Novel Processing for Diamond Quantum Technologies

最先进的块状单晶金刚石材料，例如非常低的杂质污染、低结构缺陷密度、同位素工程，已经实现，但许多量子技术要求表面氮空位(NV)中心附近的可重复性能接近于放置在钻石块状区域时的最佳状态。NV中心可以是内生的，可以通过辐照损伤和通过预先存在的替代氮捕获移动空位的退火法产生，也可以通过氮离子注入和退火法产生。在整体上(通常距离表面10微米)，NV中心可能具有特殊的量子特性，但这些特性通常会在接近表面的地方由于抛光产生的亚表面损伤(例如微裂缝、陷阱电荷、寄生自旋、应变)而显著退化。即使钻石可以机械抛光(例如，用镶嵌在铸铁砂轮中的小钻石颗粒)，表面粗糙度低(&lt；1 nm)，亚表面区域也会损坏。由于生长的表面不够平坦，不能满足许多应用的需要，但当前的“抛光”技术严重损害了近表面NV中心的性能，因此需要一种易于转化为生产的新技术。本项目致力于单晶金刚石化学机械抛光(CMP)的实施和优化，以获得低(&lt；&lt；1 nm)表面粗糙度和低表面损伤，从而充分实现被吹捧的近表面(&lt；50 nm)NV中心的最高和可展开的量子特性。此外，这项工作将促进具有优化表面光洁度的超薄(&lt；30微米)大面积单晶金刚石片的常规生产。各种光子和量子技术对这种材料有相当大的需求；在这里，化学机械抛光是一种使能器。研究计划将提供无可辩驳的证据，证明钻石的化学机械抛光是量子技术的使能器。众所周知，传统的抛光技术，如标准树脂结合和Scaife抛光，会产生不同的损伤轮廓，影响近表面的NV中心。目前，电感耦合等离子体刻蚀是用钻石制造量子器件的标准工具，但众所周知，它也会对钻石造成损害。因此，将使用(I)高分辨率单中心共聚焦光致发光显微镜来实现近表面NV的特性的统计分析，例如，相对于与顶面的距离和表面处理方法(例如，化学机械抛光、蚀刻、终止等)，能够对NV的特性进行统计分析，例如，与顶面的距离和表面处理方法(例如化学机械抛光、蚀刻、终止等)。以及(Ii)在环境条件和低温下使用最先进的高通量设备，光学检测到的磁共振。这提供了关于作为深度、表面准备和加工的函数的各个中心的最重要的自旋寿命的信息。由于纳米尺度上的其他不可控参数(即13C的位置、置换氮、位错、表面自旋、表面电荷)，预计NV的性质将有显著的统计变化，因此统计分析是必要的。近表面NV中心将在使用低能离子注入(通过合作，免费编程，与莱比锡大学的Jan Meijer合作)的CMP抛光过程之后和之前被注入(和退火)并完全表征。低能离子注入提供了对NV定位的最终控制，是器件制造的理想选择，也是证明化学机械抛光可以显著提高有用的近表面注入NV中心的成品率的理想方法。

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.