An Atomic Force Microscope is used to alter one part of a single layer graphene sample locally. Transport experiments at low temperatures are then used to characterize the different parts independently with field effect and Hall measurements. It is shown, that the nanomachining leads to an effective doping in the altered area and therefore to a difference in the charge carrier density of Δn = 3.5·1015m-2 between the unchanged and changed part. These two parts can be tuned with a global backgate to form a junction of different polarity, i.e. a p-n junction. © 2013 AIP Publishing LLC.