Vacuum variable temperature seebeck coefficient measurement apparatus based on sample scanning

Abstract

The application provides a vacuum variable-temperature Seebeck coefficient measuring device based on sample scanning, which comprises a vacuum cavity, a probe assembly, a sample assembly and a data acquisition and processing system, the probe assembly comprises a fixed temperature-controlled probe, a first thermocouple and a first temperature control unit; the sample assembly comprises a temperature-controlled sample base, a sample stage, a second thermocouple and a second temperature control unit, and is driven by a low-temperature piezoelectric displacement stage to make two-dimensional scanning movement relative to the probe. The first and second temperature control units are independent of each other and control the temperatures of the probe and the sample base respectively to form a stable temperature gradient at the contact point; the data acquisition and processing system acquires thermoelectric potential and temperature signals under the temperature gradient and calculates the micro-area Seebeck coefficient. The device breaks through the limitation that the existing equipment can only work at room temperature, realizes high-precision and high-resolution scanning test of the micro-area Seebeck coefficient of materials in a vacuum low-temperature environment, and provides a new technical means for low-temperature thermoelectric material research.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric material performance testing, specifically relating to a vacuum temperature-variable Seebeck coefficient measuring device based on sample scanning. Background Technology

[0002] Thermoelectric technology, as a new energy technology that converts electrical energy and heat energy into each other, has been widely used in many fields. The performance of thermoelectric devices mainly depends on the performance of the thermoelectric materials used within them, and the performance of thermoelectric materials is usually characterized by the dimensionless figure of merit zT, the expression of which is:

[0003]

[0004] Where S is the Seebeck coefficient of the material, and σ is the electrical conductivity. S represents thermal conductivity, and T represents absolute temperature. The Seebeck coefficient, defined as S = dV / dT, is a physical quantity reflecting a material's ability to generate a potential difference under a temperature gradient. It characterizes the diffusion behavior of charge carriers (electrons or holes) under the influence of a temperature gradient and directly affects the energy conversion efficiency of thermoelectric materials. Therefore, accurate and efficient testing of the Seebeck coefficient of thermoelectric materials is of great significance for evaluating the performance of thermoelectric devices.

[0005] Currently, several commercial instruments are available for measuring the Seebeck coefficient of materials, such as the ZEM-3 manufactured by ULVAC-RIKO in Japan, the LSR-3 manufactured by LINSEIS in Germany, and the CTA-3 manufactured by Beijing Kerui Technology Co., Ltd. These instruments are all based on the static method, establishing a temperature gradient by placing heating and heat sinks at both ends of the sample, and then using thermocouple probes to measure the temperature and potential differences between the two points to calculate the Seebeck coefficient. However, the static method requires measuring a series of minute temperature differences and corresponding potential differences point by point, resulting in a relatively slow overall measurement speed.

[0006] Patent CN102967624B discloses a Seebeck coefficient measuring device using a quasi-static method. This method can rapidly measure the Seebeck coefficient of a sample within a certain temperature range and obtain a large number of data points, thereby accurately reflecting the changing trend and peak value of the Seebeck coefficient. However, this method is only applicable to macroscopic scale (millimeter level) measurements, and the obtained result is the average Seebeck coefficient within the measurement area, which cannot achieve Seebeck coefficient measurement at the microscale.

[0007] For the measurement of Seebeck coefficient in micro-areas, patent CN104614557B proposes a measurement device and method based on atomic force microscopy. In addition, some studies have used scanning tunneling microscopy or scanning thermal microscopy for the measurement of Seebeck coefficient in micro-areas, but these methods are typically complex to operate, require expensive equipment, and have high testing costs.

[0008] PANCO, a German company, in collaboration with the German Aerospace Center (DLR), has developed a commercial instrument, the Potential-Seebeck Microprobe (PSM), capable of accurately measuring the two-dimensional distribution of the Seebeck coefficient. Its structure is as follows: Figure 1 As shown, the main components include: P1 - a three-vector axis positioning platform and its controller, P2 - a base, P3 - a sample stage and sample clamp, P4 - a probe, P5 - a heating ceramic tube, P6 - a conductive copper block holding the sample, P7 - the sample, and P8 - two T-type thermocouples. This device moves the heating probe to the sample surface and uses the thermocouple connected to the probe to measure the temperature T1. The sample maintains good electrothermal contact with the copper block, and the temperature T0 is measured by another thermocouple. The probe tip creates a temperature gradient locally on the sample. Combined with the Cu-Cu and CuNi-CuNi wires of the thermocouple, the voltages U0 and U1 are measured, and then the Seebeck coefficient S is calculated using formulas (1.1) to (1.3). s .

[0009]

[0010] However, the device is relatively large and can only perform Seebeck coefficient scanning tests at room temperature under atmospheric conditions, unable to achieve variable-temperature scanning measurements at low temperatures. This poses a significant limitation for in-depth research on the local thermoelectric properties of materials. Many low-temperature thermoelectric materials only exhibit significant Seebeck coefficient differences under specific low-temperature conditions, and their intrinsic properties are often only fully revealed in low-temperature environments.

[0011] Therefore, developing a device capable of performing Seebeck coefficient scanning tests under varying temperature conditions in a vacuum or controlled atmosphere is of great value for advancing the study of the local properties of thermoelectric materials, especially low-temperature thermoelectric materials. Summary of the Invention

[0012] The purpose of this invention is to overcome the limitation of existing commercial Seebeck coefficient scanning measurement devices (such as PSM) that cannot operate in low-temperature environments, and to provide a device capable of rapid and accurate two-dimensional scanning tests of the Seebeck coefficient of micro-regions of materials in a vacuum and over a wide low-temperature range of 100–300 K. This device has a compact structure, controllable testing costs, and is particularly suitable for the performance research and evaluation of low-temperature thermoelectric materials.

