Novel Processing for Diamond Quantum Technologies

点击翻译按钮获取中文摘要

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 ofthe diamond. NV centres can be grown-in, produced by irradiation damage plus annealing where by pre-existingsubstitutional 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 typicallysignificantly 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 particlesembedded in a cast iron wheel) with low surface roughness (< 1 nm), the sub-surface regions are damaged. As grownsurfaces are not sufficiently flat for many applications but current "polishing" technology significantly impairs theperformance 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 crystaldiamond to achieve both low (<< 1 nm) surface roughness and low surface damage such that the touted supreme andexploitable quantum properties of near surface (< 50 nm) NV centres are fully realised. Moreover, this work will facilitate theroutine 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 anenabler.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 damageprofiles that affect the near surface NV centres. ICP etching is currently the standard tool used to make quantum devicesout of diamond but is also known to impart damage to the diamond. Hence, studies on NVs near to a variety of differentlypolished, etched and as-grown surfaces, as well as those in the bulk will be employed to bench-mark against the CMPprocess.Characterisation of near surface NV centres will be achieved using (i) high resolution single centre confocalphotoluminescence 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 processingmethodology (e.g. CMP, etching, termination etc.) and (ii) optically detected magnetic resonance, using state of the art highthrough-put equipment under ambient conditions and at cryogenic temperatures. This provides information on the allimportantspin 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 isessential.Near surface NV centres will be implanted (and annealed) after and before the CMP polishing process using low energy ionimplantation (via collaboration, at no cost to program, with Jan Meijer, Leipzig University) and fully characterised. Lowenergy ion implantation provides the ultimate control in NV positioning ideal for device manufacture, and is an ideal way todemonstrate that CMP can significantly improve the yield of useful near surface implanted NV centres.