Abstracts of Technical Articles by Bell System Authors 



Television Network Facilities} L. G. Abraham and H. I. Romnes. Tele- 

 vision networks, like sound broadcasting networks, must be available to 

 make distribution of high quahty programs economical. For television cir- 

 cuits interconnecting studios in different cities, coaxial cable and radio relay 

 are the most suitable methods. For short distance transmission balanced 

 wire pairs also may be used. Local conditions will control the type circuit 

 selected. 



Protective Coatings on Bell System Cables} V. J. Albano and Robert 

 Pope. The practice of placing some Bell System cables directly in the 

 ground without the use of conduit was introduced in about 1929. Since 

 bare cable thus installed would be subject to the corrosive action of soils, 

 or damage from lightning or gophers, suitable protective coatings to guard 

 against these hazards had to be developed. Seven types of such coverings 

 are described, and their particular field of application is indicated. 



Surface States and Rectification at a Metal Semi-Conductor Contact.^ John 

 Bardeen. Localized states (Tamm levels), having energies distributed in 

 the "forbidden" range between the filled band and the conduction band, may 

 exist at the surface of a semi-conductor. A condition of no net charge on 

 the surface atoms may correspond to a partial filling of these states. If the 

 density of surface levels is sufficiently high, there will be an appreciable 

 double layer at the free surface of a semi-conductor formed from a net 

 charge from electrons in surface states and a space charge of opposite sign, 

 similar to that at a rectifying junction, extending into the semi-conductor. 

 This double layer tends to make the work function independent of the height 

 of the Fermi level in the interior (which in turn depends on impurity con- 

 tent). If contact is made with a metal, the difference in work function be- 

 tween metal and semi-conductor is compensated by surface states charge, 

 rather than by a space charge as is ordinarily assumed, so that the space 

 charge layer is independent of the metal. Rectification characteristics are 

 then independent of the metal. These ideas are used to explain results of 

 Meyerhof and others on the relation between contact potential differences 

 and rectification. 



' Electrical Engineering, May 1947. 

 2 Corrosion, May 1947. 

 ^Phys. i?ei»., May 15, 1947. 



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