[0013] To achieve the above objectives, the present invention provides a vacuum variable-temperature Seebeck coefficient measuring device based on sample scanning, referring to... Figure 2 and 3 The apparatus of the present invention includes:

[0014] Vacuum chamber 20 is used to provide the vacuum environment required for testing;

[0015] The probe assembly includes a temperature-controlled probe 7, a first thermocouple for measuring the probe temperature, and a first temperature control unit for controlling the probe temperature; the probe assembly is fixedly disposed within the vacuum chamber 20.

[0016] The sample assembly includes a temperature-controlled sample base 16, a sample stage for mounting a sample 26, a second thermocouple for measuring the temperature of the sample 26, and a second temperature control unit for controlling the temperature of the sample 26. The sample assembly is mounted in the vacuum chamber 20 via a low-temperature piezoelectric displacement stage 18, which is configured to drive the sample assembly to perform planar two-dimensional motion relative to the fixed probe assembly at a set temperature to achieve scanning testing.

[0017] The first temperature control unit and the second temperature control unit are independent of each other and respectively control the temperature of the temperature control probe 7 and the temperature control sample base 16 to form a stable temperature gradient at the contact point between the temperature control probe 7 and the sample 26.

[0018] The data acquisition and processing system is used to acquire the thermoelectric potential signal and temperature signal generated by the sample 26 under the temperature gradient, and to calculate the Seebeck coefficient of the micro-region of the sample 26.

[0019] In this invention, the term "sample-based scanning" refers to a scanning testing method unique in that: during the testing process, the spatial position of the probe remains fixed, while the sample, driven by a displacement stage, moves in a two-dimensional plane relative to the fixed probe, thereby achieving point-by-point or continuous scanning measurement of a specified area on the sample surface. This method is an innovative motion mode that is completely different from the traditional "probe moving, sample fixed" scanning method.

[0020] In general, the vacuum variable temperature Seebeck coefficient measurement device based on sample scanning provided by this invention mainly includes the following technical concepts:

[0021] 1. Overall composition: It includes a vacuum chamber, probe assembly, sample assembly, and data acquisition and processing system.

[0022] 2. Vacuum environment: The vacuum chamber is used to provide and maintain the high vacuum environment required for testing.

[0023] 3. Probe assembly: Fixedly installed inside the vacuum chamber, including a temperature-controlled probe, a first thermocouple for measuring the probe temperature, and a first temperature control unit for controlling the probe temperature.

[0024] 4. Sample Assembly and Scanning Method: The device includes a temperature-controlled sample base, a sample stage for mounting the sample, a second thermocouple for measuring the sample temperature, and a second temperature control unit for controlling the sample temperature. The sample assembly is mounted in a vacuum chamber via a cryogenic piezoelectric displacement stage. The unique scanning motion design of this invention lies in the fact that the cryogenic piezoelectric displacement stage is configured to drive the entire sample assembly to perform precise two-dimensional planar motion relative to a stationary probe assembly at a set cryogenic temperature. This "sample moving, probe stationary" configuration offers significant advantages over the traditional "probe moving, sample stationary" PSM device: firstly, it avoids the technical difficulties and thermal disturbances associated with driving complex and bulky probe displacement mechanisms at low temperatures; secondly, it requires only a small, precise cryogenic piezoelectric displacement stage to drive the sample, making the entire device more compact and enabling higher displacement accuracy and stability at low temperatures, providing a mechanical basis for cryogenic scanning testing.

[0025] 5. Independent Dual-Path Temperature Control and Temperature Difference Formation: The first and second temperature control units operate independently, enabling precise temperature control of the temperature-controlled probe and sample base within a range of 100–300 K. This design allows the operator to actively and independently set the temperatures of the probe and sample, thereby actively forming and maintaining a controllable, low-temperature difference suitable for Seebeck coefficient measurement at their contact point. Typically, this temperature difference (ΔT) is controlled within the range of 5–30 K, preferably 10–20 K, to balance measurement signal strength and stability. This successfully overcomes the limitation of devices such as PSMs, which rely solely on the environment and heated probe to form a room temperature difference, and is a key design feature for achieving variable-temperature (especially low-temperature) Seebeck coefficient scanning tests.

[0026] 6. Signal Acquisition and Processing: The data acquisition and processing system is used to acquire in real time the thermoelectric potential signal generated in the sample micro-region under the above-mentioned actively formed temperature difference, as well as the temperature signal measured by the first and second thermocouples, and calculate the Seebeck coefficient of the specified micro-region of the sample accordingly.

[0027] Furthermore, the first temperature control unit and the second temperature control unit are independent of each other in terms of temperature control function, and preferably share a set of temperature control hardware to implement their respective temperature control functions. Specifically, the first temperature control unit and the second temperature control unit may include:

[0028] The cooling module, including a Stirling refrigerator 33, is connected to the temperature control probe 7 and the temperature control sample base 16 via a first flexible heat conductor 23 and a second flexible heat conductor 13, respectively.

[0029] The heating module consists of a first heating element 2 and a second heating element 27 respectively attached to the temperature control probe 7 and the temperature control sample base 16.

[0030] The temperature measurement module consists of a first temperature sensor 1 and a second temperature sensor 25 respectively attached to the temperature control probe 7 and the temperature control sample base 16.

[0031] The temperature controller 30 receives signals from the first temperature sensor 1 and the second temperature sensor 25, and uses a PID control algorithm to drive the first heating element 2 and the second heating element 27 to work, thereby achieving precise temperature control.

