CN105628673B - The method of the Transition-metal dichalcogenide sample number of plies on test compound silicon substrate - Google Patents

The method of the Transition-metal dichalcogenide sample number of plies on test compound silicon substrate Download PDF

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CN105628673B
CN105628673B CN201510957716.5A CN201510957716A CN105628673B CN 105628673 B CN105628673 B CN 105628673B CN 201510957716 A CN201510957716 A CN 201510957716A CN 105628673 B CN105628673 B CN 105628673B
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metal dichalcogenide
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CN105628673A (en
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谭平恒
李晓莉
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Institute of Semiconductors of CAS
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/65—Raman scattering

Abstract

The invention discloses a kind of methods of the ultra-thin Transition-metal dichalcogenide sample number of plies on test compound silicon substrate, include the following steps：Test compound surface of silicon SiO2The thickness h of layerSiO2；Ultra-thin Transition-metal dichalcogenide sample is prepared on compound silicon substrate；Measure I2D(Si) and I0(Si) actual value of intensity rate；Calculate the theoretical value for swashing intensity rate；By the actual value of the intensity rate compared with the theoretical value of the intensity rate, it may be determined that survey the number of plies of ultra-thin Transition-metal dichalcogenide sample.Test method proposed by the present invention is simple, independent of the orientation of compound silicon substrate and the polarization state of incident laser, is characterized suitable for the number of plies of Transition-metal dichalcogenide sample within 10 layers.

Description

The method of the Transition-metal dichalcogenide sample number of plies on test compound silicon substrate
Technical field
The present invention relates to the test method and spectral technique field of material physical properties parameter, more particularly to Raman spectrum Technology tests the ultra-thin Transition-metal dichalcogenide sample being positioned on compound silicon substrate using substrate silicon Raman peak intensity The number of plies.
Background technology
Transition-metal dichalcogenide MX2 is that two-dimensional layer material is ground (including molybdenum disulfide, tungsten disulfide, two tungsten selenides) The important directions studied carefully.Successively stacking forms the elementary layer that these materials are made of three atomic layers.These two-dimensional materials Thickness it is directly proportional to the number of plies of stacking, therefore measure and be directly multiplied by unit layer thickness after the number of plies of these two-dimensional materials and can obtain To the thickness of two-dimensional material.Atom in elementary layer is combined by covalently bonded, and the interaction between elementary layer is then Very weak van der waals force interaction.Therefore, the atomic interaction in elementary layer is very strong, and atomic structure is very steady It is fixed, and the interaction of unit interlayer is very weak.There are many types for the way of stacking of unit interlayer.With the increase of the number of plies, multilayer MX2 materials show the electronic band structure and physical property different from monolayer material.For example, the band gap of multilayer MX2 is with the number of plies Increase significant changes can occur, the individual layer MX2 of general 2H structures is direct band-gap semicondictor, but from two layers of MX2 and more Layer is then indirect band-gap semiconductor.Band structure determines the dielectric constant of material, therefore the multilayer MX2 in visible-range Dielectric property and complex refractivity indexAlso change with the variation of the number of plies.Accordingly, it is determined that Transition-metal dichalcogenide MX2 The number of plies it is significant for studying the physical property of these materials and its application in terms of semiconductor devices.
Nearly ten years, people have invented the side of the MX2 numbers of plies such as various measure molybdenum disulfide, tungsten disulfide and two tungsten selenides Method.For example, directly the thickness of sample can be measured using atomic force microscope, but due to the thickness of its monolayer material The usually only magnitude of nanometer even angstrom, thus the sample number of plies derived by the test result of atomic force microscope easily by Cause test result there may be relatively large deviation to the influence of the factors such as substrate roughness and sample surfaces absorption, and test It is inefficient.It can be by individual layer molybdenum disulfide, tungsten disulfide, two tungsten selenides from multilayer using photoluminescence spectra (PL spectrums) It distinguishes.Using on the theoretical method of optics contrast can to few layer of molybdenum disulfide, tungsten disulfide and two tungsten selenide samples into The row number of plies characterizes, but the complex refractivity index due to these materials in visible-rangeChange with the change of the number of plies, lead The calculated results and empirical value of cause optics contrast are there are relatively large deviation, therefore optics contrast is not enough to characterize exactly and put It is placed in the number of plies of the multilayer MX2 samples on arbitrary SiO2 thickness.In addition, utilize multilayer molybdenum disulfide, tungsten disulfide and two selenizings The shearing mould of tungsten sample and breathing mould can judge the number of plies of few layer (being generally less than 10 layers) sample exactly, but sample itself The peak position information of Raman signatures pattern is easily influenced be subject to the factors such as defect in sample and sample interlayer way of stacking, and Ultralow wavenumber Raman spectra instrument is complicated, and test process is not easy and takes, therefore utilizes ultralow frequency Raman mould test MX2 The sample number of plies is not readily to a kind of method promoted.
