CVD diamond layers grown by the microwave-assisted plasma-CVD technique were investigated by TEM. The microstructures of samples from different sites in the growth area, which showed different surface morphologies owing to the limited size of the microwave plasma ball, were characterized: large diamond grains which enclose agglomerations of first-order twin lamellae form the well faceted layers which are deposited in the center of the growth area at high plasma intensities. Near to the edges of the growth area, where the plasma intensity is low, branching and frequent orientation changes of the twin agglomerations result in the growth of ballas-type layers consisting of sub-micron diamond grains. Almost perfect 〈100〉-oriented grains, together with microcrystalline diamond, form the layers in between these sites. The relation between the surface morphology and the formation of these microstructures is discussed.
