EVOLUTION OF SURFACE-TOPOGRAPHY IN PULSED-LASER-DEPOSITED THIN-FILMS OF MOS2

Films of MoS2 were grown at various thicknesses onto silicon substrate s at room temperature using pulsed laser deposition. Planar and cleave d cross-sectional samples examined in a scanning electron microscope s howed that very thick films (thicker than about 450 nm) transitioned f rom being fully dense to having ''tensive porosity. The porosity is di rectly correlated with the accumulated incorporation of spherical part icles within the film. Transmission electron microscopy (TEM) results from samples of differential thicknesses, acquired from early and late r stages of deposition, showed that the volume fraction of the particl es increased with the thickness. Decreasing the energy density of the laser beam by underfocusing relative to the target was shown to decrea se dramatically the number of particles. Simulation of the deposition process by adding digitized, binary TEM images of the differential thi ckness samples, to an equivalent thickness of 450 nm, indicated that t he porosity begins at a total particle projected area fraction of abou t 35%.