METALS BY TRANSMISSION 



technique for the electron microscope using 

 the simultaneous evaporation of platinum 

 and carbon," Brit. J. Appl. Phys., 10, 198 

 (1959). 



Dewey, O. R., Gregory, P., and Pfeiffer, R,. 

 K., "Factors affecting the susceptibility of 

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DoRSCHNER, K. P. AND BucHHOLTz, K. P., "Ef- 

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Fogg, G. E., "Quantitative studies on the wetting 

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HOLDGATE, M. W., MeNTER, J. W., AND SeAL, M., 



"A study of an insect's surface by reflection 

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Juniper, B. E. and Bradley, D. E., "The carbon 

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B. E. Juniper 



METALS BY TRANSMISSION* 



Although replica techniques have been 

 used with great success for the examination 

 of metals, these methods have their limita- 

 tions. With the development, therefore, of 

 instruments having high resolving power and 

 fitted with a double condenser lens that en- 

 ables high beam intensities to be obtained on 

 the specimen, a new approach was made to 

 the problem of preparing metals in a form 

 suitable for examination by transmission in 

 the electron microscope. During the past few 

 years a number of suitable techniques for 

 preparing metal foils with a thickness of 

 100-2000 A have been devised. These tech- 



* Abridged from paper in Jour. Inst. Metals, 87, 

 385 (1959), by permission 



niques, which will be reviewed in this paper, 

 can be classified into three principal groups: 



(a) Deposition. 



(6) Deformation. 



(c) Dissolution. 



The deposition methods involve the pro- 

 duction of metal foils by condensation of the 

 metal vapor in vacuo, the precipitation or 

 elect rodeposit ion of thin crystals from aque- 

 ous solution, and the casting of foils from 

 the liquid state. These techniques are of Hm- 

 ited use only, since the results obtained from 

 foils prepared in this way are seldom typical 

 of bulk material. 



The deformation methods used to pre- 

 pare thin foils comprise beating and machin- 

 ing in diamond-bladed microtomes. The 

 former is very limited in its application, but 

 the latter shows interesting possibihties, par- 

 ticularly for the examination of multiphase 

 alloys. 



The dissolution techniques are perhaps the 

 most generally applicable to the preparation 

 of foils of pure metals and alloys. The meth- 

 ods adopted have involved simple chemical 

 etching, ionic bombardment, and electro- 

 polishing. The latter is the most successful 

 and has been widely used, since it is thought 

 that the structures obtained from foils pre- 

 pared in this way are typical of those to be 

 expected in bulk material. 



Deposition Methods 



Vacuum Evaporation. It has been 

 known for some time that thin films of 

 metal, transparent to electrons, can be pro- 

 duced by evaporating a metal in vacuo and 

 condensing the vapor onto a substrate. 

 The evaporated film may then be stripped 

 from the substrate, or the substrate dis- 

 solved away. If the vapor is deposited onto 

 a crystalline substrate at high temperatures, 

 the metal film exhibits "epitaxy," an effect 

 discussed by Pashley (1). In this way it is 

 possible to grow single-crystal fihns of cer- 

 tain metals. 



The structure of evaporated fihns is not 

 on the whole typical of bulk material, and 



181 



