CN108732156B - A Detection Method for Prohibited Phonon Modes by Selection Rules - Google Patents

Abstract

The invention provides a detection method for selecting a rule forbidding phonon mode, and relates to the field of nano-optics technology, wherein the detection method includes: preparing a material to be characterized and a single-layer closely packed metal particle pattern, so that the metal particles are mutually Closely arranged and form gaps with preset dimensions; collect electric field gradient Raman spectra of the material to be characterized in the gaps of metal particles to detect phonon modes that are forbidden by conventional Raman selection rules in the material to be characterized according to the electric field gradient Raman spectra . The invention has the advantages of low cost, simple operation and strong flexibility, and solves the difficulty in the research on electric field gradient Raman scattering in the sub-nanometer scale due to the limitation of the selection rule of conventional Raman scattering in the prior art. question.

Description

A Detection Method for Prohibited Phonon Modes by Selection Rules

technical field

The invention relates to the technical field of nano-optics, in particular to a detection method for selecting rule-forbidden phonon modes.

Background technique

Raman spectroscopy is a fast and non-destructive material scattering spectrum characterization method. Raman scattering is an inelastic scattering process of photons. The Raman frequency shift, intensity and polarization indicate the phonon (or molecular vibration) properties of the scattering material. Thereby, the information of material structure and composition can be derived, which can be used as the "fingerprint" of materials, and can also accurately reflect the subtle changes of material properties. Therefore, it is widely used in various fields such as physics, chemistry, material science, and biology. And in a material, not all phonon modes can be detected by Raman spectroscopy.

When light interacts with matter, the linear term of polarizability changes with lattice vibration, causing Raman scattering. For the nonlinear term of polarizability, the contribution to inelastic scattering is small under usual experimental conditions. , so it is usually ignored. In the prior art, changes in Raman selection rules caused by electric field gradients have been found. However, since the manipulation of light and materials at the sub-nanometer scale has always been difficult, the research and application of electric field gradient Raman scattering has been limited. a lot of restrictions.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a detection method for selection rules forbidding phonon modes, to solve the problem of the electric field gradient pulling on the sub-nanometer scale due to the limitation of the selection rules of conventional Raman scattering in the prior art. Mann scattering is a difficult problem to study.

In particular, the present invention provides a detection method for selecting rule-forbidden phonon modes, comprising:

preparing the material to be characterized and a single-layer closely packed metal particle pattern, so that the metal particles are closely arranged with each other and form a gap with a preset size;

The electric field gradient Raman spectrum of the material to be characterized in the interstitial space of the metal particles is collected, so as to detect the phonon mode prohibited by the conventional Raman selection rule in the material to be characterized according to the electric field gradient Raman spectrum.

Further, prepare the material to be characterized and a single-layer closely packed metal particle pattern, so that the metal particles are closely arranged with each other and form a gap with a preset size range, including:

preparing the material to be characterized on a substrate;

The single-layer closely packed metal particle pattern is prepared on the material to be characterized, and the metal particles are closely arranged with each other and form gaps with predetermined dimensions.

Further, prepare the material to be characterized and a single-layer closely packed metal particle pattern, so that the metal particles are closely arranged with each other and form a gap with a preset size range, including:

preparing the single-layer closely packed metal particle pattern on the substrate, and making the metal particles closely arranged with each other and forming a gap with a preset size;

The material to be characterized is prepared on the monolayer closely packed metal particle pattern.

Further, the material to be characterized is a non-metallic material that can be characterized by Raman spectroscopy, and can be coupled with the metal particles or the plasmon of the gap structure formed between the metal particles to achieve Raman enhancement. . Wherein, the gap between the adjacent metal particles is within the range of the preset size.

Further, the material to be characterized is a non-metallic material that can be characterized by Raman spectroscopy, and can be coupled with the plasmon element of the metal nanostructure, and the gap of the metal nanostructure is within the range of the preset size. Inside. Wherein, the metal nanostructure is a nanostructure composed of the metal particles and having surface plasmon resonance.

Further, the preset size is less than 10 nm;

Further, the preset dimension is less than 5 nm.

Further, the material to be characterized includes organic molecules, carbon nanotubes, graphene and/or monolayer molybdenum sulfide.

