GB2492822A - Modifying diamond components by irradiation - Google Patents

Abstract

A method of forming a diamond material with a defined vacancy density is disclosed where the method comprises the irradiation of diamond to yield vacancy point defects having a concentration in a range 1 x 1014 to 1 x 1021 vacancies/cm3. The radiation used could be electrons, neutrons, X-rays, gamma rays, protons or alpha particles. An apparatus is disclosed comprising: a diamond component; a mounting for supporting said diamond component; and a controller configured to control one or more functional parameters of the apparatus, wherein the apparatus is configured such that in normal use the diamond component is subjected to thermal, mechanical or electromagnetic stress but substantially no abrasive wear, and wherein the diamond component is formed of at least one portion of irradiated diamond material. Further disclosed is the use of irradiation to increase the crack resistance of diamond.

Description

DIAMOND COMPONENTS FOR NON-WEAR APPUCATIONS

Field of Invention

The present invention relates to diamond components for non-wear applications, apparatus comprising such diamond components and methods of manufacturing such components and apparatus.

Background of Invention

Diamond materials are the materials of choice for many premium performance wear applications such as cutting, drilling, grinding and polishing tools. Diamond materials are used in tooling solutions across a range of industries including a variety of metal, stone and woodworking industries. Examples include aerospace and automotive manufacturing, furniture production, stone quarrying, construction, mining and tunnelling, mineral processing, and the oil and gas industries.

Diamond's hardness properties make it the ultimate material in terms of wear.

However, diamond's limited ability to plastically deform under stress at the tool's working temperature leads to more rapid crack propagation in comparison to much tougher materials such as steel.

Diamond materials can also advantageously be used in certain non-wear applications.

For example, diamond's extremely high thermal conductivity and extremely low thermal expansion coefficient make it a useful material for thermal management applications. Furthermore, diamond's extreme rigidity makes is a useftil material for use as a resonator. Further still, diamond material's broad optical transmittance makes it a useful material for optical application, particularly high energy beam applications which may also utilize the thermal properties of the diamond material.

It is an aim of certain embodiments of the present invention to provide improved diamond components for such non-wear applications.

Summary of Invention

According to a first aspect of the present invention there is provided an apparatus compnsrng: a diamond component; a mounting for supporting said diamond component; and a controller configured to control one or more functional parameters of the apparatus, wherein the apparatus is configured such that in normal use the diamond component is subjected to thermal, mechanical or electromagnetic stress but substantially no abrasive wear, and wherein the diamond component is formed of at least one portion of irradiated diamond material comprising a plurality of vacancy point defects, the vacancy point defects having a concentration in a range 1 x 1014 to I x 1021 vacancies/cm3.

According to a second aspect of the present invention there is provided a method of manufacturing an apparatus as described above, the method comprising: irradiating a diamond material with radiation, wherein the radiation is controlled such that after irradiating the diamond material comprises a plurality of vacancy point defects, the vacancy point defects having a concentration in a range I x 1014 to I x I021 vacancies/cm3; forming a diamond component comprising the irradiated diamond material; and mounting the diamond component in the apparatus such that in normal use the diamond component is subjected to thermal, mechanical or electromagnetic stress but substantially no abrasive wear.

According to a third aspect of the present invention there is provided a diamond component for use in an apparatus as described above, the diamond component being formed of at least one portion of irradiated diamond material comprising a plurality of vacancy point defects, the vacancy point defects having a concentration in a range 1 x 1014 to I x 1021 vacancies/cm3, wherein the diamond component is configured to form a substrate, a heat sink, a vacuum barrier, or a resonator.

A fourth aspcct of the present invention concerns the use of irradiation to increase the crack resistance of a non-gem, non-wear-part diamond material component.

Brief Description of the Drawings

For a better understanding of the present invention and to show how the same may be carried into effect, embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 illustrates a schematic diagram of an apparatus according to an embodiment of the present invention; Figures 2(a) and 2(b) illustrate a plan view and a side view respectively of a plate-shaped irradiated vacuum seal component according to an embodiment of the present invention; Figure 3 illustrates a side view of an irradiated composite substrate assembly component according to another embodiment of the present invention; Figures 4(a) and 4(b) illustrate a plan view and a side view respectively of a dome-shaped irradiated resonator component according to another embodiment of the present invention; Figure 5 illustrate a perspective view of a rod-shaped irradiated resonator component according to another embodiment of the present invention; and Figure 6 illustrates the basic steps involved in a method of manufacturing an apparatus according to an embodiment of the present invention.

Detailed Description of Certain Embodiments

It is known that irradiating diamond material can change its colour for non-technical gem applications. See, for example, EP 0615 954 Al, EP 0316 S56 and "The Type Classification System of Diamonds and Its Importance in Gem&ogy", Gems and Gemology, Vol. 45, No. 2, pp96-1 11, 2009. Furthermorc, it is known that irradiating diamond material can change the wear charactcristics of diamond tools. See, for example, US4]84079, GBI 588445, 6B1588418, US4012300, S1J134641 8, US4273561, SU1813812, 1154533812, US4319889 and JP2006021963.

In contrast to the above, the present inventors are proposing to use irradiation to reduce the problem of cracking of diamond components in non-wear technical applications (i.e. non-gem, non-wear applications). While not been bound by theory, the present inventors believe that vacancy defects introduced into a diamond component by irradiating thc component may function as crack-stops to prcvcnt, or at least reduce, crack propagation through the diamond component due to thermally induced or mechanically induced stresses which are not wear-related.

