RU2804497C2 - Fluorescent diamond and method for its production - Google Patents

Abstract

FIELD: production of fluorescent diamonds.

SUBSTANCE: invention is related to a method for producing fluorescent diamond containing an MV centre in a concentration of 1×10¹⁴/cm³ or higher, where M is selected from a metal or metalloid such as Si, Ge, Sn, Pb, Ni or Co, and V represents a vacancy. The first stage involves the synthesis of diamond by chemical vapor deposition (CVD) or detonation, for example an inward explosion, introducing from 0.0001 to 1 at% of the specified metal or metalloid and additionally ensuring the presence of a metal or metalloid other than M, for example Fe, Co or Ni. In the second stage, the resulting diamond containing M is irradiated with a high-energy beam, for example a beam of He or H ions, or an electron beam to form the V vacancy. After this, the diamond is annealed to form a fluorescent MV centre.

EFFECT: resulting fluorescent diamond is characterized by high luminous efficiency and low background fluorescence due to the specified concentration of MV centres and M content, as well as due to the V to M ratio from 0.1 to 10,000; concentration of nitrogen-vacancy centres (NV-centers) 1×10¹⁷/cm³ or lower and vacancy densities from 1×10¹⁶ to 3×10²¹/cm³.

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Description

TECHNICAL FIELD

[0001] The present invention relates to fluorescent diamond and a method for its production.

[0002] The following abbreviations are used throughout the present description.

MV-center: metal-vacancy center

NV-center: nitrogen-vacancy center

SiV center: silicon vacancy center

BACKGROUND OF THE INVENTION

[0003] The luminescent center in diamond is a nano-sized chemically stable fluorescent chromophore and does not exhibit in vivo degradation, fading or flickering that often occurs in organic fluorescence, and is therefore expected to be used as fluorescence imaging probes. In addition, information about the spins of electrons excited in the luminescent center can sometimes be measured externally, and therefore the application of the luminescent center in optically detected magnetic resonance (ODMR) or as a quantum bit is also expected.

[0004] The currently available luminescent center is a nitrogen-vacancy (NV) center, which consists of a N atom as an impurity present at a lattice site in diamond and a vacancy occupying a lattice site adjacent to the N atom. There are two types of NV centers: NV ⁰ , which is electrically neutral, and NV ^- , in which one electron is captured at a vacancy site. NV center only ^- can be used in ODMR or quantum bit applications, while both can be used as fluorescence imaging probes.

[0005] The NV center itself is rarely present in natural diamonds and is formed when artificial diamond produced by high temperature and high pressure or plasma chemical vapor deposition (CVD) is irradiated with an electron beam or ion beam to introduce vacancies and subjected to proper annealing treatment. As reported, such a process is capable of forming NV centers up to a concentration of 1×10 ¹⁸ /cm ³ . Most of the N present in natural diamonds is in the form of molecules or microbubbles, which means that even if natural diamond were subjected to a similar treatment, it would form many luminescent centers, called H3 centers, rather than NV centers. In artificial diamond, N is contained in atomic form and embedded in a lattice site. Nitrogen is also often added to the raw material to allow the nitrogen to act as a catalyst during diamond formation. Thus, a certain amount (eg, 10 ppm to 100 ppm) of N is initially contained and present at the lattice sites during the formation of the artificial diamond. Therefore, to form NV centers, vacancies are introduced and annealing treatment is carried out so that the vacancies and N can meet and bond together.

[0006] As shown in FIG. 1, the fluorescence luminescence wavelength spectrum consists of a sharp peak called zero-phonon line (ZPL) and a broad peak called side band. Only ZPL can be used in ODMR or quantum bit applications, and therefore only approximately 4% of the luminescence can be effectively used. When the NV center is used as a fluorescence imaging probe, all radiation can be used; However, in this case, autofluorescence (fluorescence emitted by the biological tissue or body fluid itself) interferes with the measurement as noise, so a wide distribution of wavelengths degrades the signal-to-noise (S/N) ratio and leads to reduced sensitivity.

[0007] On the other hand, a luminescent center such as one having a luminescence spectrum in which the majority of the luminescence is due to ZPL is also available. Such a luminescent center corresponds to a SiV center (non-patent document 1) and a GeV center (patent document 1). An example of the luminescence spectrum of a SiV center is shown in Fig. 6. Approximately 70% of the luminescence is due to ZPL, the peak width is small, and therefore the noise effect due to autofluorescence is small. In particular, the SiV center has a ZPL at 738 nm, located in the so-called biological window (the wavelength band in which excitation light or fluorescence enters a living organism). This allows external excitation and external measurement, making the SiV center an ideal luminescent center as a bioimaging probe.

