CN108254591B - Diamond nano all-optical magnetic field sensor, probe and atomic force microscope - Google Patents

Abstract

The invention relates to a diamond nano all-optical magnetic field sensor, a probe and an atomic force microscope. Wherein, the diamond nanometer all-optical magnetic field sensor includes: a diamond nanostructure containing nitrogen-vacancy color centers configured to change fluorescence lifetime and photoluminescence intensity under different magnetic fields; a photoluminescence detection device configured to detect the photoluminescence intensity and/or a fluorescence lifetime detection device configured to detect the fluorescence lifetime.

Description

Diamond nano-optical magnetic field sensor, probe and atomic force microscope

Technical Field

The present invention belongs to the field of nanosensing and is mainly used for all-optical magnetic field measurement. It is suitable for induction magnetic field measurement in special environments such as complex electromagnetic environments and high voltages. It specifically relates to a diamond nano all-optical magnetic field sensor, a probe of a diamond nanostructure containing a nitrogen-vacancy color center, and further to an atomic force microscope containing the above probe.

Background technique

Nanosensors are sensors whose size or sensitivity reaches the nanometer level, or the interaction distance between the sensor and the substance or object to be detected is at the nanometer level. Sensors made using nanotechnology have reduced size, increased accuracy, and greatly improved performance. Nanosensors are based on the atomic scale, which greatly enriches the theory of sensors, promotes the level of sensor production, and broadens the application field of sensors. Nanosensors have now been widely developed in the fields of biology, chemistry, machinery, aviation, and military.

The current nanodiamond magnetic field nano-imaging technology mainly uses nanodiamond particles containing nitrogen-vacancy color centers (NV) attached to the atomic force microscope (AFM) probe, and uses optical readout electron spin resonance technology (ODMR) to perform nanoscale high-precision magnetic field imaging of the object to be measured. In the ODMR technology, an important condition is the need to introduce microwaves to manipulate the electron spins in the NV. However, the introduction of this condition makes it impossible to achieve all-optical magnetic field sensing technology.

Summary of the invention

1. Technical issues to be resolved

In view of this, an object of the present invention is to provide a diamond nano all-optical magnetic field sensor, a probe and an atomic force microscope to at least partially solve the above-mentioned technical problems.

(II) Technical solution

According to one aspect of the present invention, there is provided a diamond nano all-optical magnetic field sensor, comprising:

Diamond nanostructures containing nitrogen-vacancy color centers configured to change fluorescence lifetime and photoluminescence intensity under different magnetic fields;

A photoluminescence detection device and/or a fluorescence lifetime detection device, wherein the photoluminescence detection device is configured to detect the photoluminescence intensity, and the fluorescence lifetime detection device is configured to detect the fluorescence lifetime.

In a further embodiment, the photoluminescence detection device includes an avalanche diode, a single photon counter and a high-speed digital acquisition card; the fluorescence lifetime detection device includes an avalanche diode, a single photon counter, a pulse signal generator and a high-speed digital acquisition card.

In further embodiments, the diamond nanostructured material containing nitrogen-vacancy color centers is a nanoparticle or a nanowire.

In a further embodiment, the diamond nanostructure containing nitrogen-vacancy color centers is disposed on a diamond substrate, and the diamond substrate is a single crystal or polycrystalline material.

In a further embodiment, the diamond nanostructure containing a nitrogen-vacancy color center contains a single nitrogen-vacancy color center or a plurality of nitrogen-vacancy color centers arranged in an array.

According to another aspect of the present invention, there is provided a diamond nanoprobe containing a nitrogen-vacancy color center, comprising:

Diamond nanostructures containing nitrogen-vacancy color centers configured to change fluorescence lifetime and photoluminescence intensity under different magnetic fields.

In a further embodiment, a single nanodiamond containing a nitrogen-vacancy color center is installed in the probe; or the probe contains multiple nanodiamonds containing nitrogen-vacancy color centers, and the multiple nanodiamonds containing nitrogen-vacancy color centers are arranged in an array.

