CN111323617A - Nitrogen-vacancy color center sensor and preparation method thereof - Google Patents
Nitrogen-vacancy color center sensor and preparation method thereof Download PDFInfo
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Abstract
The invention provides a nitrogen vacancy color center sensor, which comprises: a circuit board; the circuit board is provided with electrodes; a tuning fork device; the tail end of the tuning fork device is electrically connected with the electrode of the circuit board; a transfer beam; the switching beam is arranged at the front end of the tuning fork device; the switching beam can penetrate through fluorescence emitted by the nitrogen vacancy color center and laser for exciting the nitrogen vacancy color center; a diamond substrate; one surface of the diamond substrate is connected with the transfer beam; the opposite surface is provided with a diamond nano-pillar waveguide array; and a nitrogen vacancy color center is arranged on the diamond nano-pillar waveguide. Compared with the prior art, the sensor provided by the invention is provided with the diamond nano-pillar waveguide array to form a plurality of probes containing nitrogen vacancy color centers, so that the efficiency and the service life of the nitrogen vacancy color center sensor are improved; the probe is arranged on the diamond substrate and connected through the transfer beam, so that the rigidity of the probe is enhanced; the sensitivity of the diamond nano-pillar waveguide is further improved by arranging the shape of the diamond nano-pillar waveguide.
Description
Technical Field
The invention belongs to the technical field of scanning sensors, and particularly relates to a nitrogen vacancy color center sensor and a preparation method thereof.
Background
The nitrogen vacancy colour centre (NV centre) is a solid state point defect in diamond, consisting of a nitrogen atom and an adjacent vacancy, and is a three-level structural system with a spin of 1. The quantum state of the nitrogen vacancy color center can be initialized by laser, quantum manipulation is performed by using microwaves, and readout is performed by fluorescence. The NV color center can be used as a sensitive sensor with molecular scale for measuring physical quantities such as a magnetic field, temperature, an electric field and the like in the environment, the physical quantities can cause the electron spin energy level of the NV color center to change, and the physical quantities can be reversely deduced by testing the disturbance of the NV energy level. The NV color center in the diamond is made into a scanning sensor, and the nanoscale scanning imaging of a measured target can be realized by combining an atomic force microscope scanning system, so that images of the target, such as a magnetic field, an electric field, temperature and the like, can be obtained.
Such NV colour centre based scanning sensors currently mainly use a single diamond nanoparticle or a single diamond nanopillar as scanning probe.
There are two main ways of using diamond nanoparticles as probes. The first is to sprinkle diamond nanoparticles on the sample to be tested. Nanoparticles of about 10nm size allow the NV colour centre to detect signals within nearly 10nm of the sample surface. However, the yield of diamond nanoparticles containing a single NV colour centre is low, the randomness of the way in which the diamond particles are scattered on the surface of the sample is high, and the nanoparticles can only detect nearby sample signals, which makes it difficult to image a wide range of sample signals. The second uses a fiber optic tip to pick up the diamond nanoparticles. The movement of the optical fiber head can drive the diamond nano particles to move, and signal imaging is carried out on the surface of the sample. However, since the fiber tip and the sample are distributed on both sides of the diamond nanoparticle, the objective lens for collecting the fluorescence signal can be placed only on one side of the sample, and only the transparent sample can be measured, which causes limitations.
The single nanometer column type probe is only provided with one nanometer column optical waveguide on a ten-micron diamond substrate, and the NV color center is within 10nm of the front end of the nanometer column and can be combined with an AFM system to directly scan and image a sample. However, the yield of a single nano-column probe is low, the process is complex, scanning can be interrupted only after a single NV color center is damaged, the probe is replaced, and continuous measurement cannot be realized.
In summary, the conventional NV color center scanning sensor scheme mainly has the problems of poor NV color center quality, low sensitivity, low yield of probe manufacture, short probe life and the like.
Disclosure of Invention
In view of this, the technical problem to be solved by the present invention is to provide a nitrogen vacancy color center sensor with high rigidity and high sensitivity and a preparation method thereof.
The invention provides a nitrogen vacancy color center sensor, which comprises:
a circuit board; the circuit board is provided with electrodes;
a tuning fork device; the tail end of the tuning fork device is electrically connected with the electrode of the circuit board;
a transfer beam; the switching beam is arranged at the front end of the tuning fork device; the switching beam can penetrate through fluorescence emitted by the nitrogen vacancy color center and laser for exciting the nitrogen vacancy color center;
a diamond substrate; one surface of the diamond substrate is connected with the transfer beam; the opposite surface is provided with a diamond nano-pillar waveguide array; and a nitrogen vacancy color center is arranged on the diamond nano-pillar waveguide.