BIBLIOGRAPHY

PATENT DOCUMENT

[0008] Patent Document 1: JP 2016-117852 A

NON-PATENT LITERATURE

[0009] Non-Patent Literature 1: E. Neu et al. APPLIED PHYSICS LETTERS 98, 243107 (2011)

SUMMARY OF THE INVENTION

TECHNICAL PROBLEM

[0010] As described above, methods for producing NV centers have been developed to some extent, and NV centers can be produced in high concentrations. However, methods for producing high concentrations of other luminescent centers, especially SiV centers, expected for utility, are still being developed through trial and error.

[0011] In high-temperature-high-pressure diamond or plasma-CVD diamond, which is used as a raw material for producing NV centers, few or no SiV centers are formed when Si is introduced by ion implantation. Reported methods for producing SiV centers include an example in which a diamond film was formed on a Si substrate by hot filament CVD or plasma CVD, and SiV centers were formed in the resulting polycrystalline diamond; and another example in which Si was introduced by ion implantation into high purity natural diamond (Type IIa) or high purity artificial diamond (plasma CVD method) and subjected the diamond to annealing treatment. However, it was reported that the concentrations of luminescent SiV centers formed by both methods were quite low, and the luminescence efficiencies were also low. Irradiation with heavy ions, such as Si ions, as in the last example, produces vacancies concentrated in high concentration immediately around the path that the heavy ions take and around the position at which the heavy ions eventually stop. The present inventors believe that this will result in the abandonment of a defect, the formation of a dislocation or the like, and will prevent the formation of luminescent centers near the vacancies.

[0012] An object of the present invention is to provide a method for producing an MV center (luminescent center) containing a metal or metalloid M in a high concentration by an efficient method and a fluorescent diamond with excellent luminous efficiency.

SOLUTION

[0013] The inventors of the present invention have developed conditions for obtaining an optimal luminescent center as a method for obtaining an MV center (M is a metal or a metalloid) emitting fluorescence. This method includes: the first stage of the formation of a diamond containing the appropriate concentration of the target impurity M; and a second step including ion implantation or high energy beam irradiation, such as electron beam irradiation, and annealing, in which the ion implantation or high energy beam irradiation is not intended to introduce an impurity, but is intended only to introduce a uniform and corresponding to a certain concentration of vacancies. This two-step process was able to provide a high concentration of the luminescent center.

[0014] The present invention provides the following fluorescent diamond and a method for producing the same.

(1) A fluorescent diamond containing an MV center at a concentration of 1×10 ¹⁴ /cm ³ or higher, where M represents a metal or metalloid and V represents a vacancy.

(2) A fluorescent diamond according to paragraph (1), satisfying at least one of (i), (ii) or (iii):

(i) has a ratio of the number of introduced vacancies to the number of metal or metalloid atoms from 0.1 to 10000 (V number/M number),

(ii) contains from 0.0001 to 1 atomic % of a metal or metalloid (M), or

(iii) has a concentration of NV centers of 1×10 ¹⁷ /cm ³ or lower.

(3) The fluorescent diamond according to item (1) or (2), in which the metal element or metalloid is Si, Ge or Sn.

(4) The fluorescent diamond according to (1) or (2), in which the metalloid element is Si.

(5) The fluorescent diamond according to any one of (1) to (4), containing a metal element or metalloid other than the metal element or metalloid constituting the MV center.

(6) The fluorescent diamond according to item (5), wherein the metal element or metalloid other than the metal element or metalloid constituting the MV center is Fe, Co or Ni.

(7) The method for producing fluorescent diamond described in paragraphs (1) to (6), including the first step and the second step:

first step: introducing the proper concentration of metal or metalloid (M) into the synthesis process so as to obtain a diamond containing metal or metalloid (M); And

second stage: irradiation of a diamond containing a metal or metalloid (M) with a high-energy beam to form a vacancy and subsequent annealing of the diamond so that an MV center is formed, emitting fluorescence.

(8) The method for producing fluorescent diamond according to item (7), in which the high-energy beam is a He or H ion beam, or an electron beam.

(9) The method for producing fluorescent diamond according to item (7), wherein in the first step, the presence of a metal or metalloid other than the metal element or metalloid constituting the MV center is ensured.

(10) The method for producing fluorescent diamond according to item (9), wherein the metal or metalloid other than the metal element or metalloid constituting the MV center is Fe, Co or Ni.

(11) The method for producing fluorescent diamond according to any one of items (7) to (10), wherein the method for synthesizing the diamond in the first step is a chemical vapor deposition method (CVD method).

(12) The method for producing fluorescent diamond according to any one of items (7) to (10), in which the method for synthesizing diamond in the first stage is the detonation method.

(13) The method for producing fluorescent diamond according to any one of items (7) to (10), wherein the method for synthesizing the diamond in the first step is the inward explosion method.

