Radiation powered devices comprising diamond material and electrical power sources for radiation powered devices

Abstract

A radiation powered device includes a first electrode, a second electrode, a semiconductor disposed between the first and second electrodes, and a radioactive source configured to generate a flow of electrons through the semiconductor between the first and second electrodes, wherein the semiconductor comprises diamond material, wherein the radioactive source is embedded within the diamond material, wherein the radioactive source comprises a beta-emitting radioisotope, and atoms of the radioisotope are either substitutionally or interstitially integrated into the diamond material, wherein the diamond material comprises a plurality of regions in the form of layers within a continuous crystal lattice of the diamond material, and wherein at least one layer of the diamond material comprises the radioactive source and at least one layer of the diamond material does not comprise the radioactive source.

Claims

1. A radiation powered device comprising: a first electrode; a second electrode; a semiconductor disposed between the first and second electrodes; and a radioactive source configured to generate a flow of electrons through the semiconductor between the first and second electrodes, wherein the semiconductor comprises diamond material, wherein the radioactive source is embedded within the diamond material, wherein the radioactive source comprises a beta-emitting radioisotope, and atoms of the radioisotope are either substitutionally or interstitially integrated into the diamond material, wherein the diamond material comprises a plurality of regions in the form of layers within a continuous crystal lattice of the diamond material, and wherein at least one layer of the diamond material comprises the radioactive source and at least one layer of the diamond material does not comprise the radioactive source.

2. The radiation powered device of claim 1, wherein the radioactive source embedded within the diamond material is formed of one or more of tritium, .sup.14C, .sup.10Be and phosphorus-33.

3. The radiation powered device of claim 1, wherein the radioactive source is provided in a layer of diamond having a thickness in a range 50 nanometres to 150 micrometres.

4. The radiation powered device of claim 1, wherein the diamond material includes a .sup.13C diamond region which comprises isotopically purified diamond material having an increased .sup.13C content compared to natural isotopic abundance.

5. The radiation powered device of claim 4, wherein the .sup.13C diamond region is in the form of a layer having a thickness in a range 2 nanometres to 2 millimetres.

6. The radiation powered device of claim 4, wherein the .sup.13C diamond region has an atomic concentration of .sup.13C of at least 2%, 3%, 4%, 5%, 10%, 20%, 50%, 75%, 85%, 95%, 99%, or 99.9%.

7. The radiation powered device of claim 1, wherein the diamond material includes a .sup.12C diamond layer.

8. The radiation powered device of claim 7, wherein the .sup.12C diamond layer is a boron-doped .sup.12C diamond layer.

9. The radiation powered device of claim 8, wherein the .sup.12C diamond layer has a thickness in a range 200 nanometres to 2 millimetres.

10. The radiation powered device of claim 1, wherein the diamond material includes a tri-layer structure comprising a layer of .sup.14C containing diamond, a layer of .sup.12C diamond, and a layer of .sup.13C diamond.

11. The radiation powered device of claim 1, wherein the layers of the diamond material are isotopic layers within the diamond material.

12. The radiation powered device of claim 1, wherein the radioactive source is provided within the diamond material at an atom concentration of at least 0.1%, 1%, 5%, 10%, 20%, 50%, 75%, 85%, 95%, 99%, or 99.9%.

13. The radiation powered device of claim 1, wherein the diamond material has a single substitutional nitrogen concentration of no more than 5 ppm, 1 ppm, 500 ppb, 300 ppb or 100 ppb in at least one region thereof.

14. The radiation powered device of claim 1, wherein the diamond material in which a radioactive source is embedded is a synthetic diamond material in which radioisotope atoms are integrated during formation of the synthetic diamond material.

15. The radiation powered device of claim 1, wherein the first electrode forms an ohmic contact and comprises a layer of carbide forming material and a noble metal layer.

16. The radiation powered device of claim 1, wherein the second electrode forms a Schottky contact and is formed of a metal or metal alloy, the metal or metal alloy being formed of a metal or metals having an atomic number z of no more than 20.

17. The radiation powered device of claim 16, wherein the second electrode is formed of Al or LiAl.

18. The radiation powered device of claim 1, wherein the diamond material has a thickness in a range 20 micrometres to 25 millimetres.

19. The radiation powered device of claim 1, wherein the radiation powered device is configured to provide a thermal bias between the first and second electrodes.

20. The radiation powered device of claim 1, further comprising a charge storage device coupled to the first and second electrodes for storing charge flowing out of the diamond material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention are described by way of example only with reference to the accompanying drawings in which:

(2) FIG. 1 shows a configuration of a radiation powered device utilizing an external radiation power source;

(3) FIG. 2a shows a configuration of a radiation powered device utilizing an internal radiation power source;

(4) FIG. 2b shows a configuration of a radiation powered device utilizing an internal radiation power source;

(5) FIG. 3 shows a configuration of a radiation powered device comprising a .sup.13C diamond region;

(6) FIG. 4 shows a configuration of a radiation powered device comprising a .sup.14C diamond region and a .sup.13C diamond region;

(7) FIG. 5 shows another configuration of a radiation powered device comprising a .sup.13C diamond region and a .sup.14C diamond region in a repeat structure;

(8) FIG. 6 shows another configuration of a radiation powered device comprising a .sup.13C diamond region and a .sup.14C diamond region including a super capacitor layered structure and a beta-voltaic layered structure;

(9) FIG. 7 shows a thermionic diamond energy converter configuration;

(10) FIG. 8 shows a thermionic beta Schottky emitter configuration;

(11) FIG. 9 shows a diamond Schottky diode beta-voltaic configuration comprising a capacitor for storing up charge;

(12) FIG. 10 is a pictorial representation of a radioisotope electrical power source;

(13) FIG. 11 is a pictorial representation of a radioisotope electrical power source; and

(14) FIG. 12 is a schematic drawing of a radioisotope electrical power source.

