A scanning NV-probe microscope

Abstract

The embodiment of the application discloses a scanning NV probe microscope, which comprises an atomic force microscope system for detecting surface topography information of a sample and an optical detection magnetic resonance system for detecting magnetic field distribution information of the sample, the atomic force microscope system comprises a vibrating arm and a diamond probe, and the optical detection magnetic resonance system comprises an NV color center, a transition excitation light path and a fluorescence detection light path; the sample to be scanned and the transition excitation light path are located on opposite sides of the diamond probe respectively, and the transition excitation light path and the fluorescence detection light path are located on the same side of the diamond probe; a first metal plating film is arranged on the side of the diamond probe close to the sample, and the first metal plating film is used for blocking surface fluorescence of the sample. The scanning NV probe microscope provided by the embodiment of the application blocks stray fluorescence from the surface of the sample by arranging a metal plating film at the bottom of the diamond probe, so that the problems of low signal-to-noise ratio of magnetic field imaging and limited measurement accuracy of the existing scanning NV probe microscope are solved.

Description

Technical Field

[0001] The present invention relates to the field of atomic force microscopy, and more particularly to a scanning NV probe microscope. Background Technology

[0002] Scanning probe magnetic force microscopy based on diamond nitrogen-vacancy (NV) centers uses laser to excite the NV centers at the tip of the probe and collect their fluorescence, and combines this with microwave scanning to detect their electronic spin resonance state, thus achieving nanoscale microscopic magnetic imaging.

[0003] However, existing technologies have significant limitations when dealing with samples with certain specific properties. When the sample itself can fluoresce under NV center excitation laser irradiation, and its fluorescence band overlaps with the NV center fluorescence band, the strong background fluorescence from the sample will cause severe interference. This interference signal will directly enter the detector's counting through the dichroic mirror and pinhole in the confocal optical path, resulting in the measured fluorescence spectrum containing a large amount of background noise unrelated to the magnetic field. The contrast of the NV center resonance spectrum is severely weakened or even completely eliminated, making magnetic information demodulation based on fluorescence changes impossible, ultimately leading to magnetic imaging failure. Summary of the Invention

[0004] This invention provides a scanning NV probe microscope, which suppresses background noise in the fluorescence detection optical path by setting a metal coating on the bottom of the diamond probe to block stray fluorescence from the sample surface. This solves the problem of low signal-to-noise ratio and limited measurement accuracy of magnetic field imaging caused by excessive background fluorescence of the sample when existing scanning NV probe microscopes detect nanoscale magnetic fields.

[0005] In a first aspect, embodiments of the present invention provide a scanning NV probe microscope, comprising an atomic force microscopy system for detecting sample surface morphology information and an optically detected magnetic resonance system for detecting sample surface magnetic field distribution information. The atomic force microscopy system includes a vibrating arm and a diamond probe, and the optically detected magnetic resonance system includes an NV color center, a transition excitation optical path, and a fluorescence detection optical path. The NV color center is disposed in the diamond probe, and the sample to be scanned and the transition excitation optical path are located on opposite sides of the diamond probe, respectively. The transition excitation optical path and the fluorescence detection optical path are located on the same side of the diamond probe. The vibrating arm is fixedly connected to the diamond probe, and the diamond probe is disposed on the side of the vibrating arm closer to the sample. The vibrating arm is used to drive the diamond probe to move relative to the sample. A first metal coating is disposed on the side of the diamond probe closer to the sample, and the first metal coating is used to block the surface fluorescence of the sample.

[0006] Optionally, the diamond probe is conical, with the conical tip of the diamond probe facing the sample, and the conical bottom end of the diamond probe is connected to the vibrating arm; the transition excitation light path illuminates the NV color center from the conical bottom end of the diamond probe, and the fluorescence detection light path illuminates the NV color center from the conical bottom end of the diamond probe.

[0007] Optionally, the scanning NV probe microscope also includes a diamond base; a vibrating arm is fixedly connected to the diamond base, and the diamond probe is set on the side of the diamond base closer to the sample; the transition excitation light path illuminates the NV color center from the diamond base, and the fluorescence detection light path illuminates the diamond base from the NV color center; a second metal coating is provided on the side of the diamond base closer to the sample, and the second metal coating is used to block the surface fluorescence of the sample.

[0008] Optionally, the atomic force microscopy system also includes a frequency modulation feedback module; the frequency modulation feedback module is used to use the resonant frequency shift of the vibrating arm as a feedback signal during the scanning process of the diamond probe, and output a control signal to adjust the distance between the diamond probe and the sample surface.

[0009] Optionally, the atomic force microscopy system also includes an amplitude control module, which is used to ensure that the atomic force microscopy system satisfies: or ,or ,or Where A is the amplitude of the vibrating arm, and k is the elastic coefficient of the vibrating arm. The phase offset corresponding to the target frequency offset value set for frequency feedback, Q is the quality factor of the vibrating arm, and Δ is the preset threshold value used to ensure that the service life of the first metal coating reaches the expected value.

[0010] Optionally, the frequency modulation feedback module includes a phase-locked loop (PLL) and a feedback controller. The PLL is used to acquire the real-time resonant frequency offset of the vibrating arm. The feedback controller is electrically connected to the PLL and is used to compare the resonant frequency offset with a preset target frequency offset. Based on the comparison result, the controller controls the diamond probe to move in a direction with an adjustable distance from the sample surface, so that the resonant frequency offset approaches and stabilizes at the preset target frequency offset.