In a further embodiment, the probe has a diamond substrate on which the diamond nanostructure containing nitrogen-vacancy color centers is disposed.

According to another aspect of the present invention, there is provided an atomic force microscope, comprising:

Any of the above probes is configured to be close to a magnetic field, and the fluorescence lifetime and the photoluminescence intensity change when the received light remains unchanged and the magnetic field changes;

A photoluminescence detection device and/or a fluorescence lifetime detection device, wherein the photoluminescence detection device is configured to detect the photoluminescence intensity, and the fluorescence lifetime detection device is configured to detect the fluorescence lifetime.

In a further embodiment, the photoluminescence detection device includes an avalanche diode, a single photon counter and a high-speed digital acquisition card; the fluorescence lifetime detection device includes an avalanche diode, a single photon counter, a pulse signal generator and a high-speed digital acquisition card

Compared with the traditional nanodiamond magnetic field sensing technology, the sensing method of the present invention using the photoluminescence change and lifetime change of diamond NV defects in a magnetic field can obviously avoid the introduction of external microwave radiation and related microwave devices, greatly simplifying the equipment assembly and related equipment costs;

The technology of the present invention can be further utilized to realize the miniaturization of equipment and the integration of core devices, such as integrating diamond nanostructures containing nitrogen-vacancy color centers with photoluminescence detection devices and fluorescence lifetime detection devices, laying a technical foundation for fiber-optic all-optical magnetic field sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of an energy level system and a microwave manipulation model of the physical principle NV in the absence of an external magnetic field B according to an embodiment of the present invention;

2A and 2B are schematic diagrams of a seven-level system comparison model of the physical principle NV in the absence and presence of an external magnetic field B according to an embodiment of the present invention;

FIG3 is a schematic diagram of important physical conclusions of an embodiment of the present invention, wherein the upper portion of FIG3 shows that the lifetime of NV decreases with increasing magnetic field, and the lower portion of FIG3 shows that the photoluminescence intensity decreases with increasing magnetic field;

FIG4 is a schematic diagram of a micro-nano processing process of a diamond nanowire probe array containing a single NV according to an embodiment of the present invention;

FIG5 is a scanning electron microscope image of an object processed according to the process of FIG4 ;

FIG6 is a diagram of a probe type application device according to an embodiment of the present invention;

FIG. 7 a is a schematic diagram of the relationship between the fluorescence intensity and the magnetic field according to an embodiment of the present invention; FIG. 7 b is a schematic diagram of the relationship between the fluorescence lifetime and the magnetic field according to an embodiment of the present invention.

Detailed ways

In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. The advantages and effects of the present invention will be more significant through the contents disclosed in the present invention. The accompanying drawings attached to this description are simplified and used as examples. The number, shape and size of components shown in the drawings can be modified according to actual conditions, and the configuration of the components may be more complicated. Other aspects of practice or application can also be carried out in the present invention, and various changes and adjustments can be made without departing from the spirit and scope defined in the present invention.

According to the existing nanodiamond magnetic field sensing technology, microwaves need to be introduced to manipulate the electron spins in the NV. However, the introduction of this condition makes it impossible to achieve all-optical magnetic field sensing technology.

The basic concept of the present invention is to realize all-optical magnetic field sensing and method by utilizing nano fluorescent structure - NV color center in diamond, and to use all-optical magnetic field measurement technology to eliminate some device structure complexity and avoid introducing external microwave radiation and related microwave devices.

According to one aspect of an embodiment of the present invention, there is provided a diamond nano all-optical magnetic field sensor, comprising:

Diamond nanostructures containing nitrogen-vacancy color centers configured to change fluorescence lifetime and photoluminescence intensity under different magnetic fields;

A photoluminescence detection device and/or a fluorescence lifetime detection device, wherein the photoluminescence detection device is configured to detect the photoluminescence intensity, and the fluorescence lifetime detection device is configured to detect the fluorescence lifetime.

