HIGH RESOLUTION X-RAY MICROSCOPY WITH ZONE PLATE MICROSCOPES

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HIGH RESOLUTION X-RAY MICROSCOPY WITH ZONE PLATE MICROSCOPES

G. Schmahl, D. Rudolph, B. Niemann

To cite this version:

G. Schmahl, D. Rudolph, B. Niemann. HIGH RESOLUTION X-RAY MICROSCOPY WITH ZONE PLATE MICROSCOPES. Journal de Physique Colloques, 1984, 45 (C2), pp.C2-77-C2-81.

�10.1051/jphyscol:1984219�. �jpa-00223865�

H I G H R E S O L U T I O N X-RAY MICROSCOPY W I T H ZONE P L A T E MICROSCOPES

G . Schmahl, D. Rudolph and B. Niemann

Universitat Gd'ttingen, Forschungsgrmppe Rd'ntgenmikroskopie, GeismarZandstrasse 11, 34 GSjttingen, F.R.G.

R6sum6 - Des e x p 6 r i e n c e s d e microscopic p a r r a y o n s X o n t 6 t 6 r g a l i s 6 e s a l ' a i d e d ' u n microscope 2 r a y o n s X i n s t a l l 6 s u r l ' a n n e a u de s t o c k a g e BESSY 1 B e r l i n .

A b s t r a c t - X-ray microscopy e x p e r i m e n t s a r e d e s c r i b e d which have been performed w i t h an x-ray microscope a t t h e e l e c t r o n s t o r a g e r i n g BESSY i n B e r l i n .

I - INTRODUCTION

X-ray microscopy can be used f o r i n v e s t i g a t i o n s i n t h e f i e l d s of biology, medicine, p h y s i c s , e s p e c i a l l y m a t e r i a l s s c i e n c e , and p r o - bably o t h e r f i e l d s , a s polymer s c i e n c e , ceramics, geology, and t h i n f i l m technology.

For t h e e x a m i n a t i o n of b i o l o g i c a l specimens t h e i r i s a gap between l i g h t and e l e c t r o n microscopy. Such specimens a r e normally h y d r a t e d and a r e composed of low atomic number atoms t h u s h a v i n g low c o n t r a s t f o r v i s i b l e l i g h t and e l e c t r o n s . F o r t h e examination i n l i g h t - and e s p e c i a l l y e l e c t r o n microscopes t h e b i o l o g i c a l samples have t o be t r e a t e d c h e m i c a l l y a n d / o r p h y s i c a l l y which may a l t e r t h e e l e m e n t a l composition o r u l t r a s t r m c t u r e of t h e sample.

I n t h e s o f t x-ray wavelength r e g i o n between 2,3 t o 4,4 nm t h e absorp- t i o n c o e f f i c i e n t s of w a t e r and e.g. p r o t e i n d i f f e r by a b o u t one o r d e r of magnitude. As a l r e a d y p o i n t e d o u t by Wolter / 1 / t h i s d i f f e r e n c e p r o v i d e s a n a t u r a l c o n t r a s t mechanism f o r t h e i n v e s t i g a t i o n o f wet

Fig. 1 - X-ray microscope a t t h e BESSY s t o r a g e r i n g i n B e r l i n .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984219

JOURNAL DE _PHYSIQUE

Fig. 2 - Schematic arrangement of t h e x-ray microscope.

Microscopy w i t h s o f t x-rays r e q u i r e s i n t e n s e x-ray s o u r c e s a s w e l l a s h i g h r e s o l u t i o n x-ray l e n s e s . I n t e n s e x - r a d i a t i o n i s p r o v i d e d by t h e

s y n c h r o t r o n r a d i a t i o n of e l e c t r o n s t o r a g e r i n g s . A d d i t i o n a l l y , x-ray plasma s o u r c e s , p o s s i b l y s u i t e d a s l a b o r a t o r y s o u r c e s f o r x-ray micro-

scopy, a r e under development. S u i t e d o p t i c a l e l e m e n t s f o r x-ray micro- scopy work a r e zone p l a t e s .

The s t a t e of t h e a r t of x-ray microscopy - i n c l u d i n g x-ray s o u r c e s , x-ray o p t i c a l elements, x-ray microscopes and a p p l i c a t i o n s of x-ray microscopy - ^{i s} d e s c r i b e d i n t h e volume "X-RAY MICROSCOPYt1 / 2 / .

, , ' , , ,

polychromatic

X-radiation -,-.

,

0

,

-

image field

,

--, apo(.Jized !

region \

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- - - _

micro zone ' , , image -. __ ^{_. plate} . _{'. lSt order}

condenser zone

plate . _'.

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Fig. 3 - Arrangement of t h e x-ray o p t i c a l elements.

A = 4, 5nm, x-ray m a g n i f i c a t i o n 250 X .

