Synthetic diamond material

Abstract

To optimize a diamond material for a new detection use, while various kinds of diamond material are proposed for a magnetism measurement use.SOLUTION: A synthetic diamond material contains a surface that includes a first surface region having a first quantum spin defect concentration. A second surface region having a predetermined range is disposed adjacently to the first surface region and has a second quantum spin defect concentration. The first quantum spin defect concentration is at least 10 times higher than the second quantum spin defect concentration. At least one of the first surface region and the second surface region includes chemical vapor deposition, CVD, and synthetic diamond. A method for manufacturing a synthetic diamond material is also disclosed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to the field of synthetic diamond materials and methods of producing synthetic diamond materials. [Background technology]

[0002] Point defects, in particular quantum spin defects and / or optically active defects, in synthetic diamond material have been proposed for use in a variety of sensing, detection and quantum processing applications including magnetometers, spin resonance instruments such as nuclear magnetic resonance (NMR) and electron spin resonance (ESR) instruments, spin resonance imaging instruments for magnetic resonance imaging (MRI) and quantum information processing instruments, for example for quantum computing. Many point defects have been studied in synthetic diamond materials, including silicon-containing defects such as silicon vacancy (Si-V), silicon complex vacancy (Si-V2), silicon vacancy hydrogen (Si-V:H), silicon complex vacancy hydrogen (S-V2:H), nickel-containing defects, chromium-containing defects, and nitrogen-containing defects such as nitrogen vacancy (NV), dinitrogen vacancy (NVN), and nitrogen vacancy hydrogen (NVH). These defects are typically found in neutral charge states or negative charge states. It should also be noted that these point defects extend over two or more crystal lattice points. The term point defect as used herein is intended to include such defects, but not to include larger cluster defects, such as those that extend over 10 or more lattice points, or extended defects such as dislocations that may extend over many lattice points.

[0003] Certain defects, when in their negatively charged state, have been found to be particularly useful in sensing, detection and quantum processing applications. For example, the negatively charged nitrogen vacancy defect (NV - ) has attracted much interest as a useful quantum spin defect because it has several desirable features: (i) Long coherence times at room temperature (transverse relaxation times T2 and / or T2* (which can be quantified and compared using (ii) their electronic structure allows defects to be optically pumped into their electronic ground state, placing such defects into specific electronic spin states even at non-cryogenic temperatures, eliminating the need for expensive and bulky cryogenic cooling equipment for certain applications where miniaturization is desirable. Furthermore, defects can act as a source of photons that all have the same spin state; and (iii) Its electronic structure contains luminescent and non-luminescent electron spin states, which allow the defect's electron spin state to be read out via photons. This is favorable for reading out information from synthetic diamond materials for use in sensing applications such as magnetometers, spin resonance spectroscopy, and imaging. Furthermore, it is expected that NV diamonds will be useful as quantum bits for long-distance quantum communication and scalable quantum computing. - These results suggest that NV - Defects are competitive candidates for solid-state quantum information processing (QIP) Because it has.

[0004] NV in diamond - The defect consists of a substitutional nitrogen atom adjacent to a carbon vacancy. Its two unpaired electrons form a spin triplet ( 3 A) and degenerate m s = ±1 sublevels, m s = 0 level is 2.87 GHz away. s The m = 0 sublevel exhibits high fluorescence efficiency when optically pumped. In contrast, s When excited at the =±1 levels, the non-radiative singlet state ( 1 A) crosses over to m s = 0. As a result, the spin state can be optically read out, and m s =0 state is "bright", m s= ±1 states are "dark". When an external magnetic field is applied, the spin sublevels m s The degeneracy of NV = ±1 is broken by Zeeman splitting, which results in a splitting of the resonance lines depending on the magnitude and direction of the applied magnetic field. If all four possible NV alignments are present in the excitation and detection regions of the sample, this dependence can be used for vector magnetometry, since the resonant spin transitions can be probed by sweeping the microwave (MW) frequency, resulting in a characteristic dip in the optically detected magnetic resonance (ODMR) spectrum.

