Synthetic diamond material

Abstract

A synthetic diamond material comprises a surface, wherein the surface comprises a first surface region comprising a first concentration of quantum spin defects. A second surface region has a predetermined area and is located adjacent to the first surface region, the second region comprising a second concentration of quantum spin defects. The first concentration of quantum spin defects is at least ten times greater than the second concentration of quantum spin defects, and at least one of the first or second surface regions comprises chemical vapour deposition, CVD, synthetic diamond. A method of producing the synthetic diamond material is also disclosed.

Claims

1. A synthetic diamond material comprising: a surface, wherein the surface comprises: a first surface region comprising a first concentration of quantum spin defects; a second surface region having a predetermined area and located adjacent to the first surface region, the second region comprising a second concentration of quantum spin defects, wherein the first concentration of quantum spin defects is at least ten times greater than the second concentration of quantum spin defects; wherein a depth of the first region below the planar front surface is between 100 nm and 100 μm; and wherein at least one of the first or second surface regions comprises chemical vapour deposition, CVD, synthetic diamond.

2. The synthetic diamond material according to claim 1, wherein the quantum spin defects are selected from any of: negatively charged nitrogen-vacancy defects NV.sup.−; silicon containing defects; nickel containing defects; chromium containing defects; germanium containing defects; tin containing defects; and nitrogen containing defects.

3. The synthetic diamond material according to claim 1, wherein the first concentration of quantum spin defects is at least one hundred times greater than the second concentration of quantum spin defects.

4. The synthetic diamond material according to claim wherein the first concentration of quantum spin defects is equal to or greater than: 1×10.sup.13 defects/cm.sup.3.

5. The synthetic diamond material according to claim 1, wherein the concentration of quantum spin defects in the first surface region is equal to or less than: 4×10.sup.18 defects/cm.sup.3.

6. The synthetic diamond material according to claim 1, wherein the quantum spin defects have a Hahn-echo decoherence time T.sub.2 equal to or greater than 0.01 ms.

7. The synthetic diamond material according to claim 1, further comprising a plurality of first surface regions.

8. The synthetic diamond material according to claim 1, wherein the surface further comprises a third surface region, the third surface region comprising boron.

9. The synthetic diamond material according to claim 1, wherein the second surface region surrounds the first surface region.

10. A method of fabricating the synthetic diamond material as claimed in claim 1, the method comprising: providing a synthetic diamond substrate having a front surface; using a chemical vapour deposition process to grow further diamond material over the front surface of the single crystal diamond substrate; processing the front surface of the synthetic diamond substrate to form a sensing surface having a first surface region of further diamond material adjacent to a second surface region of diamond substrate material, wherein a quantum spin defect concentration of the further diamond material is at least ten times greater than a quantum spin defect of the synthetic diamond substrate material, and wherein a depth of the first region below the planar front surface is between 100 nm and 100 μm.

11. The method according to claim 10, comprising: forming at least one depression in the front surface of the diamond substrate; growing the further diamond material in the depression; processing the further diamond material to form the sensing surface.

12. The method according to claim 10, comprising: locating a mask having at least one opening over the front surface; growing the further diamond material over the mask such that further diamond material is grown in a selected area over the front surface; removing the mask; growing second further diamond material over the front surface; and processing back the second further diamond material over the front surface of the synthetic diamond substrate to form the sensing surface.

13. The method according to claim 10, wherein the quantum spin defects are selected from any of: negatively charged nitrogen-vacancy defects, NV.sup.−; silicon containing defects; nickel containing defects; chromium containing defects; germanium containing defects; tin containing defects; and nitrogen containing defects.

14. A microfluidic cell comprising: a microfluidic channel for receiving a fluid sample; and a sensor located adjacent the microfluidic channel; wherein the sensor comprises the synthetic diamond material according to claim 1.