I1 - ^X-RAY MICROSCOPE

The x-ray microscope c o n s i s t s of a condenser zone p l a t e , a diaphragm i n t h e o b j e c t p l a n e , a micro zone p l a t e , a camera and a c h a n n e l p l a t e t o c o n v e r t t h e x-ray image t o a v i s i b l e image ( F i g . 1 and 2 ) .

The condenser zone p l a t e i s i l l u m i n a t e d by p o l y c h r o m a t i c x - r a d i a t i o n of t h e x-ray s o u r c e l o c a t e d a t a d i s t a n c e of 15x11 and c o n c e n t r a t e s t h e r a d i a t i o n i n t o t h e o b j e c t p l a n e . I n a d d i t i o n t h e condenser a c t s t o g e t h e r w i t h t h e diaphragm a s a l i n e a r monochromator t o p r o v i d e t h e quasimonochromatic r a d i a t i o n w i t h A /Ahan/2 n e c e s s a r y f o r imaging w i t h t h e micro zone p l a t e h a v i n g n zones. The s p e c t r a l r e s o l u t i o n i s g i v e n by A / d = ~ / 2 d w i t h D = d i a m e t e r of t h e condenser and d = d i a - m e t e r of t h e diaphragm. lZle micro zone p l a t e g e n e r a t e s a n e n l a r g e d image of t h e o b j e c t p l a c e d on t h e diaphragm. This image can e i t h e r be viewed d i r e c t l y u s i n g t h e c h a n n e l p l a t e o r be photographed.

To avoid r e d u c t i o n of t h e c o n t r a s t i n t h e e n l a r g e d x-ray image by z e r o o r d e r r a d i a t i o n t h e condenser was apodized a s shown i n Fig.3. The apodized r e g i o n of t h e condenser f i r s t l y a v o i d s z e r o o r d e r r a d i a t i o n of t h e condenser r e a c h i n g t h e o b j e c t and second e n s u r e s t h a t i n t h e image f i e l d t h e c e n t r a l r e g i o n i s f r e e from z e r o o r d e r r a d i a t i o n and r a d i a t i o n from a l l n e g a t i v o r d e r s of t h e micro zone p l a t e . I n ad- d i t i o n , a s t o p shades second and h i g h e r o r d e r r a d i a t i o n .

The zone p l a t e s a r e made by an i n t e r f e r o g r a p h i c method a s d e s c r i b e d by Schmahl e t a 1 /3/ . The p a r a m e t e r s of t h e micro zone p l a t e s (MZP) and condenser zone p l a t e s ( K Z P ) u s e d up t o now i n o u r x-ray microsco- py e x p e r i m e n t s a r e g i v e n i n t a b l e 1 ( r, = r a d i u s of t h e f i r s t zone,

= r a d i u s of t h e outermost zone, d m = w i d t h of t h e outermost zone,

3= zone number, f = f o c a l l e n g t h ).

JOURNAL DE PHYSIQUE

Table 1 - Parameters of zone p l a t e s

A t t h e BESSY s t o r a g e r i n g , x-ray microscopy experiments have been made u s i n g t h e condenser zone p l a t e KZP 3 and t h e micro zone p l a t e MZP 3 and t h e wavelength A = 4,5 nm. With a s o u r c e d i a m e t e r of a b o u t

1 mrn t h e monochromatic image of t h e s o u r c e i n t h e o b j e c t p l a n e h a s a d i a m e t e r of d = 20 p r e s u l t i n g i n A A = 225. This meets t h e r e q u i r e m e n t s of MZP 3.

With t h e s t o r a g e r i n g c u r r e n t of 100 mA, a condenser zone p l a t e e f f i - c i e n c y of 4% and a b s o r p t i o n l o s s e s i n t h e membranes of t h e e n t r a n c e window and o b j e c t chambeg of a b o u t 50% t h e photon d e n s i t y i n t h e ob-

j e c t p l a n e i s a b o u t 4.10 photons/

w 2 , s PI ( p )

rn (PI

d m (PI

n

4, 5nm(mm) f 2 , 3nm ( m m )

X-ray photographs have been made w i t h - an x-ray m a g n i f i c a t i o n between 250 x and 500 x w i t h exposure times r a n g i n g from 2 t o 30 seconds.

Examples a r e shown i n Fig. 4 and Fig. 5with a r e s o l u t i o n of about 0905 tun*

MZP 1 MZP 2 MZP 3 KZP 2 KZP 3

6 1,16 1,76 43,8 37

150 11,6 27,8 3000 4500

0,12 0,058 0,055 0932 0915

625 100 251 4,7.io3 i , 5 . i o 4

8 0,30 0,69 425 304

15,6 0,59 1 , 3 5 833 595

111 - SCANNING X-HAY MICROSCOPE

The n e c e s s i t y t o b u i l d a scanning x-ray microscope r e s u l t s from t h e advantageously reduced r a d i a t i o n dose of such a system compared w i t h a n imaging x-ray microscope.