While it has previously been proposed to use irradiation to change the wear characteristics of diamond tools and other wear parts, the present inventors have realized that the underlying mechanism by which irradiation can alter the wear characteristics of diamond material is also applicable to non-wear applications where cracking is an issue. As such, the present inventors are proposing to use irradiation to improve crack resistance of diamond material used in non-wear technical applications such as substrates, vacuum barriers, heat sinks, and resonators. The inventors have realized that cracking of diamond material can be problematic beyond tool and other wcar part applications and that there are sevcral uscs where cracking may bc an issue disposed in the technical space between such tool or wear part applications and the use of irradiation to merely change the colour of the material for visual purposes in gem applications. Uses such as in substrates for diamond synthcsis, substrates for electronic device fabrication, and heat sinks can impart thermally induced stresses in the diamond material resulting in cracking. Furthermore, use of diamond material as a vacuum barrier or as a resonator can impart mechanically induced stresses in the diamond material resulting iii cracking. Accordingly, the present inventors have realized that irradiating diamond material can be useful in these other technical applications. Such applications do not require an improvement in wear characteristics and do not require a particular colour to be achieved. As such, the use of irradiation for such applications does not appear to be suggested in the previously discussed prior art.

In addition to the aforementioned applications, it is also envisaged that the radiation treatments described herein may also be useful in optical applications to stabilize the optical characteristics of diamond material. For example, while it is known that high levels of irradiation can change the colour of diamond material for gem applications, it is believed that lower levels of radiation can introduce vacancy defects at a level that does not significantly change the colour of the diamond material but and a level sufficient to act as charge traps. Such vacancy defects can fttnct ion to inhibit charge transfer to optically active defects within the diamond material which have different optical characteristics according to their charge state. Such charge transfer may occur as a result of exposure to heat or an electromagnetic stress, such as an external electromagnetic field, and can cause a change in the optical characteristics of the material thus affecting the optical stability of the material in use. Introducing a controlled level of vacancy defects into the material to inhibit such charge transfer may therefore aid in improving optical stability.

Figure 1 illustrates a schematic diagram of an apparatus according to an embodiment of the present invention. The apparatus 2 comprises a diamond component 4, a mounting 6 for supporting the diamond component 4, and a controRer S configured to control one or more functional parameters of the apparatus 2. The apparatus 2 is configured such that in normal use the diamond component 4 is subjected to thermal or mechanical stress but substantially no abrasive wear. The diamond component 4 is formed of at least one portion of irradiated diamond material comprising a plurality of vacancy point defects, the vacancy point defects having a concentration in a range: I 1014 to 1 x 1021 vacancies/em3; 1 x 1015 to I x 1021 vacancies/cm3; 5 x 1015 to 1 x 1020 vacancies/cm3; 1 x 1016 to 5 x 1019 vacancies/cm3; or 5 x 1016 to 1 x 1019 vacancies/em3.

Figures 2(a) and 2(b) illustrate a plan view and a side view respectively of a plate-shaped irradiated vacuum seal component 10 according to an embodiment of the present invention. The vacuum seal component lOis in the form of a flat plate which can be used to vacuum seal an opening in a housing of an apparatus and also may flmction as a window, e.g. for a high energy beam such as a laser.

Figure 3 illustrates a side view of an irradiated composite substrate assembly component 12 according to another embodiment of the present invention. The composite substrate assembly comprises a carrier substrate 1 4 on which a plurality of single crystal diamond substrates 16 are mounted. The single crystal diamond substrates 16 can be irradiated to increase their crack resistance. The single crystal diamond substrates can then be used to form electronic device components thereon or for synthesis of further diamond material thereon. The carrier substrate 14 may be formed ofpolycrystalline diamond material and optionally both the carrier substrate 14 and the single crystal diamond substrates 16 arc irradiated to improve there crack resistance. Cracking may be a problem due to thermally induced stress and thermal expansion coefficient mismatches between the diamond material and other components in the apparatus.

Figures 4(a) and 4(b) illustrate a plan view and a side view respectively of a dome-shaped irradiated resonator component 18 according to another embodiment of the present invention. The dome-shaped irradiated resonator component 18 is in the form of a curved dome which can be used, for example, as a speaker dome in an audio speaker.

FigureS illustrate a perspective view of a rod-shaped irradiated resonator component according to another embodiment of the present invention. Other shapes of resonator may be formed according to the desired end-use. Resonators arc subject to mechanically induced stress which may cause cracking of the diamond material.

Accordingly, it may be advantageous in such situations to use an irradiated diamond material to introduce vacancy defects into the material which can act as crack-stops.

Figure 6 illustrates the basic steps involved in a method of manufacturing an apparatus according to an embodiment of the present invention. The method comprises: irradiating a diamond material with radiation, wherein the radiation is controlled such that after irradiating the diamond material comprises a plurality of vacancy point defects, the vacancy point defects having a concentration in a range I x 1014 to I x 1 021 vacancies/cm3; forming a diamond component comprising the irradiated diamond material; and mounting the diamond component in the apparatus such that in normal use the diamond component is subjected to thermal or mechanical stress but substantially no abrasive wear.

The diamond material may be selected from the group consisting of: a H P1-IT diamond material having a total equivalent isolated nitrogen concentration in the range I to 800 ppm; a CVD diamond material having a total equivalent isolated nitrogen concentration in the range 0.005 to 100 ppm; and a natural diamond material having a total nitrogen concentration in the range I to 2000 ppm.

