Developing methods for deterministic dopant incorporation in diamond is necessary to achieve the precision required to fabricate diamond quantum technology. While FIB’s and control of the ion energy can achieve the required spatial precision, a method is needed to count the number of ions implanted. The ion beam induced charge method (IBIC) uses the electron hole pairs created by ionisation during ion implantation to create a charge proportional pulse. This pulse signal is used to detect when single ions are implanted and can be indicative of channeling, double implants, and other unwanted events. 

The biggest difficulty with this method, is bringing the detection efficiency to require levels for the 10-45 keV N⁺ or ~100 keV Si/Ge/Sn/Pb energy ions required for single colour centre devices (NV/SiV…). With diamond, this technique has long been used for high energy (>MeV) radiation detection in harsh environments due to the materials radiation hardness and long lived bulk carrier lifetimes. When keV energy ions are implanted into such a detector, they would end up within the conductive material and useless for their intended purpose. 

However, placing regions with bare diamond is shown here is unviable due to surface effects stemming from the complex surface of diamond [1]. We demonstrate how a graphene capping layer creates an ultra-thin conductive electrode that retains high detection efficiency as a thick electrode, but with minimal disruption to the ion. We report single ion detection confidence values of >99% for 6 keV H⁺ and 85% for 24 keV N⁺ ions. 

[1] N.F.L.Collins et. al., Graphene-Enhanced Single Ion Detectors for Deterministic Near-Surface Dopant Implantation in Diamond, Advanced Functional Materials, 2023