Effect of the Type of Support on the Photoelectric Work Function of Silver Films

Silver was doubly and fractionally distilled with the middle fraction deposited on previously outgassed bulk silver, on smooth fused quartz, and on outgassed molybdenum sheet in a sealed-off, gettered tube. Photoelectric measurements were made using the Fowler method. Deposit of a film of silver on bulk silver caused $\varphi$ to decrease by varying amounts as great as 0.25 ev to 4.50±0.02 ev. Subsequent heating estimated at below 100°C caused $\phi$ to increase to the original value. $\varphi$ for a silver film on smooth fused quartz and on outgassed molybdenum sheet is 4.41 ev. The results are unaffected by residual gas pressure in the tube. The low values of $\varphi$ for the film appear to be due to a surface structure composed of microcrystals which are much smaller than those of the bulk silver. The variations in the observed values of $\varphi$ for films on different supports is attributed to a dependence of the sizes of the microcrystals on the structure of the support. Information is given regarding the effect of the equilibrium conditions between volume and surface gas on the value of $\varphi$ during the outgassing period of bulk silver.