[0032] The advantages of the temperature control system proposed in this invention are as follows: the Stirling refrigerator provides a powerful cold source covering 100~300 K; the flexible heat conductor (such as annealed copper braid) ensures efficient and stable heat transfer while reducing the influence of mechanical stress; the combination of the heating element and the PID temperature controller achieves rapid and accurate temperature compensation and stabilization, enabling the probe and sample base to reach and maintain extremely high temperature stability (such as ±0.1 K) at the target low temperature point, which is a prerequisite for obtaining accurate and repeatable measurement results.

[0033] More specifically, to ensure the establishment of a sufficiently stable and controlled local temperature field in a low-temperature vacuum environment of 100~300 K, the device provided by this invention integrates a set of coordinated thermal management configurations, specifically including:

[0034] a. Basic thermal insulation: The vacuum chamber 20 is connected to the vacuum pump assembly 34 and is configured to maintain a temperature not exceeding 10°C. -3 A vacuum level of Pa is used to eliminate gas convection heat transfer and prevent frost formation inside the cavity at low temperatures.

[0035] b. Active temperature control design: The cooling module in the first temperature control unit and the second temperature control unit connects the cold head of the Stirling refrigerator 33 to the temperature control probe 7 and the temperature control sample base 16 through the first flexible heat conductor 23 and the second flexible heat conductor 13 respectively, so as to realize the cooling of the probe and the sample base, and combined with the compensation heating of the first heating element 2 and the second heating element 27, the probe and the sample base are independently and precisely temperature controlled.

[0036] c. Thermal control and isolation of the connection, including:

[0037] c1. Thermal isolation of the probe fixing assembly: The temperature control probe 7 is connected through a pressure sensor 3, which is installed in the vacuum chamber 20 via an L-shaped fixing bracket 4 containing a heat insulation gasket 5 to suppress heat leakage from the temperature control probe 7 to the bracket through its fixing structure.

[0038] c2. Insulation and thermal conductivity of the sample assembly: The sample holder 10 for mounting the sample 26 and the temperature-controlled sample base 16 are connected by an insulating thermally conductive sheet 11 combined with low-temperature adhesive to achieve thermal conductivity and electrical insulation between the two.

[0039] c3. Temperature stability of the thermocouple reference junction: The non-temperature measuring junctions of the first thermocouple 8 and the second thermocouple 9 are welded together to the copper-clad AlN substrate 12 fixed on the temperature control sample base 16, so that the reference junctions of the two thermocouples are at the same and stable temperature.

[0040] Specifically, the purpose of the active temperature control design is that simple cooling cannot meet the need for precise temperature setting, while the active temperature control mode of "cooling + heating" provides bidirectional adjustment capability, making it possible to set a stable and rapid temperature and establish a temperature difference at any temperature point in the range of 100~300 K.

[0041] According to the vacuum variable temperature Seebeck coefficient measuring device provided by the present invention, the first heating element 2 and the second heating element 27 are preferably ceramic heating elements. The first temperature sensor 1 and the second temperature sensor 25 can be Pt100 thermometers. The temperature controller 30 is preferably a dual-channel temperature controller.

[0042] According to the vacuum variable temperature Seebeck coefficient measuring device provided by the present invention, the low temperature piezoelectric displacement stage 18 is preferably driven by the inverse piezoelectric effect of piezoelectric ceramic material, and its displacement accuracy is at the micrometer or submicrometer level.

[0043] The cryogenic piezoelectric displacement stage is the actuator for achieving a "sample moving, probe stationary" scanning method. Maintaining sub-micron level motion accuracy under high vacuum and low temperature environments is crucial. Preferably, the cryogenic piezoelectric displacement stage used in this invention can operate stably within a wide low-temperature range of 100~300 K, ensuring a displacement accuracy of no less than 1 μm. Ordinary displacement stages suffer from decreased accuracy or even jamming at low temperatures due to material shrinkage and lubrication failure. However, the piezoelectric displacement stage, specifically designed for low temperatures, avoids mechanical transmission, thus overcoming the adverse effects of low temperature on motion accuracy. This ensures the positioning accuracy and motion repeatability of the scanning test. Combined with the probe tip size, the scanning spatial resolution of the entire device can reach the 1-micron level, achieving high-resolution characterization of the thermoelectric properties of micro-regions of materials.

[0044] According to the vacuum variable temperature Seebeck coefficient measuring device provided by the present invention, the probe assembly further includes a pressure sensor 3, which is connected to the temperature control probe 7 and is used to monitor and control the contact force between the temperature control probe 7 and the sample 26 in real time.

[0045] The pressure sensor is integrated into the probe assembly to monitor and control the contact force between the probe and the sample in real time. This contact force is typically set between 1 and 20 mN, which ensures the reliability of the electrothermal contact during each test while preventing excessive contact force from damaging brittle samples or precision needle tips, thus improving the success rate and safety of the test.

[0046] According to the vacuum variable temperature Seebeck coefficient measuring device provided by the present invention, the data acquisition and processing system includes a nanovoltmeter 28 and a multi-channel matrix switch 29; wherein the input terminal of the multi-channel matrix switch 29 is connected to multiple voltage test points, and the output terminal is connected to the input channel of the nanovoltmeter 28. By switching the path of the multi-channel matrix switch 29, a single nanovoltmeter 28 can sequentially or selectively acquire multiple voltage signals.

[0047] The data acquisition system of this invention is designed by using a high-precision nanovoltmeter 28 in conjunction with a multi-channel matrix switch 29 to construct multiple voltage acquisition paths. Its advantage lies in the fact that measuring the Seebeck coefficient requires synchronous or rapid switching to acquire multiple small voltages; equipping each signal with an independent nanovoltmeter would drastically increase costs. This invention, by using the multi-channel matrix switch 29, time-multiplexes a single nanovoltmeter 28, ensuring measurement accuracy at the millivolt or even microvolt level while significantly reducing system complexity and hardware costs, achieving a good balance between high performance and low cost.