(15) It should be noted that in the drawings like reference numerals have been used for corresponding components to illustrate common features of the various device configurations.

DETAILED DESCRIPTION

(16) Device Configurations

(17) FIG. 1 shows a radiation powered device which comprises: a first electrode 10; a second electrode 12; and a semiconductor 14 disposed between the first and second electrodes, wherein the semiconductor comprises diamond material which generates a flow of electrons between the first and second electrodes when exposed to radiation.

(18) An external radiation source 18, such as a gamma-radiation source, is shown in the configuration of FIG. 1 with the device placed in a radiation field such that electron-hole pairs are generated in the diamond material. The device may be placed adjacent the radiation source 18 or configured to surround the radiation source, e.g. by providing a cylindrical device structure within which the radiation source is disposed.

(19) An alternative to the external radiation source is to provide a radioisotope within the layered device structure as illustrated in the FIG. 2a which shows a radiation powered device comprising: a first electrode 10; a second electrode 12; a semiconductor 14 disposed between the first and second electrodes; and a radioactive source 20 configured to generate a flow of electrons through the semiconductor between the first and second electrodes, wherein the semiconductor comprises diamond material.

(20) The radioactive source 20 can be embedded within the diamond material rather than provided as a separate layer of material (see for examples the pictorial representations of the semiconductor shown in FIGS. 10 and 11). It has been found that if the radioactive source is embedded within the diamond material then losses associated with surface interfaces, air gaps, and limited penetration into the diamond structure are reduced. This provides much higher energy conversion efficiency than previous devices. Furthermore, the dense atomic packing in the diamond structure means that radiation does not effectively escape from the diamond material thus reducing radiation leakage. The embedded radioactive source may be, for example, tritium, .sup.14C, .sup.10Be, or Phosphorus-33; or tritium, .sup.14C, or .sup.10Be, more preferably tritium and/or .sup.14C. While it is possible to encapsulate relatively small radioisotopes such as tritium, .sup.14C, .sup.10Be and phosphorus-33 into the diamond lattice, the present inventors have found that it is difficult to incorporate larger atoms into the high atomic number density diamond lattice without causing significant damage to the diamond crystal structure which negatively impacts electronic charge transporting performance. The present inventors have found that embedding .sup.14C, .sup.10Be and/or tritium into the diamond material is particularly advantageous in terms of providing a diamond material in which a radioactive source is embedded whilst also maintaining the diamond crystal structure.

(21) FIG. 2b shows a radiation powered device similar to the device described in FIG. 2a, although the device of FIG. 2b has an alternative arrangement. The device of FIG. 2b comprises a semiconductor 14 comprising a diamond material in which a radioactive source is embedded. Both of the devices shown in FIGS. 2a and 2b comprise a semiconductor having first and second opposing faces. In the device shown in FIG. 2a, the first electrode 10 contacts a first face of the semiconductor and the second electrode 12 contacts the second face of the semiconductor. In the device shown in FIG. 2b, both the first and second electrodes 10, 12 contact a first face of the semiconductor. Both arrangements shown in FIGS. 2a and 2b allow electrons to flow between the first and second electrodes via the semiconductor.

(22) Furthermore, encapsulation of the radioisotope material within the hard, chemically inert diamond structure reduces the possibility of damage and leakage of radioactive material from the device thus improving device stability and performance and increasing the robustness and chemical inertness of the device thus reducing problems associated with toxicity and/or biocompatibility.

(23) An additional advantage of using tritium or .sup.14C is that both hydrogen and carbon are conventionally used in a diamond synthesis process and readily incorporate into the diamond lattice during synthesis. Accordingly, introducing tritium (a hydrogen isotope) and/or .sup.14C into the diamond synthesis process will not unduly affect the diamond synthesis chemistry.

(24) Yet a further advantage of using tritium or .sup.14C is that they are both bi-products of nuclear power plants. Using this approach, radioactive bi-products of nuclear power plants can be encapsulated into diamond material to render them safe and the resultant diamond material utilized to construct radioisotope batteries thus converting problematic waste materials into a useful power source.

(25) The diamond material optionally has a layered structure with at least one layer comprising the radioactive source and at least one layer which does not comprise the radioactive source. The layered structure may have a plurality of layers comprising the radioactive source and a plurality of layers which do not comprise the radioactive source. Such a layered structure enables the provision of thin layers of diamond material comprising a radioactive source separated by diamond layers which do not have the radioactive source. This can be advantageous as radiation does not penetrate far through the diamond lattice and so a layered structure can provide alternating layers of charge generating material and charge propagation and/or charge multiplication material. For example, the radioactive source can be provided in a layer or layers of diamond having a thickness in a range 50 nanometres to 150 micrometres, optionally 500 nanometres to 50 micrometres.

(26) The layer(s) of diamond material comprising the radioactive source may be a layer(s) of diamond material in which atoms of a radioisotope of the radioactive source are either substitutionally or interstitially integrated into the diamond material (that is substitutionally or interstitially integrated into the crystal lattice of the diamond material, to form a constituent part of the diamond material).

(27) In certain embodiments, the diamond material comprises a plurality of regions, where the plurality of regions are isotopic regions within the diamond material (i.e. isotopic regions within the continuous crystal lattice of the diamond material).

(28) In certain embodiments, the diamond material comprises a plurality of layers, where the plurality of layers are isotopic layers within the diamond material (i.e. isotopic layers within the continuous crystal lattice of the diamond material).

