  Atomically precise tailoring of graphene can enable unusual transport
pathways and new nanometer-scale functional devices. Here we describe a recipe
for the controlled production of highly regular "5-5-8" line defects in
graphene by means of simultaneous electron irradiation and Joule heating by
applied electric current. High-resolution transmission electron microscopy
reveals individual steps of the growth process. Extending earlier theoretical
work suggesting valley-discriminating capabilities of a graphene 5-5-8 line
defect, we perform first-principles calculations of transport and find a strong
energy dependence of valley polarization of the charge carriers across the
defect. These findings inspire us to propose a compact electrostatically gated
"valley valve" device, a critical component for valleytronics.