[0011] Optionally, the thickness of the first metal coating is less than or equal to the thickness of the second metal coating.

[0012] Optionally, the thickness of the first metal coating is less than or equal to a first thickness value and greater than or equal to a second thickness value: the first thickness value is the critical thickness value of the first metal coating when the thickness of the first metal coating is gradually increased until the resonance peak contrast of the NV color center no longer increases; the second thickness value is the thickness value of the first metal coating when the thickness of the first metal coating is gradually decreased until the transmittance of visible light through the first metal coating is greater than or equal to a preset value.

[0013] Optionally, the material for the metal coating can be a non-ferromagnetic magnetic metal.

[0014] Optional, the non-ferromagnetic metallic material is titanium.

[0015] Optionally, the thickness of the first metal coating is between 10nm and 60nm.

[0016] The present invention provides a scanning NV probe microscope, which includes an atomic force microscopy system for detecting sample surface morphology information and a photodetector magnetic resonance system for detecting sample surface magnetic field distribution information. The atomic force microscopy system includes a vibrating arm and a diamond probe. The vibrating arm drives the diamond probe to approach the sample surface for scanning motion. The optically detected magnetic resonance system includes an NV color center, a transition excitation optical path, and a fluorescence detection optical path. The NV color center is located at the tip of the diamond probe and is used to sense the local magnetic field on the sample surface and emit a fluorescence signal carrying magnetic field information. This fluorescence can be conducted inside the diamond probe to ensure effective signal transmission. The sample to be scanned and the transition excitation optical path are located on opposite sides of the diamond probe, and the transition excitation optical path and the fluorescence detection optical path are located on the same side of the diamond probe. The diamond probe has a first metal coating on the side closest to the sample. The first metal coating is used to block stray fluorescence generated by the transition excitation optical path from the sample, avoiding background fluorescence that overlaps with the fluorescence band of the NV color center and forms noise that interferes with the effective signal, thereby improving the signal-to-noise ratio of the NV fluorescence signal. Finally, through synchronous scanning and signal acquisition, the morphology of the same area of ​​the sample and the corresponding spatial magnetic field distribution are acquired simultaneously, solving the problem of low signal-to-noise ratio and limited measurement accuracy of magnetic field imaging caused by background fluorescence interference in existing scanning NV probe microscopes. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a scanning NV probe microscope provided in an embodiment of the present invention;

[0018] Figure 2 This is a partial structural schematic diagram of a scanning NV probe microscope provided in an embodiment of the present invention;

[0019] Figure 3 This is a schematic diagram illustrating the influence of probe-sample spacing on the amplitude of the vibrating arm, frequency shift, and fluorescence intensity of the NV color center, as provided in an embodiment of the present invention.

[0020] Figure 4 This is a sample fluorescence scan image of a common probe provided in this embodiment of the invention at a distance of 10 μm;

[0021] Figure 5 This is a sample fluorescence scan image of a probe with a 10nm titanium film provided in an embodiment of the present invention at a distance of 10μm;

[0022] Figure 6 This is a Z-axis surface observation image of a common probe provided in an embodiment of the present invention;

[0023] Figure 7 This is a Z-axis surface observation image of a probe with a 60nm titanium film provided in an embodiment of the present invention;

[0024] Figure 8 This is the ODMR spectrum of a common probe provided in this embodiment of the invention under strong fluorescence interference;

[0025] Figure 9 This is a matrix diagram of the magnetic resonance signal detected by continuous wave light under strong fluorescence interference using a common probe provided in this embodiment of the invention.

[0026] Figure 10 This is the ODMR spectrum of the 10nm titanium film-coated probe provided in this embodiment of the invention under strong fluorescence interference;

[0027] Figure 11 This is a matrix diagram of the magnetic resonance signal detected by continuous wave light under strong fluorescence interference using a probe with a 10nm titanium film provided in an embodiment of the present invention.

[0028] Figure 12 This is the ODMR spectrum of the 60nm titanium film-coated probe provided in this embodiment of the invention under strong fluorescence interference;

[0029] Figure 13 This is a matrix diagram of the magnetic resonance signal detected by continuous wave light under strong fluorescence interference using a probe with a 60nm titanium film provided in an embodiment of the present invention. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0031] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0032] Figure 1 This is a schematic diagram of the structure of a scanning NV probe microscope provided in an embodiment of the present invention, with reference to... Figure 1 The scanning NV probe microscope includes an atomic force microscopy system for detecting sample surface morphology information and an optical detection magnetic resonance system for detecting sample surface magnetic field distribution information. The atomic force microscopy system includes a vibrating arm 10 and a diamond probe 20, and the optical detection magnetic resonance system includes an NV color center 30, a transition excitation optical path 40, and a fluorescence detection optical path 50.

[0033] The NV color center 30 is set in the diamond probe 20. The sample 60 to be scanned and the transition excitation optical path 40 are located on opposite sides of the diamond probe 20, and the transition excitation optical path 40 and the fluorescence detection optical path 50 are located on the same side of the diamond probe 20.

[0034] The vibrating arm 10 is fixedly connected to the diamond probe 20. The diamond probe 20 is located on the side of the vibrating arm 10 close to the sample 60. The vibrating arm 10 is used to drive the diamond probe 20 to move relative to the sample 60.