While not been bound by theory, the present inventors propose that there is an interaction between the mechanism by which irradiation increases crack resistance and the nitrogen content within the diamond crystal matrix. Although this mechanism is not fully characterized, one possibility is that irradiation introduces a relatively even distribution of vacancy defects within the crystal matrix which can act as crack stops and/or introduce regions of stress/strain within the diamond crystal matrix which may act to inhibit crack propagation. Nitrogen impurities within the crystal matrix may function to trap vacancies introduced by the irradiation to form N-V-N or N-V centres. During manufacture, and in use, a diamond tool piece becomes hot. As such, vacancies introduced by irradiation may become mobile within the crystal matrix. However, it is desirable to provide a relatively even distribution of vacancies within the crystal matrix to act as crack stops. As such, a relatively even distribution of vacancies introduced by irradiation may be maintained by ensuring that a suitable concentration of nitrogen is present within the crystal matrix to prevent the vacancies migrating through the diamond crystal structure.

In addition to the above, it has been recognized that CVD, HPHT, and natural diamond are structurally different materials with, for example, different distributions of nitrogen. Natural diamond for example, tends to have aggregated nitrogen defects (Type Ia) whereas synthetic CVD and 1-IPI-IT diamond material tends to have isolated nitrogen defects (Type Tb). Materials having different types and distributions of nitrogen defects behave differently after being subjected to irradiation. Furthermore, the nitrogen content can affect other characteristics such as CVD diamond growth.

As such, the optimum amount of nitrogen required to be present in the diamond material to interact with vacancy defects introduced by irradiation will vary according to the type of diamond material which is irradiated.

In light of the above, it is proposed that for irradiated material, the optimum isolated nitrogen concentration for 1-IPI--IT diamond material lies in the range I to 800 ppm, the optimum isolated nitrogen concentration for CYD diamond material lies in the range 0.005 to 100 ppm, and the optimum isolated nitrogen concentration for natural diamond material lies in the range 1 to 2000 ppm. Using such materials, the irradiation and the nitrogen act in a compatible manner to provide a more crack-resistant diamond component.

The FIPHT diamond material may have a total equivalent isolated nitrogen concentration in the range Ito 600 ppm, 10 to 300 ppm, 10 to 200 ppm, 50 to 250 ppm, lOOto200ppm, lOto lOOppm,orl0to5oppm.

The CVD diamond material may have a total equivalent isolated nitrogen concentration in the range 0.01 to 50 ppm, 0.05 to 20 ppm, 0.08 to 5 ppm, or 0.1 to 2 ppm.

The natural diamond material may have a total nitrogen concentration in the range to 2000 ppm, 500 to 1500 ppm, 800 to 1300 ppm, or 1000 to 1200 ppm.

It is to be noted that the nitrogen concentrations discussed above are measured as an average concentration over a majority volume of the diamond material. The majority volume may be greater than or equal to 50%, 60%, 70%, 80%, or 90% of the total volume of the diamond material. This is to account for the fact that different diamond growth sectors have different rates of nitrogen uptake leading to concentration variations.

The total equivalent isolated nitrogen concentration for a diamond material can be measured by techniques known by persons skilled in the art, for example the concentration can be calculated by deconvoluting the absorption spectrum of the one phonon part of the FTIR spectrum. The total concentration of nitrogen including aggregated nitrogen may be determined using secondary ion mass spectroscopy (SIMS).

The irradiation may comprise electrons, neutrons, X-rays, gamma radiation, protons, or alpha particles.

The irradiation should be of sufficient energy to generate isolated vacancies or relatively small cluster defects in the diamond material which can act as crack stops.

If the energy if the radiation is relatively high or the radiation comprises relatively heavy particles, carbon atoms are knocked off their lattice sites with enough energy to knock further carbon atoms of their lattice sites resulting in what is known as cascade damage. This results in clusters of defects and a region of stress/strain within the diamond crystal matrix which may act to inhibit crack propagation and increase toughness. Small cluster defects are acceptable. However, if the energy of the radiation is too high, the cascade damage becomes too extensive and crack resistance may be reduced. Furthermore, if the energy of the radiation is too low, the radiation does not penetrate sufficiently into the diamond material to provide a bulk treatment of the diamond material.

In light of the above, it is advantageous to irradiate the diamond material in order to form a large number of relatively evenly spaced isolated vacancies or small cluster defects without the individual clusters becoming too large in size. If cluster defects are formed, they should preferably have a maximum length no greater than 50 atoms, atoms; 10 atoms; or 5 atoms in length. The size of the cluster defects can be measured using transmission electron microscopy (TEM) or positron annihilation techniques.

The energy of the radiation will depend on the type of radiation and the mechanism of energy transfer between the radiation and a carbon atom it hits within the diamond crystal matrix. The dose of radiation will also depend on the type of radiation and the number of vacancies produced per particle of radiation.

An iterative process can be used to find optimum vacancy defect levels. A diamond material can be irradiated, tested, re-irradiated, and so on to find the optimum defect levels for a particular diamond material for a particular type of diamond component and application.

According to certain embodiments, the irradiation is preferably above an energy and dose rate which leads to a change in colour of the diamond material. It is also advantageous that the irradiation is kept below an energy and dose rate which would lead to amorphization of the diamond material. Amorphization has a detrimental effect on the mechanical properties of the diamond material. In general, the longer the irradiation dose the more vacancy defects will be introduced. However, the rate of vacancy incorporation may vary according to the nature of the starting material and the nature of the radiation used.

