Diamond anvil cell high-pressure thermoelectric effect measuring device and measuring method

Abstract

The invention belongs to the technical field of material thermoelectric effect measurement, and particularly relates to a diamond anvil cell high-pressure thermoelectric effect measuring device and method. The measuring device comprises a diamond anvil cell and a multifunctional bottom electrode arranged on the lower anvil surface of the diamond anvil cell, wherein the bottom electrode comprises a heating wire, a thermoelectric voltage measuring electrode, a first temperature measuring electrode and a second temperature measuring electrode which are independently arranged and form a sample measuring area. During measurement, a sample to be measured is placed in a measurement area, electrodes and a measurement instrument are connected through platinum strips and wires to form a measurement system, after pressure calibration and temperature calibration, a heating wire is electrified to establish a stable temperature difference and apply a vertical magnetic field, the temperature difference and a voltage value are obtained through the electrodes and the measurement instrument, and then the Seebeck coefficient and the Nernst coefficient are calculated. According to the method, in-situ high-precision measurement of the thermoelectric parameters of the two-dimensional material can be realized in a high-voltage, extremely-low-temperature and high-intensity magnetic field environment, and key technical support is provided for thermoelectric material research and device development in an extreme environment.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric effect measurement technology of materials, specifically relating to a diamond anvil cell high-pressure thermoelectric effect measurement device and method for two-dimensional materials. Background Technology

[0002] Thermoelectric effects, as a type of physical phenomenon that directly converts heat energy into electrical energy, have significant application prospects in clean energy conversion and efficient thermal management systems. In particular, the Seebeck effect (electricity generation due to temperature difference) and the Nernst effect (thermoelectric effect under the combined action of magnetic field and temperature gradient) have become the core physical mechanisms for developing efficient thermoelectric conversion materials.

[0003] The thermoelectric conversion efficiency of the material is given by the dimensionless figure of merit ZT=(S 2 The conductivity is determined by σT / κ, where S is the Seebeck coefficient and σ is the electrical conductivity. It is thermal conductivity. It refers to absolute temperature. However, the ZT value of most material systems is still at a low level, making it difficult for their power generation efficiency and cooling performance to meet the needs of large-scale industrial applications, thus becoming a major bottleneck in promoting the industrialization of thermoelectric technology.

[0004] The main challenge in improving the ZT value lies in overcoming the inherent interrelationships among multiple parameters such as the Seebeck coefficient, electrical conductivity, and thermal conductivity. In recent years, two-dimensional layered materials, due to their quantum confinement effect, tunable electronic structure, abundant interlayer coupling, and potential low-dimensional phonon transport properties, have been regarded as a crucial system for overcoming the performance limitations of thermoelectric materials and achieving technological breakthroughs. Theoretical research and preliminary experimental results show that by precisely controlling the interlayer spacing, interlayer coupling strength, and interlayer interactions of two-dimensional materials, their band structure, carrier concentration and mobility, and phonon scattering behavior can be effectively modulated, thereby significantly improving thermoelectric conversion efficiency and enhancing their engineering application potential.

[0005] Applying external pressure is a clean, undoped physical modulation method that can effectively modulate the interlayer interactions of two-dimensional materials, avoiding carrier scattering introduced by chemical disorder, and is suitable for developing high-performance thermoelectric materials for industrial applications. However, existing thermoelectric measurement techniques under pressure (such as piston-cylinder devices) are usually limited to pressures below 3 GPa, which cannot reach the high-pressure region that may induce a step-like improvement in thermoelectric performance or even the emergence of new functional phases, severely limiting the development and application of such materials in high-end thermoelectric energy systems.

[0006] Therefore, there is an urgent industrial need to provide a new technology that enables in-situ high-precision thermoelectric parameter measurement of two-dimensional materials under extreme high pressure conditions. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention first provides a diamond anvil cell high-pressure thermoelectric effect measuring device.

[0008] The technical solution adopted in this invention is as follows: A diamond anvil cell high-pressure thermoelectric effect measurement device is disclosed for measuring the high-pressure thermoelectric effect of two-dimensional materials. The device includes a diamond anvil cell with a multifunctional bottom electrode disposed on the lower anvil surface. The multifunctional bottom electrode includes a heating wire and a first temperature measuring electrode, a thermoelectric voltage measuring electrode, and a second temperature measuring electrode arranged independently and sequentially on one side of the heating wire. The thermoelectric voltage measuring electrode includes four identical and parallel linear electrodes, symmetrically arranged in two rows. The heating wire, the first temperature measuring electrode, the thermoelectric voltage measuring electrode, and the second temperature measuring electrode are all coated with a Ti / Au composite film. These components together constitute the sample measurement area.

[0009] Preferably, the heating wire, the first temperature measuring electrode, and the second temperature measuring electrode are all strip-shaped, wherein the heating wire is arranged in a serpentine pattern to increase the heating area, and the first temperature measuring electrode, the second temperature measuring electrode, and the thermoelectric voltage measuring electrode are arranged in parallel.

[0010] Preferably, in the thermoelectric voltage measuring electrodes, the interval between the two columns is smaller than the width of the sample to be measured, and the lengths of the first and second temperature measuring electrodes are greater than the width of the sample to be measured.