USEFUL EFFECTS OF THE INVENTION

[0015] The present disclosure can provide a fluorescent diamond with high luminous efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is an example of the luminescence spectrum of an NV center (excitation wavelength 488 nm).

Fig. 2 is a conceptual diagram of a hot filament CVD device.

Fig. 3 is an optical micrograph of the sample surface immediately after the formation of the diamond film in Example 1, showing an area of 100 μm × 100 μm.

Fig. 4 - Raman spectrum immediately after the formation of the diamond film in example 1.

Fig. 5 - the result of measuring photoluminescence (PL) immediately after the formation of the diamond film in example 1.

Fig. 6 - the result of PL measurement after completion of ion irradiation and annealing treatment of the diamond film in example 1.

Fig. 7 is an optical micrograph of the sample surface (the site of Ni vapor deposition) immediately after the formation of the diamond film in Example 2, showing an area of 100 μm × 100 μm.

Fig. 8 - Raman spectrum immediately after the formation of the diamond film in example 2.

Fig. 9 - the result of measuring PL immediately after the formation of a diamond film in example 2.

Fig. 10 is the result of PL measurement after completion of ion irradiation and annealing treatment of the diamond film in example 2, where the vertical axis indicates 1/10 of the real values, since a neutral non-selective filter was used.

Fig. 11 is an optical micrograph of the sample surface (the site of Ni vapor deposition) immediately after the formation of the diamond film in Example 3, showing an area of 100 μm × 100 μm.

Fig. 12 - Raman spectrum immediately after the formation of the diamond film in example 3.

Fig. 13 - the result of measuring PL immediately after the formation of a diamond film in example 3.

Fig. 14 - the result of PL measurement after completion of ion irradiation and annealing treatment of the diamond film in example 3.

DESCRIPTION OF IMPLEMENTATION OPTIONS

[0017] Well-known methods for determining the concentration of luminescent centers in diamond, such as MV centers, SiV centers, or NV centers, include the electron paramagnetic resonance (EPR) method, the extinction coefficient method, and the direct fluorescent luminescence intensity estimation method. The EPR method is a method for determining the concentration of unpaired electrons at the level of the ground state of a luminescent center, and the extinction coefficient method is intended to determine the concentration of electrons passing from the ground state to the excited state of a luminescent center. Any of the concentrations of luminescent centers determined by both methods does not correspond to the intensity of fluorescent luminescence, and the concentration of luminescent centers corresponding to the intensity of fluorescent luminescence is obtained only after multiplying either of these concentrations of luminescent centers by the quantum efficiency of fluorescence (which is known to vary widely from the value , infinitely close to zero, to a value close to 1, depending on the environment where the luminescent centers are located, and the like). The fluorescence center concentration described in the present invention refers to the fluorescence center concentration obtained by directly estimating the fluorescent luminescence intensity or by multiplying the luminescent center concentration obtained by another method by the fluorescence quantum yield.

[0018] A method for directly assessing fluorescence luminescence intensity can be carried out, for example, using a microlaser Raman spectrometer (LabRam HR) manufactured by HORIBA, Ltd. This is a simple evaluation method, but when a sample with a known concentration of luminescent centers (e.g., NV centers) and a sample containing MV centers are measured for fluorescence luminescence intensity using exactly the same device and under the same conditions, the measured luminescence intensity is proportional to the density luminescent centers, fluorescence quantum yield and cross-sectional area for absorption of excited light in the measured volume. In this case, the proportionality constant (which reflects the general part, such as the number of photons of the exciting light and the solid detection angle of the measuring system) can be calculated using the measurement results of a sample with a known concentration of luminescent centers (for NV centers, samples with an established concentration of luminescent centers are available for sale ). The concentration of MV centers can be estimated using this proportionality constant and taking literature data for the fluorescence quantum yield and absorption cross section of MV centers.

(1) Fluorescent diamond

[0019] Fluorescent diamond contains an MV center (M represents a metal or metalloid), an M atom and a vacancy (V).

[0020] Examples of metal represented as M include group 3 elements (scandium, lanthanide elements and actinide elements), group 4 elements (Ti, Zr and Hf), group 5 elements (V, Nb and Ta), group 6 elements ( Cr, Mo and W), group 7 elements (Mn), group 8 elements (Fe, Ru and Os), group 9 elements (Co, Rh and Ir), group 10 elements (Ni, Pd and Pt), group 11 elements (Cu, Ag and Au), group 12 elements (Zn, Cd and Hg), group 13 elements (Al, Ga and In) and group 14 elements (Pb), and metalloid examples include B, Si, Ge, Sn, P , As, Sb, Bi, Se and Te. Preferred M is Si, Ge and Sn, and in particular Si and Ge. One M may be used alone, or two or more M may be used in combination. When two or more M's are used, two or more metals may be present, two or more metalloids may be present, or one or more metals and one or more metalloids may be present.