[0048] According to the vacuum variable temperature Seebeck coefficient measuring device provided by the present invention, the sample stage includes a sample holder 10, and the sample 26 is fixed in the sample holder 10 by Wood alloy 24; wherein an insulating heat-conducting sheet 11 (e.g., a sapphire sheet) is provided between the sample holder 10 and the temperature-controlled sample base 16 to achieve electrical insulation and thermal conductivity.

[0049] The sample fixation and installation scheme includes two details: First, the sample 26 is fixed in the sample holder 10 using Wood's alloy 24. Wood's alloy is a low-melting-point alloy that, after melting, can wet the sample surface. After solidification, it forms a strong mechanical fixation as well as excellent electrical and thermal contact, making it particularly suitable for irregularly shaped or brittle bulk and thin film samples, ensuring the stability and reliability of the test. Second, an insulating thermally conductive sheet 11, preferably a sapphire sheet, is provided between the sample holder 10 and the temperature-controlled sample base 16. Sapphire has high thermal conductivity and excellent electrical insulation. The purpose of this design is to achieve the effect of "thermal conduction" and "electrical insulation": high thermal conductivity ensures that the sample temperature can be efficiently and accurately controlled by the sample base; high resistivity ensures that the thermoelectric potential signal measured from the sample will not be short-circuited or interfered with by the base.

[0050] According to the vacuum variable temperature Seebeck coefficient measuring device provided by the present invention, preferably, the sample assembly further includes a copper-clad AlN substrate 12 fixed on the temperature-controlled sample base 16, wherein the non-temperature measuring ends of the first thermocouple 8 and the second thermocouple 9 are welded on the copper-clad AlN substrate 12, and the copper-clad AlN substrate 12 is also welded with wires for leading out voltage test signals.

[0051] In a preferred embodiment of the present invention, the copper-clad AlN substrate 12 serves as an electrical connection hub in the system. First, the non-temperature-measuring ends (i.e., reference ends) of the two thermocouples are jointly soldered onto the copper-clad conductors of this substrate, ensuring they are at the same and stable temperature, thereby eliminating temperature measurement errors caused by inconsistencies or drift in the reference end temperatures. Second, the substrate also integrates conductors for extracting the sample thermoelectric potential measurement signal, which are led out of the cavity through a centralized wiring base 15, resulting in neat and reliable internal wiring and reducing thermal disturbances and signal interference caused by the leads.

[0052] According to the vacuum variable temperature Seebeck coefficient measuring device provided by the present invention, preferably, the device is configured to perform a two-dimensional scanning test on the Seebeck coefficient of a sample at any temperature point between 100 and 300 K with a measurement error of less than 10%.

[0053] The testing principle of the vacuum variable temperature Seebeck coefficient measuring device provided by this invention is as follows: Figure 2As shown, a dual-channel temperature controller is used to create a temperature difference between the probe and the sample. When the probe and sample come into contact, a micro-temperature gradient forms in the sample near the probe tip, resulting in a localized thermoelectric potential. In the diagram, 7 represents the temperature-controlled probe, 26 represents the sample, 24 represents Wood's alloy, and T represents... base It is the reference temperature, i.e., the temperature of the sample base, T. probe It is the probe temperature, T sample It is the sample temperature. Different voltages are achieved through a multi-channel matrix switch. Figure 2 The voltage V shown GH V FE V FG V EH With rapid switching acquisition, the Seebeck coefficient S of the sample micro-region can be calculated according to formulas (1.4) to (1.8). sample .

[0054]

[0055] It is particularly important to note that this invention performs micro-area scanning, where the probe contact area is extremely small, resulting in extremely weak thermoelectric potential signals (often in the microvolt or even nanovolt range). Simultaneously, the measurement environment is vacuum and low temperature (e.g., 100-300 K), requiring the sample to undergo two-dimensional motion scanning relative to the probe. Under these conditions, various types of noise (thermal noise, mechanical vibration noise, electromagnetic interference) are amplified, making it far more difficult to ensure measurement accuracy than static macroscopic measurements. Therefore, this invention, under conditions far more complex and challenging than PSM, achieves comparable measurement accuracy for the first time, i.e., an error of <10%. This is not simply a matter of catching up with specifications, but rather extending the feasibility boundary of the technology from "room temperature" to a "wide low-temperature range"—a breakthrough from zero to one. Achieving an error of <10% signifies the successful overcoming of all the additional challenges brought by low temperatures, marking a substantial breakthrough in low-temperature micro-area thermoelectric characterization technology and providing an unprecedentedly reliable tool for the research of functional materials such as low-temperature thermoelectric materials.

[0056] The device provided by this invention integrates multiple technological innovations, including: a vacuum cryogenic environment, a "sample moving, probe stationary" scanning method, independent dual-channel active temperature control, precise thermal management, high-precision displacement, and low-noise signal acquisition. Its superiority lies in its first-ever achievement of high-precision two-dimensional scanning testing of the Seebeck coefficient distribution in micro-areas of material surfaces within a continuous cryogenic range of 100–300 K (rather than being limited to room temperature). This successfully overcomes the technical barrier of existing commercial equipment such as the German PSM, which can only perform room-temperature scanning, providing an unprecedentedly powerful experimental tool for studying low-temperature thermoelectric materials, functionally graded materials, interface effects, and material homogeneity.

[0057] The beneficial effect of this invention lies in providing a device capable of rapid and accurate two-dimensional scanning testing of the Seebeck coefficient of micro-regions in materials within a vacuum and wide low-temperature range. Its main advantages include:

[0058] Breakthrough in low-temperature testing: Overcoming the limitation of existing commercial equipment (such as PSM in Germany) that can only scan at room temperature, stable and accurate measurement is achieved in a continuous low-temperature range of 100~300 K, meeting the needs of intrinsic property research of low-temperature thermoelectric materials.