[0011] Preferably, the width of the first temperature measuring electrode, the second temperature measuring electrode, and the heating wire is 1~2 μm, and the width of the four linear electrodes is 2~3 μm.

[0012] Preferably, in the Ti / Au composite coating, Ti is the bottom adhesion layer with a thickness of 5~10 nm, and Au is the surface conductive layer with a thickness of 30~50 nm.

[0013] Preferably, the method for preparing the measuring device includes the following steps: S1. The lower anvil surface of the diamond anvil is plasma cleaned, and then photoresist is uniformly coated on the clean lower anvil surface and hardened. Then, the patterning is performed according to the required multifunctional bottom electrode arrangement position. S2. Sequentially deposit Ti thin films and Au thin films on the patterned lower anvil surface; S3. Remove excess photoresist to obtain the prepared measuring device.

[0014] Preferably, in step S1, the photoresist uses an MMA / PMMA system. The MMA is spin-coated at 4000 rpm for 30 seconds and then heated at 80°C for 2 minutes. Then, the PMMA is spin-coated at 4000 rpm for 60 seconds and then heated at 120°C for 2 minutes to complete the coating and hardening process.

[0015] Preferably, in step S1, the graphic processing involves shaping the lower anvil surface after hardening into a 2x10 mm shape. -5 Electron beam exposure is performed under mbar vacuum, followed by immersion in developer for 20 seconds and then immersion in isopropanol for 10 seconds for fixing; the developer is prepared by mixing isopropanol and tetramethyldipentanone in a volume ratio of 2:1; in step S3, the photoresist is removed using acetone.

[0016] The present invention further provides a method for measuring the high-pressure thermoelectric effect of two-dimensional materials, which is performed using the measuring device described above, and the specific steps are as follows: Step 1: Place the two-dimensional material sample to be tested in the sample measurement area, and cover the surface of the sample with a layer of hexagonal boron nitride sheet. One side of the sample is close to the heating wire but not in contact with the heating wire. The sample forms good ohmic contact with the thermoelectric voltage measuring electrode, as well as the first temperature measuring electrode and the second temperature measuring electrode. Step 2: Connect the ends of the heating wire, the first temperature measuring electrode, the thermoelectric voltage measuring electrode, and the second temperature measuring electrode with platinum bars and extend them to the edge of the lower anvil. Then, use wires to connect the platinum bars to the nanovoltmeter, the current source, and the temperature controller respectively to obtain the measurement system. Step 3: Place the prepared lower anvil and the upper anvil of the diamond anvil at the center of the hydraulic press, and then perform pressure calibration; Step four: Place the measurement system in a thermostat to cool it down, and obtain the variation of the resistance values ​​of the first and second temperature measuring electrodes with temperature, which is used for temperature calibration. Step 5: The heating wire is energized and heated to the set temperature. After a stable temperature difference is generated between the two ends of the sample, the temperature difference is obtained through the first and second temperature measuring electrodes. Then, a magnetic field perpendicular to the plane of the sample is applied, and the voltage between two linear electrodes in the same column of the electrode is measured by thermoelectric voltage. The unit is microvolts. The voltage between two linear electrodes located in different columns but symmetrically arranged in the thermoelectric voltage measurement electrode system is measured. The unit is microvolts. The Seebeck coefficient of the sample is calculated according to the following formula. and Nernst coefficient : ; In the formula, The temperature of the sample near the heating wire, measured by the first thermometric electrode, is expressed in Kelvin. ; The temperature measured by the second thermometric electrode at the end of the sample furthest from the heating wire, in Kelvin. ; The linear distance between linear electrodes in the same row of thermoelectric voltage measurement electrodes, in micrometers. ; The straight-line distance between the first and second temperature measuring electrodes is expressed in micrometers. ; ; ; In the formula, B is the magnitude of the magnetic field perpendicular to the plane containing the sample, measured in Tesla. ; The linear distance between two linear electrodes located in different columns but symmetrically arranged in the thermoelectric voltage measurement electrode system, in micrometers. .

[0017] Preferably, in step two, the nanovoltmeter is connected to the platinum bar connected to the thermoelectric voltage measuring electrode, the current source is connected to the platinum bar connected to the heating wire, and two temperature controllers are provided, which are respectively connected to the platinum bars connected to the first temperature measuring electrode and the second temperature measuring electrode.

[0018] Preferably, in step three, the pressure calibration method is ruby ​​fluorescence spectroscopy.

[0019] Preferably, in step four, the thermostat is a 12T Oxford cryostat, which is also used to generate the magnetic field perpendicular to the plane where the sample is located as described in step five. Preferably, in step four, the specific method for temperature calibration is as follows: 1) Cool down the measurement system to obtain a series of raw resistance-temperature values ​​and fit them to obtain a resistance-temperature curve; 2) Within the temperature range of 300K to 3K, generate 200 temperature points distributed as needed using the following formula: ; ; In the formula, x takes the natural number from 0, 1, 2...199; 3) Using interpolation, the resistance values ​​corresponding to the 200 generated temperature points are obtained based on the resistance-temperature curve; 4) For the low-temperature range of 20K to 3K, the resistance-temperature curve is refitted using the following power function formula: ; In the formula, R is the resistance value, and the unit is ohms. T represents temperature, measured in Kelvin. ; y0 and A are fitting constants, and n is the exponent; 5) Substitute the temperature value of the 20K~3K region generated in step 2) into the formula in step 4) to obtain the corresponding resistance value, and replace the resistance value of the 20K~3K region in step 3) with this resistance value; after integration, a complete temperature-resistance calibration curve of 300K~3K is obtained, which is used for temperature measurement of the first temperature measuring electrode and the second temperature measuring electrode.

