Photoinduced 2D plasmon modes in Cs nanoclusters on the GaAs(100) Ga-rich surface

The method of photoyield spectroscopy with s- and p-polarized light excitation is developed for studies of 2D collective modes. The formation of nanoclusters has been studied for the Cs/GaAs(100) Ga-rich interface in a wide coverage range up to similar to 2 ML. Two adsorption phases with the strong Cs-Ga bonding and weak Cs-Cs bonding are found by using both stepwise and dynamic Cs deposition regimes. In the first adsorption phase, local interaction of Cs adatoms with Ga dimers occurs. The transition from the first to the second phase is found to take place at similar to 0.7 ML that corresponds to the saturation of all the Ga-dangling bonds. In the second phase, collective modes in quasi-2D Cs clusters of several sizes depending on the coverage and surface plasmon are revealed.