Photoemission and STM, STS study of $Cs/p-GaAs(110)$

Various stage of adsorbed Cs, i.e., one-dimensional (1D) lines, polygons and coherently $c(4×4)$-ordered polygons, on cleaved $p-GaAs(110)$ are studied by scanning tunneling microscopy (STM) and scanning tunneling spectroscopies (STS) with an interest in relation to the photo-electron emission. It is understood that only the coherently $c(4×4)$-ordered Cs polygon surface (Cs coverage of 0.6 ML and 0.7 ML) can emit photo-electrons due to a sufficient reduction of the local work function down to 1.3 eV to get a negative electron affinity state.