An NV color center integrated diamond indentation probe and an indentation measurement method thereof

Abstract

The present application relates to the technical field of micro-nano mechanical testing and quantum precision measurement, and particularly relates to an NV color center integrated diamond indentation probe and an indentation measurement method thereof. The probe comprises a probe rod and a diamond indenter, the diamond indenter has a connecting end, an indentation tip and multiple side faces, at least one side face is provided with four NV color center sensing unit groups with different crystal directions in a stable sensing area. During measurement, a baseline and light detection magnetic resonance spectra of each holding stage are collected, four frequency drift amounts are obtained through multi-peak fitting, and local temperature variation, equivalent stress parameters, effective magnetic field variation parameters and effective electric field variation parameters are solved based on a calibrated and full-rank response matrix. The present application can realize in-situ synchronous measurement of multiple types of physical quantities in the indentation area.

Description

Technical Field

[0001] This invention relates to the field of micro-nano mechanical testing and quantum precision measurement technology, and in particular to an NV color center integrated diamond indentation probe and its indentation measurement method. Background Technology

[0002] Nanoindentation testing typically characterizes mechanical parameters such as hardness and elastic modulus of materials by obtaining the load-displacement relationship during the indentation process. It has been widely used in the mechanical property testing of thin films, coatings and microstructures.

[0003] During actual indentation, material deformation near the indentation area may be accompanied by phenomena such as plastic dissipation, thermo-elastic coupling, charge accumulation, and magnetic domain rearrangement in magnetic materials, resulting in changes in various physical quantities, including stress / strain, temperature, electric field, and magnetic field. Existing indentation testing typically focuses on the load-displacement relationship, making it difficult to simultaneously and quantitatively measure these multiple physical quantities in situ during indentation. Furthermore, using different instruments at different locations or times may introduce spatial and temporal registration errors. Therefore, a scheme is needed to provide an indentation measurement method that enables simultaneous in-situ measurement of multiple physical quantities during the indentation process. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides an integrated diamond indentation probe for NV color centers, comprising a probe rod and a diamond indenter fixed to the lower end of the probe rod.

[0005] The diamond indenter is made of single-crystal diamond and has a connecting end connected to the probe rod, an indentation tip for indenting the sample to be tested, and multiple sides that gradually expand outward from the indentation tip toward the connecting end.

[0006] At least one of the said sides is provided with an NV color center array.

[0007] The NV color center array is located in a stable sensing region, which is a region that avoids the maximum stress concentration area of ​​the indentation tip and can sense the stress, temperature, magnetic field and electric field changes caused by sample deformation in the indentation area.

[0008] The NV color center array includes four NV color center sensing unit groups with different crystal orientations. Each NV color center sensing unit group is used to generate photodetector magnetic resonance characteristic spectral lines corresponding to its crystal orientation.

[0009] The present invention also provides an indentation measurement method based on the above-mentioned NV color center integrated diamond indentation probe.

[0010] When the diamond indenter is not in contact with the sample to be tested, the NV color center array is excited by excitation light, a microwave sweep signal is applied to the NV color center array, and the overall fluorescence intensity of the NV color center array at different microwave frequencies is collected by CCD to obtain the baseline light detection magnetic resonance spectrum.

[0011] The baseline optical detection magnetic resonance spectrum is fitted with multiple peaks, and four baseline characteristic frequencies are obtained based on the pre-established mapping relationship between the characteristic spectral lines and the four NV color center sensing unit groups.

[0012] The diamond indenter is driven to press into the sample under test according to a preset load increment or displacement increment, and the load or displacement remains unchanged after reaching the target load or target indentation depth in each indentation stage.

[0013] During each load holding phase, the NV color center array is excited using the excitation light, the microwave sweep signal is applied to the NV color center array, and the overall fluorescence intensity at different microwave frequencies is collected using the CCD to obtain the photodetector magnetic resonance spectrum of the current load holding phase. The photodetector magnetic resonance spectrum is then fitted with multiple peaks to obtain four real-time characteristic frequencies.

[0014] Based on the four baseline characteristic frequencies and the four real-time characteristic frequencies, four frequency drifts are obtained for the current push-in phase, and the four frequency drifts satisfy the following conditions: ; The four frequency drifts are calculated to obtain the first... The calculation of the local temperature change, equivalent stress parameter, effective magnetic field change parameter, and effective electric field change parameter of the indentation region during each indentation stage satisfies the following conditions: ; in, Let be the calibrated and full-rank response matrix. This represents the local temperature change in the indentation region during the k-th indentation stage. Let be the equivalent stress parameter of the indentation region during the k-th indentation stage. The effective magnetic field variation parameter relative to the baseline. The effective electric field variation parameter is relative to the baseline.