(29) It will be appreciated that the natural abundance of carbon isotopes is approximately 98.9% .sup.12C, 1.1% .sup.13C and a trace amount of .sup.14C (approximately 1 part per trillion). When we talk about .sup.14C configured to generate a flow of electrons through diamond material, the .sup.14C concentration must be significantly higher than the 1 part per trillion trace amount occurring naturally. For example, the radioactive source can be provided within the diamond material at an atom concentration of at least 0.1%, 1%, 5%, 10%, 20%, 50%, 75%, 85%, 95%, 99%, or 99.9%. Since beta region from .sup.14C does not penetrate large distances within a diamond lattice, a relatively thin layer of material can be provided. This can also potentially reduce production costs. However, sufficient .sup.14C must be provided to generate the required electrical power output.

(30) FIG. 3 shows another radiation powered device configuration which comprises: a first electrode 10; a second electrode 12; and a semiconductor 14 disposed between the first and second electrodes, wherein the semiconductor comprises diamond material which generates a flow of electrons between the first and second electrodes when exposed to radiation, and wherein the diamond material includes a .sup.13C diamond region 16 which comprises isotopically purified diamond material having an increased .sup.13C content compared to natural isotopic abundance.

(31) An external radiation source 18, such as a gamma-radiation source, is shown in the configuration of FIG. 3 with the device placed in a radiation field such that electron-hole pairs are generated in the diamond material. The device may be placed adjacent the radiation source 18 or configured to surround the radiation source, e.g. by providing a cylindrical device structure within which the radiation source is disposed. An alternative to the external radiation source is to provide a radioisotope within the layered device structure as illustrated in FIG. 4 which comprises: a first electrode 10; a second electrode 12; a semiconductor 14 disposed between the first and second electrodes; a radioactive source configured to generate a flow of electrons through the semiconductor between the first and second electrodes, wherein the semiconductor 14 comprises diamond material and includes a region 20 in which the radioactive source is embedded and a .sup.13C diamond region 16 which comprises isotopically purified diamond material having an increased .sup.13C content compared to natural isotopic abundance.

(32) Surprisingly, it has been found that the provision of a diamond material which has at least one region which is isotopically purified to increase its .sup.13C leads to a significant increase in output voltage when compared to a corresponding device which does not contain such a .sup.13C diamond layer. It is known that isotopic substitution of .sup.12C by .sup.13C increases the band-gap energy in diamond [see, for example, H Watanabe, “Isotope composition dependence of the band-gap energy in diamond” Phys. Rev. B, 88, 2013]. Providing a larger band gap region of diamond material has been found to significantly increase output voltage in a radiation powered device and can function as an electron multiplication region or layer. For example, a diamond beta-voltaic device having an output voltage of 1.4 V has been found to have an increased output voltage of 2.1 V with the introduction of a thin .sup.13C diamond termination layer.

(33) By way of illustration, for a single diode device with an effective volume of 1.47×10.sup.−6 m.sup.3 (15 μm thick×25 mm diameter) containing 0.343 g of C-14 radiating half of its output into the diode, the open circuit voltage is approximately 2.0 V and the short circuit current is estimated to be 10 μA in a diamond diode using an integral 49 keV radioisotope beta source. When the diamond device structure is repeated many times in a single device then this imbues the capability for the device to act as an efficient gamma-voltaic when exposed to a high intensity gamma radiation fields.

(34) While not being bound by theory a betavoltaic cell voltage depends on the diode leakage current which in turn depends on the Schottky barrier height and its homogeneity. The choice of high purity C-13 influences the Schottky barrier height due to the band gap of C-13 being 17 meV larger than C-12, which also influences the magnitude of the diode leakage current.

(35) The .sup.13C diamond region can be provided in the form of a layer having a thickness in a range 2 nm to 2 mm, optionally 200 nanometres to 2 millimetres. Isotopically purified carbon source material is relatively expensive and thus fabricating a thick layer of isotopically purified .sup.13C is not desirable. In this regard, it has been found that a thin layer of such isotopically purified diamond material can provide a significant increase in output voltage without duly increasing expense.

(36) The .sup.13C diamond region may can have an atomic concentration of .sup.13C of at least 1.1%, 5%, 10%, 20%, 50%, 75%, 85%, 95%, 99%, or 99.9%. The .sup.13C diamond region may can have an atomic concentration of .sup.13C of at least 1.5%, 2%, 3%, 4%, 5%, 10%, 20%, 50%, 75%, 85%, 95%, 99%, or 99.9%. Sufficient .sup.13C should be incorporated into the diamond lattice in order to increase the diamond band gap to achieve the desired increase in output voltage. However, increasing isotopic purification also increases expense in requiring a higher degree of isotopic separation of the carbon source material utilized in the diamond synthesis process.

(37) The diamond material can also include a .sup.12C diamond layer (or region) which comprises a layer (or region) of diamond material which has a natural abundance of carbon isotopes to, for example, within 1.1% (or at least has a .sup.13C content lower that the .sup.13C diamond region and/or a .sup.14C content lower than the .sup.14C diamond region). The .sup.12C diamond layer (or region), if present, may comprises a layer (or region) of diamond material which has a substantially natural abundance of carbon, for example, within 1.1% of natural abundance of each carbon isotope. For example, the diamond material can include a tri-layer structure comprising a layer of .sup.14C containing diamond, a layer of .sup.12C diamond, and a layer of .sup.13C diamond. Alternatively, a more simple bi-layer device structure may be provided comprising diamond material including a layer in which a radioisotope is embedded and a layer of conventional .sup.12C diamond. As discussed above, the layers (or regions) of the diamond material maybe isotopic layers (or regions) within the diamond material (i.e. isotopic layers within the continuous crystal lattice of the diamond material).

