g would o c c u r

such displacement would i n v o l v e c l i m b i n g which i s excluded a t room tempera- t u r e . T h e r e f o r e a l l t h e d e f e c t s formed w i t h Frank p a r t i a l s do n o t move. The same argument can be a p p l i e d t o t h e edge d i s l o c a t i o n which cannot g l i d e on t h e (301) plane. The q u e s t i o n remains open f o r t h e 60' d i s l o c a t i o n o n l y .

Small m i s a l i g n e m e n t o f t h e p a r t i a l s i n r e s p e c t t o t h e Loll] a x i s i s v e r y d i f f i c u l t t o d e t e c t i n

0

a v e r y t h i n r e g i o n (100 A). A c t u a l l y o u r check i s

0

l i m i t e d t o 500-1000 A t h i c k r e g i o n s ( F i g . 4 )

i n t h i s range t h e r o t a t i o n of 60" d i s l o c a t i o n i s l i m i -

0

t e d t o

lo f o r d i s l o c a t i o n s 100 A a p a r t f r o m each o t h e r . R o t a t i o n s seem t o be a l t e r n a t e l y i n one sense

and i n t h e o t h e r as t h e screw components o f t h e 60"

d i s l o c a t i o n s change s i g n . T h i s m i s o r i e n t a t i o n would

0

g i v e a n e g l i g i b l e e f f e c t i n a 100 A t h i c k r e g i o n . However t h i s small r o t a t i o n c o u l d have been l i m i t e d by t h e presence o f o t h e r segments of d i s l o c a t i o n a l o n g t h e g r a i n boundary. A crude e s t i m a t e o f t h i s e f f e c t u s i n g t h e H a z z l e d i n e approach w i t h no f r i c t i o n f o r c e /7/ shows t h a t r o t a t i o n i s n e g l i g i b l e i f and o n l y i f t h e d i s t a n c e between t h e d i s l o c a t i o n s i s s m a l l e r t h a n h a l f t h e t h i c k n e s s o f t h e f o i l . Actua- l l y t h i s c o n d i t i o n i s c e r t a i n l y n o t f u l f i l l e d f o r a v e r y l o w a n g l e g r a i n boundary (0.5') and s m a l l t h i c k - ness where t h e s p l i t t i n g d i s t a n c e has been measured.

F u r t h e r e x p e r i m e n t a l work i s needed t o c l a r i f y t h i s p o i n t .

4. Conclusion.- The s t u d y of l a t t i c e d e f e c t s i n ger- manium by h i g h r e s o l u t i o n e l e c t r o n microscopy has been f r u i t f u l : Burgers v e c t o r , c h a r a c t e r o f s t a c k i n g f a u l t , and a n a l y s i s o f c o m p l i c a t e d s t r u c t u r e s e x i s t i n g i n s m a l l a n g l e g r a i n boundaries have been e a s i l y s t u - d i e d . However d i r e c t i n t e r p r e t a t i o n i s a c t u a l l y l i m i - t e d t o s t r i c l y end-on l i n e a r defect. T h i s c o n d i t i o n i s v e r i f i e d f o r s e s s i b l e c o n f i g u r a t i o n s b u t has t o be v e r i f i e d e x p e r i m e n t a l l y f o r g l i s s i l e d e f e c t s i n t h i n f o i l s

some e f f o r t s a r e necessary t o f i n d a p r a c t i c a l way o f d o i n g t h i s a t a h i g h r e s o l u t i o n l e v e l .

References.

/1/ B o u r r e t , A., Desseaux, J., P h i l . Yag. ( t o be pu- b l is h e d ) .

/2/ H o r n s t r a , J . , J . Phys. Chem. S o l i d s - 5 (1958) 129.

/3/ K r i v a n e k , O.L., Isoda, S., Kobayashi, K., P h i l .

Mag. 2 (1977) 931.

/4/ Mader, S., B l a k e s l e e , A.E., IBM JAE 2 (1975) 151.

/5/ Gomez, A., Cockayne, D.J.H., H i r s c h , P.B., V i t e k , V., P h i l . Yag. 31 (1975) 105.

/6/ H i r t h , J.P., Lothe, J., Theory o f d i s l o c a t i o n s (Mc Graw H i 11 ) 1968.

/7/ Hazzledine, P.Y., K a r n t h a l e r , H.P., W i n t n e r , E.,

P h i l . Mag. - 32 (1975) 81.