[0015] The technical solution of the present invention has at least the following beneficial effects: This invention incorporates an array of NV color centers on the side of a single-crystal diamond indenter. An NV color center is a point defect in the diamond lattice formed by a nitrogen atom replacing a carbon atom and adjacent to a vacancy; it is typically a negatively charged state. It possesses an optically readable electron spin triplet state; its zero-field splitting, Zeeman splitting, and lattice strain-related energy levels exhibit measurable frequency shifts with changes in temperature, magnetic field, electric field, and stress, respectively. Four NV color center sensing units with different crystal orientations can form corresponding optically detected magnetic resonance characteristic spectral lines. The four frequency shifts are used as interrelated observable inputs to form a calibrated, full-rank response matrix, thereby obtaining local temperature changes, equivalent stress parameters, effective magnetic field change parameters, and effective electric field change parameters.

[0016] Furthermore, the stable sensing zone avoids the area of ​​maximum stress concentration at the indentation tip. The indenter tip contact area experiences high gradient contact pressure and shear stress in the initial loading stage, with local stress reaching GPa levels. This is accompanied by surface friction, plastic extrusion, and heat accumulation, easily leading to local lattice distortion, surface state charge trapping, and... Towards Transformation can lead to NV center spectral line broadening or fluorescence quenching. These anomalies can cause shifts or drifts in the extracted resonance frequencies, thereby reducing the accuracy and stability of multi-physical quantity calculations. Placing the NV center array in a stable sensing region can reduce the risk of direct damage while preserving sensitivity to sample deformation fields.

[0017] Meanwhile, this invention completes excitation, microwave frequency sweep, and overall fluorescence acquisition using the same NV color center array within the same loading step, and obtains the characteristic frequencies corresponding to each crystal orientation through multi-peak fitting, eliminating the need for point-by-point spatial resolution of each NV color center using a CCD. The frequency drift obtained from the same sensing array and the same indentation stage is used in the calculation, reducing spatial and temporal registration errors caused by acquisition from different instruments, measurement positions, or at different times.

[0018] Furthermore, the present invention employs a measurement method that involves pressing in the load according to a preset load increment or displacement increment, maintaining the load and collecting the optical detection magnetic resonance spectrum at each pressing stage. This allows for frequency fitting within a window of relatively stable mechanical vibration decay and displacement, reducing the impact of piezoelectric platform vibration, contact noise, and spot drift on frequency extraction, and improving the comparability of measurement results at different pressing stages and the stability of multi-physical quantity calculation. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the in-situ working state of the NV color center integrated diamond indentation probe in one embodiment of this application; Figure 2 This is a schematic diagram of the NV color center integrated diamond indentation probe structure in another embodiment of this application; Figure 3 This is a schematic diagram of the in-situ indentation multiphysics measurement system in another embodiment of this application; Figure 4 This is a flowchart of an in-situ indentation multi-physical quantity measurement method in another embodiment of this application.

[0021] Figure Labels 1. Probe rod; 2. Clamping assembly; 3. Single crystal diamond indenter; 4. Indentation tip; 5. NV color center array; 6. Laser emitter; 7. Collimating lens; 8. Reflector; 9. Focusing and shaping lens group; 10. Objective lens; 11. Fluorescence receiving lens group; 12. Microwave antenna; 13. Nanoindenter body; 14. Sample stage; 15. Sample to be tested. Detailed Implementation

[0022] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0023] It should be noted that, in the absence of conflict, the following embodiments and features can be combined with each other; and, based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0024] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this disclosure, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0025] Example 1: NV (nitrogen vacancy) color center integrated diamond indentation probe As an optional embodiment of the present invention, such as Figure 1 and Figure 2 As shown, this embodiment provides an NV color center integrated diamond indentation probe. Figure 2 As shown, the indentation probe includes a probe rod 1 and a diamond indenter 3 connected to the end of the probe rod 1. The probe rod 1 is used to connect with the clamping assembly 2, and the diamond indenter 3 is used to press into the sample 15 to be tested.

[0026] The diamond indenter 3 is made of single-crystal diamond and has a connecting end and an indentation tip 4 arranged opposite each other, as well as multiple outer wall surfaces connecting the connecting end and the indentation tip 4. The lateral dimension of the connecting end is larger than the lateral dimension of the indentation tip 4, and each outer wall surface gradually converges from the connecting end to the indentation tip 4, making the diamond indenter 3 an overall pyramidal structure. The indentation tip 4 can be formed into a triangular pyramid, a square pyramid, or other sharp structures suitable for nanoindentation testing.