[0020] The beneficial effects of this invention are as follows: The measuring device, mounted in a diamond anvil cell, integrates a micro heating wire, a thermometer, and dual sets of measuring electrodes. This allows for the application of a temperature gradient to the two-dimensional sample under high pressure to induce a thermoelectric response, accurately obtaining the temperature gradient and thermoelectric voltage, and calculating the Seebeck coefficient and Nernst coefficient. Furthermore, this measuring device and method, combined with multiple controllable parameters such as high pressure, extremely low temperature, and strong magnetic field, can be used to study the variation patterns of thermoelectric signals under extreme conditions, clarifying the correlations between various novel physical phenomena in two-dimensional materials. This has significant value for developing next-generation industrial waste heat power generation systems, integrated solid-state cooling devices, and energy applications in extreme environments (such as deep space, deep earth, and deep sea exploration power sources). It also lays a solid experimental foundation for understanding the influence of quantum effects on thermoelectric behavior under high pressure and realizing on-demand design of thermoelectric materials. Attached Figure Description

[0021] Figure 1 This is an optical microscope image of the measuring device under a diamond anvil.

[0022] Figure 2 The figures are schematic diagrams of the measuring device. Figure a shows the device under an optical microscope (on a diamond anvil), and Figure b shows the structure of the multifunctional bottom electrode within the red dashed box in Figure a.

[0023] Figure 3 This is a schematic diagram showing the positional relationship of each electrode in a multifunctional bottom electrode.

[0024] Figure 4 This shows the change in resistance values ​​of the first and second temperature measuring electrodes obtained after calibration in Example 2 as a function of temperature.

[0025] Figure 5 Figure a shows the temperature changes of the first and second temperature measuring electrodes when different currents are applied to the heating wire at a system temperature of 16 K, and the temperature gradient as a function of the heating wire current (Figure b).

[0026] Figure 6To stabilize the system temperature at 4 K, a 2 mA current was passed through the heating wire. The Seebeck (Figure a) and Nernst thermoelectric signals (Figure b) were obtained by performing ±12T magnetic field scanning measurements under different pressures.

[0027] Figure 7 This is a cross-sectional height distribution map of the MoTe2 sample obtained using AFM. Detailed Implementation

[0028] Unless otherwise stated, the terms used herein have the meanings commonly understood by those skilled in the art.

[0029] The technical solution of the present invention will be described in more detail below with reference to specific embodiments: Example 1 The preparation of the measuring device includes the following steps: S1. Place the lower anvil face of the diamond anvil cell (DAC) on the sample stage of the plasma cleaner, ensuring the anvil face is facing upwards. Close the cleaning chamber and evacuate to the baseline pressure (typically 10). -2 ~10 -3 (mbar). Introduce cleaning gas, set the gas flow rate, start the plasma generator, set the power to 50 W and the cleaning time to 10 min. After cleaning is complete, turn off the plasma, stop the gas supply, and slowly release the vacuum.

[0030] Remove the diamond anvil, avoiding direct contact with the surface with your hands. Use clean tweezers to firmly place the diamond anvil onto the spin coater. Spin coat a few drops of MMA photoresist evenly at 4000 rpm for 30 seconds, then heat at 80°C for 2 minutes. Next, spin coat PMMA photoresist evenly at 4000 rpm for 60 seconds, then heat at 120°C for 2 minutes.

[0031] The pre-designed pattern in the drawing software klayout is imported into the control terminal computer of the electron beam exposure system. After the photoresist is evenly homogenized on the anvil surface and placed under vacuum for 2 hours, it is placed in the vacuum chamber of the electron microscope. When the vacuum level reaches 2x10⁻⁶, the electron beam exposure system is prepared. -5 After mbar exposure, the anvil is located under the electron beam, the center is determined, and exposure begins.

[0032] After exposure, the sample is developed using a developer solution with a volume ratio of isopropanol:tetramethyldipentanone of 2:1 to remove the photoresist in the exposed areas. This process requires approximately 20 seconds of soaking, followed by fixation in isopropanol for about 10 seconds to stabilize the photoresist structure in the unexposed areas.

[0033] S2. Place the diamond anvil with the etched electrode in an electron beam evaporation and resistance evaporation composite coating instrument, and perform titanium (5 nm) / gold (30 nm) evaporation under vacuum to form a conductive layer.

[0034] S3. After the evaporation is completed, the sample is immersed in an acetone solution to remove the residual photoresist and the excess metal layer attached thereto. Finally, the required multifunctional bottom electrode is formed on the diamond anvil, and the measuring device is obtained.