Preferably, the diamond nanorod waveguide is in a truncated cone shape.
Preferably, the diameter of the upper surface of the circular truncated cone shape is 200-800 nm; the inclination angle of the edge is 5-30 degrees; the height is 0.3 to 2 μm.
Preferably, the depth of the nitrogen vacancy color center on the diamond nano-pillar waveguide from the surface is 3-50 nm.
Preferably, the length of the circuit board is 1-50 mm, the width of the circuit board is 1-50 mm, and the thickness of the circuit board is 0.5-5 mm; the length of the transfer beam is 0.1-3 mm, the width is 0.01-1 mm, and the thickness is 30-500 mu m; the length of the diamond substrate is 50-300 mu m, the width of the diamond substrate is 50-300 mu m, and the thickness of the diamond substrate is 10-80 mu m.
Preferably, the transfer beam is a glass transfer beam and/or a silicon cantilever beam.
Preferably, one surface of the diamond substrate and one surface of the transfer beam are precision polished surfaces, and the polishing roughness reaches rms less than 1 nm.
Preferably, an atomic force microscope system is also included; and the electrode of the circuit board is connected with a scanning imaging feedback system of the atomic force microscope system.
The invention also provides a preparation method of the nitrogen vacancy color center sensor, which comprises the following steps:
s1) carrying out nitrogen ion implantation by taking the diamond as a substrate, and annealing to obtain the diamond containing the nitrogen vacancy color center;
s2) preparing a graphical mask on the surface of the diamond containing the nitrogen vacancy color center, and etching to obtain a diamond substrate;
s3) electrically connecting the tail end of the tuning fork device with the electrode of the circuit board, connecting the transfer beam to the front end of the tuning fork device, and connecting the side, which is not provided with the nitrogen vacancy color center, of the diamond substrate to the tuning fork device to obtain the nitrogen vacancy color center sensor.
Preferably, the energy of the nitrogen ion implantation is 2.5-20 keV; the dose of implanted ions is 1010～ 1012atom/cm2。
The invention provides a nitrogen vacancy color center sensor, which comprises: a circuit board; the circuit board is provided with electrodes; a tuning fork device; the tail end of the tuning fork device is electrically connected with the electrode of the circuit board; a transfer beam; the switching beam is arranged at the front end of the tuning fork device; the switching beam can penetrate through fluorescence emitted by the nitrogen vacancy color center and laser for exciting the nitrogen vacancy color center; a diamond substrate; one surface of the diamond substrate is connected with the transfer beam; the opposite surface is provided with a diamond nano-pillar waveguide array; and a nitrogen vacancy color center is arranged on the diamond nano-pillar waveguide. Compared with the prior art, the sensor provided by the invention is provided with the diamond nano-pillar waveguide array to form a plurality of probes containing nitrogen vacancy color centers, so that the efficiency and the service life of the nitrogen vacancy color center sensor are improved; the diamond nano-pillar waveguide array is arranged on the diamond substrate and connected through the transfer beam, so that the rigidity of the probe is enhanced; the sensitivity of the diamond nano-pillar waveguide is further improved by arranging the shape of the diamond nano-pillar waveguide.
Drawings
FIG. 1 is a schematic structural view of a nitrogen-vacancy color center sensor provided by the present invention;
FIG. 2 is a schematic diagram of a waveguide-shaped structure of a diamond nanopillar in a nitrogen vacancy color center sensor provided by the present invention;
FIG. 3 is a schematic diagram of a nitrogen vacancy color center sensor provided by the present invention;
FIG. 4 is a photograph of a nitrogen-vacancy color center sensor made in example 1 of the present invention;
FIG. 5 is a scanning electron beam micrograph of a nitrogen-vacancy color center sensor made according to example 1 of the present invention;
FIG. 6 is a fluorescence plot of a nitrogen-vacancy color center in a nitrogen-vacancy color center sensor made according to example 1 of the present invention;
FIG. 7 is a plot of fluorescence count versus laser power for one of the nitrogen-vacancy color centers in a nitrogen-vacancy color center sensor made in accordance with example 1 of the present invention;
FIG. 8 is an electron paramagnetic resonance spectrum of one of the nitrogen vacancy color centers of the nitrogen vacancy color center sensor prepared in example 1 of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a nitrogen vacancy color center sensor, which comprises:
a circuit board; the circuit board is provided with electrodes;
a tuning fork device; the tail end of the tuning fork device is electrically connected with the electrode of the circuit board;
a transfer beam; the switching beam is arranged at the front end of the tuning fork device; the switching beam can penetrate through fluorescence emitted by the nitrogen vacancy color center and laser for exciting the nitrogen vacancy color center;
a diamond substrate; one surface of the diamond substrate is connected with the transfer beam; the opposite surface is provided with a diamond nano-pillar waveguide array; and a nitrogen vacancy color center is arranged on the diamond nano-pillar waveguide.