[0021] In one preferred embodiment, the content of a metal element or metalloid other than the metal element or metalloid constituting the MV center may be advantageous to increase fluorescence intensity. When a metal element or metalloid other than the metal element or metalloid constituting the MV center is contained, the metal element or metalloid that catalytically forms the MV center is likely to be introduced into the diamond during the formation of the diamond film or, when conditions are met, the metal or metalloid element probably itself forms an MV center.

[0022] The metal element or metalloid other than the metal element or metalloid constituting the MV center is preferably Fe, Co or Ni, and more preferably Ni. In one preferred embodiment of the present invention, a metal element or metalloid other than the metal element or metalloid constituting the MV center can coexist with the metal element or metalloid constituting the MV center within the fluorescent diamond, but not, for example, vicinity of the MV center, and may be present on or near the surface of the fluorescent diamond.

[0023] In one preferred embodiment of the present invention, as shown in Examples 2 and 3, a metal element or metalloid other than the metal element or metalloid constituting the MV center is vapor deposited onto a substrate containing the metal element or metalloid constituting the MV center, and on the vapor-deposited metal element or metalloid, a diamond film containing the metal element or metalloid constituting the MV center is formed by CVD or the like.

[0024] Fluorescent diamond has an MV center as a luminescent center (fluorescent chromophore). The MV center consists of M (metal or metalloid) and V (vacancies) and can emit fluorescence. In an MV center, typically one M and one or multiple Vs (eg, two, three or four, preferably two or three) are present adjacent to each other. For example, a SiV center, GeV center, SnV center and the like consist of one M and two V. An NV center has a structure in which two neighboring carbon atoms are replaced by a pair of a nitrogen atom and an atomic vacancy, and one N and one V are present adjacent to each other. The concentration of vacancies introduced by ion implantation or the like can be easily estimated by simulation.

[0025] The concentration of MV centers of the fluorescent diamond according to one preferred embodiment of the present invention is preferably 1×10 ¹⁴ /cm ³ or higher and, for example, from 2×10 ¹⁴ to 1×10 ¹⁹ /cm ³ . In MV centers of the same type, the fluorescence intensity is proportional to the concentration of MV centers. In addition, there is an optimal value for the concentration of MV centers. Luminescence intensity is the concentration of luminescent centers multiplied by the cross-sectional area of absorption of the exciting light, quantum yield, and the like. The absorption cross-sectional area varies greatly depending on the type of luminescent center, and therefore the magnitude of luminescence of different types of luminescent centers cannot be compared only by concentration.

[0026] The density of vacancies introduced into the fluorescent diamond according to one preferred embodiment of the present invention is preferably from 1 x 10 ¹⁶ /cm ³ to 3 x 10 ²¹ /cm ³ , and more preferably from 1 x 10 ¹⁸ /cm ³ to 1 ×10 ²¹ / cm ³ . If the vacancy density was too high, the diamond itself would be destroyed, and the MV center would not form. If the vacancy density is too low, there would not be enough V to form an MV center (by vacancy diffusion upon annealing and colliding with and binding to M), and therefore the concentration of MV centers would decrease.

[0027] When the number of vacancies introduced into a fluorescent diamond relative to the M number is too small, the concentration of MV centers would decrease as described above, and therefore the luminescence intensity would also decrease. The ratio of vacancy number to M number (V number/M number) of the fluorescent diamond according to one preferred embodiment of the present invention is from 0.1 to 10,000, preferably from 1 to 10,000, and more preferably from 1 to 1000.

[0028] The M (metal or metalloid) concentration of the fluorescent diamond according to one preferred embodiment of the present invention is preferably 0.0001 to 1 atomic %, and more preferably 0.0005 to 0.1 atomic %. When the M concentration is higher, the concentration of MV centers also tends to increase, but when the M concentration is too high, the fluorescence intensity will tend to decrease. Thus, there is an optimal value for the concentration M.

[0029] The concentration of NV centers contained in the fluorescent diamond according to one preferred embodiment of the present invention is preferably 1×10 ¹⁷ /cm ³ or lower, and more preferably 1×10 ¹⁶ /cm ³ or lower. The NV center would result in increased background fluorescence for the MV center, and therefore the concentration of the NV center is desirably low.

[0030] The fluorescence wavelength of the fluorescent diamond according to one preferred embodiment of the present invention is from 650 to 950 nm, and preferably from 700 to 900 nm for use as a bioimaging probe. This is advantageous because fluorescence with a fluorescence wavelength in the visible red or near-infrared region easily penetrates the skin or body tissue, even when cells in the deep part are fluorescently labeled. When fluorescent diamond is used in applications other than bioimaging, such as cellular-level observation or quantum applications, the fluorescence wavelength range is not particularly limited; however, from the point of view of ease of observation, the fluorescence wavelength is preferably in the range from visible light to near-infrared region.