Therefore, the ultra-thin transition metal such as a kind of effective test molybdenum disulfide, tungsten disulfide and two tungsten selenides how to be found The measuring technology of the chalcogenide MX2 sample numbers of plies so that test result can be reduced due to defect in sample and sample layer Between the influence of the factors to measurement such as way of stacking difference, and can quickly and accurately determine the number of plies of up to 10 layers of ultra-thin sample, It is applied for the physical property and device for studying these materials extremely important.
The content of the invention
It is an object of the invention to provide the transition such as molybdenum disulfide, tungsten disulfide and two tungsten selenides on a kind of compound silicon substrate The test method of the metal chalcogenide compound sample number of plies.This method proposed by the present invention can meet the following conditions：A) reduce due to The influence of the factors to measurement such as defect and sample interlayer way of stacking difference in sample；B) can quickly and accurately determine ultra-thin The number of plies that up to 10 layers of sample；C) independent of SiO2The orientation of/Si substrates and the polarization state of incident laser.
In order to achieve the above objectives, the present invention provides ultra-thin Transition-metal dichalcogenides on a kind of test compound silicon substrate The method of the sample number of plies, which is characterized in that include the following steps：
Step 1：Determine Transition-metal dichalcogenide sample under predetermined laser wavelength lambda ex using Raman optical spectrum method Effective complex refractivity index
Step 2：SiO is tested using elliptic polarization spectrometer2The compound surface of silicon SiO of/Si2The thickness h of layerSiO2；
Step 3：By micromechanics stripping means or transfer method in SiO2Ultra-thin transition gold is prepared on the compound silicon substrates of/Si Belong to chalcogenide sample；
Step 4：Using described in the microcobjective measurement of the laser and predetermined value aperture NA of predetermined laser wavelength lambda ex SiO2The compound silicon substrates of/Si are by the single order silicon Raman signal intensity of the ultra-thin Transition-metal dichalcogenide sample covering part I2D(Si) and not by the single order silicon Raman signal intensity I of ultra-thin Transition-metal dichalcogenide sample covering part0(Si) strong Spend ratio I2D(Si)/I0(Si) actual value；
Step 5：Using transfer matrix method, calculating optical maser wavelength is the predetermined laser wavelength lambda ex, numerical aperture of objective For the predetermined value aperture NA, SiO2Layer thickness is hSiO2And sample complex refractivity index isThe ultra-thin transition metal of Shi Suoshu Intensity rate I under the chalcogenide sample difference number of plies2D(Si)/I0(Si) theoretical value；
Step 6：The intensity rate I that will be surveyed2D(Si)/I0(Si) actual value and the intensity being calculated Ratio I2D(Si)/I0(Si) theoretical value is compared, it may be determined that surveys the number of plies of ultra-thin Transition-metal dichalcogenide sample.
The transition metal such as molybdenum disulfide, tungsten disulfide and two tungsten selenides on a kind of test compound silicon substrate provided by the invention The method of the chalcogenide sample number of plies, experimental test procedures are simple, and adaptation is wide, and accuracy is high, specifically has the following advantages：
1), using the single order Raman signal intensity of the substrate silicon covered by ultra-thin Transition-metal dichalcogenide with sample layer Several variations carries out number of plies characterization, it is only necessary to Test coverage and when not covering MX2 samples substrate silicon two Raman spectrums, survey Method for testing is simple to operation, and test result accuracy is high.
2), the intensity rate I of silicon single order Raman signal2D(Si)/I0(Si) Raman independent of MX2 samples and substrate is inclined Shake characteristic, substrate crystal orientation and incident laser polarization configurations, to different experiment test systems have replicability, it is operable Property is strong.
