152 Change in Resistance of Sputtered Film after Deposition. 



and in chemical action may vary widely with different films, 

 the results given above are not necessarily conflicting. 



In no case examined, whether the film was deposited in 

 air or hydrogen, has air produced a fall in resistance, though 

 in many instances the film had been previously treated with 

 hydrogen which had probably not been completely removed 

 by the pump. It is clear, therefore, that in such cases, 

 namely when air is in excess, the effect — if it be present at 

 all — of the combination of hydrogen and oxygen in the film 

 under the catalytic action of the platinum must be negligibly 

 small. 



Kohlschiitter and Noll state that the catalytic power of a 

 platinum deposit varies with the nature of the residual gas 

 in the discharge-vessel during deposition. It is great if the 

 gas be argon, when the deposit consists of very fine particles, 

 and less if the gas be hydrogen, when a coarser film is 

 obtained. 



It is noteworthy that the electrical properties of a film 

 deposited by cathodic disintegration are not the same as 

 those of a powder. Thus Goddard * has shown that the 

 resistance of the powders he used decree sd when gas was 

 admitted, and increased when the gas was pumped out. 

 Some rough experiments of the author on palladium-black 

 gave qualitatively similar results. The above results show 

 that with sputtered films the converse is true. 



McClelland and Dowlingf have observed some curious 

 effects by applying a transverse electrical field to a thin 

 layer of conducting powder. On removal of the field it was 

 found that the powder had in general a greatly increased 

 conductivity. There is no evidence that this occurs in the 

 case of sputtered films. Thus in a few cases the author tried 

 the effect of placing a plate parallel to and at a distance of 

 3 or 4 mm. from the film and charging it to 1600 volts at 

 atmospheric pressure. On removal of the field no change in 

 conductivity was observed to have taken place. 



Summary. 



1. A study of the physical changes occurring in a metallic 

 film after deposition by cathodic sputtering has been carried 

 out by measurements of the changes with time in the electrical 

 resistance of the film when retained in vacuo. 



2. The direct effect of admitting gas into the vessel con- 

 taining the film under observation has been shown to be a 



* Phys. Review, xxviii. p, 405 (1909). 



f Proc. Royal Irish Acad. vol. xxxii. A. No. 5 (1915). 



