  We study a crystallographic etching process of graphene nanostructures where
zigzag edges can be prepared selectively. The process involves heating
exfoliated single-layer graphene samples with a predefined pattern of antidot
arrays in an argon atmosphere at 820 C, which selectively removes carbon atoms
located on armchair sites. Atomic force microscopy and scanning electron
microscopy cannot resolve the structure on the atomic scale. However, weak
localization and Raman measurements - which both probe intervalley scattering
at armchair edges - indicate that zigzag regions are enhanced compared to
samples prepared with oxygen based reactive ion etching only.