(38) The .sup.12C diamond layer can have a thickness in a range 200 nanometres to 2 millimetres, optionally 1 micrometre to 10 micrometres. The specific layer thickness will depend to some extent on the device configuration and application. For example, in betavoltaic configurations the diamond layer can be thin as the beta radiation does not penetrate through large thicknesses of diamond material. Alternatively, for gammavoltaic configurations the diamond layer may advantageously be thick as gamma radiation will penetrate through larger distances and a large volume of diamond material will lead to more electron-hole pairs being generated and a larger charge output. For example, the diamond material may have a thickness in a range 20 micrometres to 25 millimetres, optionally 20 micrometres to 20 millimetres, optionally 50 micrometres to 1500 micrometres.

(39) The diamond material preferably has a single substitutional nitrogen concentration of no more than 5 ppm, 1 ppm, 500 ppb, 300 ppb or 100 ppb in at least one of the aforementioned regions thereof. Impurities, of which nitrogen is the most important, reduce charge carrier performance within the diamond lattice as is known, for example, from WO0196633. As such, the diamond material can be engineered to increase charge generation and also charge mobility and lifetime.

(40) The electrodes may be formed of materials to generate a bias for flow of electrons from the first electrode to the second electrode via a Schottky effect. The first electrode can form an ohmic contact. Such an electrode may comprise a layer of carbide forming material and a noble metal layer. The second electrode can form a Schottky contact. Such an electrode can be formed of a low atomic number metal or alloy. For example, a metal or metal alloy formed of a metal or metals having an atomic number z of no more than 20, e.g. Al or LiAl. In certain embodiments, the second electrode can form a Schottky contact and may be formed of a metal or metal alloy formed of a metal or metals having an atomic number z of 40 or less, e.g. Zr, Al or LiAl.

(41) It should be noted that the choice of metal used to construct the Schottky contact can be a significant factor impact device performance. Furthermore, the quality of the interface between the metal and diamond can also be important. For example, one reason for a low barrier height is the lack of homogeneity of a Schottky metal interface with an oxygen-terminated diamond surface.

(42) While certain metals can be selected based on their ability to bond to diamond material and provide a Schottky biasing effect, it is also envisaged that electrically conductive boron doped diamond could also be used either as one or both of the first and second electrodes or as a layer within the diamond layer structure. The electronic bias may also be provided or enhanced by configuring the radiation powered device to provide a thermal bias between the first and second electrodes.

(43) While the previous configurations have been described in relation to device structures which comprise a layer of .sup.13C diamond which can function as an electron multiplication layer and increase output voltage, it is also envisaged that certain devices may comprise one or more of the features as described herein without such a region of .sup.13C diamond. For example, according to one configuration, a radiation device is provided comprising: a first electrode; a second electrode; a semiconductor disposed between the first and second electrodes; and a radioactive source configured to generate a flow of electrons through the semiconductor between the first and second electrodes; wherein the semiconductor comprises diamond material; and wherein the radioactive source is embedded within the diamond material.

(44) As previously described, the radiation source may be, for example, tritium, .sup.14C, .sup.10Be or Phosphorus-33. Even if a region of .sup.13C diamond is not provided, encapsulating the radioactive source still has benefits in terms of reducing losses associated with surface interfaces, air gaps, and limited penetration into the diamond structure and reducing radiation leakage and the possibility of damage and leakage of radioactive material from the device thus improving device stability and performance and increasing the robustness and chemical inertness of the device thus reducing problems associated with toxicity and/or biocompatibility. That said, it is advantageous to combine the encapsulation configuration with the performance enhancing .sup.13C diamond layer so as to provide a diamond material which has a region in which a radioactive source is embedded and a region of .sup.13C diamond which functions as an electron multiplication layer and increases output voltage.

(45) According to yet another configuration, a radiation powered device is provided which comprises: a first electrode; a second electrode; a semiconductor disposed between the first and second electrodes; and a radioactive source configured to generate a flow of electrons through the semiconductor between the first and second electrodes; wherein the semiconductor comprises diamond material; and wherein the radioactive source is formed of .sup.14C.

(46) In this configuration it has been noted that several advantageous features can also be achieved by replacing the external radioactive source with a lower toxicity radioisotope in the form of .sup.14C such that both the radioactive source and the semiconductor are formed of carbon material even if the .sup.14C is not embedded within the diamond lattice, e.g. provided as a layer of .sup.14C containing graphite adjacent the diamond material. Such an “all carbon” radiation source and semiconductor structure is preferable to one which, for example, uses a separate heavy metal radioisotope. However, most preferably, the radioactive source is both embedded within the diamond material forming at least a part of the diamond lattice structure and most preferably is still used in combination with a .sup.13C diamond layer or region for charge multiplication and increased voltage output.

(47) It is possible to provide multiple device structures by providing multiple layered structures in a single layer stack. An example of such a configuration is shown in FIG. 5 which includes two beta-voltaic structures in a single layer stack and sharing a common central electrode. The configuration comprises: a central electrode 10; end electrodes 12; carbon-14 diamond layers 20; carbon-12 diamond layers 14; and carbon-13 diamond layers 16. The structure thus provides two beta-voltaic devices comprising a layer structure: electrode/.sup.14C diamond/.sup.12C diamond/.sup.13C diamond/electrode. Multi-layered stacked device structures and/or use of thicker layers of diamond material are particularly useful in conjunction with external gamma-radiation sources as gamma radiation can penetrate through the thicker diamond layers and produce an increase in charge generation.

