  Germanium is emerging as the substrate of choice for the growth of graphene
in CMOS-compatible processes. For future application in next generation devices
the accurate control over the properties of high-quality graphene synthesized
on Ge surfaces, such as number of layers and domain size, is of paramount
importance. Here we investigate the role of the process gas flows on the CVD
growth of graphene on Ge(100). The quality and morphology of the deposited
material is assessed by using microRaman spectroscopy, x-ray photoemission
spectroscopy, scanning electron and atomic force microscopies. We find that by
simply varying the carbon precursor flow different growth regimes - yielding to
graphene nanoribbons, graphene monolayer and graphene multilayer - are
established. We identify the growth conditions yielding to a layer-by-layer
growth regime and report on the achievement of homogeneous monolayer graphene
with an average intensity ratio of 2D and G bands in the Raman map larger than
3.