For electrons, the irradiation may have an energy: 30 key or greater in the range 0.1 MeY to 12 MeV; in the range 0.5 MeV to 10 MeV; in the range 1 MeY to 8 MeY; or in the range 4 MeV to 6 MeY. The dosage of electron irradiation may be: 1 x 1015 e / cm2 or greater; in the range 1 x 1016 e / em2 to I x 1019 6 / em2; in the range 1 x 1017 e/ cm2to I x 10196/cm2; or in the range 2 x i018 6/ em2to I x 10196/cm2.

For neutrons, the irradiation may have an energy: in the range 1.0 key to 12 McV; in the range 1.0 key to 10 MeY; in the range 100 keY to 8 MeV; in the range 100 key to 6 MeY; or in the range 500 keY to 4 MeV. The neutrons will tend to be distributed over a range of energies. Accordingly, at least 50%, at least 60%, at least 70%, or at least 80% of the neutrons fall within one of the aforementioned ranges. The dosage of neutron irradiation may be: I x I 14 neutrons / cm2 or greater in the range I x 1014 / 2 is / 2. 15 2 neutrons1 cm to I x 10 neutrons1 cm; in the range 1 x 10 neutrons / em to 5 x 1017 neutrons / cm2; or in the range 1 x 1015 neutrons / cm2to 1 x iO'7 neutrons/cm2.

For gamma rays, the irradiation may have an energy in the range 0.1 to 12 MeV, 0.2 to 10 MeV, or 0.3 to 8 MeV. The dosage of gamma ray irradiation may be 5 x 10'6y- 2. 17 21. 17 ray'em or greater, in the range 1 x 10 to 5 x 10 y-ray/cm, or in the range S x 10 to 1 x 1021 y-ray/em2.

During irradiation according to certain embodiments of the present invention, the temperature of the diamond material is kept relatively low. For example, the temperature may be: 500°C or less; 400°C or less; 300°C or less; 200 °C or less; 100 or less; or 50 °C or less. In order to keep the temperature down, the diamond material may be actively cooled during irradiation. It is advantageous to keep the temperature relatively low as an increase in temperature can result in a decrease in the number density of vacancy defects.

The method may also comprise the optional step of annealing the diamond material in addition to treatment by irradiation. The annealing step may be performed before, during or after the irradiation step, or any combination thereof In certain applications it may be preferred to perform an annealing step before irradiating as an annealing step after irradiating can result in a decrease in vacancy defects. The annealing may be performed at a temperature equal to or greater than 800°C, 1200°C, 1400°C, 1600°C, 1800°C, 2200°C, or 2400°C. Embodiments of the present invention may include a combination of irradiating and a relatively low temperature anneal, or a combination of irradiating and a high pressure high temperature anneal.

Embodiments also envisage the possibility of iterative doses of radiation and!or iterative annealing. That is, more than one annealing and/or irradiation step may be performed. For example, the diamond material may be annealed, then irradiated, and then annealed. Further alternating irradiation and annealing steps may also be performed. Alternatively, the diamond material may not be exposed to any substantial annealing step, at least after irradiation. By substantial annealing step, we mean an annealing step which substantially and measurably changes the properties of the material. Annealing below 1800°C can be conducted in an inert atmosphere whereas annealing above 1800°C may require stabilising pressures, especially if a long anneal is performed. The annealing is typically conducted for 30 seconds up to 50 hours. By inert atmosphere, we mean an atmosphere under which the diamond will not significantly degrade during annealing. Examples include Argon and Neon.

A relatively low temperature anneal may be advantageous for certain applications. In use, the diamond material can get hot, and the diamond component may also be mounted using a braze at, for example, 900°C. As such, a low temperature anneal can be useful to ensure a consistent performance of the diamond component in use. For example, a low temperature anneal at a temperature of 1500°C or less, 1300°C or less,

I

1200°C or less, 1100°C, or less, or approximately 1000°C can bc useful for certain applications.

The irradiation may be performed before, during, or after processing to form one or more components. The processing may involve treating, grinding, cutting and/or shaping the diamond material to form one or more diamond components. For example, a diamond component may have a longest dimension greater than or equal to 0.5 mm, 1 mm, 1.5 mm, 2mm, 3 mm, 5mm, 10mm, 20mm, 50mm, or 100 mm.

The method may further comprise incorporating one or more diamond components into an apparatus and the irradiating may be performed before, during, or after this incorporating step.

In addition to improving the crack resistance of the diamond component in use, an increase in crack resistance of the diamond material can allow the diamond material to be processed in different ways. For example, an increase in crack resistance can allow the diamond material to be processed into a component without cracking or chipping during processing.

The diamond material can be irradiated to a depth of I jim or greater, 10 am or greater, 100 jim or greater, 500 jim or greater or 1 mm or greater. The diamond material may be irradiated throughout a total thickness of the diamond component.

The diamond material may also be exposed to radiation on more than one side of the material. For example, a diamond plate may be exposed on both main faces to achieve an even exposure of radiation. Similarly, a plurality of small particles may be shaken during irradiation such that the particles roll and receive a reasonably even exposure to the radiation over their surface. Rotation of the sample during irradiation, or repeated rotation followed by irradiation, can assist in achieving irradiation throughout the volume of diamond material and/or assist in achieving a relatively even distribution of vacancy defects. Alternatively, irradiation from one side may be used to generate a gradient of damage through the material.

