Novel Processing for Diamond Quantum Technologies

State of the art bulk single crystal diamond material e.g. very low impurity contamination, low structural defect density,
isotopically engineered, has been realised but many quantum technologies demand near surface nitrogen-vacancy (NV)
centres "on demand" with reproducible properties approaching the best that can be achieved when positioned in the bulk of
the diamond. NV centres can be grown-in, produced by irradiation damage plus annealing where by pre-existing
substitutional nitrogen captures a mobile vacancy, or produced by nitrogen ion implantation plus annealing. In the bulk
(typically 10 mirco-m from the surface) NV centres can have exceptional quantum properties but these are typically
significantly degraded close to a surface due to subsurface damage (e.g. micro-cracks, trapped charge, parasitic spins,
strain) produced by polishing. Even though diamond can be mechanically polished (e.g. with small diamond particles
embedded in a cast iron wheel) with low surface roughness (< 1 nm), the sub-surface regions are damaged. As grown
surfaces are not sufficiently flat for many applications but current "polishing" technology significantly impairs the
performance of near surface NV centres so a new technology that can be easily transferred to production is required.
This project focuses on the implementation and optimisation of chemical mechanical polishing (CMP) of single crystal
diamond to achieve both low (<< 1 nm) surface roughness and low surface damage such that the touted supreme and
exploitable quantum properties of near surface (< 50 nm) NV centres are fully realised. Moreover, this work will facilitate the
routine production of very thin (< 30 mirco-m) large area single crystal diamond plates with optimised surface finishes.
There is considerable demand for this material for a variety of photonic and quantum technologies; here CMP is an
enabler.
The research programme will provide irrefutable evidence that CMP of diamond is a quantum technology enabler.
Traditional polishing techniques such as standard resin bond and scaife polishing are known to produce different damage
profiles that affect the near surface NV centres. ICP etching is currently the standard tool used to make quantum devices
out of diamond but is also known to impart damage to the diamond. Hence, studies on NVs near to a variety of differently
polished, etched and as-grown surfaces, as well as those in the bulk will be employed to bench-mark against the CMP
process.
Characterisation of near surface NV centres will be achieved using (i) high resolution single centre confocal
photoluminescence microscopy which enables statistical analysis of the properties of NV's e.g. probability of production,
stability, sensitivity to surface termination etc., with respect to distance from the top surface and surface processing
methodology (e.g. CMP, etching, termination etc.) and (ii) optically detected magnetic resonance, using state of the art high
through-put equipment under ambient conditions and at cryogenic temperatures. This provides information on the allimportant
spin lifetime of individual centres as a function of depth, surface preparation and processing. There is expected to be a significant statistical variation of the NVs properties due to other uncontrolled parameters on the nanoscale (i.e.
location of 13C, substitutional nitrogen, dislocations, surface spins, surface charges), hence the statistical analysis is
essential.
Near surface NV centres will be implanted (and annealed) after and before the CMP polishing process using low energy ion
implantation (via collaboration, at no cost to program, with Jan Meijer, Leipzig University) and fully characterised. Low
energy ion implantation provides the ultimate control in NV positioning ideal for device manufacture, and is an ideal way to
demonstrate that CMP can significantly improve the yield of useful near surface implanted NV centres.

Since the discovery that the nitrogen-vacancy (NV) defect in diamond offers up easily measurable quantum properties,
even at room temperature, there have been numerous demonstrations exploiting NV defects in applications ranging from
magnetic and electric field sensing to quantum repeaters and quantum computing. The potential impact of this research
ranges from new diagnostic tools for healthcare and transformative imaging methodologies for materials and life sciences,
all the way through to secure communications and quantum simulators.
These diamond based quantum technologies will be game changing in many technology sectors over a 5-30 year time
scale and their development will become a multi-million pound industry that could benefit the UK economy over the same
period. We will all benefit from new capabilities, especially in the healthcare where advances will improve the health and
quality of life of our ageing population, and communications domains essential for a thriving modern economy. It is crucially
important is that the UK is at forefront of the development and exploitation of these novel technologies. Delivering the
benefits of new industries, new jobs, etc. is at least as important as the R&D. To ensure that the UK reaps the benefit it is
essential facilitate links between the materials producer, Element Six (E6), academics developing the technology and
exploiter industries who know the potential markets. For example, UK companies manufacturing, developing and selling
magnetic resonance and spectroscopic equipment will benefit through targeted collaborative R&D on diamond based
magnetometry leading to innovative and accelerated product development. Established businesses must evolve and will
only be sustained through continued innovation. Furthermore, we envisage that SMEs will have a significant role to play in
pioneering the new diamond based quantum technologies. In all cases transformation of scientific demonstrators into new
technologies requires the scalable production of "quantum grade diamond", with low surface roughness, low surface
damage and near surface high performance NV centres on demand. The bulk material exists, but to achieve all of the
above the team will develop Chemical Mechanical Polishing techniques and characterise the material to show that high
performance NV centres can be produced with high yield near (down to a few nm) the surface.
The new Quantum Technology Hubs, and many Centres for Doctoral Training (CDT), especially the Diamond Science and
Technology CDT, will be near term beneficiaries of the work since the material will enable R&D and technology
demonstration. Working closely with Quantum Technology Hubs and CDTs will facilitate new partnerships with industry and
develop a stronger technology pull.
For young researchers who make use of the material produced it will not only benefit their immediate research but the
exposure to cutting-edge technologies and methodologies will ensure they are attractive to employers in both academic
and industrial environments.
The new material gives the UK a research advantage that will promote international collaboration and development since
visitors will want to make use of the capability. New collaborations will be established, research income leveraged into the
UK and through the expertise drawn inwards the UK research base strengthened.