ELECTRON MICROSCOPY 



Fig. 1. A packing drawing of the nickel phtha- 

 locyanine structure viewed along the bo-axis. The 

 metallic atom is black, the nitrogen atoms are 

 line-shaded. (R.W. G.Wyckoff,'' Crystal Structures'^) 



the copper and platinum derivations of 

 phthalocyanin, a blue dye with a flat ring 

 structine (Fig. 1) and the metal atom in the 

 center. The crystal structure of platinum 

 phthalocyanin may be considered to com- 

 prise fairly widely spaced planes of heavy 

 metal atoms (c^2oi = 11.94 A) embedded in 

 a matrix of the light elements nitrogen, car- 

 bon and hydrogen. The thin ribbon habit of 

 the crystal is such that when supported on a 

 specimen grid the 20l planes are almost 

 parallel to the electron beam. The electron 

 micrograph at a magnification of 1,500,000 

 (Fig. 2) shows the clearly resolved planes 

 spaced 11.94 A apart. Similarly the copper 

 phthalocyanin shows a spacing of 9.8 A. 

 These parallel lines are the image of the 

 projection of the 20l planes seen edge on. 

 Imperfections are seen sometimes in the form 

 of edge dislocations (Fig. 2) caused by in- 

 complete planes. It has been possible also to 

 resolve the 111 planes of the inorganic crys- 

 tal sodium faujasite, a silicate with the com- 



position 2 Al2O3-CaO-Na2O10SiO2-20H.,O, 

 with a spacing of 14.37 A. 



The mechanism of image formation de- 

 pends upon the fact that the ihiii crystals 

 form a cross grating diffraction spectrum. 

 With a 50-mi(*ron objective aperture the 

 spectra contributing to the image from the 

 {)hthalocyanin crystals are (20l), (402), 

 (201) and (402). These spectra recombine 

 with the zero order beam in the image plane 

 and form an image of the crystal grating in 

 accordance with the simple Abbe theory of 

 image formation by a lens. Calculations by 

 Menter suggest that it should be possible to 

 resolve planes with spacings considerably 

 smaller than 10 A providing the divergence 

 of the illuminating beam is made sufficiently 

 small. 



Figs. 2. (a). Electron micrograph of part of 

 crystal of platinum phthalocyanine showing image 

 of lattice planes 12 A apart. Magnification 1,500,- 

 OOOX. (b). Part of crystal of platinum phthalocy- 

 anine showing edge dislocation. The dislocation 

 line is perpendicular to the plane of the paper. 

 Magnification as before, (c). Sketch copied from 

 (b) showing exact position of extra plane of mole- 

 cules. (Menter) 



146 



