JP2008051744A - Method of measuring thermophysical property value of thermoelectric material, and thermoelectric material measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoelectric material measuring device and a measuring method that measure thermoelectric power distribution of the thermoelectric material and can measure thermal conductivity. <P>SOLUTION: The thermoelectric material measuring device comprises an optical camera for photographing a measured surface of a material to be measured, a probe mounted with a heating heater, a stage mechanism for mounting the material to be measured and positioning a measuring point, a controller for driving them, and a data processor for performing data processing of the measured data. The thermoelectric material measuring device collects local thermal conductivity, thermoelectric power, and surface optical image of the sample to be measured by one measurement, and analyzes the correlation between two-dimensional plane position information and the thermophysical property value. In the thermoelectric material measuring device, the measurement of the local thermal conductivity and thermoelectric power of the sample to be measured is performed by accurately estimating the surface temperature of the sample to be measured of a probe contact point using heat flow measured by a minute heat flow meter incorporated into a heated probe. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method and a thermoelectric material measuring apparatus for measuring a thermophysical value of a thermoelectric material in order to evaluate a thermophysical value of a minute region of a conductive material that is a thermoelectric material.

  The thermoelectric conversion material is a general term for substances that express the Seebeck effect and the Peltier effect and perform mutual energy conversion between heat and electricity. When a temperature difference is applied to this special material, a potential difference is generated inside the material, and by extracting this potential difference to an external circuit, power can be extracted at the external load part. Can be configured. For this reason, developing a thermoelectric material having high power generation performance at the same temperature difference is an important issue in the field today.

The performance of thermoelectric materials is generally the thermoelectric figure of merit Z
Z = S ² / (ρκ)
It is expressed by Here, S is thermoelectric power, ρ is electrical resistivity, and κ is thermal conductivity. A large thermoelectric figure of merit Z has high power generation performance and can generate more power for the same heat input, so the thermoelectric power, resistivity, and thermal conductivity can be finely adjusted to optimize the material. Many experiments have been attempted.

  Here, the thermoelectric power S and the thermal conductivity κ are important factors that determine the thermoelectric performance index. That is, in the performance evaluation of thermoelectric materials, it is necessary to quantitatively determine these physical property values at a certain temperature. In general, for example, thermoelectric power is determined by a steady two-terminal method, and heat conduction Regarding the rate, each physical property value is determined by a laser flash method.

  However, the general thermoelectric power measurement method and thermal conductivity measurement method as described above are measurement methods that can be applied only to a homogeneous bulk material, for example, 3 mm × 3 mm × 15 mm, or diameter 10 mm × thickness 1 mm. This is a measurement method for determining a physical property value under the assumption that the inside of the sample having the shape is completely homogeneous. In an actual sample, in order to verify whether this assumption of homogeneity holds, a method for measuring thermoelectric power having a finer position resolution of several microns to several tens of microns, and a method for measuring thermal conductivity It was necessary to measure using

  In addition, from the viewpoint of material development, thermoelectric materials with optimized microstructures and nanostructures may have improved performance due to reduced thermal conductivity or changes in the electronic structure. It is necessary to verify whether such a microcomposite material is actually synthesized as designed, and for that purpose, a thermoelectric power measurement method having a finer position resolution of several microns to several tens of microns, and heat conduction Measurement using the rate measurement method was necessary.

Several examination examples and inventions have already been made for techniques related to heat measurement in such a fine region. For example, STHM (Scanning Thermal Microscope) technology (Non-Patent Document 1) that measures thermal images using AFM (Atomic Force Microscope) technology and temperature information on the sample surface is collected using a thermocouple with a narrow tip as a cantilever. STP (Scanning Thermal Profiler) method (non-patent document 2) used for surface shape measurement has been proposed, and thermal probe method (non-patent document 3, non-patent document 3,) Patent Document 1) has been proposed.
ScanningNear-Field Optical Microscopy and Scanning Thermal Microscopy; Jpn.J.Appl.Phys.Vol. 33, pp.3785-3790 (1994); RJ Pylkki, PJ Moyer and PE West. Scanning ThermalProfiler; Appl. Phys. Lett., Vol. 49, No. 23, pp. 1587-1589 (1986); CCWilliams and HK Wickamasinghe. Sussmann, etal., Proc. 12th Int. Conf. On Thermoelectrics, Yokohama, 86 (1993). JP 2004-003872 A

  However, in the measurement method using STM (Scanning Tunneling Microscope) or AFM (Atomic Force Microscope) technology, the tip of the sample to be measured is not slender and the cantilever is very close to the sample. When the cantilever is heated for scanning, the sample is heated by radiation and is subject to drift, and it is difficult to give a large temperature gradient to any local point of the sample. In addition, there is a problem in that it cannot be used for the purpose of measuring the thermoelectric power distribution of a thermoelectric material because it does not have a function for outputting local thermoelectric power nor an analysis algorithm.