[0005] NV of synthetic diamond materials - The defect can occur in a few different ways: (i) The formation during the growth of synthetic diamond material, where a nitrogen atom and a vacancy are incorporated into the crystal lattice as a nitrogen-vacancy pair during growth. (ii) forming, after synthesis of the diamond material, from the native nitrogen and vacancy defects incorporated during the growth process by post-growth annealing of the material at a temperature (approximately 800° C.), thereby causing the migration of vacancy defects through the crystal lattice to pair with native single substitutional nitrogen defects; (iii) forming, after synthesis of the diamond material, from natural nitrogen defects incorporated during the growth process, by irradiating the synthetic diamond material with electrons or neutrons to introduce vacancy defects and subsequently annealing the material at a temperature, thereby causing the migration of the vacancy defects through the crystal lattice to pair with natural single substitutional nitrogen defects; (iv) formation after synthesis of the diamond material by embedding nitrogen defects into a synthetic diamond material after synthesis of the diamond material and then annealing the material at a temperature, thereby causing migration of native vacancy defects through the crystal lattice to pair with the embedded single substitutional nitrogen defects; (v) forming a diamond material post-synthesis by irradiating the synthetic diamond material to introduce vacancy defects, embedding nitrogen defects in the synthetic diamond material before or after irradiation, and annealing the material at a temperature, thereby causing the migration of the vacancy defects through the crystal lattice to pair with the embedded single substitutional nitrogen defects; It can be formed in

[0006] In the prior art, different types of diamond materials have been disclosed for use in different types of magnetic measurement applications: The properties of high pressure, high temperature (HPHT) diamond material for magnetic measurement applications are discussed, Acosta et al., Phys. Rev. B80, 115202 WO 2010 / 010352 and WO 2010 / 010344 disclose low nitrogen content, single crystal chemical vapor deposition (CVD) diamond material for applications such as magnetic measurements. WO 2010 / 149775 disclosed irradiated, annealed, single crystal CVD diamond material for applications such as magnetic measurements. Summary of the Invention

[0007] Various types of diamond materials have been proposed for magnetic measurement applications, however, it is an aim of embodiments of the present invention to optimise diamond materials for novel sensing applications. According to a first aspect, there is provided a synthetic diamond material comprising a surface, the surface comprising a first surface region comprising a first quantum spin defect concentration. A second surface region has a predetermined extent and is disposed adjacent to the first surface region, the second region comprising a second quantum spin defect concentration. The first quantum spin defect concentration is at least 10 times higher than the second quantum spin defect concentration, and at least one of the first surface region or the second surface region comprises chemical vapor deposition (CVD) synthetic diamond. Various kinds of quantum spin defects can be engineered into synthetic diamond material. Examples of quantum spin defects in diamond include defects that contain any of silicon, nickel, chromium, germanium, tin, and nitrogen. Some of these can be negatively charged, neutral, or positively charged. As an alternative, the quantum spin defect may be a negatively charged nitrogen vacancy defect, NV - It is. The first quantum spin defect concentration may be at least 100 times higher than the second quantum spin defect concentration. The present invention can be applied to any type of surface, including substantially flat surfaces.

[0008] The first quantum spin defect concentration is 1x10 13 Defects / cm 3 , 1x10 14 Defects / cm 3 , 1x10 15 Defects / cm 3 , 1x10 16 Defects / cm 3 , 1x10 17 Defects / cm 3 , 1x10 18 Defects / cm 3 It may be equal to or higher than them. The quantum spin defect concentration in the first surface region is 4x10 18 Defects / cm 3 , 2x10 18 Defects / cm 3 , 1x10 18 Defects / cm 3 , 1x10 17 Defects / cm 3 , or 1x10 16 Defects / cm 3 It may be equal to or lower than these. As an option, the quantum spin defect has a Hahn-echo decoherence time, T2, that is equal to or longer than 0.01 ms, 0.05 ms, 0.1 ms, 0.3 ms, 0.6 ms, 1 ms, 5 ms, or 15 ms. The synthetic diamond material may include a plurality of first surface regions. The first region may have a depth below the planar front surface of from 100 nm to 100 μm. As a further option, the surface further comprises a third surface region comprising boron. The boron doping makes the diamond electrically conductive and therefore can be used to apply an electric field adjacent to the first surface region. As an option, the second surface region surrounds the first surface region.