In some embodiments, the photoluminescence detection device includes an avalanche diode, a single photon counter, and a high-speed digital acquisition card.

In some embodiments, the fluorescence lifetime detection device includes an avalanche diode, a single photon counter, a pulse signal generator, and a high-speed digital acquisition card.

The materials to which the embodiments of the present invention can be applied include: diamond nanostructured materials (nanoparticles, nanowires, etc.) containing NV and diamond single crystal or polycrystalline bulk materials containing NV, as well as their various derivatives or micro-nano processed structures containing the basic structure of diamond NV color centers.

The embodiments of the present invention utilize the following principles:

i) The negatively charged nitrogen-vacancy color center (NV) defect in diamond is composed of a substitutional nitrogen atom (N) associated with a vacancy (V) in an adjacent lattice position of diamond, with a C3v symmetric structure, with the symmetry axis on the nitrogen atom-vacancy line, where the vacancy captures an electron. Under external magnetic field conditions, the light-induced spin polarization and spin-related photoluminescence (PL) of this NV defect become inefficient, and the NV defect optical response can be used to extract information about the magnetic field of the field. Because the minimum size of the lattice structure of the NV color center is ~0.5nm, it can be used in the field of nanosensing.

Taking a single NV as an example, as shown in Figure 1, a 532m millisecond pulse light is used to polarize the NV color center and spin in the bulk diamond to the excited state of ms=0, and then a microwave half-cycle pulse is applied to flip the excited state from ms=0 to ms=±1, and then the fluorescence lifetime is measured. The lifetime of the excited state ms=0 measured multiple times is 12.0ns, while the lifetime of the excited state ms=±1 is 7.8ns. The difference in lifetime is mainly caused by the non-radiative transition process from ms=±1 to the metastable state.

As shown in Figures 2A and 2B, the NV model is considered as a seven-level system. Because the energy level lifetime and fluorescence emission intensity of each energy level (including splitting energy level and intermediate state energy level) are different. When the external laser and other conditions remain unchanged and only the magnetic field is changed, the external magnetic field will cause the number of NV electronic energy level layouts to change (the polarization effect of the laser on the NV electron spin is reduced), and the relaxation time of its fine energy level will change, resulting in a decrease in fluorescence lifetime, and the photoluminescence intensity will decrease with the increase of the magnetic field.

ii) The quantum mechanical explanation for the above reasons is as follows:

Considering the existence of an external field, the NV ^- ground state Hamiltonian is written as:

It can be seen that the energy level of NV ^- is greatly affected by the magnetic field, and the magnetic field in different directions has different effects on the energy level. Usually, the effect of stress in diamond is very small, so we will ignore it here. Consider a system with spin 1 and solve the Schrödinger equation get:

Will Abbreviated as β, and let Then we get the energy eigenvalue equation (for simplicity, the natural unit system will be used later, that is,

Solving equation (1.3) gives the ground state energy level distribution. But usually for simplicity, we can use the perturbation approximation. Because the zero field splitting D corresponds to a magnetic field of 1000 Gauss along the NV symmetry axis, the magnetic field effect of tens of Gauss can be considered as a perturbation ( _ge μ _B |B|＜＜D). Thus:

The matrix form of is:

The zero-order eigenenergy is:

The first-order correction of the energy is The second-order correction is Therefore, after adding the magnetic field, the energy correction term is:

From equation (1.9), we can see that in the case of weak magnetic field, the contribution of the vertical magnetic field to the energy level movement is smaller than that of the axial magnetic field. In the case of an external magnetic field along the axial direction, the originally degenerate two energy levels m _s = ±1 are split. At the same time, due to the magnetic field perpendicular to the axial direction, the energy level spacing between m _s = ±1 and m _s = 0 is widened.