  The thermal probe method, which was developed for the purpose of analyzing micro regions of thermoelectric materials, is the only measurement method that can simultaneously analyze the thermoelectric power distribution and thermal conductivity distribution, but the heating probe used in this measurement method is a sheath. There is a problem that the surface temperature of the sample at the point where the probe is in contact with the temperature of the tip of the probe measured by the sheath thermocouple does not match.

FIG. 1 is a diagram for explaining a measurement method by a conventional thermal probe method. In the conventional thermal probe technique, as shown in FIG. 1, a metal probe provided with a heater is brought into contact with the material to be measured, and the surface of the material to be measured by a thermocouple provided at the tip of the probe. In the estimation of the local thermoelectric power of the sample by measuring the temperature, the thermoelectric power S is obtained by the following equation. That is,
S = V / (T _tip −T ₀ ) = V / (T _surf −T ₀ )
To obtain the thermoelectric power S. However, at that time, there is a temperature difference at the time of measurement between the temperature T _tip at the thermocouple at the probe _tip and the surface temperature T _{surf of the} material to be measured, and always T _tip > T _surf, and the amount of this difference It is clear that “T _tip −T _surf ” is about several K, which is a temperature difference that cannot be ignored. This led to an underestimation of the thermoelectric power, which was a problem that cannot be ignored as an error in the measurement aimed at quantitative mapping of the local thermoelectric power and thermoelectric power distribution of the thermoelectric material.

  Therefore, in the measurement of thermoelectric power distribution and thermal conductivity distribution by the conventional thermal probe method described above, data is collected after confirming that the temperature is in a steady state after the heated probe contacts the sample surface. The method to be adopted is adopted. This means that a waiting time of several seconds to several tens of seconds is actually required, and causes a long measurement time for mapping measurement that requires measurement at a large number of measurement points such as 1000 points and 10000 points. It was. For this reason, when considering the practicality, an increase in measurement speed that shortens the measurement time emerges as one important issue to be solved.

  In addition, providing a long waiting time after the heating probe contacts the sample surface means that the temperature gradient spreads in the vicinity from the point of contact over time, and as a result, the position resolution of thermoelectric power and thermal conductivity is reduced. Another problem is that it will be lowered.

  The above-described conventional measurement method and apparatus using the thermal probe method are difficult techniques in the sense that the probe is brought into contact with any desired point on the sample surface. In other words, it is difficult to contact the probe with the desired measurement position by visual inspection, assuming a measurement of a small area of several to several tens of microns. It is clear which part of the actual sample corresponds to the mapping measurement result. A mechanism to make it necessary was necessary.

  The present invention has been made to overcome the above-described problems of the prior art, and an object of the present invention is to provide a method for measuring a thermoelectric material that is highly quantitative and practical. Specifically, it is to provide a thermoelectric material measuring apparatus and a measuring method capable of measuring a thermoelectric power distribution of a thermoelectric material and measuring a thermal conductivity.

That is, the problem to be solved by the present invention is specifically,
(1) A problem that a sample surface is heated under the influence of radiation when a heater for heating the probe comes close to the sample, and the image is affected.
(2) A problem that a temperature difference occurs between the sample surface temperature and the probe tip temperature, resulting in a temperature measurement error, leading to an underestimation of thermoelectric power,
(3) In the existing measurement apparatus, the problem that the measurement time per point is long and the measurement time required to take a distribution image of thermophysical property values is long,
(4) The problem of poor position resolution of thermoelectric power and thermal conductivity,
(5) The problem that the correspondence between the local measurement position of the thermophysical property value and the position on the actual sample cannot be easily confirmed,
Therefore, in order to solve these problems, the present invention has been made through experimental studies.

  In order to solve the above problems, the thermoelectric material measuring apparatus according to the present invention includes an optical camera for photographing a measurement surface of a material to be measured, a probe equipped with a heater, and a measurement point by placing the material to be measured. It is equipped with a stage mechanism for positioning, a control device for driving these, and a data processing device for data processing of measurement data, and collects local thermal conductivity, thermoelectric power, and surface optical images of the sample to be measured in one measurement. This is a thermoelectric material measuring device that analyzes the correlation between two-dimensional plane position information and thermophysical property values. Using this thermoelectric material measuring device, the local thermal conductivity, thermoelectric power, and surface optical image of the sample to be measured are obtained. In a thermophysical property measurement method that collects a single measurement and analyzes the correlation between two-dimensional plane position information and thermophysical property values, a surface optical image of the material to be measured is captured by the optical camera, and the probe is scanned by the probe. A local thermal conductivity and thermoelectric power of a fixed sample are measured, and the two-dimensional plane is correlated with the local thermal conductivity, thermoelectric power and surface optical image of the measured sample measured by the data processing device. Analyzes the correlation between position information and thermophysical values.