[0009] According to a second aspect, there is provided a method for producing a synthetic diamond material, as described above in the first aspect. The method includes the steps of providing a synthetic diamond substrate having a front surface. Using a CVD method, a further diamond material is grown on the front surface of the single crystal diamond substrate. The front surface of the synthetic diamond substrate is then treated to form a sensing surface having a first surface region of the further diamond material adjacent to a second surface region of the diamond substrate material, and the quantum spin defect concentration of the further diamond material is at least 10 times higher than the quantum spin defect concentration of the synthetic diamond substrate material. In one option, the method includes forming at least one recess in a front surface of the diamond substrate, growing further diamond material in the recess, and again processing the further diamond material on the front surface of the synthetic diamond substrate to form a sensing surface. The recess may be formed by any of etching, masked etching, grinding and polishing and has a depth of from 100 nm to 100 μm.

[0010] As an alternative option, the method includes placing a mask having at least one opening on the front surface, and growing a further diamond material on the mask to grow the further diamond material in selected areas on the front surface. The mask is then removed and a second further diamond material is grown on the front surface. The second further diamond material is then treated to form the sensing surface. As an option, the quantum spin defect includes any of silicon, nickel, chromium, germanium, tin, and nitrogen. As a further option, the quantum spin defect can be the negatively charged nitrogen vacancy defect, NV - It is. The step of treating may include either irradiating or annealing. For example, this may be used to convert nitrogen in diamond to NV - Convert to center. According to a third aspect, there is provided a microfluidic cell comprising a microfluidic channel for receiving a fluid sample, a sensor positioned adjacent to the microfluidic channel, the sensor comprising the synthetic diamond material as described above in the first aspect.

[0011] According to a fourth aspect there is provided a magnetometric sensing probe comprising the synthetic diamond material as described above in the first aspect. To illustrate the present disclosure, non-limiting example configurations are described below with reference to the accompanying drawings. [Brief description of the drawings]

[0012] [Figure 1] 1 is a flow chart showing steps for producing synthetic diamond material. [Diagram 2] 1 is a flow diagram illustrating the steps for producing synthetic diamond material of a first exemplary embodiment; [Diagram 3] FIG. 2 shows a schematic cross-sectional side view of an etched diamond substrate. [Figure 4]FIG. 5 shows a schematic plan view of the etched diamond substrate of FIG. 4. [Diagram 5] FIG. 2 shows a schematic cross-sectional side view of further diamond material grown on a diamond substrate. [Figure 6] FIG. 2 shows a schematic cross-sectional side view of further diamond material grown on the treated diamond substrate; [Figure 7] FIG. 7 shows a schematic diagram of a plan view of the diamond material of FIG. 6 after processing. [Figure 8] 1 is a UV-illuminated photograph showing an exemplary diamond material. [Figure 9] FIG. 13 is a side view of a further exemplary embodiment in which a third diamond layer is provided. [Figure 10] FIG. 10 is a schematic plan view of the diamond material of FIG. 9. [Figure 11] FIG. 13 is a side view of another further exemplary embodiment. [Figure 12] FIG. 12 is a schematic plan view of the diamond material of FIG. 11. [Figure 13] 4 is a flow diagram illustrating the steps for producing synthetic diamond material in a further exemplary embodiment; [Figure 14] FIG. 2 is a schematic diagram showing a cross-sectional side view of a diamond substrate and a mask. [Figure 15] FIG. 15 shows a schematic cross-sectional side view of the diamond substrate and mask of FIG. 14 with further diamond material grown in the openings in the mask. [Figure 16] FIG. 16 is a schematic diagram showing a cross-sectional side view of the diamond substrate of FIG. 15 with the mask removed. [Figure 17] FIG. 17 shows a schematic cross-sectional side view of the diamond substrate of FIG. 16 having further diamond material grown on the surface. [Figure 18] FIG. 18 is a schematic diagram showing a cross-sectional side view of the diamond substrate of FIG. 17 after processing. [Figure 19] FIG. 1 is a schematic diagram showing a cross-sectional side view of a microfluidic cell. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] As previously mentioned, diamond material having a known large number of quantum spin defects can be used as a sensor. However, more sensor functionality and sensor resolution could be achieved by producing diamond material that includes predefined regions of diamond material having a higher concentration of quantum spin defects than the surrounding regions. These regions of high quantum spin defect concentration can be formed in patterns as required. The inventors have developed techniques to form such regions. The following description is an example of a high NV - Although defect concentrations are shown, it should be recognized that the same or similar techniques can be used to form other types of quantum spin defects, such as silicon-containing defects, nickel-containing defects, chromium-containing defects, germanium-containing defects, tin-containing defects, and nitrogen-containing defects.

