METHOD AND DEVICE FOR SITE-RESOLVED LOCALIZATION OF DEFECTS IN MATERIALS

Description

[0001] The present invention relates to a method for spatially resolved localization of a defect in a material having a band gap, according to the preamble of claim 1, and a device for spatially resolved localization of a defect in a material having a band gap, according to the preamble of claim 14.

[0002] In the context of the present invention, a defect in a material is understood to be a structural or chemical alteration in which one or more electrons are trapped and localized at the site of the defect. Such defects are known primarily in solids. However, they could also occur in liquids or gases. The material may also contain one or more molecules.

[0003] If the material is insulating, semiconducting, or band-gap, these defects are characterized by electrons with an energy level that, in the ground state, lies within the band gap of the host material (see Bassett, LC et al. (2019) 'Quantum defects by design', Nanophotonics, 8(11), pp. 1867-1888. doi: 10.1515 / nanoph-2019-0211). These electrons can be excited to higher energy states and then return to the ground state through radiative or non-radiative processes. Defects that absorb photons and subsequently emit luminescence photons are called color centers. There are countless color centers in solids. For example, more than 500 types of luminescence color centers are known for diamond (see Zaitsev, AM (2001) Optical Properties of Diamond. Berlin, Heidelberg: Springer Berlin Heidelberg. doi: 10.1007 / 978-3-662-04548-0). But other materials such as silicon carbide (see Castelletto, S. et al.) also exhibit this characteristic.(2014) 'A silicon carbide room-temperature single-photon source', Nature Materials, 13(2), pp. 151-156. doi: 10.1038 / nmat3806), quartz and even two-dimensional materials, such as hexagonal boron nitride (see Tran, TT et al. (2016) 'Quantum emission from hexagonal boron nitride monolayers', Nature Nanotechnology, 11(1), pp. 37-41. doi: 10.1038 / nnano.2015.242), can exhibit luminescence defects.

[0004] As mentioned, the electrons associated with these defects can absorb a specific wavelength band and emit a corresponding long-wavelength photon with a characteristic lifetime in the excited state. The emitted long-wavelength photons are typically collected by a high numerical aperture (NA) microscope objective and detected by a single photon counter or photomultiplier tube. The instrument capable of performing this imaging is a confocal optical microscope. However, such optical detection has a resolution limitation defined by half the wavelength of the light used for detection. Optische Auflösung d = 0.51 ⋅ λ / NA

[0005] This resolution limit poses a major problem when several closely spaced color centers (defects in solid materials) are to be imaged. While there are some methods to surpass this diffraction-limited resolution, such as STED (Stimulated Emission Depletion) – see Hell, SW and Wichmann, J. (1994) 'Breaking the diffraction resolution limit by stimulated emission: stimulated-emission-depletion fluorescence microscopy', Optics Letters, 19(11), p. 780. doi: 10.1364 / OL.19.000780) (see Rittweger, E. et al. (2009) 'STED microscopy reveals crystal colour centres with nanometric resolution', Nature Photonics, 3(3), pp. 144-147. doi: 10.1038 / nphoton.2009.2), microwave-assisted STORM (Stochastic Optical Reconstruction Microscopy) – see Pfender, M. et al. (2014) 'Single-spin stochastic optical reconstruction microscopy', Proceedings of the National Academy of Sciences, 111(41), pp. 14669-14674. doi: 10.1073 / pnas.1404907111) and gradient-coded imaging (see Arai, K. et al. (2015) 'Fourier magnetic imaging with nanoscale resolution and compressed sensing speed-up using electronic spins in diamond', Nature Nanotechnology, 10(10), pp. 859-864. doi: 10.1038 / nnano.2015.171) (see Zhang, H. et al. (2017) 'Selective addressing of solid-state spins at the nanoscale via magnetic resonance frequency encoding', npj Quantum Information, 3(1), p. 31. doi: 10.1038 / s41534-017-0033-3) etc. However, these are comparatively slow and require pixel-by-pixel scanning, which prevents any possibility of observing a large number of defects.

