Micro-spectrum measurement system for two-dimensional material under variable-temperature condition

Abstract

The invention discloses a two-dimensional material micro-spectrum measurement system under a variable temperature condition, which relates to the technical field of two-dimensional material spectrum detection, and comprises an excitation light source module, a light path transmission module, a variable temperature sample module, a spectrum acquisition module and a data processing module, the excitation light source module comprises a wide-spectrum halogen tungsten lamp and 532nm laser; the light path transmission module comprises an optical fiber, an objective lens, a pinhole, a collimating lens, a reflector and a focusing lens; the variable-temperature sample module comprises a cold and hot table inverted on the microscope objective table; the spectrum acquisition module is an optical fiber spectrometer, and a reflection mode is adopted during absorption spectrum measurement; the data processing module is used for carrying out Lorentz fitting on the acquired spectral data and calculating a lattice thermal expansion coefficient through the change of an absorption spectrum peak position; according to the invention, two measurement functions of absorption spectrum and fluorescence spectrum are integrated, measurement of different spectrum types can be realized through light source switching, the system does not need to be disassembled or reconstructed, and the measurement efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of two-dimensional material spectral detection technology, and particularly to a two-dimensional material microscopic spectral measurement system under variable temperature conditions. BACKGROUND

[0002] Since the invention of the transistor, integrated circuit technology has developed rapidly following Moore's Law, but as device feature sizes continue to shrink, short-channel effects have caused Moore's Law to approach the physical limit. As a new type of two-dimensional material, transition metal dichalcogenides (TMDs) represented by MoS2 have a layered structure and unique electronic and optical properties. Single-layer MoS2 is a direct bandgap semiconductor that exhibits strong fluorescence characteristics, and the broken center inversion symmetry and strong spin-orbit coupling effect provide an ideal carrier for valleytronics research.

[0003] Temperature changes can regulate the bandgap structure of two-dimensional materials through lattice thermal expansion, thereby affecting their optical properties. Therefore, spectral measurement under variable temperature conditions is a key means of studying the basic physical properties of materials. Existing measurement systems have the problems of single function, insufficient variable temperature control precision, low spectral signal-to-noise ratio, etc., and are difficult to simultaneously realize in-situ measurement of absorption and fluorescence spectra, and cannot accurately obtain temperature-dependent band parameters and lattice thermal expansion coefficients. Therefore, it is urgent to develop a two-dimensional material microscopic spectral measurement system with high integration, high measurement accuracy, and adaptation to variable temperature environments. SUMMARY

[0004] To solve the above problems, the present application provides a two-dimensional material microscopic spectral measurement system under variable temperature conditions.

[0005] The two-dimensional material microscopic spectral measurement system under variable temperature conditions of the present application includes an excitation light source module, an optical path transmission module, a variable temperature sample module, a spectral acquisition module, and a data processing module, which work cooperatively to realize accurate measurement of two-dimensional material absorption and fluorescence spectra under variable temperature conditions.

[0006] Excitation light source module:

[0007] A wide-spectrum, low-noise halogen tungsten lamp is configured as the excitation light source for absorption spectrum measurement, which can provide stable visible light band illumination.

[0008] A 532nm laser is configured as the excitation light source for fluorescence spectrum measurement, which meets the excitation requirements of single-layer MoS2 exciton luminescence.

[0009] The two light sources are switched by fiber coupling to adapt to the needs of different spectral measurement scenarios.

[0010] Optical path transmission module:

[0011] The optical path transmission path is: excitation light source -> optical fiber -> objective lens 1 -> pinhole -> collimating lens -> mirror -> inverted microscope -> objective lens 2 -> sample -> focusing lens -> fiber spectrometer.

[0012] The pinhole is used for filtering stray light and improving the purity of the light signal; the collimating lens converts divergent light into parallel light, ensuring stable transmission of the light signal; and the objective lens 2 realizes accurate focusing of the light signal on the sample surface, thereby guaranteeing the spatial resolution of the measurement.

[0013] The variable-temperature sample module comprises a cold-hot stage.

[0014] The core component is a cold-hot stage, which is installed on the inverted microscope stage, and the sample is fixed in the cold-hot stage to realize in-situ variable-temperature measurement.

[0015] The temperature regulation range of the cold-hot stage covers 25-185 DEG C, the temperature control precision is high, and the temperature control precision is high, which meets the spectral measurement requirements under different temperature gradients.

[0016] The cold-hot stage is filled with argon as a protective atmosphere to avoid oxidation of the sample during the variable-temperature process and to ensure the stability of the sample.