[0014] Figure 1 shows that the NV is at least 10 times larger than the surrounding area. - 1 is a flow diagram showing exemplary steps for producing a diamond material having regions containing a defect concentration. The following numbering corresponds to that of FIG. 1: S1. Provide a synthetic diamond substrate, which may be a CVD, HPHT, or another form of synthetic diamond. S2. Further diamond is grown on the front side of the substrate using CVD. S3. The surface is then treated to form a first surface region of diamond having a first quantum spin defect concentration, and a second surface region adjacent to the first surface region having a second quantum spin defect concentration, the first quantum spin defect concentration being at least 10 times higher than the second quantum spin defect concentration. This further treating step may also include irradiating and annealing steps.

[0015] 2 is a flow diagram illustrating exemplary steps of a first exemplary embodiment. The following numbering corresponds to that of FIG. 2: S4. Provide a synthetic diamond substrate. This may be a CVD, HPHT or another form of synthetic diamond. S5. A pattern of recesses is formed on the flat front surface of the synthetic diamond substrate. Exemplary methods of forming such recesses include etching with a mask, grinding selected areas, polishing selected areas, etc. FIG. 3 is a schematic side cross-sectional view of an exemplary synthetic diamond substrate 1, and FIG. 4 is a schematic top view of the same diamond substrate 1. A circle 2 and two concentric rings 3, 4 are etched to different depths on the surface 5 of the synthetic diamond substrate 1 using a mask etch. The depth of the recesses can vary from about 100 nm to about 100 μm. The recesses shown in FIG. 3 have 90° corners when viewed in cross section. It should be appreciated that other shapes such as curved corners, chamfered corners, or V-shaped recesses can be used, as these can improve the growth of further diamond on them in the following step S6. S6. Further diamond material is grown on the flat front surface 5 of the synthetic diamond material using a CVD method. - NV at least 10 times higher than the defect concentration - Further diamond material is grown under conditions which result in a defect concentration. Figure 5 shows, in schematic form, a cross-sectional side view of the synthetic diamond substrate of Figures 3 and 4 after further diamond material 6 has been grown thereon, at the synthetic diamond substrate 1. Further diamond material 6 has been grown in the recesses 2, 3, 4 of the synthetic diamond substrate 1, and also in a layer on the planar front surface 5 of the synthetic diamond material 1. S7. The resulting composite diamond material is treated again to remove excess further diamond material 6. The treating step can be carried out using standard techniques, for example polishing, grinding, mechanical polishing and etching. Figure 6 shows a schematic side cross-sectional view of the diamond substrate 1 after further diamond treatment. Figure 7 shows the same material as in Figure 6 in plan view. The surface 10 of the diamond substrate 1 has a circle 7 of further diamond material surrounded by two concentric rings 8, 9 of further diamond material. The region of further diamond material is removed by the NV of the surrounding synthetic diamond substrate 1. - At least 10 times higher than the concentration of NV - It has a concentration.