[0027] like Figure 2 As shown, at least one outer wall surface is provided with a stabilizing sensing zone. This stabilizing sensing zone is located at a position that avoids the maximum stress concentration area of ​​the indentation tip 4 and can sense the stress, temperature, magnetic field, and electric field changes caused by the deformation of the sample in the indentation area. The stabilizing sensing zone can be determined based on the finite element stress distribution of the diamond indenter 3 under a preset maximum load, a pre-established indenter stress distribution, or experimental calibration results.

[0028] The predetermined strength criterion referred to in this embodiment means that, within a predetermined loading range, the local equivalent stress in the stable sensing region is lower than a stress threshold determined based on the allowable stress of the diamond material, the resolvable optical detection magnetic resonance response range of the NV color center, and a safety factor. This ensures that the diamond indenter 3 does not break during loading and that the resonance spectral lines of the NV color center remain within an identifiable and calibrable range. The stable sensing region can be selected according to the maximum principal stress criterion, the equivalent stress criterion, or other strength criteria applicable to brittle materials.

[0029] When using the equivalent stress criterion, the equivalent stress parameters can be obtained from each principal stress. The equivalent stress parameter is used to characterize the multiaxial stress state of the stable induction region as a single scalar. For example, when using the von Mises equivalent stress calculation criterion, the equivalent stress parameter satisfies the following condition: ; in, , and These are the first principal stress, second principal stress, and third principal stress in the stable induction zone. When using other equivalent stress calculation criteria for calibration, the same calculation criteria are used in the measurement phase as in the calibration phase.

[0030] like Figure 1 As shown, an NV color center array 5 is arranged within the stable sensing region. The NV color center array 5 includes four NV color center sensing unit groups: NV1, NV2, NV3, and NV4. Each NV color center sensing unit group includes one or more NV color centers. As a specific example, the crystal orientations of NV1, NV2, NV3, and NV4 are respectively... , , and NV color centers with different crystal orientations have different projection responses under the same external physical field, thus enabling the formation of distinguishable characteristic spectral lines in optically detected magnetic resonance spectra.

[0031] The NV color center array 5 can be arranged into multiple array points along the length and width directions of the outer wall. As an optional configuration, the length and width of the stable sensing area are respectively located at... The depth of the NV color center from the outer wall surface is within... Within; the spacing between adjacent array points is within The areal density of the NV color center array 5 can be within... The dimensions and density described above can be adjusted according to the required spatial resolution, fluorescence count rate, and imaging range of the optical system.

[0032] The NV color center array 5 can be fabricated by mask-defined ion implantation, focused ion beam implantation, or by first forming implantation windows through electron beam exposure followed by nitrogen ion implantation. Taking mask-defined ion implantation as an example, a resist layer or inorganic mask layer is first formed on the outer wall of the target of the diamond indenter 3, and then implantation windows corresponding to each array point are formed by photolithography or electron beam exposure; then, the nitrogen ion implantation energy is selected according to the target embedment depth, and the implantation dose is selected according to the target NV color center density.

[0033] After nitrogen ion implantation is completed, it can be performed in a vacuum, inert gas, or reducing atmosphere. The internal annealing process allows the implanted nitrogen atoms to combine with vacancies in the diamond lattice to form NV color centers. After annealing, the mask is removed, and the graphitization layer and surface contaminants are removed through acid washing, oxygen plasma treatment, oxygen terminal treatment, or other surface treatments to enhance the negative charge state NV. - The stability of the array is also considered. In actual fabrication, confocal fluorescence imaging and photodetector magnetic resonance imaging can be used to screen array points that meet the requirements for fluorescence intensity, spectral contrast, and linewidth.

[0034] NV color centers are point defects formed by substituted nitrogen atoms and their adjacent vacancies in the diamond lattice, exhibiting a negatively charged NV state. - It possesses an electron spin triplet state that can be excited by laser and read out via fluorescence. Temperature changes cause changes in the zero-field splitting parameter, magnetic fields induce energy level splitting through the Zeeman effect, electric fields cause energy level shifts through the Stark effect, and stress or strain alters the spin energy levels through lattice coupling. Therefore, during microwave frequency sweeping, the photodetector magnetic resonance characteristic frequencies corresponding to NV color centers with different crystal orientations will undergo measurable frequency shifts with the aforementioned physical quantities.

[0035] Because the NV color center array 5 is positioned in a stable sensing region that avoids the area of ​​maximum stress concentration at the indentation tip 4, it can still receive local stress transmitted from sample deformation to the diamond indenter 3, as well as changes in the temperature, electric, and magnetic fields of the indentation region. Simultaneously, it reduces the direct impact of high-gradient contact pressure, shear stress, friction, and heat accumulation on the NV color centers. This reduces excessive lattice distortion, spectral broadening, fluorescence quenching, and NV color center degradation. - To NV 0 The characteristic frequency shift or drift caused by the transformation improves the stability and measurement accuracy of frequency observations during indentation.

