Fig. 1. Schematic drawing of the grazing incidence X-ray fluorescence configuration. Fluorescence emission from the sample were detected by the wavelength dispersive spectrometer using parallel optics. GRAZING INCIDENCE X-RAY FLUORESCENCE OF MAGNETIC MULTILAYERS Incident X-ray Reflected X-ray Sample PC (Shield type) Soller slits SC / PC (Flow type) Analyzing crystal 2 θ θ Fluorescence 2 φ φ In recent years, much activity has been devoted t o t h e d e v e l o p m e n t o f g i a n t m a g n e t o r e s i s t a n c e ( G M R ) m u l t i l a y e r s u s e d i n t h e M R h e a d f o r h i g h - density magnetic recording. X - r a y r e f l e c t o m e t r y h a s b e e n a p p l i e d t o t h e an al yz es of ul tr at hi n mu l ti l ay er (a pp ro xi ma te l y 10 - l a y e r ) s t r u c t u r e s s u c h a s f i l m t h i c k n e s s , d e n s i t y , i n t e r f a c i a l r o u g h n e s s , o r t h e e x i s t e n c e o f m i x i n g la ye r. Ho we ve r, si nc e th is me th od ev al ua te s th e l a y e r p r o f i l e b y e x a m i n i n g e l e c t r o n d e n s i t y a s ma ni fe st ed by re fr ac ti ve in de x fo r ea ch la ye r, th e s p i n - v a l v e c o m p o n e n t s c o n s i s t i n g o f C o F e B , C u a n d N i F e a r e d i f f i c u l t t o d i s t i n g u i s h s i n c e t h e i r atomic numbers, and densities, which directly relate t o t h e i r r e f r a c t i v e i n d i c e s a r e n e a r l y i d e n t i c a l . I n a d d i t i o n t o t h a t , t h e m e t h o d c a n n o t p r o v i d e t h e direct information regarding isolated elements such a s t h e d i f f u s i o n o f s p e c i f i c a t o m s a t t h e l a y e r bo un da ry . To solve this problem, we developed a grazing i n c i d e n c e X - r a y f l u o r e s c e n c e ( G I X F ) t e c h n i q u e s us in g wa ve le ng th di sp er si ve ( WD ) eq ui pm en t [1 ] . Fi gu re 1 is a sc he ma ti c dr aw in g of the mea su re me nt configuration. GIXF has been proposed to specify the composition profile for several years [ 2 - 5 ] , but has not applied to the evaluation of real samples. This is due to the complexities in the data analysis in ad di ti on to th e po or qu al it y of th e fl uo re sc en ce d a t a o b t a i n e d b y t h e e n e r g y - d i s p e r s i v e S S D detector, whose maximum count rate is lower than 1 0 k c p s a n d p o s s e s s e s p o o r e n e r g y r e s o l u t i o n . We overcame these difficulties using a WD detector with a high count rate and good energy resolution for mea sur eme nt and inc orp ora tin g the ref lec tiv ity d a t a i n t o t h e e s t i m a t i o n o f X - r a y f i e l d i n t e n s i t y i n the analysis. T h e X - r a y f l u o r e s c e n c e e q u i p m e n t h a s b e e n constructed at the undulator beamline BL16XU by a consortium of 13 industrial companies. This may r e p r e s e n t t h e f i r s t d e v i c e t h a t c a n m e a s u r e t h e fluorescent X-rays from the samples placed under t h e g r a z i n g o r t h e t o t a l r e f l e c t i o n c o n d i t i o n s b y a WD spectrometer with high detection sensitivity. In the experiment, a spin-valve sample with a stratified structure of T a ( 6 ) / P d P t M n ( 2 5 ) / C o F e B ( 2 ) / C u ( 3 ) / C o F e B ( 2 ) / N i F e ( 4 ) / T a ( 5 ) / S i - sub was measured. The number in pa re nt he si s in di ca te th e th ic kn es s i n n m . T h e X - r a y s f r o m t h e u n d u l a t o r were monochromatized to 16 keV. A downstream Rh-coated focusing m i r r o r s u p p r e s s e s t h e h i g h e r h a r m o n i c s , r e d u c i n g b a c k g r o u n d f l u o r e s c e n c e s i g n a l s f r o m t h e s a m p l e s . I n a d d i t i o n , t h e h i g h - e n e r g y r e s o l u t i o n o f t h e W D s p e c t r o m e t e r r e s o l v e d m a n y F i g . 