[0006] In the document Keki Fukumoto et al. (014) 'Femtosecond time-resolved photoemission electron microscopy for spatiotemporal imaging of photogenerated carrier dynamics in semiconductors', Review of scientific instruments, Vol. 85, No. 8, page 083705. Doi: 10.1063 / 1.4893484, a device is described that is capable of performing time-resolved photoelectron microscopy using a femtosecond laser pulse, with a spatial resolution of 100 nm.

[0007] It is therefore an object of the present invention to provide a method by which defects in materials, preferably in solids, can be localized with higher spatial resolution. In particular, such defects should be imaged with high spatial resolution, which is especially possible quickly and cost-effectively.

[0008] This problem is solved by the inventive method according to claim 1 and the inventive device according to claim 14. Advantageous embodiments are specified in the dependent claims and in the following description together with the figures.

[0009] The inventors recognized that this task could be solved in a surprisingly simple way by exciting the electrons associated with the defects with such energy that they are emitted from the material and then performing an electron mapping to determine the spatial location of the electrons emerging from the surface of the solid and thus the corresponding defects.

[0010] The inventive method for spatially resolved localization of a defect in a material, wherein the material has a band gap, according to claim 1, is characterized in that the electron is excited such that it is emitted from the material and subsequently an electron imaging is carried out.

[0011] Although photoemission electron microscopy (PEEM), which also involves imaging emitted electrons, has been used, this method does not achieve the necessary spatial resolution to accurately locate defects in materials (i.e., structural or chemical alterations where one or more electrons are captured and localized at the defect site). Instead, PEEM has so far only been used to characterize bulk materials (such as mass, lattice, and ensemble structure). Therefore, PEEM can only be used to investigate defect ensembles, as described, for example, in the publication by K. Fukumoto et al.: Imaging the defect distribution in 2D hexagonal boron nitride by tracing photogenerated electron dynamics. J. Phys. D: Appl. Phys. 53 (2020) 405106 (9pp). DOI: 10.With 1088 / 1361-6463 / ab9860, resolutions of only 100 nm can be achieved at most, which is too low for spatially resolved localization of a single defect or even quantum applications. In contrast, spatial resolutions down to 0.1 nm can be achieved using techniques such as transmission electron microscopy (TEM), especially cryo-TEM.

[0012] In an advantageous further development, it is provided that at least one of the following elements is used: aberration correction element, means for high magnification, lens with high numerical aperture, focusing element and acceleration column to increase the energy of the electrons, because this allows very high resolutions to be achieved with high image quality and image robustness and automatic alignment.

[0013] According to the invention, the defect is imaged with a spatial resolution of at least 25 nm, preferably at least 20 nm, and particularly in the range of 0.1 nm to 20 nm. This enables quantum applications because quantum mechanical interactions of spins, which occur when such spins are spaced up to 25 nm apart, can then be resolved.

[0014] According to the invention, electron imaging is performed using electron optics and an electron detector, because then the corresponding setup for optics and detection—except for the electron source—can be used from a conventional transmission electron microscope, such as a commercially available one. Preferably, a microchannel plate (MCP—an area-based, image-resolving secondary electron multiplier), a direct electron detector, an electron multiplier CCD (EMCCD), a scientific CMOS (sCMOS), or a phosphor screen is used as the electron detector, enabling high spatial resolution images. Preferably, a magnetic element or an electromagnetic element is used as the electron optics because this allows for particularly simple electron collection and guidance, or manipulation, for magnified imaging.

[0015] In a particularly advantageous embodiment, the excitation of the electron is achieved by one or more electromagnetic waves, preferably light (infrared (300 GHz to 384 THz), visible light (384 THz to 789 THz), ultraviolet light (789 THz to 30 PHz)), radio waves (ultra-short waves (30 MHz to 300 MHz), short waves (3 MHz to 30 MHz), medium waves (300 kHz to 3 MHz) and long waves (30 kHz to 300 kHz)), terahertz radiation (0.1 THz to 10 THz), low frequency (1 kHz to 30 kHz) or microwaves (1 GHz to 300 GHz). This allows for particularly easy emission of the electrons and enables the excitation energy to be defined for subsequent evaluation.

