14 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1953 



0.8 



0.7 



[3 0.6 



O 



> 



^0.5 



q: 

 U 



0.3 



Fig. 9 — Contact potential for zero light effect, (c.p.)o , versus cycle number, 

 two runs for each sample. 



as water vapor. To prove that this was not caused by traces of water in 

 the alcohol or acid the N2 w^as bubbled through water solutions of 

 H2SO4. These results indicated that one needs appreciable amounts of 

 water vapor to produce the effect, much more than could be present in 

 the alcohol or acid. Other vapors, such as carbon tetrachloride, methyl- 

 chloride, nitrobenzene and ether, were found to have no effect on either 

 the contact potential or (Ac.p.)l . Acetone has a small effect in the same 

 direction as water. This is to be expected because this compound exists 

 in part in a tautomeric form having an OH group. Vapor from 30 per 

 cent H2O2, 70 per cent H2O acted at first like a peroxide vapor and 

 with a longer time of exposure behaved like water vapor. Small amounts 

 of CI2 gas in N2 produced the same change as the spark discharge in O2 

 and after 14 minutes of flushing the bell jar with N2 produced an ad- 

 ditional effect when water vapor was introduced. On n-type samples 

 before the usual increase in c.p. and decrease in (Ac.p.)l there was a 

 large increase in (Ac.p.)^, . This was attributed to the reaction between 

 the water vapor and the CI left on the Ge surface, producing oxygen. 

 The nature of the change was a rapid shift in (Ac.p.)o and thus a mo- 

 mentary increase in (Ac.p.)l . This effect is only large in the first cycle. 

 It indicates that the shifts in (Ac.p.)o plotted in Fig. 9 are probably due 

 to an oxidation of the Ge surface as the cycling progresses. In all these 

 experiments the relation between the c.p. and (Ac.p.)^ was essentially 

 the same as that obtained in the standard cycle. 



One can detect the presence of thin surface films by electron diffrac- 

 tion techniques. R. D. Heidenreich took electron diffraction pictures of 

 a germanium surface immediately after the polishing etch and water 



