Interface Exafs Using Glancing Angles

The use of glancing angles to obtain EXAFS s igna ls from th in i n t e r f a c i a l regions is described. The technique is appl icable to the case of a l i g h t overlayer on a heavy subs t ra te f o r which t o t a l ex te rna l r e f l e c t i o n can be caused to occur a t the in te r face. I n t h i s case the penetrat ion i n t o the s u b s t r a t e i s very small (520-30 A i n many cases) . Data have been obtained on two systems: A 1 on Cu and Ag on Au. The A 1 on Cu samples had 1000 A of A 1 on Cu and measurements were made on the i n t e r f a c e s t r u c t u r e a s a funct ion of annealing temperature. For anneals above 140°C c l e a r ind ica t ion of the growth of CuAIZ a t the i n t e r f a c e is observed. The i n t e r f a c e s e n s i t i v i t y was then v e r i f i e d by varying the glancing angle to determine the CuA12 layer thickness. Even f o r CuA12 layers a s th in a s 100 A, the EXAFS s igna l is ess e n t i a l l y pure CuAl2 with l i t t l e contamination from the underlying Cu. For Ag on Au there is no compound formation and these techniques were used to look a t i n t e r d i f fus ion a s a funct ion of annealing. I n p a r t i c u l a r the Au environment i n Ag gra in boundaries could be detected. Understanding the s t r u c t u r e of s o l i d s t a t e i n t e r f a c e s is important f o r s tud ies of s o l i d s t a t e reac t ions , th in film adhesion and s t a b i l i t y . Trad i t iona l probes such a s Auger s p u t t e r p r o f i l i n g and Rutherford backscat ter ing can provide compositional information but no de ta i led s t r u c t u r a l information, and f o r buried in te r faces of ten have only l imited depth resolut ion. For s ing le c r y s t a l i n t e r f a c e s e lec t ron microscopy can provide beau t i fu l images, but sample preparat ion can be tedious and many systems involve po lycrys ta l l ine or amorphous in te r faces . I n t h i s paper the app l i cat ions of glancing angle x-rays to the study of buried i n t e r f a c e s a r e discussed with p a r t i c u l a r emphasis on in te r face extended x-ray absorption f i n e s t r u c t u r e (ExAFS) measurements. Previous glancing angle EXAFS s tud ies have concentrated on surface s tud ies [I-51 using de tec t ion of e i t h e r the re f lec ted s igna l 11-41 or the fluorescence s igna l emitted by the surface atoms 151. The same techniques can be applied to s o l i d s t a t e i n t e r f a c e systems [6 ,7 ] and t h i s paper w i l l summarize our recent resu l t s . So l id s t a t e in te r faces can a l s o be studied i n absorpt ion i f mult i layer s t ruc tures a r e used t o enhance the i n t e r f a c e s igna l [8,9] but t h i s paper w i l l concentrate on s tud ies of s ing le b i layer systems. I n p a r t i c u l a r , r e s u l t s on Cu-A1 and Au-Ag bil ayers w i l l be reported. The Cu-A1 r e s u l t s demonstrate the i n t e r f a c e s e n s i t i v i t y of the glancing angle techniques while the Au-Ag system demonstrates the a b i l i t y of these techniques t o monitor g ra in boundary i n t e r d i f f u s i o n i n b i layer systems. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19868158