15. A magnetometry sensing probe comprising the synthetic diamond material according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Non-limiting example arrangements to illustrate the present disclosure are described hereafter with reference to the accompanying drawings, of which:

(2) FIG. 1 is a flow diagram showing steps for fabricating a synthetic diamond material;

(3) FIG. 2 is a flow diagram showing steps for fabricating a synthetic diamond material according to a first exemplary embodiment;

(4) FIG. 3 illustrates schematically a side elevation cross-section view of an etched diamond substrate;

(5) FIG. 4 illustrates schematically a plan view of the etched diamond substrate of FIG. 4;

(6) FIG. 5 illustrates schematically a side elevation cross-section view of a further diamond material grown on the diamond substrate;

(7) FIG. 6 illustrates schematically a side elevation cross-section view of a further diamond material grown on the diamond substrate after processing;

(8) FIG. 7 illustrates schematically a plan view of the diamond material of FIG. 6 after processing;

(9) FIG. 8 is a UV illuminated photograph showing an exemplary diamond material;

(10) FIG. 9 is a side elevation view of a further exemplary embodiment in which a third diamond layer is provided; and

(11) FIG. 10 illustrates schematically a plan view of the diamond material of FIG. 9.

(12) FIG. 11 is a side elevation view of a still further exemplary embodiment; and

(13) FIG. 12 illustrates schematically a plan view of the diamond material of FIG. 11;

(14) FIG. 13 is a flow diagram showing steps for fabricating a synthetic diamond material according to a further exemplary embodiment;

(15) FIG. 14 illustrates schematically a side elevation cross-section view of a diamond substrate and a mask;

(16) FIG. 15 illustrates schematically a side elevation cross-section view of the diamond substrate and mask of FIG. 14, with further diamond material grown in openings in the mask;

(17) FIG. 16 illustrates schematically a side elevation cross-section view of the diamond substrate of FIG. 15, with the mask removed;

(18) FIG. 17 illustrates schematically a side elevation cross-section view of the diamond substrate of FIG. 16, with further diamond material grown on the surface;

(19) FIG. 18 illustrates schematically a side elevation cross-section view of the diamond substrate of FIG. 17 after processing; and

(20) FIG. 19 illustrates schematically a side elevation cross-section view of a microfluidic cell.

DETAILED DESCRIPTION

(21) As described above, known diamond materials with high numbers of quantum spin defects can be used as sensors. However, more sensor functionality and resolution could be achieved by forming a diamond material with predetermined regions of a diamond material having a higher concentration of quantum spin defects than the surrounding regions. These regions of high concentration quantum spin defects can be formed in patterns as required. The inventors have developed techniques for forming such regions.

(22) The following description refers to high concentrations of NV− defects by way of example, but it will be appreciated that the same or similar techniques can be used for forming 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.

(23) FIG. 1 is a flow diagram showing exemplary steps for forming a diamond material that has regions containing at least ten times the concentration of NV.sup.− defects than the surrounding regions. The following numbering corresponds to that of FIG. 1: S1. A synthetic diamond substrate is provided. This may be CVD, HPHT, or another form of synthetic diamond. S2. Further diamond is grown using a CVD on a front surface of the substrate. S3. The surface is then processed 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, the second surface region having a second quantum spin defect concentration, wherein the first quantum spin defect concentration is at least ten times greater than the second concentration of quantum spin defects. This further processing may also include irradiation and annealing steps.

