Process and device for the spatially resolved localization of defects in materials

Abstract

A novel process allows defects in materials, in particular in solid bodies (18), to be localized with considerably higher spatial resolution than before. Defects can be quickly and economically imaged with high spatial resolution. It is possible to contactlessly spin-selectively excite and capture or image defects in the solid body with high sensitivity, high dynamic range, large field of view and excellent resolution, which far exceeds the present capabilities of optical detection processes. Furthermore, with the process there is an excellent possibility for detecting spin even in individual images, wherein high contrast of the spin states and better fidelity of reproduction of the spin states are made possible. The device (10) and the process are suitable for quantum calculation using defect spins in solid bodies (18), for quantum-capable capturing and for quantum-capable measurement networks.

Claims

1.-16. (canceled)

17. A process for spatially resolved localization of a defect in a material that has a band gap, the defect having an electron having at least one energy level that lies in the band gap, the process comprising: arranging the material within a structure of a transmission electron microscope in place of an electron filament; exciting the electron such that the electron is emitted from the material; subsequently carrying out an electron imaging with an electron optics and an electron detector; and imaging the defect with a spatial resolution sub-25 nm.

18. The process according to claim 17, wherein the material (18) is a solid body and comprises a substance selected from the group consisting of 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 solid body is an atomically thin layer in a sub nanometer range or a crystalline two-dimensional layer or a bulk material, and/or wherein the defect is imaged with a spatial resolution in a range of 0.1 nm to 20 nm.

19. The process according to claim 17, wherein the electron detector is a microchannel plate, a direct electron detector, an electron multiplier CCD, an sCMOS, or a phosphor screen, and/or wherein the electron optics is a magnetic element or electromagnetic element.

20. The process according to claim 17, wherein exciting the electron is effected by electromagnetic waves.

21. The process according to claim 20, wherein exciting the electron is effected by focusing light with an objective lens on a surface region of the material, and/or wherein exciting the electron is effected by a LASER light source, and/or wherein exciting the electron is effected in evanescent wave geometry, and/or wherein the defect is arranged in a light-confining nanostructure, cavity or optical resonator.

22. The process according to claim 17, further comprising determining a spin state of the electron by additional excitation with electromagnetic waves, by electromagnetic fields, by thermal processes, or by thermionic processes.

23. The process according to claim 17, further comprising electrically grounding the material (18).

24. The process according to claim 17, further comprising applying a positive bias voltage (26) to a grid (26) or a tip above a surface of the material.

25. The process according to claim 17, wherein the material (18) is doped with a donor.

26. The process according to claim 17, further comprising: creating the defect by at least one of implantation after production of the material, doping during production of the material, or electron irradiation during or after production of the material.

27. The process according to claim 17, further comprising: providing a thin metallic or a metal-coordinated molecular conductive layer on a surface of the material, wherein the layer comprises one to five monolayers.

28. The process according to claim 17, further comprising: surrounding the material by a magnetic shielding, and/or surrounding the material by a Faraday cage.

29. The process according to claim 17, further comprising: cooling the material in a temperature range from 0.1 K to 210 K.

30. A device for spatially resolved localization of a defect in a material, the material having a band gap, and the defect having an electron that has at least one energy level that lies in the band gap, the device comprising: means for exciting the electron that are configured to excite the electron such that it is emitted from the material; and means for electron imaging with an electron optics and an electron detector, wherein the device comprises a structure of a transmission electron microscope, wherein the device is adapted such, that the material can be arranged instead of an electron filament of the transmission electron microscope, and wherein the device is adapted such, that the defect is imaged with a spatial resolution sub-25 nm.

31. The device according to claim 30, wherein the device is a component of a quantum computer or a quantum sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG. 1 shows the process for the spatially resolved localization of a defect in a material according to a first preferred embodiment.

[0036] FIG. 2 shows the process for the spatially resolved localization of a defect in a material according to a second preferred embodiment.

DETAILED DESCRIPTION

[0037] FIG. 1 shows the device for the spatially resolved localization of a defect in a material in accordance with a first preferred embodiment.

[0038] It can be seen that the device 10 has means 12 for electron excitation and means 14 for electron imaging.

[0039] The electron excitation means 12 have, 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), wherein one or more optical elements 19, such as high refraction objective lenses, lenses and optical beam sharpeners, can be used to define the beam. The electron excitation means 12 can be movable in their orientation with respect to the sample 18, such that the LASER beam 16 can be directed to a specific point 20 on the surface 22 of the sample 18. Thereby, the sample is grounded such that it cannot become charged.

[0040] In the example shown, the optical source 12 illuminates the sample 18 from above. This is particularly useful for samples that are not radiolucent. If, on the other hand, the sample 18 is opaque, the irradiation 16 can in principle also occur from any side of the sample 18, i.e. also through a side surface of the sample 18 or from below through the sample 18.