3), MX2 samples it is lightly doped or there are a small amount of defect situation under little, therefore the party is influenced on its complex refractivity index Method also can be suitably used for there are the ultra-thin sample of lightly doped or a small amount of defect the number of plies characterization.
4), the intensity rate I of silicon single order Raman signal2D(Si)/I0(Si) dullness is showed with the number of plies increase of MX2 samples The variation relation to successively decrease, suitable for the Transition-metal dichalcogenides such as molybdenum disulfide, tungsten disulfide and two tungsten selenides within 10 layers The number of plies characterization of sample.
Description of the drawings
Below in conjunction with the accompanying drawings and subordinate list, by doing technical scheme into one to the detailed description of specific example The explanation of step, wherein：
Fig. 1 is the method flow diagram of the test compound silicon substrate Transition-metal dichalcogenide sample number of plies in the present invention.
Fig. 2 is to test I using micro-Raman spectroscopy in the present invention2D(Si) and I0(Si) schematic diagram.
Fig. 3 is to be fitted I under Raman spectrogram and different optical maser wavelengths in the present invention2D(Si)/I0(Si) obtained by experiment value Effective complex refractivity index matched curve, tested wherein (a) is the lower microcobjective using NA=0.45 of 532 nanometer lasers excitation Be positioned over SiO2Thickness is 100 nanometers of SiO2The Raman spectrogram of one to ten layers of molybdenum disulfide on/Si substrates.It can be seen that silicon Raman peak intensity increase with the molybdenum disulfide number of plies and dull reduce；(b) it is the lower I of 532 nanometers of excitations2D(Si)/I0(Si) with two The variation relation of the molybdenum sulfide number of plies and corresponding effective complex refractivity indexWhen I2D(Si)/I0(Si) theoretical value； (c) I tested for the lower microcobjective using NA=0.45 of 488 nanometers of excitations2D(Si)/I0(Si) with the change of the molybdenum disulfide number of plies Change relation and corresponding effective complex refractivity indexWhen I2D(Si)/I0(Si) theoretical value.
Fig. 4 is for being positioned over SiO in the present invention2Thickness is 302 nanometers of SiO21,3,4,6,7 layers of two sulphur on/Si substrates Change molybdenum：(a) 532 nanometers of excitations are lower utilizesThe I of calculating2D(Si)/I0(Si) theoretical value, with experiment test As a result fit like a glove；(b) 488 nanometers of excitations are lower utilizesThe I of calculating2D(Si)/I0(Si) theoretical value, with Experimental results fit like a glove.
Specific embodiment
Understand to make the object, technical solutions and advantages of the present invention clearer, below in conjunction with specific embodiment, and reference Attached drawing, the present invention is described in further detail.
The present invention provides the transition metal such as molybdenum disulfide, tungsten disulfide and two tungsten selenides on a kind of test compound silicon substrate The method of the chalcogenide sample number of plies, as shown in Figure 1, it includes the following steps：
Step 1：Transition-metal dichalcogenide sample effectively multiple folding at a particular wavelength is determined using Raman optical spectrum method Penetrate rate
Effective complex refractivity index described in the stepIt is identified below：
Step 101, in known surface SiO2The SiO of layer thickness2On the compound silicon substrates of/Si by micromechanics stripping means or Transfer method prepares a set of ultra-thin Transition-metal dichalcogenide sample；
Step 102, the number of plies that each ultra-thin Transition-metal dichalcogenide sample is determined using Low-frequency Raman spectroscopy instrument；
Step 103, the microcobjective for being NA using the laser and numerical aperture of specific wavelength λ ex test SiO respectively2/Si Compound silicon substrate (is located at 520cm by the single order silicon Raman peaks of ultra-thin Transition-metal dichalcogenide sample covering part-1Near) Intensity I2D(Si) and not by the single order silicon Raman signal intensity I of ultra-thin Transition-metal dichalcogenide sample covering part0(Si) Ratio I2D(Si)/I0(Si), experimental result is obtained；
Step 104, assuming that sample complex refractivity index real part neffWith under single layer samples unanimous circumstances, by sample birefringence Rate imaginary part κeffAs fitting constant, consideration optical maser wavelength is λ ex, numerical aperture of objective NA, SiO2Layer thickness is hSiO2Deng ginseng In the case of number, the I that is calculated with transfer matrix method2D(Si)/I0(Si) theoretical value is carried out to above-mentioned corresponding experimental result Fitting obtains the sample complex refractivity index imaginary part of best fit；Finally obtain the effective complex refractivity index of sample
Step 2：SiO is tested using elliptic polarization spectrometer2The compound surface of silicon SiO of/Si2The thickness h of layerSiO2。
Step 3：By micromechanics stripping means or transfer method step 2 SiO2Being prepared on the compound silicon substrates of/Si should Ultra-thin Transition-metal dichalcogenide sample.