3 . G r a z i n g a n g l e d e p e n d e n c e o f f l u o r e s c e n c e y i e l d s f o r t h e e l e m e n t corresponding to each layer. The solid line represents the calculation based on the layered model. Fig. 2. Fluorescence peaks seen by the energy scan of the GMR multilayer with grazing angle of 1.5 deg. 20 30 40 50 60 70 80 0 1000 2000 3000 4000 5000 LiF 2 θ θ ( deg ) Intensity (counts) Compton 16 keV elastic Pt L γ Pt L β 2 Pt L α Pt L β 1 Ta L γ Ta L β 2 Cu K β Ni K β Ta L β 1 Ta L α Co K β Cu K α Ni K α Co K α Mn K β Fe K α Mn K α Ta - L α α Pt - L β β β β 1 Co - K Cu - K Ni - K α α φ φ ( deg ) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 200 0 400 600 800 1000 1200 1400 1600 50 0 100 150 200 250 300 2000 0 1000 3000 4000 5000 6000 0 2000 4000 6000 8000 200 0 400 600 800 1000 1200 1400 Fluorescence Intensity (counts) fluo resc ent peak s from the elem ents in the samp le, as shown in Fig. 2 . These features could not be attained by t h e e n e r g y d i s p e r s i v e m e a s u r e m e n t s o r b y t h e conventional WD equipment using continuous X-rays in the laboratory. I n t h e a n g l e r e s o l v e d m e a s u r e m e n t s , a n o n - overlapping peak of fluorescent X-rays for each element was chosen and the Bragg angle of the analyzing crystal was set at the peak. The results of a grazing angle scan f o r e l e m e n t s c o r r e s p o n d i n g t o e a c h l a y e r u p t o 0 . 7 degrees are shown in Fig. 3 . The reflectivity was also recorded as shown in Fig. 4 . The fluorescence intensity s h o w s a c l e a r o s c i l l a t i o n t h a t o r i g i n a t e s f r o m t h e sta ndi ng wav e of X-r ays gen era ted by the int erf ere nce inside the layers. I n t h e a n a l y s i s , w e e x t e n d e d t h e o p t i m i z a t i o n p r o g r a m d e v e l o p e d f o r t h e X - r a y r e f l e c t i v i t y , w h i c h b a s e d o n t h e l a y e r e d m o d e l o f V i d a l & V i n c e n t [ 6 ] , t o calculate the energy flow of X-rays in the film from which t h e f l u o r e s c e n c e y i e l d c a n b e c a l c u l a t e d . T h e f l u o r e s c e n c e p r o f i l e s f r o m e a c h e l e m e n t a n d t h e ref lec tiv ity pro fil e wer e sim ult ane ous ly opt imi zed to the l a y e r e d m o d e l . I n t h e a n a l y s i s , l a y e r s w i t h a s i m i l a r d e n s i t y o f d i f f e r e n t e l e m e n t s a r e r e s o l v e d f r o m t h e constraints on fluorescence yield for the elements. The Naoki Awaji Fujitsu Laboratories LTD. E-mail: awaji @ ccg.flab.fujitsu.co.jp [3] D.K.G. de Boer, Phys. Rev. B 44 (1991) 498. [4] A. Iida, Adv. in X-ray Anl. 35 (1992) 2. [ 5 ] K . S a k u r a i , S R S c i . & T e c h n o l . I n f o . , J A S R I , No.2, 6 (1996) 2. (in Japanese) [6 ] B. Vi da l an d P. Vi nc en t, Ap pl . Op t. 23 (1 98 4) 1794. [ 7 ] N . A w a j i , K . N o m u r a a n d S . K o m i y a , t o b e submitted in Jpn. J. Appl. Phys. References [1] N. Awaji et. al. , Jpn. J. Appl. Phys. 39 (2000) L1252. [2] A. Krol et. al. , Phys. Rev. B 38 (1988) 8579. Fig. 5. Layer profile of the sample reconstructed from t h e r e s u l t s o f G I X F a n a l y s i s , w h e r e T . L . i s t h e transition layer and D.L. is the dead layer introduced t o r e p r o d u c e t h e m e a s u r e d d a t a . N u m b e r s w i t h arrow indicate the interfacial roughness. Fig. 4. Reflection profile of the GMR sample. The s o l i d l i n e s h o w s t h e r e s u l t o f a c a l c u l a t i o n optimized with the fluorescence yield. c a l c u l a t e d p r o f i l e s r e p r o d u c e t h e c o m p l e x fluorescence profile very well, as indicated by t h e s o l i d l i n e i n F i g . 3 a n d F i g . 4 . T h e r e c o n s t r u c t e d layer profile of the sample from GIXF analysis is shown in Fig. 5 . In su mm ar y, a ne w WD -G IX F me th od ha s be en de ve lo pe d in wh ic h th e at om ic pr of il es of s a m p l e s c a n b e e s t i m a t e d a n d a p p l i e d s u c c e s s f u l l y i n o r d e r t o e v a l u a t e t h e c o m p l e x G M R s p i n - v a l v e s a m p l e s . W e s u c c e e d e d i n observing the change of a layered structure after thermal annealing by applying this method [7] .
home
- JP
- EN