[0041] The electron 24 associated with a defect in the sample 18 is emitted by the excitation 16, if this has a sufficiently high energy, and is subsequent accelerated 27 by a metallic lattice 26 arranged above the surface 22 of the sample 18, to which a positive bias voltage is applied, such that it can be taken over by the electron image 14, or more precisely by a condenser lens 28. The bias voltage must be selected as a function of the geometry of the electrode and can range from a few mV to a plurality of kV, for example.

[0042] The accelerated electron 27 subsequently passes through an objective lens 30 and a projective lens 32 to ultimately hit a CCD surface 34. The resulting image (not shown) represents, depending on the selected optical parameters, a complete image of image in sections of the spatial coordinates of the surface 22 and shows the locations at which the electrons 24 were emitted, indicating directly the position of the defects in relation to the surface 22 of the sample 18.

[0043] The elements of the electron optics, i.e. condenser lens 28, objective lens 30 and projective lens 32, along with the electron detector 34 are standard components of a transmission electron microscope and are known to the person skilled in the art, which is why they are not explained in more detail here. Thus, conventional TEMs can preferably be used within the framework of the present invention, wherein, however, the electron filament is removed and the sample 18 is placed there instead. The actual sample holder of the TEM remains empty instead. Thereby, all other elements of the TEM can still be used, although the first of two standard capacitors of a TEM, for example, would not be required, but can still be used. This allows very high resolutions to be achieved with high image quality and image robustness and automatic alignment, because such TEM has aberration correction elements, high magnification, objective lenses with high numerical aperture, focusing elements and acceleration columns to increase the energy of the electrons.

[0044] The person skilled in the art is also familiar with the fact that there should be a vacuum between the sample surface 22 and the electron detector 34, so that the electrons 24, 27 are not undesirably influenced.

[0045] A commercial electron microscope, in particular a commercial transmission electron microscope, can thus be used for the realization of the device for the spatially resolved localization of a defect in a material, wherein its electron source and the electron accelerator can be dispensed with, but need not be. 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.

[0046] The process for the spatially resolved localization of a defect in a material using the device 10 is to 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 process can also be used for any other defects and materials.

[0047] Nitrogen-vacancy (NV) centers in diamond are defects in the carbon lattice that occur when a single carbon atom is substituted by a nitrogen atom and at the same time a gap is created in adjacent lattice sites. In the negative charge state, the NV center has two unpaired electrons that form an S=1 system with triplet electron spin states (ms=0, ?1). For an NV center, the electronic interaction with the crystal symmetry results in the ms=?1 being degenerate and separated from the ms=0 around 2.87 GHz, which is called zero-field splitting. The spin subplanes ms=?1 further divide into two planes in a non-zero magnetic field given by ?=2?B.

[0048] Under ambient conditions, the electron allocated to the NV center can be optically excited from the 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 falls back to the 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, M. L., 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 und Goldman, M. L., Doherty, M. W., 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, so 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 cross-system crossing rates of the excited manifold are also spin-selective. This leads to a special feature in the case of nitrogen defects. The spin state can also be optically initialized at room temperature with very high efficiency using light alone. After a few microseconds of green illumination, a single NV center could be initialized to spin ms=0 sub-level (see Harrison, J., Sellars, M. J. and Manson, N. B. (2006) Measurement of the optically induced spin polarisation of N-V centres 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 centres in diamond, New Journal of Physics, 13 (2), p. 025013, DOI: 10.1088/1367-2630/13/2/025013).

[0049] Since the spin state can be initialized in the state ms=0, a microwave field can be applied in order to induce a spin transition to the state ms=+1 or ms=1, as is possible with the device 100 shown in FIG. 2, which additionally has a microwave source 102 for microwaves 104 to be radiated in, while all other components correspond to those of the device 10 of FIG. 1.

[0050] This spin flip leads to a new ground level of the electron, which is why it undergoes a different optical excitation-de-excitation cycle. This leads to a decrease in the intensity of the luminescence emission. This is referred to as optically captured magnetic resonance. Since this is a far-field technique, it suffers from the limited optical resolution, which practically prohibits imaging or resolving two such NV defects separated within the diffraction limit (approximately 200-250 nm).

[0051] Such diamond NV centers are promising solid-body 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 has 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, E. D. et al. (2019) Ultra-long 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 possible quantum processor/computer. Such qubits could be produced, for example, 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 and 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).

[0052] Such NV centers are advantageous for quantum computers, because they can be generated in close proximity to one another. A single NV center is atomic in size (in practice, the electrons are confined to a few lattice constants that are only approximately 200 picometers in size). Such single quantum spin system interacts with other quantum systems in a defined way, which is predetermined by the laws of quantum physics. In the context of quantum information science, a single-electron quantum system can be referred to as a qubit. Such qubits can be made to interact with another qubit or a network of qubits. In the case of electron spins, they can be made to interact by magnetic dipole-dipole coupling. However, this interaction strength, which is given in terms of the coupling strength, decreases with the third power 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). It is therefore important to arrange the qubits (NV centers) close to one another 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 outlined above, a network of two or more NV centers cannot be resolved individually by optical means in these tight conditions. Therefore, their spin state, which would be useful for processing quantum information, cannot be read out.

