CVD single crystal diamond

Abstract

A method of processing a CVD single crystal diamond, the method comprises providing a CVD single crystal diamond with a minimum lateral dimension of at least 20 mm, the CVD single crystal diamond further comprising a major surface. The major surface is processed using a diamond-matrix wheel, the diamond-matrix wheel comprising embedded diamond particles embedded in a matrix. There is also provided a CVD single crystal diamond having a largest linear dimension of at least 20 mm and a major surface, the major surface having a surface roughness Sa of less than 1 nm over at least 90% of the major surface.

Description

[0001] CVD SINGLE CRYSTAL DIAMOND

[0002] FIELD OF THE INVENTION

[0003] The invention relates to the field of CVD single crystal diamond, and to methods of processing CVD single crystal diamond.

[0004] BACKGROUND

[0005] Diamond materials may be categorized into three main types: natural diamond materials; HPHT (high pressure high temperature) synthetic diamond materials, and CVD (chemical vapour deposited) synthetic diamond materials. These categories reflect the way in which the diamond materials are formed. Furthermore, these categories reflect the structural and functional characteristics of the materials. This is because while natural, HPHT synthetic, and CVD synthetic diamond materials are all based on a theoretically perfect diamond lattice the defects in these materials are not the same. For example, CVD synthetic diamond contains many defects unique to the process of CVD, and whilst some defects are found in other diamond forms, their relative concentration and contribution is very different. As such, CVD synthetic diamond materials are different to both natural and HPHT synthetic diamond materials.

[0006] Diamond materials may also be categorized according to their physical form. In this regard, diamond materials may be categorized into three main types: single crystal diamond materials; polycrystalline diamond materials; and composite diamond materials. Single crystal diamond materials are in the form of individual single crystals of various sizes ranging from small “grit” particles used in abrasive applications through to large single crystals suitable for use in a variety of technical applications as well for gemstones in jewellery applications. Polycrystalline diamond materials are in the form of a plurality of small diamond crystals bonded together by diamond-to-diamond bonding to form a polycrystalline body of diamond material such as a polycrystalline diamond wafer. Such polycrystalline diamond materials can be useful in various applications including thermal management substrates, optical windows, and mechanical applications. Composite diamond materials are generally in the form of a plurality of small diamond crystals bonded together by diamond-to-diamond or a non-diamond matrix to form a body of composite material. Various diamond composites are known including diamond containing metal matrix composites, particularly cobalt metal matrix composites known as polycrystalline diamond (PCD), and skeleton cemented diamond (ScD) which is a composite comprising silicon, silicon carbide, and diamond particles. It should also be appreciated that within each of the aforementioned categories there is much scope for engineering diamond materials to have particular concentrations and distributions of defects in order to tailor diamond materials to have particular desirable properties for particular applications. The present disclosure is concerned with CVD single crystal synthetic diamond materials.

[0007] CVD processes for synthesis of diamond material are well known. Being in the region where diamond is metastable compared to graphite, synthesis of diamond under CVD conditions is driven by surface kinetics and not bulk thermodynamics. Diamond synthesis by CVD is normally performed using a small fraction of carbon (typically <5%), in the form of a carbon containing gases, in an excess of molecular hydrogen. If molecular hydrogen is heated to temperatures in excess of 2000 K, there is a significant dissociation to atomic hydrogen. In the presence of a suitable substrate material, CVD synthetic diamond material can be deposited. Polycrystalline CVD diamond material may be formed on a non-diamond substrate such as a refractory metal or silicon substrate. Single crystal CVD synthetic diamond material may be formed by homoepitaxial growth on a single crystal diamond substrate.

[0008] Atomic hydrogen present in the process selectively etches off non-diamond carbon from the substrate such that diamond growth can occur. Various methods are available for heating carbon containing gas species and molecular hydrogen in order to generate the reactive carbon containing radicals and atomic hydrogen required for CVD synthetic diamond growth including arc-jet, hot filament, DC arc, oxy-acetylene flame, and microwave plasma.