[0036] Example 2: In-situ Indentation Multi-physical Quantity Measurement System As an optional embodiment of the present invention, such as Figure 3 As shown, this embodiment provides an in-situ indentation multi-physical quantity measurement system, including a clamping component 2, an excitation optical path component, a fluorescence receiving optical path component, a microwave excitation component, and the NV color center integrated diamond indentation probe described in Embodiment 1. The system may also include a nanoindenter 13 and a synchronization control and data processing module.

[0037] The nanoindenter 13 includes a frame, a loading unit, a load detection unit, a displacement detection unit, a sample stage 14, and a displacement stage for adjusting the relative position of the sample. The loading unit is connected to the clamping assembly 2 and is used to drive the diamond indenter 3 closer to or further away from the sample 15 to be tested. The load detection unit and the displacement detection unit are used to obtain the load and indentation depth during the indentation process, respectively. The nanoindenter 13 can be a commercial nanoindentation device with load closed-loop, displacement closed-loop, and load holding control functions, such as the Bruker TI 980 nanoindenter, the Anton Paar UNHT series nanoindenter, or other devices with similar functions.

[0038] The clamping assembly 2 includes a clamping part that surrounds and encircles the connecting end of the probe rod 1 or the diamond indenter 3, forming a force transmission connection between the clamping part and the probe rod 1 or the diamond indenter 3. A hollow optical path channel extending along the direction of excitation light propagation is provided in the middle of the clamping assembly 2, allowing the excitation light to propagate from the connecting end side of the diamond indenter 3 to the indenter area. The clamping assembly 2 can employ a split-type jaw, a sleeve-type clamp, an elastic chuck, or other structures capable of stable clamping while retaining a central light-transmitting space.

[0039] The excitation optical path assembly, along the propagation direction of the excitation light, includes, in sequence, a laser emitter 6, a collimating lens 7, a reflecting mirror 8, a focusing and shaping lens group 9, and an objective lens 10. The laser emitter 6 emits the excitation light; the collimating lens 7 reduces the divergence angle of the excitation light; the reflecting mirror 8 changes the propagation direction of the excitation light and aligns it with the hollow optical path channel; the focusing and shaping lens group 9 adjusts the beam diameter, divergence angle, and pre-focusing position of the excitation light; and the objective lens 10 adjusts the final focusing position and irradiation range of the excitation light in the diamond indenter 3 region.

[0040] As a specific optical assembly, the focusing and shaping lens group 9 may include a first concave lens, a first convex lens, and a second convex lens arranged sequentially along the optical path. The first concave lens is used to expand the beam diameter, and the first convex lens cooperates with the first concave lens to form a beam-expanding and collimating structure to maintain the predetermined parallelism of the excitation light after long-distance transmission; the second convex lens is used to pre-focus the collimated excitation light and match the beam with the entrance pupil of the objective lens 10. The focusing and shaping lens group 9 is not limited to three lenses, but may also consist of two or more lenses, as long as it can perform one or more of the following processes: beam expansion, beam contraction, collimation maintenance, and pre-focusing.

[0041] The focusing and shaping lens group 9 and the objective lens 10 can be entirely or partially housed within the hollow optical path channel. The objective lens 10 can consist of a single lens or a lens group composed of multiple lenses. By adjusting the axial position of the focusing and shaping lens group 9 and the objective lens 10, the position of the final focal point and the illumination range can be changed, allowing the excitation light to enter the pyramidal diamond indenter 3 from the connecting end side and cover the NV color center array 5 located in the stable sensing area on the outer wall. Since the indenter gradually converges from the connecting end to the indentation tip 4, when the excitation light covers the lateral range corresponding to the stable sensing area on the connecting end side, the beam propagating towards the indentation tip 4 can cover the corresponding outer wall.

[0042] The laser emitter 6, collimating lens 7, and reflector 8 can be mounted on the moving control arm of the nanoindenter 13, allowing it to move synchronously with the loading head; alternatively, they can be mounted on an optical support fixed relative to the frame, ensuring that the displacement of the diamond indenter 3 relative to the beam within a preset indentation stroke remains within the focal depth or adjustable focus range of the objective lens 10. Both mounting methods meet the functional requirement of continuous excitation light coverage of the NV color center array 5. The excitation light can be a 532 nm laser, and the laser power can be adjusted according to the NV color center fluorescence count rate and photothermal drift, for example, at a wavelength of 532 nm. Inside.

[0043] The fluorescence receiving optical path assembly is located to the side of the diamond indenter 3, including a fluorescence receiving lens group 11 facing the stable sensing area and a charge-coupled device (CCD) optically connected to the fluorescence receiving lens group 11. The fluorescence receiving lens group 11 is used to collect the fluorescence generated by the NV color center array 5 under the action of excitation light and to image or focus the fluorescence onto the CCD. The fluorescence receiving optical path assembly may also include optical components disposed between the fluorescence receiving lens group 11 and the CCD, such as a long-pass filter, a band-pass filter, a dichroic mirror, an aperture, or a fiber coupler, to suppress excitation light and ambient stray light and improve the fluorescence signal-to-noise ratio.