(48) FIG. 6 shows another configuration of a radiation powered device including a super capacitor layered structure and a beta-voltaic layered structure. The layer structure is similar to that shown in FIG. 5 with the difference that one of the two beta-voltaic devices has been modified by reversing the .sup.13C and .sup.12C layers such that one of the devices is transformed into a super capacitor. The configuration comprises: a central electrode 10; end electrodes 12; carbon-14 diamond layers 20; carbon-12 diamond layers 14; and carbon-13 diamond layers 16. The structure thus provides a beta-voltaic device 24 comprising a layer structure: electrode/.sup.14C diamond/.sup.12C diamond/.sup.13C diamond/electrode. The structure further comprises a super capacitor comprising the layer structure: electrode/.sup.14C diamond/.sup.13C diamond/.sup.12C diamond/electrode.

(49) FIG. 7 shows a thermionic diamond energy converter configuration. The device configuration is similar to that shown in FIG. 4 and comprises: a first electrode 10; a .sup.14C diamond layer 20; a .sup.12C diamond layer 14; a .sup.13C diamond layer 16; and a second electrode 12. An electric load 26 is also shown coupled between the first and second electrodes with current flow as illustrated by the arrows to and from the electric load 26. In this configuration the first electrode 10 is heated 22 and the second electrode 12 is cooled 24. As such, a hot cathode 12 and a cooled collector 12 are provided to provide a thermal bias between the cathode 12 and collector 12. In one configuration heating of the cathode is provided by sunlight in order to provide a solar thermionic diamond energy converter.

(50) FIG. 8 shows a thermionic beta Schottky emitter configuration. Again, the device configuration is similar to that shown in FIG. 4 and comprises: a first electrode 10; a .sup.14C diamond layer 20; a .sup.12C diamond layer 14; a .sup.13C diamond layer 16; and a second electrode 12. The difference here is that through holes are provided in the second electrode such that hot electrons 28 can be emitted into a vacuum gap or chamber.

(51) FIG. 9 shows a diamond Schottky diode beta-voltaic configuration comprising a capacitor for storing up charge. Again, the device configuration is similar to that shown in FIG. 4 and comprises: a first electrode 10; a .sup.14C diamond layer 20; a .sup.12C diamond layer 14; a .sup.13C diamond layer 16; and a second electrode 12. A capacitor 30 is provided to collect a trickle charge from the layered structure such that a useful quantity of charge can be built up for subsequent use.

(52) In general terms, a device structure can be provided which comprises: a first electrode; a second electrode; and a semiconductor disposed between the first and second electrodes, wherein the semiconductor comprises diamond material which generates a flow of electrons between the first and second electrodes when exposed to radiation without the application of a biasing voltage, and wherein the radiation powered device further comprises a charge storage device coupled to the first and second electrodes for storing charge flowing out of the diamond material.

(53) In this regard, it has been found that diamond based configurations can provide charge flow when exposed to radiation without a biasing voltage. However, the charge flow is still relatively small for certain applications and thus it is advantageous to provide a charge storage device, such as a capacitor, coupled to the first and second electrodes for storing charge flowing out of the diamond material. Charge can thus be accumulated and then utilized. Charge flow can also be enhanced for charging up the charge storage device. Examples include use of a Schottky biasing effect via an electrode/diamond interface and/or thermal biasing by heating the first electrode and/or cooling the second electrode. The radiation source may be external to the device and in use the device is placed in a radiation field such as a gamma irradiation field. Alternatively, the radiation source may be incorporated into the device, for example in a manner as previously described.

(54) While the device structures illustrated in the figures are shown in a planar layered geometry, it is also envisaged that non-planar layered structures may be provided for certain applications. For example, for radioactive waste stored in cylinders it is envisaged that the device structures as described herein can be fabricated in a cylindrical configuration such that they surround the radioactive cylinders.

(55) It will also be understood that all the preceding configurations can be combined in a variety of different ways depending on application requirements.

(56) Power Sources

(57) FIG. 10 provides a pictorial representation of an electrical power source 100 as described herein. The power source 100 is a radioisotope electrical power source comprising a semiconductor 14 comprising a diamond material and a radioactive source embedded within the diamond material. In the configuration shown in FIG. 10, the radioactive source is .sup.14C which is substitutionally integrated into the diamond material, in this example a boron-doped diamond material. The electrical power source 100 provides electrical power as the radioactive source .sup.14C decays via beta emission (e.sup.−).

(58) FIG. 11 provides a pictorial representation of an electrical power source 100 as described herein. The power source 100 is a radioisotope electrical power source comprising a semiconductor 14 comprising a diamond material and a radioactive source embedded within the diamond material. In the configuration shown in FIG. 10, the radioactive source is .sup.4C which is substitutionally integrated into the diamond material, in this example a boron-doped diamond material. The electrical power source 100 provides electrical power as the radioactive source .sup.14C decays via beta emission (e.sup.−).

(59) FIG. 12 is a diagram of an electrical power source 100 as described herein. The power source 100 is a radioisotope electrical power source comprising a semiconductor 14 comprising a diamond material and a radioactive source embedded within the diamond material. The electrical power source 100 shown in FIG. 12 also comprises a Schottky metal layer 12 to provide a Schottky contact.

(60) Methods of Manufacture

(61) A chemical vapour deposition (CVD) technique can be used to fabricate the diamond material for incorporation into devices according to the various configurations described herein. CVD diamond synthesis is well known in the art. An example is described in WO0196633 for fabricating high purity electronic grade single crystal CVD diamond material. Such high purity synthetic diamond material is particularly useful for the devices as described herein as it has better charge mobility and charge lifetime characteristics when compared with lower purity diamond material in which impurities act as charge traps. However, it is also envisaged that other well-known diamond synthesis techniques can be used including, for example, those to produce nitrogen doped single crystal diamond materials, boron doped single crystal CVD diamond materials, and polycrystalline diamond materials.