  In this case, based on the heat flow data measured by the micro heat flow meter incorporated in the probe, the data processing device performs data processing for estimating the surface temperature of the sample to be measured at the probe contact point, and the estimated surface Based on the temperature, the measurement data of the local thermal conductivity and thermoelectric power of the sample to be measured are processed. In the measurement of local thermal conductivity and thermoelectric power of the sample to be measured, a micro heat flow meter built into the probe is used, and the surface temperature of the sample to be measured at the probe contact point is determined by the heat flow measured by the micro heat flow meter. Estimate accurately.

  Here, the structure of the probe of the thermoelectric material measuring apparatus is such that a heater attached to heat the probe is attached to the probe at least 5 mm vertically above the point where the tip of the probe contacts the surface of the sample to be measured. It is said that the structure. Further, the probe is fixed to a cantilever beam extending in the horizontal direction from the vertical probe moving mechanism, and means for estimating the pressure applied to the probe by measuring the deflection amount of the cantilever is provided. Provided.

  The micro heat flow meter incorporated in the probe is composed of an elongated substance having a known thermal conductivity and two thermocouples fixed on the elongated substance at a certain distance.

  When local thermal conductivity and thermoelectric power are measured with this probe, measurement data is obtained by contact of the probe, so that the local thermal conductivity, thermoelectric power, and surface optical image of the sample to be measured are 1 It is collected by measuring the degree, and the correlation between two-dimensional plane position information and thermophysical property value is analyzed. Data processing for this is performed by program processing by a data processing device. The program for estimating the thermal conductivity estimates the relative thermal conductivity and outputs the time-dependent data of the temperature gradient in the longitudinal direction of the heating probe immediately after the heating probe contacts the sample surface. Perform the process. This functional means is provided by installing the program in a data processing device that performs data processing of measurement data.

  In addition, in the program for estimating the thermoelectric power, the time change data of the temperature gradient in the longitudinal direction of the heating probe and the temperature at the temperature measurement point fixed on the elongated heating probe immediately after the heating probe contacts the sample surface. , And the time change of the potential difference between the probe contact portion and the other reference point of the sample to be measured are input, and the thermoelectric power is estimated and output. This functional means is provided by installing the program in a data processing device that performs data processing of measurement data.

In the thermoelectric material measuring apparatus according to the present invention, the problems in the conventional thermal probe method are solved as follows by having the above-described configuration.
That is,
(1) Collect the local thermal conductivity, thermoelectric power and surface optical image of the sample to be measured in one measurement, and correlate the coordinates on the optical image captured in the personal computer with the actual probe contact coordinates on the sample. With the reproducibility of micrometer size, it is possible to reliably measure any desired position on the actual measurement sample surface,
(2) In the above measurement, the measurement of the local thermal conductivity and thermoelectric power of the sample to be measured is performed by using a micro heat flow meter incorporated in the heated probe, and the surface of the sample to be measured at the probe contact point. Measure temperature accurately,
(3) In the probe, a small heater attached to heat the probe is attached at least 5 mm vertically from the point where the tip of the probe contacts the surface of the sample to be measured. Consideration is made so that the sample to be measured is not heated by convection,
(4) The probe is fixed to a metal cantilever extending horizontally from the vertical probe moving mechanism, and the pressure applied to the probe is estimated by measuring the deflection of the cantilever. To be able to
(5) The micro heat flow meter incorporated in the probe is composed of an elongated substance having a known thermal conductivity and two thermocouples fixed on the elongated substance at a certain distance,
(6) In the data processing for estimating the thermal conductivity, the relative thermal conductivity is obtained by inputting the time change data of the temperature gradient in the longitudinal direction of the heating probe immediately after the heating probe contacts the sample surface. Using a program that estimates and outputs this data,
(7) In the data processing for estimating the thermoelectric power, the time change data of the temperature gradient in the longitudinal direction of the heating probe immediately after the heating probe contacts the sample surface and the elongated heating probe were fixed. A program that estimates and outputs the thermoelectric power using the time change data of the temperature at the temperature measurement point and the time change of the potential difference between the probe contact part and another reference point in the sample to be measured as inputs. To process the data.

  As a result, the above-described problems are solved, and a measurement method capable of simultaneously measuring thermal conductivity and thermoelectric power with high accuracy in a short time as compared with the measurement method and measurement apparatus of the conventional thermal probe technique is provided. Is done.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. FIG. 2 is a schematic diagram for explaining the configuration of the measuring device of the thermoelectric material measuring device of the present invention. FIG. 3 is a diagram for explaining in detail the configuration of the heating probe in the thermoelectric material measuring apparatus of the present invention.