Step 4：Using with the laser and numerical aperture of step 1 phase co-wavelength the ultra-thin mistake is measured for the microcobjective of NA Cross the I corresponding to metal chalcogenide compound sample2D(Si)/I0(Si)。
Step 5：Using transfer matrix method, calculating optical maser wavelength is λ ex, numerical aperture of objective NA, SiO2Layer thickness For hSiO2And sample complex refractivity index isWhen the ultra-thin sample difference number of plies under I2D(Si)/I0(Si) theoretical value.
Step 6：The I that step 4 is surveyed2D(Si)/I0(Si) I that experiment value is calculated with step 52D(Si)/I0(Si) manage It is compared by value, you can determine to survey the number of plies of ultra-thin sample.
In said program, if the effective complex refractivity index of Transition-metal dichalcogenide sample at a particular wavelength Through being determined or it is known that then step 1 is negligible.
In said program, the optical maser wavelength selected in step 1 and step 4 should be suitably larger than the direct band gap of material, In order to avoid measurement error larger caused by the factors such as exciton resonance.
The spectral resolution of Raman spectrometer used is better than when Raman spectrum is tested in said program, in step 1 and step 4 0.5cm-1。
Laser power used will be less than 0.2mW when Raman spectrum is tested in said program, in step 1 and step 4, to keep away Exempt from laser power has heating effect very much to sample by force.
In said program, the silicon single order Raman signal intensity I described in step 1 and step 42D(Si) and I0(Si) should use Areal intensity, to reduce experiment test error.
In said program, I is tested in step 1 and step 40(Si) when, should not covered close to institute's sample by sample nearby Region, obtain the maximum intensity I of silicon single order Raman signal by adjusting the focus knob of microcobjective0(Si), Ran Houzhi It connects and compound silicon substrate is moved into sample footprint domain to measure silicon single order Raman signal I2D(Si).It not carry out in the process It focuses on again, in order to avoid the measurement error that focus condition different band is come twice.
As shown in Fig. 2, the present invention tests SiO respectively by using a certain specific wavelength such as 532 nanometers of laser2/Si Substrate is by the single order silicon Raman signal intensity I of N layers of ultra-thin Transition-metal dichalcogenide sample NL-MX2 covering parts2D(Si) and Not by the single order silicon Raman signal intensity I of N layers of ultra-thin Transition-metal dichalcogenide sample NL-MX2 covering parts0(Si) Ratio I2D(Si)/I0(Si) number of plies of ultra-thin Transition-metal dichalcogenide sample is determined.
Fig. 3 gives and is positioned over SiO under the excitation of 532 nanometer lasers2Thickness is 100 nanometers of SiO2One to ten on/Si substrates The Raman spectrogram of layer molybdenum disulfide.The number of plies of molybdenum disulfide is accurately determined by the shearing mould of its ultralow frequency and the frequency of breathing mould 's.The Raman peak intensity of silicon increases and dull reduction with the molybdenum disulfide number of plies.When laser pass through molybdenum disulfide sample when, can by Multiple reflections and refraction in 4 layers of dielectric structure of two air/molybdenum sulfide/silica/silicon composition, and occur in silicon dielectric layer Interference, the amplitude distribution that laser changes after silicon dielectric layer internal interference with depth can be solved by transmission matrix.It is meanwhile different Depth silicon substrate by laser excitation Raman signal can multiple reflections and refraction in 4 layers of dielectric structure, finally reach air In after interfere, the silicon Raman signal intensity after interference can also be solved by transmission matrix.