An advantage of certain types of radiation, such as electron or neutron radiation, over ion implantation methods is that such radiation can provide a bulk treatment of the diamond material rather than just a surface treatment. Accordingly, the irradiation can be done before processing the diamond material into a component and incorporating the component into an apparatus. Furthermore, bulk treatment can be applied to a large volume of material pieces with relatively simple handling requirements. For example, diamond pieces do not need to be carefully mounted in a certain orientation as is required for many surface treatments. In contrast, ion implantation methods need to be performed after processing of the diamond material.

This is because ion implantation methods generally result in a surface treatment only.

Processing of the material into a component by, for example, cutting, shaping and/or grinding the diamond material will remove the treated surface of such materials.

The diamond materia' according to embodiments of the invention may be natural diamond or synthetic diamond. The synthetic diamond may be formed by a high pressure high temperature (HPHT) method or by a chemical vapour deposition (CVD) method. The diamond material could be single crystal, polycrystalline, a composite material comprising a non-diamond matrix such as PCD or ScD, or grit. The diamond material may comprise crystals having a size: 1 nm or greater; 100 nm or greater; 500 nm or greater; 1 micrometer or greater; 5 micrometer or greater; 0.5 mm or greater; I mm or greater; 3 mm or greater; or 10 mm or greater. The diamond material may comprise one or more crystals and may form a body having at least one dimension up to, for example, 200 mm or more (for example, in a polycrystalline diamond plate or dome). The invention is particularly suited for application to HPHT and CVD diamond. However, certain embodiments may also be applied to natural diamond.

In addition to increasing the crack resistance of diamond components, the irradiation treatment of embodiments of the present invention has the bonus effect of producing diamond components with more desirable colours. A diamond component of a specific colour is useful as the colour also relates to its performance, thus giving the components of the present invention a distinctive colour branding in addition to performance advantages. A range of colours may be achieved depending on the exact type of starting material, the type of radiation, and whether an annealing step is performed in addition to irradiation. For example, colourless or near colourless CYD diamond may turn blue or yellowish-grccn when irradiated in accordance with an embodiment of the present invention. If irradiated and then heated to a temperature greater than approximately 700°C then the CVD diamond which was originally colourless or near colourless may turn colourless, orange, brown or a pink colour dependant on irradiation and annealing treatment. In contrast, yellow HPHT Type lb diamond may turn green when irradiated (depending on dose) in accordance with an embodiment of the present invention. If irradiated and then heated to a temperature greater than approximately 700°C then the yellow HPHT Type lb diamond may turn a red or purple colour (depending on irradiation and anneal).

Further still, the colour of diamond material according to certain embodiments of the present invention can change, for example, when a certain temperature is exceeded for a certain length oftime. This colour change can be used as a quality control indicator and/or an indicator that a diamond component requires replacement. For example, a green HPFIT Type lb diamond material according to one embodiment of the present invention may turn red/purple after prolonged use at high temperatures. This can act as an indicator that the diamond component requires replacement and/or if there is excessive heating due to manufacturing issues, e.g. with the mounting or apparatus design and therefore excessive heating is occurring.

The diamond material used in embodiments of the present invention maybe natural diamond, HPHT diamond and CYD diamond. It will be understood that natural diamond, HPHT diamond and CVD diamond have their own distinctive structural and functional characteristics and thus the terms "natural", "HPHT" and "CVD" not only refer to the method of formation of the diamond material but also refer to specific structural and thnctional characteristics of the materials themselves.

The diamond material used in embodiments of the present invention may be Type Ia, Type Ib, Type Ila, or Type lIb. Type I diamonds contain nitrogen. Although Type II diamonds are usually defined as containing no nitrogen, in practice they can contain low concentrations of nitrogen. In Type Ia, the nitrogen atoms form various types of aggregate defect whereas in Type lb diamonds, the nitrogen atoms tend to be isolated as single impurities. Type Ia diamonds can be colourless, brown, pink, and violet.

Natural Type Tb diamonds can be deep yellow ("canary"), orange, brown or greenish.

The colour of a diamond is determined by the number, type and distribution of defects within the crystal structure. Crystal defects include dislocations, microcracks, twin boundaries, point defects, and low angle boundaries. As such, for example, the colour of diamond will depend on the type and distribution of impurities such as nitrogen as well as the type and distribution of other defects such as dislocations. There is a large number of different types and subclasses of defects within diamond. For example, there are numerous different types of nitrogen defect alone, each having its own spectral characteristics.

The diamond material in the component may be configured into a number of possible crystallographic orientations including faces corresponding to {1 l0, {113}, {111} and/or {l00} crystallographic planes (within 200, 100, 5°, 30 2°, or 10).

Examples

Election Irradiation Electron irradiation (for example, using electrons with energies less than or equal to 12 MeV) typically introduces vacancies in an isolated form. These may be in the neutral (V°) and negative charge states (V). The total vacancy concentration ([VTI = [V°] + [Vi) post irradiation should preferably be in the range: 1 x i014 to I x 1021 vacancies/cm3; 1 x 1015 to 1 x 1021 vacancies/cm3; 5x10' to 1 x 1020 vacancies/cm3; 1 x 1016 to 5 x 1019 vacancies/em3; or S x 1016 to 1 x 1019 vacancies/cm3. Such a concentration of defects can be formed, for example, using electron irradiation having a dose rate: 1 x 1015 e / cm2 or greater; in the range I x 1016 e / cm2 to I x 1019 e / cm2; in the range 1 x 1017 e / cm2to 1 x 1019 e / cm2; or in the range 2 x 1017 e / cm2 to 1 x 1019 6 / cm2.