[0044] The CCD is used to acquire the overall fluorescence intensity changes of the entire NV color center array 5 at different microwave frequencies, without requiring spatial resolution of individual NV color centers on the image. The optically detected magnetic resonance (ODMR) spectrum of the overall fluorescence intensity as a function of microwave frequency is obtained by microwave frequency sweep. Then, based on the calibrated frequency range, peak order, and response relationship, multiple resonance peaks are fitted to extract multiple characteristic frequencies corresponding to different NV color center sensing unit groups.

[0045] The microwave excitation assembly includes a microwave source, a microwave control module, and a microwave antenna 12. The microwave antenna 12 is positioned to couple microwave signals to the NV color center array 5, for example, near the clamping assembly 2, probe rod 1, diamond indenter 3, or sample stage 14. The specific installation location of the microwave antenna 12 is not limited, as long as the microwave field it generates can cover the NV color center array 5 and produce a detectable ODMR response for each orientation NV color center.

[0046] The synchronization control and data processing module is communicatively connected to the nanoindenter 13, laser emitter 6, CCD, and microwave control module, respectively. It coordinates the timing of loading, load holding, microwave frequency sweeping, and fluorescence acquisition, and performs multi-peak fitting on the ODMR spectrum. It also calculates local temperature changes, equivalent stress parameters, effective magnetic field changes, and effective electric field changes based on calibration results. The synchronization control and data processing module can consist of a computer, a data acquisition card, a trigger controller, and corresponding software programs.

[0047] During system operation, clamping assembly 2 connects the load transfer path of diamond indenter 3 with the hollow optical path channel, and the loading unit drives diamond indenter 3 to press into the sample 15 to be tested. Excitation light, after collimation, redirection, beam shaping, and final focusing, passes through the hollow optical path channel and continuously covers the NV color center array 5. Microwave antenna 12 applies a sweep frequency signal to the NV color center array 5 during the load holding phase. Fluorescence receiving lens group 11 collects fluorescence from the side of diamond indenter 3, and the overall fluorescence intensity is recorded by a CCD. The aforementioned optical, microwave, and loading components work collaboratively at the same pressing position and during the same load holding phase, enabling the system to obtain ODMR spectra without removing the indenter or changing the measuring equipment.

[0048] Therefore, this system can establish a unified data index for the indentation loading state, microwave frequency, and fluorescence data, reducing the time delay caused by offline measurement after indentation and the spatial registration error between different devices and positions. Furthermore, the focusing and shaping lens group 9 and the objective lens 10 jointly adjust the beam diameter, divergence angle, and focal point position, compensating for the impact of long-distance beam transmission and small-stroke movement of the indenter on the irradiated area; the fluorescence receiving lens group 11 and the filter assembly improve the collection efficiency and signal-to-noise ratio of red fluorescence; and the microwave excitation assembly provides the necessary frequency sweep excitation for reading the spin resonance frequencies of different NV crystal orientations.

[0049] Example 3: In-situ Multi-physical Quantity Indentation Measurement Method As an optional embodiment of the present invention, this embodiment utilizes the NV color center integrated diamond indentation probe described in Embodiment 1 and the in-situ indentation multi-physical quantity measurement system described in Embodiment 2 to measure the local temperature change, equivalent stress parameter, effective magnetic field change parameter, and effective electric field change parameter of the sample 15 under test during the indentation process. Figure 4 As shown, the method includes the following steps.

[0050] Step S1: System Calibration. Before formal measurement, the temperature, stress, magnetic field, and electric field responses are calibrated separately. For temperature calibration, the probe is placed on a temperature control platform, and ODMR spectra are collected at multiple known temperature points, such as 25 ℃, 50 ℃, and 75 ℃. The temperature response coefficient is determined based on the change of each characteristic frequency relative to the reference temperature. For stress calibration, the probe is pressed into a standard sample with known mechanical parameters such as Young's modulus and Poisson's ratio, such as a fused silica sample. ODMR spectra are collected under multiple loads or indentation depths, and the local stress in the stable sensing region is obtained by combining finite element analysis to determine the stress response coefficient corresponding to each NV color center sensing unit group.

