Polycrystalline diamond films were deposited by the microwave-plasma chemical-vapor-deposition (CVD) on Si substrates using a mixture of methane and hydrogen for the source gas. In the morphology study of diamond films using a scanning electron microscope (SEM), it was found that upon increasing the methane concentration (hereafter denoted by c in units of vol%), the surface texture changed discontinuously from (111) to (100) at around c=0.4%, and gradually from (100) to microcrys-talline above c=1.2%. The diamond-Si interfaces and the defect struc-tures in the films were investigated by transmission electron micro-scopy (TEM). The film growth process was investigated by SEM, and it was found that the appearance of small grains and the formation of well-defined diamond faces took place repeatedly with time during the CVD synthesis. The film morphology of boron-doped diamond films on Si substrates and on non-doped diamond films were also presented.