Cs is a promoter of Cu-based catalysts for the synthesis of alcohols from CO hydrogenation. Scanning tunneling microscopy and ambient-pressure x-ray photoelectron spectroscopy were used to study the morphology and chemical properties of surfaces generated by the deposition of cesium on CuO/Cu(111) and Cu(111) substrates. CsO nanostructures were formed after Cs metal was deposited on CuO/Cu(111) at 300 K. The formed CsO protrude over the surface of copper oxide by 2-4 Å, with the dimension at the base of the nanostructures being in the range of 1-3 nm. Heating to elevated temperature induced significant changes in the size and dispersion of the CsO nanostructures, and there was a clear reconstruction of the copper oxide substrate, which then exhibited long range order with a hexagonally packed structure. The as-deposited and annealed surfaces of CsO/CuO/Cu(111) were more reactive toward CO than plain CuO/Cu(111) or clean Cu(111). However, none of them were stable in the presence of H, which fully reduced the copper oxide at 400-450 K. In CsO/Cu(111), the CsO nanoclusters were dispersed all over the metallic copper in no particular order. The CsO species had an average width of 2 nm and ∼1 Å height. The CsO/Cu(111) systems exhibited the highest activity for the binding and dissociation of CO, suggesting that the CsO-copper interface plays a key role in alcohol synthesis.