[0035] The diamond probe 20 has a first metal coating 70 on the side close to the sample 60, which is used to block the surface fluorescence of the sample 60.

[0036] Among them, the atomic force microscopy system can be understood as a measurement system that uses the interaction force between the probe and the atoms on the sample surface to detect its micro-morphology; the optical detection magnetic resonance system can be understood as a quantum sensing system based on the optical and magnetic properties of NV color centers, which detects the intensity and distribution of the local magnetic field on the sample surface by detecting the shift of the NV color center to the microwave resonance frequency; NV color center 30 can be understood as a nitrogen-vacancy site defect in diamond crystal.

[0037] Specifically, the vibrating arm 10 can be a tuning fork arm with piezoelectric ceramic mounted on it. Driven by the piezoelectric ceramic, the diamond probe 20 vibrates near its resonant frequency and approaches the sample surface for scanning motion. When the atomic force between the tip of the diamond probe 20 and the sample surface causes its vibration frequency to change, the feedback system adjusts the relative distance between the diamond probe 20 and the sample to keep the force constant, thereby ensuring a constant distance between the diamond probe 20 and the sample 60. During this process, the transition excitation optical path 40 focuses the laser onto the NV color center 30 at the tip of the probe. Under the influence of the local magnetic field on the sample surface, the NV color center 30 undergoes a spin resonance frequency shift and emits a fluorescence signal carrying this information. This fluorescence is mainly conducted upwards through total internal reflection from the sidewalls inside the diamond probe 20 to form the detection optical path 50, and is finally captured by the collection optical path above. Meanwhile, the transition excitation optical path 40 may also excite the sample 60 to generate background fluorescence. The wavelength range of the background fluorescence often overlaps with the fluorescence band of the NV color center. If not suppressed, it will propagate directly upward into the fluorescence detection optical path 50, forming strong background noise that severely interferes with or even drowns out the weak NV fluorescence signal. The first metal coating 70 deposited on the bottom of the diamond probe 20 acts as an optical barrier, reflecting or absorbing this stray fluorescence from below, thereby effectively preventing it from propagating upward into the detection optical path 50 and improving the signal-to-noise ratio of the NV fluorescence signal. Through synchronous scanning and signal acquisition, the nanoscale morphology map of the same region of the sample and its corresponding nanoscale spatial magnetic field distribution map are obtained.

[0038] The present invention provides a scanning NV probe microscope, which includes an atomic force microscopy system for detecting sample surface morphology information and a photodetector magnetic resonance system for detecting sample surface magnetic field distribution information. The atomic force microscopy system includes a vibrating arm and a diamond probe. The vibrating arm drives the diamond probe to approach the sample surface for scanning motion. The optically detected magnetic resonance system includes an NV color center, a transition excitation optical path, and a fluorescence detection optical path. The NV color center is located at the tip of the diamond probe and is used to sense the local magnetic field on the sample surface and emit a fluorescence signal carrying magnetic field information. This fluorescence can be conducted inside the diamond probe to ensure effective signal transmission. The sample to be scanned and the transition excitation optical path are located on opposite sides of the diamond probe, and the transition excitation optical path and the fluorescence detection optical path are located on the same side of the diamond probe. The diamond probe has a first metal coating on the side closest to the sample. The first metal coating is used to block stray fluorescence generated by the transition excitation optical path from the sample, avoiding background fluorescence that overlaps with the fluorescence band of the NV color center and forms noise that interferes with the effective signal, thereby improving the signal-to-noise ratio of the NV fluorescence signal. Finally, through synchronous scanning and signal acquisition, the morphology of the same area of ​​the sample and the corresponding spatial magnetic field distribution are acquired simultaneously, solving the problem of low signal-to-noise ratio and limited measurement accuracy of magnetic field imaging caused by background fluorescence interference in existing scanning NV probe microscopes.

[0039] Continue to refer to Figure 1 In an optional embodiment, the diamond probe 20 is conical, with the conical tip of the diamond probe 20 facing the sample 60, and the conical bottom end of the diamond probe 20 is connected to the vibrating arm 10.

[0040] The transition excitation optical path 40 illuminates the NV color center 30 from the conical bottom end of the diamond probe 20, and the fluorescence detection optical path 50 illuminates the conical bottom end of the diamond probe 20 from the NV color center 30.

[0041] Specifically, the diamond probe 20 has a conical structure, with its conical tip facing the sample 60 and supporting the NV color center 30, while the conical bottom is fixedly connected to the vibrating arm 10. The excitation laser emitted by the transition excitation optical path 40 enters from the conical bottom of the diamond probe, is conducted through the diamond material to the NV color center 30 located at the conical tip, initializes its electron spin state, and provides a basis for subsequently applying a microwave field to modulate its spin resonance. After excitation, the fluorescence signal carrying magnetic field information emitted by the NV color center 30 also propagates through the interior of the diamond (mainly relying on total internal reflection of the conical sidewalls) to the conical bottom, and then exits into the fluorescence detection optical path 50 for collection and detection.