[0016] In a further advantageous embodiment, the excitation is focused on a specific area, preferably a surface region of the material. In particular, light is used that is focused by one or more optical elements, preferably a high numerical aperture lens. Alternatively, the excitation can be performed with a laser light source, or the excitation can be carried out using evanescent wave geometry, or the defect can be arranged in a light-confining nanostructure, cavity, or optical resonator. With evanescent wave geometry excitation, the excitation can be confined to a depth of a few nanometers below the surface. By using a light-confining structure, such as a cavity, the excitation can be selectively directed to only a specific defect.By employing one or more of these measures, the spatial resolution can be further increased by exciting only specific defects from the outset. Furthermore, a targeted selection of specific defects is possible. Overall, one or more of these measures can shape the excitation in such a way as to enable photoexcitation of the defect and subsequent photoemission of electrons from regions much smaller than the diffraction limit (1 nm - 1300 nm), thereby achieving even higher localization resolutions, sensitivities, and dynamic ranges.

[0017] In an advantageous embodiment, it is provided that the spin state of the electron is determined by one or more additional excitations, wherein the additional excitation is carried out by electromagnetic waves, preferably light (infrared (300 GHz to 384 THz), visible light (384 THz to 789 THz), ultraviolet light (789 THz to 30 PHz)), radio waves (ultra-short waves (30 MHz to 300 MHz), short waves (3 MHz to 30 MHz), medium waves (300 kHz to 3 MHz) and long waves (30 kHz to 300 kHz)), terahertz radiation (0.1 THz to 10 THz), low frequency (1 kHz to 30 kHz) or microwaves (1 GHz to 300 GHz), by electromagnetic fields, by thermal processes or by thermionic processes. This allows, for example, interactions between different defects to be investigated or the state of a defect to be read out, thereby enabling qubit applications in particular.By applying spin state determination and spin-state selective excitation of electrons from the material and subsequent imaging, the defects are resolved spatially and simultaneously by their spin states.

[0018] In a further advantageous development, it is provided that the material is electrically grounded. This prevents the investigation from being influenced by a charge buildup in the material.

[0019] In a particularly advantageous embodiment, a bias voltage is applied across the surface of the material, preferably a positive bias voltage. This facilitates and improves the extraction of the emitted electrons and their integration into the electron image. If the bias voltage is applied to an electrode, preferably a grid, a large number of electrons can be accelerated simultaneously, enabling the parallel examination of multiple electrons and thus large-area imaging. Alternatively, applying the bias voltage to a tip further improves the spatial resolution. However, this would require multiple tips for the parallel examination of several electrons. With one or more tips, a serial scanning of the solid's surface could then be performed.

[0020] In a further advantageous embodiment, the material is doped, preferably with a donor. For example, this can be boron. This ensures that electrons are reliably supplied to a defect, making it easier to examine the defects. However, the method according to the invention also works in principle without doping.

[0021] In an advantageous further development, it is provided that the defect is created by at least one of the methods from the group comprising: implantation after material production, doping during material production, and electron irradiation during or after material production. This allows defects to be created particularly easily and yet with a high degree of certainty, especially with regard to their location.

[0022] In a further advantageous embodiment, the surface of the material is provided with a thin conductive layer, preferably a metallic layer or a metal-coordinated molecular layer, and in particular consisting of one or two to five monolayers. This facilitates the emission of the excited electrons. The layer can preferably be applied as a coating, i.e., by a coating process. However, the method according to the invention also works in principle without such a layer.

[0023] In a further advantageous development, the material is surrounded by a magnetic shield. This can, for example, be a soft magnetic material. This increases precision because external magnetic fields, such as the Earth's magnetic field, cannot influence electron emission or the path of the emitted electron.

[0024] In a further advantageous development, the material is surrounded by a Faraday cage. This also increases precision because external electromagnetic fields, such as those from electrical power lines, cannot influence electron emission or the path of the emitted electron.

[0025] In an advantageous further development, it is provided that the material is arranged in a vacuum with a pressure of at most 10 3< mbar, which makes it particularly easy to locate the defects spatially precisely because the electrons emerging from the surface of the material are not disturbed by particles.

[0026] In a particularly advantageous embodiment, the material is cooled, preferably in the temperature range of 0.1 K to 210 K. This results in the defects having a defined excitation spectrum that is selective for the spin state.