I n an imaging x-ray microscope t h e x-rays f i r s t e n t e r t h e o b j e c t and t h e n p a s s t h e magnifying micro zone p l a t e , which h a s u s u a l l y a d i f - f r a c t i o n e f f i c i e n c y of l e s s t h a n t e n p e r c e n t . Thus, more r a d i a t i o n p a s s e s t h e o b j e c t than i s d i f f r a c t e d i n t o t h e image. I n a n x-ray

s c a n n i n g microscope t h e x-rays f i r s t p a s s t h e micro zone p l a t e . Only t h e x-rays which a r e d i f f r a c t e d i n t o t h e s c a n s p o t e n t e r t h e o b j e c t and t h e y a l l c o n t r i b u t e t o t h e image. Also t h e d e t e c t i v e quantum e f f i c i e n c y of t h e c o u n t e r i n t h e scanning microscope i s much h i g h e r than of p h o t o g r a p h i c p l a t e s u s e d up t o now i n t h e imaging microscope.

But one h a s t o b e a r i n mind t h a t t h e dosage advantage of a scanning

x-ray microscope d e c r e a s e s w i t h t h e development of e f f i c i e n t a r e a

d e t e c t o r s and zone p l a t e s w i t h h i g h d i f f r a c t i o n e f f i c i e n c i e s ( phase

zone p l a t e s ). I t should a l s o be mentioned t h a t t h e time n e c e s s a r y

t o s c a n an image i s always l o n g e r t h a n t h e time n e c e s s a r y i n t h e

imaging mode.

F i g . 6 shows a schematic of t h e s c a n n i n g system which h a s been b u i l t a t t h e G t t t i n g e n U n i v e r s i t y and w i l l be t e s t e d a t t h e e l e c t r o n s t o r a g e r i n g BESSY. The s m a l l x-ray image s p o t which i s n e c e s s a r y f o r a scan- n i n g microscope i s achieved w i t h two zone p l a t e s . The f i r s t zone p l a t e i s s e v e r a l rnm i n d i a m e t e r and by a d j u s t i n g a p i n h o l e o f some )~m i n d i a m e t e r t o t h e f o c u s of a s e l e c t e d wavelength, i t a c t s a l s o a s a l i n e a r monochromator. The f o l l o w i n g micro zone p l a t e , now i l l u m i n a t e d w i t h quasimonochromatic r a d i a t i o n from t h e p i n h o l e , produces t h e s c a n

s p o t of some t e n nanometer i n d i a m e t e r ; t h e s p o t i s t h e demagnified image of t h e p i n h o l e . The t r a n s m i t t e d r a d i a t i o n w i l l be measured by a h i g h e f f i c i e n t x-ray d e t e c t o r and a p i c t u r e w i l l be b u i l t up on a monitor. A s a n x-ray d e t e c t o r gas p r o p o r t i o n a l o r gas s c i n t i l l a t i o n c o u n t e r s can be u s e d w i t h 50 A o r more d e t e c t i v e quantum e f f i c i e n c y . This h i g h quantum e f f i c i e n c y i n combination w i t h t h e s p e c i a l o p t i c a l arrangement l e a d s t o a r a d i a t i o n dose i n t h e o b j e c t a b o u t two o r d e r s of magnitude l e s s than i n t h e imaging x-ray microscope used up t o now.

The s c a n n i n g s t a g e i s performed mechanically and must be a b l e t o pro- duce s t e p s i z e s of 5 nm i n o r d e r t o a c h i e v e 10 nm r e s o l u t i o n . The s t e p s w i l l be done w i t h arms of l e v e r which r e s t a t t o r s i o n - j o i n t s f r e e of backlash. The amplitude w i l l be measured a t t h e f r e e end of t h e l e v e r . The motions and t h e image f o r m a t i o n i s c o n t r o l l e d by a computer.

References

1 - WOLTER,H.,Ann.Phys. L e i p z i g 10 (1952) 94 - ^114.

2 - ^X-RAY MICROSCOPY, Eds. G.Schmah1 and D.Rudolph, S p r i n g e r 1983.

J - ^{SCHMAHL, G.,} D.RUDOLPH,P. GUTTMANN, B.NIEFANN, and 0. CHRIST, Zone P l a t e s f o r X-Ray Microscopy, i n i b i d .

The c o n s t r u c t i o n of t h e zone p l a t e s and x-ray microscopes have been

supported by t h e S t i f t u n g Volkswagenwerk. The experiments a t , BESSY a r e

being s u p p o r t e d by t h e Eundesministerium f i i r Forschung und Technologic.