[0016] Using the techniques described above, diamond materials can be produced that have regions of high quantum spin defect concentration surrounded by regions of lower quantum spin defect concentration. Such materials can be used in sensing applications, such as wide field imaging, based on magnetic field sensing. EXAMPLES

[0017] Example 1 A single crystal diamond substrate was provided having dimensions 3×3×0.5 mm and a nitrogen concentration of 1.5 ppb. A mask was placed on the growth surface of the substrate and the growth surface was selectively etched using inductively coupled plasma etching. This was performed using Ar and Cl feed gases, although it is recognized that oxygen could be used. The etching produced a recess pattern in the growth surface of the substrate. It will be appreciated by the artisan that other methods such as grinding, machining, chemical mechanical polishing, etc., can be used to produce the 10 μm recesses. The etched diamond substrate was then placed in a vacuum chamber and a surface cleaning etch was performed using hydrogen plasma. The etched diamond substrate was placed in a CVD reactor chamber and additional diamond was grown on the substrate to a thickness greater than the depth of the etched recess pattern. The additional diamond was grown under the following conditions: Microwave power = 5kW Pressure = 230 Torr Hydrogen flow rate = 600sccm Methane flow rate = 30sccm Nitrogen doping = 60sccm of N2 1000ppm in H2 It was grown using.

[0018] The nitrogen doping level was chosen to be relatively high to minimize the NV - Even higher NV than concentration - The concentration ensured that more diamonds would grow. The further diamond was then polished again using mechanical polishing to remove a surface layer of the further diamond leaving a similar structure at the surface of the diamond material to that shown in Figures 4 and 5, with regions 7, 8, and 9 of high nitrogen diamond and region 1 of low nitrogen diamond. Parameters such as nitrogen level can be varied depending on the desired nitrogen concentration in the final product. Optionally, oxygen, CO, or CO2 can also be added to the growth process. After growth, the single crystal diamond material was treated using irradiation and annealing techniques. This was done with an electron flux of 3x10 14 cm -2 seconds -1 The steps included irradiating the material under UV light for 6 hours and annealing it at 400°C for 4 hours, 800°C for 16 hours, and then 1200°C for 2 hours. This method converted the nitrogen in the diamond into NV - centers, making them useful as quantum spin defects.

[0019] Example 2 FIG. 8 is a photograph of a synthetic diamond material produced in the same manner as previously described in FIG. 1, but with a higher NV -Photographs of regions with different patterns of defect concentration. When the material is optically pumped using optional UV excitation, higher NV - Areas containing defect concentrations emit fluorescence. Example 3 As a further exemplary embodiment, further layers may be deposited on the diamond material.Referring to Figures 9 and 10, the diamond material of Figures 6 and 7 has been further processed. A third diamond layer 10 , having a low nitrogen content (1.5 ppb), was grown on the surface 11 of the synthetic diamond substrate material 1 . A mask was placed on the surface of the third diamond layer 10 and the surface was selectively etched using inductively coupled plasma etching. This was performed using Ar and Cl feed gases, although it is recognized that oxygen could be used. The etching produced a pattern of recesses in the growth surface of the substrate. It will be appreciated by the artisan that other methods can be used to produce the recesses, such as, for example, grinding, machining, chemical mechanical polishing, etc. The etched, third diamond layer 10 was then cleaned with a hydrogen plasma as described in Example 1.

[0020] The etched third diamond layer was then placed in a CVD reactor chamber and additional diamond was grown in the substrate to a thickness greater than the depth of the recessed pattern etched therein. The additional diamond was grown under the following conditions: Microwave power = 3.6kW Pressure = 140 Torr Hydrogen flow rate = 600sccm Methane flow rate = 32sccm B2H6 flow rate=19sccm It was grown using. The addition of boron was to ensure that the additional diamond had sufficient boron content to form conductive synthetic diamond. The additional diamond was then polished again using mechanical polishing to remove the surface layer of the additional diamond leaving a structure similar to that shown in Figures 8 and 9. The surface of the third diamond layer 10 includes a region of boron doped diamond 11 in the form of a ring. This region 11 is electrically conductive and can therefore be used to apply an electric field in the vicinity of the further diamond regions 7, 8, 9, which have high quantum spin defect concentrations. The electrically conductive region 11 can also be used as a method of generating microwaves.

