REFLECTION 11 



examination of fibers both natural and syn- 

 thetic and in the study of wear. 



jMore recent work has enabled some of the 

 above disadvantages to be overcome. Brad- 

 ley (11) has suggested the use of sohd metal 

 replicas for those specimens which suffer 

 beam damage. Halliday and Newman (12) 

 have photographed etched germanium sur- 

 faces at high resolution by imaging diffracted 

 electrons which have a lower energy spread 

 than scattered electrons. The greatest ad- 

 vance has, however, been in a return to 

 much larger angles of beam deviation though 

 not to the extreme value of 90° used b\^ 

 Ruska. Fert, Marty and Saporte (13), Page 

 (14) and Ito, Ito, Aotsu and ]\liyamae (15) 

 have all used angles of deviation in the region 

 of 25 to 30°. The considerably reduced fore- 

 shortening obtained at the higher angles of 

 viewing gives to the image a strikingly three- 

 dimensional appearance which can be highly 

 informative. It would seem though that no 

 further significant advance in the reflection 

 technique will be made until lens designers 

 can find a practical method for the correc- 

 tion of axial chromatic aberration. If such a 

 correction became feasible we might have 

 an instrument capable of direct and rapid 

 observation of surfaces at a resolution com- 

 parable to that attained at present by rep- 

 lica methods. 



REFERENCES 



1. Ruska, E. Z., Phys., 83, 492 (1933). 



2. Ruska, E. and MtiuLER, H. O., Z. Phys., 116, 



366 (1940). 



3. vox BoRRiES, B., Z. Phys., 116, 370 (1940). 



4. Ku.sHxiR, Yu. M., Biberman, L. M., and 



Levkin, N. p., Bull. Acad. Sci., URSS Per. 

 Phys., 15, 306 (1951). 



5. Cosslett, V. E. AND Jones, D., J. Sci. In- 



strum., 32, 86 (1955). 



6. Fert, C. and Saporte, R., C. R. Acad. Sci., 



Paris, 235, 1490 (1952). 



7. Menter, J. W., /. Inst. Metals, 81, 163 (1952). 



8. Haine, M. E. and Hirst, W., Brit. J. Appl. 



Phys., 4, 239 (1953). 



9. Emerton, H. W., Research (London), 7, S56 



(1954). 



10. Page, D. H., Brit. J. Appl. Phys., 9, 268 



(1958). 



11. Bradley, D. E., Brit. J. Appl. Phys., 6, 191 



(1955). 



12. Halliday, J. S. and Newman, R. C, "Fourth 



International Conference on Electron 

 Microscopy," Berlin, September 1958. 



13. Fert, C, Marty, B., and Saporte, R., C. R. 



Acad. Sci., Paris, 240, 1975 (1955). 



14. Page, D. H., Bn7. J. Appl. Phys., 9,60 (1958). 



15. Ito, K., Ito, T., Aotsu, T., and Miyamae, T., 



/. Electron Microscopy, 5, (1957). 



D. H. Page 



REFLECTION II 



In electron microscopy, as in fight micros- 

 copy, it is possible to examine both trans- 

 lucent and opaque objects — ^the former with 

 transmitted and the latter with reflected 

 illumination. Most of the electron micro- 

 scopes built have been of the transmission 

 type since higher resolutions are attainable 

 with this arrangement. Only the thinnest 

 films are translucent to electrons and so it 

 has been common practice to use replica 

 methods when information about the surface 

 structure of solid specimens was wanted. 

 However, considerable progress has been 

 made with techniques for the direct examina- 

 tion of the surfaces of solid objects. Those 

 used at present include scanning, emission, 

 and reflection electron microscopy. Each 

 gives a different type of information and this 

 article will deal with one of them only — 

 reflection electron microscopy. 



In the reflection electron microscope the 

 electron gun is tilted with respect to the axis 

 of the objective and projector lenses. The 

 specimen is also tilted with respect to this 

 axis but at a smaller angle to it. The arrange- 

 ment is shown in Figure 1. The beam of 

 electrons from the electron gun strikes the 

 specimen at an angle di and the electrons are 

 there scattered in all directions. Those scat- 

 tered at angle 62 to the surface in the direc- 

 tion of the objective aperture pass through 

 it and subsequently through objective and 



223 