  Next, the configuration of the measuring device part of the thermoelectric material measuring device will be described with reference to FIGS. In FIG. 2, 1 is a sample holder, 2 is a probe, 3 is a heater, 4 is a support member for supporting the probe and the heater, 5 is a mirror for distance measurement, 6 is a cantilever, and 7 is a laser. A distance meter, 8 is a stage (Z-axis moving stage), 9 is a support, and 10 is a sample to be measured. In FIG. 3, 2 is a probe, 3 is a heater, 4 is a support member, 14 is a first thermocouple for measuring a first temperature upstream of the probe heat flow, and 15 is a downstream of the probe heat flow. A second thermocouple 16 for measuring the second temperature, and a third thermocouple 16 for measuring the surface temperature of the sample to be measured.

  As shown in FIG. 2, the heater 3 and the probe 2 are held on the support member 4, and below the sample, the sample 10 to be measured has good thermal and electrical contact. It is fixed to the holder 1. The sample holder 1 is made of a conductive material having good thermal conductivity such as copper or aluminum and having a uniform temperature. Since the sample holder 1 serves as one reference electrode when measuring the thermoelectromotive force, a metal material having low thermoelectric power is used as the material of the sample holder 1. The sample holder 1 is fixed to a biaxial motor and a linear guide (not shown), and a mechanism that can freely move on the XY plane is provided. The probe 2 scans the sample 10 to be measured while repeating contact on / contact off at the tip thereof, and repeats the operation of measuring the sample 10 to be measured. In addition, a small heater 3 is attached to the probe 2 so that a predetermined amount of heat for measurement is supplied. These measurements are controlled by controlling the movement of the stage 8 and the sample holder 1 by a control unit (not shown).

  The probe 2 is configured so that the length of the metal probe portion is 10 mm or more, and the measurement is performed with a sufficient distance between the heater 3 for heating and the sample 10 to be measured. It is manufactured in a shape that can be performed, and is configured so that the surface of the sample is not heated by an effect such as thermal convection.

  The probe 2 and the heater 3 are fixed to the cantilever 6 by a support member 4. The support member 4 is made of a rod-like material having poor thermal conductivity and is thermally insulated. Each member of the probe 2, the heater 3, the support member 4, and the cantilever 6 is mechanically firmly fixed, and is configured to transmit the displacement of the probe contact point to the cantilever 6 as it is. That is, the cantilever beam 6 bends upward when the probe 2 contacts the surface of the sample 10 to be measured without easily twisting or bending the support member 4, the heater 3, and the probe 2. It is said that the structure plays a role. The displacement at this time can be accurately quantified in units of 1 micron by measuring the position of the mirror 5 mounted on the cantilever 6 with a laser distance meter 7.

  Based on the quantified displacement, the pressure applied to the tip of the probe 2 is estimated from this displacement and the rigidity of the material constituting the cantilever 6. Both the cantilever beam 6 and the laser distance meter 7 are fixed to a Z-axis moving stage 8, and the Z-axis moving stage 8 moves up and down smoothly along the support column 9 by driving a motor.

  In order to freely move the sample holder 1 on which the sample 10 to be measured 10 is fixed on the XY plane and to freely move the probe 2 in the vertical direction, the drive control of the X axis, the Y axis, and the Z axis is as follows: It is controlled by a control unit (not shown). Positioning is controlled by automatic control by a computer. As for the positioning control operation for moving the X axis, the Y axis, and the Z axis for scanning the probe in three dimensions, if the movement of the probe 2 relative to the sample to be measured is relatively similar, The motor may be installed in any part and may be configured to move.

  By adopting such a configuration, heating for measurement that can position the arbitrary sample while scanning the surface of the sample to be measured 10 on the XY plane and heat the sample to be measured for measurement. A probe is provided. Furthermore, by adopting this configuration, it is possible to measure the amount of displacement of the probe up and down and the pressure applied to the probe. Moreover, since the position of the heater 3 for heating is far from the sample, it is possible to avoid a situation in which the entire sample to be measured is warmed and the sensitivity of the local heating response is lowered.

