Sample Corner Pinhol 12.7 mm 25.4 mm 743 mm Beam stop Photodiode CCD X-rays than pecimen T o w a r d s A t o m i c R e s o l u t i o n 3 - D X - r a y D i f f r a c t i o n M i c r o s c o p y Fig. 1. Schematic layout of the experimental instrumen t used to record the coherent X-ray diffraction patterns. Figure 1 0. F igure 2(a) Figure 2(b) Fig. 2(c) D ue to the fact that X-ray wavelengths are on the order of the size of atoms, scientists have long dreamed of atomic resolution X -ray microscopes which c ould visualize a rrangement of atoms in three dimensions. However, X-rays are much more difficult to focus than electrons. T he smallest X-ray focal spot currently achievable is around 30 nm [1]. This limitation c an be overcome by usin g c oherent X-ray diffraction and t he oversamplin g phasing method. W hen a finite s pecimen is illuminated by c oherent X -rays, t he w eakly scattered X -ray photons f orm a c ontinuous diffraction pattern in the far field. This continuous pattern can be sampled at spacin gs finer th e Nyquist frequency ( i.e. t he inverse of the s si ze), which we call “oversampling”. Oversamplin g a diffraction pattern corresponds to surrounding th e electron density of the specimen with a no-densit y r egion. T he higher t he sampling frequency, th e larger the no-density region. W hen the no-densit y region is larger than the electron density region, th e phase information is in principle available from th e diffraction pattern itself and can be directly retrieved by using an iterative algorithm [2]. T he firs t demonstration experiment of this form of microscopy was carried out by using c oherent soft X -rays in 1999 [3]. More recently, it has been extended to image the shapes of nano-crystals by using hard X- rays [4]. However, the experiments that have been carried out thus far have been limited to imaging 2- D samples, and the highest resolution achieved to date is around 70 nm [3,4]. H ere , we describe the first experiment to image the 3-D structure of a non-crystalline material at 50 - nm resolution, which was r eported in Phys. Rev. Lett. [5]. T he experiment was carried out at th e undulator beamlin e BL29X U . s hows a schematic layout of the experimental instrument in w hich all t he components are in vacuum with a pressure of ~1 0 -6 t orr. T he sample, fabricated by electron beam lithography, c onsists of two single- layered Ni patterns (each with a size of 2. 5 × 2 × 1 μ m) rotated 65º relativ e to each other in-plane and separated by a distance of 1 μ m. T he sample is s upported by a thin silicon nitride membrane w indow. s hows a scanning electron microscopy (SEM) image of the sample. Due to th e 1 μ m separation of the two layers, the SEM image shows the pattern in the top layer, and the pattern in the bottom layer is visible only as a soft blur. s hows a 2-D diffraction pattern at a resolution of 8 nm recorded from t he s ample by using c oherent X -rays with a wavelength of 2 Å. T he total exposure time of t he diffraction pattern is about 45 minutes using unfocused X- rays from t he undulator beamline. By usin g t he oversampling phasing method, th e diffraction pattern was directly converte d to the high - resolution image shown in . T he top and bottom layered pattern s are clearly seen as overlapped in this 2-D image projection, and the variation of th e electron density at the nanometer scale is also visible. To obtain the 3-D structural information, a series of t hirty-one 2-D 109 ( c ) ( b ) 3 0 0 n m ( a ) ( d ) F i g . 