The interaction of cesium-oxide overlayers with Ge(1 1 1) as a function of annealing temperature

Abstract The overlayers of Cs 2 O, Cs 2 O 2 and CsO 2 /Cs 2 O 2 were prepared by simultaneous oxygen-cesium adsorption on Ge(1 1 1) at room temperature. Electron spectroscopy has been used to investigate the surfaces of Cs 2 O/Ge, Cs 2 O 2 /Ge and CsO 2 /Cs 2 O 2 /Ge as a function of annealing temperature. The interaction of Cs 2 O with Ge(1 1 1) is weak and the surface has a work-function value of 0.8–0.9 eV before the decomposition of Cs 2 O at 660 K. The work function of the Cs 2 O 2 /Ge surface is 1.3 eV and decreases to a minimum value of 0.95 eV after annealing at 440 K. Both CsO and GeO bonds are formed before the Cs 2 O 2 species decomposes at 550 K. The results show that the CsO 2 /Cs 2 O 2 /Ge system is reactive as some Ge atoms are bonded to oxygen after coadsorption. The work function of the surface remains 2.15 eV before the decomposition of CsO 2 . For all surfaces, when the cesium oxides decompose, both CsO and GeO bonds are dominant with a work function of about 1.2 eV. Further annealing gives rise to the increases of the work function.