  Referring to FIG. 3, an enlarged schematic view of the portion of the probe 2 heated by the heater 3 is shown. The probe 2 has a sharp tip with a radius of curvature of about 10 to 50 microns, which is desirable in terms of improving the position resolution. Use a probe with a larger radius. The sample 10 to be measured measures a mechanically strong and rigid thin metal rod-like material. However, if the thermal conductivity is known and there is a conductor portion that draws the potential of the probe contact point, the surface A ceramic material or the like provided with a wiring for extracting a potential can also be measured as a sample to be measured. Heat is transmitted from the heater 3 to the probe 2, and the heat is transmitted to the material to be measured 10 via the probe 2, and in the direction of the heat flow, the first thermocouple 14 and the second thermocouple 15 Two thermocouples are provided. By measuring the temperature at two points with these two thermocouples, the probe 2 to which the heat flow is transmitted has a known thermal conductivity and length and cross-sectional area of the material, so the first thermocouple 14 and The amount of heat flowing through the probe 2 can be estimated by measuring the temperature at two points with the second thermocouple 15, and this is used for measurement data processing.

ここで、図３に示すように、Ｌは第１の熱電対１４および第２の熱電対１５の間の距離、Ｍは第２の熱電対１５とプローブ２の先端との距離である。このようにして、プローブ２の接触点の表面温度を推定できるため、プローブ２の先端部分に熱電対や温度センサを作り込む必要がなく、測定装置の構成がシンプルになる。また、プローブ２の熱容量や先端の径を小さくすることができるので、装置の設計上の利点となる。 The first thermocouple 14 and the second thermocouple 15 have a certain temperature difference due to the balance of heat transfer such as radiation, heat transfer, and convection, but when the probe 2 comes into contact with the surface of the sample 10 to be measured. As the heat flow increases, the temperature difference between the first thermocouple 14 and the second thermocouple 15 increases, but the temperature at the tip of the probe 2 at this time is calculated by the following equation. Desired.

Here, as shown in FIG. 3, L is the distance between the first thermocouple 14 and the second thermocouple 15, and M is the distance between the second thermocouple 15 and the tip of the probe 2. In this way, since the surface temperature of the contact point of the probe 2 can be estimated, there is no need to make a thermocouple or a temperature sensor at the tip of the probe 2, and the configuration of the measuring apparatus is simplified. Further, since the heat capacity of the probe 2 and the diameter of the tip can be reduced, this is an advantage in designing the apparatus.

この熱流は、被測定試料１０の表面のプローブ接触点の近傍の熱伝導率と強い相関があるので、この熱流を定量的に計測することにより、被測定試料１０の表面のプローブ接触点近傍の局所熱伝導率の推定を演算処理により行うことができる。 When a sheathed thermocouple is used as in the conventional thermal probe method, a finite thermal resistance is generated between the actual temperature measurement point of the thermocouple and the sample / probe contact point, resulting in a temperature measurement error. However, in this way, a measurement method that estimates the heat flow using two thermocouples and a conductor whose material and thermal characteristics are known to estimate the temperature at the tip reduces the error and improves the accuracy. There is an advantage that the sample surface temperature can be measured. Assuming the thermal conductivity κ of the material of the probe 2, the heat flow flowing through the probe 2 can be obtained by the following equation.

This heat flow has a strong correlation with the thermal conductivity in the vicinity of the probe contact point on the surface of the sample 10 to be measured. Therefore, by quantitatively measuring this heat flow, the heat flow near the probe contact point on the surface of the sample 10 to be measured is measured. Local heat conductivity can be estimated by arithmetic processing.

  Although an example of heat flow measurement using two thermocouples is shown here, the present invention is not limited to the use of a thermocouple as long as the heat flow flowing through a thin probe can be accurately estimated. That is, a sensor using a semiconductor can be substituted for the sensor, and the sensor can be incorporated in a small size, can measure a heat amount of several tens of microwatts to several tens of milliwatts, and has a temperature corresponding to the second thermocouple 15. If it can measure, it will not be restricted to said structure.

FIG. 4 shows the time change of the temperature difference “T ₁ -T ₂ ” calculated from the thermoelectric power V / (T ₁ −T ₂ ) obtained when the heating probe contacts the sample surface and the thermocouple for measuring the heat flow. This is a graph showing the time-dependent characteristics of measured data. For example, at t _0, it indicates that the probe has come into contact with the sample surface, and since the heat flow flowing from the probe to the sample gradually increases, the temperature difference also increases. This increase in heat flow can be quantified simply as the slope of the linear approximation of the part after t ₀ , that is, the rate of increase in temperature difference. The larger the inclination, the more heat is injected into the sample to be measured, which corresponds to the higher thermal conductivity at the probe contact point. Therefore, the local thermal conductivity can be estimated by utilizing the correlation between the rising speed of the temperature difference and the thermal conductivity. In the present invention, it is configured to estimate the local thermal conductivity using the temperature of the probe tip and the time change of the heat flow flowing from the probe to the sample, thereby comparing with the conventional thermal probe method, Measurement reproducibility and stability are ensured.

