TRANSMISSION ELECTRON MICROSCOPY OF METALS 



illation shows that in large areas of the sec- Textures by Means of Thin Sections" (1). 

 tions both components of the matrix remain In this paper Hes the origin of practically- 

 intact. This suggests that fluorine protects all the future developments in the field of 

 teeth from decay by drastically reducing the transmission electron microscopy — the theo- 

 solubility of the organic matrix. retical explanation of the observed effects, 



the preparation technique and the applica- 



K. Little ^ions to metal physics, Hke deformation, re- 

 crystallization and precipitation. In Europe 



TRANSMISSION ELECTRON MICROSCOPY ^Jj^ ^^'^^^ was continued by Castamg (2) on 



OF METALS- DISLOCATIONS AND ^^l precipitation of CuAl. m Al + 4 % Cu. 



p___.p._ _._^ Other transmission microscopy was done in 



Japan by Suito and Uyeda (3), Hashimoto 

 All high resolution electron microscopy is (4), Takahashi et al. (5). 

 made by transmission, but the phrase "trans- Until 1956 essentially the effects due to 

 mission electron microscopy" is used here in perfect crystals and two-phase systems 

 a restricted sense, whereby the electrons (precipitates) were studied, for example, ex- 

 having transmitted a specimen form an im- tinction contours (dark bands arising from 

 age which furnishes information about the Bragg diffraction). A new possibility ap- 

 interior of the material and not merely about peared when it was shown by Hirsch, Home 

 the surface, as in the repHca method. Elec- and Whelan (6) for aluminum, and independ- 

 trons passing through matter can be ab- entty by Bollmann (7) for stainless steel, 

 sorbed or scattered inelastically or elasti- that dislocations could be obsen^ed directly 

 cally. In the latter case the scattering may inside the metal by transmission electron 

 be incoherent or coherent; coherent scatter- microscopy. The theory of dislocations had 

 ing is known as "diffraction". Absorption been extensively developed before. (The 

 and incoherent scattering give "radio- books of Cottrell (8) and Read (9) appeared 

 grams" indicating variations in thickness in 1953). Transmission microscopy furnished 

 and density, but the interesting information direct verification of these theories. In par- 

 justifying a separate article on "transmis- ticular the cinefilms of the group Hirsch, 

 sion electron microscopy" is obtained from Whelan et al. showing the movement of dis- 

 diffraction effects. This means that the speci- locations in aluminum (6) and in stainless 

 mens to be studied have to be crystalline, steel (10) helped to make the dislocation 

 For practical reasons most of the specimens theory appreciated by metallurgists. So 

 studied mitil now have been metallic but transmission electron microscopy today is 

 minerals are in principle not excluded. A an important tool for research in metal phys- 

 further advantage of transmission electron ics. 



microscopy is that in addition to micros- It is of interest that the first pictures of 

 copy, selected area diffraction can be ap- dislocations by transmission microscopy 

 pUed, which furnishes information about the were pubhshed by Heidenreich in his basic 

 crystal structure and the orientation of the article (1) and that he even mentioned that: 

 specimen. "... a studj'' of the fine details of the con- 

 Certain transmission effects have been ob- tours in sections plastically deformed under 

 served since the beginning of electron mi- controlled conditions may yield important 

 croscopy, but transmission electron micros- information concerning dislocations". But 

 copy in its proper sense started in 1949 with the theory of dislocations at that time was 

 Heidenreich's paper "Electron Microscope not sufficiently developed to give a full inter- 

 and Diffraction Study of Metal Crystal pretation of the pictures. 



291 



