Abstract
The nitrogen vacancy (NV) center in diamond exhibits spin-dependent fluorescence and long spin coherence times under ambient conditions, enabling applications in quantum information processing and sensing. NV centers near the surface can have strong interactions with external materials and spins, enabling new forms of nanoscale spectroscopy. However, NV spin coherence degrades within 100 nanometers of the surface, suggesting that diamond surfaces are plagued with ubiquitous defects. Prior work on characterizing near-surface noise has primarily relied on using NV centers themselves as probes; while this has the advantage of exquisite sensitivity, it provides only indirect information about the origin of the noise. Here we demonstrate that surface spectroscopy methods and single spin measurements can be used as complementary diagnostics to understand sources of noise. We find that surface morphology is crucial for realizing reproducible chemical termination, and use these insights to achieve a highly ordered, oxygen-terminated surface with suppressed noise. We observe NV centers within 10 nm of the surface with coherence times extended by an order of magnitude.
Highlights
We observe that coherence time degrades with proximity to the surface in numerous samples with different surface conditions [Fig. 1(b)], consistent with prior studies [9,10,11], pointing to the need for new techniques to understand and control diamond surfaces
We find that surface roughness leads to poor NV coherence, and we observe that surface morphology changes the density of electronic defects observed with photoelectron spectroscopy, even for the same nominal chemical termination, implying that it is critical to maintain precise control over surface purity and morphology at every processing step
We remove surface and subsurface damage resulting from polishing and reactive ion etching (RIE) before ion implantation, perform high-temperature annealing to remove implantation damage, and use oxygen annealing followed by wet oxidation to terminate the surface [Fig. 1(c); see Appendix A 2]
Summary
Nitrogen-vacancy (NV) centers in diamond are a promising platform for quantum information processing and sensing [1,2], and shallow NV centers near the diamond surface are actively explored as highly sensitive sensors with. It is easy to place NV centers near the surface by low-energy ion implantation [7,8] or delta doping [7,9], the surface itself can host defects that lead to noise that obscures the sensing target [Fig. 1(a)]. Surface morphology is difficult to control because diamond’s hardness makes etching and polishing nontrivial. State-of-the-art diamond polishing can achieve surface roughness below 1 nm, but the resulting surface is highly strained. We find that surface roughness leads to poor NV coherence, and we observe that surface morphology changes the density of electronic defects observed with photoelectron spectroscopy, even for the same nominal chemical termination, implying that it is critical to maintain precise control over surface purity and morphology at every processing step
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