[0042] Figure 2 This is a partial structural schematic diagram of a scanning NV probe microscope provided in an embodiment of the present invention, for reference. Figure 1 and Figure 2 In an optional embodiment, the scanning NV probe microscope further includes a diamond base 80;

[0043] The vibrating arm 10 is fixedly connected to the diamond base 80, and the diamond probe 20 is set on the side of the diamond base 80 close to the sample 60; the transition excitation optical path 40 illuminates the NV color center 30 from the diamond base 80, and the fluorescence detection optical path 50 illuminates the diamond base 80 from the NV color center 30.

[0044] The diamond base 80 has a second metal coating 90 on the side near the sample 60, which is used to block the surface fluorescence of the sample 60.

[0045] Specifically, the diamond probe 20 is fixed to the bottom of the diamond base 80, which is fixedly connected to the vibrating arm 10. The transition excitation light path 40 is incident from the top or side of the diamond base 80. After being conducted inside the base, the excitation light enters the diamond probe 20 at its bottom and finally illuminates the NV color center 30. The fluorescence emitted by the NV color center 30 is emitted in the opposite direction along the same path and exits from the diamond base 80 to form the fluorescence detection light path 50. During this process, the second metal coating 90 deposited on the bottom of the diamond base 80 and the first metal coating 70 deposited on the bottom of the diamond probe 20 together form an optical barrier to block the background fluorescence from the surface of the sample 60 from propagating upward into the detection light path, thereby ensuring that the scanning NV probe microscope can work stably at a high signal-to-noise ratio and obtain clear nanomagnetic field imaging.

[0046] In diamond nitrogen-vacancy (NV) center scanning magnetic imaging, the distance between the NV center and the sample surface is crucial to spatial resolution. While coating modification can effectively suppress sample fluorescence interference, it introduces two major problems: first, coating thickness increases the distance between the NV center and the sample, potentially reducing spatial resolution and weakening the ability to capture weak magnetic signals; second, maintaining high resolution requires reducing the probe-sample distance, leading to increased interaction forces and significantly increasing the risk of coating damage, thus negating the advantages of modification. Conventional amplitude modulation (AM) feedback mode adjusts the distance by maintaining a constant amplitude of the vibrating arm. However, this approach is less suitable for coating probes, as improper force control can exacerbate film damage, and it struggles to balance resolution and coating protection requirements.

[0047] Figure 3 This is a schematic diagram illustrating the influence of probe-sample spacing on the amplitude, frequency shift, and fluorescence intensity of the NV color center, as provided in an embodiment of the present invention. (Refer to...) Figure 3 The horizontal axis in the figure represents the distance between the probe and the sample. The unit is nanometers (nm). Positive values ​​indicate the distance between the probe and the sample, while negative values ​​indicate the probe has been pressed into the sample surface. The left vertical axis represents the resonant amplitude of the vibrating arm (tuning fork). The middle vertical axis represents the resonant frequency shift of the vibrating arm. The unit is Hertz (Hz). The right vertical axis represents the fluorescence intensity (photon count rate) of the NV color center, in kcps (thousands of counts per second). Blue curve: amplitude changes with spacing; green curve: frequency shift changes with spacing; red curve: fluorescence intensity changes with spacing. The figure is divided into five regions, corresponding to the complete process of the probe moving away from the sample and pressing into it. Region A: Free space, spacing dt is much greater than 0, the probe is far from the sample, there is no interaction, and the amplitude does not decay. Frequency shift: close to 0 Hz. Fluorescence intensity: high and stable (about 280–290 kcps), with little background fluorescence interference. Region B: Non-contact region, spacing dt approaches 0, the probe begins to feel the long-range attraction of the sample (such as van der Waals forces), and the amplitude begins to decrease rapidly, reflecting the damping effect of long-range forces on vibration. Frequency shift: increases from 0, reflecting the appearance of a force gradient. Fluorescence intensity: begins to decrease because background fluorescence interference increases when the probe approaches the sample. Region C: Non-contact area, about to make contact, distance dt≈0, probe is about to contact the sample surface, amplitude decreases, damping effect is significant. Frequency shift: rapidly rises to about 100Hz, force gradient increases sharply. Fluorescence intensity: continues to decrease, background fluorescence interference further increases. Region D: Soft contact area, distance dt<0, probe has been slightly pressed into the sample surface, in the elastic deformation stage, amplitude continues to decrease, but the rate slows down, reflecting the continued effect of contact damping. Frequency shift: continues to rise, force gradient increases with increasing indentation depth. Fluorescence intensity: continues to decrease to about 240kcps, background fluorescence interference reaches its strongest. Region E: Hard contact area, distance dt is much less than 0, probe is pressed deeper into the sample surface, entering the plastic deformation stage, amplitude drops to near 0%, vibration is almost completely suppressed. Frequency shift: tends to stabilize at about 200Hz, force gradient reaches saturation. Fluorescence intensity: tends to stabilize at about 240kcps, background fluorescence interference no longer increases significantly.

[0048] refer to Figure 3 It is evident that during the non-contact and soft-contact phases, the amplitude decrease and frequency increase occur simultaneously. The frequency shift more sensitively reflects changes in the force gradient, which is the core reason why the frequency modulation (FM) feedback mode is superior to the amplitude modulation (AM) feedback mode. By maintaining a constant frequency shift (rather than a constant amplitude), the frequency modulation mode can stably control the probe-sample distance with a smaller contact force, thereby effectively reducing the risk of coating damage and facilitating a shorter probe-sample distance to ensure spatial resolution. As the probe approaches the sample, the fluorescence intensity continuously decreases, indicating that background fluorescence interference increases with decreasing distance, which also confirms the necessity of coating to suppress background fluorescence.

