SPECIAL METHODS 



reservoir (4) is introduced through the leak 

 valve (5) into the specimen chamber and 

 evacuated through outlet (6) on the occa- 

 sion of reaction with a specimen. The gas 

 pressure in the specimen chamber is able to 

 be controlled from about 10~* to 1 mm Hg 

 and is measured by a manometer and 

 McLeod gauge. A specimen can be heated 

 up to 1,000°C from the room temperature by 

 the heating device, which is the same as the 

 old type; (9) is the heating coil and (8) is 

 the thermocouple for measuring the speci- 

 men temperature. 



When the electron beam passes through 

 the atmosphere of gas, it is scattered by the 

 gas molecules. Here it is significant to intro- 

 duce the concept of mass thickness into the 

 discussion on the interaction of electrons 

 with the gas molecules. When the present 

 device is filled with 1 mm Hg of air, the mass 

 thickness is 3 X 10~^ g/cm^ and when with 

 1 mm Hg of hydrogen, it is 2 X 10"^ g/cm^. 

 (In the present device the path length that 

 electron passes through in the gas atmosphere 

 is 2 cm.) Since the mass thickness of copper 

 film with thickness of 300 A is 2.7 X 10-^ 

 g/cm^, that of gas molecules in the present 

 device is as small as one tenth that of the 

 copper film of 300 A. Accordingly, the gas 

 pressure can theoretically be raised. When 

 the gas pressure in the device is raised more 

 than 1 mm Hg, however, high tension dis- 

 charge occurs at the electron gun. To prevent 

 leakage from the specimen chamber, the 

 diaphragm must be doubled and evacuated 

 separately. 



Taking the above into consideration, a 

 new type of gas reaction device (16) has 

 been constructed (Fig. 20). Since its perform- 

 ance has been tested, only its construction is 

 mentioned here: (1) is inlet of gas, (2) gas 

 reaction chamber and (3) a specimen. The 

 gas diffused through diaphragm (4) is evac- 

 uated through the evacuation chamber (5) 

 and (6), and gas diffused through diaphragm 

 (7) is evacuated by the evacuation system 

 of the electron microscope. The specimen 



shifting mechanism of this device is the 

 same as that for general use of electron mi- 

 croscope. 



Fig. 20. Construction of new type gas reaction 

 device. 



(a) 



(b) 



(0 



Fig. 21. Crystal growth of copper sulfide in an 

 atmosphere of IQ-^ mm Hg. (top) at 300°C; (cen- 

 ter) at 350°C. 5 min. after above; (bottom) at 

 400°C, 15 min. after center. 



269 