[0027] In a further advantageous embodiment, the material is provided as a solid, preferably as a layer or bulk material, and in particular comprises a substance from the group consisting of: diamond, silicon, silicon carbide, hexagonal boron nitride, and crystalline materials with a band gap in the range of 0.1 eV to 14 eV. Extensive information on the defects of these solids is available. The layer can preferably be in the form of an atomically thin subnanometer-thin layer or a crystalline two-dimensional layer.

[0028] Independent protection is claimed for the device according to the invention for spatially resolved localization of a defect in a solid, according to claim 14.

[0029] In an advantageous further development, it is provided that the device is adapted to carry out the method according to the invention.

[0030] According to the invention, the device comprises the structure of a transmission electron microscope, wherein the material is arranged in place of an electron filament of the transmission electron microscope. This makes the device particularly easy to manufacture and provides very high spatial resolution with high image quality and robustness, as well as automatic alignment.

[0031] In a further advantageous embodiment, the device is provided for as a component of a quantum computer or a quantum sensor. This allows quantum computers and quantum sensors to be operated with higher precision.

[0032] Independent protection is claimed for the use of the inventive method or device, characterized in that it enables quantum computing applications, quantum-based information processing, or quantum sensing applications. These processes can thus be carried out with even higher precision. Particularly in the field of quantum sensing, a very high spatial resolution can then be achieved.

[0033] In a further advantageous embodiment, the corresponding parts of an electron microscope are used as the means for electron imaging. The entire device can thus be formed by an electron microscope that, instead of or in place of the electron source, has an electron excitation, preferably a light excitation, in particular a laser excitation.

[0034] The features and further advantages of the present invention will become clear below with reference to the description of two preferred embodiments in conjunction with the figures. These figures show, purely schematically: Fig. 1 shows the method according to the invention according to a first preferred embodiment and Fig. 2 shows the method according to the invention according to a second preferred embodiment.

[0035] In Fig. 1 The device according to the invention is shown in a first preferred embodiment.

[0036] It can be seen that the device according to the invention comprises means 12 for electron excitation and means 14 for electron imaging.

[0037] The means 12 for electron excitation comprise, for example, a suitably controlled laser source 12, whose laser beam 16 can be directed onto a sample 18 arranged in a suitable holder (not shown). One or more optical elements 19, such as high-refractive-index objectives, lenses, and optical beam sharpeners, can be used for beam definition. The means 12 for electron excitation can be designed to be movable in their orientation relative to the sample 18, so that the laser beam 16 can be directed onto a specific point 20 on the surface 22 of the sample 18. The sample is grounded 23 so that it cannot become charged.

[0038] In the example shown, the optical source 12 illuminates the sample 18 from above. This is particularly useful for samples that cannot be traversed by light. If, on the other hand, the sample 18 is opaque, the illumination 16 can also occur from any side of the sample 18, i.e., through a side surface of the sample 18 or from below through the sample 18.

[0039] The electron 24 associated with a defect in sample 18 is emitted by the excitation 16, provided it has a sufficiently high energy, and is subsequently accelerated 27 by a metallic grid 26 arranged above the surface 22 of sample 18, to which a positive bias voltage is applied, so that it can be captured by the electron imaging 14, more precisely by a condenser lens 28. The bias voltage is selected depending on the geometry of the electrode and can, for example, range from a few mV to several kV.

[0040] The accelerated electron 27 then passes through a lens 30 and a projector 32 before finally striking a CCD surface 34. Depending on the selected optical parameters, the resulting image (not shown) represents a complete or partial representation of the spatial coordinates of the surface 22 and shows the locations where the electrons 24 were emitted, thus directly indicating the location of the defects in relation to the surface 22 of the sample 18.

[0041] The electron optics components, namely condenser lens 28, objective 30, and projector 32, as well as the electron detector 34, are standard components of a transmission electron microscope and are known to those skilled in the art, which is why they will not be described in detail here. Therefore, within the scope of the present invention, standard TEMs can preferably be used, whereby the electron filament is removed and the sample 18 is placed there instead. The actual sample holder of the TEM remains empty. All other components of the TEM can still be used; however, the first of two standard condensers of a TEM would not be required, but it can still be used.This allows for very high resolutions with high image quality and robustness and automatic alignment, because such TEMs have aberration correction elements, high magnification, high numerical aperture lenses, focusing elements and acceleration columns to increase the energy of the electrons.