[0049] Therefore, in an optional embodiment, the atomic force microscopy system further includes a frequency modulation feedback module 100; the frequency modulation feedback module 100 is used to output a control signal to adjust the distance between the diamond probe 20 and the sample 60 surface by taking the resonant frequency shift of the vibrating arm 10 as a feedback signal during the scanning process of the diamond probe 20.

[0050] The frequency modulation feedback module 100 can be understood as the servo control system of the atomic force microscope (AFM). Its function is to monitor and process the changes in the resonant frequency of the vibrating arm in real time and generate corresponding control signals.

[0051] Specifically, during the scanning process, the diamond probe 20 vibrates near its resonant frequency under the drive of the vibrating arm 10. When the probe approaches the surface of the sample 60, the atomic forces (such as van der Waals forces) between them cause the resonant frequency of the vibrating arm 10 to shift. The frequency modulation feedback module 100 continuously detects this frequency shift and uses it as a feedback signal: if the frequency decreases (corresponding to an increase in attractive force), the frequency modulation feedback module 100 drives the piezoelectric ceramic to move the probe slightly away from the sample surface; conversely, if the frequency increases (corresponding to an increase in repulsive force or a decrease in attractive force), it controls the probe to move slightly closer. Through this closed-loop control, the distance between the diamond probe 20 and the surface of the sample 60 is dynamically adjusted to keep the force constant, thereby accurately tracking the surface morphology of the sample while maintaining a stable and known detection distance for subsequent magnetic field measurements.

[0052] In an optional embodiment, the atomic force microscopy system further includes an amplitude control module 110, which is used to ensure that the atomic force microscopy system satisfies: or ,or ,or ,

[0053] Where A is the amplitude of the vibrating arm 10, k is the elastic coefficient of the vibrating arm 10, and Q is the quality factor of the vibrating arm 10. The phase offset corresponding to the target frequency offset value set for frequency feedback, Δ is the preset threshold for ensuring the expected service life of the first metal coating 70; the amplitude control module can be understood as the control unit responsible for adjusting and stabilizing the vibration amplitude of the vibrating arm so that the amplitude of the vibrating arm meets the preset conditions; the amplitude A can be understood as the maximum displacement of the vibrating arm reciprocating near its equilibrium position, and its function is to characterize the intensity of the probe vibration; the elastic coefficient k can be understood as the stiffness of the vibrating arm; the quality factor Q can be understood as a dimensionless parameter of the sharpness of the vibration arm resonance. The higher the Q value, the sharper the resonance peak and the more sensitive it is to external forces. The phase offset corresponding to the target frequency offset value set for frequency feedback, the threshold Δ can be understood as a physical quantity upper limit preset according to the wear resistance or impact resistance performance of the metal coating, used to ensure that the mechanical load applied to the coating during the scanning process does not exceed its safety limit, thereby ensuring that its service life reaches the expected level.

[0054] Specifically, when the amplitude control module 110 is working, it is used to monitor and adjust the vibration amplitude A of the vibrating arm 10 in real time to ensure that it meets the requirements. or ,or The essence of the above inequality is to control the amplitude A, or the equivalent physical quantity formed by combining it with the system stiffness k and quality factor Q, and to take into account the phase shift δ set by the frequency feedback as a proportionality coefficient, thereby limiting the mechanical load that may be transmitted to the first metal coating 70 through the probe during the scanning process to within a preset threshold Δ. This ensures that while maintaining detection sensitivity, it effectively reduces the mechanical wear and impact on the metal coating caused by the interaction between the probe and the sample, thus extending the service life of the metal coating and ensuring the long-term stable operation and optical shielding effectiveness of the NV microscope.

[0055] In an optional embodiment, the frequency modulation feedback module 100 includes a phase-locked loop 101 and a feedback controller 102; the phase-locked loop 101 is used to acquire the real-time resonant frequency offset of the vibrating arm 10; the feedback controller 102 is electrically connected to the phase-locked loop 101 and is used to compare the resonant frequency offset with a preset target frequency offset, and control the diamond probe 20 to move in a direction with an adjustable distance from the surface of the sample 60 based on the comparison result, so that the resonant frequency offset approaches and stabilizes at the preset target frequency offset.

[0056] Specifically, during the scanning process, the phase-locked loop 101 is used to excite the drive signal for vibration and the vibration detection signal reflecting the actual vibration state. The phase-locked loop 101 calculates the real-time resonant frequency offset caused by the interaction force between the diamond probe 20 and the sample 60 by comparing the phase or frequency difference between these two signals in real time. The feedback controller 102 compares this real-time offset with an internally set preset target frequency offset: if the real-time offset is greater than the target value, a control signal is output to drive the Z-axis (pointing towards the tip of the diamond probe 20) piezoelectric ceramic to move the diamond probe 20 slightly away from the surface of the sample 60; if the real-time offset is less than the target value, the probe is controlled to move slightly closer to the sample, thereby maintaining a constant interaction force between the probe and the sample surface during the scanning process.

[0057] In an optional embodiment, the thickness of the first metal coating 70 is less than or equal to the thickness of the second metal coating 90.

