  A beam of holes formed in graphene by a collimating contact is imaged using a
liquid-He cooled scanning probe microscope (SPM). The mean free path of holes
is greater than the device dimensions. A zigzag shaped pattern on both sides of
the collimating contact absorb holes that enter at large angles. The image
charge beneath the SPM tip defects holes, and the pattern of flow is imaged by
displaying the change in conductance between contacts on opposite sides, as the
tip is raster scanned across the sample. Collimation is confirmed by bending
hole trajectories away from the receiving contact with an applied magnetic
field. The SPM images agree well with ray-tracing simulations.
