REFLECTION 11 



therefore the possibihty of performing ex- 

 periments on the surface while obsenang it. 

 This has not received the attention it de- 

 serves, but Cosslett and Jones (1955) have 

 buih a reflection electron microscope with a 

 hot -stage and have been able to observe the 

 changes brought about by heating silver and 

 other materials. 



Most work in reflection electron micros- 

 copy has been done with metal specimens 

 but it is possible to examine other materials. 

 It is necessary for the specimen surface to be 

 electrically conducting since otherwise it be- 

 comes charged and repels the electron beam. 

 If an electrical non-conductor is to be ex- 

 amined, it is usual to render its surface con- 

 ducting by evaporating a layer of metal 

 (usually a few hundred angstroms thickness 

 of silver) onto it. There are also some diffi- 

 culties in examining organic materials since 

 these are readily decomposed by the electron 

 beam: the use of very low beam intensities 

 is often necessary in order to obtain pictures 

 of these materials. These difficulties can be 

 overcome by using the replica technique of 

 Bradley (1955) — a rigid metal replica of 

 the surface to be examined is prepared and 

 forms a robust specimen for the reflection 

 electron microscope. There appears to be no 

 loss in resolution, but the advantage of direct 

 examination of the surface is of course lost. 



A few references to typical applications 

 of reflection electron microscop}^ follow. 

 Metals with different surface preparations 

 have been studied by Halliday (1955, 1957); 

 diamond surfaces of different types by Seal 

 and Menter (1953) and Seal (1956, 1958a 

 and b); the epicuticular surfaces of insects 

 by Holdgate and Seal (1956); natural and 

 synthetic fibers and the effect of abrasion 

 on them by Chapman and Menter (1954); 

 lubricant layers of graphite and other lamel- 

 lar solids by Deacon and Goodman (1958): 

 cleavage faces of zinc crystals by Moore 

 (1955); surface damage on mica by Bailey 

 and Courtney-Pratt (1955) and on rocksalt 

 by King and Tabor (1954); paper and pulp 



Fig. 4. Reflection electron micrograph of a 

 single groove of a gramophone record. There is a 

 sine wave modulation of which rather more than 

 one cycle is visible. © i = 2°, © 2 = 9°. nij. = 570 X, 

 mil = 90 X 



Fig. 5. Reflection electron micrograph of part 

 of a lathe-turned brass surface. The circular 

 grooves left by the cutting tool appear foreshort- 

 ened as portions of ellipses. © 1 = 2°, © 2 = 9°. 

 nij. = 1000 X,mi! = 160 X. 



fibers by Amboss, Emerton, and Watts 

 (1954) ; the fretting corrosion of mild steel by 

 Halliday and Hirst (1956). 



Since the main part of this article was 

 written, further papers on the subject have 

 appeared. Halliday and Newman (1958, 

 19G0) have published the results of an in- 

 vestigation of reflection electron microscopy 

 using diffracted electrons. In these experi- 

 ments crj^stalline specimens were used and 

 the angles of tilt of the electron gun and 

 specimen adjusted so that a diffracted beam 

 passed through the objective aperture. This 

 beam was used to form an image, analogous 

 to the "dark field" image often used with 



227 