[0051] For magnetic field calibration, a standard magnetic field of known direction and intensity is applied around the probe, and ODMR spectra are acquired. For electric field calibration, a standard electric field of known direction and intensity is applied around the probe, and ODMR spectra are acquired. Based on the frequency variations of the NV centers under different crystal orientations, the response relationships of four characteristic frequencies to local temperature changes, equivalent stress parameters, effective magnetic field variation parameters, and effective electric field variation parameters are established. During calibration, the four response equations should be independent of each other, and the resulting response matrices should be full-rank matrices to ensure that the four measured parameters have unique solutions or stable solutions obtainable through the least squares method.

[0052] The frequency shift of NV color centers is typically caused by the combined effects of temperature, strain, magnetic field, and electric field. For the first... For each NV color center sensing unit group, the frequency drift satisfies the following condition: ; in, For local strain tensor, For the first Crystal orientation of each NV color center sensing unit group and The magnetic field and electric field along the first line are respectively Effective projection of NV crystal orientation For strain coupling terms, The temperature response coefficient, and The first The magnetic field response coefficient and electric field response coefficient of each NV color center sensing unit group.

[0053] In the measurement process of this embodiment, the response corresponding to the local strain tensor is converted into equivalent stress parameters through finite element analysis and standard sample calibration. The magnetic and electric field projections corresponding to each NV crystal orientation are converted into effective magnetic field variation parameters. and effective electric field variation parameters Within a pre-defined linear response range, the above general response relationship is linearized as follows: ; in, , , and The first The temperature, equivalent stress, effective magnetic field, and effective electric field response coefficients corresponding to each NV color center sensing unit group are calculated. Combining the linearized equations corresponding to the four NV color center sensing unit groups yields the response matrix equation. As long as the response equations generated by the four NV color center sensing unit groups are independent, the response matrix... It is a full-rank matrix, which allows us to calculate the local temperature change, equivalent stress parameter, effective magnetic field change parameter, and effective electric field change parameter through four frequency drifts.

[0054] Step S2: Sample Mounting and Optical Path Adjustment. Fix the sample 15 to be tested on the sample stage 14 of the nanoindenter 13, and use the displacement stage to position the test location directly below the diamond indenter 3; adjust the focusing and shaping lens group 9 and the objective lens 10 to ensure the excitation light covers the stable sensing area where the NV color center array 5 is located; adjust the fluorescence receiving lens group 11, the filter assembly, and the CCD's receiving state until a clear and stable fluorescence signal is obtained. As an example, the fluorescence count rate, expressed in counts per second (cps), can be adjusted to... Inside, the laser power is controlled to avoid significant photothermal drift.

[0055] Step S3: Baseline Data Acquisition. With the diamond indenter 3 not in contact with the sample 15 or under zero load, the microwave source is activated and frequency sweep is performed within a preset range including the NV color center resonance frequency, for example, within the range of 2.6 GHz to 3.0 GHz. The CCD acquires the overall fluorescence intensity at different microwave frequencies to form the baseline ODMR spectrum. Based on the frequency range, peak order, and NV color center sensing unit group mapping relationship established during the calibration phase, the baseline ODMR spectrum is subjected to multi-peak fitting to obtain four baseline characteristic frequencies. , , and .

[0056] Step S4: Step Loading and Holding. Start the nanoindenter 13, causing the diamond indenter 3 to press into the sample 15 according to a preset load increment or displacement increment. After reaching each target load or target indentation depth, maintain the load or displacement unchanged and wait for the mechanical vibration to decay before performing ODMR data acquisition within a stable measurement window. The holding time can be within [specified range]. Alternatively, data acquisition can begin after the displacement drift rate, load drift rate, or fluorescence count rate fluctuations fall below the corresponding threshold. This step-load-hold-measurement method can reduce the impact of loading mechanism vibration, contact noise, and spot drift on resonance peak fitting.

[0057] Step S5: Real-time ODMR spectrum acquisition and frequency drift measurement. In the... During the loading phase, the microwave excitation component applies a frequency sweep signal to the NV color center array 5, and the CCD acquires the overall fluorescence intensity to form the ODMR spectrum of the current loading phase; multi-peak fitting is performed on this ODMR spectrum to obtain four real-time characteristic frequencies. , , and The first [value] is obtained based on four real-time characteristic frequencies and four baseline characteristic frequencies. The four frequency drift values ​​in each push-in stage satisfy the following condition: ; in, For the first The first pressing phase Frequency drift corresponding to each NV color center sensing unit group For the corresponding real-time feature frequencies, This represents the corresponding baseline characteristic frequency.

