  Modifying material properties at the nanoscale is crucially important for
devices in nanoelectronics, nanophotonics and quantum information. Optically
active defects in wide band gap materials, for instance, are vital constituents
for the realisation of quantum technologies. Yet, the introduction of atomic
defects through direct ion implantation remains a fundamental challenge.
Herein, we establish a universal method for material doping by exploiting one
of the most fundamental principles of physics - momentum transfer. As a proof
of concept, we direct-write arrays of emitters into diamond via momentum
transfer from a Xe+ focused ion beam (FIB) to thin films of the group IV
dopants pre-deposited onto a diamond surface. We conclusively show that the
technique, which we term knock-on doping, can yield ultra-shallow dopant
profiles localized to the top 5 nm of the target surface, and use it to achieve
sub-50 nm lateral resolution. The knock-on doping method is cost-effective, yet
very versatile, powerful and universally suitable for applications such as
electronic and magnetic doping of atomically thin materials and engineering of
near-surface states of semiconductor devices.