[0059] Achieving high-precision scanning: Employing a unique scanning configuration of "sample moving, probe stationary" and combined with a low-temperature piezoelectric displacement stage, it can still achieve high-precision two-dimensional motion at low temperatures, with a spatial resolution of 1 μm.

[0060] Measurement accuracy and stability: Through an independent dual-path active temperature control system and thermal management configuration, a stable and controllable low-temperature gradient is formed and maintained between the sample and the probe, achieving a Seebeck coefficient measurement error of less than 10%.

[0061] Compact structure and controllable cost: The overall structure of the device is simplified and compact; the data acquisition system uses a multi-channel matrix switch to multiplex a single nanovoltmeter, which effectively reduces hardware costs while ensuring accuracy.

[0062] With a wide range of applications, it is suitable for studying the distribution of Seebeck coefficients in micro-regions of bulk materials, thin films, inhomogeneous materials, functionally graded materials, and heterogeneous interfaces under varying temperature conditions, providing a powerful new tool for evaluating the thermoelectric properties of materials. Attached Figure Description

[0063] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0064] Figure 1 This is a schematic diagram of the equipment structure of a conductivity-Seebeck coefficient scanning probe microscope (PSM) in the prior art.

[0065] Figure 2 This is a schematic diagram illustrating the testing principle of the vacuum variable temperature Seebeck coefficient measuring device of the present invention;

[0066] Figure 3 This is a schematic diagram of the overall structure of the vacuum variable temperature Seebeck coefficient measuring device of the present invention;

[0067] Figure 4 This is a schematic diagram of the wiring method for the vacuum variable temperature Seebeck coefficient measuring device of the present invention;

[0068] Figure 5Two-dimensional distribution of the temperature-dependent Seebeck coefficient of the P-type bismuth telluride sample in Example 1 of the present invention: (a) 300 K; (b) 200 K;

[0069] Figure 6 The non-uniform Bi component in Example 2 of this invention 88 Sb 12 Two-dimensional distribution plot of the Seebeck coefficient at room temperature of the sample;

[0070] Figure 7 This is a two-dimensional distribution diagram of the Seebeck coefficient of the N-type bismuth telluride sample measured in Example 3 of the present invention;

[0071] Figure 8 The following is a two-dimensional distribution diagram of the Seebeck coefficient of the constantan sample in Example 4 of the present invention: (a) 300K test results, (b) 180K test results.

[0072] Figure 9 The Seebeck coefficient reference data for the constantan sample obtained by testing with commercial instruments in Example 4 is shown. Detailed Implementation

[0073] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0074] Reference Figure 3 The vacuum variable temperature Seebeck coefficient measurement device based on sample scanning provided by the present invention includes: a vacuum pump group 34 for providing a vacuum environment, a Stirling refrigerator 33 for cooling the entire device, a chiller 32 for cooling the Stirling refrigerator 33, a dual-channel temperature controller 30 for precise temperature control of the probe and sample, a piezoelectric displacement stage 18 and its controller 31 for scanning motion, and a multi-channel matrix switch 29 and a nanovoltmeter 28 (e.g., a nanovoltmeter of model 2182a) for voltage acquisition.

[0075] 1. Vacuum chamber 20

[0076] The test components of the device are integrated within the vacuum chamber 20. The vacuum chamber 20 mainly includes the following components: a gasket 21 for mounting and fixing the internal components, a fixing base 19, a piezoelectric displacement stage 18, a cylindrical fixing bracket 17, a flat annular fixing bracket 6, a heat insulation gasket 5, an L-shaped fixing bracket 4, a force gauge 3, and a wiring base 15.

[0077] 2. Probe assembly

[0078] The core of the probe assembly is a temperature control probe 7 made of preferably copper. To achieve precise temperature control and measurement of this probe 7, the following specific measures are taken: a first temperature sensor 1 (e.g., a thin-film Pt100 thermometer) and a first heating element 2 (e.g., a small ceramic heating element) are fixed to the probe 7 using low-temperature adhesive (e.g., GE Varnish). Simultaneously, a copper block 22 with a first flexible heat conductor 23 (e.g., an annealed flexible copper braid) welded to it is also fixed to the probe. The other end of the first flexible heat conductor 23 is connected to the cold head of the Stirling refrigerator 33, forming the cooling path for the probe.

[0079] 3. Sample Components

[0080] The sample assembly includes a temperature-controlled sample base 16, preferably made of copper. To achieve temperature control of the sample area, a second temperature sensor 25 (e.g., a thin-film Pt100 thermometer) and a second heating element 27 (e.g., a small ceramic heating element) are also fixed to the temperature-controlled sample base 16 with low-temperature adhesive. A copper block 14 with a second flexible heat conductor 13 (e.g., an annealed flexible copper braid) welded on it is fixed to the temperature-controlled sample base 16 with screws. The other end of the second flexible heat conductor 13 is also connected to the cold head of the Stirling refrigerator 33, forming a cooling path for the sample.

[0081] The sample holder 10 for mounting sample 26 is connected to the temperature-controlled sample base 16 via a thin insulating thermally conductive sheet 11 (such as a sapphire sheet with a thickness of 0.2 mm). The insulating thermally conductive sheet 11 is fixed to the base with low-temperature adhesive to achieve electrical insulation and thermal conductivity between the sample holder 10 and the temperature-controlled sample base 16. Sample 26 is fixed by Wood's alloy 24 filled inside the sample holder 10.