[0058] Specifically, considering that the tip of the diamond probe 20 interacts directly with the sample surface and carries the NV color center, the thickness of the first metal coating 70 at its bottom is designed to be less than or equal to the thickness of the second metal coating 90 at the bottom of the diamond base 80, provided that the basic requirements for optical shielding are met (sufficient reflectivity / absorption for fluorescence at a specific wavelength).

[0059] In an optional embodiment, the thickness of the first metal coating 70 is less than or equal to a first thickness value and greater than or equal to a second thickness value: the first thickness value is the critical thickness value of the first metal coating 70 when the thickness of the first metal coating 70 is gradually increased until the resonance peak contrast of the NV color center 30 no longer increases; the second thickness value is the thickness value of the first metal coating 70 when the thickness of the first metal coating 70 is gradually decreased until the transmittance of visible light through the first metal coating 70 is greater than or equal to a preset value.

[0060] Specifically, the thickness of the first metal coating 70 is determined through preliminary experiments, and satisfies the condition that the second thickness value ≤ the actual thickness ≤ the first thickness value. This range is obtained through the following steps:

[0061] Determining the first thickness value (performance saturation point): During the coating preparation process, the change in the resonance peak contrast of the NV color center with increasing coating thickness is monitored. When the contrast increases with thickness and the trend becomes gradual, reaching a critical value where it no longer increases significantly, the thickness at this point is recorded as the first thickness value. The first thickness is used to ensure that the coating thickness is sufficient to provide adequate optical shielding.

[0062] Determining the second thickness value (transmittance threshold): While ensuring the aforementioned optical performance, the coating is gradually thinned starting from a thicker state, and the visible light transmittance is measured. When the transmittance is greater than or equal to a preset threshold to ensure the normal operation of the excitation and detection optical paths, the thickness at this point is recorded as the second thickness value. The second thickness is used to ensure the normal operation of the detection optical path.

[0063] In an optional embodiment, the material of the metal coating is a non-ferromagnetic magnetic metal material.

[0064] Specifically, non-ferromagnetic metallic materials (such as gold, aluminum, copper, platinum, titanium, etc.) do not have ferromagnetic order (i.e., they do not have macroscopic spontaneous magnetization) at room temperature and under working conditions. They do not introduce significant and stable stray magnetic fields, thus avoiding interference with the accurate detection of the magnetic field to be measured on the sample surface by the NV color center.

[0065] In a preferred embodiment, the non-ferromagnetic magnetic metal material is titanium.

[0066] Specifically, titanium is preferred when selecting materials for the first metal coating 70 and / or the second metal coating 90. Titanium exhibits good coating bonding stability with diamond, and it does not interfere with the surface magnetic field of the sample or the magnetic measurement of the NV color center.

[0067] In a preferred embodiment, the thickness of the first metal coating 70 is between 10 nm and 60 nm.

[0068] Specifically, for the first metal coating 70 made of titanium, a thickness between 10 nm and 60 nm is preferred. This range was determined through an optical and transmission performance optimization process, aiming to meet the dual constraints of a first thickness value and a second thickness value.

[0069] Figure 4 This is a sample fluorescence scan image at a distance of 10 μm using a common probe provided in this embodiment of the invention. Figure 5 This is a fluorescence scan of a sample with a 10nm titanium film-coated probe at a distance of 10μm, provided in an embodiment of the present invention. Figure 6 This is a Z-axis surface observation image of a common probe provided in an embodiment of the present invention. Figure 7 This is a Z-axis surface observation image of a probe with a 60nm titanium film provided in an embodiment of the present invention. In the image, the X, Y, and Z directions are mutually perpendicular. The X and Y directions are horizontal directions parallel to the sample surface, representing the scanning directions of the probe on the sample surface; the Z direction is a vertical direction perpendicular to the XY plane. In a specific embodiment, titanium is selected as the metal coating material, and based on a dual-index pre-experiment of optical shielding performance saturation and optical path transmittance thresholds, the thickness range of the first metal coating 70 is determined, satisfying that the second thickness value ≤ actual thickness ≤ first thickness value. The logic and steps for obtaining this thickness range are as follows:

[0070] NV probes with titanium films of varying thicknesses were prepared using a gradient coating process. Under the same strong fluorescence interference conditions, the change in ODMR resonance peak contrast of the NV color center with increasing coating thickness was monitored. As the titanium film thickness increased, the shielding effect of the coating on background fluorescence gradually strengthened, and the ODMR contrast increased accordingly. When the titanium film thickness increased to a certain critical value, the upward trend of contrast tended to level off, no longer significantly increasing with further thickness. At this point, the optical shielding performance of the coating reached saturation. This critical value was recorded as the first thickness value, which ensures that the coating provides sufficient optical shielding to resist strong fluorescence interference.

[0071] Under the premise of ensuring that the coating has sufficient optical shielding performance, starting from a first thickness value, the thickness of the titanium film is gradually reduced, and the visible light transmittance of the probe is measured simultaneously. A visible light transmittance threshold is set, which is the minimum transmittance requirement to ensure the normal operation of the laser excitation optical path and the fluorescence detection optical path. When the thickness of the titanium film is reduced to a certain critical value, and the visible light transmittance is greater than or equal to the preset threshold, the thickness at this moment is recorded as the second thickness value. This thickness can ensure the normal operation of the excitation and detection optical paths and meet the needs of sample surface observation.

