AlxGa1·x As layers

436

Abstracts of The Netherlands Society of Electron Microscopy

electron microscopy and requires optimal structural preservation of cellular components prior to labelling in order to adequately relate label and structure~ It is thus important to d i s t u r b the protein and subcellular structures as little as possible so as not to alter or destroy the antigenic sites. In freeze-substitution experiments improved preservation of the ultrastructure was demonstrated. Reduced ultrastructural artifact formation may also have its benefits in preserving the antigenic sites (it is possible to reduce or even omit fixatives during preparation without significant loss of structural detail). Freeze-substitution is based on cryofixation with all its positive and negative implications. The advantage is the fixation or arrest of the actual physiological state of the cell. It is possible to trap fast physiological processes such as transmitter release in nerve synapses. This methis well suited for single cells. Large probes such as tissues, unfortunately, are only fixed within a border zone of 15 ~m without visible damage due to ice crystal formation. For freeze-substitution the probes are transferred into a suitable organic solvent at 180 K. During the substitution process i) the ice of the biological sample is dissolved and 2) if fixatives are used, fixation is initiated by raising the temperature ~p to 240 I. The cells are dehydrated and fixed in a one-step process. The substitution is followed by low--temperature embedding at 240 K or lower. The final embedded probe can be sectioned with a conventional microtome at ambient temperature as easily as Epon. In addition, the sample can be stored in a library tc re-use whenever a new test serum is available.

TRANSMISSION ELECTRON MICROSCOPY OF CLAY MINERALS A. de Jager, E.M. Bouw*, L. van der Plas and A. Boekestein* Dept. o f S o i l S c i e n c e & G e o l o g y ; A g r i c u l t u r a l U n i v e r s i t y ; ~ T e c h n . and Phys. Eng. Res. S e r v i c e ; W a g e n i n g e n , The N e t h e r l a n d s

A study of the ultrastrucbure of clay minerals has been carried out using ultrathin sections of embedded clay specimens and transmission electron microscopy. The specimens chosen for this study were a kaolinite-rich soil and pure powdered clay minerals (illite and smectite). The

specimens were exposed to a s p e c i f i c relative humidity in order to d e f i n e the spacings between crystal layers. Subsequently clays were embedded in Spurr's epoxy resin, w h i l e special arrangements were undertaken in order to p o s i t i o n the specimens in such a way that in ultrathin sectioning transverse sections were obtained across the crystal layers. The embedded specimens were cut in a LKB Ill ultramicrotome equipped with a Diatome diamond knife. Ultra-thin sections (70 nm thick) were collected on copper grids with a Formvar supporting film. A f t e r evaporation of a carbon layer onto the specimen sections were examined in a Philips EM 4OOT transmission e l e c t r o n microscope. It appeared that sections cooled down to approximately 120 K in a special cryostage in the electron microscope were less susceptible to the thermal effects of the electron bombardment. In this way spacings between layers in microcrystalline material of clay minerals could be o b s e r v e d and a c c u r a t e l y measured.

TEM INVESTIGATION OF THIN GaAs/AlxGal. x As LAYERS A.F. de Jong P h i l i p s R e s e a r c h L a b o r a t o r i e s W Y 2, P.O. B o x 8 0 0 0 0 , 5600 JA E i n d h o v e n , The N e t h e r l a n d s

Several d i f f e r e n t TEM techniques are used to investigate structu~_,l features of thin GaAs/AlxGal.xAs layers and superlattices. Features of interest are the morphology and composition of the layers and the abzuptness and exact p o s i t i o n of the interfaces. Using structure-factor contrast, images are made in cross-section which directly reveal the morphology of the layers. C o m p o s i t i o n a l changes of about 5% can be d e t e c t e d and are related to secondary ion mass spectroscopy (SIMS) measurements. Using GaAs layers as a marker we o b s e r v e d surface r o u g h e n i n g ...... ~ growth v~^ the ~ ±.~.u. .a~a~ . layer metal organic-vapour phase epitaxy, and the subsequent smoothening effect of growing a superlattice. To investigate the abruptness and the exact position of GaAs/AIAs ~nterfaces~ HREM images are made and compared with simulated images. Reliable image matching is obtained when using defocus positions away from Scherzer defocus. The layers are distinguished by differences in the fine pattern of the images. Image

Abstracts o1" 17~eNetherlands SocieO' of Electron Micn,scopy

p r o c e s s i n g is used to e n h a n c e these differences. Results are c h e c k e d by processing s i m u l a t e d images and thus the exact position of the interface can be determined. To analyse the c o m p o s i t i o n of the layers on a nanometer scale, thickn e s s - f r i n g e m e a s u r e m e n t s o n small cleaved samples seems the m o s t promising technique. Results will be shown of a m o l e c u l a r b e a m epitaxy (MBE)-grown layered structure, e s p e c i a l l y designed to test the sensitivity of the technique.