The electron irradiation may have an energy of: 30 keV or greater; in the range 0.1 MeV to 12 MeV; in the range 0.5 MeV to 10 MeV; or in the range 1 MeV to 8 MeV.

The preferred energy is that which introduces a near uniform concentration of vacancies in a nitrogen doped diamond, while minimizing the formation of cascade damage e.g. vacancy chains. For the resuhs reported here it was found that 4.5 MeV provided a good compromise between these two factors.

Factors such as diamond temperature, beam energy, beam flux, and even the starting diamond's properties can affect the [Vr] produced for a fixed experimental irradiation set-up and time. Irradiation is typically carried out with the sample mounted under ambient conditions -300 K with only minimal temperature rise during the irradiation dose (e.g. less than 100 K). However, factors such as beam energy and beam flux can lead to sample heating. Preferably the sample is held as cold as possible (with even cryogenic cooling at 77 K being advantageous under some circumstances) to enable high dose rates without compromising temperature control and thus minimize the irradiation time. This is advantageous for commercial reasons.

The vacancy concentration can be measured spectroscopically. For example, to measure concentrations of isolated vacancies, spectra arc obtained at 77 K, using liquid nitrogen to cool the samples, since at that temperature sharp pcaks at 741 nm and 394 nm are seen that are attributable to neutral and negatively charged isolated vacancies respectively. The coefficients that are used for the calculations of concentrations of isolated vacancies in the present specification arc those set out by 0.

Davies in Physica B 273-274 (1999) 15-23, as detailed in Table 1 below. In Table 1, "A" is the integrated absorption (mcv cm') in the zero phonon line of the transition, measured at 77 K, with the absorption coefficient in cm' and the photon energy in meV. The concentration is in cm5.

Table 1

Defect Calibration AND1 = (4.8 ± 0.2) x 10-is[V] V° AGRI = (1.2 ± 0.3) x 10.16[VU] Neutron Irradiation Neutron irradiation tends to knock carbon atoms off their lattice sites with enough energy to knock further carbon atoms of their lattice sites resulting in what is known as cascade damage. This results in clusters of defects and a region of stress/strain within the diamond crystal matrix which may act to inhibit crack propagation. If the energy of the ncutrons is too high, the cascade damage becomes too extensive and crack resistance is reduced.

In light of the above, it is advantageous to irradiate the diamond material in order to form a large number of isolated and/or relatively small cluster defects without the individual clusters becoming too large in size. It has been found that a suitable size of cluster defects can be formed using neutron radiation having an energy: in the range 1.0 key to 12 MeV; in the range 1.0 key to 10 MeV; in the range 100 keY to 8 MeV; in the range 100 key to 6 MeV; or in the range 500 key to 4MeV. The neutrons will tend to be distributed over a range of energies. Accordingly, at least 50%, at least 60%, at least 70%, or at least 80% of the neutrons fall within one of the aforementioned ranges.

Neutron irradiation according to the present invention can introduce a near uniform concentration of is&ated vacancies and/or small cluster defects, while minimizing the formation of extensive cascade damage e.g. long vacancy chains. It is difficult to measure the concentration of cluster defects. However, the concentration of isolated defects can be readily characterized spectroscopically. Vacancy point defects may be in the neutral (V°) and negative charge states (V). The total isolated vacancy concentration ([VTJ = [V°j + [VI) may be in the range: 1 x iO'4 to 1 x 1020 vacancies/cm3; 1 x 1015 to I x 1019 vacancies/cm3; I x 1015 to 1 x lOIS vacancies/cm3; 1 x 1015 to I x 1017 vacancies/cm3 or I x 1016 to 1 x 1017 vacancies/cm3. The presence of cluster defects can be detected by a broadening of the absorption peak for isolated vacancies. Such a concentration of vacancy defects can be formed, for example, using neutron irradiation having a dose rate: 1 x 1014 neutrons / cm2 or greater; in the range I x 1014 neutrons / cm2 to 1 x lO neutrons / cm2; in the range 1 x 1015 neutrons / cm2 to 5 x 1017 neutrons / cm2; or in the range I x 1015 neutrons / cm2 to 1 x b'7 neutrons / cm2.

Embodiments of the present invention envisage the possibility of forming a large number of evenly spread isolated vacancies and/or relatively small cluster defects using neutron irradiation, while avoiding large extensive cluster defects formed by extensive cascade damage as a result of neutrons which are too high in energy. This requires the careful selection of a neutron flux of an appropriate energy. It is advantageous to select an energy which results in cluster defects having a maximum size limitation for individual clusters. This is consistent with the understanding that it is desirable to form r&atively small, relatively evenly spread defect clusters rather than large sprawling regions of cascade damage. Accordingly, it is preferable that each of a plurality of cluster defects has a maximum size no greater than 50 atoms in length, more preferably no greater than 20 atoms in length, more preferably still no greater than 10 atoms in length, and most preferably no greater than S atoms in length.

The size of the cluster defects can be measured using transmission electron microscopy (TEM) or positron annihilation techniques.

As previously described, it is advantageous to keep the temperature of the diamond material relatively low during irradiation as an increase in temperature can result in a decrease in the number density of defects. One advantage of neutron irradiation is that it tends not to raise the temperature of the diamond material as much as, for example, electron irradiation. As such, according to certain embodiments of the present invention no active cooling is required.

Another advantage of neutron irradiation is that the diamond material does not usually need to be rotated during neutron irradiation to achieve a relatively even distribution of defects. In fact, one advantage of neutron irradiation over, for example, electron irradiation is that neutrons tend to penetrate more easily through an entire sample to obtain a relatively even distribution of defects without rotation of the sample. It can thus be easier to achieve a high dose of radiation through a sample of diamond in a commercially viable way.