In the graph of FIG. 4, the vertical axis represents the thermoelectric brain “S = V / {T ₂ − (T ₁ −T ₂ ) M / L−T ₃ }”, and the horizontal axis represents time t. This graph shows the change in thermoelectric power over time, but a large or small thermoelectric power is observed immediately after the probe contact due to the existence of a finite thermal resistance between the probe and the sample surface. It shows a tendency to settle down. This is considered to be because the situation where the heat stays in the immediate vicinity of the probe contact position is realized in a short time immediately after the contact. In order to increase the position resolution of local thermoelectric power measurement, it is important to measure the thermoelectromotive force and temperature difference in this short time. Depending on the thermal conductivity of the sample to be measured, if the measurement is performed after waiting for one second or several seconds or more, the heat diffuses over the wide range, the position resolution is deteriorated, and the measurement time is greatly increased. Therefore, immediately after the probe contact, the temperature difference “{T ₂ − (T ₁ −T ₂ ) M / L−T ₃ }” and the electromotive force V are measured.

  FIG. 5 is a diagram for explaining the positional relationship of the optical image capturing device in the thermoelectric material measuring device of the present invention. In FIG. 5, 21 is an X-axis moving stage, 22 is a sample holder, 24 is an optical camera, and 25 is a sample to be measured. FIG. 5 shows an arrangement relationship between the optical camera 24 as an optical image data collection device and the probe 2 for measuring thermoelectric power and thermal conductivity. Although not shown, the Z-axis moving stage of the probe 2 and the optical camera 24 are fixed to the same structure (supporting member), and the optical image data of the surface of the sample to be measured by the optical camera 24 while maintaining the same positional relationship. And the measurement data of the thermoelectric power and the thermal conductivity in the local region by the heated probe 2 are simultaneously performed.

  The moving distance of the X-axis moving stage 21 is larger than that of a Y-axis moving stage (not shown) so that the sample 25 to be measured and the sample holder 22 can move back and forth between the probe 2 and the camera. . The image captured by the optical camera 24 is taken into a data processing device (personal computer), and the coordinates (Xc, Yc) on the image and the actual coordinates (Xp, Yp) at which the probe contacts the sample 25 to be measured are taken. To establish a correspondence between the optical image and the actual measurement location. For example, an image captured by a personal computer of a data processing apparatus is displayed on the display, and a stage is driven by the control device by designating one point on the image. Drive the X-axis and Y-axis, acquire data to estimate the local thermoelectric power or local thermal conductivity of the desired local region, perform data processing, and measure the local thermoelectric power or local thermal conductivity of the thermoelectric material be able to. The measured local thermoelectric power or local thermal conductivity is mapped by data processing and displayed as a thermoelectric power distribution and a thermal conductivity distribution. These data processes will be described in the embodiments described later.

  Next, an example of a measuring method in the case of measuring the thermoelectric power and thermal conductivity of the thermoelectric material using the thermoelectric material measuring apparatus according to the present invention will be described. The present invention is not limited to the following examples.

[Example 1]
(1) In order to measure the distribution of the thermoelectric power and thermal conductivity of the bismuth tellurium alloy produced by the melt solidification method, the measurement was performed using an apparatus having the same configuration as that shown in FIGS.
(2) The bismuth tellurium alloy has a diameter of 20 mm and a thickness of 1 mm, and 200 points × 200 points were measured at intervals of 120 microns on the bismuth tellurium alloy.
(3) The probe uses a 0.25 mm diameter alloy rod, the tip of which is sharpened to a radius of curvature of 50 μm or less, and the thermocouple corresponding to 15 and 14 in FIG. Is fixed in a thermally good form. As the thermocouple, an ultra-fine type K-type thermocouple was used. The heating value of the heater was 120 mW. The material of the cantilever was an aluminum alloy, a length of 40 mm, a width of 30 mm, and a thickness of 1 mm.
(4) Data is collected by sampling 1000 times per second, temperature T ₁ , T ₂ , T ₃ every millisecond, potential V between the probe tip and the sample holder, displacement of the probe cantilever, These are the objects of data analysis.
(5) The probe is pushed in by 50 microns after contacting the sample, and S = V / {T ₂ − (T ₁ −T ₂ ) M / L− by using data when 0.5 second has elapsed after contact. Thermoelectric power was determined in the form of T ₃ }. Further, the thermal conductivity was obtained by linear approximation of the rate of increase in the heat flow of the probe, and the value was constituted by standard sample measurement, and was estimated as the thermal conductivity (W / mK).

  FIG. 6 shows the measurement results of the thermal conductivity distribution (top) and the thermoelectric power distribution (bottom). In the measurement of thermal conductivity, although noise is present in the horizontal direction, it can be seen that the distribution of thermal conductivity and thermoelectric power due to the compositional unevenness of the sample is clearly confirmed, and the thermoelectric power distribution is measured.