[0031] The shape of the fluorescent diamond is not particularly limited, and the fluorescent diamond can have any shape, such as a sheet shape, a membrane or film shape, a column shape (cylinder or prism), or a grain shape (sphere, ellipsoid, cuboid, cube or polyhedron). The thickness of the sheet form or film form is preferably from about 0.5 to 5 microns. The diameter of the columnar shape or granular shape or the like is preferably from about 2 to 500 nm. The MV center of a fluorescent diamond is often preferentially present throughout the sample, but may sometimes preferentially be present in a portion near the surface.

(2) Method for producing fluorescent diamond

[0032] Fluorescent diamond can be produced by a process that includes using a diamond containing a metal or metalloid (M) as a raw material, irradiating the raw diamond with a high-energy beam to create a vacancy, and annealing the diamond containing the resulting vacancy to form MV- center.

[0033] The concentration of M in the diamond used as raw material is equivalent to the concentration in the fluorescent diamond described above.

[0034] Raw diamond containing metal or metalloid (M) can be produced by a known method, for example, the following methods (I)-(IV):

(I) using a support containing a metal element or metalloid (M) desired to be introduced to synthesize diamond;

(ii) vapor deposition of another metal or the like, in whole or in part, onto a support containing the metal element or metalloid (M) desired to be introduced, and using this support for the synthesis of diamond;

(III) adding a gas containing a metal element or metalloid (M) desired to be introduced into the feed gas; or

(IV) placing an evaporation source of the metal element or metalloid (M) desired to be introduced and a sputtering source in the vicinity of the substrate and supplying the element desired to be introduced during the formation of the diamond film into the diamond film.

[0035] Methods (I) to (IV) described above can be carried out by CVD methods such as hot filament CVD or plasma CVD, but are not limited to these methods. In addition, when obtaining rough diamonds by the detonation method, the method of an inward explosion, i.e. implosion (shock compression method), high temperature and high pressure method or the like, rough diamond containing a metal or metalloid (M) can be produced by producing diamond in the presence of a compound containing a metal or metalloid.

[0036] For the density of vacancies introduced into a raw diamond containing a metal or metalloid (M) by ion beam irradiation or electron beam irradiation, the upper limit is limited by the concentration at which the diamond is destroyed (vacancy concentration >1×10 ²¹ /cm ³ ) , but the lower limit is, for example, 1×10 ¹⁶ /cm ³ or higher, or even 1×10 ¹⁸ /cm ³ or higher. Examples of the high-energy beam used to irradiate this diamond raw material with a high-energy beam include an ion beam and an electron beam, and the high-energy beam is preferably an ion beam. The ion beam is preferably a hydrogen (H) or helium (He) ion beam. For example, the energy of the hydrogen ion beam is preferably from 10 to 1500 keV, and the energy of the helium ion beam is preferably from 20 to 2000 keV. The electron beam energy is preferably between 500 and 5000 keV.

[0037] To bring the vacancy concentration to a target value (distribution), a method can be used in which the proper injection doses are pre-set by modeling for multiple energies, called multi-stage injection, to obtain a concentration distribution in any depth direction. A 360 keV He ion beam can introduce vacancies into diamond down to a depth of 800 nm. A 180 keV H ion beam can introduce vacancies into diamond down to a depth of 800 nm.

[0038] Vacancies could be introduced by irradiation with heavy ions other than H or He ions. However, maintaining an equivalent depth of vacancies that could be introduced would require energy approximately proportional to the atomic number, leading to costly irradiation. In addition, vacancies would concentrate in the immediate vicinity of the ion path and in the vicinity of the stopping position, and this would locally increase the vacancy concentration and ultimately damage the structure of the diamond itself and would likely often interfere with luminescence. Therefore, this method does not appear to be appropriate for introducing vacancies.

[0039] With electron beam irradiation, penetration is more pronounced than with ion beam irradiation, and, for example, even a 500 keV electron beam reaches a depth of approximately 500 μm in diamond. Energy of approximately 400 keV or higher is known to create a vacancy in diamond. However, the efficiency of creating a vacancy is lower than with ion implantation, and therefore those skilled in the art can appropriately determine the radiation dose to create sufficient vacancies.

[0040] Diamond with vacancies introduced by high-energy irradiation is subjected to annealing treatment to diffuse vacancies and form MV centers, and this can cause fluorescence luminescence. The annealing temperature is preferably 600°C or higher, more preferably 700 to 1600°C, and even more preferably 750 to 900°C. The annealing time is preferably 5 to 60 minutes, and more preferably 10 to 30 minutes.

