342 



M. SEAL 



Fig. 1. Reflection electron micrographs of a type 1 diamond 



cleavage surface, m^ ~ 2000 : m^ 



250 



Fig. 2. Reflection electron micrograph of a type II diamond 

 cleavage surface. /«i ~ 3000 : /^u ~ 400 



ultra violet absorption. The diamonds were cleaned 

 in nitric acid, followed by distilled water. A layer 

 of silver about 500 A thick was evaporated onto the 

 surface to prevent charging of the specimen in the 

 electron beam. The examination was carried out 

 using the Metropolitan Vickers EM3 electron micro- 

 scope modified for use in reflection (4). 



Reflection electron micrographs typical of dia- 

 monds of the two types are shown in figures I and 2. 

 The conchoidal nature of the type I cleavage and 

 the much smoother nature of the type II cleavage 

 are apparent. The surface roughnesses may be 

 estimated from measurements on the micrographs. 

 The type I cleavage surfaces are so rough, however, 

 that it is difficult to give an accurate value of the 

 change in height which corresponds to a particular 

 shadow, since the local slope of the surface on which 

 the shadow falls is not known. Certainly, there are 

 fairly abrupt changes in height of a micron or more 

 on the part of the surface shown in figure I. Other 

 parts of the surface of this diamond were consider- 

 ably rougher and were too rough for examination 

 by reflection electron microscopy. The type II sur- 

 face shown in figure 2 is considerably smoother. 

 The steps seen here are probably all less than 1500 A 

 in height, and many of the regions between the larger 

 steps are flat to within 300 A. Other regions of type 

 II diamond cleavage surfaces are similar in appear- 

 ance, but there are occasional large steps of perhaps 

 a micron in height. These large steps differ from those 

 on type 1 diamonds in that they separate relatively 

 smooth regions. 



The lines running in the direction A on figure 2 

 are of interest. It is believed that they correspond 

 to lamellae in the diamond. Type II diamonds are 

 known to have a lamellar structure. Robertson, 

 Fox, and Martin (7) reported the existence of fine 



laminations parallel to (ill) planes on type IT cleav- 

 age surfaces. These laminations were about 10 /t 

 apart, but some may have been as narrow as I //. 

 Such laminations have since been observed by 

 Ramachandran (6) (thicknesses 10 to 100//) and by 

 Custers (5) (thicknesses of the order of 5 //). The 

 lines A on figure 2 are also spaced about 5 // apart. 

 Similar lines are visible on most of the other micro- 

 graphs of type II diamonds. 



Type I diamonds do not, however, always have an 

 appearance similar to that of fig. 1. Regions of a type 

 I cleavage surface have been found which appear 

 in the reflection electron microscope indistinguish- 

 able from a type II cleavage. Micrographs have also 

 been obtained showing regions where the two types 

 of cleavage join along quite a sharp and well defined 

 boundary. It is suggested that, in these cases, the 

 type I diamond has regions of type II material 

 within it. It is probable (2) that type I diamonds 

 have a mosaic structure and are for the most part 

 highly dislocated, whereas type II diamonds consist 

 of lamellae of relatively perfect material. It would 

 then be quite reasonable for there to be inhomo- 

 geneity in the perfection of individual diamond crys- 

 tals. Indeed. Ahearn ( I ) has shown that there may be 

 inhomogeneities in the ultra violet (2550 A) trans- 

 mission and alpha particle bombardment conduction 

 of individual diamonds and suggests that some dia- 

 monds may contain regions of both type I and type II 

 material. Furthermore, inhomogeneity in the ultra 

 violet transmission (at 2850 A) of a diamond has 

 recently been observed by the author. The observa- 

 tions on diamond cleavage surfaces thus support 

 Ahearn's views. 



Conclusion. — Cleavage surfaces of diamonds of 

 types I and II appear difterent in character and 

 roughness when examined in the reflection electron 



