Title: Impact of surface functionalisation on the quantum coherence of nitrogen vacancy centres in nanodiamond,
Abstract: Nanoscale quantum probes such as the nitrogen-vacancy centre in diamond have
demonstrated remarkable sensing capabilities over the past decade as control
over the fabrication and manipulation of these systems has evolved. However, as
the size of these nanoscale quantum probes is reduced, the surface termination
of the host material begins to play a prominent role as a source of magnetic
and electric field noise. In this work, we show that borane-reduced nanodiamond
surfaces can on average double the spin relaxation time of individual
nitrogen-vacancy centres in nanodiamonds when compared to the thermally
oxidised surfaces. Using a combination of infra-red and x-ray absorption
spectroscopy techniques, we correlate the changes in quantum relaxation rates
with the conversion of sp2 carbon to C-O and C-H bonds on the diamond surface.
These findings implicate double-bonded carbon species as a dominant source of
spin noise for near surface NV centres and show that through tailored
engineering of the surface, we can improve the quantum properties and magnetic
sensitivity of these nanoscale probes.