A THERMAL-DESORPTION ANALYSIS FOR THE ADSORPTION OF CO2 ON GAAS PHOTOCATHODES

Both cesiated and Cs/O activated GaAs(100) photocathodes exposed to CO2 have been studied with temperature programmed desorption (TPD) spectroscopy to investigate the CO2 effect on negative electron affinity (NEA) GaAs. Most of CO2 desorbed with Cs and O2 at approximately 200-250-degrees-C from the cesiated GaAs exposed to CO2. Another peak of CO2 desorption, with Cs, appeared at approximately 420-degrees-C for the Cs/O activated GaAs after exposure to CO2. The appearance of the higher peak and simultaneous desorption suggest a dissociative adsorption of CO2 on the Cs/O surface layer. The results are discussed in terms of CO2 influence on negative electron affinity (NEA) GaAs.