Referring to fig. 1, fig. 1 is a schematic structural diagram of a nitrogen vacancy color center sensor provided by the present invention.
The nitrogen-vacancy color center sensor provided by the invention comprises a circuit board; the circuit board is preferably a printed circuit board; the circuit board is provided with electrodes, preferably metal electrodes, more preferably metal electrodes are symmetrically arranged on two sides of the same surface, and the two symmetrical metal electrodes are not electrically connected; the circuit board is used for connecting the sensor with the atomic force microscope scanning imaging feedback system; the length of the circuit board is preferably 1-50 mm; the width is preferably 1-50 mm; the thickness is preferably 0.5 to 5 mm.
A tuning fork device is loaded on an electrode of the circuit board, and the tail end of the tuning fork device is electrically connected with the electrode of the circuit board and used for atomic force microscope contact force feedback; the tuning fork device is preferably a quartz tuning fork device. In the invention, the tuning fork device is used as a carrier of the sensor probe, and when the sensor waveguide probe (diamond substrate) is close enough to the surface of a material to be detected, because extremely weak repulsive force exists between atoms at the tip of the probe and atoms on the surface of a sample, the resonance frequency of the tuning fork crystal oscillator can be changed under the influence of the extremely weak repulsive force. The change of the tuning fork crystal oscillator resonant frequency is obtained by monitoring the piezoelectric signal of the tuning fork device, and a feedback loop is formed by the piezoelectric signal and the piezoelectric ceramic for controlling the height of the sensor, so that the distance between the probe and the measured material is kept in a nanometer size, and meanwhile, the NV color center optical detection magnetic resonance signal is detected, and the physical quantity information such as a magnetic field, a temperature, an electric field and the like in the environment can be obtained.
The front end of the tuning fork device is provided with a transfer beam; the switching beam can transmit fluorescence emitted by the nitrogen vacancy color center and laser for exciting the nitrogen vacancy color center, and preferably can transmit light with the wavelength of 532-800 nm; the transfer beam is preferably a glass transfer beam and/or a silicon cantilever beam, and more preferably a silicon cantilever beam, a fine quartz glass tube or ultrathin quartz glass; the length of the transfer beam is preferably 0.1-3 mm, more preferably 0.5-2 mm, and further preferably 1-2 mm; the width is preferably 0.01-1 mm, more preferably 0.05-0.8 mm, still more preferably 0.1-0.5 mm, and most preferably 0.2-0.5 mm; the thickness is preferably 30 to 500 μm, more preferably 50 to 400 μm, still more preferably 100 to 200 μm, and most preferably 150 to 170 μm; the length of the part of the adapter beam, which is exposed out of the tuning fork device, is preferably at least 400 μm so as to ensure that the fluorescence of the nitrogen vacancy color center is not shielded by the tuning fork.
The diamond substrate is arranged on the transfer beam, the length of the diamond substrate is preferably 50-300 mu m, the width of the diamond substrate is preferably 50-300 mu m, the thickness of the diamond substrate is preferably 10-80 mu m, more preferably 30-80 mu m, further preferably 40-60 mu m, most preferably 50 mu m, one surface of the diamond substrate is connected with the transfer beam, the surface is preferably a precisely polished surface, the polishing roughness of the surface is preferably less than 1nm, the diamond substrate and the transfer beam are preferably rigidly fixed through light-transmitting resin, the light-transmitting resin is preferably light-transmitting epoxy resin, one surface opposite to the connection surface of the transfer beam is provided with a diamond nano-pillar waveguide array, the number of diamond nano-pillar waveguides in the array is preferably more than or equal to 2 × 2, more preferably 2 × 2-20 × 20, further preferably 5 × 5-15 × 15, most preferably 7 × 7-10 × 10, the diamond nano-pillar waveguide array is preferably in a truncated cone shape, the diamond nano-pillar waveguide array is preferably in a truncated cone shape, the graph 2 is preferably a structure in a truncated cone shape, the diameter of the upper surface of the truncated cone shape is preferably 200 nm, the color pillar is preferably 300-300 nm, the color pillar surface is preferably 10-10 nm, the color pillar is preferably in a color pillar surface of the color pillar is preferably 10-10 nm, the graph of the1Side inclination angle theta, circular truncated cone height H and color centerThe position of the fluorescent light is simulated by a Finite Difference Time Domain (Finite Difference Time Domain) method that the fluorescent light emitted from the NV color center is emitted from the lower part of the circular table, and the light intensity distribution, I, of the fluorescent light along each divergence angles、ηp. And integrating the solid angle according to the obtained light intensity distribution information and according to the laws of geometric optics and Fresnel reflection and refraction to calculate the fluorescence emission efficiency within the range of the collection angle of the lens when the fluorescence penetrates through the lower surface of the diamond.
