Formation Mechanism And Regulation Of Internal Defects In Diamond Under High Temperature And High Pressure Condition

Diamond is a unique material that combines various excellent mechanical,physical,and chemical properties.The defect structures introduced by doping with nitrogen and boron atoms endow diamonds with additional functional characteristics,making them playing important roles in the fields of quantum technology and semiconductors.Although certain progress has been made in the application research,there are still unresolved issues concerning the diamond material itself.Moreover,while China is a major producer of diamonds,it is not yet a dominant force in high-quality functional diamond production,with the domestic demand largely dependent on foreign supply.As international competition intensifies,Western countries have begun to implement technological blockades and supply isolation against China in the field of diamond materials,turning functional diamonds into a bottleneck for the development of related technologies in China.To tackle the challenges arising in the development of pertinent applications and to surmount the"bottleneck" issues that China confronts in the realms of quantum technology and semiconductor advancements using diamonds,we conduct researches surrounding the mechanisms of formation and control of defects within diamonds under conditions of high temperature and high pressure.The specific research content includes three aspects,as follows:(Ⅰ)Controlled synthesis of high coherent single NV-centers under high pressure and high temperature conditions.As a stable quantum system,the NV-center exhibits unique properties at room temperature and plays a crucial role in contemporary quantum technology fields.High coherent single NV-centers,which are diffusely distributed and can be optically addressed,are crucial for the advancement of quantum computing,quantum networks,and high-resolution quantum precision sensing.The state-of-the-art way to fabricate single NV-centers involves implanting nitrogen and vacancy into CVD diamond substrate,followed by subsequent annealing to complete the preparation.However,the intrinsic stress,along with stress induced by lattice-damaging post-growth processes,will cause variability in the coherence properties among produced NV-centers and result in a scarcity of high-quality centers..Diamonds grown under high pressure and high temperature conditions exhibit superior crystalline quality and lower growth stress,making them ideal substrates for the fabrication of high-quality single NV-centers.Additionally,high pressure and high temperature(HPHT)annealing can more effectively promote the aggregation of nitrogen atoms and vacancies,further reducing the growth stress in diamonds.Therefore,by integrating the growth and annealing processes under high pressure and high temperature conditions,there exists potential to fabricate high coherent single NV-centers.Under high-pressure,high-temperature conditions,we achieved controlled fabrication of high-quality single NV-centers,with coherence times in the<111>crystal growth region exceeding 300μs.Notably,we fabricated an single NVcenter with T2～721 μs,achieve the highest coherence property among NV-centers in naturally abundant 13C diamonds.This work has developed a non-destructive and controllable method for preparing high-quality single NV-centers,proposing a new direction for enhancing the coherence properties of single NV-centers.It holds significant importance for advancing the development of single NV-centers in quantum computing,quantum networks,and high spatial resolution precision detection,among other areas.At the same time,it overcomes the international supply restrictions faced by China in the field of single NV-center quantum-grade diamond.(Ⅱ)Controlled synthesis of high-quality ensemble NV-centers under high pressure and high temperature conditions.High-density and highly coherent NVcenters are outstanding candidates for high-sensitivity quantum precision detection.High nitrogen doping is key to achieving high-density NV-centers.Compared to commonly used CVD diamonds,diamonds grown with high pressure and high temperature conditions are more conducive to achieving high nitrogen doping.Furthermore,the stress generated during the high pressure and high temperature growth process is lower,making it an ideal substrate for the preparation of high-quality NV-centers.Despite this,the formation mechanism of NV-centers in high-temperature,high-pressure diamonds remains unclear,resulting in low density and poor coherence properties of the produced centers.They have not yet been applied in the field of quantum technology.Therefore,fabricating quantum-grade NVcenters in high pressure and high temperature,diamonds still poses significant challenges.In this work,we explored the formation mechanisms and evolutionary patterns of NV-centers during the growth and annealing processes of high pressure and high temperature(HPHT)diamonds.We explored the impact of nitrogen content,diamond growth orientation,and HPHT annealing techniques on the coherence properties of NV-centers.Successfully,we fabricated high-density,high-coherence NV-centers in the<100>growth sector of type Ib diamonds,achieving a density of over 110 ppb and a coherence time exceeding 52 μs through non-destructive methods.The centers created in the<100>growth region exhibit exceptionally narrow zero-phonon lines and minimal zero-field ODMR splitting,comparable to those in ultra-low nitrogen content type Ⅱa diamonds.Additionally,we found that promoting the aggregation of nitrogen atoms around NV-centers into neutral H3 during the annealing process can significantly purifies the NV-centers’ spin environment,thus greatly enhancing their coherence time.This research elevates HPHT diamonds to the level of quantum-grade cluster NV-center diamonds,opening new possibilities for HPHT diamonds in quantum technology applications.(Ⅲ)The impact of high pressure and high temperature annealing on the electrical conductivity of boron-doped diamonds.Boron-doped diamond(BDD)is expected as a promising semiconductor candidate for potential application in next-generation high-power and high-voltage electronics.Unfortunately,a feasible strategy that focuses on the improvement for the semiconducting performance of BDD materials is still lack and remains a fundamental challenge in material science.Thus,we aim to study the stability and modulation behaviors of boron dopants in BDD materials through post-annealing treatment at high pressure and high temperature(HPHT).In this work,our study demonstrates that boron dopants show high structural stability,and no extra complex defects were observed during the HPHT annealing process,a superior advantage for the device application in extreme environments.Our work further reveals that the HPHT post-annealing process is effective to eliminate the intrinsic stress and local lattice strain that were inherently formed during the growth process in the BDD crystals.This process is accompanied by the enhancement of ionization ratio of boron dopants.The carrier concentration of one<111>-GS BDD increases by more than ten times after post-annealing at 1000℃and 5.5 GPa,resulting in an improvement of conductivity by a factor of 2.This result provides an effective strategy to improve the semiconducting performance of BDD materials through HPHT annealing approach and promote their practical device applications.Diamonds are not just functional materials with enormous potential;the variety of dopants in natural diamond provides crucial insights into the elemental and mineral cycles deep within the Earth.Specifically,natural boron-doped diamonds(blue diamonds),sourced from the deepest parts of the Earth,offer possibilities for uncovering secrets of regions yet unexplored by humanity.Blue diamonds from Earth’s lower mantle are unique messengers with rare insights into the otherwise inaccessible depths,but the materials origin and formation mechanisms of these enigmatic diamonds have long remained uncertain.(Ⅳ)The origin of natural blue diamond.In our work,we explore the potential sources of boron in natural diamonds,revealing that metal borides and boric acid can decompose under extreme conditions to release boron.This suggests that metal borides deposited in the lower mantle or carried into it by subducting plates could be a source of boron for natural blue diamonds.Two distinct routes are identified for diamond crystallization,via direct decomposition of carbonatites near the top of the lower mantle or breakdown of carbon dioxide in the deeper lower mantle.Contrary to previous beliefs that boron exists in natural diamonds as isolated substitutional defects,we discovered that boron primarily forms B-O complex defects.Additionally,we observed boron’s role as a nitrogen getter during diamond formation,explaining the rarity of nitrogen in natural blue diamonds.These findings offer crucial insights into the formation processes of natural blue diamonds in the Earth’s deep interior,holding significant scientific value for unveiling the cycles of boron and oxygen within the Earth.