[0082] 4. Scan drive and measurement connection

[0083] The temperature-controlled sample base 16 is fixed to the low-temperature piezoelectric displacement stage 18 by screws, allowing the entire sample assembly to perform precise two-dimensional planar motion under the drive of the displacement stage. To measure the Seebeck coefficient, the measuring end of the first thermocouple 8 (e.g., a type E thermocouple) is fixed to the temperature-controlled probe 7 with silver paste, while the measuring end of the second thermocouple 9 (e.g., a type E thermocouple) is fixed to the Wood's alloy 24 of the sample holder 10. The non-measuring ends (a total of 4 thermocouple wires) of the first thermocouple 8 and the second thermocouple 9 are respectively soldered to a copper-clad AlN substrate 12, which is fixed to the temperature-controlled sample base 16 with low-temperature adhesive. Four phosphor bronze wires corresponding to the 4 thermocouple wires are also soldered to the copper-clad AlN substrate 12. The other ends of these phosphor bronze wires are soldered to a wiring base 15, which is connected to a multi-channel matrix switch 29 outside the vacuum chamber 20 via wires. For specific wiring details, please refer to [link to wiring diagram]. Figure 4 The diagram shown is shown in the image.

[0084] The temperature control probe 7 is connected to the L-shaped fixing bracket 4 via the pressure sensor 3. The L-shaped fixing bracket 4 is fixed in the vacuum chamber 20 by means of an installation method including a heat insulation gasket 5, so as to reduce heat leakage caused by heat conduction.

[0085] 5. Testing Principles

[0086] The testing principle of this invention is as follows: Figure 2 As shown. Using the dual-channel temperature controller 30, the temperatures of the temperature control probe 7 and the temperature control sample base 16 (and thus the sample 26) can be independently set and controlled, so that a stable temperature difference (ΔT = T) is formed between them. probe - T sample When the sample moves under the drive of the piezoelectric displacement stage 18 until it contacts the fixed temperature-controlled probe 7, a localized temperature gradient is formed in the sample micro-region near the probe tip, thereby generating a corresponding thermoelectric potential. This thermoelectric potential and the corresponding temperature T are measured. probe and T sample The Seebeck coefficient of the sample micro-region can then be calculated. Specifically, the acquisition is switched via a multi-channel matrix switch 29. Figure 2 The voltage V shown GH V FE V FG V EH Using the same signal and formulas (1.4) to (1.8), the Seebeck coefficient S of the sample can be calculated. sample .

[0087] 6. Testing and Verification vs. Accuracy Comparison

[0088] To verify the accuracy of the measurement results of the device of the present invention, the following comparison method is adopted:

[0089] First, the Seebeck coefficient of the sample under test was measured using the commercial thermoelectric performance testing instrument MultiFields® ColdTUBE. This instrument is based on a static method, and its measurement result is the average Seebeck coefficient of the macroscopic region of the sample, which can be used as a performance benchmark. Then, the vacuum variable-temperature Seebeck coefficient measurement device based on sample scanning provided in this invention was used to perform micro-area scanning tests on the same sample at the same temperature point. Finally, the average Seebeck coefficient measured within the scanning area of ​​this invention's device was compared and analyzed with the macroscopic average result measured by the commercial instrument. The good consistency between the two sets of data verifies the accuracy and reliability of this invention's device in the micro-area scanning measurement mode.

[0090] Example 1

[0091] Combination Figure 2-4 Using bulk P-type bismuth telluride samples (chemical formula Bi) 0.4 Sb 1.6 Taking Te3 as an example, the process and results of variable-temperature Seebeck coefficient scanning measurement by the device of the present invention are shown.

[0092] First, start all subsystems of the device: start the Stirling chiller 33 and its associated chiller 32; turn on the dual-channel temperature controller 30, piezoelectric displacement platform controller 31, multi-channel matrix switch 29 and nanovoltmeter 28; simultaneously start the vacuum pump group 34 to evacuate the vacuum level in the vacuum chamber 20 to 10. -3 Below Pa.

[0093] The p-type bismuth telluride sample 26 to be tested was fixed in the sample holder 10 using Wood's alloy 24 as described above. Test parameters were set via host computer software, including the scan range and movement step size, the preset contact force between the probe and the sample, and the target temperatures for both the temperature-controlled probe 7 and the temperature-controlled sample base 16. This embodiment tested the Seebeck coefficient at sample temperatures of 300K and 200K respectively.

[0094] (I) The temperature control probe 7 is set to 310 K, and the temperature control sample base 16 is set to 300 K;

[0095] (II) The temperature control probe 7 is set to 220 K and the temperature control sample base 16 is set to 200 K.

[0096] After the temperatures of the temperature-controlled probe 7 and the temperature-controlled sample base 16 reach the set values ​​and remain stable, the automatic testing program is run. The low-temperature piezoelectric displacement stage 18 drives the sample assembly to perform two-dimensional scanning motion according to the preset path and step size. When the sample moves to the coordinate point set by the program and comes into contact with the temperature-controlled probe 7, and the contact force fed back by the pressure sensor 3 reaches the set value (10 mN in this embodiment), the system switches the path through the multi-channel matrix switch 29 and automatically collects the multi-channel voltage signal (V) corresponding to that point using the nanovoltmeter 28. GH V FE (etc.) and temperature signal (T) probe T sample The data processing system calculates the Seebeck coefficient value S of the micro-region in real time according to formulas (1.4) to (1.8). sample And store all the data.

[0097] Repeating this process will yield a complete two-dimensional distribution map of the Seebeck coefficient for the sample at the set temperature, as shown in the figure. Figure 5 As shown.

[0098] analyze Figure 5The measurement results shown indicate that at 300 K ( Figure 5 (a) and 200 K ( Figure 5 (Figure b) At the two temperatures, the Seebeck coefficient values ​​measured by scanning the same sample area were uniformly distributed, with average values ​​of approximately 213 μV / K and 177 μV / K, respectively.