[0035] Specifically, in this measuring device, the multifunctional bottom electrode includes a heating wire and a first temperature measuring electrode, a thermoelectric voltage measuring electrode, and a second temperature measuring electrode (Ti / Au composite coating) arranged independently and sequentially on one side of the heating wire. The heating wire, the first temperature measuring electrode, and the second temperature measuring electrode are all strip-shaped with a width of 1-2 μm. The heating wire is arranged in a serpentine pattern to increase the heating area, and the first and second temperature measuring electrodes are arranged linearly parallel to the thermoelectric voltage measuring electrode. The thermoelectric voltage measuring electrode includes four identical and parallel linear electrodes, each 2-3 μm wide, arranged symmetrically in two rows. The interval between the two rows of the thermoelectric voltage measuring electrode is less than the width of the sample to be measured, and the length of the first and second temperature measuring electrodes is greater than the width of the sample to be measured. The heating wire, the first temperature measuring electrode, the thermoelectric voltage measuring electrode, and the second temperature measuring electrode together constitute the sample measurement area.

[0036] The thermoelectric effect of two-dimensional materials was measured using the aforementioned measuring device, and the method was as follows: Step one: Using a micromanipulator on the transfer platform, place the two-dimensional material sample to be tested in the sample measurement area. Then, using the same method, transfer a hexagonal boron nitride (hBN) sheet onto the surface of the sample to isolate it from air and prevent oxidation. See [link to relevant documentation]. Figure 1 One side of the sample is close to the heating wire but not in contact with it. The sample forms good ohmic contact with the thermoelectric voltage measuring electrode, the first temperature measuring electrode, and the second temperature measuring electrode.

[0037] The two-dimensional materials in this application include various single-crystal materials with different thermoelectric responses, such as molybdenum ditelluride (MoTe2) and rubidium vanadium triantimony pentoxide (RbV3Sb5).

[0038] In this step, care should be taken to ensure that the sample does not come into electrical contact with the heating wire during sample transfer. This is to ensure that the measured signal is entirely generated by the heat provided by the heating wire, thus guaranteeing the authenticity of the results. During the transfer process, the transfer process can be monitored in real time using an optical microscope or a micromanipulation system to ensure that the contact interface between the two-dimensional material and the electrode is flat and that the electrodes make ohmic contact. Ultimately, this achieves efficient integration of the two-dimensional material and the electrode circuit, laying the foundation for subsequent thermoelectric testing and device functionality.

[0039] Step 2: Connect the heating wire, the first temperature measuring electrode, the thermoelectric voltage measuring electrode, and the second temperature measuring electrode to the ends of the heating wire, extending them to the edge of the lower anvil. Then, use enameled copper wire to connect the platinum strip to the nanovoltmeter, the current source, and the temperature controller respectively to obtain the measurement system.

[0040] In the above connection, the nanovoltmeter is connected to the platinum bar that connects to the thermoelectric voltage measuring electrode, the current source is connected to the platinum bar that connects to the heating wire, and two temperature controllers are provided, which are respectively connected to the platinum bars that connect to the first temperature measuring electrode and the second temperature measuring electrode.

[0041] In this step, the measuring instruments used to accurately measure the thermoelectric signals of the Seebeck and Nernst coefficients of samples with thicknesses at the nanometer level under the high-pressure environment formed by the diamond anvil cell are, including but not limited to, a 2182A nanovolt voltmeter, a 6221 DC and AC current source, a Lake Shore 350 temperature controller, and a pressure calibration system.

[0042] Step 3: Place the prepared lower anvil and the upper anvil of the diamond anvil at the center of the hydraulic press, and then perform pressure calibration. The pressure calibration method is ruby ​​fluorescence spectroscopy, specifically: A small amount of ruby ​​powder was placed on the lower anvil, ensuring that the ruby ​​powder and the two-dimensional sample to be tested were under the same pressure environment. The fluorescence spectrum of the ruby ​​powder was measured using an instrument, and the characteristic wavelengths were recorded. For example, a force of 200 kg is pre-applied to the DAC, and the pressure sensor value is reduced by tightening the screw, so that the pressure acts on the lower anvil surface, and the characteristic wavelength is recorded. Based on the characteristic wavelength of ruby ​​under standard atmospheric pressure. Calculate the standard pressure using the following formula. : ; This allows for accurate pressure measurement.

[0043] Step four: The measurement system is cooled in a 12T Oxford cryostat to obtain the resistance values ​​of the first and second temperature-sensing electrodes as a function of temperature, which is used for temperature calibration. Specifically: 1) Cool down the measurement system to obtain a series of raw resistance-temperature data, and fit the resistance-temperature curve.

[0044] 2) Within the temperature range of 300K to 3K, generate 200 temperature points distributed as needed (x is a natural number from 0, 1, 2…199) according to the following formula, covering the entire temperature measurement range: ; ; 3) For the resistance-temperature curve, the corresponding resistance values ​​are obtained on the curve using the 200 generated temperature points through interpolation, forming a temperature-resistance dataset; 4) For the low-temperature range of 20K to 3K, the resistance-temperature curve is refitted using the following power function formula: ; In the formula, R is the resistance value, T is the temperature, y0 and A are fitting constants, and n is the exponent; 5) Substitute the temperature values ​​of the 20K~3K region generated in step 2) into the formula in step 4) to obtain the corresponding resistance values. Replace the resistance values ​​of the corresponding temperature region of 20K~3K in step 3) with these resistance values. After integration, we obtain 200 optimized temperature-resistance datasets, forming a complete temperature-resistance calibration curve of 300K~3K.

