SPECIAL MKIHODS 



Fig. 8. Cu-Phthalocyanine taken at 

 spacing 12.5°A. 



-50°C, 



(7). The performance of this device has 

 proved very satisfactory. 



Contamination of Specimen. One of 



the principal difficulties of the specimen- 

 cooUng device is the contamination of spec- 

 imen due to materials condensing from resid- 

 ual \'apors. In the conventional vacuum of 

 5 X 10-* to 1 X 10-^ mm Hg, condensed 

 materials increased remarkably below 

 -80°C to - 100°C and covered the specimen 

 surface within a few minutes. Fig. 9 shows 

 an electron micrograph and diffraction pat- 

 tern of ice condensed on collodion film at 

 — 80°C from residual vapor pressure of 

 1 X 10-* mm Hg. This proves that the 

 larger part of the residual vapors is usually 

 water vapor. 



Contamination of another nature has been 

 observed in electron microscopic experi- 



device is inserted into the round port located 

 at the head of the specimen chamber. When 

 the specimen is to be exchanged, the reser- 

 voir is elevated in the same way. Then the 

 specimen cartridge G is moved in and out 

 independently through another chamber for 

 pre-evacuation. The specimen cartridge can 

 be inserted deep in the field of the objective 

 lens R. In order to cool the specimen, the 

 refrigerant reservoir is lowered to contact 

 the specimen holder F. At the lowest position 

 the reservoir is pushed down to the specimen 

 holder by the release of spring S and the 

 elongation of sylphon bellows C and D. 



The specimen-shifting mechanism is just 

 the same as that for general use of electron 

 microscope and can control the specimen 

 position as fine as 0.1 /x. When the reservoir 

 was filled with liquid oxygen, the tempera- 

 ture of the specimen holder reached to 

 — 160°C. This temperature could be ob- 

 tained within 15-20 min, using about 150 

 cc of liquid oxygen. 



The resolution obtained by using this de- 

 vice is measured by copper phthalocyanine. 

 Fig. 8 shows the lattice image of spacing 

 12.5 A of this specimen taken at — 50°C. 



Fig. 9. Electron micrograph (above) and dif- 

 fraction pattern (below) of ice condensed on col- 

 lodion film. 



263 