[0021] Example 4 As an alternative to Example 3, a third diamond layer, doped with boron, can be deposited on the same plane as the further diamond of Example 1. This is shown in Figures 11 and 12. In this case, the material is produced in the same manner as previously described in Example 1. A mask is then placed on the surface of the diamond material and a pattern is etched into the surface. The mask is removed, leaving a surface with etched recesses. A third diamond material is then grown on the surface and in the recesses. The third diamond material in this example is doped with boron. The new surface is then polished again, leaving the structure shown in Figures 11 and 12. The resulting surface includes surface region 7 having a high quantum spin defect concentration, surface region 8, surface region 9, and surface region 12 having boron doped diamond.

[0022] The above embodiments and examples describe one method for obtaining a synthetic diamond material comprising a surface including a first surface region including a first quantum spin defect concentration, and a second surface region having a predetermined extent and disposed adjacent to the first surface region. An alternative technique is shown in Figure 13. The following numbering corresponds to that of Figure 13: S8. Provide a synthetic diamond substrate 13. This may be a CVD, HPHT or another form of synthetic diamond. S9. Referring to FIG. 14, a mask 14 having at least one opening 15 is placed on the surface of the synthetic diamond substrate 13. S10. As shown in Figure 15, further diamond material 16 is grown on the mask 14, filling the openings in the mask 14. The further diamond material has a higher nitrogen concentration than the synthetic diamond substrate 13. S11. The mask 14 is removed leaving the synthetic diamond substrate including the protruding growth of further diamonds 16, as shown in FIG. S12. As shown in FIG. 17, diamond material 16 (corresponding to the diamond material of the synthetic diamond substrate 13 in this embodiment) is then grown on the diamond substrate 13. S13. As shown in Figure 18, the new surface of the diamond material 16 is again treated using any suitable means to form the structure shown in Figure 18, in which the surface comprises regions 15 of diamond material having a higher nitrogen content adjacent regions 16 of diamond material having a lower nitrogen content. Subsequent irradiation and annealing steps are used to convert the nitrogen in the diamond material to NV - It can be moved to the center.

[0023] Using the techniques described above, diamond materials can be produced that have regions of high quantum spin defect concentration surrounded by regions of lower quantum spin defect concentration. Such materials can be used as sensing probes for sensing applications such as wide field imaging based on magnetic field sensing. Another exemplary use of synthetic diamond material is in the field of microfluidic sensing. Figure 19 shows a schematic of an exemplary microfluidic cell 17 including a diamond material 13 having a region 16 of diamond with a high quantum spin defect concentration. The microfluidic cell includes a channel 18 adjacent the region 16 of diamond with a high quantum spin defect concentration and can be used to analyze fluids. A discussion and description of microfluidic sensing using quantum spin defects in diamond can be found in WO 2012 / 034924.

[0024] The present invention, as set forth in the appended claims, has been shown and described with reference to embodiments, but it will be understood by those skilled in the art that various changes in form and detail can be made therein without departing from the scope of the invention, as defined by the appended claims.

Claims

1. 1. A synthetic diamond material comprising a surface, the surface comprising: a first surface region including a first quantum spin defect concentration; a second surface region having a predetermined extent and including a second quantum spin defect concentration disposed adjacent to the first surface region, the first quantum spin defect concentration being at least 10 times greater than the second quantum spin defect concentration; Including, A synthetic diamond material, wherein at least one of the first surface region or the second surface region comprises chemical vapor deposition, CVD, synthetic diamond.