[0017] The spectral acquisition module comprises a fiber spectrometer.

[0018] The fiber spectrometer is used as the signal acquisition core and has high resolution and high detection sensitivity, so that the weak spectral signal can be effectively captured.

[0019] The absorption spectrum measurement adopts a reflection mode: first, the reflectivity spectrum R of a blank substrate (such as a SiO2 / Si substrate) is collected, and then the reflectivity spectrum Rsample of the sample is collected, and the absorption spectrum is obtained by difference calculation.

[0020] During the fluorescence spectrum measurement, a long-wave pass filter is configured to filter the laser stray light, so that only the fluorescence signal generated by the sample enters the spectrometer, thereby improving the signal-to-noise ratio of the fluorescence spectrum.

[0021] The data processing module comprises a computer.

[0022] The absorption spectrum data is subjected to Lorentz fitting, the peak position information of the A exciton peak and the B exciton peak is extracted, and the lattice thermal expansion coefficient is calculated based on the linear redshift relationship of the peak position with the temperature.

[0023] The fluorescence spectrum data is analyzed, the relationship between the A exciton peak position and the temperature is fitted by using the Varshni formula, and the band gap parameters Eg(0), the temperature coefficient alpha and the Debye temperature related parameter beta of the material are obtained.

[0024] The real-time processing and visual display of the spectral data are supported, and the influence of the temperature on the spectral characteristics can be observed intuitively.

[0025] The present application has the following beneficial effects compared with the prior art:

[0026] 1. The present application integrates absorption spectroscopy and fluorescence spectroscopy, and can realize different spectral measurements by switching the light source without disassembly or reconstruction of the system, thereby improving the measurement efficiency.

[0027] 2. The variable temperature sample module uses an argon-protected cooling and heating stage, which has high temperature control precision and wide range, and can realize in-situ variable temperature measurement of the sample, avoid sample oxidation and damage, and ensure the reliability of the measurement results.

[0028] 3. By optimizing the optical path design and spectral acquisition parameters (such as integration time, average number, filter configuration), the signal-to-noise ratio of the spectral signal is significantly improved, and the weak spectral characteristics of two-dimensional materials can be effectively captured.

[0029] 4. The data processing module integrates multiple fitting algorithms, which can directly obtain key physical quantities such as lattice thermal expansion coefficient and band gap parameter, and provides strong support for the low-dimensional physical property research and optoelectronic device development of two-dimensional materials. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The figure is a schematic diagram of the optical path of the two-dimensional material microscopic spectroscopy measurement system under variable temperature conditions:

[0031] Among them: M1, M2, M3: mirror M1, mirror M2, mirror M3;

[0032] Pinhole: pinhole (10 μm);

[0033] F1=25mm: collimating lens;

[0034] Lens1: objective lens 1;

[0035] Light: light source;

[0036] Aperture: diaphragm;

[0037] ReflectanceMode: reflection mode;

[0038] Lens2: objective lens 2;

[0039] Stage: stage;

[0040] Spectrometer: spectrometer;

[0041] TransmittanceMode: transmission mode;

[0042] Lens3: lens 3;

[0043] Figure 2 The figure is the absorption spectrum of single-layer MoS2 (including an optical image insert).

[0044] Figure 3 Figure 2 is a graph of the change in the absorption spectrum of monolayer MoS2 in the temperature range of 25-185℃;

[0045] Figure 4 Figure 3 is a graph of the functional relationship of the absorption characteristic peak of monolayer MoS2 as a function of temperature (including two subgraphs a and b);

[0046] Subgraph a: Figure 4 is a graph of the peak position of the B exciton peak as a function of temperature; Figure 4

[0047] Subgraph b: Figure 5 is a graph of the peak position of the A exciton peak as a function of temperature; Figure 4

[0048] Figure 5 Figure 6 is a graph of the change in the PL (fluorescence) spectrum of monolayer MoS2 in the temperature range of 25-185℃;

[0049] Figure 6 Figure 7 is a graph of the change in the peak position of the A exciton peak as a function of temperature. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0051] The two-dimensional material microscopic spectrum measurement system under variable temperature conditions of the present application will be described in detail below in conjunction with specific experimental devices, operation steps and data verification. All experiments take high-quality monolayer MoS2 grown by CVD as the research object. The substrate is selected to be 300nm SiO2 / Si (the thickness of the SiO2 layer is 300nm, the Si substrate is P-type doped, and the resistivity is 1-10Ω·cm). The experimental environment temperature is 25℃, and the relative humidity is 45%-55%, so as to avoid the interference of environmental factors on the spectrum measurement.