[0045] The obtained temperature-resistance calibration curve is imported into the temperature controller. The resistance signals of the first and second temperature measuring electrodes collected in subsequent measurements are automatically converted into actual temperature values ​​according to the calibration curve, thus completing the real-time temperature display.

[0046] Step 5: Apply different currents to the heating wire at different stable system temperatures. (mA) to generate different thermal gradients, and obtain the temperature difference through the first and second temperature measuring electrodes. : ; In the formula, The temperature of the sample near the heating wire, measured by the first thermometric electrode, is expressed in Kelvin. ; The temperature measured by the second thermometric electrode at the end of the sample furthest from the heating wire, in Kelvin. ; The linear distance between linear electrodes in the same row of thermoelectric voltage measurement electrodes, in micrometers. ; The straight-line distance between the first and second temperature measuring electrodes is expressed in micrometers. .

[0047] Then, a magnetic field perpendicular to the plane of the sample was applied using a 12T Oxford cryostat, and the voltage between two linear electrodes in the same column of the electrode was measured by thermoelectric voltage measurement. The unit is microvolts. The voltage between two linear electrodes located in different columns but symmetrically arranged in the thermoelectric voltage measurement electrode system is measured. The unit is microvolts. Calculate the Seebeck coefficient of the sample according to the following formula. and Nernst coefficient : ; ; In the formula, B is the magnitude of the magnetic field perpendicular to the plane containing the sample, measured in Tesla. ; The linear distance between two linear electrodes located in different columns but symmetrically arranged in the thermoelectric voltage measurement electrode system, in micrometers. .

[0048] In this application, the variation law of thermoelectric signal under extreme environment can be further studied by using multiple control parameters such as high pressure, extremely low temperature, and strong magnetic field.

[0049] Furthermore, after completing the test, the sample thickness is measured using an atomic force microscope (AFM) to obtain a cross-sectional height distribution map, thereby determining the sample thickness and providing a dimensional reference for analyzing material properties.

[0050] Example 2 Measurement of the high-pressure thermoelectric effect of a certain two-dimensional MoTe2 single crystal material: 1. Preparation of MoTe2 two-dimensional single crystal materials: A certain proportion of sealed single-crystal molybdenum tellurium (mixture) was placed in a KSL-1200X-J muffle furnace for annealing. Note that the sample should be placed in a position to ensure uniform heating and avoid local overheating or combustion. After annealing, it was slowly cooled to room temperature to obtain the two-dimensional single-crystal material MoTe2 in this example.

[0051] 2. Preparation of the measuring device: Place the lower anvil of the diamond anvil cell (DAC) on the sample stage of the plasma cleaner, ensuring the anvil faces upwards. Close the cleaning chamber and evacuate to the baseline pressure (typically 10). -2 ~10 -3 (mbar). Introduce cleaning gas, set the gas flow rate, start the plasma generator, set the power to 50 W and the cleaning time to 10 min. After cleaning is complete, turn off the plasma, stop the gas supply, and slowly release the vacuum.

[0052] Remove the diamond anvil, avoiding direct contact with the surface with your hands. Use clean tweezers to firmly place the diamond anvil onto the spin coater. Spin coat a few drops of MMA photoresist evenly at 4000 rpm for 30 seconds, then heat at 80°C for 2 minutes. Next, spin coat PMMA photoresist evenly at 4000 rpm for 60 seconds, then heat at 120°C for 2 minutes.

[0053] The pre-designed pattern in the drawing software klayout is imported into the control terminal computer of the electron beam exposure system. After the anvil surface with homogenized photoresist is placed under vacuum for 2 hours, it is placed in the vacuum chamber of the electron microscope. When the vacuum degree reaches 2×10⁻⁶... -5 After mbar exposure, the anvil is located under the electron beam, the center is determined, and exposure begins.

[0054] After exposure, the sample is developed using a developer solution with a volume ratio of isopropanol:tetramethyldipentanone of 2:1 to remove the photoresist in the exposed areas. This process requires approximately 20 seconds of soaking, followed by fixation in isopropanol for about 10 seconds to stabilize the photoresist structure in the unexposed areas.

[0055] The diamond anvil with the etched electrode is placed in an electron beam evaporation and resistance evaporation composite coating instrument, and titanium (5 nm) / gold (30 nm) is deposited in a vacuum environment to form a conductive layer.

[0056] After vapor deposition, the diamond anvil is immersed in acetone solution and left to stand for 10 minutes. Then, it is ultrasonicated for 30 seconds to remove residual photoresist and excess metal layer, ultimately forming the desired multifunctional bottom electrode on the diamond anvil. Figure 1 As shown.