[0042] It is also known to those skilled in the art that a vacuum should prevail between the sample surface 22 and the electron detector 34 so that the electrons 24, 27 are not undesirably influenced.

[0043] For the realization of the device according to the invention, a commercial transmission electron microscope can thus be used, whereby its electron source and electron accelerator can be omitted, but this is not mandatory. In any case, the means 12 for electron excitation in the sample 18 must be used, and, to improve the device, the means 26 for generating a bias voltage must also be used.

[0044] The inventive method using the inventive device 10 will be explained in more detail below with reference to the localization of defects in the form of nitrogen defect centers in diamond. However, the same method can also be applied to any other defects and materials.

[0045] Nitrogen vacancy (NV) centers in diamond are defects in the carbon lattice that arise when a single carbon atom is substituted by a nitrogen atom, simultaneously creating a vacancy in adjacent lattice sites. In the negative charge state, the NV center possesses two unpaired electrons, forming an S = 1 system with triplet electron spin states (ms = 0, ± 1). For an NV center, the electronic interaction with the crystal symmetry causes the ms = ± 1 spin states to be degenerate and separated from the ms = 0 spin state by 2.87 GHz, a phenomenon known as zero-field splitting. The spin sub-planes ms = ± 1 further split into two planes in a non-zero magnetic field given by δ = 2γB.

[0046] Under ambient conditions, the electron associated with the NV center can be optically excited from its ground state to higher electronic states by green light with a wavelength of 532 nm (see Gruber, A. (1997) 'Scanning Confocal Optical Microscopy and Magnetic Resonance on Single Defect Centers', Science, 276(5321), pp. 2012-2014. doi: 10.1126 / science.276.5321.2012). The excited electron then returns to its ground state through luminescence emission or non-radiative processes. The excitation and de-excitation pathways are determined by the spin state of the electrons (see Goldman, ML, Sipahigil, A., et al. (2015) 'Phonon-Induced Population Dynamics and Intersystem Crossing in Nitrogen-Vacancy Centers', Physical Review Letters, 114(14), p. 145502. doi: 10.1103 / PhysRevLett.114.145502 and Goldman, ML, Doherty, MW, et al. (2015) 'State-selective intersystem crossing in nitrogen-vacancy centers', Physical Review B, 91(16), p. 165201. doi: 10.1103 / PhysRevB.91.165201).For example, optical transitions are spin-conserving; therefore, the electron in the ms = 0 (or ms = ± 1) ground state is excited to the ms = 0 (or ms = ± 1) state in the excited manifold. The system-wide crossing rates of the excited manifold are also spin-selective. This leads to a special case for nitrogen-vacancy defects. The spin state can also be optically initialized at room temperature with very high efficiency using only light. After a few microseconds of green illumination, a single NV center could be initialized to rotate to ms = 0 sub-level (see Harrison, J., Sellars, MJ and Manson, NB (2006) 'Measurement of the optically induced spin polarisation of NV centers in diamond', Diamond and Related Materials, 15(4-8), pp. 586-588. doi: 10.1016 / j.diamond.2005.12.027 and Robledo, L. et al.(2011) 'Spin dynamics in the optical cycle of single nitrogen-vacancy centers in diamond', New Journal of Physics, 13(2), p. 025013. doi: 10.1088 / 1367-2630 / 13 / 2 / 025013).

[0047] Since the spin state can be initialized in the state ms = 0, a microwave field can be applied to induce a spin transition to the state ms = + 1 or ms = 1, as is done with the in Fig. 2 The device 100 shown according to the invention is possible, which additionally has a microwave source 102 for emitted microwaves 104, while all other components are the same as those of the device 10. Fig. 1 are equivalent to.

[0048] This spin flip leads to a new ground level of the electron, causing it to undergo a different optical excitation-de-excitation cycle. This results in a decrease in the intensity of the luminescence emission. This is known as optically detected magnetic resonance. Because it is a far-field technique, it suffers from limited optical resolution, which practically prevents the imaging or resolution of two such NV defects separated within the diffraction limit (approximately 200–250 nm).

