THERMIONIC ELECTRON EMISSION 



455 



close together at F = but would have approached upper Schottky 

 lines whose position varied greatly. As it is, all curves approach the 

 same upper Schottky line but "fan out" toward lower values of V F. 

 Note that the curves do not cross over as they do in Fig. 16; note also 

 that as M increases the curves become steeper and the bend toward the 

 Schottky line occurs at larger values of V F. 



At first sight it might appear that by plotting T log ijis it would be 

 possible to eliminate 7" as a parameter; while this is true for any one 

 subchecker for which /3 is a constant, it is not true for the average 

 curves. This is illustrated in Fig. 18 which shows {kTje) log ijis vs. 



0.04 



0- 



-0.02 



en -0.04 



-0.06 



-0.08 



•0.12 



20 40 60 80 too 120 140 160 180 200 



Yf~ (V volts per cm ) 



Fig. 18 — Variation of average emission current with applied field for hill and valley 

 checkerboard; T variable, h and /u fixed. 



V F for constant h and m and varying T. Note that the departure from 

 the Schottky law is more pronounced for the low temperatures. 



Comparison Between Theory and Experiment 

 It has been found possible to choose values of h and ju such that the 

 calculated average curve fits a given experimental curve over its entire 

 range. The agreement is not perfect; but a perfect fit is not to be 



