Properties of Thin Metal Films. 



677 



Thi< view in regard to the transition-layers existing at 

 the surface of a metal is included in the corpuscular theory 

 of electrical conduction in metal films. From the equation 



1 lne 2 l t /. X , 3\ 



the specific resistance for a film of thickness X is ^ of the 

 normal specific resistance. This would give a value for X of 

 about 6 X 10 -6 cm. from Vincent's results. The value calcu- 

 lated from the change of resistance of pure silver in a transverse 

 magnetic field is 1"3 x 10~ 6 cm*, and from the silver film 

 itself it is l'lx 10 -6 cm. The numbers are all of the same 

 order. The specific resistance for a given thickness is plotted 

 against the thickness in curve C, fig. 15, where the upper 

 limit 6 x 10 -6 cm. is taken for X and the normal specific 

 resistance as 2'65 x 10 ~ 6 ohms per cm. cube, which would be 

 the value given by Vincent's results from the above formula. 

 The experimental values obtained by Vincent are given in 

 curve D. 



Fig. 15. 







1 



1 



1 





i 



5, 



r 











iV \ 











£ v 













;>.= e*ic~ 6 cM 



It will be seen from the above curves that the experimental 

 values also vary more rapidly than the theoretical. 



At the surface of the metal, in order that equilibrium may- 

 be maintained between the air and the metal, there exists a 

 layer of negative corpuscles!. It is most probable that 

 owing to this layer of negative corpuscles the number of 

 corpuscles per unit volume is not constant throughout the 

 surface-layer \, but that it decreases towards the outside. 

 This would make the resistance 1 vary still more rapidly than 

 the above theoretical equation would indicate. 



Vincent and Moreau (locc. citt.) concluded from their obser- 

 vations that the transition-layer was the same thickness for all 



* Phil. Mag. June 1902, p. Goo. 



f J. J. Thomson, Rapports presentes an Congres International de 

 Physique, vol iii. p. 138, Paris, 1900. 