[0009] A problem with prior art methodologies is how to achieve large area single crystal CVD synthetic diamond material. It has been found that large area single crystal diamond can be grown by a process known as “heteroepitaxial growth”. This is where diamond nucleates and grows epitaxially on a non-diamond substrate. Iridium has been found to be a suitable substrate to allow diamond nucleation and growth, but other substrates such as silicon, silicon carbide, copper, nickel, rhenium and titanium carbide have been investigated. US 7,396,408 describes such a process. In this case, diamond is grown in a CVD process using a silicon carbide, sapphire, or silicon single crystal wafer that has a layer of iridium deposited on its surface. This is used as a substrate on which to heteroepitaxially deposit and grow diamond. During the growth process, diamond crystallites nucleate on the iridium film. These crystallites grow and merge to form a single crystal layer, which is continued until a single crystal diamond wafer of the desired thickness is formed. Typically the dislocation density reduces via dislocation interactions (fusion and annihilation) as growth proceeds, leading to a single crystal diamond wafer that has a higher dislocation density adjacent to the original nucleation face compared to the growth face.

[0010] For large area CVD single crystal diamond, some applications require a very low surface roughness. Such applications include optical windows, heat spreader that require a good thermal contact, or if the surface is to be used to homoepitaxially grow a further layer of single crystal diamond.

[0011] Typically, diamond surfaces are prepared by scaife polishing, a technique in which the diamond surface is brought into contact with a rotating iron or iron-based disc and pressure applied. Further surface processing often includes an oxygen plasma etch.

[0012] SUMMARY

[0013] A problem with scaife polishing is that it is only suitable for single crystal diamond with relatively small dimensions. A problem with oxygen plasma etching is while it can reduce sub-surface damage, it can increase the roughness of the surface.

[0014] An object of the invention is to provide a CVD single crystal diamond with a relatively large surface area and a relatively low surface roughness.

[0015] According to a first aspect, there is provided a method of processing a CVD single crystal diamond, the method comprising: providing a CVD single crystal diamond with a minimum lateral dimension of at least 20 mm, the CVD single crystal diamond further comprising a major surface; processing the major surface using a diamond-matrix wheel, the diamond-matrix wheel comprising embedded diamond particles embedded in a matrix.

[0016] As an option, the method further comprises applying a treatment to the major surface to reduce subsurface damage at the major surface without substantially increasing surface roughness.

[0017] As a further option, the treatment comprises inductively couple plasma, ICP, etching.

[0018] As an alternative option, the treatment comprises chemical mechanical polishing, CMP. The diamond-matrix wheel optionally has a surface roughness of Ra of less than 2 pm.

[0019] The method optionally further comprises, prior to processing the major surface using the diamond-matrix wheel, conditioning the diamond-matrix wheel to control its surface roughness.

[0020] The conditioning optionally comprises using the diamond-matrix wheel to process a sacrificial part, the sacrificial part comprising a superhard material.

[0021] The superhard material optionally comprises any of diamond, polycrystalline diamond PCD, and polycrystalline cubic boron nitride.

[0022] The method optionally further comprises in a CVD reactor, homoepitaxially growing further diamond on the major surface of the CVD single crystal diamond.

[0023] According to a second aspect, there is provided a CVD single crystal diamond having a largest linear dimension of at least 20 mm and a major surface, the major surface having a surface roughness Sa of less than 1 nm over at least 90% of the major surface.

[0024] As an option, the surface roughness Sa is selected from any of less than 0.8 nm, less than 0.6 nm, less than 0.4 nm, and less than 0.2 nm.

[0025] As an option, the CVD single crystal diamond has a surface roughness Ra selected from any of less than 1 nm, less than 0.8 nm, less than 0.6 nm, less than 0.4 nm, and less than 0.2 nm.

[0026] As an option, the major surface has a surface roughness Sa of less than 1 nm an area of the major surface selected from any of least 95%, at least 98% and at least 99%.

[0027] As an option, the largest linear dimension is selected from any of at least 50 mm, at least 75 mm, at least 100 mm and at least 120 mm.

[0028] The CVD single crystal diamond optionally further has a thickness selected from any of at least 100 pm, at least 500 pm, at least 1 mm, at least 2 mm and at least 4 mm. Optionally, the major surface has an average surface dislocation density over at least 90% of the major surface selected from any of no more than 105cm-2, no more than 5 x 104cm-2, no more than 104cm-2, no more than 5 x 103cm-2and no more than 103cm-2.

[0029] The CVD single crystal diamond optionally further comprises a single substitutional nitrogen concentration as measured by electron paramagnetic resonance (EPR) of at least 1x1013atoms cm-3and no more than 5x1018cnv3. As a further option, the single substitutional nitrogen concentration as measured by electron paramagnetic resonance (EPR) is at least 3x1015atoms cm-3and no more than 5x1017cnv3.

