Resistance of a Sputtered Film after Deposition. 149 



The main point to notice in these results is the rapid 

 initial rise in resistance followed by a more gradual rise 

 which may he prolonged for a long period of time. Again, 

 no relationship between the change in resistance and the 

 thickness was obtained, the effect of the gas depending on 

 the nature of the film. 



In film F, the pump was put on 2 minutes after the air 

 had been admitted. The result was to produce a rapid fall 

 in resistance changing to a more gradual fall. It is seen 

 that the effect of the air is not immediately counteracted by 

 putting on the pump, and that, as in the experiments of 

 Kohlschiitter and Noll with nitrogen, the ageing continues in 

 a film placed in vacuo after a treatment with air. 



It would have been interesting to have obtained sorption 

 curves by measuring the change in pressure with time in 

 order to compare them with the resistance-time curves ; but 

 owing to the smallness of the amount of platinum in a film, it 

 was quite impossible to do this. Indirect evidence that there 

 is an intimate connexion between the two phenomena may, 

 however, be given. Of the various experiments on the 

 sorption of gases by solids, those of Bergter * on charcoal 

 are of particular interest, as they were carried out under 

 conditions of temperature and pressure comparable with the 

 above. The curves that he obtained by plotting volumes of 

 gas taken up with time are very similar to the resistance-time 

 curves shown here. 



This connexion between sorption and change of resistance 

 if real is interesting. A mere cessation of ageing could be 

 attributed to a decrease in surface-tension accompanying the 

 adsorption of gas. But the fact that a rise in resistance 

 occurs, and moreover continues for a long time, suggests that 

 the result of admitting gas into the discharge-vessel is not 

 solely a surface-tension effect. It is more possible that some 

 change in orientation of the individual units taking part in 

 conduction is brought about by the air adsorbed on the film 

 and absorbed in the molecular clusters themselves. In the 

 present state of the theory of conduction in metals, further 

 discussion of this point would be unprofitable. 



Admission of Hydrogen. 



The effect of adding hydrogen to platinum and palladium 

 films is not in the general case a simple one. There may be 

 (1) the normal rise in resistance following the admission 

 of gas; (2) a fall in resistance due to the evolution of heat 



* Ann. d. Phys.xxxxil p. 472 (1912). , 



