F i g . 1 . S c h e m a t i c d r a w i n g o f microcrystalline material (provided b y N a t i o n a l I n s t i t u t e o f A d v a n c e d Industrial Science and Technology). Fluorescence XAFS Analysis of Some Industrial Materials BL16B2 and BL16XU, named “ SUNBEAM”, are c o n t r a c t b e a m l i n e s c o n s t r u c t e d b y a n I n d u s t r i a l C o n s o r t i u m o f 1 3 c o m p a n i e s i n c o o p e r a t i o n w i t h J A S R I i n 1 9 9 9 [ 1 ] . W e , r e p r e s e n t i n g s e v e n i n t e r e s t e d c o m p a n i e s [ 2 ] i n t h e c o n s o r t i u m , h a v e frequently made the opportunity to measure various i n d u s t r i a l m a t e r i a l s i n c o o p e r a t i o n b y o f f e r i n g o u r skills to each other. During the first semester of 2001, we performed a flu ore sce nce XAF S ana lys is of cer tai n ind ust ria l m a t e r i a l s , s u c h a s s e m i c o n d u c t o r d e v i c e s , c a t a l y s t s , f l u o r e s c e n t s u b s t a n c e s , a n d f u e l c e l l s u s i n g a L y t l e d e t e c t o r [ 3 ] a t B L 1 6 B 2 . H e r e , w e report the results of the analysis of SiGe thin films f o r a n a r r o w b a n d g a p s e m i c o n d u c t o r d e v i c e , Lanthanum Manganese oxides for a solid oxide fuel cell. SiGe film, which is a narrow band gap thin film semiconductor material, is being researched for use i n h i g h e l e c t r o n m o b i l i t y s e m i c o n d u c t o r m a t e r i a l s a n d i n f r a r e d s e n s o r s . T h i s m a t e r i a l c a n b e am or ph ou s, mi cr oc ry st al li ne or a mi xt ur e of th es e s t a t e s , a c c o r d i n g t o f a b r i c a t i o n c o n d i t i o n s . W e a t t e m p t e d l o c a l s t r u c t u r e a n a l y s e s b y X A F S , b e c a u s e t h e e l e c t r o n i c a n d o p t i c a l p r o p e r t i e s o f S i G e f i l m s a r e s i g n i f i c a n t l y a f f e c t e d b y t h e i r structural conditions. An amorphous Ge (a-Ge) film a n d t h r e e m i c r o c r y s t a l l i n e S i G e ( μ c - S i G e ) f i l m s , w h i c h h a v e d i f f e r e n t S i / G e c o m p o s i t i o n s , w e r e examined. The Ge concentration was determined by X-ray photoelectron spectroscopy ( XPS ). Each film (about 0.5 μ m in thickness) was fabricated on a glass substrate. F i g u r e 1 s h o w s a s c h e m a t i c d r a w i n g o f a m i c r o c r y s t a l l i n e m a t e r i a l t h a t c o n s i s t s o f a n a m o r p h o u s r e g i o n a n d m i c r o c r y s t a l l i n e r e g i o n s . The μ c-SiGe films which we measured have similar structures to those in Fig. 1 , and the grain size was within the range of 10 to 20 nm. The XAFS measurements were performed using a L y t l e d e t e c t o r , s i n c e t h e c o u n t i n g r a t e o f s o l i d s t a t e d e t e c t o r s ( S S D ) i s i n s u f f i c i e n t f o r t h e s e sa mp le s. A Ga fi lt er wa s s et in fr on t o f t he io ni za ti on c h a m b e r o f t h e L y t l e d e t e c t o r t o r e d u c e t h e sc at te ri ng X -r ay s. Kr w as u se d as a n io ni za ti on g as . Figure 2 shows the Fourier transforms ( RDF ) of th e EX AF S sp ec tr a fo r ea ch sa mp le . Th e di ff er en ce between the distance to the first neighbor atom of crystalline Si and that of crystalline Ge is 0.1 Å, and those of SiGe are thought to be within this range. 