2 . ( a ) A n S E M i m a g e o f a n N i s a m p l e w i t h b u r i e d s t r u c t u r e s . ( b ) A h i g h - r e s o l u t i o n d i f f r a c t i o n p a t t e r n r e c o r d e d f r o m t h e s a m p l e . ( c ) A h i g h - r e s o l u t i o n i m a g e r e c o n s t r u c t e d f r o m ( b ) . ( d ) T h e r e c o n s t r u c t i o n o f a 3 - D n a n o s t r u c t u r e d m a t e r i a l a t 5 0 n m r e s o l u t i o n ( d i s p l a y e d i n i s o - s u r f a c e r e n d e r i n g ) . [ R e p r o d u c t i o n f r o m r e f . 5 . ] J i a n w e i M i a o a , T e t s u y a I s h i k a w a b a n d K e i t h O . H o d g s o n a , c ( a ) S t a n f o r d S y n c h . R a d . L a b . , S t a n f o r d U n i v . , U S A ( b ) S P r i n g - 8 / R I K E N ( c ) S t a n f o r d U n i v e r s i t y , U S A E - m a i l : M i a o @ S L A C . S t a n f o r d . E D U R e f e r e n c e s [ 1 ] J . K i r z e t a l . , Q . R e v . B i o p h y s . 2 8 ( 1 9 9 5 ) 1 . [ 2 ] J . M i a o e t a l . , J . O p t . S o c . A m . A 1 5 ( 1 9 9 8 ) 1 6 6 2 . [ 3 ] J . M i a o e t a l . , N a t u r e 4 0 0 ( 1 9 9 9 ) 3 4 2 . [ 4 ] I . K . R o b i n s o n e t a l . , P h y s . R e v . L e t t . 8 7 ( 2 0 0 1 ) 1 9 5 5 0 5 . [ 5 ] J . M i a o , T . I s h i k a w a , B . J o h n s o n , E . H . A n d e r s o n , B . L a i a n d K . O . H o d g s o n , P h y s . R e v . L e t t . 8 9 ( 2 0 0 2 ) 0 8 8 3 0 3 . d i f f r a c t i o n p a t t e r n s w e r e r e c o r d e d f r o m t h e s a m p l e w i t h t h e r o t a t i o n a n g l e s r a n g i n g f r o m – 7 5 º t o 7 5 º i n 5 º i n c r e m e n t s . T h e 2 - D d i f f r a c t i o n p a t t e r n s w e r e t h e n a s s e m b l e d t o p r o d u c e a 3 - D d i f f r a c t i o n p a t t e r n . B y u s i n g a 3 - D p h a s e r e t r i e v a l a l g o r i t h m [ 5 ] , t h e 3 - D s t r u c t u r e o f t h e n o n - c r y s t a l l i n e m a t e r i a l w a s s u c c e s s f u l l y r e c o n s t r u c t e d a t a r e s o l u t i o n o f 5 0 n m . F i g u r e 2 ( d ) s h o w s a 3 - D i s o - s u r f a c e r e n d e r i n g o f t h e r e c o n s t r u c t e d i m a g e . T h e f i n e s t d i v i s i o n i n t h e z - a x i s c o r r e s p o n d s t o 2 5 n m a n d t h e d i s t a n c e b e t w e e n t w o p a t t e r n s i s a b o u t 1 μ m , w h i c h i s c o n s i s t e n t w i t h t h e k n o w n c h a r a c t e r i s t i c s o f t h e s a m p l e . W e a n t i c i p a t e t h a t t h i s f o r m o f m i c r o s c o p y w i l l h a v e w i d e a p p l i c a t i o n s i n b o t h m a t e r i a l s a n d b i o l o g i c a l s c i e n c e s . F o r m a t e r i a l s s c i e n c e s a m p l e s , w h i c h a r e l e s s s e n s i t i v e t o r a d i a t i o n d a m a g e , t h i s f o r m o f m i c r o s c o p y c a n , i n p r i n c i p l e , a c h i e v e a t o m i c r e s o l u t i o n i n t h r e e d i m e n s i o n s . I n b i o l o g y , t h i s f o r m o f m i c r o s c o p y c a n b e a p p l i e d t o i m a g e t h e 3 - D s t r u c t u r e s o f w h o l e c e l l s , c e l l u l a r o r g a n e l l e s a n d s u p r a m o l e c u l a r s t r u c t u r e s a t h i g h r e s o l u t i o n , w h i l e t h e r e s o l u t i o n w i l l b e m a i n l y l i m i t e d b y r a d i a t i o n d a m a g e t o t h e s p e c i m e n s . 20 40 60 0 0 20 40 60 80 100 10 20 30 40 80 110
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