Resistance of a Sputtered Film after Deposition, 147 



Thus a number of films have been observed in which the 

 resistance during deposition has fallen at a very rapid rate,, 

 far greater than in air, although it is known that hydrogen 

 is not a gas specially favourable to cathodic sputtering. 

 Moreover, the resulting film had a transparency which sug- 

 gested a much higher resistance. It is probable that this 

 rapid change is set in action by the sorption * of hydrogen 

 during deposition ; and this view receives support from 

 results given below on the effect of admitting hydrogen to 

 the discharge-vessel ; it will be discussed again in that 

 connexion. 



Effect of Addition oj Gas. 



It is known that films of sputtered metal take up gas during 

 deposition. Owing to the relatively large surface, some 

 sorption of gas in a film will occur when gas is admitted into 

 the discharge-vessel after deposition ; an investigation of its 

 effect on the electrical resistance was made. 



In the first experiments, dry air was admitted to the vessel 

 containing a film which had been ageing for some time. 

 The pressure reached a constant value (atmospheric) within 

 a few seconds after the stopcock, through which the air 

 entered, had been opened. Typical results for a number of 

 films are shown as full curves in fig. 2. The ordinates are 

 changes in resistance expressed as a percentage of the 

 resistance of the film at the moment that the gas is admitted. 

 The abscissae are values of time in minutes. The initial 

 parts of the curves give the later stages of ageing, the air 

 being admitted at the point (a) in every case. The films to 

 which the full curves shown here refer are those for which 

 the complete ageing curves are given in fig. 1 ; they are 

 designated by the same symbols. 



Kohlschiitter and Noll (loc. cit.) record some results of 

 admitting nitrogen to silver films, deposited in nitrogen, 

 immediately after their deposition. In one case only do they 

 appear to have observed a rise in resistance, but state that in 

 general the ageing is apparently stopped, though a mea- 

 surement of the resistance of one film .1 5 hours after the 

 admission of the gas shows that in reality the process is 

 delayed and not brought to a complete standstill. On the 

 removal of the nitrogen, the ageing proceeded. 



In the author's experiments a rise in resistance with time 



* The term sorption has been suggested by McBain to include under 

 one title the phenomena of adsorption (surface condensation) and ab- 

 sorption (solid solution). 



L2 