(62) The fabrication techniques are modified compared with standard diamond synthesis processes by utilizing isotopically purified starting materials which are incorporated into the growing diamond lattice. For example, methane or an alternative carbon containing gas can be provided in C-12, C-13, and/or C-14 form to provide a continuous single crystal CVD diamond lattice with a layered structure with varying carbon isotope concentration. Fabrication of isotopically purified layers of single crystal CVD diamond material is known in the art. What is different here is the finding that specific combinations of C-12, C-13, and C-14 diamond layers can be used to provide improved radiation powered devices with, for example, increased output voltage.

(63) A diamond material embedded with a radioactive source may be provided by synthetically producing a diamond material in which atoms of a radioisotope are integrated (e.g. substitutionally or interstitially) during formation of the synthetic diamond material, for example by chemical vapour deposition (CVD).

(64) In certain embodiments a diamond material may be synthetically obtained by: providing a carbon containing gas comprising carbon atoms and a radioisotope source gas comprising radioisotope source atoms; and depositing carbon atoms and radioisotope source atoms by chemical vapour deposition to form a diamond material.

(65) The carbon containing gas may comprise .sup.12C, .sup.13C, and/or .sup.13C. In certain embodiments the carbon containing gas comprises .sup.12C and/or .sup.13C. In certain embodiments the carbon containing gas comprises .sup.12C.

(66) The radioisotope source gas may comprise deuterium, tritium, .sup.13C, .sup.14C, and/or .sup.33P. In certain embodiments, the radioisotope source gas is a radioisotope containing gas. The radioisotope containing gas may containing may contain tritium, .sup.14C, and/or .sup.33P. The radioisotope containing gas may containing may contain tritium and/or .sup.14C. The radioisotope containing gas may containing may contain .sup.14C.

(67) The radioisotope source gas may comprise atoms of a radioisotope atoms (i.e. a radioisotope containing gas) or atoms of a non-radioactive isotope that may be converted to a radioisotope by neutron irradiation. For example, the radioisotope source gas may comprise tritium, .sup.14C, and/or .sup.33P as radioisotope atoms; and/or .sup.13C and/or deuterium as atoms which may be converted to a radioisotope on neutron irradiation (deuterium can be converted to tritium using neutron irradiation and .sup.13C can be converted to .sup.10Be using neutron irradiation).

(68) In certain embodiments the carbon containing gas comprises .sup.12C and/or .sup.13C, and the radioisotope source gas comprises .sup.14C, deuterium and/or tritium.

(69) In certain embodiments the carbon containing gas comprises .sup.12C and/or .sup.13C, and the radioisotope source gas comprises .sup.14C and/or tritium. In certain embodiments the carbon containing gas comprises .sup.12C, and the radioisotope source gas comprises .sup.14C and/or tritium.

(70) In certain embodiments the carbon containing gas comprises .sup.12C, and the radioisotope source gas comprises .sup.13C and/or deuterium.

(71) In certain embodiments the process of synthetically producing a diamond material further comprises neutron irradiating the diamond material produced by chemical vapour deposition to produce a diamond material embedded with a radioactive source. For example, the process may comprises providing a carbon containing gas comprising .sup.12C and a radioisotope source gas comprising .sup.13C and/or deuterium; depositing carbon atoms and radioisotope source atoms by chemical vapour deposition to form a diamond material; and neutron irradiating the diamond material deposited by chemical vapour deposition to form a diamond material embedded with a radioactive source, where the radioactive source is .sup.10Be, .sup.14C and/or tritium.

(72) Electrode contacts can be provided on the diamond material using a physical vapour deposition (PVD) process to permit connection to an electrical circuit. Again, metallization techniques for providing electrical contacts to diamond material are known in the art. Certain embodiments of the present invention select particular metals for the electrodes based on their ability to bias charge flow through diamond material when exposed to radiation without application of a biasing voltage.

(73) An advantage of using tritium and/or .sup.14C as the radioisotope is that they are both bi-products of nuclear power plants. Tritium is formed in coolant water in nuclear power plants and water containing tritium is normally released from nuclear plants under controlled, monitored conditions. This tritium containing water can be electrolytically decomposed into oxygen and hydrogen gas including tritium. The tritium containing hydrogen gas can then be used in a hydrogen plasma chemical vapour deposition (CVD) diamond synthesis process. A hydrogen plasma CVD diamond synthesis process tends to incorporate a significant amount of hydrogen within the diamond lattice and thus using this approach a significant amount of tritium can be incorporated into the diamond lattice. In some examples, a hydrogen plasma for CVD diamond synthesis may comprise deuterium. Deuterium incorporated into the diamond lattice may be converted to tritium by neutron irradiation.

(74) .sup.14C is also a bi-products of nuclear power plants and has been found to form as a surface layer on neutron irradiated graphite rods or blocks used to moderate the nuclear reaction. The .sup.14C can be extracted from the blocks and then converted to methane via, for example, reaction with hydrogen or a catalysed reaction with water vapour. Methane is conventionally used as the carbon source in a hydrogen plasma CVD diamond synthesis process. As such, .sup.14C can be used as the carbon source in such a hydrogen plasma CVD diamond synthesis process resulting in a diamond lattice incorporating .sup.14C.

(75) Alternatively, solid .sup.14C containing graphite can be placed in a CVD reactor in a location such that the plasma etches the graphite which is subsequently incorporated into the growing diamond lattice.

(76) Alternatively still, solid graphite material comprising .sup.14C can be used in a high pressure high temperature diamond synthesis process which conventionally converts graphite to diamond under high pressure and temperature using a metal catalyst composition.

