90 



J. W, MENTER 



HlWWi^ 





m 



Fig. 8. Copper phthalocyanine crystal showing dislocated 

 region associated with change in width of crystal. 



nitrocellulose supporting film, containing a large 

 number of holes. It was found that the image was 

 seen to the best advantage when not overlaid with 

 the structure of the supporting film. The specimens 

 were examined in the Elmiskop I operated at 80 kV, 

 using the fine focus condenser (aperture 200 //) and 

 a 50 /( objective aperture (unless otherwise stated) 

 and recorded on Ilford Contrasty Lantern plates at 

 a magnification of 77,000 times. 



Results. Platinum phthalocyanine. — A considerable 

 number of plates revealed the structure shown in fig- 

 ure 5, consisting of a series of parallel linesinthe[010] 

 direction, the spacing of which was 12.0 A, averaged 

 from measurements on 26 crystals with a standard 

 deviation of 0.2 A (see Table 1 ). These lines may be 

 regarded as the image of the projection of (201) 

 planes seen edge on. Bent crystals have been observed 

 in which the bending of the crystal planes follows 

 the external form of the crystal as would be expected. 

 Imperfections are sometimes seen in the structure in 

 the form of edge dislocations. A particularly simple 

 example is shown in figure 6, the exact position of 

 the incomplete plane being clarified by the sketch in 

 figure 7 which has been copied from the micrograph. 



Copper phthalocyanine. — Similar results have been 

 obtained with copper phthalocyanine, although less 

 frequently, since the probability of finding a crystal 

 in a suitable orientation for diftYaction is lower on 

 account of the smaller value of (001)A(20T). Two 

 values have been obtained for the spacing of the 

 planes. The first 10.30 ±0.3 A averaged from eight 

 measurements differs significantly from the x-ray 



value of 9.8 A, and a few isolated values of about 

 13 A have been observed. There are a number of 

 possible reasons for this discrepancy which are dis- 

 cussed more fully elsewhere (5). A particularly good 

 example of a dislocated lattice is shown in figure 

 8 where a severe disturbance of the lattice is associ- 

 ated with a change in width of the crystal at the point 

 X. Cracks have been observed in crystals in which 

 the crack may be seen to propagate from one plane 

 to its neighbour as it traverses the lattice. 



Sodium faujasite. — This is the first inorganic mate- 

 rial in which the crystal planes have been resolved. 

 It is a network silicate structure with the composition 

 2Al,O3-CaO.Na2O.10 SiO,.20 H.p, being cubic with 

 ao = 24.84 A. The (111) spacing is 14.37 A and the 

 mean of measurements from 16 micrographs gives 

 ^,111; =" 14.4 ± 0.2 A (see Table 2). Figure 9 shows a 

 crystal of this compound revealing the (111) planes. 

 Fig. 10 shows a crystal viewed along the [110] axis 

 in which two sets of ( 1 1 1) planes intersecting at 70^ 

 are resolved. 



Mechanism of image formation. — The crystals 

 being thin, form a cross-grating diffraction spectrum 

 since the third Laue condition for diffraction from 



Table 1. Spacing of lines in platinum phthalocyanine. 

 (All plate magnifications 77,000 ) 