Further, the size and shape of the metal particles are selected such that their plasmonic resonance peaks match the wavelength of the excitation laser.

Further, the metal particles are metal particles with surface plasmon resonance, including but not limited to noble metal nanoparticles.

Further, the structure composed of the metal particles is a nanostructure with surface plasmon resonance.

Further, the metal particles are noble metal-containing nanoparticles, and the nanostructures formed by the noble metal-containing nanoparticles are nanostructures having surface plasmon resonance.

The metal particulate material includes metal element and/or alloy and/or heterostructure;

Preferably, the metal nanoparticulate material comprises a noble metal-containing element and/or alloy and/or heterostructure;

The size of the metal particles is selected to be nanoscale or micronanoscale or microscale; and

The shape of the metal particles is selected to be one or more of nanospheres, nanodiscs, nanocubes, nanopolyhedra, and nanorods.

Further, the preparation method of the material to be characterized includes spin coating, spraying, and infiltration of a solution or dispersion containing the component of the characterizing material, and also includes one of electrochemistry, chemical vapor deposition, thermal evaporation, electron beam evaporation, and micromachining. or more.

Further, the material to be characterized is a one-dimensional nanowire or nanorod or nanotube;

Further, the material to be characterized is two-dimensional graphene or molybdenum disulfide or nanoparticles.

The beneficial effects of the present invention are:

First, prepare the material to be characterized and a single-layer closely packed metal particle pattern, so that the metal particles are closely arranged with each other to form a gap with a preset size, and then collect the electric field gradient Raman of the material to be characterized in the gap between the metal particles spectrum to detect phonon modes in the material to be characterized that are forbidden by conventional Raman selection rules according to electric field gradient Raman spectroscopy. In this way, the detection method of the present invention can utilize the sub-nanoscale gaps between the self-assembled metal particles to combine with the material to be characterized to construct a strong electric field gradient, so that the electric field gradient Raman scattering can be enhanced to detect the conventional pull in the material to be characterized. Mann's choice rule forbids phonon modes. That is to say, in the material to be characterized without defects, the D-mode cannot be detected by conventional Raman spectroscopy, and after compounding with the metal particle patterns that are closely arranged with each other and form gaps with a predetermined scale range, except for the surface plasmon caused by In addition to the Raman enhancement of , a strong D mode can also be detected, which indicates that the electric field gradient Raman scattering breaks the selection rule of conventional Raman scattering and realizes the detection of the central phonon mode in the non-Brillouin zone. Therefore, the detection method of the present invention solves the problem that the research on electric field gradient Raman scattering in the sub-nanometer scale is difficult due to the limitation of the selection rule of conventional Raman scattering in the prior art.

Secondly, since the size and shape of the metal nanoparticles are configured so that their plasmonic resonance peaks can match the wavelength of the excitation laser, the gap size and size between adjacent noble metal nanoparticles can be achieved through different assembly methods and conditions. The configuration of the shape, like this, can bring great convenience to the study of electric field gradient Raman scattering.

Furthermore, the steps of preparing the material to be characterized and the steps of preparing the single-layer closely packed metal particle pattern can be reversed. Therefore, the detection method of the present invention is not only simple and fast, but also relatively flexible.

Description of drawings

FIG. 1 is a schematic flow chart of a detection method for selecting a rule-forbidden phonon mode according to an embodiment of the present invention;

FIG. 2 is a schematic flow chart of a detection method for selecting rule-forbidden phonon modes according to another embodiment of the present invention;

3 is a schematic flow chart of a method for detecting a phonon mode that is prohibited by a selection rule according to a third embodiment of the present invention;

Fig. 4 is the schematic working principle diagram of the detection method for selection rule forbidding phonon mode in Fig. 2;

Fig. 5 is the schematic working principle diagram of the detection method for selecting rule forbidding phonon mode in Fig. 3;

Fig. 6 is the SEM schematic structural diagram of the carbon nanotube prepared in the first specific embodiment and the schematic structural diagram of the gold nanoparticle close-packed pattern prepared on the carbon nanotube;

Fig. 7 is the schematic dark field spectrogram of the gold nanoparticle close-packed pattern in Fig. 5;

8 is a schematic in-situ Raman spectrogram of single-walled carbon nanotubes before and after a close-packed pattern of composite gold nanoparticles according to an embodiment of the present invention;

9 is a schematic diagram of D-mode Raman scattering and electric field gradient Raman scattering in carbon nanotubes according to an embodiment of the present invention.