Care needs to be taken when selecting the diamond material to be neutron irradiated so that samples do not remain radioactive for an unreasonably long period of time post irradiation. It is therefore necessary to ensure the diamond material selected for neutron irradiation contains substantially no metallic or other inclusions which will remain radioactive for an unreasonable length of time after exposure to neutron irradiation. In this regard, the diamond material may only be released post neutron irradiation if the radioactivity is less than 4 Bq/g. The diamond material selected for neutron irradiation should therefore preferably contain no metallic inclusions having a size equal to or less 10 im, 5 tim, or 1 jim. The metallic inclusions should preferably be equal to or less than 0.1%, 0.01%, 0.001%, or 0.0001% of the total mass of the diamond. The diamond material should also preferably be acid cleaned immediately before irradiation to remove any potentially radioactive species from the surface, thereby ensuring that the level of radioactivity falls below 4 Bq/g after being held to cool' for equal to or less than 6 months, 4 months, 2 months, I month, 2 weeks, or I week.

Several CVD diamond samples have been irradiated with neutrons (typically containing approximately 0.1 -0.5 ppm N). Imperial College's Ur235 Consort reactor at Silwood Park, Ascot, UK was used for these treatments (this reactor has now been decommissioned -an alternative can be that found at Delft University, Holland.) The diamond material was typically irradiated for between 14 and 28 hours, with an energy distribution within the reactor which peaked at 1 MeV, 59% of the neutrons falling into the energy range of 0.2 to 2.2 MeV and 86% of neutrons falling into the energy range 0.2 to 12 MeV.

The diamond samples therefore received a dose of approximately S x 1015 to 1 x 1016 neutrons / cm2. A colour change was observed from colourless to yellow-green as a result of the neutron irradiation. Using cold UV-Visible spectroseopic measurements (using the same method of calculation as described above) the concentration of isolated neutral vacancies was measured to be in the range of0.2 -0.51 ppm (2 x 1016 to 5.1 x 1016 vacancies / cm3). There was a clear broadening of the GR1 peak compared to corresponding electron irradiated samples, which shows evidence for the formation of vacancy clusters in addition to isolated vacancies.

Gamma Irradiation Gamma rays can also be used to form vacancy defects within a diamond material. For Gamma radiation, the irradiation may have an energy in the range 0.1 to 12 MeV, 0.2 to 10 MeV, or 0.3 to 8 MeV. The dosage of gamma ray irradiation may be 5 x 1016 ray/cm2 or greater, in the range I x 1017 to 5 x 1021 y-ray/em2, or in the rangeS x lol/ to 1 x 1021 y-ray/em2. Again, nitrogen impurities can be used to optimize the affect of introducing vacancies on the crack resistance of the diamond material.

While this invention has been particularly shown and described with reference to preferred embodiments, it will be understood to 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 appendant claims.

Claims (1)