Ts、TpCoefficients for the S and P polarization components, respectively, across the diamond and air interfaces, derived from Fresnel' S law of reflection and refraction ηs、ηpThe fluorescence emission efficiencies of the S and P polarization components, respectively. Finally, parameters corresponding to better fluorescence collection efficiency can be obtained through simulation, and the NV color center fluorescence emission efficiency conforming to the morphology is higher than 30%. Nitrogen vacancies are six electron systems, three electrons from carbon atoms adjacent to the vacancies, two electrons from nitrogen atoms adjacent to the vacancies, and one electron from the crystal lattice are trapped, so NV is a three-level system whose electron paramagnetic resonance spectrum can reflect information about magnetic field, electric field, and temperature in the vicinity of NV. The sensor provided by the invention is provided with a plurality of isolated probes containing single NV color center, and is used for realizing nanoscale and high-sensitivity measurement and scanning imaging of a magnetic field, spin magnetic resonance and an electric field.
According to the present invention, an atomic force microscope system is preferably also included; and the electrode of the circuit board is connected with a scanning imaging feedback system of the atomic force microscope system.
The nitrogen vacancy color center sensor provided by the invention can be used for nanoscale scanning imaging, a circuit board carrying a tuning fork device, a transfer beam and a diamond substrate is also provided with a mechanical interface to be fixedly connected to an experimental platform, a high-frequency signal driving the tuning fork device is connected into the tuning fork device and the diamond substrate through an electrode on the circuit board, the diamond substrate is used as a high-frequency signal fed back by a probe and is conducted out through another electrode on the circuit board, and the diamond substrate, namely the probe, is controlled by a phase-locked amplifier to move relative to the distance of a sample. When the probe is close to or far from the surface, the damping sensed by the tuning fork device changes, the amplitude of the tuning fork changes, a tuning fork feedback high-frequency signal is amplified and transmitted to the phase-locked amplifier, and the movement of the Z-direction displacement table where the probe system is located can be feedback-controlled by adjusting the PID parameter of the phase-locked amplifier, so that the nondestructive scanning imaging of the surface of the sample is carried out. Referring to fig. 3, fig. 3 is a schematic diagram of a nitrogen vacancy color center sensor provided by the present invention.
The sensor provided by the invention is provided with the diamond nano-pillar waveguide array to form a plurality of probes containing nitrogen vacancy color centers, so that the efficiency and the service life of the nitrogen vacancy color center sensor are improved; the diamond nano-pillar waveguide array is arranged on the diamond substrate and connected through the transfer beam, so that the rigidity of the probe is enhanced; the sensitivity of the diamond nano-pillar waveguide is further improved by arranging the shape of the diamond nano-pillar waveguide.
The invention also provides a preparation method of the nitrogen vacancy color center sensor, which comprises the following steps: s1) carrying out nitrogen ion implantation by taking the diamond as a substrate, and annealing to obtain the diamond containing the nitrogen vacancy color center; s2) preparing a graphical mask on the surface of the diamond containing the nitrogen vacancy color center, and etching to obtain a diamond substrate; s3) electrically connecting the tail end of the tuning fork device with the electrode of the circuit board, connecting the transfer beam to the front end of the tuning fork device, and connecting the side, which is not provided with the nitrogen vacancy color center, of the diamond substrate to the tuning fork device to obtain the nitrogen vacancy color center sensor.