Detailed ways

In a material, not all phonon modes can be detected by Raman spectroscopy. First, the Raman scattering process is closely related to the symmetry of the target material. Only the phonon (or phonon vibration) modes that satisfy the specific symmetry can inelastically scatter with the electrons in the excited state to appear Raman peaks. Second, in the process of Raman scattering, since the dispersion curve of photons is particularly steep, in the visible-near-infrared band, the optical transition of electrons is a vertical transition. For first-order Raman scattering (only one electron-phonon scattering occurs) Only phonons in the center of the Brillouin zone can be detected.

In the prior art, changes in Raman selection rules caused by electric field gradients have been found. However, since the manipulation of light and materials at the sub-nanometer scale has always been difficult, the research and application of electric field gradient Raman scattering has been limited. a lot of restrictions. In some experiments, angle-resolved microsphere lithography was used to process the sub-nanoscale metal nanogap, and the existence of the electric field gradient Raman scattering enhancement effect was confirmed. , the cost is high and the efficiency is low.

In order to solve the above technical problem, the present embodiment provides a detection method for the selection rule forbidding the phonon mode, so as to solve the limitation of the conventional Raman scattering selection rule in the prior art, which leads to the limitation of the electric field on the sub-nanometer scale. Gradient Raman scattering is a difficult problem to study. As shown in FIG. 1 , the detection method of this embodiment may include:

S100. Prepare the material to be characterized and a single-layer closely packed metal particle pattern, so that the metal particles are closely arranged with each other and form a gap with a preset size;

S200. Collect the electric field gradient Raman spectrum of the material to be characterized in the gaps of the metal particles, so as to detect the phonon mode prohibited by the conventional Raman selection rule in the material to be characterized according to the electric field gradient Raman spectrum.

Wherein, in step S100, as shown in FIG. 2 and FIG. 4, the operation of preparing the material to be characterized and a single-layer closely-packed metal particle pattern, so that the metal particles are closely arranged with each other and form a gap with a preset size range, can include:

S10. Prepare the material to be characterized on the substrate;

S20. Prepare a single-layer closely packed metal particle pattern on the material to be characterized, and make the metal particles closely arrange each other and form a gap with a predetermined size.

Alternatively, in another embodiment, as shown in FIG. 3 or FIG. 5 , in step S100 , a material to be characterized and a single-layer closely-packed metal particle pattern are prepared, so that the metal particles are closely arranged with each other and form a pattern with a preset size A range of clearance operations can include:

S1. Prepare a single-layer closely packed metal particle pattern on a substrate, and make the metal particles closely arrange each other and form a gap with a preset size;

S2. Prepare the material to be characterized on a monolayer closely packed metal particle pattern.

In the detection method of the above-mentioned embodiment, the material to be characterized can be prepared on the substrate first, and then a single-layer closely packed metal particle pattern can be prepared on the material to be characterized, so that the metal particles are closely arranged with each other and form a pattern with a preset size range. gap (monolayer closely packed metal particles can also be prepared on the substrate first, and then the material to be characterized is prepared on the metal particles), and then the electric field gradient Raman spectrum of the material to be characterized in the gap of the metal particles is collected. In this way, the detection method of this embodiment can utilize the sub-nanoscale gaps between the self-assembled metal particles to combine with the material to be characterized to construct a strong electric field gradient (that is, without using micro-nano processing technology, liquid surface self-assembly, Evaporation-induced self-assembly and other simple ways to achieve strong local electric field gradients), which can enhance electric field gradient Raman scattering to detect phonon modes that are forbidden by conventional Raman selection rules in the materials to be characterized. That is to say, in the material to be characterized without defects, the D-mode cannot be detected by conventional Raman spectroscopy, and after compounding with the metal particle patterns that are closely arranged with each other and form gaps with a predetermined scale range, except for the surface plasmon caused by In addition to the Raman enhancement of , a strong D mode can also be detected, which indicates that the electric field gradient Raman scattering breaks the selection rule of conventional Raman scattering and realizes the detection of the central phonon mode in the non-Brillouin zone. Therefore, the detection method of this embodiment solves the problem that the research on electric field gradient Raman scattering in the sub-nanometer scale is difficult due to the limitation of the selection rule of conventional Raman scattering in the prior art.