1. <claim-text>Claims 1. An apparatus comprising: a diamond component; a mounting for supporting said diamond component; and a controller configured to control one or more functional parameters of the apparatus, wherein the apparatus is configured such that in normal use the diamond component is subjected to thermal, mechanical or electromagnetic stress but substantially no abrasive wear, and wherein the diamond component is formed of at least one portion of irradiated diamond material comprising a plurality of vacancy point defects, the vacancy point defects having a concentration in a range I x 1014 to 1 x 1021 vacancies/cm3.</claim-text> <claim-text>2. An apparatus according to claim 1, wherein the concentration of vacancy point defects is in a range: 1 x 1015 to 1 x 1021 vacancies/cm3; 5 x 1015 to 1 x 1020 vacancies/cm3; I x 1016 to 5 x 1019 vacancies/em; or 5 x 1016 to 1 x 1019 vaeaneies/em.</claim-text> <claim-text>3. An apparatus according to claim 1 or 2, wherein the at least one portion of irradiated diamond material extends to a depth of: 1 m or greater; 10 m or greater; m or greater; 500 im or greater; 1 mm or greater; or throughout a total thickness of the diamond component.</claim-text> <claim-text>4. An apparatus according to any preceding claim, wherein the diamond component is formed from one or more of the following diamond materials: a single crystal diamond material, a polyerystalline diamond material, or a composite diamond material comprising grains of diamond material in a non-diamond matrix.</claim-text> <claim-text>5. An apparatus according to claim 4, wherein the diamond component is formed from single crystal diamond material or polycrystalline diamond material.</claim-text> <claim-text>6. An apparatus according to claim 5, wherein the diamond component is formed from single crystal diamond material.</claim-text> <claim-text>7. An apparatus according to any preceding claim, wherein the diamond component is formed from diamond material comprising crystals having a size: 1 nm or greater; 100 nm or greater; 500 nm or greater; 1 micrometer or greater; S micrometer or greater; 0.5 mm or greater; 1 mm or greater; 3 mm or greater; or 10 mm or greater.</claim-text> <claim-text>8. An apparatus according to any preceding claim, wherein the diamond component is formed from one of: synthetic HPHT diamond material having a total equivalent isolated nitrogen concentration in the range 1 to 800 ppm; synthetic CVD diamond material having a total equivalent isolated nitrogen concentration in the range 0.005 to 1 00 ppm; or natural diamond material having a total nitrogen concentration in the range 1 to 2000 ppm.</claim-text> <claim-text>9. An apparatus according to claim 8, wherein the HPHT diamond material has a total equivalent isolated nitrogen concentration in the range I to 600 ppm, 10 to 300 ppm, 10 to 200 ppm, 50 to 250 ppm, 100 to 200 ppm, 10 to 100 ppm, or 10 to 50 ppm.</claim-text> <claim-text>10. An apparatus according to claim 8, wherein the CVD diamond material has a total equivalent isolated nitrogen concentration in the range 0.01 to 50 ppm, 0.05 to ppm, 0.08 to 5 ppm, or 0.1 to 2 ppm.</claim-text> <claim-text>11. An apparatus according to claim 8, wherein the natural diamond material has a total nitrogen concentration in the range 200 to 2000 ppm, 500 to 1500 ppm, 800 to 1300 ppm, or 1000 to 1200 ppm.</claim-text> <claim-text>12. An apparatus according to any preceding claim, wherein the at least one portion of irradiated diamond material has a concentration of cluster defects in a range: 1 x io'4 to I x 102 clusters/cm3; 1 x io to I x 1021 clusters/cm3; 5 x 1015 to 1 1029 clusters/cm3; I x 1016 to 5 x lo' clusters/cm3; or 5 x i06 to I x 1019 clusters/cm3.</claim-text> <claim-text>13. An apparatus according to claim 12. wherein the cluster defects have a maximum size no greater than: 50 atoms; 20 atoms; 10 atoms; or 5 atoms in length.</claim-text> <claim-text>14. An apparatus according to any preceding claim, wherein the at least one portion of irradiated diamond material is irradiated to form a blue, orange, brown, green, red, purple, or black colouration.</claim-text> <claim-text>15. An apparatus according to any preceding claim, wherein at least 50%, 60%, 70%, 80%, 90% or 99% of a volume of the diamond component is formed of the irradiated diamond material.</claim-text> <claim-text>16. An apparatus according to any preceding claim, wherein the diamond component is configured to be a substrate, a heat sink, a vacuum barrier, or a resonator.</claim-text> <claim-text>17. An apparatus according to any preceding claim, wherein the controller is configured to generate and/or control the thermal or mechanical load imparted on the diamond component.</claim-text> <claim-text>18. An apparatus according to claim 17, wherein the controller is configured to control an electronic, optical, vacuum, or mechanical actuator component of the apparatus which imparts the thermal or mechanical load on the diamond component.</claim-text> <claim-text>19. An apparatus according to any preceding claim, wherein the diamond component is in the form of a flat plate or curved dome.</claim-text> <claim-text>20. A method of manufacturing an apparatus according to any preceding claim, the method comprising: irradiating a diamond material with radiation, wherein the radiation is controlled such that after irradiating the diamond material comprises a plurality of vacancy point dcfects, the vacancy point defects having a concentration in a range 1 x 1014 to 1 x 1021 vacancies/cm3; forming a diamond component comprising the irradiated diamond material; and mounting the diamond component in the apparatus such that in normal usc thc diamond component is subjected to thermal, mechanical or electromagnetic stress but substantially no abrasive wear.</claim-text> <claim-text>21. A method according to claim 20, wherein the irradiating comprises irradiating with electrons, neutrons, X-rays, gamma rays, protons, or alpha particles.</claim-text> <claim-text>22. A method according to claim 20 or 21, wherein the irradiating comprises irradiation below an energy and dose rate which would lead to amorphization of the diamond material.</claim-text> <claim-text>23. A method according to any one of claims 20 to 22, wherein the irradiating comprises irradiating the diamond material above an energy and dose rate which leads to a change in colour of the diamond material.</claim-text> <claim-text>24. A method according to any one of claints 20 to 23, wherein the irradiating is performed at a temperature of: 500°C or less; 400°C or less; 300°C or less; 200°C or less; 100°C or less; or 50°C or less.</claim-text> <claim-text>25. A method according to any one of claims 20 to 24, further comprising: cooling the diamond material during the irradiating.</claim-text> <claim-text>26. A method according to any one of claims 20 to 25, further comprising: annealing the diamond material.</claim-text> <claim-text>27. A method according to claim 26, wherein the annealing is performed before, during or after the irradiating.</claim-text> <claim-text>28. A method according to claim 26 or 27, wherein the annealing is performed at a temperature equal to or greater than 800°C, 1200°C, 1400°C, 1600°C, 1800°C, 2200°C, or 2400°C.</claim-text> <claim-text>29. A method according to any one of claims 20 to 25, wherein the diamond material is not exposed to a substantial annealing step.</claim-text> <claim-text>30. A method according to any one of claims 20 to 29,herein the irradiating comprises one of: rotating the diamond material during irradiation; or irradiating the diamond material, rotating the diamond material, and irradiating the diamond material.</claim-text> <claim-text>31. A method according to any one of claims 20 to 30, wherein the diamond component is formed before, during, or after the diamond material is irradiated.</claim-text> <claim-text>32. A diamond component for use in an apparatus according to any one of claims ito 19, the diamond component being formed of at least one portion of irradiated diamond material comprising a plurality of vacancy point defects, the vacancy point defects haying a concentration in a range x 1014 to 1 x 1021 vacancies/cm3, wherein the diamond component is configured to form a substrate, a heat sink, a vacuum barrier, or a resonator.</claim-text> <claim-text>33. A diamond component according to claim 32, wherein the diamond component is in the form of a flat plate or curved dome, 34. Use of irradiation to increase the crack resistance of a non-gem, non-wear-part diamond material component.</claim-text>