[0072] Based on the thickness range determined in the preliminary experiments, titanium film probes with thicknesses at the two endpoints (second thickness value (10nm) and first thickness value (60nm) were selected, along with uncoated ordinary probes, for comparative verification experiments. The experimental steps and results are as follows:

[0073] The probe first performs a preliminary scan at a height of approximately 10 micrometers from the sample; this stage is solely for locating the diamond probe surface. (Reference) Figure 4 Uncoated standard probes were used to scan the XY plane at a 10 μm interval. The relationship between the scanning position (X, Y) and the corresponding fluorescence count rate (unit: kilobits / second) was obtained. The results showed that the maximum fluorescence intensity of the standard probe could reach 6192.5 kcps, indicating strong background fluorescence interference at this point. (Reference) Figure 5 Using an NV probe coated with a 10nm titanium film under the same experimental conditions, the maximum fluorescence intensity decreased to 2795.6kcps, demonstrating that the titanium coating can effectively block some background fluorescence and reduce fluorescence interference intensity. (Reference) Figure 6 During scanning with a conventional probe, the 650nm long-pass filter allows fluorescence emitted by the sample at wavelengths above 650nm to pass through, thus enabling clear observation of the Z-axis surface morphology of the sample (2) and the Z-axis surface of the diamond probe itself (3). (Reference) Figure 7 When scanning with an NV probe coated with a 60nm titanium film, only the Z-axis surface 3 of the diamond probe itself can be observed, and the surface morphology of the sample cannot be observed. This indicates that the 60nm thickness is close to the critical threshold of optical path transmittance. Although it can block background fluorescence, the transmittance of visible light can no longer meet the requirements for observing the sample surface.

[0074] On the other hand, this application aims to demonstrate, through ODMR contrast verification under strong fluorescence interference, the relationship between the thickness of the titanium film of the first metal coating 70 and the probe's ability to resist fluorescence interference and signal stability, and that the thickness range of 10nm–60nm determined through preliminary experiments can achieve the optimal balance between optical shielding performance and optical path transmission performance. Figure 8 This is the ODMR spectrum of a common probe provided in an embodiment of the present invention under strong fluorescence interference, for reference. Figure 8In the figure, the horizontal axis represents the microwave frequency of 2.80 GHz–2.94 GHz, corresponding to the typical range of zero-field splitting at the NV color center, and the vertical axis represents fluorescence intensity. The red curve represents the original measurement data, which is significantly noisy. The blue curve () represents the fitted Lorentz peaks, showing obvious fluorescence dips at 2.83 GHz and 2.90 GHz, i.e., ODMR resonance peaks. By calculating the contrast of the two ODMR resonance peaks, contrast = (fluorescence intensity at resonance - baseline fluorescence intensity) / baseline fluorescence intensity. The contrasts of the two ODMR resonance peaks are -0.0211 and -0.0200, respectively, indicating that the ODMR contrast of ordinary probes under strong fluorescence interference is only about 2%, far lower than the ideal working range (10–20%).

[0075] Figure 9 This is a matrix diagram of a conventional probe used in an embodiment of the present invention for continuous wave optical detection of magnetic resonance signals under strong fluorescence interference. (Reference) Figure 9 The graph shows the microwave frequency on the horizontal axis and the number of scan lines on the vertical axis. Pixel color represents the fluorescence intensity at the corresponding frequency and scan line. Red represents high fluorescence intensity, corresponding to the state where the NV center spin has not undergone a resonant transition. Blue represents low fluorescence intensity, corresponding to the state where the microwave frequency matches the NV center spin energy level and a resonant transition occurs, which is the location of the ODMR resonance peak. Dark blue bands, representing the ODMR resonance peaks, are visible across the scan lines at 2.83 GHz and 2.90 GHz. However, the difference between the dark bands and the background color is very slight, further demonstrating that the ODMR contrast of ordinary probes is extremely low, indicating insufficient anti-interference capability.

[0076] Figure 10 This is the ODMR spectrum of the 10nm titanium film-coated probe provided in this embodiment of the invention under strong fluorescence interference, for reference. Figure 10 In the ODMR spectrum of the 10nm titanium film probe under the same experimental conditions, the noise of the red raw data curve is significantly reduced, and the Lorentz peak of the blue curve fitting is clearer; the contrast of the two ODMR resonance peaks are -0.118 and -0.101, respectively. The test results show that its ODMR contrast is about 10%, proving that the scanning NV probe microscope is in the ideal working range when the 10nm titanium film is coated.

[0077] Figure 11 This is a matrix diagram of the magnetic resonance signal detected by continuous wave light under strong fluorescence interference using a probe with a 10nm titanium film provided in an embodiment of the present invention. (Reference) Figure 11 The blue dark band in the matrix image shows a significant difference from the background color, indicating that the ODMR resonance peak signal is clear, further verifying that the 10nm titanium coating can significantly improve the ODMR contrast of the probe.

[0078] Figure 12 This is the ODMR spectrum of the 60nm titanium film-coated probe provided in this embodiment of the invention under strong fluorescence interference, for reference. Figure 12 The noise in the raw data (red) in the ODMR spectrum of this probe is further reduced, and the depth of the fitted Lorentz peak (orange) is greater. The test results show that its ODMR contrast is about 12%, which is slightly higher than that of the probe with a 10nm titanium film.