The method prepares the near-surface NV color center by utilizing an ion injection and annealing process, realizes the doping of nitrogen elements and vacancies on the surface of the diamond through an ion injection technology, and realizes the combination of the vacancies and the nitrogen elements through an ultrahigh vacuum high-temperature annealing process to generate the NV color center. Injecting nitrogen ions by taking diamond as a substrate; the thickness of the diamond is 10-80 mum, more preferably 30 to 80 μm, still more preferably 40 to 60 μm, and most preferably 50 μm; the diamond is an electronic grade purity single crystal diamond; the nitrogen ion implantation is selected to contain N+、N2+Carrying out ion implantation on nitrogen-containing ions; the energy of the ion implantation is preferably 2.5-20 keV; the dose of implanted ions is preferably 1010～1012atom/cm2More preferably 1011atom/cm2(ii) a Annealing the substrate after ion implantation to obtain the diamond containing the nitrogen vacancy color center; the temperature of the annealing treatment is preferably 600-1200 ℃, more preferably 700-1100 ℃, and further preferably 800-1000 ℃; the time of the annealing treatment is preferably two hours or more; the annealing treatment is preferably performed in a vacuum degree of more than 10-4Pa or under the protection of inert gas to ensure that the diamond is not graphitized.
Preparing a graphical mask on the surface of the diamond containing the nitrogen vacancy color center, and transferring the mask graph to the surface of the diamond through a diamond etching process to realize the preparation of the waveguide with high fluorescence collection efficiency. Wherein, the material used for the patterned mask is preferably metal, metal oxide, SiO2HSQ electron beam photoresist; and etching after preparing the graphical mask, preferably etching the diamond containing the nitrogen vacancy color center by adopting oxygen or oxygen-containing gas as etching gas through reactive plasma etching to obtain the diamond substrate containing the diamond nano-pillar waveguide array.
Taking the metal material Ti as an example of a mask, the following method is preferably adopted:
and (3) preparing a PMMA (polymethyl methacrylate) small hole array on the surface of the diamond by electron beam lithography.
And (3) uniformly gluing PMMA: and (3) performing electron beam exposure on positive photoresist PMMA 950k on a diamond in a spinning mode at the rotating speed of 7000 rpm for 1 min. Baked on a hot plate at 130 ℃ for 15 minutes. The thickness of the obtained PMMA glue reaches 160-240 nm.
Spin coating a conductive layer: spin coating conductive adhesive SX AR-PC 5000/90.2 on the PMMA surface, rotating at 4000 rpm, baking on a hot plate at 90 ℃ for 2 minutes, and volatilizing the solvent.
Electron beam exposure:electron beam energy 10KeV, exposure dose 170uC/cm2Circular arrays of different diameters of the exposure pattern. In order to make the stripping process smoother, an exposure system with lower energy of 10KeV electron energy is used, or double-layer glue stripping is used.
And (3) developing: and putting the diamond into deionized water for 2min, cleaning the conductive adhesive, and then blowing the conductive adhesive by nitrogen. Then developed in a developing solution (MIBK: IPA, 1:3) for 110s, and then fixed in a fixing solution (IPA) for 100 s. And finally blowing the mixture by using nitrogen.
The preparation of the surface mask is realized through film coating and stripping.
Electron beam evaporation coating: and coating the titanium metal by 80-120 nm in a manner of electronic evaporation coating and in a direction vertical to the surface of the diamond.
Stripping by dissolution: and putting the diamond into acetone or a degumming agent, soaking for more than 10min, washing the surface of the diamond, and removing the photoresist on the surface.
Pure oxygen is introduced into the inductively coupled reactive plasma etcher for etching, and the circular truncated cone structure is etched by utilizing the physical facet phenomenon.
The etching parameters of the inductively coupled reactive plasma etching machine used in the invention are preferably as follows: RF power: 40W, ICP Power: 800W, O2Flow rate: 30scmm, pressure: 20 mTorr.
The mask thickness is reduced with the increase of the etching depth under the etching process due to the excessive consumption of the mask by the ion sputtering. The shape of the mask also deforms with the sputtering of the ion beam because the mask at the sharp corner always wears away first and fastest. The side wall of the etching structure under the mask also generates an inclination angle therewith, and finally a waveguide shape with higher fluorescence collection efficiency is formed
The mask of the remaining waveguide end face is removed by a wet process.
In mixed acid solution (HClO)4：H2SO4: HNO3 ═ 1:1:1) wet etching at 200 deg.C for 1 hr. And (5) washing with deionized water.
The method comprises the steps of taking electronic-grade purity single crystal diamond as a substrate, wherein the size of the single crystal needs to be larger than 1mm × 1mm, cutting the etched diamond preferably to obtain a diamond substrate, cutting preferably by adopting laser scribing equipment, continuously cleaning by a wet method, cleaning by a chemical wet method, removing residual pollutants in the micro-nano processing process, and improving the quality of nitrogen vacancy color centers so as to improve the sensitivity.
Electrically connecting the tail end of the tuning fork device with an electrode of the circuit board; in the invention, electric soldering iron is preferably adopted for heating and soldering to complete the electrical connection between the tuning fork device and the electrode.