0 1 2 3 4 5 6 0 5 10 15 20 FT magnitude Ge: 100% Ge: 77% Ge: 43% Ge: 26% R (Å) Fig. 2. Fourier transforms of k 3 -weighted Ge K-edge EXAFS spectra of SiGe films. 80 The figure reveals that the distance is longer as the Ge concentration increases within less than 0.1 Å. This method provides excellent radial resolution for these kinds of thin film materials. In Fi g. 3 , th e di st an ce va lu es to th e fi rs t ne ig hb or atom derived from a curve-fitting analysis of XAFS spectra were plotted against Ge concentration. The d i s t a n c e v a l u e s d e r i v e d f r o m p o w d e r X - r a y d i f f r a c t i o n ( X R D ) d a t a f o r c r y s t a l l i n e S i a n d G e w e r e a l s o p l o t t e d . T h e r e i s a t e n d e n c y f o r t h e d i s t a n c e derived from XAFS to be longer than the average distance between crystalline Si and Ge. X A F S o b s e r v e s b o t h m i c r o c r y s t a l l i n e a n d a m o r p h o u s r e g i o n s , a n d t h e d i s t a n c e v a l u e s b y X A F S r e v e a l t h e a v e r a g e v a l u e s o f b o t h r e g i o n s . Generally, the bond length of amorphous material is longer than that of crystalline material. Therefore, ou r XAF S re su lt s su gg es t th at th e Si Ge ma te ri al s c o n t a i n b o t h a m o r p h o u s r e g i o n s a n d c r y s t a l l i n e r e g i o n s . O n t h e o t h e r h a n d , c r y s t a l l o g r a p h i c a n a l y s e s o b s e r v e o n l y c r y s t a l l i n e r e g i o n s . W e believe a combination of Lytle detector based XAFS a n d c r y s t a l l o g r a p h i c a n a l y s e s c a n d e t e r m i n e t h e structure of m i c r o c r y s t a l l i n e t h i n f i l m m a t e r i a l s . The perovskite-manganites are technologically i m p o r t a n t m a t e r i a l s a s e l e c t r o - c a t a l y s t s a n d e l e c t r o d e m a t e r i a l s f o r h i g h t e m p e r a t u r e f u e l c e l l ap pl ic at io ns . Th ei r el ec tr on ic , ca ta ly ti c an d ma gn et ic powder Si XAFS powder Ge 0 20 40 60 80 100 2.34 2.38 2.42 2.46 Ge concentration ( at.%) Distance (Å) La( Sr ) – O Mn – O La Mn O properties are of intrinsic interest, since the crystal a n d e l e c t r o n s t r u c t u r e a r e c h a n g e d b y t h e constituted elements. The Lanthanum Manganese o x i d e , L a M n O 3 , i s s e m i c o n d u c t o r a n d h a s o r t h o r h o m b i c l a t t i c e ( P b n m ) , w h e r e a s S r - d o p e d s o l i d - s o l u t i o n s L a 1 - x S r x M n O 3 h a v e r h o m b o h e d r a l lattice ( R-3c ) and their electrical properties around r o o m t e m p e r a t u r e v a r i e s f r o m s e m i c o n d u c t i n g t o metallic behavior in the composition range between x = 0.3 and 0.4. A schematic drawing of LaMnO 3 is s h o w n i n F i g . 4 . R e c e n t l y , w e c h a r a c t e r i z e d t h e t e m p e r a t u r e d e p e n d e n c e o f t h e e l e c t r i c a l p r o p e r t i e s o f L a 1 - x S r x M n O 3 a n d t h e i r c r y s t a l structure by X-ray Rietveld analysis. However, the r o l e o f S r i n L a - s i t e , w h i c h o c c u p i e s t h e crystallographically equivalent site, is not yet clear. In this study, XAFS spectra near the Mn, Sr and La- K e d g e o f t h e L a M n O 3 a n d L a 1 - x S r x M n O 3 s o l i d - solut ions were measu red by the fluor escen t X-ray method using a Lytle-detector. The LaMnO 3 and ( La 1-x Sr x ) MnO 3 (0.1 x 0.4) so li d so lu ti on s re sp ec ti ve ly ha ve an or th or ho mb ic GaFeO 3 -type ( Pnma ) and a rhombohedral LaAlO 3 - type ( R-3c ) structure. Although a slight change of threshold energy in the Mn- K edge was observed, the obvious difference was not seen to the XANES spectrum of La( K ), Sr ( K ) and Mn ( K ) -edge in these Fig. 3. Distance to the nearest atom taken by XAFS and powder diffraction. Fig. 4. Schematic drawing of crystal structure of perovskite-type Lanthanum Manganese oxide. 