[0079] Figure 13 This is a matrix diagram of the magnetic resonance signal detected by continuous wave light under strong fluorescence interference using a probe with a 60nm titanium film provided in an embodiment of the present invention. (Reference) Figure 13 The blue dark band corresponding to the ODMR resonance peak in the matrix diagram is the clearest, further verifying that the 60nm titanium coating can significantly improve the ODMR contrast of the probe.

[0080] It should be noted that this embodiment only shows the probe performance test results corresponding to the two endpoints of the thickness range determined in the above-mentioned preliminary experiments (10nm as the second thickness value and 60nm as the first thickness value), namely, the relevant experimental data and spectra of the 10nm titanium film-coated probe and the 60nm titanium film-coated probe. In fact, within the thickness range of 10nm–60nm determined in the preliminary experiments, titanium film probes of any thickness can achieve a balance between optical shielding performance and optical path transmission performance. They have both an ODMR contrast of not less than 10% to resist strong fluorescence interference and sufficient visible light transmittance to meet the requirements of sample surface observation and normal optical path operation. This embodiment, through the performance verification of the endpoint values, can fully demonstrate the rationality and practicality of this thickness range, without the need to show the test results of all thicknesses within the range one by one.

[0081] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A scanning NV probe microscope, characterized in that, The system includes an atomic force microscopy system for detecting sample surface morphology information and an optical detection magnetic resonance system for detecting sample surface magnetic field distribution information. The atomic force microscopy system includes a vibrating arm and a diamond probe, and the optical detection magnetic resonance system includes an NV color center, a transition excitation optical path, and a fluorescence detection optical path. The NV color center is disposed in the diamond probe, the sample to be scanned and the transition excitation optical path are located on opposite sides of the diamond probe, and the transition excitation optical path and the fluorescence detection optical path are located on the same side of the diamond probe. The vibrating arm is fixedly connected to the diamond probe, and the diamond probe is disposed on the side of the vibrating arm close to the sample. The vibrating arm is used to drive the diamond probe to move relative to the sample. The diamond probe has a first metal coating on the side close to the sample, which is used to block the surface fluorescence of the sample.

2. The scanning NV probe microscope according to claim 1, characterized in that, The diamond probe is conical, with the conical tip of the diamond probe facing the sample, and the conical bottom end of the diamond probe is connected to the vibrating arm; The transition excitation optical path illuminates the NV color center from the conical bottom end of the diamond probe, and the fluorescence detection optical path illuminates the NV color center from the conical bottom end of the diamond probe.

3. The scanning NV probe microscope according to claim 1, characterized in that, The scanning NV probe microscope also includes a diamond base; The vibrating arm is fixedly connected to the diamond base, and the diamond probe is disposed on the side of the diamond base close to the sample; the transition excitation optical path illuminates the NV color center from the diamond base, and the fluorescence detection optical path illuminates the diamond base from the NV color center. The diamond base has a second metal coating on the side close to the sample, which is used to block the surface fluorescence of the sample.

4. The scanning NV probe microscope according to claim 1, characterized in that, The atomic force microscopy system also includes a frequency modulation feedback module; The frequency modulation feedback module is used to use the resonant frequency shift of the vibrating arm as a feedback signal during the scanning process of the diamond probe, and output a control signal to adjust the distance between the diamond probe and the sample surface.

5. The scanning NV probe microscope according to claim 4, characterized in that, The atomic force microscopy system further includes an amplitude control module, which is used to ensure that the atomic force microscopy system satisfies: or ,or ,or , Where A is the amplitude of the vibrating arm, k is the elastic coefficient of the vibrating arm, and Q is the quality factor of the vibrating arm. The phase offset corresponding to the target frequency offset value set for frequency feedback, Δ is a preset threshold value used to ensure that the service life of the first metal coating reaches the expected value.

6. The scanning NV probe microscope according to claim 4, characterized in that, The frequency modulation feedback module includes a phase-locked loop and a feedback controller; The phase-locked loop is used to obtain the real-time resonant frequency offset of the vibrating arm; The feedback controller is electrically connected to the phase-locked loop and is used to compare the resonant frequency offset with the preset target frequency offset. Based on the comparison result, the controller controls the diamond probe to move in a direction with an adjustable distance from the sample surface, so that the resonant frequency offset approaches and stabilizes at the preset target frequency offset.

7. The scanning NV probe microscope according to claim 3, characterized in that, The thickness of the first metal coating is less than or equal to the thickness of the second metal coating.

8. The scanning NV probe microscope according to claim 1, characterized in that, The thickness of the first metal coating is less than or equal to a first thickness value, and greater than or equal to a second thickness value. The first thickness value is the critical thickness value of the first metal coating when the thickness of the first metal coating is gradually increased until the contrast of the resonance peak of the NV color center no longer increases. The second thickness value is the thickness of the first metal coating when the thickness of the first metal coating is gradually reduced until the transmittance of visible light through the first metal coating is greater than or equal to a preset value.

9. The scanning NV probe microscope according to claim 1, characterized in that, The material of the metal coating is a non-ferromagnetic magnetic metal material.

10. The scanning NV probe microscope according to claim 9, characterized in that, The non-ferromagnetic metallic material is titanium.

11. The scanning NV probe microscope according to claim 10, characterized in that, The thickness of the first metal coating is between 10nm and 60nm.

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