[0030] As an option, the major surface of the CVD single crystal diamond is oriented within 10° of a {100} crystallographic plane.

[0031] As an alternative option, the major surface of the CVD single crystal diamond is oriented within 10° of a {111} crystallographic plane.

[0032] The CVD single crystal diamond optionally displays SiV' luminescence, quantified by a ratio of a total peak area of the SiV' zero-phonon lines to a peak area of the first-order diamond Raman signal in a photoluminescence measurement performed at a temperature of 77 K using an excitation wavelength of 660 nm, selected from any of less than 1.0, less than 0.5; less than 0.1 ; less than 0.05; and less than 0.01.

[0033] The CVD single crystal diamond optionally comprises at least two discrete layers.

[0034] According to a third aspect, there is provided a device comprising the CVD single crystal diamond described above in the second aspect.

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

[0037] Figure 1 is a flow diagram illustrating exemplary steps in processing a CVD single crystal diamond;

[0038] Figure 2 illustrates schematically a side elevation of a diamond-matrix wheel before and after wheel conditioning; Figures 3a and 3b are scanning electron micrographs showing a surface of a diamondmatrix wheel before and after wheel conditioning;

[0039] Figures 4a and 4b are atomic force microscope, AFM, images of single crystal diamond with a processed surface; and

[0040] Figure 5 is an optical micrograph of a surface of a grown diamond showing surface defects.

[0041] The figures are not drawn to scale. Throughout the description, similar parts have been assigned the same reference numerals, and a detailed description is omitted for brevity.

[0042] DETAILED DESCRIPTION

[0043] The inventors have developed a technique in which large area CVD single crystal diamond can be processed to have a major surface with a roughness below 1 nm. Figure 1 is a flow diagram setting out exemplary steps. The following numbering corresponds to that of Figure 1 :

[0044] S1 . A CVD single crystal diamond is provided that has at least one lateral dimension of least 25 mm. One way to achieve this is to heteroepitaxially grow diamond in a CVD process as described in US 7,396,408.

[0045] The largest linear dimension may be at least 50 mm, at least 75 mm, at least 100 mm and at least 120 mm. Such large areas can be achieved using heteroepitaxial growth, as described above, or any other techniques such as tiling a plurality of substrates together before growth.

[0046] The thickness of the CVD single crystal diamond depends on the final use. Thickness as low as 100 pm may be useful if the diamond is to be used as a substrate for further homoepitaxial growth of single crystal diamond material. Thicknesses of 4 mm and above may be used if the CVD single crystal diamond is to be used directly in an application, such as an optical window or a heat spreader.

[0047] The crystallographic orientation of the diamond may also be important for some applications. The major surface of the CVD single crystal diamond may be oriented within 10° of a {100} crystallographic plane, or 10° of a {111} crystallographic plane. Other orientations are possible but {100} and {111} are the most common. S2. A major surface of the single crystal diamond is processed using a diamondmatrix wheel, the diamond-matrix wheel comprising diamond particles embedded in a matrix. Processing is performed until a surface roughness Sa over at least 90% of the area of the major surface is below 1 nm. It is difficult to get a low surface roughness over 100% of the area, because edge and corner effects can have a detrimental effect on the roughness. However, surface roughness as low as 0.2 nm have been achieved over 99% of the area of the major surface.

[0048] Similar values of Ra roughness have also been measured using interferometry.

[0049] There are several different techniques for measuring surface roughness. In this document, Ra and Sa are both referred to.

[0050] An Ra measurement is described in the ISO 4287:1997 standard and is based on the mean line system. A mean line is taken and the amplitude of the surface with respect to the mean line is measured. This can be done, for example, using white light interferometry. Ra is an arithmetic mean profile height.

[0051] An Sa measurement is obtained not across a mean line over the surface, but over the entire area. It is defined in the ISO 25178 series of standards. Sa is an extension of Ra and expresses the difference in height of each measured point of the surface compared to the arithmetical mean of the surface. In this work, Sa roughness values were obtained using an atomic force microscope (AFM). Measuring surface roughness using an atomic force microscope (AFM) involves scanning the surface of a sample with a sharp tip and recording the variations in height as the tip moves across the surface. The skilled person will understand how to adjust imaging parameters such as scan size, scan rate, and setpoint (the desired force between the tip and the sample). The tip is brought close to the sample surface without making contact and a scan is performed over the area of interest. The AFM moves the tip laterally across the sample while simultaneously recording the height variations. Note that other techniques such as white light interferometry can be used to measure surface roughness.