The Hamiltonian change of the NV ground state energy level (spin triplet) caused by the magnetic field in the direction of the NV symmetry axis has only diagonal terms, which will not change the eigenstate of the spin; while the Hamiltonian of the magnetic field perpendicular to the symmetry axis has non-diagonal terms. When the vertical magnetic field is very strong, the eigenstate of the system is no longer spin m _s = 0, ±1, but their superposition state. In this way, the polarization effect of the laser on the spin will be reduced.

Therefore, the overall trend of the change in the number of NV color center layouts caused by the enhancement of the external magnetic field is: the number of layouts corresponding to energy levels with shorter lifetimes and smaller photoluminescence intensities increases. As a result, the experimental measurement shows that the lifetime of the single NV color center decreases with increasing magnetic field, and the photoluminescence intensity decreases with increasing magnetic field, as shown in Figures 7a and 7b.

According to the above analysis, the physical principle and conclusion of the embodiment of the present invention are shown in FIG3. When the external magnetic field (B) is in the range of 0-150G, the statistical intensity value of the photoluminescence (PL) of a single NV in the diamond nanostructure decreases with the increase of the magnetic field (B), and the contrast decreases by more than 30% in general; its fluorescence lifetime statistical value also decreases with the increase of the magnetic field. It can be seen that the upper part of FIG3 describes that the lifetime of NV decreases with the increase of the magnetic field, and the lower part of FIG3 illustrates that the photoluminescence intensity decreases with the increase of the magnetic field.

The present invention also provides a diamond nanoprobe containing a single NV, which is used as an all-optical magnetic field detection sensor. A typical micro-nano processing process of a diamond nanoprobe array is shown in FIG4 , and the steps are as follows:

First, 300nm thick SiNx was deposited on diamond and then 300nm thick HSQ was applied (see sub-figure (a)).

The following steps are then performed: electron beam exposure followed by development and fixing (see sub-figure (b)), with the disk size being 200 nm in diameter; reactive ion etching of SiNx (see sub-figure (c)); inductively coupled ion etching of diamond to form a probe array with a height of 1.6 um (see sub-figure (d)); nitrogen ion implantation (see sub-figure (e)); and high vacuum annealing to generate NV (see sub-figure (f)).

The scanning electron microscope image of the actual object processed according to the process of Figure 4 is shown in Figure 5, and the verification and fluorescence lifetime detection of a single NV are shown in Figures 7a and 7b.

According to another aspect of an embodiment of the present invention, a method for measuring a magnetic field by operating a nanodiamond containing NV color centers using an atomic force microscope is provided, comprising:

Diamond nanostructures containing nitrogen-vacancy color centers configured to change fluorescence lifetime and photoluminescence intensity under different magnetic fields.

In some examples, a single nanodiamond containing a nitrogen-vacancy color center is installed in the probe; or the probe contains multiple nanodiamonds containing nitrogen-vacancy color centers, and the multiple nanodiamonds containing nitrogen-vacancy color centers are arranged in an array.

In some embodiments, the probe has a diamond substrate on which a diamond nanostructure containing nitrogen-vacancy color centers is disposed.

According to another aspect of the embodiments of the present invention, there is provided an atomic force microscope, comprising:

The probe described above is configured to be close to a magnetic field, and the fluorescence lifetime and the photoluminescence intensity change when the received light remains unchanged and the magnetic field changes;

A photoluminescence detection device and/or a fluorescence lifetime detection device, wherein the photoluminescence detection device is configured to detect the photoluminescence intensity, and the fluorescence lifetime detection device is configured to detect the fluorescence lifetime.

The photoluminescence detection device here includes an avalanche diode, a single photon counter and a high-speed digital acquisition card; the fluorescence lifetime detection device includes an avalanche diode, a single photon counter, a pulse signal generator and a high-speed digital acquisition card.

