STM, STS, and local work function study of Cs/p-GaAs(1 1 0)

Various surface configurations of Cs/p-GaAs(1 1 0) have been studied by scanning tunneling microscopy and scanning tunneling spectroscopy with an interest in relation to the photoelectron emission. The local work function is found to be 4.8, 3.3, and 3.3 eV from clean p-GaAs(1 1 0), Cs one-dimensional (1D) lines (Cs coverage of 0.23 ML), and partially-ordered Cs polygons (Cs coverage of 0.5 ML), respectively. It is understood that only a coherently c(4×4)-ordered Cs-polygon surface (Cs coverage of 0.6 and 0.7 ML) can emit photoelectrons due to a sufficient reduction of the local work function down to 1.3 eV to get the negative electron affinity state. The local work function image shows that the boundary of Cs atoms has a lower local work function than at the top of Cs atoms.