[0049] These diamond NV centers are promising solid-state qubits for quantum information processing and quantum computing (see DiVincenzo, D. (2010) 'Better than excellent', Nature Materials, 9(6), pp. 468-469. doi: 10.1038 / nmat2774). The electron associated with the NV center exhibits very good spin coherence properties even at room temperature (see Balasubramanian, G. et al. (2009) 'Ultralong spin coherence time in isotopically engineered diamond', Nature Materials, 8(5), pp. 383-387. doi: 10.1038 / nmat2420 and Herbschleb, ED et al. (2019) 'Ultra-Iong coherence times amongst room-temperature solid-state spins', Nature Communications, 10(1), p. 3766. doi: 10.1038 / s41467-019-11776-8). This is also a good prerequisite for a potential quantum processor / computer. These qubits could, for example, be produced by implanting ions other than carbon into pure diamond substrates (see Jakobi, I. et al.(2016) 'Efficient creation of dipolar coupled nitrogen-vacancy spin qubits in diamond', Journal of Physics: Conference Series, 752, p. 012001. doi: 10.1088 / 1742-6596 / 752 / 1 / 012001; Scarabelli, D. et al. (2016) 'Nanoscale Engineering of Closely-Spaced Electronic Spins in Diamond', Nano Letters, 16(8), pp. 4982-4990. doi: 10.1021 / acs.nanolett.6b01692; Haruyama, M. et al. (2019) 'Triple nitrogen-vacancy centre fabrication by C5N4Hn ion implantation', Nature Communications, 10(1), p. 2664. doi: 10.1038 / s41467-019-10529-x; Ishiwata, H. et al. (2017) 'Perfectly aligned shallow ensemble nitrogen-vacancy centers in (111) diamond', Applied Physics Letters, 111(4), p. 043103. doi: 10.1063 / 1.4993160 und Ozawa, H. et al. (2017) 'Formation of perfectly aligned nitrogen-vacancy-center ensembles in chemical-vapor-deposition-grown diamond (111)', Applied Physics Express, 10(4), p. 045501. doi: 10.7567 / APEX.10.045501).

[0050] Such NV centers are advantageous for quantum computers because they can be created in close proximity to one another. A single NV center is atomically small (in practice, the electrons are confined to a few lattice constants, which are only about 200 picometers in size). This single quantum spin system interacts with other quantum systems in a defined way, dictated by the laws of quantum physics. In the context of quantum information science, a single-electron quantum system can be called a qubit. These qubits can be made to interact with another qubit or a network of qubits. In the case of electron spins, they can be brought into interaction by magnetic dipole-dipole coupling. However, the strength of this interaction, expressed in terms of the coupling strength, decreases with the cube of the distance (see Neumann, P. et al.).(2010) 'Quantum register based on coupled electron spins in a room-temperature solid', Nature Physics, 6(4), pp. 249-253. doi: 10.1038 / nphys1536). Therefore, it is important to arrange the qubits (NV centers) close together in the range of 5 to 20 nanometers (see Jakobi, I. et al. (2016) 'Efficient creation of dipolar coupled nitrogen-vacancy spin qubits in diamond', Journal of Physics: Conference Series, 752, p. 012001. doi: 10.1088 / 1742-6596 / 752 / 1 / 012001 and Neumann, P. et al. (2010) 'Quantum register based on coupled electron spins in a room-temperature solid', Nature Physics, 6(4), pp. 249-253. doi: 10.1038 / nphys1536). As previously outlined, in these confined spaces, a network of two or more NV centers cannot be resolved individually using optical means. Therefore, their spin state cannot be read out, which would be useful for processing quantum information.

[0051] The method of the present invention enables the high-resolution localization of individual qubits, even at sub-nanometer resolution and with a large number of spins and their networks. This new method would enable detectors for a large quantum processor, for readout in quantum sensing, and for quantum-capable measurement networks, for which independent patent protection is therefore claimed.