It should be noted that when the optical field is confined to the atomic scale (such as 0.1–5 nm), the strong electric field gradient will make the material polarizability nonlinear effect become significant, and the electric field gradient can be ignored in conventional Raman scattering. Raman scattering becomes so strong that the selection rule of traditional Raman scattering can be invalidated, and many molecular vibrational modes that are forbidden by traditional Raman selection rules can be activated. Therefore, electric field gradient Raman scattering can detect phonon modes forbidden by the selection rule, which is complementary to conventional Raman scattering and phonon infrared absorption, and can expand the application space of phonon spectral characterization.

Among them, as shown in Figure 2, the material to be characterized can be deposited on the substrate in advance, which is useful for accurately locating the material to be characterized and in situ, comparing the changes of the Raman spectrum of the material before and after enhancement, and accurately judging the contribution of the electric field gradient Raman scattering. Size plays an important role.

In addition, the order of preparing the material to be characterized and preparing the single-layer closely-packed metal particle pattern can be reversed. Therefore, the detection method of the above embodiment has low cost, simple operation and strong flexibility, etc., and can be widely used in material structure analysis, physical phase analysis, etc. Analysis, biological characterization and many other fields.

In the above-mentioned first to third embodiments, the material to be characterized can be a non-metallic material characterized by Raman spectroscopy, and can be coupled with the plasmonic structure of metal particles to achieve Raman enhancement, or can be coupled with metal particles The plasmons in the gap structure are coupled, and the gaps between adjacent metal particles are within the range of preset dimensions. The preset dimension may be less than 20 nm. Further, the preset dimension may be smaller than 10 nm. Preferably, the preset dimension can also be smaller than 5 nm. The range of the preset dimension may be 0.1-10 nm, or may be 0.2-0.8 nm, or may be less than about 5 nm, that is, the gap between adjacent metal particles may be less than about 5 nm. That is, the material to be characterized needs to be limited to the sub-nanometer scale (usually less than 5 nm), which can include but not limited to organic molecules, carbon nanotubes, graphene, monolayer molybdenum sulfide, etc.

The material to be characterized can be one-dimensional nanowires, nanorods or nanotubes, and the material to be characterized can also be two-dimensional graphene or molybdenum disulfide or nanoparticles. That is, the dimension of the material to be characterized is not limited, and it can be one-dimensional nanowires, nanorods, nanotubes, or two-dimensional graphene, molybdenum disulfide, or nanoparticles.

The preparation method of the material to be characterized can be bottom-up or top-down, and the preparation method may include, but is not limited to: spin coating, spraying, infiltration of the solution or dispersion containing the components of the characterizing material, and may also include electrochemical, chemical One or more of vapor deposition, thermal evaporation, electron beam evaporation, micromachining.

The size and shape of the metal particles are selected so that the plasmon resonance peak of the metal particles can match the wavelength of the excitation laser, that is, the size and shape of the metal particles are selected, and the nanostructures formed need to make the surface plasmon resonance peaks match the wavelength of the excitation laser. The excitation wavelength of the Raman spectrum is matched (usually the laser wavelength is required to be within the half-width of the plasmon resonance peak). Since the size and morphology of metal nanoparticles are configured to match their plasmonic resonance peaks with the wavelength of the excitation laser, the gap size between adjacent noble metal nanoparticles can be achieved through different assembly methods and conditions. and shape configuration to achieve electric field gradient Raman scattering excited at different wavelengths. Moreover, the size and shape of the nanogap can also be achieved by different assembly methods and conditions, which brings great convenience to the study of electric field gradient Raman scattering.

