930 the bell system technical journal, october 1951 



Temperature Effect on Clusters 



The photos in Figs. 9 and 10 show that, for all values of from 1.0 to .10, 

 the emission comes largely from clusters. It is interesting to observe, but 

 difficult to portray in photographs, what happens if the temperature is 

 raised above room T but kept below that at which it had previously been 

 heated to reduce 6. As a specific instance we choose a case in which the 

 treatment T was 1380°K for five minutes — photo b in Fig. 10 — for which 

 6 = .28. With an applied voltage at T = 300°K, the whole pattern and the 

 clusters in particular are very steady. If T is now raised to about 700°K, 

 the clusters bordering on the 211 planes and those in the 111 zone appear 

 to be agitated: the brightness of any one cluster fluctuates up and down and 

 the center of the cluster moves over about half a cluster diameter. Clusters 

 in other regions are perfectly steady. As T is raised the 211 clusters agitate 

 more violently and the clusters in nearby regions begin to agitate. At still 

 higher T, the clusters in the 111 region begin to agitate but those surround- 



Table I 



Dependence of <p (Average Work Function) and 6 (Layers of Ba) on 



Temperature and Time 



Tin°K 1045 1130 1210 1275 1330 1380 1430 1515 1670 2200 



t in min 5 5 5 6 5 5 5 5 3 1 



v> volts 1.98 2.00 2.20 2.47 2.81 3.30 3.70 4.10 4.53 4.40 



d ~1.0 -^1.0 .80 .62 .46 .28 .18 .08^.00 .Oq 



ing the 100 plane are still steady. For T near 800°K all clusters show some 

 agitation. At 1045°K, the clusters near the 110, 211, and 111 planes agitate 

 so violently that individual clusters can no longer be distinguished but 

 merge into one another producing bright bands which presumably reveal 

 contours on the tungsten surface. However, the clusters in the regions sur- 

 rounding the 100 plane agitate so slowly that in a photo of J sec exposure 

 they appear to be stationary. Photo a. Fig. 11 shows the result. Photo b 

 shows the pattern immediately afterward at T = 300°K. These observations 

 can be repeated as often as one pleases. 



Effect of Field on the Redistribution of Ba on W 



Photos c to f of Fig. 11 show that fields of 30 to 40 million volts/cm can 

 redistribute some Ba from the 110, 211 and HI regions to the regions sur- 

 rounding 100. Photo c shows the pattern after glowing at 1430°K for five 

 minutes with V = 0. Photo d shows the pattern at T = 800°K after 3 min. 

 with T = 800°K and V = 7380 volts. When T was reduced to 300°K, the 

 pattern did not change appreciably. However, when T was kept at 800°K 

 for three minutes with F = 0, the pattern changed drastically as shown in 

 photo e. Photo f shows that the redistribution is not the result of glowing 