[Example 2]
In order to show that the present invention is advantageous in terms of quantitativeness over the thermal probe method using a sheathed thermocouple of the prior art as a probe, an example in which a thermoelectric material is measured will be described.
(1) The thermoelectric power of the cobalt antimony tellurium alloy, which is a thermoelectric material, was measured. The measurement conditions were the same as in Example 1 except that the scanning interval for measurement was 20 micron. The measurement results are shown in Table 1.

  In the measurement by the conventional thermal probe method using the sheath thermocouple type (FIG. 1), the temperature indicated by the sheath thermocouple becomes higher than the actual surface temperature, and as a result, the thermoelectric power tends to be underestimated. It can be seen that according to the measurement method of the present invention provided with a heat flow meter, the measurement error of the thermoelectric power of the thermoelectric material is small and good quantitative performance is realized.

[Example 3]
A case where it is necessary to acquire and analyze time-varying data in local thermoelectric power measurement will be described. An example for this will be shown. FIG. 7 shows the measurement result of the cobalt antimony tellurium alloy, which is the same as the sample measured in Example 2. When the probe comes into contact with the sample and the cantilever floats 0.02 mm (-0.02 mm), a trigger is applied to collect data for 0.5 seconds at a sampling period of 1000 Hz.

Looking at the graph of the time variation of thermoelectric power shown in the third part of FIG. 7, once (after 0.15 seconds), the absolute value of thermoelectric power shows a maximum value of 140 μV / K, and then settles to 133 μV / K. I understand that. The thermoelectric power at room temperature of this material was separately measured by a reliable steady-state method and confirmed to be −140 μV / K. That is, the value of thermoelectric power at each time is expressed as S = V / {T ₂ − (T ₁ −T ₂ ) M / L−T ₃ } in the model in FIG.
It is understood that it is possible to estimate the thermoelectric power close to the true value by analyzing the time change of this value and calculating the maximum value of the thermoelectric power.

[Example 4]
For local thermal conductivity measurements on copper, titanium and cobalt antimony tellurium alloys, there is a fixed relationship between the rate of heat flow increase and thermal conductivity, and this allows us to experiment with specific relationships. It is explained that it can be used as a method for estimating the local thermal conductivity.

FIG. 8 shows the relationship between the heat flow increase rate shown in FIG. 4, that is, the time dependency of the temperature difference increase between the two thermocouples incorporated in the probe, and the thermal conductivity of the sample. When the thermal conductivity of the _sample is κ _sample and the rate of increase in heat flow is χ, there is a clear correlation between them.
Log (κ _sample ) = aχ + b
Can be approximated by Here, a and b are fitting parameters. Thus, by measuring a known material in advance and creating a calibration curve, it is possible to measure the local thermal conductivity with excellent quantitative properties.

[Example 5]
A program for performing data processing for estimating a physical property value from time change data shown in the third embodiment will be described. This program is created by “LabVIEW 7.1” operating on Windows XP. This program (subroutine) accepts as input a numerical value of 6 columns × 1000 rows transferred in a spreadsheet format. The first column of this data column is time information, the second column is probe displacement (mm), the third column is thermoelectromotive force (V), the fourth column, the fifth column, and the sixth column are T ₁ and T ₂ , respectively. , T ₃ temperature (° C.). These data are received, and the evaluation value at a certain time inside is S = V / {T ₂ − (T ₁ −T ₂ ) M / L−T ₃ }
This value is output as an estimated value of thermoelectric power. This subroutine is called every time one point measurement is performed, performs data processing for estimating the thermoelectric power, and passes the value to the two-dimensional mapping routine. In the two-dimensional mapping routine, an image indicating the distribution of thermoelectric power is generated and output according to the information on the position of the measurement point.

[Example 6]
A program for performing data processing for estimating a physical property value from time change data shown in the fourth embodiment will be described. This program is created by “LabVIEW 7.1” operating on Windows XP. This program (subroutine) accepts as input a numerical value of 6 columns × 1000 rows transferred in a spreadsheet format. The first column of this data column is time information, the second column is probe displacement (mm), the third column is thermoelectromotive force (V), the fourth column, the fifth column, and the sixth column are T ₁ , T ₂ and the temperature of T ₃ (° C.). This program receives these data, graphs the time dependence of T ₁ -T ₂ based on these data, and returns the slope of the linear approximation as an output. Also, using calibration data created in advance and stored in a table, the gradient obtained by approximating the straight line is converted into thermal conductivity and returned as a subroutine output. This subroutine is called for each point measurement to estimate the thermal conductivity and pass the value to the two-dimensional mapping routine. In the two-dimensional mapping routine, an image showing the thermal conductivity distribution is generated and output according to the position information of the measurement points.