The metal particles may be metal particles with surface-enhanced Raman scattering effect, for example, the metal particles may be noble metal nanoparticles, that is, the metal nanoparticles may be nanostructures with surface plasmon resonance, and the composition thereof is not limited. The material of the metal particles may include noble metals and/or alloys and/or heterostructures, including but not limited to gold, silver and other metal elements and their alloys. The size of the metal particles is not limited, and can be selected to be nano-scale, micro-nano-scale or micro-scale, or nano-particles or nano-structures. The shape of the metal particles is also not limited, and can be selected as one or more of nanospheres, nanodiscs, nanocubes, nanopolyhedrons, nanorods, and the like. It can also be said that the shape, size and material of metal particles are not limited, that is, particles of different shapes, sizes, and materials, as long as the particles and structures of different shapes, sizes, and materials are constructed into sub-nanometer-scale gaps. That's it. Wherein, the size of the gaps between adjacent metal particles may be less than 5 nm, and may be ordered or disordered. The structure composed of metal particles is a metal nanostructure, which is a nanostructure with surface plasmon resonance. Wherein, the metal nanostructure can also be composed of other structures.

In any of the above embodiments, a single-layer closely packed metal particle pattern is prepared on the substrate or on the material to be characterized, wherein the close packing refers to making the metal nanoparticles closely arranged with each other to form sub-nanoscale gaps (usually Requires less than 5 nm), and methods for preparing monolayer closely packed metal particle patterns include, but are not limited to: liquid surface self-assembly, evaporation-induced self-assembly, and the like.

In addition, the steps of preparing the material to be characterized and the step of preparing the single-layer closely packed metal particle pattern can be reversed. Therefore, the detection method described in any of the above embodiments is not only simple and fast, but also relatively flexible.

In the first specific embodiment, which can be described in conjunction with FIG. 2 and FIG. 4 , the detection method for selecting the rule-forbidden phonon mode may include:

Step (1): prepare a horizontal array of ultra-long single-walled carbon nanotubes on a Si/SiOx substrate containing positioning marks by chemical vapor deposition, and collect the Raman spectrum of a single ultra-long single-walled carbon nanotube according to the positioning marks.

Step (2): prepare a dilute solution of polyhedral gold nanoparticles with a diameter of 30 nm, drop 20 μL of the dilute solution on the marked substrate where there are ultra-long single-walled carbon nanotubes, and bake under an incandescent lamp for 15 min to form a hexagonal dense Heap of gold nanoparticles pattern.

Step (3): Find the position of the ultra-long single-walled carbon nanotubes and the hexagonal close-packed gold nanoparticle pattern under the electron microscope, and collect the Raman of the single-walled carbon nanotubes with a 785nm laser under the microscope confocal Raman spectrometer. Spectrum.

Figure 6 shows the SEM images of the ultra-long single-walled carbon nanotubes before and after the composite pattern of the hexagonal close-packed gold nanoparticles, in which, Figure a is the alignment of the single ultra-long single-walled carbon nanotubes grown on the substrate. SEM photo, Figure b is the SEM photo of the same position after assembling with 30nm gold nanoparticles close-packed pattern. The dark-field spectrum of the hexagonal close-packed gold nanoparticle pattern is shown in Fig. 7, indicating that the plasmonic resonance peak of the pattern can be well matched with the 785 nm laser. The diameter of a single single-walled carbon nanotube is about 1.3 nm, which is highly collimated, and no bending is found within the range of 500 μm along the tube axis. FIG. 8 can be the in-situ Raman spectra of single-walled carbon nanotubes before and after the close-packed pattern of composite gold nanoparticles. The D mode in FIG. 8 belongs to the phonon mode of the Brillouin zone boundary. It can be explained in conjunction with Fig. 6-Fig. 9. In the carbon nanotubes without defects, the D mode cannot be detected by conventional Raman spectroscopy, but after compounding with the close-packed pattern of gold nanoparticles, in addition to the Raman caused by surface plasmons. In addition to the enhancement, a strong D mode can also be detected. In this way, the electric field gradient Raman scattering breaks the selection rule of conventional Raman scattering and realizes the detection of the central phonon mode in the non-Brillouin zone.

In a second specific embodiment, which can be described with reference to FIG. 2 and FIG. 4 , the detection method for selecting rule-forbidden phonon modes may include:

Step (1): prepare a horizontal array of ultra-long single-walled carbon nanotubes on a Si/SiOx substrate containing positioning marks by chemical vapor deposition, and collect the Raman spectrum of a single ultra-long single-walled carbon nanotube according to the positioning marks.

Step (2): prepare a dilute solution of gold nanorods with a diameter of about 25 nm, drop 50 μL of the dilute solution on the marked substrate where there are ultra-long single-walled carbon nanotubes, and bake under an incandescent lamp for 20 minutes to form self-organization Close-packed gold nanorod pattern.