[0099] The results deviate by less than 10% from those obtained using the commercially available MultiFields® ColdTUBE device on the same sample (approximately 213 μV / K @ 300 K, approximately 165 μV / K @ 200 K). This verifies that the device of the present invention achieves measurement accuracy comparable to the macroscopic static method when performing micro-area Seebeck coefficient scanning measurements over a wide temperature range of 200–300 K, while simultaneously achieving spatial resolution on the order of μm.

[0100] Example 2

[0101] Bi with uneven composition 88 Sb 12 Taking alloy samples as an example, this demonstrates the application of this device in characterizing the composition and property distribution of materials.

[0102] The Bi used in this embodiment 88 Sb 12 The alloy sample preparation process is as follows: High-purity bismuth (Bi) and antimony (Sb) raw materials are mixed in a molar ratio of 88:12 and heated to 700℃ under an inert atmosphere for high-temperature melting, and held at that temperature for 10 h to allow for full alloying. Subsequently, the sample is slowly cooled at a cooling rate of 1 K / h. During this slow cooling process, due to the segregation effect of bismuth and antimony, a non-uniform distribution of components at the microscale is ultimately formed within the sample.

[0103] Referring to the apparatus and operating procedure described in Example 1, the Seebeck coefficient of the above sample was scanned and tested at a temperature of 300 K. The Bi to be tested... 88 Sb 12 The sample is fixed. The temperature control system is set to maintain a stable set temperature (10 K temperature gradient) between the temperature control probe 7 and the temperature control sample base 16 (i.e., the sample). Subsequently, a high-resolution two-dimensional scanning measurement is performed on the selected area of ​​the sample.

[0104] The two-dimensional distribution plot of the measured Seebeck coefficient is as follows: Figure 6 As shown in the figure, analysis reveals significant differences in Seebeck coefficient values ​​across different micro-regions of the sample surface, represented by varying color intensities. This non-uniform distribution of the Seebeck coefficient directly reflects the properties of Bi... 88 Sb 12The inhomogeneity of chemical composition (i.e., the ratio of Bi to Sb) in the sample at the micrometer scale.

[0105] This embodiment demonstrates that the device of the present invention not only provides accurate absolute measurements, but its high spatial resolution scanning capability also enables a more intuitive and quantitative characterization of the performance fluctuations and compositional gradients at the microscale of materials. This has significant application value for evaluating the uniformity of material preparation, studying the performance variation patterns of functionally graded materials, and analyzing the thermoelectric properties of heterojunction or composite material interfaces.

[0106] Example 3

[0107] For N-type bismuth telluride samples (chemical formula Bi₂Te) 2.7 Se 0.3 A two-dimensional scan of the Seebeck coefficient in a micro-area was performed at a temperature of 160 K. Following the apparatus and operating procedure described in Example 1, the N-type bismuth telluride sample to be tested was fixed. The temperature control system was set to maintain the temperatures of the temperature-controlled probe 7 and the temperature-controlled sample base 16 (i.e., the sample) at 180 K and 160 K, respectively. Subsequently, a high-resolution two-dimensional scan measurement was performed on a selected area of ​​the sample.

[0108] The two-dimensional distribution plot of the measured Seebeck coefficient is as follows: Figure 7 As shown in the figure, the Seebeck coefficient of the sample is relatively uniform at the test temperature of 160 K, with an average value of approximately -158 μV / K. This result deviates from the result obtained using the commercially available MultiFields® ColdTUBE device for the same sample (approximately -150 μV / K @ 160 K) by less than 10%.

[0109] Example 4

[0110] This embodiment uses a standard constantan sample with good homogeneity as the test object, and performs two-dimensional scanning of the Seebeck coefficient in the micro-area at temperatures of 300 K and 180 K respectively, to further verify the feasibility and accuracy of the device in testing different types of samples.

[0111] Referring to the apparatus and operating procedure described in Example 1, the constantan sample is fixed, and the temperatures of the temperature control probe 7 and the temperature control sample base 16 are independently set by the temperature control system to create a stable temperature gradient of approximately 10-20 K between them. Subsequently, a high-resolution two-dimensional scanning measurement is performed on a selected area of ​​the sample at the set temperature.

[0112] Measurement results as follows Figure 8 As shown. Figure 8Figures (a) and (b) are two-dimensional distribution diagrams of the Seebeck coefficient measured by the device of the present invention at 300 K and 180 K, respectively. The results show that at the above two temperatures, the measured values ​​of the Seebeck coefficient at each point of the sample are uniformly distributed, and the standard deviation and variance are both less than 1 (unit: μV / K), indicating that the sample itself has good uniformity and also demonstrating the high measurement stability of the device.

[0113] The average Seebeck coefficient measured by this invention and Figure 9 The data obtained by the commercial instrument (LSR equipment from Lindsay AG, Germany) were compared, and the deviation between the two was less than 10%. This result further proves that the device of the present invention is not only applicable to Bi-Sb-based thermoelectric materials, but also capable of accurate and reliable micro-area Seebeck coefficient scanning measurement of other metallic materials in a wide temperature range down to 180 K.

[0114] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention.