Then connecting the adapter beam to the front end of the tuning fork device, and bonding the adapter beam to the front end of the tuning fork device through resin preferably under a microscope; the resin is preferably an epoxy resin.
Connecting the side of the diamond substrate, which is not provided with the nitrogen vacancy color center, to the tuning fork device, preferably connecting the side of the diamond substrate, which is not provided with the nitrogen vacancy color center, to the tuning fork device through resin, so as to obtain a nitrogen vacancy color center sensor; the resin is preferably an epoxy resin.
The invention provides a micro-nano processing method of a diamond nano-pillar waveguide array on a diamond substrate, which is used for improving the collection efficiency of NV color center fluorescence and improving the signal intensity; and the diamond substrate is subjected to miniaturization cutting by using direct laser cutting, further cleaned and then bonded and assembled at the micrometer scale, so that the surface of the sensor after manufacture is clean, and the quality of the sensor is further ensured.
In order to further illustrate the present invention, the following describes a nitrogen vacancy color center sensor and a method for manufacturing the same in detail with reference to the following examples.
The reagents used in the following examples are all commercially available.
Example 1
The nitrogen vacancy color center sensor provided by the embodiment comprises a printed circuit board, a quartz tuning fork, a transfer beam and a diamond substrate; the printed circuit board may have a length of 50mm, a width of 50mm and a thickness of 0.5 mm. Wherein the length of the transfer beam is 1mm, the width is 0.2mm, and the thickness is 170 mu m; the printed circuit board comprises a printed circuit board connected with the tuning fork, metal electrodes are symmetrically plated on two sides of the upper surface of the printed circuit board, and the front ends of the electrodes are connected with the quartz tuning fork electrodes. The quartz tuning fork comprises a quartz tuning fork positioned on the upper surface of the printed circuit board, the quartz tuning fork is positioned in the middle of the tail end of the electrode of the printed circuit board, the root of the quartz tuning fork is connected with the printed circuit board, and the electrode of the quartz tuning fork is connected with the corresponding electrode of the printed circuit board. The switching beam can transmit 532-800 nm wavelength light and is located at one end of the quartz tuning fork. The diamond substrate consists of a diamond substrate and an array truncated cone-shaped nano waveguide positioned in the center, wherein the smooth surface of the diamond substrate is connected with the lower surface of the glass beam through light-transmitting epoxy resin, the smooth surface is a precision polishing surface, and the polishing roughness reaches rms (rms) less than 1 nm. The other surface is a nano round table array, the number of the nano round tables is 7x 7, the root of the nano waveguide column is connected with the diamond substrate, and the end surface of the nano waveguide column contains an NV color center with the depth of about 30nm close to the surface. The waveguide is in the shape of a circular truncated cone (the diameter of the upper surface is 400nm, the side inclination angle is 15 degrees, the height of the circular truncated cone is 2 microns), and the emission efficiency of NV color center fluorescence is higher than 30%.
Manufacturing a diamond substrate:
(a) NV color center preparation
Using an electronic grade purity monocrystal diamond with a surface polishing thickness of 50 μm as a substrate, wherein the size of the monocrystal is larger than 1mm × 1mm, and selecting N+、N2+Plasma nitrogen-containing ions are used as implantation ions; the energy interval of the implantation is 20 keV; implanted ion dose 1011atom/cm2(ii) a The annealing temperature interval of the annealing process is 800 ℃, the annealing time is 2 hours, and the vacuum degree during the annealing is better than 10- 4Pa protects to ensure that the diamond is not graphitized.
(b) High fluorescence collection efficiency waveguide fabrication
Preparing a patterned mask on the diamond surface treated in the step (a), and transferring the mask pattern to the diamond surface through a diamond etching process to realize the preparation of the waveguide with high fluorescence collection efficiency. The mask material can be selected from metal, metal oxide, and SiO2HSQ e-beam photoresist, etc.
Taking a metal material Ti as an example of a mask, the specific embodiment is as follows:
and (3) preparing a PMMA (polymethyl methacrylate) small hole array on the surface of the diamond by electron beam lithography.
And (3) uniformly gluing PMMA: and (3) performing electron beam exposure on positive photoresist PMMA 950k on a diamond in a spinning mode at the rotating speed of 7000 rpm for 1 min. Baked on a hot plate at 130 ℃ for 15 minutes. The thickness of the obtained PMMA glue reaches 160-240 nm.
Spin coating a conductive layer: spin coating conductive adhesive SX AR-PC 5000/90.2 on the PMMA surface, rotating at 4000 rpm, baking on a hot plate at 90 ℃ for 2 minutes, and volatilizing the solvent.