When incident laser is focused on through microcobjective, the internal depth for reaching medium Si is propagated by multilayer dielectricity by air layer For diPosition when, in the correspondence depth z of medium SiiRaman scattering signal is excited, then Raman light is relevant most through multiple solutions reflection Travel to air layer eventually, collected by microcobjective, wherein since Raman scattering firing time is shorter (picosecond magnitude), exciting light and It can also be coupled between Raman light.Only consider normal incidence, integrated by the laser depth of shine to medium Si, It can obtain the reduced mechanical model of Raman modes intensity：
Wherein FLAnd FRRespectively incident laser enhancer and Raman diffused light enhancer.
In order to improve accuracy in computation, it is necessary to which influence of the numerical aperture of microcobjective to Raman luminous intensity is considered It is interior.At this point, incident laser and outgoing Raman diffused light are oblique incidence situation, to consider light to the solid angle of microcobjective Integration, it is necessary to their electromagnetic field component be resolved into s- polarizations and p- polarized components discuss respectively, wherein s- polarized components For transverse electric field componentPerpendicular to the c-axis of ultra-thin MX2 samples, p- polarized components are transverse magnetic component in its directionWith electric field point Conversion relation between amount meetsWhereinFor complex refractivity index, direction meetsWhereinIt is passed for light The wave vector broadcast.In orthogonal coordinate system, p- polarized components are divided into p again⊥, p//Component.Due to the intensity point of incident laser beam Cloth is Gaussian lineshape, is translated into collimated light beam using optical beam expander in an experiment, while also simplifies correlation computations.Separately Outside, it is contemplated that MX2 layers and Si layers have different lattice symmetries, so the Si molds of Si layers of outgoing have different polarizabilities, It needs to add in the coupling to the Raman tensor R and incident laser and outgoing Raman diffused light of phonon when calculating Raman modes intensity The discussion of situation.Therefore the calculation formula of following Raman modes intensity is obtained：
The electric field component of incident light is decomposed into s- polarizations and p- polarized components in calculation formula, respectively with s, p⊥, p//Table Show, the electric field component of Raman diffused light is also decomposed into s- polarizations and p- polarized components, respectively with s ', p '⊥, p '//It represents.Formula In add incident laser and be emitted Raman diffused light to the integration of the solid angle of microcobjective (whereinWith The respectively angle of latitude and longitude angle of incident laser and outgoing Raman diffused light, wherein θmaxWith θ 'maxEqual to arcsin (NA)), The coupling of the Raman tensor R and incident laser and outgoing Raman diffused light of phonon are also contemplated simultaneously, whereinWithRespectively The transmitting position z of Raman modes in corresponding mediumiThe Raman diffused light at place and the electric field component basic vector of incident laser.Formula (2) Middle FLAnd FRIt can be solved by transfer matrix method.
Formula (1) and formula (2) have been used for the intensity for calculating silicon substrate Raman mould under multi-layer graphene, but formula (1) and formula (2) is not immediately used for ultra-thin MX2 samples, occurs the reason is that the electronic band structure of MX2 materials increases with the number of plies Variation, dielectric property and complex refractivity index can all change with the change of the number of plies, therefore MX2 materials are not united from individual layer to multilayer One complex refractivity indexTherefore we need to propose and solve effective complex refractivity index suitable for individual layer to multilayer MX2 materialsIf we are without considering light in the multiple reflections of multilayer dielectricity interface and the coherent effect of media interior, I2D(Si)/I0 (Si) ratio is mainly determined by transmission matrix B.B matrix descriptions are the propagation of light in media as well, and the attenuation of intensity is main Depending on complex refractivity indexImaginary part κ, it is little with real part n relations.Therefore, we take the real part of the complex refractivity index of individual layer MX2 to make For effective complex refractivity indexReal part, be denoted as neff, willImaginary part be set to a parameter, by by I2D(Si)/I0(Si) Calculated value and Fig. 3 in I2D(Si)/I0(Si) test value is compared, and fitting obtainsImaginary part, be denoted as κeff.It is worth Although it is noted that incident laser and outgoing Raman diffused light there are difference on the frequency, since two ripples can not be fitted simultaneously Strong pointIgnore their difference at this time, it is believed that at incident light and scattering light corresponding wavelengthIt is equal.