[0041] Single-crystalline or polycrystalline fluorescent diamond with a thickness of approximately a few microns or less can be made into fluorescent nanodiamond powder.

[0042] The formation of vacancies during ion implantation or irradiation with an electron beam also means the formation of C atoms emerging from lattice sites and moving into interstitial spaces. Such interstitial C atoms can also diffuse under approximately the same conditions as the conditions for vacancy diffusion, reach the surface and form amorphous layer or layer of graphite. It is advisable to exclude the presence of these layers, since they can cause absorption of exciting light or fluorescence. The amorphous layer or graphite layer can be removed by gas-phase oxidation or liquid-phase oxidation.

EXAMPLES

[0043] In the following, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

(1) Example 1

[0044] The substrate is a sample prepared by chopping a commercially available silicon substrate into approximately 2 cm squares. One or two drops of a commercially available nanodiamond dispersion liquid (for example, MSY0-0.5 GAF from Microdiamant) drop onto the silicon substrate using a dropper and rub the surface of the substrate with a cotton swab. This is intended to cause micro-scratches on the surface of the silicon substrate to create a starting point for diamond film deposition and subsequent growth, and to use the nanodiamond remaining on the substrate as a seed for diamond growth. The silicon substrate thus pretreated was introduced into a hot filament CVD device.

[0045] A conceptual drawing of a hot filament CVD device is shown in FIG. 2. A hot filament CVD device has a tantalum (Ta) filament, an electrode supporting the filament, and a substrate holder in a stainless steel vacuum chamber, and a filament power supply (DC power supply) is connected to the filament outside the vacuum chamber. Connected to the vacuum chamber are a feed gas supply system (CH ₄ and H ₂ ), a vacuum system that includes a high-vacuum pump (turbo-molecular pump) and a low-vacuum pump (rotary pump), as well as a vacuum gauge. Although tantalum wire is usually used for the filament, metal wire with a high melting point such as tungsten wire or niobium wire can also be used.

[0046] Hot filament CVD was performed by placing a pretreated silicon substrate on a substrate holder, then fixing the filament at a position approximately 7 mm from the substrate, evacuating with a vacuum system at 1×10 ^-3 Pa or lower, stopping the high vacuum pump, then injecting feed gases CH ₄ at a flow rate of 3 sccm ³ /min and H ₂ at a flow rate of 200 sccm ³ /min and supplying power to the filament after the pressure inside the vacuum chamber has stabilized at about 10 kPa. Film formation was carried out by powering the filament at 250 W for 2 hours.

[0047] The polycrystalline diamond film once formed had a film thickness of approximately 1.5 μm. The size of the crystal grains is approximately 2 µm in the central part of the substrate (location near the filament), becomes smaller towards the periphery and is 1 µm or less at the end part. In fig. 3 shows an optical micrograph of the intermediate part between the central part and the peripheral part of the diamond film. In fig. Figure 4 shows the Raman spectrum measured in this part of the sample. A LabRam HR Raman microspectrometer from HORIBA with an excitation wavelength of 488 nm was used for measurements. A peak at 1332/cm, which is characteristic of diamond, is clearly observed, indicating that a good quality diamond has been formed. In fig. Figure 5 shows the result of measuring PL in this state using the same device (LabRam HR). The luminescence peak of the SiV center is observed at 738 nm. This spectrum is typical for polycrystalline diamond samples immediately after film formation by the hot filament method. The concentration of SiV centers, determined on the basis of fluorescence luminescence intensity measured using a LabRam HR Raman microspectrometer from HORIBA, is estimated to be approximately 6 x 10 ¹² /cm ³ (concentrations in diamond estimated by the same method are shown in the present description, but they are simply reference values). The broad luminescence with a peak from 600 to 630 nm is close to the luminescence of the NV center in wavelength, but does not have the characteristics of the luminescence spectrum of the NV center. Thus, this is probably not the luminescence of the NV center, but the luminescence of organic matter formed at the boundaries of diamond grains.

[0048] The diamond sample was then irradiated with a 2 MeV He beam in the range from 6 x 10 ¹³ /cm ² to 6 x 10 ¹⁵ /cm ² (from 1 x 10 ¹⁸ to 1 x 10 ²⁰ /cm ³ in terms of vacancy concentration ), followed by annealing in vacuum at 800°C for 10 minutes, and then followed by oxidation in atmosphere at 470°C for 2 hours. The sample thus subjected to ion irradiation and heat treatment was subjected to PL measurement using a device used to measure the Raman spectrum. In fig. Figure 6 shows the result of measuring PL after annealing a sample irradiated with ions under the condition of 2×10 ¹⁵ /cm ² . The luminescence intensity of SiV centers is approximately 30 times greater (the concentration of SiV centers is approximately 1.8×10 ¹⁴ /cm ³ ) compared to that immediately after film formation. The intensity of the broad luminescence on the short-wavelength side has increased slightly, but none of the characteristics characteristic of NV center luminescence is observed, which suggests that the NV center is not included and satisfies the requirement: “the concentration of NV centers is 1×10 ¹⁷ /cm ³ or lower.” .