Electron beam exposure: electron beam energy 10KeV, exposure dose 170uC/cm2Circular arrays of different diameters of the exposure pattern. In order to make the stripping process smoother, an exposure system with lower energy of 10KeV electron energy is used, or double-layer glue stripping is used.
And (3) developing: and putting the diamond into deionized water for 2min, cleaning the conductive adhesive, and then blowing the conductive adhesive by nitrogen. Then developed in a developing solution (MIBK: IPA, 1:3) for 110s, and then fixed in a fixing solution (IPA) for 100 s. And finally blowing the mixture by using nitrogen.
Preparation of surface mask by plating and stripping
Electron beam evaporation coating: and coating the titanium metal by 80-120 nm in a manner of electronic evaporation coating and in a direction vertical to the surface of the diamond.
Stripping by dissolution: and putting the diamond into acetone or a degumming agent, soaking for more than 10min, washing the surface of the diamond, and removing the photoresist on the surface.
Pure oxygen is introduced into the inductively coupled reactive plasma etcher for etching, and the circular truncated cone structure is etched by utilizing the physical facet phenomenon.
The etching parameters of the inductively coupled reactive plasma etching machine used in the manufacturing scheme are preferably as follows: RF power: 40W, ICP Power: 800W, O2Flow rate: 30scmm, pressure: 20 mTorr; the etching time is 10 min.
The mask thickness is reduced with the increase of the etching depth under the etching process due to the excessive consumption of the mask by the ion sputtering. The shape of the mask also deforms with the sputtering of the ion beam because the mask at the sharp corner always wears away first and fastest. The side wall of the etching structure under the mask also generates an inclination angle therewith, and finally a waveguide shape with higher fluorescence collection efficiency is formed
Removing mask of residual waveguide end face by wet method
In a mixed acid solution (HClO 4: H)2SO4: HNO3 ═ 1:1:1) wet etching at 200 deg.C for 1 hr. And (5) washing with deionized water.
(c) Laser cutting and cleaving of sensor substrates
The method comprises the following steps of bonding the waveguide surface of the diamond sheet to a transparent quartz substrate through epoxy resin glue upwards, using high-power ultraviolet laser cutting equipment to cut the diamond along a reserved cutting path, putting the cut diamond sheet and the quartz substrate into a glass container, and adding triacid (HClO)4：HNO3： H2SO41:1:1) submerging the material, heating at 200 ℃ for more than 5 hours. The graphite produced by the ultraviolet cutting is removed, and quartz and diamond are debonded. Finally, deionized water is used for diluting and replacing the triacid in the container. The quartz substrate in the container is taken out, the deionized water in the container together with the diamond sheet is poured on the surface of the flat cured Polydimethylsiloxane (PDMS), and the deionized water is evaporated in an oven. And finding the diamond sheet under a microscope, and turning the diamond sheet with the waveguide surface facing upwards through a micro-nano manipulator to enable the waveguide surface to face downwards. To prepare the assembly bond for the sensor.
Sensor assembly bonding
(a) Bonding clamp and quartz tuning fork crystal oscillator
The quartz tuning fork crystal oscillator is fixed on the clamp, and electrodes on the quartz tuning fork are required to be connected with electrodes on the clamp in order to obtain a piezoelectric signal of the quartz tuning fork crystal oscillator. The specific implementation scheme is as follows: and removing the shell, the pins and the glass Vermilion of the tuning fork crystal oscillator electronic component to obtain a central quartz tuning fork, welding the tail of the tuning fork with a clamp, and connecting the electrode on the tuning fork with the upper electrode of the clamp through lead bonding.
(b) Bonding sensor substrate and tuning fork crystal oscillator
The tuning fork crystal oscillator and the sensor substrate can be connected through small-sized objects such as a silicon cantilever beam, a thin quartz glass tube, ultrathin quartz glass and the like. Taking ultrathin quartz glass as an example, the specific implementation scheme is as follows: a quartz glass sheet with the thickness of 170 mu m is selected and cut into long strips with the length of 700mm and the width of 400 mu m, and the quartz beam with smaller size is beneficial to having better vibration quality factors with tuning fork crystal vibration. One end of the glass beam is bonded to one of the legs of the tuning fork by epoxy, and the quartz beam is exposed to at least 400 μm of the tuning fork to ensure that the fluorescence of the NV colour center is not blocked by the tuning fork.
And coating a small amount of epoxy resin glue which is good in light transmission and can be cured by ultraviolet on the quartz beam, and aligning and contacting the quartz beam with the sensor substrate with the waveguide downwards on the PDMS through a micro-operation platform under an optical microscope. And curing the epoxy resin adhesive through the irradiation of ultraviolet light to complete the bonding of the sensor substrate and the quartz beam.