[0058] Step S6: Multi-physical quantity solution. For the nonlinear response case, the first... The frequency drift can be expressed as a response function to local temperature change, equivalent stress parameter, effective magnetic field change parameter, and effective electric field change parameter, satisfying the following conditions: ; in, For the first The response functions of each NV color center sensing unit group are obtained after calibration. When using a linear response model within the calibration range, the calibrated response matrix is ​​used. The four frequency drifts are calculated to obtain the first... Local temperature change in the indentation area during each pressing stage Equivalent stress parameters Effective magnetic field variation parameters and effective electric field variation parameters The calculation satisfies the following conditions: ; in, This is the calibrated, full-rank response matrix; For the first The local temperature change in the indentation area during each pressing stage; The equivalent stress parameters are obtained according to the same equivalent stress calculation criteria used in the calibration phase; The effective magnetic field variation parameter relative to the baseline; The effective electric field variation parameter is relative to the baseline. The data processing module can solve the above equation using matrix inversion or least squares methods.

[0059] To illustrate the above solution process, the following numerical example is given. Assume that in the... During the compression stage, the four frequency shifts obtained through multi-peak fitting are: ; The response matrix obtained through temperature calibration, stress calibration, magnetic field calibration, and electric field calibration for: ; The four columns of this response matrix correspond to the local temperature change, equivalent stress parameter, effective magnetic field change parameter, and effective electric field change parameter, respectively; the units of the coefficients in each column correspond to MHz / K, MHz / GPa, MHz / mT, and MHz / (V / μm), respectively. This matrix is ​​a full-rank matrix. Substituting the frequency drift into the response equation and performing matrix inversion, we can obtain: .

[0060] Therefore, during this indentation stage, the local temperature of the indentation region increases by 4 K relative to the baseline state, the equivalent stress parameter is 0.2 GPa, the effective magnetic field change is 0.01 mT, and the effective electric field change is 0.4 V / μm. These values ​​are only used to illustrate the process of solving for the four physical parameters from the four frequency drifts; the actual response matrix and measurement results are determined by the specific probe and calibration process.

[0061] Step S7: Continue loading. After completing the ODMR acquisition and parameter calculation for the current load holding stage, continue loading to the next target load or target depth according to the preset load increment or displacement increment, and repeat steps S4 to S6 until the preset maximum load, maximum indentation depth, or other termination conditions are reached. This yields a multi-physical quantity data sequence corresponding one-to-one with each indentation stage, load, indentation depth, and acquisition time.

[0062] Step S8: Multi-location field reconstruction and visualization. The above measurement process is repeated at multiple locations on the surface of the sample 15 to obtain the local temperature change, equivalent stress parameters, effective magnetic field change parameters, and effective electric field change parameters corresponding to different measurement locations and indentation depths. The data processing module combines or spatially interpolates data from the same or similar indentation stages based on the coordinates of each measurement location, forming distribution maps of the temperature field, stress field, magnetic field, and electric field, and visualizing them according to the indentation depth or loading time. Operators can thus observe the distribution of various physical quantities at different locations on the sample and their changes during the loading process, such as determining temperature rise caused by plastic dissipation or thermo-elastic coupling, local stress concentration, stress-induced magnetic domain rearrangement or flipping, and electric field changes caused by piezoelectric effect, flexural effect, or local charge accumulation.

[0063] Since the data of each physical quantity originate from the ODMR spectra acquired by the same NV color center array 5 during the corresponding load holding phase, and share the measurement position, load, indentation depth, and acquisition time index, there is no need to re-register the spatial and temporal data obtained by different instruments or at different times when performing field reconstruction and visualization. This is beneficial to improving the accuracy of the correspondence between the distribution and evolution relationships of multiple physical quantities.

[0064] Step S9: Anomaly Monitoring and Protection. During continuous measurement, at least one of the following parameters of the NV color center array 5 can be monitored: fluorescence count rate, ODMR contrast, resonant linewidth, and fluorescence lifetime. Fluorescence lifetime can be measured using pulsed laser excitation and time-correlated single-photon counting (TCSPC) modules. An anomaly can be identified if the fluorescence lifetime changes by more than 20% to 40% relative to the baseline, the fluorescence count rate decreases by more than 30%, the ODMR contrast is lower than 50% of the initial value, or the resonant linewidth increases to more than twice the initial value.

[0065] Upon detecting an anomaly, the synchronization control and data processing module can pause loading and raise the pressure head to a safe height, saving the current load-displacement curve, the original ODMR spectrum, and the anomaly monitoring data. Then, it re-acquires the zero-load baseline for verification. If the signal recovers after verification, the data from the corresponding loading stage is marked as low confidence, and measurement continues. If the signal remains abnormal, the measurement is terminated, and a prompt is given to replace the probe or readjust the optical path. This protection process reduces invalid data caused by NV center charge state transitions, local lattice damage, or optical path drift, and lowers the risk of probe damage due to continued loading under abnormal conditions.