2. Quantum spin defects, Silicon-containing defects, Nickel-containing defects, Chromium-containing defects, germanium-containing defects, Tin-containing defects, and Nitrogen-containing defects 2. The synthetic diamond material of claim 1 , selected from any of the following:

3. The quantum spin defect is a negatively charged nitrogen vacancy defect (NV) - 2. The synthetic diamond material of claim 1 , wherein:

4. A synthetic diamond material according to any preceding claim, wherein the first quantum spin defect concentration is at least 100 times higher than the second quantum spin defect concentration.

5. A synthetic diamond material according to any preceding claim, wherein the surface is a substantially flat surface.

6. The first quantum spin defect concentration is 1×10 13 Defects / cm 3 , 1x10 14 Defects / cm 3 , 1x10 15 Defects / cm 3 , 1x10 16 Defects / cm 3 , 1x10 17 Defects / cm 3 , 1x10 18 Defects / cm 3 6. The synthetic diamond material of any one of claims 1 to 5, wherein the Mn content is equal to or higher than

7. The quantum spin defect concentration of the first surface region is 4×10 18 Defects / cm 3 , 2x10 18 Defects / cm 3 , 1x10 18 Defects / cm 3 , 1x10 17 Defects / cm 3 , or 1x10 16 Defects / cm 3 A synthetic diamond material according to any one of the preceding claims, wherein the .lambda.-value is equal to or lower than:

8. The quantum spin defect has a Hahn echo coherence time T that is equal to or longer than 0.01 ms, 0.05 ms, 0.1 ms, 0.3 ms, 0.6 ms, 1 ms, 5 ms, or 15 ms. 2 A synthetic diamond material according to any preceding claim, having the following structure:

9. A synthetic diamond material according to any preceding claim, further comprising a plurality of first surface regions.

10. A synthetic diamond material according to any preceding claim, wherein the depth of the first region below the flat front surface is between 100 nm and 100 μm.

11. A synthetic diamond material according to any preceding claim, wherein the surface further comprises a third surface region comprising boron.

12. A synthetic diamond material according to any preceding claim, wherein the second surface region surrounds the first surface region.

13. A method of producing a synthetic diamond material according to any one of claims 1 to 12, comprising the steps of: Providing a synthetic diamond substrate having a front surface; growing further diamond material on a front side of the single crystal diamond substrate using chemical vapour deposition; treating a front surface of the synthetic diamond substrate to form a sensing surface having a first surface region of a further diamond material adjacent a second surface region of the diamond substrate material, the further diamond material having a quantum spin defect concentration at least ten times higher than the quantum spin defects of the synthetic diamond substrate material; A method comprising:

14. forming at least one recess in a front surface of a diamond substrate; growing further diamond material in the recess; Processing the further diamond material to form a sensing surface. The method of claim 13, comprising:

15. The method of claim 14 , further comprising forming the recess by any one of etching, mask etching, grinding, and polishing.

16. A method according to claim 14 or claim 15, comprising forming recesses having a depth of between 100 nm and 100 μm.

17. disposing a mask having at least one opening on the front surface; growing further diamond material on the mask so as to grow further diamond material in selected areas on the front surface; removing the mask; growing a second further diamond material on the front surface; and again processing a second further diamond material on the front side of the synthetic diamond substrate to form a sensing surface. The method of claim 13, comprising:

18. Quantum spin defects, Silicon-containing defects, Nickel-containing defects, Chromium-containing defects, germanium-containing defects, Tin-containing defects, and Nitrogen-containing defects The method according to any one of claims 13 to 17, wherein the method is selected from any one of the following:

19. The quantum spin defect is a negatively charged nitrogen vacancy defect (NV) - The method according to any one of claims 13 to 18, wherein

20. The method of any one of claims 13 to 18, wherein the step of treating comprises any one of the steps of irradiating and annealing.

21. a microfluidic channel for receiving a fluid sample; and Sensors positioned adjacent to microfluidic channels 1. A microfluidic cell comprising: A microfluidic cell in which the sensor comprises the synthetic diamond material of any one of claims 1 to 12.

22. A magnetometric sensing probe comprising the synthetic diamond material of any preceding claim.

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