Such as in Fig. 4 (a), the real part 4.85 that we set 532 nanometers individual layer molybdenum disulfide complex refractivity indexes is used as two sulphur Change effective complex refractivity index of molybdenumReal part neff, by κeffFitting experimental result is gone as fitting parameter, we obtain κeffFor 1.20.Equally, as shown in Fig. 4 (b), we are by testing under 488 nanometers silicon substrate below 1 to 10 layers of molybdenum disulfide Raman peak intensity, the effective refractive index that can obtain 488 nanometers of lower molybdenum disulfide are
After we determine effective complex refractivity index of 488 nanometers and 532 nanometers lower molybdenum disulfide, it is possible to this two Effective complex refractivity index of molybdenum sulfide calculates 488 nanometers and 532 nanometers of lower SiO2Layer is the SiO of any thickness2/ Si substrates are in office The intensity ratio I of Si substrate Raman moulds under the ultra-thin molybdenum disulfide sample of any layers number2D(Si)/I0(Si), and by being tied with experiment Fruit relatively determines the number of plies of ultra-thin molybdenum disulfide sample.Such as we are in SiO2SiO when layer thickness is 302 nanometers2/ Si is served as a contrast A series of ultra-thin molybdenum disulfide samples are prepared on bottom.We are effective using ultra-thin molybdenum disulfide sample definite in figure 3 Complex refractivity index calculates I2D(Si)/I0(Si), and by with Comparison of experiment results, identified several ultra-thin molybdenum disulfide samples The number of plies be respectively 1,3,4,6 and 7 layer.We accurately test the number of plies of these samples using ultralow wave number Raman spectroscopy, With passing through I2D(Si)/I0(Si) number of plies of test is coincide very good.
Table one
We list the molybdenum disulfide determined by silicon Raman spectrum, tungsten disulfide and two tungsten selenides 488 in table one Nanometer, effective complex refractivity index of 532 nanometers and 593 nanometers.This effective complex refractivity index can be used for receiving using 488 nanometers, 532 Rice and the test of 593 nanometer lasers are placed in any SiO2The SiO of thickness2Ultra-thin molybdenum disulfide, tungsten disulfide and two selenium on/Si substrates Change the number of plies of tungsten sample.
In test, the grating resolution of spectrometer is used to be preferable over 0.5 wave number, is irradiated to the laser of sample surfaces Power is preferably lower than 0.2mW, to avoid heating effect of the laser to sample；Test I0It (Si), should be attached close to institute's sample when The region not covered by sample closely by adjusting the focus knob of microcobjective, obtains the maximum intensity of silicon single order Raman signal, Then compound silicon substrate is directly moved to neighbouring sample footprint domain, measure silicon single order Raman signal I again2D(Si), exist It not focused on again during this, in order to avoid the measurement error that focus condition different band is come twice；I2D(Si) and I0(Si) should Using areal intensity, to reduce experiment test error.
If the complex refractivity index of Transition-metal dichalcogenide sample or pass through measure under our certain known optical maser wavelength Specific SiO2The SiO of thickness2The I of/Si substrates2D(Si)/I0(Si) it is fitted to obtain corresponding complex refractivity index, we can be non- Often I is measured conveniently by under this optical maser wavelength2D(Si)/I0(Si) come determine have any SiO2The SiO of thickness2/ Si substrates The number of plies of upper Transition-metal dichalcogenide sample.
Above method can be generalized to any ultra-thin two-dimension crystalline material that complex refractivity index is closely related with the number of plies.
By particular embodiments described above, the purpose of the present invention, technical solution and advantageous effect have been carried out into one Step is described in detail, it should be understood that the above is only a specific embodiment of the present invention, is not limited to this hair Bright, within the spirit and principles of the invention, any modification, equivalent substitution, improvement and etc. done should be included in the present invention Protection domain within.