[0066] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An integrated diamond indentation probe for NV color centers, comprising a probe rod and a diamond indenter fixed to the lower end of the probe rod, characterized in that: The diamond indenter is made of single-crystal diamond and has a connecting end connected to the probe rod, an indentation tip for indenting the sample to be tested, and multiple sides that gradually expand outward from the indentation tip toward the connecting end. At least one of the said sides is provided with an NV color center array; The NV color center array is located in a stable sensing region, which is a region that avoids the maximum stress concentration area of ​​the indentation tip and can sense the stress, temperature, magnetic field and electric field changes caused by sample deformation in the indentation area. The NV color center array includes four NV color center sensing unit groups with different crystal orientations. Each NV color center sensing unit group is used to generate photodetector magnetic resonance characteristic spectral lines corresponding to its crystal orientation.

2. The NV color center integrated diamond indentation probe according to claim 1, characterized in that, The stable sensing zone is determined based on the finite element stress analysis results of the diamond indenter under a predetermined maximum indentation load or a pre-established indenter stress distribution. The maximum equivalent stress within the stable sensing region is less than the maximum equivalent stress within the maximum stress concentration region of the indentation tip.

3. The NV color center integrated diamond indentation probe according to claim 2, characterized in that, The equivalent stress is a scalar mechanical parameter obtained by converting the local stress tensor in the stable sensing region according to a predetermined equivalent stress criterion.

4. The NV color center integrated diamond indentation probe according to claim 1, characterized in that, The four NV color center sensing unit groups correspond to four equivalent <111> type NV color center crystal orientations in a single-crystal diamond lattice.

5. The NV color center integrated diamond indentation probe according to claim 1, characterized in that, The NV color center array is a linear array or a two-dimensional array arranged along the side extension direction; The minimum distance between the NV color center array and the pressed tip is: ; The areal density of the NV color center array is: .

6. An indentation measurement method based on the NV color center integrated diamond indentation probe according to any one of claims 1 to 5, characterized in that, include: When the diamond indenter is not in contact with the sample to be tested, the NV color center array is excited by excitation light, a microwave sweep signal is applied to the NV color center array, and the overall fluorescence intensity of the NV color center array at different microwave frequencies is collected by CCD to obtain the baseline light detection magnetic resonance spectrum. Multi-peak fitting is performed on the baseline optical detection magnetic resonance spectrum, and four baseline characteristic frequencies are obtained based on the pre-established mapping relationship between the characteristic spectral lines and the four NV color center sensing unit groups. The diamond indenter is driven to press into the sample under test according to a preset load increment or displacement increment, and the load or displacement remains unchanged after reaching the target load or target indentation depth in each indentation stage; In each load holding phase, the NV color center array is excited by the excitation light, the microwave sweep signal is applied to the NV color center array, and the overall fluorescence intensity at different microwave frequencies is collected by the CCD to obtain the photodetector magnetic resonance spectrum of the current indentation phase. The photodetector magnetic resonance spectrum is then fitted with multiple peaks to obtain four real-time characteristic frequencies. Based on the four baseline characteristic frequencies and the four real-time characteristic frequencies, four frequency drifts are obtained for the current push-in phase, and the four frequency drifts satisfy the following conditions: ； The four frequency drifts are calculated to obtain the local temperature change, equivalent stress parameter, effective magnetic field change parameter, and effective electric field change parameter of the indentation region in the k-th indentation stage. The calculation satisfies the following condition: ； in, Let be the calibrated and full-rank response matrix. This represents the local temperature change in the indentation region during the k-th indentation stage. Let be the equivalent stress parameter of the indentation region during the k-th indentation stage. The effective magnetic field variation parameter relative to the baseline. The effective electric field variation parameter is relative to the baseline.

7. The indentation measurement method according to claim 6, characterized in that, Before obtaining the baseline optically detected magnetic resonance spectrum, the optically detected magnetic resonance spectrum of the NV color center array was acquired under known temperature, known local stress, known magnetic field and known electric field conditions, respectively. The response matrix K is established based on the acquired optically detected magnetic resonance spectrum; wherein the known local stress is determined by the load data obtained from pressing in a standard sample and the results of finite element analysis.

8. The indentation measurement method according to claim 6, characterized in that, After maintaining the load or displacement constant in each pressing stage, the optical detection magnetic resonance spectrum of the current pressing stage is collected when the displacement drift rate is lower than a preset threshold. The load holding time during the load holding phase is: .

9. The indentation measurement method according to claim 6, characterized in that, When two photodetector magnetic resonance frequencies correspond to the same NV color center sensing unit group, the center value of the two photodetector magnetic resonance frequencies is taken as the characteristic frequency corresponding to the NV color center sensing unit group.

10. The indentation measurement method according to claim 6, characterized in that, The indentation measurement method is performed at multiple indentation locations and / or multiple indentation depths on the sample to be tested, and the local temperature change, equivalent stress parameter, effective magnetic field change parameter, and effective electric field change parameter are correlated and output according to the indentation location and indentation depth.

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