As shown in Figure 6, a specific implementation method for measuring magnetic field by operating nanodiamond containing NV color center under atomic force microscope is to read magnetic field information by optical method using a single NV color center in the nanodiamond particle on the AFM tip (or an AFM integral probe processed from a block diamond). The measurement process is as follows: the probe 501 moves the nanodiamond particle containing NV color center on the tip to the vicinity of the magnetic field emitted by the magnetic field generator 502, and with the assistance of the movable reflector 505, the coaxial digital CCD lens 506 and the reflector 504, the objective lens 503 is focused on the nanodiamond particle; then the movable reflector 505 is moved away. The laser diode 507 emits 532nm light through a short-pass filter 508 to illuminate the nanodiamond of the probe 501, and the NV color center therein is excited to emit fluorescence of about 637nm. The fluorescence is collected by a single photon counter 509 (a type of photoluminescence detection device and/or fluorescence lifetime detection device) after filtering. The fluorescence intensity information and fluorescence lifetime information are obtained by processing the signal of the single photon counter 509. Based on the photoluminescence and fluorescence lifetime, the sample surface is scanned point by point and imaged, which can reflect the nanoscale magnetic field changes on the sample surface.

The data of measuring a NV color center are shown in Figure 7a and Figure 7b. Therefore, the fluorescence intensity and fluorescence lifetime observed in the experiment will be affected by the size and direction of the magnetic field. The NV lifetime decreases with the increase of the magnetic field, and the photoluminescence intensity decreases with the increase of the magnetic field.

The embodiments of the present invention realize all-optical magnetic field sensing and methods by studying and utilizing nano fluorescent structures - NV color centers in diamond, thereby avoiding the introduction of external microwave radiation to realize nano magnetic field sensing; using all-optical magnetic field measurement technology, the complexity of some device structures is eliminated, the structure is simple and reliable, the application is convenient, the measurement response speed is fast, and the magnetic field intensity measurement range is wide.

The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims (3)

1. A diamond nano all-optical magnetic field sensor, comprising:

A diamond nanostructure containing nitrogen-vacancy color centers configured to change fluorescence lifetime and photoluminescence intensity under different magnetic fields;

A photoluminescence detection device configured to detect the photoluminescence intensity and/or a fluorescence lifetime detection device configured to detect the fluorescence lifetime;

The photoluminescence detection device comprises an avalanche diode, a single photon counter and a high-speed digital acquisition card; the fluorescence lifetime detection device comprises an avalanche diode, a single photon counter, a pulse signal generator and a high-speed digital acquisition card;

the fluorescence is collected by a single photon counter of the photoluminescence detection device and/or the fluorescence lifetime detection device, and fluorescence intensity information and fluorescence lifetime information are obtained through signal processing of the single photon counter;

Wherein, when the magnetic field in the direction perpendicular to the symmetry axis of the nitrogen-vacancy color center is strong, the eigenstate of the system is not spin any more But rather their superimposed states; extracting information of an external magnetic field from an optical response of a nitrogen-vacancy color center, the optical response including a decrease in fluorescence lifetime of an individual nitrogen-vacancy color center with an increase in the external magnetic field and a decrease in photoluminescence intensity of the individual nitrogen-vacancy color center with an increase in the external magnetic field;

Depositing 300nm thick SiNx on the diamond nano-structure containing the nitrogen-vacancy color center, and then uniformly sizing HSQ to 300nm to prepare a diamond nano-probe containing single NV, wherein the diamond probe containing single NV can be used as the magnetic field sensor;

The diamond nanostructure material containing the nitrogen-vacancy color center is a nanoparticle or a nanowire, or is a derivative or micro-nano processing structure containing the diamond NV color center basic structure; the diamond nanostructure containing the nitrogen-vacancy color center is arranged on a diamond substrate, and the diamond substrate is made of single crystal or polycrystalline materials.

2. The diamond nano all-optical magnetic field sensor according to claim 1, wherein the diamond nanostructure containing nitrogen-vacancy color centers contains a single nitrogen-vacancy color center or a plurality of nitrogen-vacancy color centers arranged in an array.

3. An atomic force microscope, comprising:

The diamond nano all-optical magnetic field sensor of any one of claims 1-2.