(24) FIG. 2 is a flow diagram showing exemplary steps for a first exemplary embodiment. The following numbering corresponds to that of FIG. 2: S4. A synthetic diamond substrate is provided. This may be CVD, HPHT, or another form of synthetic diamond. S5. A pattern of depressions is formed in a planar front surface of the synthetic diamond substrate. Exemplary ways of forming such depressions include etching using a mask, grinding selected areas, polishing selected areas and so on. FIG. 3 is a schematic side elevation cross-section view of an exemplary synthetic diamond substrate 1, and FIG. 4 is a schematic plan view of the same diamond substrate 1. A circle 2 and two concentric rings 3, 4 have been etched into the surface 5 of the synthetic diamond substrate 1 to different depths using masked etching. The depth of the depression may vary between around 100 nm and 100 μm. The depressions shown in FIG. 3 have 90° corners when viewed in cross-section. It will be appreciated that other shapes such as curved corners, chamfered corners, or V-shaped depressions may be used as these may give improved overgrowth of further diamond in the following step S6. S6. Using a CVD process, a further diamond material is grown onto the planar front surface 5 of the synthetic diamond material. The further diamond material is grown under conditions to provide a concentration of NV.sup.− defects at least ten times higher than that the concentration of NV.sup.- defects in the synthetic diamond substrate. FIG. 5 illustrates schematically a side elevation cross section view of the synthetic diamond substrate of FIGS. 3 and 4 after overgrown of the further diamond material 6 onto the synthetic diamond substrate 1. Further diamond material 6 has grown in the depressions 2, 3, 4 in the synthetic diamond substrate 1 and also in a layer on the planar front surface 5 of the synthetic diamond material 1. S7. The resultant composite diamond material is processed back to remove excess further diamond material 6. Processing may be performed using standard techniques, such as polishing, grinding, mechanical polishing and etching. FIG. 6 illustrates schematically a side elevation cross section view of the diamond substrate 1 after the further diamond has been processed back. FIG. 7 illustrates schematically in plan view the same material as FIG. 6. 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 regions of further diamond material have an NV.sup.− concentration of at least ten times higher than that of the surrounding synthetic diamond substrate 1.

(25) Using the techniques described above, a diamond material can be produced that has regions of high concentration of quantum spin defects surrounded by regions of lower concentration of quantum spin defects. Such materials can be used in sensing applications such as wide field imaging based on magnetic field sensing.

Example 1

(26) A single crystal diamond substrate was provided with dimensions of 3×3×0.5 mm and a nitrogen concentration of 1.5 ppb. A mask was placed over a growth surface of substrate and the growth surface was selectively etched using inductively coupled plasma etching. This was performed using Ar and Cl feed gases, although it will be appreciated that oxygen could be used. The etching formed a depression pattern in the growth surface of the substrate. The skilled person will appreciate that other methods could be used to form 10 μm depressions, for example, grinding, machining, chemical-mechanical polishing and so on.

(27) The etched diamond substrate was then placed in a vacuum chamber and a surface cleaning etch was performed using a hydrogen plasma.

(28) The etched diamond substrate was placed in a CVD reactor chamber and further diamond was grown on the substrate to a thickness greater than the depth of the etched depression pattern. The further diamond was grown using the following conditions: Microwave power=5 kW Pressure=230 Torr Hydrogen Flow Rate=600 sccm Methane Flow Rate=30 sccm Nitrogen dopant=60 sccm of 1000 ppm N.sub.2 in H.sub.2

(29) The level of nitrogen doping was selected to be relatively high to ensure that the further diamond was grown with a much higher NV.sup.− concentration than that of the diamond substrate.

(30) The further diamond was then polished back using mechanical polishing to remove a surface layer of the further diamond, to leave a structure similar to that shown in FIGS. 4 and 5, in which at the surface of the diamond material, there were regions of high nitrogen diamond 7, 8, 9 and low nitrogen diamond 1.

(31) Parameters such as the nitrogen level can be varied according to the desired nitrogen concentration in the final product. Optionally, oxygen, CO or CO.sub.2 can also be added to the growth process. After growth, the single crystal diamond material was treated using an irradiation and annealing process. This involved irradiating the material for six hours under an electron flux of 3×10.sup.14 cm.sup.−2 s.sup.−1 and annealing at 400° C. for 4 hours, 800° C. for 16 hours and then 1200° C. for 2 hours. This process converts nitrogen in the diamond into NV.sup.− centres, making them useful as quantum spin defects.

Example 2

(32) FIG. 8 is a photograph of a synthetic diamond material made in the same way as that described above in FIG. 1, but using a different pattern of regions of higher concentrations of NV.sup.− defects. As the material is optically pumped using UV excitation, the regions containing a higher concentration of NV.sup.− defects fluoresce.

Example 3

(33) As a further exemplary embodiment, further layers can be deposited onto the diamond material. Referring to FIGS. 9 and 10, the diamond material of FIGS. 6 and 7 has been further processed.

(34) A third diamond layer 10 having a low nitrogen content (1.5 ppb) was grown onto the surface 11 of the synthetic diamond substrate material 1.

