11. Some salient observations in processing CS 3Sb photocathodes on thin-film coated glass substrates

Abstract

The semitransparent alkali antimonide photocathodes such as CS 3 Sb and Na 2 KSb(Cs) are processed in uhv region on glass substrates, wherein they are not prone to substrate contaminants. In interference photpemission after Kossel (1969) , the photocathodes are processed on thin dielectric films of high refractive index like TiO 2 , SiO etc. While processing the transmissive interference photocathode of CS 3 Sb thin films on SiO coated substrates by the normal method (activation of evaporated Sb film by Cs vapours at 150°C), the cathode luminous sensitivity turns out to be very low, about 5 μA/1m. In the case of cathodes on TiO 2 substrates, luminous sensitivity of 25 μA/1m is registered. Several investigations have been conducted to analyse the cause of the deterioration phenomena mainly due to the chemical compatibility of the photocathode with the substrate and the surface effects. This has been taken care of by changing the normal processing technique to a coevaporation method, by which consistent photoelectric yields of 45 μA/1m are obtained for photocathodes on SiO as well as TiO 2 thin-film coated glass substrates. The optical and photoelectrical properties of interference photocathodes are presented. A photoelectric gain of 1.45 for TiO 2 -CS 3 Sb and 1.25 for SiO-CS 3 Sb combinations in the tuned region are respectively achieved. This development of interference photocathode technology offers an additional advantage of spectral maximum selectivity.