[0052] The term “diamond-matrix wheel” is used to denote a wheel that comprises a matrix containing embedded diamond particles. Examples of matrixes include a metal matrix, a vitrified matrix and a resinoid matrix. 53. In some cases, it is desirable to provide a further processing step to reduce subsurface damage. This may be, for example, an inductively coupled plasma (ICP) etch or chemical mechanical polishing (CMP). ICP etching is described in Mildren and Rabeau, Optical Engineering of Diamond, Wiley-VCH 2013 page 130. CMP processing may be performed, for example, using a Logitech™ Tribo CMP system.

[0053] This kind of treatment is important where the CVD single crystal diamond is to be used as a substrate for further homoepitaxial growth of diamond on its major surface. During homoepitaxial growth, subsurface damage and defects such as dislocations at the growth surface often propagate into the grown diamond, so it is important to reduce the subsurface damage as much as possible.

[0054] If the CVD single crystal diamond is to be used as a substrate, it is also desirable to use one with a surface dislocation density of no more than 105cm-2, no more than 5 x 104cm-2, no more than 104cm-2, no more than 5 x 103cm-2and no more than 103cm-2.

[0055] 54. The method according to any one of claims 1 to 8, further comprising in a CVD reactor, homoepitaxially growing further diamond on the major surface of the CVD single crystal diamond. In this instance, the resultant diamond typically has a two-layer structure, with a growth interface between the CVD single crystal diamond and the homoepitaxially grown further CVD single crystal diamond. These layers need not have an identical chemical composition. For example, the CVD single crystal diamond may be used as a substrate for growing diamond with a low nitrogen content, or doped with boron or other desirable dopants for achieving particular properties. It is possible for the two layers of CVD single crystal to be separated, for example by grinding off one layer, thin cutting, or using a lift-off process using ion implantation and electrochemical etching. For large area samples, lift off and grinding processes may be more suitable.

[0056] Turning now to Figure 2, it has been found that conditioning of the diamond-matrix wheel prior to use can further reduce the surface roughness of the CVD single crystal diamond. Figure 2a illustrates schematically a side elevation cross section of a diamond-matrix wheel. It can be seen that sharp diamond grains protrude from the surface of the diamond-matrix. After conditioning, as shown in Figure 2b, these diamond grains become blunted. Figures 3a and 3b show a surface of a diamond-matrix wheel before and after wheel conditioning. The diamond-matrix wheel is conditioned by using it to process sacrificial parts. These sacrificial parts include a superhard material such as diamond, polycrystalline diamond (PCD) produced using a high temperature high pressure process, or polycrystalline cubic boron nitride (PCBN). This processing reduced the surface roughness of the diamondmatrix wheel.

[0057] The degree of conditioning can be assessed by measuring the surface roughness of the diamond-matrix wheel. A roughness Ra of less than 2 pm, or less than 1.5 pm is suitable for achieving a roughness Sa of less than 1 nm on the CVD single crystal diamond surface. The appearance of the diamond-matrix wheel also changes, going from a rough appearance to a smooth, shiny appearance. The diamond-matrix wheel is sometimes termed as “glazed” after conditioning.

[0058] Example

[0059] A diamond-matrix grinding wheel supplied by DK Holdings™ Limited and comprising diamond grits with an average particle diamond size of 33 pm embedded in a resinoid matrix was provided. The surface roughness Ra of the diamond-matrix wheel was 3 pm. The wheel was conditioned by polishing a sacrificial HPHT PCD diamond part with a pressure of greater than 50 kPa and a rotation speed of 3000 rpm for more than 48 hours until the surface roughness Ra of the diamond-matrix was reduced to below 1.5 pm.

[0060] A diamond-matrix grinding wheel comprising diamond grits with an average diamond particle size of 76 pm was conditioned in the same way as the 33 pm diamond-matrix wheel. A standard, unconditioned 76 pm wheel was also provided.

[0061] Various roughness measurements were taken from the surface of the diamond-matrix grinding wheel, as shown in Table 1 :

[0062] Table 1

[0063] As described above, Ra is an average surface roughness value, the mean deviation. Rz is a measure of the maximum peak to valley height. Rsk is a skewness parameter where positive values indicate a surface dominated by peaks and asperities, whilst a negative value is valley dominated.