[Example 7]
Examples of how the present invention contributes to speeding up the measurement are shown below. FIG. 9 shows a comparative example in the case where 50 × 50 = 2500 points of thermoelectric power distribution measurement is performed using a conventional thermal probe method and the same measurement is performed using the apparatus of the present invention. About the quantitative property of the measurement, the result was almost the same as in Example 2. As can be seen from Table 2, the measurement time is about 1/5, and it can be seen that the high-speed measurement has been achieved.

It is a figure for demonstrating the measuring method by the conventional thermal probe method. It is a schematic diagram for demonstrating the structure of the measuring apparatus of the thermoelectric material measuring apparatus of this invention. It is a figure for demonstrating in detail the structure of the heating probe in the thermoelectric material measuring apparatus of this invention. It is a figure explaining the characteristic of the time dependence of measurement data. It is a figure explaining the positional relationship of the optical image capture device in the thermoelectric material measuring apparatus of this invention. It is a measurement result data of thermal conductivity distribution and thermoelectric power distribution of a bismuth tellurium alloy. It is a figure which shows the characteristic data of the time dependence of measurement data. It is a figure which shows the relationship between thermal conductivity and a measured value (heat flow increase rate).

Explanation of symbols

1 Sample holder 2 Probe 3 Heating heater 4 Support member 5 Mirror 6 Cantilever 7 Laser distance meter 8 Stage (Z-axis moving stage)
9 Column 10 Sample to be measured 14 First thermocouple 15 Second thermocouple 16 Third thermocouple 21 X-axis moving stage 22 Sample holder 24 Optical camera 25 Sample to be measured

Claims (8)

An optical camera that images the measurement surface of the material to be measured, a probe equipped with a heater, a stage mechanism that places the material to be measured and positions the measurement point, a controller that drives these, and data processing of measurement data A data processing device to perform,
A thermoelectric material measuring apparatus that collects local thermal conductivity, thermoelectric power, and surface optical images of a sample to be measured in one measurement and analyzes the correlation between two-dimensional plane position information and thermophysical properties. Using the thermoelectric material measuring apparatus according to claim 1, the local thermal conductivity, thermoelectric power, and surface optical image of the sample to be measured are collected in one measurement, and the correlation between the two-dimensional plane position information and the thermophysical property value is collected. A thermophysical property measurement method for analyzing
Taking a surface optical image of the material to be measured with the optical camera,
Measure the local thermal conductivity and thermoelectric power of the sample to be measured with the probe,
In correspondence with the local thermal conductivity, thermoelectric power and surface optical image of the sample to be measured measured by the data processing device,
A thermophysical value measurement method characterized by analyzing a correlation between two-dimensional plane position information and thermophysical property values. In the thermophysical property value measuring method according to claim 2,
Based on the heat flow data measured by the micro heat flow meter incorporated in the probe, the data processing device performs data processing for estimating the surface temperature of the sample to be measured at the probe contact point, and based on the estimated surface temperature. A method for measuring a thermophysical property value, wherein the measurement data of the local thermal conductivity and thermoelectric power of the sample to be measured are processed. In the thermoelectric material measuring apparatus according to claim 1,
A thermoelectric material measuring apparatus, wherein the heater attached to heat the probe is attached to the probe at least 5 mm away vertically from the point where the tip of the probe contacts the surface of the sample to be measured. In the thermoelectric material measuring apparatus according to claim 1,
The probe is fixed to the cantilever beam extending in the horizontal direction from the vertical probe moving mechanism,
A thermoelectric material measuring apparatus comprising: means for measuring a deflection amount of the cantilever and estimating a pressure applied to the probe. In the thermoelectric material measuring apparatus according to claim 1,
The micro heat flow meter incorporated in the probe is composed of an elongated substance having a known thermal conductivity and two thermocouples fixed on the elongated substance at a certain distance. Material measuring device. In the thermoelectric material measuring apparatus according to claim 1,
Data processing devices that perform data processing of measurement data include
A program that installs a program that functions as a means to estimate the relative thermal conductivity and output the time-dependent data of the temperature gradient in the longitudinal direction of the heating probe immediately after the heating probe touches the sample surface. A thermoelectric material measuring device characterized by comprising: In the thermoelectric material measuring apparatus according to claim 1,
Data processing devices that perform data processing of measurement data include
The time variation data of the temperature gradient in the longitudinal direction of the heating probe immediately after the heating probe contacts the sample surface, the time variation data of the temperature at the temperature measurement point fixed on the elongated heating probe, and the probe contact portion A thermoelectric material measuring apparatus, in which a program is installed that functions as a means for estimating and outputting thermoelectric power by inputting a time change of a potential difference with another reference point of a sample to be measured.

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