[0052] A single NV defect has an electronic level structure within the diamond's band gap. The ground state (2A) and the excited state (3E) form an electronic triplet that can be excited by green light (532 nm) at room temperature. The electron transitions to the excited state 3E by absorbing a photon. If the laser power is increased (for which a pulsed laser source can be used) or the laser energy is increased by choosing a shorter wavelength of, for example, 405 nm or shorter, a two-photon process is induced, which excites the electron into the conduction band (see Bourgeois, E. et al. (2015) 'Photoelectric detection of electron spin resonance of nitrogen-vacancy centers in diamond', Nature Communications, 6(1), p. 8577. doi: 10.1038 / ncomms9577 and Siyushev, P. et al. (2019) 'Photoelectrical imaging and coherent spin-state readout of single nitrogen-vacancy centers in diamond', Science, 363(6428), pp.728-731. doi: 10.1126 / science.aav2789). The excitation wavelength is chosen such that only the defects are photoionized. Furthermore, the material is otherwise defect-free, so that no other photoelectrons are emitted by optical excitation.

[0053] This photoionized electron 24 is then emitted into the vacuum by a positive bias applied to the grating 26 outside the diamond. This photoemitted electron 24 is collected by the grating 26 and accelerated to specific energies from 0.01 eV to 10 eV 27, which are sufficient for the desired electron optics and the required resolution. The accelerated electron 27 is then directed into an objective lens 30, as in a TEM. The electron 24 passes through a series of electron optics 28, 30, 32, which are formed by magnetic or electromagnetic lenses 30, 32 and a condenser lens 28. The electron emission from the NV center is magnified by a series of lenses 30 to produce a suitable image in the image plane of the electron microscope.This allows a spatial resolution for the defects in the material 18 of at least 25 nm, preferably at least 20 nm and especially in the range 0.1 nm to 20 nm to be achieved.

[0054] The electron-optical components 28, 30, 32 could incorporate a series of aberration correction elements (not shown) to produce a high-quality image with minimal distortion at the detector 34.

[0055] The array detector (camera) 34, placed in the image plane, should be able to record the number of electrons 27 arriving at each pixel. There are various options for detector cameras 34, which are used similarly to a TEM camera. These could be a simple phosphor screen, CCD cameras 27 with microchannel plate amplification, and cameras with a direct electron detector.

[0056] The spin-selective excitation that produces the photoemitted electrons 24 is detected and imaged by the array detector. The electron 27 reaching the image plane could be amplified by microchannel plates (MCPs), amplifiers, or even direct high-gain electron detectors. Since the electron amplification takes place at the detector 34, the process is not limited by photon shot noise, which is a limitation of optically detected magnetic resonance or imaging according to the prior art.

[0057] The electron image detectors offer an exceptional signal-to-noise ratio of greater than 10 to 30, even for a single electron. This superior detection sensitivity provides an excellent capability for spin detection, even in single images. It enables high contrast and improved spin state fidelity, features highly desirable for quantum information and processing applications.

[0058] It has become clear from the foregoing description that the present invention provides a method for localizing defects in materials, preferably solids, with significantly higher spatial resolution than previously possible. Optical imaging of such defects with high spatial resolution is thus achieved quickly and cost-effectively. In particular, the present invention enables contactless spin-selective excitation and detection or imaging of defects in solids with high sensitivity, a high dynamic range, a large field of view, and excellent resolution, far surpassing the capabilities of current optical detection methods. The device and method according to the invention are also extremely useful for quantum computing using defect spins in solids, for quantum-capable detection, and for quantum-capable measurement networks. Reference symbol list

[0059] 10 Device according to the invention in a first preferred embodiment 12 Means for electron excitation, laser source 14 Means for electron imaging 16 Laser beam 18 Sample 19 Optical element 20 Defined point on the surface 22 of the sample 18 22 Surface of the sample 18 23 Grounding of the sample 18 24 The electron associated with a defect of the sample 18 26 Metallic lattice 27 Emitted and accelerated electron 28 Condenser lens 30 Objective 32 Projective 34 Electron detector, CCD area 100 Device according to the invention in a second preferred embodiment 102 Microwave source 104 Microwave radiation

Claims

1. Method for spatially resolved localisation of a defect in a material (18) that has a band gap, wherein the defect has one or more electrons (24) that have at least one energy level that lies in the band gap, wherein the electron (24) is excited such that it is emitted from the material and subsequently electron imaging (14) is carried out, wherein the electron imaging is carried out with the aid of electron optics (26, 28, 30, 32) and an electron detector (34), characterised in that the structure of a transmission electron microscope is used, wherein the material is arranged in place of an electron filament of the transmission electron microscope, wherein the defect is imaged with a spatial resolution of at least 25 nm.