[0064] Diamond grit particles are typically measured using the well-known mesh system by passing diamond grits through a series of screens with increasingly finer mesh sizes. Particles stopped by a screen of a particular mesh were measured by that mesh number. The mesh number can be easily converted to pm.

[0065] The 33 pm wheel was used to process a major surface of a CVD single crystal diamond having lateral dimensions of 30 x 30 mm and a thickness of 500 pm. The processing was at a diamond-matrix wheel speed of between 1000 and 2000 rpm, and a load of between 10 kPa and 28 kPa for 48 hours.

[0066] Figures 4a and 4b show AFM, images of the CVD single crystal diamond with a processed surface. Figure 4a shows the surface of a CVD single crystal diamond processed using a standard 76 pm diamond-matrix wheel. The roughness Sa of the major surface of the CVD single crystal diamond was found to be under 1 nm. Figure 4b shows the surface of a CVD single crystal diamond processed using a conditioned 33 pm diamond-matrix wheel. The roughness Sa of the major surface of the CVD single crystal diamond was found to be less than 0.2 nm over substantially the whole surface area.

[0067] The CVD single crystal diamond processed using the conditioned 33 pm diamond-matrix wheel was then subjected to an ICP etch to reduce subsurface damage. The ICP etch was applied to the surface of the diamond using ICP / RF power of 500 W 1200 W for 50 minutes using a platen temperature of 5 °C and in an atmosphere of Ar (10 seem) and Ch (20 seem). A portion of the surface of the diamond is shown in Figure 5, which had a dislocation density measured at the surface of around 105cm-2.

[0068] The CVD single crystal diamond was then placed into a CVD reactor for use as a substrate on which to homoepitaxially grow further CVD single crystal diamond. In order to grow the further CVD single crystal diamond, process gases are fed into the CVD reactor. Such process gases typically include a carbon-containing gas such as methane, and hydrogen. A plasma is formed from the gases and the further CVD single crystal diamond grows on the buffer layer. CVD synthesis conditions are typically controlled such that the CVD single crystal diamond substrate is held at a desired temperature (typically between 800°C and 1200°C). If the temperature is too low, then growth rates are low. An upper limit to the growth temperature of 1200°C is generally required to avoid detrimental defect formation in the homoepitaxially grown diamond material such as twins. Furthermore, the temperature, in combination with other parameters such as carbon containing gas concentration, affects the morphology of the homoepitaxially grown diamond material and thus can be selected and controlled to achieve a desired morphology.

[0069] CVD synthesis conditions are also typically controlled such that a CVD synthesis atmosphere comprises a carbon containing gas (e.g. methane) at a concentration by volume in a range 3 to 8%, more preferably in a range 4 to 6%. If the carbon containing gas concentration is too low, then growth rates are too low. If the carbon containing gas concentration is too high, then cracking may occur and / or the material may have a poor optical quality. Furthermore, as previously stated, carbon containing gas concentration, in combination with other parameters such as the CVD single crystal diamond substrate temperature, affects the morphology of homoepitaxially grown diamond material and thus is selected and controlled to achieve the desired morphology close to net shape of the final processed product.

[0070] CVD synthesis conditions are further controlled to provide a high power density across the substrate of at least 150 W / cm2, 180 W / cm2, 200 W / cm2, 230 W / cm2, 250 W / cm2, 270 W / cm2, 290 W / cm2, 310 W / cm2, or 330 W / cm2. The power density will generally be less than 600 W / cm2, 500 W / cm2, or 400 W / cm2. In the context of this specification, power density is defined as the total microwave input power divided by the area of the substrate, or the substrate holder, whichever has the greater area.

[0071] CVD synthesis conditions are further controlled to achieve a further CVD single crystal diamond growth rate selected from any of at least 4 pm per hour, at least 5 pm per hour, at least 10 pm per hour and at least 15 pm per hour until it reaches a descried thickness.

[0072] If required, a surface processing operation is performed on the further CVD single crystal diamond to reduce surface damage. Examples of processing techniques include one or more of cutting, cleaving, lapping, polishing, scaife polishing and / or etching. This may reduce any surface roughness that arises during the growth process. While this invention has been particularly shown and described with reference to embodiments, 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.