(77) Using the aforementioned approaches, radioactive bi-products of nuclear power plants can be encapsulated into diamond material to render them safe and the resultant diamond material utilized, for example, to construct radioisotope batteries thus converting problematic waste materials into a useful power source.

(78) An alternative approach to incorporate .sup.14C into a diamond lattice is to nitrogen dope the diamond material during synthesis and then neutron irradiate the nitrogen doped diamond material to convert .sup.14N into .sup.14C. For example, a nitrogen doped C-13 layer of diamond can be grown and then irradiated to convert .sup.14N into .sup.14C. The advantage of using a C-13 layer of diamond in this approach is that a small proportion of C-13 is also converted into C-14. Alternatively, it may be sufficient to nitrogen dope a natural isotopic abundance diamond material during synthesis and then neutron irradiate the nitrogen doped diamond material to convert .sup.14N into .sup.14C.

(79) Alternatively still, beryllium-10 can be incorporated into a diamond lattice by introducing a .sup.13C containing species into the growth plasma during CVD diamond synthesis and neutron irradiating the diamond material containing .sup.13C to form .sup.10Be.

(80) Alternatively still, it is also known that phosphorus can be incorporated into a diamond lattice by introducing a phosphorus containing species into the growth plasma during CVD diamond synthesis or by subsequent ion implantation. However, it should be noted that these doping/converting/implanting approaches will not achieve the same levels of isotopic purity as using isotopically purified starting materials.

(81) Applications

(82) The technology as described herein has been developed to use nuclear waste to generate electricity in a nuclear-powered batteries. The inventors have grown synthetic diamond samples that, when placed in a radioactive field, for example a gamma radiation field, are able to generate a useful electrical current. Furthermore, synthetic diamond samples have been grown which incorporate their own power source in the form of, for example, beta emitting .sup.14C in the diamond lattice.

(83) These developments have the potential to solve some of the problems of nuclear waste, clean electricity generation, and battery life. Unlike the majority of electricity-generation technologies, which use energy to move a magnet through a coil of wire to generate a current, the synthetic diamond samples are able to produce a charge simply by being placed in close proximity to a radioactive source and/or incorporating their own radioisotope source. There are no moving parts involved, no emissions generated, and no maintenance required, just direct electricity generation. By encapsulating radioactive material inside diamonds, a long-term problem of nuclear waste has been turned into a nuclear-powered battery and a long-term supply of clean energy.

(84) Initial research work demonstrated a prototype diamond battery using Nickel-63 as the radiation source. However, significantly improved efficiency has been achieved by utilising carbon-14, a radioactive version of carbon, which is generated in graphite blocks used to moderate the reaction in nuclear power plants. Research has shown that the radioactive carbon-14 is concentrated at the surface of these blocks, making it possible to process it to remove the majority of the radioactive material. The extracted carbon-14 is then incorporated into diamond material to produce a nuclear-powered battery. The UK alone currently holds almost 95,000 tonnes of graphite blocks at the time of writing and by extracting carbon-14 from these blocks, their radioactivity decreases, reducing the cost and challenge of safely storing this nuclear waste.

(85) In accordance with certain configurations, carbon-14 is chosen as a source material because it emits a short-range radiation, which is quickly absorbed by a solid material. This make it dangerous to ingest or touch with naked skin, but when safely held within diamond material no short-range radiation can escape. In fact, since diamond is the hardest substance known to man it is the ideal material to provide safe storage of radioactive waste material.

(86) Despite their low-power, relative to current battery technologies, the life-time of the diamond batteries described herein could revolutionise the powering of devices over long timescales. The actual amount of carbon-14 in each battery will depend on application requirements. One battery containing 1 g of carbon-14, would deliver 15 Joules per day. This is less than a standard AA battery. However, standard alkaline AA batteries are designed for short timeframe discharge: one battery weighing about 20 g has an energy storage rating of 700 J/g. If operated continuously, this would run out in 24 hours. Using carbon-14 the battery would take 5,730 years to reach 50 percent power, which is about as long as human civilization has existed.

(87) It is envisaged that these batteries will be used in situations where it is not feasible to charge or replace conventional batteries. Applications include low-power electrical devices where long life of the energy source is needed such as pacemakers, satellites, high-altitude drones, spacecraft, seabed communications, monitoring devices etc. Another application is in systems for monitoring radioactive waste using self-powered devices. In this regard, a device as described herein could be adapted to function as both a battery and a detector by switching between non-voltage-biased and voltage-biased modes of operation. Self-powered sensor devices are envisaged for monitoring of radiation, humidity, temperature and gases, e.g. in high radiation environments. In essence, the technology is designed for applications where low power is required constantly to keep devices on/retain memory etc. and where changing a battery is not possible/inherently expensive due to the difficult location of the device. The markets include, but are not limited to: the civil nuclear sector; the ‘internet of things’; space exploration; vehicle tyre pressure monitoring; and certain implanted medical devices. It is also envisaged that when using diamond material in electronic applications, the diamond material can be used both as a power source and a heat spreader or heat sink.

(88) Yet another application is in downhole drilling. Diamond is already used as cutters on drill bits for improved drilling performance. Sensors are also provided on drill bits or drill strings for sensing numerous parameters for optimizing drilling performance. The downhole physical and chemical environment during drilling is challenging. As such, the provision of robust, radiation powered diamond devices in such applications would be advantageous in some respects over more standard power sources.

(89) It is also envisaged that beyond the radiation powered devices as described herein, other diamond products can be provided. That is, in general terms a method of disposing of radioactive waste is provided which comprises encapsulating the radioactive waste in diamond material. The diamond material can then be utilized in a range of applications as is known in the art.