FIG. 4 is a photograph of a nitrogen-vacancy color center sensor prepared in example 1.
The nitrogen-vacancy color center sensor prepared in example 1 was analyzed using a scanning electron beam microscope to obtain a scanning electron beam microscope photograph thereof, as shown in fig. 5.
Fluorescence imaging of the nitrogen vacancy color center in the nitrogen vacancy color center sensor prepared in example 1 on a photodetection magnetic resonance platform using a 532nm laser gave a fluorescence pattern as shown in fig. 6.
Magnetic detection sensitivity of sensor
δ B can be expressed in relation to the fluorescence count N of the nitrogen vacancy color center as the magnetic detection sensitivity is higher as the fluorescence count is higher. As shown in FIG. 7, a fluorescence saturation curve is tested for a nitrogen vacancy color center in example 1, and the fluorescence count obtained by fitting can reach 500kcounts/s, which is much larger than that of a single nanopillar probe.
Example 1 on a photo-detection magnetic resonance platform using a 532nm laser, the electron paramagnetic resonance spectrum of one of the nitrogen-vacancy colour centers of the fabricated nitrogen-vacancy colour-center scanning sensor was experimentally determined to be shown in figure 8.
Claims (10)
1. A nitrogen-vacancy color center sensor, comprising:
a circuit board; the circuit board is provided with electrodes;
a tuning fork device; the tail end of the tuning fork device is electrically connected with the electrode of the circuit board;
a transfer beam; the switching beam is arranged at the front end of the tuning fork device; the switching beam can penetrate through fluorescence emitted by the nitrogen vacancy color center and laser for exciting the nitrogen vacancy color center;
a diamond substrate; one surface of the diamond substrate is connected with the transfer beam; the opposite surface is provided with a diamond nano-pillar waveguide array; and a nitrogen vacancy color center is arranged on the diamond nano-pillar waveguide.
2. The nitrogen-vacancy color center sensor of claim 1, wherein the diamond nanopillar waveguide is frustum-shaped.
3. The nitrogen vacancy color center sensor according to claim 2, wherein the diameter of the upper surface of the truncated cone shape is 200-800 nm; the inclination angle of the edge is 5-30 degrees; the height is 0.3 to 2 μm.
4. The nitrogen vacancy color center sensor of claim 1, wherein the depth of the nitrogen vacancy color center on the diamond nanopillar waveguide from the surface is 3 to 50 nm.
5. The nitrogen-vacancy color center sensor according to claim 1, wherein the circuit board has a length of 1 to 50mm, a width of 1 to 50mm, and a thickness of 0.5 to 5 mm; the length of the transfer beam is 0.1-3 mm, the width is 0.01-1 mm, and the thickness is 30-500 mu m; the length of the diamond substrate is 50-300 mu m, the width of the diamond substrate is 50-300 mu m, and the thickness of the diamond substrate is 10-80 mu m.
6. The nitrogen-vacancy color center sensor of claim 1, wherein the transfer beam is a glass transfer beam and/or a silicon cantilever beam.
7. The nitrogen vacancy color center sensor of claim 1, wherein one side of the diamond substrate and the transfer beam is a precision polished side with a polishing roughness of rms less than 1 nm.
8. The nitrogen-vacancy color center sensor of claim 1, further comprising an atomic force microscope system; and the electrode of the circuit board is connected with a scanning imaging feedback system of the atomic force microscope system.
9. A method for preparing a nitrogen-vacancy color center sensor is characterized by comprising the following steps:
s1) carrying out nitrogen ion implantation by taking the diamond as a substrate, and annealing to obtain the diamond containing the nitrogen vacancy color center;
s2) preparing a graphical mask on the surface of the diamond containing the nitrogen vacancy color center, and etching to obtain a diamond substrate;
s3) electrically connecting the tail end of the tuning fork device with the electrode of the circuit board, connecting the transfer beam to the front end of the tuning fork device, and connecting the side, which is not provided with the nitrogen vacancy color center, of the diamond substrate to the tuning fork device to obtain the nitrogen vacancy color center sensor.
10. The method according to claim 9, wherein the energy of the nitrogen ion implantation is 2.5-20 keV; the dose of implanted ions is 1010～1012atom/cm2。
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| PCT/CN2020/091242 WO2021164142A1 (en) | 2020-02-18 | 2020-05-20 | Nitrogen vacancy color center-based sensor and preparation method therefor |
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