(2) Example 2

[0049] Pre-treatment of a piece of silicon substrate was accomplished by applying a small amount of commercially available nanodiamond powder (eg, MSY0-0.5 from Microdiamont) onto the silicon substrate and rubbing the nanodiamond onto the surface of the substrate using a cotton swab. On the substrate thus pretreated, nickel with a film thickness of approximately 50 nm was vapor deposited over an area approximately equal to half the surface area of the sample using a magnetron sputtering device. Using this substrate and using the hot filament CVD device shown in FIG. 2, formed a diamond film in the same way as in example 1.

[0050] Film formation conditions were approximately the same as in example 1; the filament was fixed in position at a distance of approximately 7 mm from the substrate, evacuation was carried out using a vacuum system at a level of 1×10 ^-3 Pa or lower, and after stopping the high-vacuum pump, the feed gases CH ₄ at 3 sccm ³ /min and H ₂ were introduced at 200 sccm ³ /min, and after the pressure inside the vacuum chamber had stabilized at about 10 kPa, electrical power was applied to the filament. Film formation was carried out by powering the filament at 250 W for 2 hours. As a result, a diamond film grew over the entire substrate, and the distributions of particle sizes and film thickness turned out to be approximately the same as in example 1. Of these, an optical micrograph of the sample surface in the region of nickel vapor deposition is shown in FIG. 7, the Raman spectrum measured in the peripheral region is shown in FIG. 8, and the result of PL measurement is in Fig. 9. When measuring Raman scattering, a clear peak of diamond is observed at 1332/cm, indicating that a good quality diamond was formed, as in Example 1. The result of PL measurement indicates that immediately after the formation of the film, SiV centers with a high concentration of ( 3×10 ¹³ /cm ³ in accordance with the same method for estimating the concentration), approximately 5 times greater than in example 1.

[0051] This sample was similarly subjected to He beam ion implantation and annealing treatment. The highest concentration of SiV centers was obtained under injection conditions of 6×10 ¹⁵ /cm ² . The result of the PL measurement is shown in Fig. 10. The concentration of SiV centers, determined from the luminescence intensity of the SiV centers obtained here, is estimated at 7 × 10 ¹⁴ /cm ³ . This concentration is far from the concentration of SiV centers naturally formed after CVD film formation, and attempting to introduce this concentration of Si by Si ion implantation would cause irreparable damage to the diamond. Thus, this concentration is likely to be achieved only after applying the method of the present invention.

[0052] No characteristic of NV center luminescence is observed as in Example 1, suggesting that NV centers are not included and the requirement "NV center concentration is 1×10 ¹⁷ /cm ³ or lower" is met.

[0053] Although the mechanism by which partial formation of the nickel film prior to the formation of the diamond film increases the concentration of the resulting SiV centers has not been clearly analyzed, the present inventors hypothesize that nickel and silicon in the diamond or on the surface of the diamond are distributed beyond the boundary of the vapor deposition region, and this allows both elements to serve as catalysts during the formation of the diamond film and to be admixed as the diamond grows, and the presence of nickel increases the effect of admixture compared to that in the absence of nickel, and this results in an increased incorporation of silicon atoms into the diamond.

(3) Example 3

[0054] After the silicon substrate was pretreated using a commercially available nanodiamond as in Example 2, a cobalt film was formed on approximately half the surface area of the sample using a magnetron sputtering device. The thickness of the cobalt film was approximately 50 nm. Using this substrate and using the hot filament CVD device shown in FIG. 2, formed a diamond film in the same way as in examples 1 and 2. The film formation conditions were approximately the same as in examples 1 and 2; the filament was fixed in position at a distance of approximately 7 mm from the substrate, evacuation was carried out using a vacuum system at a level of 1×10 ^-3 Pa or lower, and the high vacuum pump was stopped, feed gases CH ₄ at 3 cm ³ /min and H ₂ were introduced at 200 sccm ³ /min, and after the pressure inside the vacuum chamber had stabilized at about 10 kPa, electrical power was applied to the filament. Film formation was carried out by powering the filament at 250 W for 2 hours. As a result, a diamond film grew over the entire substrate, and the particle size distributions and film thicknesses were approximately the same as in Examples 1 and 2. Of these, an optical micrograph of the sample surface in the region of cobalt vapor deposition is shown in FIG. 11, the Raman spectrum measured in the peripheral region is shown in FIG. 12, and the PL measurement result is shown in FIG. 13. These results revealed a clear diamond peak observed at 1332/cm in Raman measurements as in Examples 1 and 2, indicating the formation of a good quality diamond. The PL measurement result was approximately 3 times greater than in example 1 and approximately 0.6 times less than in example 2, indicating that SiV centers with a concentration of (1.8 × 10 ¹³ /cm ³ in accordance with the same method for assessing the concentration) between the concentration obtained without metal deposition and the concentration obtained in the presence of a nickel film.