[0052] Embodiment 1: Measurement of variable temperature absorption spectrum of monolayer MoS2

[0053] 1.1 Preparation before experiment

[0054] ​​System calibration: turn on the halogen tungsten lamp (model: Ocean Optics HL-2000, wavelength range 360-2000 nm, output power 10 W) and preheat for 30 min until the light source output is stable; connect the fiber spectrometer (model: Ocean Optics HR4000, spectral resolution 0.02 nm, detection range 200-1100 nm) to the computer, open the spectrum acquisition software (OceanView2.0), set the integration time to 50 ms, the average number to 100 times, and the dark current correction function to on, and perform baseline calibration on the spectrometer - block the light path, collect the dark background spectrum and save it for subsequent background subtraction of spectral data.

[0055] Cold and hot stage debugging: install the cold and hot stage (model: Linkam THMS600, temperature control range -196°C-600°C, temperature accuracy ±0.1°C) on the inverted microscope (model: Olympus IX73) stage, connect the temperature controller and argon cylinder; introduce argon gas into the cold and hot stage (flow rate 200 sccm) for 10 min to expel the air in the cavity, ensuring that the oxygen content in the cavity is ≤0.1%, preventing the sample from oxidizing at high temperature; set the cold and hot stage temperature program: initial temperature 25°C, incubate for 5 min to balance the sample temperature with the cavity temperature, then heat at a rate of 30°C / min to 185°C, incubate for 3 min every 10°C to ensure stable sample temperature before spectral acquisition.

[0056] 1.2 Light path adjustment and spectrum acquisition

[0057] Blank substrate reflectivity Rcollection: The blank SiO2 / Si substrate (consistent with the sample substrate specifications) was fixed on the cold and hot stage sample stage. The detection area (about 50 pm in diameter) on the surface of the substrate was observed through the eyepiece of the inverted microscope, and the position of the stage was adjusted so that the detection area was located at the center of the field of view of the objective lens 2 (model: Olympus LCPLN50XIR, magnification 50x, numerical aperture 0.55, working distance 9.8 mm). The halogen lamp was turned on, and the optical signal was coupled to the objective lens 1 (model: Olympus MPLFLN10X, magnification 10x, numerical aperture 0.3) through the optical fiber (model: Ocean Optics QP400-2-VIS-NIR, core diameter 400 pm), focused on the 10 pm pinhole (model: Thorlabs P10S, accuracy ±0.5 pm), and filtered stray light. Then it was converted into parallel light by a collimating lens (model: Thorlabs AC254-025-A, focal length 25 mm, diameter 25.4 mm), reflected by two mirrors (model: Thorlabs BB1-E02, reflectivity ≥99.5%) into the inverted microscope, and focused on the surface of the blank substrate by the objective lens 2. After the reflected light was collected by the objective lens 2, it was coupled to the optical fiber spectrometer through the focusing lens (model: Thorlabs AC254-050-A, focal length 50 mm), and the reflectivity spectrum was collected, denoted as R. Each temperature point was collected 3 times, and the average value was taken as the blank substrate reflectivity data at that temperature.

[0058] Sample reflectivity Rsamplecollection: The blank substrate was removed, and the pretreated single-layer MoS2 sample was fixed on the cold and hot stage sample stage. The optical path parameters (objective lens position, light source power, spectrometer parameters) were kept unchanged, and the MoS2 region was positioned by microscope observation (optical image as shown in Figure 2 The reflectivity spectrum of the MoS2 region was collected at each temperature point (25°C, 35°C, 45°C…185°C) set on the cold and hot stage, denoted as Rsample. Similarly, each temperature point was collected 3 times, and the average value was taken.

[0059] 1.3 Data processing and result analysis

[0060] Difference reflectivity calculation: Using the data processing module (spectral analysis program based on MATLAB R2023a), the wavelength-by-wavelength difference between R and Rsample at each temperature point was calculated to obtain AR = R - Rsample. Then the difference reflectivity was calculated according to the formula R(λ) = AR / R, which was the absorption spectrum of the single-layer MoS2.

[0061] Peak fitting and parameter extraction: Lorentzian fitting was performed on the A exciton peak (620-630 nm band) and B exciton peak (670-680 nm band) in the absorption spectrum, and the fitting function is: wherein wherein, is the spectral intensity, A is the peak height, λ0 is the peak position, Γ is the full width at half maximum (FWHM), is the background intensity. After fitting, the peak position data of A and B exciton peaks at each temperature are obtained, and the results are shown in Figure 3 .

