SURFACE SELF-DIFFUSION OF Pt ON THE Pt(311) PLANE

The sur face d i f fus ion of s ing le P t atoms and P t c l u s t e r s on t h e channe led (31 1 ) p l a n e of Pt has been inves t iga ted by f i e l d ion microscopy. Single atoms were found t o migrate within a given channel of the (31 1 ) plane a t t empera tures above 215 K with an ac t iva t ion energy of 0.60 k 0.03 eV and a d i f f u s i v i t y of 1 .9 X 10-* cm2/sec. No c ross -channe l d i f f u s i o n was observed f o r s i n g l e atoms. Two atoms wi th in the same channel associated i n t o a dimer which was immobile and s t a b l e up t o t e m p e r a t u r e s of 340 K . Subsequent a d d i t i o n of atoms t o t h e same channel resu l ted i n t h e formation of chains of atoms along the channel. The motion of two atoms d i f f u s i n g i n a d j a c e n t c h a n n e l s were n o t s t r o n g l y c o r r e l a t e d . However, o c c a s i o n a l occurrences of cross-channel processes between adjacent channels t o produce t h e s t a b l e dimer c o n f i g u r a t i o n were observed . O b s e r v a t i o n s of atoms d i f f u s i n g i n n e x t a d j a c e n t c h a n n e l s s u g g e s t e d a weak a t t r a c t i o n a t s e p a r a t i o n s from 9 .2 t o 12.4A. Small c l u s t e r s of atoms l e f t on the plane a f t e r f i e l d evaporation were s t a b l e below 370 K , but a t 370 K and above, the atoms r e a r r a n g e d t o form a l o n g c h a i n w i t h i n one channel. These r e s u l t s suggest t h a t the mechanism f o r the formation of m i s s i n g rows i n t h e (1x2) r e c o n s t r u c t i o n of channe led s u r f a c e s of P t , I r , and Au involves sur face d i f fus ion of atoms which a r e s t a b i l i z e d by short-ranged atomic in te rac t ions .