[0055] This sample was similarly subjected to He beam ion implantation and annealing treatment. The highest concentration of SiV centers was obtained under injection conditions of 6×10 ¹⁴ /cm ² . The result of the PL measurement is shown in Fig. 14. The luminescence intensity of the SiV centers obtained here is approximately half that of the sample obtained by forming the nickel film shown in Example 2, and the concentration is estimated to be approximately 3.5 x 10 ¹⁴ /cm ³ . Although the concentration is thus not comparable to that in Example 2, where nickel was used, the effect of increasing the concentration of SiV centers during metal vapor deposition is obvious. Thus, the present inventors hypothesize that other transition metals, such as iron, also have the same effect.

[0056] No characteristic of NV center luminescence is observed as in Example 1, suggesting no NV center inclusion and satisfying the requirement: “NV center concentration is 1×10 ¹⁷ /cm ³ or lower.”

Claims (23)

1. A fluorescent diamond containing an MV center at a concentration of 1×10 ¹⁴ /cm ³ or higher, wherein M represents a metal element or metalloid selected from Si, Ge, Sn, Pb, Ni or Co, and V represents a vacancy , while the fluorescent diamond satisfies (i), (ii), (iii) and (iv): (i) has a ratio of the number of introduced vacancies to the number of metal or metalloid atoms from 0.1 to 10,000 (V number/M number); (ii) contains from 0.0001 to 1 atomic percent metal or metalloid (M); (iii) has a concentration of nitrogen-vacancy centers of 1×10 ¹⁷ /cm ³ or lower; And (iv) has a vacancy density from 1×10 ¹⁶ /cm ³ to 3×10 ²¹ /cm ³ . 2. The fluorescent diamond according to claim 1, wherein the metal element or metalloid is Si, Ge or Sn. 3. Fluorescent diamond according to claim 1 or 2, in which the metalloid element is Si. 4. Fluorescent diamond according to any one of paragraphs. 1-3, containing a metal element or metalloid different from the metal element or metalloid constituting the MV center. 5. The fluorescent diamond according to claim 4, wherein the metal element or metalloid other than the metal element or metalloid constituting the MV center is Fe, Co or Ni. 6. A method for producing a fluorescent diamond containing an MV center at a concentration of 1×10 ¹⁴ /cm ³ or higher, wherein M represents Si, Ge, Sn, Pb, Ni or Co, and V represents a vacancy, and the method for obtaining fluorescent diamond includes the first stage and the second stage: first step: introducing from 0.0001 to 1 atomic % of a metal or metalloid (M) selected from Si, Ge, Sn, Pb, Ni or Co, in the diamond synthesis process so as to obtain a diamond containing the metal or metalloid (M) ; And second stage: irradiation of a diamond containing a metal or metalloid (M) with a high-energy beam to form a vacancy and subsequent annealing of the diamond so that an MV center is formed, emitting fluorescence; in this case, the fluorescent diamond satisfies (i), (ii), (iii) and (iv): (i) has a ratio of the number of introduced vacancies to the number of metal or metalloid atoms from 0.1 to 10,000 (V number/M number); (ii) contains from 0.0001 to 1 atomic percent metal or metalloid (M); (iii) has a concentration of nitrogen-vacancy centers of 1×10 ¹⁷ /cm ³ or lower; And (iv) has a vacancy density from 1×10 ¹⁶ /cm ³ to 3×10 ²¹ /cm ³ . 7. The method for producing fluorescent diamond according to claim 6, in which the high-energy beam is a beam of He or H ions or an electron beam. 8. The method for producing fluorescent diamond according to claim 6, wherein the first step is to ensure the presence of a metal or metalloid other than the metal element or metalloid constituting the MV center. 9. The method for producing fluorescent diamond according to claim 8, wherein the metal or metalloid other than the metal element or metalloid constituting the MV center is Fe, Co or Ni. 10. A method for producing fluorescent diamond according to any one of claims. 6-9, in which the method for synthesizing diamond in the first stage is the chemical vapor deposition method (CVD method). 11. A method for producing fluorescent diamond according to any one of claims. 6-9, in which the method for synthesizing diamond at the first stage is the detonation method. 12. A method for producing fluorescent diamond according to any one of claims. 6-9, in which the method of synthesizing diamond at the first stage is the method of inward explosion.