Step (3): Find the position of the ultra-long single-walled carbon nanotubes between the close-packed gold nanorods under an electron microscope, and collect the Raman of the single-walled carbon nanotubes with a 785 nm laser under a confocal Raman microscope. Spectrum.

The plasmon resonance peaks of the aligned close-packed gold nanorod patterns can be well matched with the 785 nm laser, and the single-walled carbon nanotubes before and after the composite of ultra-long single-walled carbon nanotubes and self-organized close-packed gold nanorod patterns are measured. in situ Raman spectra. In defect-free carbon nanotubes, D-mode cannot be detected by conventional Raman spectroscopy, whereas after composite with align-packed gold nanorods, in addition to the Raman enhancement due to surface plasmons, a strong D-mode can be detected. In the D mode, the electric field gradient Raman scattering breaks the selection rule of conventional Raman scattering and realizes the detection of the central phonon mode in the non-Brillouin zone.

In a third specific embodiment, which can be described with reference to FIG. 2 and FIG. 4 , the detection method for selecting a rule-forbidden phonon mode may include:

Step (1): prepare a horizontal array of ultra-long single-walled carbon nanotubes on a Si/SiOx substrate containing positioning marks by chemical vapor deposition, and collect the Raman spectrum of a single ultra-long single-walled carbon nanotube according to the positioning marks.

Step (2): prepare a dilute solution of gold@palladium core-shell structure polyhedron with a diameter of 30 nm, drop 30 μL of the dilute solution on the marked substrate where the ultra-long single-walled carbon nanotubes are located, and bake under an incandescent lamp for 30 min, A self-organized close-packed gold@palladium core-shell pattern was formed.

Step (3): Find the positions of the ultra-long SWNTs and the self-organized close-packed gold@palladium core-shell structure pattern under the electron microscope, and collect the SWNTs with a 785 nm laser under the microscope confocal Raman spectrometer Raman spectrum of .

The plasmonic resonance peaks of the self-organized close-packed gold@palladium core-shell pattern can be well matched with the 785 nm laser. The in situ Raman spectra of single-walled carbon nanotubes before and after the composite of ultra-long single-walled carbon nanotubes with close-packed gold@palladium core-shell structure patterns were measured. In defect-free carbon nanotubes, the D mode cannot be detected by conventional Raman spectroscopy, while a strong D mode can be detected in addition to the Raman enhancement due to surface plasmons after compounding with the close-packed pattern of gold nanoparticles. In this way, the electric field gradient Raman scattering breaks the selection rule of conventional Raman scattering and realizes the detection of the central phonon mode in the non-Brillouin zone.

In a fourth specific embodiment, which can be described with reference to FIG. 2 and FIG. 4 , the detection method for selecting rule-forbidden phonon modes may include:

Step (1): prepare single-crystal graphene on a Si/SiOx substrate containing positioning marks by chemical vapor deposition, and collect the Raman spectrum of the single-crystal graphene according to the positioning marks.

Step (2): prepare a dilute solution of polyhedral gold nanoparticles with a diameter of 30 nm, drop 30 μL of the dilute solution on the marked substrate where there is single crystal graphene, and bake it under an incandescent lamp for 15 minutes to form hexagonal close-packed gold Nanoparticle pattern.

Step (3): Find the position of the single-crystal graphene and the hexagonal close-packed gold nanoparticle pattern under an electron microscope, and collect the Raman spectrum of the single-crystal graphene with a 785 nm laser under a micro confocal Raman spectrometer.

In defect-free single-crystal graphene, the D-mode cannot be detected by conventional Raman spectroscopy, while the combination with the close-packed pattern of gold nanoparticles can detect a strong D-mode in addition to the Raman enhancement due to surface plasmons. In this way, the electric field gradient Raman scattering can break the selection rule of conventional Raman scattering and realize the detection of the central phonon mode in the non-Brillouin zone.

In a fifth specific embodiment, which can be described with reference to FIG. 3 and FIG. 5 , the detection method for selecting a rule-forbidden phonon mode may include:

Step (1): Prepare a dilute solution of polyhedral gold nanoparticles with a diameter of 30 nm, drop 30 μL of the dilute solution on the marked Si/SiOx substrate, and bake under an incandescent lamp for 15 min to form a hexagonal close-packed gold nanoparticle pattern .