(90) While this invention has been described in relation to certain embodiments it will be appreciated that various alternative embodiments can be provided without departing from the scope of the invention which is defined by the appending claims.

(91) Unless otherwise stated, the features of any dependent claim can be combined with the features of any of the other dependent claims, and any other independent claim.

(92) Aspects of the present invention may be described in the following numbered statements:

(93) 1. A radiation powered device comprising: a first electrode; a second electrode; a semiconductor disposed between the first and second electrodes; and a radioactive source configured to generate a flow of electrons through the semiconductor between the first and second electrodes; wherein the semiconductor comprises diamond material; and wherein the radioactive source is embedded within the diamond material.

(94) 2. A radiation powered device according to statement 1, wherein the radioactive source embedded within the diamond material is formed of one or more of tritium, .sup.14C, and phosphorus-33.

(95) 3. A radiation powered device according to statement 2, wherein the radioactive source is .sup.14C and/or tritium.

(96) 4. A radiation powered device according to statement 3, wherein the radioactive source is .sup.14C.

(97) 5. A radiation powered device according to any preceding statement, wherein the diamond material has a layered structure with at least one layer comprising the radioactive source and at least one layer which does not comprise the radioactive source.

(98) 6. A radiation powered device according to statement 5, wherein the layered structure has a plurality of layers comprising the radioactive source and a plurality of layers which do not comprise the radioactive source.

(99) 7. A radiation powered device according to any preceding statement, wherein the radioactive source is provided in a layer of diamond having a thickness in a range 50 nanometres to 150 micrometres, optionally 500 nanometres to 50 micrometres.

(100) 8. A radiation powered device according to any preceding statement, wherein the radioactive source is provided within the diamond material at an atom concentration of at least 0.1%, 1%, 5%, 10%, 20%, 50%, 75%, 85%, 95%, 99%, or 99.9%.

(101) 9. A radiation powered device according to any preceding statement, wherein the diamond material includes a .sup.13C diamond region which comprises isotopically purified diamond material having an increased .sup.13C content compared to natural isotopic abundance.

(102) 10. A radiation powered device according to statement 9, wherein the .sup.13C diamond region is in the form of a layer having a thickness in a range 200 nanometres to 2 millimetres.

(103) 11. A radiation powered device according to statement 9 or 10, wherein the .sup.13C diamond region has an atomic concentration of .sup.13C of at least 0.1%, 1%, 5%, 10%, 20%, 50%, 75%, 85%, 95%, 99%, or 99.9%.

(104) 12. A radiation powered device according to any preceding statement, wherein the diamond material includes a .sup.12C diamond layer which comprises a layer of diamond material which has a natural abundance of carbon isotopes to within 1.1%.

(105) 13. A radiation powered device according to statement 12, wherein the .sup.12C diamond layer has a thickness in a range 200 nanometres to 2 millimetres, optionally 1 micrometre to 10 micrometres.

(106) 14. A radiation powered device according to any preceding statement, wherein the diamond material includes a tri-layer structure comprising a layer of .sup.14C containing diamond, a layer of .sup.12C diamond, and a layer of .sup.13C diamond.

(107) 15. A radiation powered device according to any preceding statement, wherein the diamond material has a single substitutional nitrogen concentration of no more than 5 ppm, 1 ppm, 500 ppb, 300 ppb or 100 ppb in at least one region thereof.

(108) 16. A radiation powered device according to any preceding statement, wherein the first electrode forms an ohmic contact.

(109) 17. A radiation powered device according to statement 16, wherein the first electrode comprises a layer of carbide forming material and a noble metal layer.

(110) 18. A radiation powered device according to any preceding statement, wherein the second electrode forms a Schottky contact.

(111) 19. A radiation powered device according to statement 18, wherein the second electrode is formed of a metal or metal alloy, the metal or metal alloy being formed of a metal or metals having an atomic number z of no more than 20.

(112) 20. A radiation powered device according to statement 19, wherein the second electrode is formed of Al or LiAl.

(113) 21. A radiation powered device according to any preceding statement, wherein the diamond material has a thickness in a range 20 micrometres to 25 millimetres, optionally 20 micrometres to 20 millimetres, optionally 50 micrometres to 1500 micrometres.

(114) 22. A radiation powered device according to any preceding statement, wherein the radiation powered device is configured to provide a thermal bias between the first and second electrodes.

(115) 23. A radiation powered device according to any preceding statement, further comprising a charge storage device coupled to the first and second electrodes for storing charge flowing out of the diamond material.

(116) 24. A radiation powered device comprising: a first electrode; a second electrode; and a semiconductor disposed between the first and second electrodes, wherein the semiconductor comprises diamond material which generates a flow of electrons between the first and second electrodes when exposed to radiation, and wherein the diamond material includes a .sup.13C diamond region which comprises isotopically purified diamond material having an increased .sup.13C content compared to natural isotopic abundance.

(117) 25. A radiation powered device comprising: a first electrode; a second electrode; a semiconductor disposed between the first and second electrodes; and a radioactive source configured to generate a flow of electrons through the semiconductor between the first and second electrodes; wherein the semiconductor comprises diamond material; and wherein the radioactive source is formed of .sup.14C.

(118) 26. A radiation powered device comprising: a first electrode; a second electrode; and a semiconductor disposed between the first and second electrodes, wherein the semiconductor comprises diamond material which generates a flow of electrons between the first and second electrodes when exposed to radiation without the application of a biasing voltage, and wherein the radiation powered device further comprises a charge storage device coupled to the first and second electrodes for storing charge flowing out of the diamond material.

(119) 27. A method of disposing of radioactive waste comprising encapsulating the radioactive waste in diamond material.

(120) 28. A method according to statement 27, wherein the radioactive waste is .sup.14C or tritium.