81 Sr-O XAFS La/ Sr-O XRD La-O XAFS Mn-O XRD Mn-O XAFS R (Å) R (Å) 2.1 2.0 1.9 1.8 0 0.1 0.2 0.3 0.4 x in ( La 1-x Sr x ) Mn 3 2.9 2.8 2.7 2.6 Fig. 6. Compositional dependence of La-O, Sr-O and Mn-O distances in La 1-x Sr x MnO 3 solid solutions. F i g . 5 . F o u r i e r t r a n s f o r m s o f k 3 - w e i g h t e d Mn K-edge XAFS spectra of La 0.7 Sr 0.3 MnO 3 . H i r o s h i D e g u c h i a , A k i r a M i k a m i b a n d Tohru Yamamoto c (a) Kansai Electric Power Co., INC. (b) SANYO Electric Co., LTD. (c) Central Research Institute of Electric Power Industry E-mail: K422950 @ kepco.co.jp solid solutions. Figure 5 shows the Fourier t r a n s f o r m s ( R D F ) o f L a 0 . 7 S r 0 . 3 M n O 3 compound at Mn- K edge. The RDF derived from the fluorescent X-ray method agrees with that of the transmitted X-ray method. F i g u r e 6 s h o w s t h e c o m p o s i t i o n d e p e n d e n c e o f L a - O , S r - O a n d M n - O d i s t a n c e s o b t a i n e d b y X A F S a n a l y s i s , together with La( Sr ) -O and Mn-O obtained by X- ra y Ri et ve ld an al ys is ( XR D ) in La 1- x S r x M n O 3 s o l i d s o l u t i o n s . T h e M n - O a n d L a - O d i s t a n c e s o f L a M n O 3 ( x = 0 . 0 ) a r e r e s p e c t i v e l y 1 . 9 8 Å a n d 2 . 7 7 Å , w h i c h s h o w s g o o d a g r e e m e n t w i t h t h o s e d e r i v e d f r o m i o n i c radius. The first neighbor Mn-O distance obtained by XAFS continuously decreases from 1.98 Å at x = 0. 0 to 1. 94 Å at x = 0.4 , wh ic h is in go od ac co rd an ce with that obtained by XRD. The La( Sr ) -O distance obtained by the XRD also decreases from 2.77 Å to 2.74 Å in all the compositional range. However the La -O ob ta in ed by th e XA FS dr as ti ca ll y de cr ea se s and becomes 2.67 Å in the compositional range of 0 . 3 x < 0 . 4 . T h i s d i s t a n c e i s s h o r t e r t h a n t h a t o b t a i n e d b y X R D a n d d e r i v e d f r o m i o n i c r a d i u s . T h e S r - O r e m a i n e d a r o u n d 2 . 7 8 Å i n a l l t h e c o m p o s i t i o n a l range. These facts indicate that the valence state of Mn and the local structure around substituted Sr in La-site was different from those in LaMnO 3 . References [1] Y . H i r a i , S P r i n g - 8 A n n u a l R e p o r t 1 9 9 9 ( 1 9 9 9 ) 1 0 0 . [ 2 ] M a t s u s h i t a T e c h n o r e s e a r c h , I N C . , S u m i t o m o Electric Industries, LTD., Toyota Central Research & Develop. Labs., INC., SANYO Electric Co., LTD., C e n t r a l R e s e a r c h I n s t i t u t e o f E l e c t r i c P o w e r I n d u s t r y , Ka ns ai E le ct ri c Po we r Co ., I NC . & Os ak a U ni ve rs it y. [ 3 ] F . W . L y t l e e t a l . , N u c l . I n s t r u m . M e t h . 2 2 6 (1984) 542. 82 FT magnitude Ψ Ψ (r ) –d Mn-La / Sr –d Mn-Mn fluorescent X-ray data transmitted X-ray data –d Mn-O r (Å) –d Mn-Mn 1 2 3 4 5 6 0.2 0.1 0
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