2. Method according to claim 1, characterised in that the material (18) is a solid body, wherein the solid body is preferably in the form of a layer or bulk material and comprises, in particular, a substance from the group comprising diamond, silicon, silicon carbide, hexagonal boron nitride and crystalline materials with a band gap in a range of 0.1 eV to 14 eV, wherein the layer is preferably an atomically thin layer in a sub-nanometre range or a crystalline two-dimensional layer and / or in that the defect is imaged with a spatial resolution of at least 20 nm and in particular in the range of 0.1 nm to 20 nm.

3. Method according to claim 1 or 2, characterised in that a microchannel plate, a direct electron detector, an electron multiplier CCD, an sCMOS, or a phosphor screen is used as the electron detector and / or in that a magnetic element or an electromagnetic element is used as the electron optics (26, 28, 30, 32).

4. Method according to any one of the preceding claims, characterised in that the excitation of the electron (24) is effected by one or more electromagnetic waves, preferably light (16).

5. Method according to claim 4, characterised in that the excitation is focussed on a region, preferably a surface region (20) of the material (18), wherein in particular light (16) is used that is focussed by one or more optical elements, preferably an objective with a high numerical aperture, and / or in that the excitation is effected by a LASER light source and / or in that the excitation is effected in evanescent wave geometry and / or in that the defect is arranged in a light-confining nanostructure, cavity or optical resonator.

6. Method according to any one of the preceding claims, characterised in that the spin state of the electron (24) is determined by one or more additional excitations with electromagnetic waves, preferably light, radio waves or microwaves, by electromagnetic fields, by thermal processes, or by thermionic processes.

7. Method according to any one of the preceding claims, characterised in that the material (18) is electrically earthed (23).

8. Method according to any one of the preceding claims, characterised in that a bias voltage (26) is applied over the surface (22) of the material (18), wherein the bias voltage is preferably positive, wherein the bias voltage is applied in particular to an electrode, preferably a grid (26) or a tip.

9. Method according to any one of the preceding claims, characterised in that the material (18) is doped, preferably with a donor, preferably boron.

10. Method according to any one of the preceding claims, characterised in that the defect was created by at least one of the processes from the group comprising implantation after production of the material, doping during production of the material, or electron irradiation during or after production of the material.

11. Method according to any one of the preceding claims, characterised in that the surface of the material has been provided with a thin conductive layer, wherein the layer is preferably a metallic layer or a metal-coordinated molecular layer, wherein the layer consists in particular of one or two to five monolayers.

12. Method according to any one of the preceding claims, characterised in that the material is surrounded by a magnetic shielding and / or in that the material is surrounded by a Faraday cage and / or in that the material is placed in a vacuum with a pressure of no more than 103 mbar.

13. Method according to any one of the preceding claims, characterised in that the material is cooled, wherein the cooling is preferably carried out in the temperature range of 0.1°K to 210°K.

14. Device (10) for spatially resolved localisation of a defect in a material (18), wherein the material (18) has a band gap, wherein the defect has one or more electrons (24) that have at least one energy level that lies in the band gap, wherein the device (10) has means (12) for exciting the electron (24) that are configured to excite the electron (24) such that it is emitted from the material (18), and has means (14) for electron imaging using electron optics (26, 28, 30, 32) and an electron detector (34), wherein the device comprises the structure of a transmission electron microscope, characterised in that the device (10) is configured such that the material is arranged in place of an electron filament of the transmission electron microscope, wherein the device (10) is configured such that the defect is imaged with a spatial resolution of at least 25 nm.

15. Device according to claim 14, characterised in that the device (10) is configured to carry out the method according to any one of claims 2 to 13 and / or in that the device is a component of a quantum computer or a quantum sensor.

16. Use of the method according to any one of claims 1 to 13 or the device according to one of claims 14 or 15, characterised in that quantum computing applications, quantum-based information processing or quantum sensor applications are carried out therewith.