[0062] Lattice thermal expansion coefficient verification: Since the band gap of the material has a linear relationship with the lattice constant, the redshift rate of the exciton peak position is directly related to the lattice thermal expansion coefficient (TEC). According to the fitting results, in the range of 25-185℃, the redshift rate of the A exciton peak is -3.47×10 -4 eV / ℃, and the redshift rate of the B exciton peak is -3.76×10 -4 eV / ℃; combined with the elastic modulus (about 180 GPa) and the thermal expansion coefficient theoretical model of MoS2, the in-plane thermal expansion coefficient of single-layer MoS2 is calculated to be (2.1±0.2)×10 -5 K -1 , which is consistent with the reported TEC value (1.8-2.3×10 -5 K -1 ) of single-layer MoS2, verifying the accuracy of the measurement results of the system.

[0063] Example 2: Measurement of variable-temperature fluorescence spectrum of single-layer MoS2

[0064] 2.1 Preparation before experiment

[0065] Switching of light source and filter: turn off the halogen tungsten lamp, remove the collimating lens and pinhole in the light path (parallel light is not required for fluorescence measurement), and switch the excitation light source to a 532 nm laser (model: Coherent Compass 315M-100, output power 100 mW, line width ≤1 nm); add a polarizer (model: Thorlabs LPVIS050-MP, extinction ratio 1000:1) in the laser incident light path, adjust the polarization direction to p-polarization, and ensure that the polarization state of the excitation light is consistent; install a long-wave pass filter (model: Thorlabs FEL0600, cutoff wavelength 600 nm, transmittance ≥90% @600-1100 nm) in the fluorescence collection light path to filter out 532 nm laser stray light and avoid interference with the fluorescence signal detection.

[0066] System sensitivity calibration: the fluorescence standard sample (rhodamine 6G ethanol solution, concentration 1×10 -5The standard sample was placed on the cooling and heating stage, and the laser was turned on (power was adjusted to 5 mW to avoid photobleaching). The fluorescence spectrum of the standard sample was collected by the spectrometer, and the peak position and intensity were recorded. The detection sensitivity and wavelength accuracy of the spectrometer were confirmed by comparing the standard spectrum. The measured peak position was 550.2 nm, which deviated from the standard peak position by less than 0.2 nm, and the intensity deviation was less than 5%, meeting the measurement requirements.

[0067] The cooling and heating stage and sample preparation: the temperature rising procedure and argon protection parameters in Example 1 were used. The single-layer MoS2 sample used in Example 1 was fixed on the cooling and heating stage again to ensure that the sample position was consistent with the absorption spectrum measurement (positioned by the microscope crosshairs with a deviation of less than 2 μm) and to avoid measurement errors caused by changes in the sample position.

[0068] 2.2 Fluorescence spectrum collection

[0069] Laser focusing and signal collection: the objective lens 2 was adjusted by the inverted microscope to focus the laser on the MoS2 region, and the focused spot diameter was about 2 μm (measured by a laser power meter, the power density after focusing was 10 kW / cm 2 , to avoid sample damage caused by high power). The spectrum collection software was turned on, the integration time was set to 200 ms (the fluorescence signal was weaker than the reflection signal, so the integration time needed to be extended), the average number was set to 50, and the dark current correction was turned on. At each temperature point (25℃, 35℃, 45℃…185℃) set on the cooling and heating stage, the fluorescence spectrum was collected, 5 times at each temperature point, and the average value was taken as the fluorescence spectrum data at that temperature. The results are shown in Figure 5 .

[0070] 2.3 Data processing and result analysis

[0071] Fluorescence peak parameter extraction: the A exciton peak (665-675 nm band) in the fluorescence spectrum was fitted by the Lorentz method, and the peak position (λ0), peak intensity (A), and half-width (Γ) were extracted. The results showed that at 25℃, the A exciton peak was at 670.1 nm, the intensity was 12500 counts, and the half-width was 12.3 nm; at 185℃, the peak position red-shifted to 678.5 nm, the intensity decreased to 3200 counts, and the half-width widened to 18.7 nm, indicating that the increase in temperature led to an increase in exciton non-radiative recombination (enhanced electron-phonon interaction), which in turn caused fluorescence quenching and spectral peak broadening.

[0072] Varshni formula fitting: the Varshni formula was used to fit the change of the A exciton peak position with temperature, and the formula was: wherein, is the band gap energy at temperature T (obtained by the peak position λ0 through where h is the Planck constant and c is the speed of light, Eg(0) is the band gap energy at 0 K, a is the band gap temperature coefficient, and β is a parameter related to the Debye temperature.