[0057] See Figures 2-3 In this embodiment, the multifunctional bottom electrode on the diamond anvil cell mainly consists of a serpentine heating wire (approximately 600 μm in total length and 2 μm in line width), a strip-shaped first temperature measuring electrode (approximately 120 μm in length and 1.8 μm in line width), a second temperature measuring electrode (approximately 80 μm in length), and a thermoelectric voltage measuring electrode (2 μm in line width). The electrodes are arranged in the following order: heating wire, first temperature measuring electrode, thermoelectric voltage measuring electrode, and second temperature measuring electrode. All electrodes must be parallel and maintain an appropriate spacing. In this embodiment, the first temperature measuring electrode is approximately 4 μm away from the heating wire electrode, and the straight-line distance between the first and second temperature measuring electrodes is... Approximately 28 μm; the straight-line distance between linear electrodes in the same row of thermoelectric voltage measurement electrodes. The linear distance between two linear electrodes located in different columns but arranged symmetrically is approximately 14 μm. The distance is approximately 4 μm, excluding the electrode linewidth. The spacing between the electrodes is carefully chosen to ensure that each parallel electrode does not touch each other while being as close as possible to the heating wire to create a larger thermal gradient.

[0058] A MoTe2 single crystal sample was placed on a slightly viscous blue adhesive tape and mechanically peeled off to the desired thickness. Polydimethylsiloxane (PDMS) was then applied to the tape containing the sample, extracting a thinner portion of the sample. The PDMS was then observed under an optical microscope to identify samples with a smooth surface, suitable thickness, and size. A transfer platform micromanipulator was then used to precisely transfer the two-dimensional sample from the PDMS surface onto the sample measurement area of ​​the diamond anvil. It is crucial that the sample not come into contact with the heating wire. Figure 2 The dark blue MoTe2 sample (approximately 120 nm thick, 60 μm long and 50 μm wide) is shown in Figure a. A hexagonal boron nitride (hBN) sheet is then transferred onto the sample surface using the same method to isolate it from air and prevent oxidation. The principle for selecting the size and thickness of the hBN is that its size should completely cover the sample to achieve good air isolation, while the thickness is not critical and should be as uniform as possible. Finally, on the surface of the diamond anvil cell, from bottom to top, are the bottom electrode, the sample (MoTe2), and the hBN sheet, as shown. Figure 2 As shown in Figure b.

[0059] The electrodes of the lower diamond anvil are extended to the outside of the anvil using pre-cut platinum strips. Then, the platinum strips are connected and led to the outside of the upper diamond anvil using enameled copper wires of different colors. Finally, the upper diamond anvil is aligned with the lower diamond anvil and the upper anvil is closed to complete the fabrication of the diamond anvil cell (DAC) micro-nano thermoelectric device with two-dimensional material MoTe2.

[0060] 3. Measurement of the thermoelectric effect of MoTe2 under different pressures using the above measuring device: First, a diamond anvil cell is placed in the center of a hydraulic press and a force of approximately 100 kg is applied. The pressure sensor reading is reduced by tightening a screw to apply pressure to the sample chamber. The prepared diamond anvil cell (DAC) micro-nano thermoelectric device is then placed in the pressure calibration system. Pressure calibration is performed using ruby ​​fluorescence spectroscopy. By monitoring the wavelength changes in the ruby ​​fluorescence spectrum, a redshift phenomenon is observed in the spectral wavelength as the pressure increases, thus achieving accurate pressure measurement.

[0061] ; In the formula, and These represent the wavelengths of the spectrum at a specific pressurized pressure and a standard atmosphere, respectively, where p is the standard pressure. In this embodiment, the first pressure point tested was calibrated to 0.5 GPa.

[0062] The enameled copper wire of the prepared diamond anvil cell (DAC) thermoelectric device is soldered to the measuring rod of the Oxford cryostat, and the enameled copper wire is gently moved to ensure a stable connection with the measuring instrument.

[0063] The measuring rod was placed in a 12T Oxford cryostat for cooling. Simultaneously, the first and second temperature-sensing electrodes were connected to a Lake Shore 350 temperature control instrument, and their resistance changes with system temperature were recorded for later thermometer calibration. See Example 1 for details. The final calibration curve of the thermometer obtained in this embodiment is shown below. Figure 4 As shown, the 200 data points obtained by interpolation match the original data very well. The calibration curves of the first and second temperature measuring electrodes were then imported into the Lake Shore 350 temperature control instrument, which can then perform real-time conversion from resistance to temperature.

[0064] Different currents were applied to the heating wire at different stable system temperatures. Different thermal gradients are generated, and the temperature gradient is obtained by measuring the temperature difference between two temperature-sensing electrodes. The first temperature-sensing electrode is denoted as... The second temperature measuring electrode is denoted as The temperature gradient on the sample is then tested as follows: ; in The distance between the two electrodes used to measure the longitudinal thermoelectric voltage is d, where d is the distance between the two thermometers. In this example... It is 14 μm. The sample temperature is 28 μm. When a heating wire provides the heat source, the temperature on the sample is no longer the same as the system temperature; the temperature T at the center of the sample is taken. mid = ( T hot + T cold ) / 2 is taken as the actual temperature of the sample.

[0065] The specific temperature gradient can be adjusted based on the thermoelectric response of the material being measured and the adaptability of the system to different temperatures. In this embodiment, the temperature gradient provided by the micro heating wire to the sample at a system temperature of 16 K is as follows: Figure 5 As shown, since the substrate is diamond, the establishment of the temperature gradient is affected by the thermal conductivity of the substrate. As the system temperature increases, the temperature gradient generated by the same current will decrease. Therefore, the current of the heating wire will generally be greater at higher temperatures. The original data of the first thermometer, the second thermometer, the sample temperature, and the temperature gradient when different currents (1 mA to 8 mA) are applied to the heating wire are shown in Table 1.