Step (2): preparing single crystal graphene by chemical vapor deposition. Single-crystal graphene was transferred onto a pattern of hexagonal close-packed gold nanoparticles with an orientation-marked substrate.

Step (3): Find the position of the single-crystal graphene and the hexagonal close-packed gold nanoparticle pattern under the electron microscope, and use a 785nm laser to collect the single-crystal graphene with and without hexagonal close-packed under a confocal Raman spectrometer. Raman spectra of stacked gold nanoparticle pattern locations. Thus, the in-situ Raman spectra of single-crystal graphene before and after the composite of single-crystal graphene and hexagonal close-packed gold nanoparticle patterns can be measured. In defect-free single-crystal graphene, the D-mode cannot be detected by conventional Raman spectroscopy, while the combination with the close-packed pattern of gold nanoparticles can detect a strong D-mode in addition to the Raman enhancement due to surface plasmons. The D mode, in this way, shows that the electric field gradient Raman scattering can break the selection rule of conventional Raman scattering, and realize the detection of the central phonon mode in the non-Brillouin zone.

By now, those skilled in the art will recognize that, although exemplary embodiments of the present invention have been illustrated and described in detail herein, it is still possible to directly follow the present disclosure without departing from the spirit and scope of the present invention. Numerous other variations or modifications can be identified or derived consistent with the principles of the present invention. Accordingly, the scope of the present invention should be understood and deemed to cover all such other variations or modifications.

Claims (10)

1. A detection method for selecting rule-banned phonon modes, comprising: Prepare the material to be characterized and a single-layer closely packed metal particle pattern, so that the metal particles are closely arranged with each other and form a gap with a preset size, and the preset size is less than 10 nm, wherein the material to be characterized is free of defects , the single-layer closely packed metal particle pattern is prepared by a self-assembly method; collecting the electric field gradient Raman spectrum of the material to be characterized in the metal particle gap; According to electric field gradient Raman spectroscopy, after the material to be characterized is combined with metal particle patterns that are closely arranged with each other and form gaps in a predetermined scale range, in addition to the Raman enhancement caused by surface plasmons, strong D mode, which realizes the detection of the central phonon mode in the non-Brillouin zone. 2 . The detection method according to claim 1 , wherein the material to be characterized and a monolayer closely packed metal particle pattern are prepared, so that the metal particles are closely arranged with each other and form a gap with a preset size range, comprising: 3 . preparing the material to be characterized on a substrate; The single-layer closely packed metal particle pattern is prepared on the material to be characterized, and the metal particles are closely arranged with each other and form gaps with predetermined dimensions. 3 . The detection method according to claim 1 , wherein the material to be characterized and a monolayer closely packed metal particle pattern are prepared, so that the metal particles are closely arranged with each other and form a gap with a preset size range, comprising: 3 . preparing the single-layer closely packed metal particle pattern on the substrate, and making the metal particles closely arranged with each other and forming a gap with a preset size; The material to be characterized is prepared on the monolayer closely packed metal particle pattern. 4. The detection method according to claim 1, wherein, The material to be characterized is selected as a non-metallic material that can be characterized by Raman spectroscopy, and can be coupled with the metal particle plasmonic structure to achieve Raman enhancement. 5. The detection method according to any one of claims 1-4, wherein, The preset dimension is less than 5 nm. 6. The detection method according to any one of claims 1-4, wherein, The size and shape of the metal particles are selected to match their plasmonic resonance peaks to the wavelength of the excitation laser. 7. The detection method according to any one of claims 1-4, wherein, The metal particles are metal particles having surface plasmon resonance, and the structure composed of the metal particles is a nanostructure having surface plasmon resonance. 8. The detection method according to any one of claims 1-4, wherein, The metal particulate material includes metal element and/or alloy and/or heterostructure. 9. The detection method of claim 1, wherein, The material to be characterized is one-dimensional nanowires or nanorods or nanotubes. 10. The detection method of claim 1, wherein, The materials to be characterized include organic molecular materials, carbon nanotube materials, graphene and/or monolayer molybdenum sulfide.

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