Claims (6)

1. a kind of method of the ultra-thin Transition-metal dichalcogenide sample number of plies on test compound silicon substrate, which is characterized in that bag Include following steps：
Step 1：Determine that Transition-metal dichalcogenide sample is effective under predetermined laser wavelength lambda ex using Raman optical spectrum method Complex refractivity index
Step 2：SiO is tested using elliptic polarization spectrometer2The compound surface of silicon SiO of/Si2The thickness h of layerSiO2；
Step 3：By micromechanics stripping means or transfer method in SiO2Ultra-thin Transition Metal Sulfur is prepared on the compound silicon substrates of/Si Compounds of group sample；
Step 4：The SiO is measured using the laser of predetermined laser wavelength lambda ex and the microcobjective of predetermined value aperture NA2/ Si is multiple Silicon substrate is closed by the single order silicon Raman signal intensity I of the ultra-thin Transition-metal dichalcogenide sample covering part2D(Si) and Not by the single order silicon Raman signal intensity I of ultra-thin Transition-metal dichalcogenide sample covering part0(Si) intensity rate I2D (Si)/I0(Si) actual value；
Step 5：Using transfer matrix method, calculating optical maser wavelength is the predetermined laser wavelength lambda ex, numerical aperture of objective is institute State predetermined value aperture NA, SiO2Layer thickness is hSiO2And the effective complex refractivity index of sample isThe ultra-thin transition metal of Shi Suoshu Intensity rate I under the chalcogenide sample difference number of plies2D(Si)/I0(Si) theoretical value；
Step 6：The intensity rate I that will be surveyed2D(Si)/I0(Si) actual value and the intensity rate being calculated I2D(Si)/I0(Si) theoretical value is compared, it may be determined that surveys the number of plies of ultra-thin Transition-metal dichalcogenide sample；
Wherein, step 1 includes：
Step 101, in known surface SiO2The SiO of layer thickness2Pass through micromechanics stripping means or transfer on the compound silicon substrates of/Si Method prepares different layers of ultra-thin Transition-metal dichalcogenide samples；
Step 102, the number of plies that each ultra-thin Transition-metal dichalcogenide sample is determined using Low-frequency Raman spectroscopy instrument；
Step 103, the microcobjective for being NA using the laser and numerical aperture of predetermined laser wavelength lambda ex test SiO respectively2/ Si is multiple Silicon substrate is closed by the single order silicon Raman signal intensity I of ultra-thin Transition-metal dichalcogenide sample covering part2D(Si) and not by The single order silicon Raman signal intensity I of ultra-thin Transition-metal dichalcogenide sample covering part0(Si) intensity rate I2D(Si)/ I0(Si) actual value；
Step 104, assuming that the Complete effective refractive index real part n of each ultra-thin Transition-metal dichalcogenide sampleeffWith individual layer Under ultra-thin Transition-metal dichalcogenide sample unanimous circumstances, by answering for each ultra-thin Transition-metal dichalcogenide sample Effective refractive index imaginary part κeffAs fitting constant, consideration optical maser wavelength is λ ex, numerical aperture of objective NA, SiO2Layer thickness is hSiO2In the case of, the intensity rate I that is calculated with transfer matrix method2D(Si)/I0(Si) theoretical value with it is described strong Spend ratio I2D(Si)/I0(Si) actual value is fitted, and obtains the sample complex refractivity index imaginary part of best fit；Finally obtain sample The effective complex refractivity index of product
2. according to the method described in claim 1, it is characterized in that, the optical maser wavelength selected in step 1 and step 4 must be big In the direct band gap of specimen material.
3. according to the method described in claim 1, it is characterized in that, the spectrum of Raman spectrometer used divides in step 1 and step 4 Resolution is more than 0.5cm-1。
4. according to the method described in claim 1, it is characterized in that, laser power used is less than 0.2mW in step 1 and step 4.
5. the according to the method described in claim 1, it is characterized in that, I2D(Si) and I0(Si) areal intensity is used.
6. according to the method described in claim 1, it is characterized in that, the test is not by ultra-thin Transition-metal dichalcogenide sample The single order silicon Raman signal intensity I of product covering part0It (Si), will be not by ultra-thin Transition-metal dichalcogenide sample covering part when The measured zone that is placed in obtains single order silicon Raman signal intensity I by adjusting the focus knob of microcobjective0(Si), then will The SiO2Measured zone is moved to survey by ultra-thin Transition-metal dichalcogenide sample covering part on the compound silicon substrates of/Si Measure single order silicon Raman signal intensity I2D(Si)；In the process without focusing on again.
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