(35) A mask was placed over 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 will be appreciated that oxygen could be used. The etching formed a depression pattern in the growth surface of the substrate. The skilled person will appreciate that other methods could be used to form depressions, for example, grinding, machining, chemical-mechanical polishing and so on.

(36) The etched third diamond layer 10 was then cleaned in a hydrogen plasma as described in Example 1.

(37) The etched third diamond layer was then placed in a CVD reactor chamber and additional diamond was grown on the substrate to a thickness greater than the depth of the etched depression pattern. The additional diamond was grown using the following conditions: Microwave power=3.6 kW Pressure=140 Torr Hydrogen Flow Rate=600 sccm Methane Flow Rate=32 sccm B.sub.2H.sub.6 Flow Rate=19 sccm

(38) The addition of boron was to ensure that the additional diamond had a boron content sufficient to form an electrically conductive synthetic diamond.

(39) The additional diamond was then polished back using mechanical polishing to remove a surface layer of the additional diamond, to leave a structure similar to that shown in FIGS. 8 and 9. The surface of the third diamond layer 10 contains a region of boron doped diamond 11 in the form of a ring. This region 11 is conductive, and so can be used to apply an electric field in proximity to the regions of further diamond 7, 8, 9 that have a high concentration of quantum spin defects. The conductive region 11 may also be used as a way of generating microwaves.

Example 4

(40) As an alternative to Example 3, the boron-doped third diamond layer can be disposed in the same plane as the further diamond of Example 1. This is shown in FIGS. 11 and 12. In this instance, a material is made in the same way as described above in example 1. A mask is then placed over the surface of the diamond material, and a pattern is etched into the surface. The mask is removed, leaving a surface with an etched depression. A third diamond material is then overgrown on the surface and into the depression. The third diamond material in this example is doped with boron. The new surface was then polished back to leave a structure as shown in FIGS. 11 and 12.

(41) The resultant surface comprises surface regions 7, 8, 9 having a high concentration of quantum spin defects, and a surface region 12 having boron doped diamond.

(42) The above embodiments and examples describe one way to obtain a synthetic diamond material with a surface comprising a first surface region comprising a first concentration of quantum spin defects and a second surface region having a predetermined area and located adjacent to the first surface region. An alternative technique is shown in FIG. 13. The following numbering corresponds to that of FIG. 13: S8. A synthetic diamond substrate 13 is provided. This may be CVD, HPHT, or another form of synthetic diamond. S9. Referring to FIG. 14, a mask 14 having at least one opening 15 is located over a surface of 1 synthetic diamond substrate 13. S10. Further diamond material 16 is grown over the mask 14 and fills the openings of the mask 14, as shown in FIG. 15. The further diamond material has a higher nitrogen concentration than the synthetic diamond substrate 13. S11. The mask 14 is removed, to leave a synthetic diamond substrate with protruding growths of further diamond 16, as shown in FIG. 16. S12. Diamond material 16 (in this example corresponding to the diamond material of the synthetic diamond substrate 13) is then grown onto the diamond substrate 13, as shown in FIG. 17. S13. The new surface of the diamond material 16 is processed back using any suitable means to form a structure as shown in FIG. 18, in which the surface comprises regions 15 of diamond material containing a higher nitrogen content adjacent regions 16 of diamond material with a lower nitrogen content. Subsequent irradiation and annealing may be used to transform nitrogen in the diamond material to NV.sup.− centres.

(43) Using the techniques described above, a diamond material can be produced that has regions of high concentration of quantum spin defects surrounded by regions of lower concentration of quantum spin defects. Such materials can be used as sensing probes in sensing applications such as wide field imaging based on magnetic field sensing.

(44) Another exemplary use for the synthetic diamond material is in microfluidic sensing. FIG. 19 illustrates schematically an exemplary microfluidic cell 17 comprising diamond material 13 with regions 16 of diamond having a high concentration of quantum spin defects. The microfluidic cell comprises channels 18 adjacent to regions 16 of diamond having a high concentration of quantum spin defects, and can be used to analyse fluids. A discussion and description of microfluidic sensing using quantum spin defects in diamond may be found in WO 2012/034924.

(45) The invention as set out in the appended claims has been shown and described with reference to embodiments. However, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.