[0053] With the method for the spatially resolved localization of a defect in a material, individual qubits can be localized with very high resolution even with a resolution in the subnanometer range and a large number of spins and their networks. Such new method would enable detectors for a large quantum processor, for readout for quantum capturing and for quantum-capable measurement networks, for which independent protection is therefore claimed.

[0054] A single NV defect has an electronic level structure within the band gap of the diamond. Thereby, the ground state (2A) and the excited state (3E) form an electronic triplet, which can be excited by green light (532 nm) at room temperature. The electron enters the excited state 3E by absorbing a photon. If the laser power is now increased (a pulsed laser source can be used for this purpose) or the laser energy is increased by selecting a shorter wavelength of, for example, 405 nm or shorter, a two-photon process is induced, through which the electron is excited into the conduction band (see Bourgeois, E. et al. (2015) Photoelectric detection of electron spin resonance of nitrogen-vacancy centres 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 selected so that only the defects are photoionized. In addition, the material is otherwise defect-free, such that no other photoelectrons are emitted by optical excitation.

[0055] Such photoionized electron 24 is then emitted into the vacuum by a positive bias voltage of the lattice 26, which is applied outside the diamond. Thereby, such photoemitted electron 24 is collected by the lattice 26 and accelerated to specific energies of 0.01 eV to 10 eV 27, which are sufficient for the desired electron optics used and the required resolution. The accelerated electron 27 is then directed into an objective lens 30 as in a TEM. Thereby, the electron 24 passes through a series of electron optics 28, 30, 32, which are produced by magnetic or electromagnetic lenses 30, 32 and condenser lens 28. Thereby, the electron emission from the NV center is magnified by a series of lenses 30, in order to produce a suitable image in the image plane of the electron microscope. As a result, a spatial resolution for the defects in the material 18 of at least 25 nm, preferably at least 20 nm and in particular in the range of 0.1 nm to 20 nm can be achieved.

[0056] The electron optical components 28, 30, 32 could have a series of aberration correction elements (not shown) in order to produce a high-quality image with minimal distortion at the detector 34.

[0057] The array detector (camera) 34 placed in the image plane are to be able to record the number of electrons 27 arriving at each pixel. There are various options for detector cameras 34, which are used in a similar way to a TEM camera. It could be a simple phosphor screen, CCD cameras 27 with microchannel plate amplification and cameras with direct electron detectors.

[0058] The spin-selective excitation that produces the photoemitted electrons 24 is captured and imaged by the array detector. The electron 27 reaching the image plane could be amplified by the microchannel plates (MCPs) or amplifiers or even direct electron detectors with high amplification. Since electron amplification occurs at the detector 34, the process is not limited by photon shot noise, which is the limitation of optically captured magnetic resonance or imaging in the prior art.

[0059] The electron image detectors offer an exceptional signal-to-noise ratio of greater than 10 to 30, even for a single electron 27. This superior detection sensitivity offers an excellent possibility for detecting spin even in individual images. This enables a high contrast of the spin states and better fidelity of reproduction of the spin states. These are features that are highly desirable for quantum information and processing applications.

[0060] From the above representation, it is clear that the present disclosure provides a method with which defects in materials, preferably in solid bodies, can be localized with a significantly higher local resolution than before. Such defects can be quickly and economically optically imaged with high spatial resolution. Above all, it is possible to contactlessly spin-selectively excite and capture or image defects in the solid body with high sensitivity, high dynamic range, large field of view and excellent resolution, which far exceeds the present capabilities of optical detection processes. The device according to the disclosure and the process according to the disclosure are also extremely useful for quantum calculation using defect spins in solid bodies, for quantum-capable capturing and for quantum-capable measurement networks.

[0061] All the features shown in the general description of the invention, the description of the exemplary embodiments, the following claims and in the drawing can be substantial to the invention, both individually and in any combination with one another. Such features or combinations of features can each constitute an independent invention, the claiming of which is expressly reserved. Individual features from the description of an exemplary embodiment do not necessarily have to be combined with one or more or all of the other features specified in the description of this exemplary embodiment; in this respect, each sub-combination is expressly disclosed. In addition, subject features of the device can also be reformulated for use as process features and process features can be reformulated for use as subject features of the device. Such a reformulation is thus automatically disclosed.

LIST OF REFERENCE SIGNS

[0062] 10 Device in accordance with a first preferred embodiment [0063] 12 Means for electron excitation, LASER source [0064] 14 Means for electron imaging [0065] 16 LASER beam [0066] 18 Sample [0067] 19 Optical element [0068] 20 Specific point on the surface 22 of the sample 18 [0069] 22 Surface of the sample 18 [0070] 23 Grounding the sample 18 [0071] 24 The electron associated with a defect in the sample 18 [0072] 26 Metallic lattice [0073] 27 Emitted and accelerated electron [0074] 28 Condenser lens [0075] 30 Objective lens [0076] 32 Projective lens [0077] 34 Electron detector, CCD surface [0078] 100 Device in accordance with a second preferred embodiment [0079] 102 Microwave source [0080] 104 Microwave radiation