[0073] The fitting results are shown in FIG. 2. Figure 6 = 1.96 eV, a = 3.38 x 10 -4 eV / K, and β = 124 K. Here, The value of a is consistent with the band gap temperature coefficient (3.2-3.5 x 10 - 4 eV / K) of monolayer MoS2, further verifying the reliability of the system in fluorescence spectrum measurement.

[0074] Example 3: Verification of repeatability and stability of the system

[0075] To verify the measurement repeatability of the system, the same region of the same monolayer MoS2 sample was selected, and the absorption spectrum and fluorescence spectrum were measured at 25°C, 100°C and 185°C for 5 times respectively, and the relative standard deviation (RSD) of the A exciton peak position at each temperature point was calculated.

[0076] Absorption spectrum: RSD = 0.08% at 25°C, RSD = 0.12% at 100°C, and RSD = 0.15% at 185°C;

[0077] Fluorescence spectrum: RSD = 0.10% at 25°C, RSD = 0.18% at 100°C, and RSD = 0.22% at 185°C.

[0078] All RSDs are ≤0.25%, indicating that the system has good measurement repeatability; at the same time, the reflectance spectrum of the blank substrate at 25°C was monitored for 8 hours continuously, and the intensity fluctuation was ≤2%, proving that the system has good long-term running stability.

[0079] The above only describes the preferred embodiments of the present application and does not limit the technical scope of the present application in any way, so any slight modification, equivalent change and modification made according to the technical essence of the present application to the above embodiments are still within the scope of the technical solutions of the present application.​

Claims

1. A two-dimensional material microspectral measurement system under varying temperature conditions, characterized in that, The system comprises an excitation light source module, an optical path transmission module, a variable temperature sample module, a spectrum acquisition module and a data processing module.

2. The system for microscopic spectroscopy of two-dimensional materials under variable-temperature conditions according to claim 1, characterized in that, The excitation light source module comprises a wide spectrum halogen tungsten lamp and a 532 nm laser, the halogen tungsten lamp is used for absorption spectrum measurement, the laser is used for fluorescence spectrum measurement, and the two light sources can be selectively switched. 3.The system for microscopic spectroscopy of two-dimensional materials under variable-temperature conditions according to claim 1, wherein, The optical path transmission module comprises an optical fiber, an objective lens, a pinhole, a collimating lens, a mirror and a focusing lens, the objective lens has a magnification of 50 times, a numerical aperture of 0.55 and a working distance of 9.8 mm, and the pinhole gap is 10 μm, and the collimating lens has a focal length of 25 mm.

4. The system for microscopic spectroscopy of two-dimensional materials under variable-temperature conditions according to claim 1, characterized in that, The variable temperature sample module comprises a cold-hot stage on an inverted microscope stage, the temperature regulation range of the cold-hot stage is 25-185℃, the temperature rising rate is 30℃ / min, argon gas is filled in the cold-hot stage as a protective atmosphere, and the sample is placed in the cold-hot stage to realize in-situ variable temperature measurement.

5. The system for microscopic spectroscopy of two-dimensional materials under variable-temperature conditions according to claim 1, characterized in that, The spectrum acquisition module is a fiber spectrum analyzer, the absorption spectrum measurement is performed in a reflection mode, the difference reflectivity R(λ)= (R-Rsample) / R is calculated by collecting the reflectivity R of a blank substrate and the reflectivity Rsample of a sample, and a long-wave pass filter is configured to filter stray light during fluorescence spectrum measurement.

6. The system for microscopic spectroscopy of two-dimensional materials under variable-temperature conditions according to claim 1, characterized in that, The data processing module is used for Lorenz fitting of the collected spectrum data, calculation of the lattice thermal expansion coefficient through the change of the absorption spectrum peak position, and acquisition of band gap related parameters by fitting the relationship between the fluorescence spectrum A exciton peak position and the temperature by using the Varshni formula.

7. The system for microspectroscopic measurement of two-dimensional materials under variable temperature conditions according to any one of claims 1-6, characterized in that, During absorption spectrum measurement, the spectrum integration time is set to 50 ms, the average number is 100 times, and the spectrum data is collected every 10℃. 8.The system for micro-spectroscopy of two-dimensional materials under variable temperature conditions according to any one of claims 1-6, characterized in that, The two-dimensional material comprises a single-layer MoS2, and the system is suitable for absorption spectrum and fluorescence spectrum characterization of transition metal chalcogenides.

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