[0066] Table 1. Raw data of temperature gradients under different currents .

[0067] Following the thermometer calibration and temperature gradient detection under different system temperatures, a suitable temperature gradient was selected for the sample, and a corresponding current was applied to the heating wire. In this embodiment, since the temperature of the MoTe2 sample under test is generally at a low level, the system temperature was stabilized at 4 K. Subsequently, a 2 mA current was applied to the heating wire using a 6221 DC and AC microcurrent source (at which point the actual temperature on the sample was 7.4 K). Two 2182A nanovoltmeters were used to detect the voltage between two linear electrodes in the same column of the thermoelectric voltage measurement electrode. (Vertical electrode voltage) and the voltage between two linear electrodes located in different columns but arranged symmetrically. (Transverse electrode voltage), after the temperature gradient has stabilized, use a 12T Oxford cryostat to start at +12T. An experiment was conducted using a 12T magnetic field sweep, and the changes in voltage with magnetic field were recorded for two sets of data.

[0068] In this embodiment, the specific test pressures are 0.5 GPa, 1.3 GPa, 2.7 GPa, 4.5 GPa, 6.1 GPa, and 9.4 GPa. After each test, the device needs to be removed from the Oxford cryostat and placed on a hydraulic press for repressurization. The pressure calibration process needs to be repeated for each change in pressure value to obtain accurate pressure.

[0069] Following the above testing method, calculate the Seebeck coefficient S and the Nernst coefficient N according to the formulas: ; ; In the formula, B is the magnitude of the magnetic field perpendicular to the plane containing the sample. The straight-line distance between two linear electrodes located in different columns but symmetrically arranged in a thermoelectric voltage measurement electrode, in this example. It is 4 μm.

[0070] Based on the series of results, the final result is... Figure 6 The series of thermoelectric signals shown indicate that the Seebeck coefficient S and Nernst coefficient N undergo a series of significant changes under different pressure values. The Seebeck signal shows a symmetrical trend with the positive and negative magnetic fields, and the sign has also flipped multiple times. In contrast, the Nernst signal shows an antisymmetric trend with the positive and negative magnetic fields, and its value decreases as the pressure increases.

[0071] After all pressure measurements are completed, the diamond anvil cell pressure pack is disassembled. The MoTe2 sample measured on the lower diamond anvil cell is placed under an atomic force microscope (AFM) to measure the sample thickness, obtaining a cross-sectional height distribution map to determine the measured MoTe2 sample thickness. Figure 7 As shown, the thickness of the MoTe2 sample in this embodiment is approximately 127 nm.

[0072] It is evident that the apparatus and method provided in this application have successfully acquired high-quality data and thermoelectric signals with certain physical significance.

[0073] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A diamond anvil cell high-pressure thermoelectric effect measuring device for measuring the high-pressure thermoelectric effect of two-dimensional materials, characterized in that, The device includes a diamond anvil cell, on the lower anvil surface of which a multifunctional bottom electrode is disposed. The multifunctional bottom electrode includes a heating wire and a first temperature measuring electrode, a thermoelectric voltage measuring electrode, and a second temperature measuring electrode arranged independently and sequentially on one side of the heating wire. The thermoelectric voltage measuring electrode includes four identical and parallel linear electrodes, which are symmetrically arranged in two rows with intervals. The heating wire, the first temperature measuring electrode, the thermoelectric voltage measuring electrode, and the second temperature measuring electrode are all Ti / Au composite coated. The heating wire, the first temperature measuring electrode, the thermoelectric voltage measuring electrode, and the second temperature measuring electrode together constitute the sample measurement area.

2. The diamond anvil cell high-voltage thermoelectric effect measuring device as described in claim 1, characterized in that, The heating wire, the first temperature measuring electrode, and the second temperature measuring electrode are all strip-shaped, with the heating wire arranged in a serpentine pattern to increase the heating area. The first temperature measuring electrode, the second temperature measuring electrode, and the thermoelectric voltage measuring electrode are arranged in parallel. The width of the first temperature measuring electrode, the second temperature measuring electrode, and the heating wire is 1~2 μm, and the width of the four linear electrodes is 2~3 μm.

3. The diamond anvil cell high-voltage thermoelectric effect measuring device as described in claim 2, characterized in that, In the thermoelectric voltage measuring electrodes, the interval between the two columns is smaller than the width of the sample to be measured, and the lengths of the first and second temperature measuring electrodes are greater than the width of the sample to be measured.

4. The diamond anvil cell high-voltage thermoelectric effect measuring device as described in claim 1, characterized in that, In the Ti / Au composite coating, Ti is the bottom adhesion layer with a thickness of 5~10 nm, and Au is the surface conductive layer with a thickness of 30~50 nm.

5. A diamond anvil cell high-pressure thermoelectric effect measuring device as described in any one of claims 1-4, characterized in that, The method for preparing the measuring device includes the following steps: S1. The lower anvil surface of the diamond anvil is plasma cleaned, and then photoresist is uniformly coated on the clean lower anvil surface and hardened. Then, the patterning is performed according to the required multifunctional bottom electrode arrangement position. S2. Sequentially deposit Ti thin films and Au thin films on the patterned lower anvil surface; S3. Remove excess photoresist to obtain the prepared measuring device.