HUMAN CATARACTOUS

W.L. Jongebloed, J.F.G. W o r s t *

LENSES

F. Dijk

AS

S E E N BY S E M

and

Centre for Medical Electron Microscopy, University of Groningen, Oostersingel 69/2, 9 7 1 3 EZ G r o n i n g e n ; *Eye Physician and Surgeon, Julianal a a n ii, 9751 BM H a r e n ; N e t h e r l a n d s

In the healthy lens the hexagonally shaped lens fibres are i n t e r c o n n e c t e d by a b a l l - a n d - s o c k e t s y s t e m and have a solid composition. The purpose of this study was to d e t e r m i n e to w h a t extent aging of the lens can be c o r r e l a t e d with changes in shape and c o m p o s i t i o n of the lens fibres. H~an cataractous lenses of patients of a d v a n c e d age (iO1 & 85 years) were examined w i t h SEM. Even w h e n the overall shape of the lens fibres remained unchanged (although with b a r e l y visible b a l l - a n d - s o c k e t interconnections) the h o m o g e n o u s fibre c o n t e n t had changed into fibrillar and/or g r a n u l a r material, or the fibres had been (partly) hollowed out. W h e r e there was s h r i n k a g e of the o r i g i n a l l y h e x a g o n a l l y - s h a p e d lens fibres to a more or less round form with a w r i n k l e d surface, the c o n t e n t s had c h a n g e d into granular m a t e r i a l with low density. Both granular and fibrillar m a t e r i a l could account for a substantial increase in light scattering, resulting in a c o n s i d e r a b l e d e c r e a s e in vision through the lens.

THE A G E I N G PROCESS AS SEEN BY SEM W.L. Jongebloed, J.F.G. Worst*

OF THE

F. Dijk

HUMAN CORNEA

and

C e n t r e for M e d i c a l E l e c t r o n M i c r o s c o p y , U n i v e r s i t y of G r o n i n g e n ~ Oostereingel 69/2, 9 7 1 3 EZ G r o n i n g e n ;

*Eye laan

437

P h y s i c i a n and S u r g e o n , J u l i a n a Ii, 9751 BM H a r e n ; N e t h e r l a n d s

The study of the natural ageing process of the h u m a n cornea is of importance for e x a m i n a t i o n of donor corneas preservation, keratoconus and possible intra-ocular lens complications. Two corneas of elderly patients (87 & 95 years) w e r e prepared for SEM and examined at both epithelial and endothelial sides. D e t a c h m e n t of epithelial cells and d e t e r i o r a t i o n of cells initiated by loss of m i c r o v i l l i lead to loss of epithelium and exposure of Bowman's membrane. The d e g e n e r a t i v e process in the endothelium leads to porosity and loss of endothelial cell membrane and finally to (partial) loss of the endothelial cell layer. The s t a r t of such a process was marked by the formation of liquid-filled blebs. The balance of d e g e n e r a t i o n versus r e g e n e r a t i o n is clearly biased in favour of the degenerative process, because the cells are not able to produce sufficient collagenous material to cover the denuded areas.

THE UPTAKE OF ~FcR-GOLD NEUTROPHIL GRANULOCYTES

BY H U ~ N

C.R. Jost, R. de Goede, J.A.M. Fransen, P.A.T. Tetteroo*, M.R. Daha *~ and L.A. Ginsel L a b o r a t o r y fol ~ l e c t r o n M l C r O s c o p u and * * D e p a r t m e : J £ of N e p h r o l o g y , L e i d e n U n i v e r s i t y , R i j n s b u r g e r w e g .10, 2333 AA L e i d e n ; * C . L . B . , A m s t e r d a m University, Amsterdam; Netherlands

P h a g o c y t e s express on their plasma membrane Fc receptors that enable them to recognize and internalize possibly harmful immune complexes. We describe the i n t r a c e l l u l a r pathway involved in the uptake of low-affinity Fc receptor (FCRIo) by h u m a n neutrophil granulocytes. For EM identification of this pathway we used a m o n o c l o n a l antibody directed against FcRIo conjugated to colloidal gold p a r t i c l e s (~FcR-qold). Neutrophils were pulsed with sFcR-gold for lh at 4°C and then chased for 1,5,15r30,60 and 120 min at 37°C. After that hour ~FcR-gold was present along the plasma membrane (PM). When cells were chased for 1 min, the sFcR--gold was mainly present along the PM and in tubular invaginations of the PM. A few small vesicles containing ~FcR-gold already appeared in the perinuclear zone (PZ). After 15 min, the