UNSOLVKD rUOBLEMS 



59. Ogawa, S., Watanabe, D., and Fujita, E., 



/. Phys. Soc. Japan, 10, 429 (1955). 



60. Ogawa, S., Mizuno, J., Watanabe, D., and 



Fujita, E., J. Phys. Soc. Japan, 12, 999 

 (1957). 



61. Reimer, L., Z. Metallkunde, 47, 631 (1956). 



62. Reimer, L., Optik, 16, 30 (1959). 



63. Fashley, D. W., Phil. Mag., 4, 324 (1959). 



64. Bassett, G. a. and Pashley, D. W., J. Inst. 



Metals, 87 (12) 449-458 (1959). 



65. Bruche, E. and Schulze, K. J., Z. Physik, 



153, 571-591 (1959). 



66. Bruche, E. and Demny, J., Z. Naturfor- 



schung, 14a, 351-354 (1959). 



67. Brame, D. R. and Evans, T., Phil. Mag., 3, 



971-986 (1958). 



68. Saulnier, a. and Mirand, P., Revue de 



I'Ahiminium, 266, 687-697 (1959). 



69. Geach, G. a., Irving, B. A., and Phillips, 



R., Research, 10, Oct., 1957. 



70. Phillips, R., /. Inst. Metals (July 1958) p. 72 



(Bull. Vol. 4). 



71. Phillips, R. and Welsh, N. C, Phil. Mag., 



3, 801 (1958). 



72. The Proceedings of the European Regional 



Conference on Electron Microscopy Delft 

 1960 (Delft 1961). 



W. BOLLMANN 



UNSOLVED PROBLEMS 



The following comments are germane 

 only to applications of the electron micro- 

 scope and related microscopy in non-bio- 

 logical areas. In general, it appears that the 

 electron microscope has been used in the 

 biological sciences more as a research tool 

 than as an analytical servdce instrument. 



Quantitative Particle Size Distribu- 

 tion Data. This is in principle a very im- 

 portant application and yet there are es- 

 sentially no accurate studies of this kind in 

 the available literature. Size and shape as- 

 says of paint pigments, magnetic powders, 

 semiconductor powders, etc., are of funda- 

 mental importance particularly where the 

 peak of the size distribution curve is of the 

 order of several hundred angstroms. The 

 color or tone of duplicating media is often 

 related to the Mie theory for particle scat- 

 tering which in turn uses the sixth power of 



the particle (sphere) radius. Also the sur- 

 face area and surface to volume ratio are 

 important to properties of semiconductors 

 such as photo- and dark conductivity. 



Ultrathin Sections. Multilayer coat- 

 ings such as magnetic tapes and photosensi- 

 tive copy papers exhibit properties which 

 are dependent on the distribution and 

 orientation of particulate solids within a 

 binder. Thin sections normal and parallel to 

 the plane of the coating are needed, but to 

 date little progress has been made in pre- 

 paring sections suitably thin for electron 

 microscopy. Unlike the biological tissue 

 sections, the difference in hardness of the 

 two or more components in the sample 

 militate against the preparation of sections 

 of the order of 500 angstroms thick. How- 

 ever more effort is needed in this area. 



Somewhat related to this problem is the 

 inability of x-ray microscopy to provide 

 useful information in such studies of coated 

 samples. Overlapping of particles makes 

 interpretation difficult, or smallness of size 

 with respect to the resolving power of the 

 instrument makes interpretation impossible. 

 For the most part the significant applica- 

 tions of the x-ray microscope have been con- 

 fined to metallic and biological materials. 



Replicas. Again, it is very difficult to pre- 

 pare surface replicas of certain coatings such 

 as magnetic tape and photosensitive papers. 

 The inertness and insolubility of the binder 

 impairs isolation of the replica by dissolu- 

 tion. H3^drophyllic stripping layers have not 

 proved to be successful. In many cases, 

 despite the inertness of the binder, the effects 

 of heat and pressure, solvents, or the radia- 

 tion and vacuum attendant to evaporation 

 techniques make the isolation of good ciuality 

 replicas difficult, or they may vitiate the 

 results. Nondestructive studies are often 

 obviated by the inadequacy of the stripping 

 layers. 



A few remarks are in ordoi- in regard to 

 the responsibility of industrial management 

 to the microscopist. First, where feasible the 



307 