6. The diamond anvil cell high-voltage thermoelectric effect measuring device as described in claim 5, characterized in that, In step S1, the photoresist uses an MMA / PMMA system. MMA is spin-coated at 4000 rpm for 30 seconds and then heated at 80°C for 2 minutes. Then PMMA is spin-coated at 4000 rpm for 60 seconds and then heated at 120°C for 2 minutes to complete the coating and hardening process.

7. The diamond anvil cell high-voltage thermoelectric effect measuring device as described in claim 5, characterized in that, In step S1, the graphic processing involves shaping the lower anvil surface after hardening into a 2x10 grid. -5 Electron beam exposure is performed under mbar vacuum, followed by immersion in developer for 20 seconds and then immersion in isopropanol for 10 seconds for fixing; the developer is prepared by mixing isopropanol and tetramethyldipentanone in a volume ratio of 2:1; in step S3, the photoresist is removed using acetone.

8. A method for measuring the high-pressure thermoelectric effect of two-dimensional materials, characterized in that, The measurement is performed using the measuring device described in any one of claims 1-4, and the specific steps are as follows: Step 1: Place the two-dimensional material sample to be tested in the sample measurement area and cover the surface of the sample with a layer of hexagonal boron nitride sheet. One side of the sample is close to the heating wire but avoids the heating wire. The sample forms good ohmic contact with the thermoelectric voltage measuring electrode, the first temperature measuring electrode, and the second temperature measuring electrode. Step 2: Connect the ends of the heating wire, the first temperature measuring electrode, the thermoelectric voltage measuring electrode, and the second temperature measuring electrode with platinum bars and extend them to the edge of the lower anvil. Then, use wires to connect the platinum bars to the nanovoltmeter, the current source, and the temperature controller respectively to obtain the measurement system. Step 3: Place the prepared lower anvil and the upper anvil of the diamond anvil at the center of the hydraulic press, and then perform pressure calibration; Step four: Place the measurement system in a thermostat to cool it down, and obtain the variation of the resistance values ​​of the first and second temperature measuring electrodes with temperature, which is used for temperature calibration. Step 5: The heating wire is energized and heated to the set temperature. After a stable temperature difference is generated between the two ends of the sample, the temperature difference is obtained through the first and second temperature measuring electrodes. Then, a magnetic field perpendicular to the plane of the sample is applied, and the voltage between two linear electrodes in the same column of the electrode is measured by thermoelectric voltage measurement. The unit is microvolts. The voltage between two linear electrodes located in different columns but symmetrically arranged in the thermoelectric voltage measurement electrode system is measured. The unit is microvolts. The Seebeck coefficient of the sample is calculated according to the following formula. and Nernst coefficient : In the formula, The temperature of the sample near the heating wire, measured by the first thermometric electrode, is expressed in Kelvin. ; The temperature measured by the second thermometric electrode at the end of the sample furthest from the heating wire, in Kelvin. ; The linear distance between linear electrodes in the same row of thermoelectric voltage measurement electrodes, in micrometers. ; The straight-line distance between the first and second temperature measuring electrodes is expressed in micrometers. ; In the formula, B is the magnitude of the magnetic field perpendicular to the plane containing the sample, measured in Tesla. ; The linear distance between two linear electrodes located in different columns but symmetrically arranged in the thermoelectric voltage measurement electrode system, in micrometers. .

9. The method for measuring the high-pressure thermoelectric effect of two-dimensional materials as described in claim 8, characterized in that, In step two, the nanovoltmeter is connected to the platinum strip connecting the thermoelectric voltage measuring electrode, the current source is connected to the platinum strip connecting the heating wire, and two temperature controllers are provided, which are respectively connected to the platinum strips connecting the first and second temperature measuring electrodes; in step three, the pressure calibration method is ruby ​​fluorescence spectroscopy; in step four, the thermostat is a 12T Oxford cryostat, which is also used to generate the magnetic field perpendicular to the plane of the sample as described in step five.

10. A method for measuring the high-pressure thermoelectric effect of a two-dimensional material as described in claim 8 or 9, characterized in that, In step four, the specific method for temperature calibration is as follows: 1) Cool down the measurement system to obtain a series of raw resistance-temperature values ​​and fit them to obtain a resistance-temperature curve; 2) Within the temperature range of 300K to 3K, generate 200 temperature points distributed as needed using the following formula: In the formula, Choose a natural number from 0, 1, 2...199; 3) Using interpolation, the resistance values ​​corresponding to the 200 generated temperature points are obtained based on the resistance-temperature curve; 4) For the low-temperature range of 20K to 3K, the resistance-temperature curve is refitted using the following power function formula: In the formula, R is the resistance value, and the unit is ohms. T represents temperature, measured in Kelvin. ; y0 and A are fitting constants, and n is the exponent; 5) Substitute the temperature value of the 20K~3K region generated in step 2) into the formula in step 4) to obtain the corresponding resistance value, and replace the resistance value of the 20K~3K region in step 3) with this resistance value; after integration, a complete temperature-resistance calibration curve of 300K~3K is obtained, which is used for temperature measurement of the first temperature measuring electrode and the second temperature measuring electrode.

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