Claims

1. A vacuum variable-temperature Seebeck coefficient measuring device based on sample scanning, characterized in that, It includes: A vacuum chamber (20) is used to provide the vacuum environment required for testing; The probe assembly includes a temperature-controlled probe (7), a first thermocouple for measuring the probe temperature, and a first temperature control unit for controlling the probe temperature; the probe assembly is fixedly disposed inside the vacuum chamber (20). The sample assembly includes a temperature-controlled sample base (16), a sample stage for mounting a sample (26), a second thermocouple for measuring the temperature of the sample (26), and a second temperature control unit for controlling the temperature of the sample (26); the sample assembly is mounted in the vacuum chamber (20) via a low-temperature piezoelectric displacement stage (18), which is configured to drive the sample assembly to perform planar two-dimensional motion relative to the fixed probe assembly to achieve scanning testing; The first temperature control unit and the second temperature control unit are independent of each other and respectively control the temperature of the temperature control probe (7) and the temperature control sample base (16) to form a stable temperature gradient at the contact point between the temperature control probe (7) and the sample (26). The first temperature control unit and the second temperature control unit include a cooling module and a heating module. The cooling module connects the cold head of the Stirling refrigerator (33) to the temperature control probe (7) and the temperature control sample base (16) through a first flexible heat conductor (23) and a second flexible heat conductor (13) to achieve cooling of the probe and the sample base. The heating module consists of a first heating element (2) and a second heating element (27) respectively attached to the temperature control probe (7) and the temperature control sample base (16) for compensatory heating. The cooling module and the heating module are combined to perform independent and precise temperature control of the probe and the sample base. The data acquisition and processing system is used to acquire the thermoelectric potential signal and temperature signal generated by the sample (26) under the temperature gradient, and to calculate the Seebeck coefficient of the micro-region of the sample (26).

2. The vacuum variable temperature Seebeck coefficient measuring device according to claim 1, wherein, The first temperature control unit and the second temperature control unit further include: The temperature measurement module consists of a first temperature sensor (1) and a second temperature sensor (25) respectively attached to the temperature control probe (7) and the temperature control sample base (16). The temperature controller (30) receives signals from the first temperature sensor (1) and the second temperature sensor (25), and uses a PID control algorithm to drive the first heating element (2) and the second heating element (27) to work, thereby achieving precise temperature control.

3. The vacuum variable temperature Seebeck coefficient measuring device according to claim 2, wherein, The device includes a thermal management configuration for establishing and maintaining a stable local temperature field, comprising: a. Basic thermal insulation: The vacuum chamber (20) is connected to the vacuum pump assembly (34) and is configured to maintain a temperature not exceeding 10°C. -3 A vacuum level of Pa is used to eliminate gas convection heat transfer and prevent frost formation inside the cavity at low temperatures. b. Active temperature control design: The cooling module in the first temperature control unit and the second temperature control unit connects the cold head of the Stirling refrigerator (33) to the temperature control probe (7) and the temperature control sample base (16) through the first flexible heat conductor (23) and the second flexible heat conductor (13) respectively, so as to realize the cooling of the probe and the sample base, and combined with the compensation heating of the first heating element (2) and the second heating element (27), the probe and the sample base are independently and precisely temperature controlled. c. Thermal control and isolation of the connection, including: c1. Thermal isolation of the probe fixing assembly: The temperature control probe (7) is connected via a pressure sensor (3), which is installed in the vacuum chamber (20) via an L-shaped fixing bracket (4) containing a heat insulation gasket (5) to suppress heat leakage from the temperature control probe (7) to the bracket via its fixing structure. c2. Thermal insulation of the sample assembly: The sample holder (10) for mounting the sample (26) and the temperature-controlled sample base (16) are connected by an insulating thermally conductive sheet (11) combined with low-temperature adhesive to achieve thermal conductivity and electrical insulation between the two. c3. Temperature stability of the thermocouple reference junction: The non-temperature measuring junctions of the first thermocouple (8) and the second thermocouple (9) are welded together on the copper-clad AlN substrate (12) fixed on the temperature control sample base (16) so that the reference junctions of the two thermocouples are at the same and stable temperature.

4. The vacuum variable temperature Seebeck coefficient measuring device according to claim 2, wherein, The first heating element (2) and the second heating element (27) are ceramic heating elements; the first temperature sensor (1) and the second temperature sensor (25) are Pt100 thermometers; the temperature controller (30) is a dual-channel temperature controller.

5. The vacuum variable temperature Seebeck coefficient measuring device according to claim 1, wherein, The low-temperature piezoelectric displacement stage (18) is driven by the inverse piezoelectric effect of piezoelectric ceramics through piezoelectric ceramic materials, and its displacement accuracy is at the micrometer or submicrometer level.

6. The vacuum variable temperature Seebeck coefficient measuring device according to claim 1, wherein, The probe assembly also includes a pressure sensor (3), which is connected to the temperature control probe (7) and is used to monitor and control the contact force between the temperature control probe (7) and the sample (26) in real time.

7. The vacuum variable temperature Seebeck coefficient measuring device according to claim 1, wherein, The data acquisition and processing system includes a nanovoltmeter (28) and a multi-channel matrix switch (29). The input terminal of the multi-channel matrix switch (29) is connected to multiple voltage test points, and the output terminal is connected to the input channel of the nanovoltmeter (28). By switching the path of the multi-channel matrix switch (29), a single nanovoltmeter (28) can sequentially or selectively acquire multiple voltage signals.

8. The vacuum variable temperature Seebeck coefficient measuring device according to claim 1, wherein, The sample stage includes a sample holder (10), and the sample (26) is fixed in the sample holder (10) by Wood's alloy (24); An insulating heat-conducting sheet (11) is provided between the sample holder (10) and the temperature-controlled sample base (16) to achieve electrical insulation and thermal conductivity.

9. The vacuum variable temperature Seebeck coefficient measuring device according to claim 1, wherein, The sample assembly also includes a copper-clad AlN substrate (12) fixed on the temperature-controlled sample base (16), wherein the non-temperature-measuring ends of the first thermocouple (8) and the second thermocouple (9) are soldered on the copper-clad AlN substrate (12), and wires for leading out voltage test signals are also soldered on the copper-clad AlN substrate (12).

10. The vacuum variable temperature Seebeck coefficient measuring device according to claim 1, wherein, The device is configured to perform a two-dimensional scan test on the Seebeck coefficient of a sample at any temperature point between 100 and 300 K with a measurement error of less than 10%.

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