Claims

CLAIMS:1 . A method of processing a CVD single crystal diamond, the method comprising: providing a CVD single crystal diamond with a minimum lateral dimension of at least 20 mm, the CVD single crystal diamond further comprising a major surface; processing the major surface using a diamond-matrix wheel, the diamond-matrix wheel comprising embedded diamond particles embedded in a matrix.

2. The method according to claim 1 , further comprising applying a treatment to the major surface to reduce subsurface damage at the major surface without substantially increasing surface roughness.

3. The method according to claim 2, wherein the treatment comprises inductively couple plasma, ICP, etching.

4. The method according to claim 2, wherein the treatment comprises chemical mechanical polishing, CMP.

5. The method according to any one of claims 1 to 4, wherein the diamond-matrix wheel has a surface roughness of Ra of less than 2 pm.

6. The method according to claim 5, further comprising, prior to processing the major surface using the diamond-matrix wheel, conditioning the diamond-matrix wheel to control its surface roughness.

7. The method according to claim 6, wherein the conditioning comprises using the diamond-matrix wheel to process a sacrificial part, the sacrificial part comprising a superhard material.

8. The method according to claim 7, wherein the superhard material comprises any of diamond, polycrystalline diamond PCD, and polycrystalline cubic boron nitride.

9. The method according to any one of claims 1 to 8, further comprising in a CVD reactor, homoepitaxially growing further diamond on the major surface of the CVD single crystal diamond.

10. A CVD single crystal diamond having a largest linear dimension of at least 20 mm and a major surface, the major surface having a surface roughness Sa of less than 1 nm over at least 90% of the major surface.

11. The CVD single crystal diamond according to claim 10, wherein the surface roughness Sa is selected from any of less than 0.8 nm, less than 0.6 nm, less than 0.4 nm, and less than 0.2 nm.

12. The CVD single crystal diamond according to claim 10 or claim 11 , further comprising a surface roughness Ra selected from any of less than 1 nm, less than 0.8 nm, less than 0.6 nm, less than 0.4 nm, and less than 0.2 nm.

13. The CVD single crystal diamond according to any one of claims 10 to 12, wherein the major surface having a surface roughness Sa of less than 1 nm an area of the major surface selected from any of least 95%, at least 98% and at least 99%.

14. The CVD single crystal diamond according to any one of claims 10 to 13, wherein the largest linear dimension is selected from any of at least 50 mm, at least 75 mm, at least 100 mm and at least 120 mm.

15. The CVD single crystal diamond according to any one of claims 10 to 14, further comprising a thickness selected from any of at least 100 pm, at least 500 pm, at least 1 mm, at least 2 mm and at least 4 mm.

16. The CVD single crystal diamond according to any one of claims 10 to 15, wherein the major surface has an average surface dislocation density over at least 90% of the major surface selected from any of no more than 105cm-2, no more than 5 x 104cm-2, no more than 104cm-2, no more than 5 x 103cm-2and no more than 103cm-2.

17. The CVD single crystal diamond according to any one of claims 10 to 16, further comprising a single substitutional nitrogen concentration as measured by electron paramagnetic resonance (EPR) of at least 1x1013atoms cm-3and no more than 5x1018crrr3.

18. The CVD single crystal diamond according to claim 17, wherein the single substitutional nitrogen concentration as measured by electron paramagnetic resonance (EPR) of at least 3x1015atoms cm-3and no more than 5x1017crrr3.

19. The CVD single crystal diamond according to any one of claims 10 to 18, wherein the major surface of the CVD single crystal diamond is oriented within 10° of a {100} crystallographic plane.

20. The CVD single crystal diamond according to any one of claims 10 to 18, wherein the major surface of the CVD single crystal diamond is oriented within 10° of a {111} crystallographic plane.21 . The CVD single crystal diamond according to any one of claims 10 to 20, wherein the CVD single crystal diamond displays SiV' luminescence, quantified by a ratio of a total peak area of the SiV' zero-phonon lines to a peak area of the first-order diamond Raman signal in a photoluminescence measurement performed at a temperature of 77 K using an excitation wavelength of 660 nm, selected from any of less than 1 .0, less than 0.5; less than 0.1 ; less than 0.05; and less than 0.01.

22. The CVD single crystal diamond according to any one of claims 10 to 21 , wherein the CVD single crystal diamond comprises at least two discrete layers.

23. A device comprising the CVD single crystal diamond according to any one of claims 10 to 22.

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