Fully automated measurement setup for non-destructive characterization of thermoelectric materials near room temperature

A measurement setup is presented that allows for a complete and non-destructive material characterization of electrochemically deposited thermoelectric material. All electrical (Seebeck coefficient α, electrical conductivity σ), thermal (thermal conductivity λ), and thermoelectric (figure of merit ZT) material parameters are determined within a single measurement run. The setup is capable of characterizing individual electrochemically deposited Bi(2+x)Te(3-x) pillars of various size and thickness down to a few 10 μm, embedded in a polymer matrix with a maximum measurement area of 1 × 1 cm(2). The temperature range is limited to an application specific window near room temperature of 10?°C to 70?°C. A maximum thermal flux of 1 W∕cm(2) can be applied to the device under test (DUT) by the Peltier element driven heat source and sink. The setup has a highly symmetric design and DUTs can be mounted and dismounted within few seconds. A novel in situ recalibration method for a simple, quick and more accurate calibration of all sensors has been developed. Thermal losses within the setup are analysed and are mathematically considered for each measurement. All random and systematic errors are encountered for by a MATLAB routine, calculating all the target parameters and their uncertainties. The setup provides a measurement accuracy of ±2.34 μV∕K for α, ±810.16 S∕m for σ, ±0.13 W∕mK for λ, and ±0.0075 for ZT at a mean temperature of 42.5?°C for the specifically designed test samples with a pillar diameter of 696 μm and thickness of 134 μm, embedded in a polyethylene terephthalate polymer matrix.     

Four-probe measurements of the in-plane thermoelectric properties of nanofilms

Measuring in-plane thermoelectric properties of submicron thin films has remained a challenging task. Here we report a method based on a suspended microdevice for four-probe measurements of the Seebeck coefficient, thermal conductivity, electrical conductivity, and thermoelectric figure of merit of patterned indium arsenide (InAs) nanofilms assembled on the microdevice. The contact thermal resistance and intrinsic thermal resistance of the 40 nm thick InAs nanofilm sample were measured by using the nanofilm itself as a differential thermocouple to determine the temperature drops at the contacts. The microdevice was also used to measure a 190 nm thick silicon dioxide (SiO(2)) film and the results were compared with those reported in the literature. A through-substrate hole under the suspended microdevice allows for transmission electron microscopy characterization of the nanofilm sample assembled on the device. This capability enables one to correlate the measured thermoelectric properties with the crystal structures of the nanofilm.     

The measurement of thermal conductivity variation with temperature for solid materials

An apparatus was designed to routinely measure the thermal conductivity variation with temperature for solid materials. The apparatus was calibrated by measuring the thermal conductivity variations with temperature for aluminum, zinc, tin and indium metals. The variations of thermal conductivity with temperature for the Zn-[x] wt.% Sb alloys (x = 10, 20, 30 and 40) were then measured by using the linear heat flow apparatus designed in present work. From experimental results it can be concluded that the linear heat flow apparatus can be used to measure thermal conductivity variation with temperature for multi component metallic alloys as well as pure metallic materials and for any kind of alloys. Variations of electrical conductivity with temperature for the Zn-[x] wt.% Sb alloys were determined from the Wiedemann–Franz (W–F) equation by using the measured values of thermal conductivity. Dependencies of the thermal and electrical conductivities on composition of Sb in the Zn–Sb alloys were also investigated. According to present experimental results, the thermal conductivity and electrical conductivity for the Zn-[x] wt.% Sb alloys decrease with increasing the temperature and the composition of Sb.     

Automated instrumentation for the determination of the high-temperature thermoelectric figure-of-merit

Here we report the fabrication of high temperature measurement instrumentation to measure the thermoelectric figure of merit. This setup facilitates the simultaneous measurement of Seebeck coefficient, thermal conductivity, and electrical resistivity required to evaluate the figure of merit. Measurement of temperature, as well as voltages using same thermocouples, simplified the design by minimizing sensors and wires. The limited number of components in the sample holder further simplify the design and make it small in size and lightweight. A dedicated thin heater has been constructed to minimize heat losses. Further, low heat loss is achieved by optimizing the insulator dimensions. To measure power delivered to the heater, the four-wire technique was used. Low cost and commonly available materials used in the fabrication of various components make it more accessible to the user as any parts can be easily replaced in case of damage. A dedicated program was built in the Python language to automate the measurement process. A p-type Bi_0.36Sb_1.45Te₃ sample was used to calibrate the instrumentation. The measured values were in good agreement with the literature results.     

探头引线热损失对TPS法测量导热系数的影响

瞬态平面热源(Transient plane source,TPS)法是一种近年来发展起来的用于测量材料导热系数的方法.在测量过程中,加热功率受到探头引线传热的影响,进而会影响导热系数的测量准确度.针对这个问题,本文研究了测量过程中探头引线热损失对加热功率的影响,推导了热损失的数学计算公式,并提出了相应的修正模型.利用hot disk热常数分析仪对不同材料进行了一系列测量实验.实验结果表明引线热损失对测量的影响随着测量材料以及测试探头尺寸的不同而发生变化.当材料的导热系数大于0.2 W/(m·K)时,探头引线热损失的影响小于0.16％,可以忽略不计;但对于低导热系数材料的测量,对引线热损失进行补偿可以有效地提高导热系数的测量准确度.     

集装箱船余热回收系统中温差发电模块的热电耦合分析

随着热电发电、热电制冷技术研究的不断深入,热电在船舶余热回收方面有了重大突破.以集装箱船余热回收系统中温差发电模块为研究对象,考虑了热电模块热端和冷端温度差存在温度变化的实际情况,运用ANSYS软件建立了热电单P-N结模型,分析了热电单元温度场的分布规律,得到了温差发电系统的输出特性,根据分析结果进行了温差发电模块用于...     

A Cell for Thermoelectric and Contact Phenomena Investigations

A cell for obtaining a large temperature gradient (up to 70 K/mm) along a sample for thermoelectric and contact phenomena investigations of a wide class of dielectric and semiconductor materials in a temperature range from 300 to 1000 K is described.     

Effect of thermal sensitivity of materials of tribojoint on friction temperature

An analytical solution of a friction-heat problem for two semi-infinite solids taking into account the temperature dependence of their thermal characteristics has been obtained. It is assumed that the specific power of friction is constant and the thermal contact of the solids is imperfect. Because of the latter assumption, the linearization of the corresponding boundary heat conduction problem carried out using the Kirchhoff transform has turned out to be incomplete. Two methods for the final linearization of this problem have been proposed, i.e., the expansion of the nonlinear function in a power series, followed by the retention of only two first terms in it, and the use of linearizing multipliers. A numerical analysis for the materials with linear dependences of the thermal conductivity and the specific heat on the temperature is carried out.     

The thermal flash technique: the inconsequential effect of contact resistance and the characterization of carbon nanotube clusters

This article presents a comprehensive mathematical treatment of the theory behind the thermal flash technique used to measure the thermal diffusivity of nanostructures. Analytical expressions predicting the temperature and its rate of change for various combinations of sample length and diffusivity confirmed that the presence of contact resistance between the heat sink/source or within a cluster of materials does not influence the measurement. Measurements on multi-walled carbon nanotube clusters provide further experimental evidence supporting the claim that contact resistance is inconsequential to this technique and yield a thermal conductivity of 2665 W/m K, which corresponds to an isolated nanotube and not the overall cluster.     

Thermal property of insulating material at cryogenic temperature

The thermal property of insulation material is essential in developing high temperature superconductor (HTS) devices operating at around liquid nitrogen temperature. Unlike metallic materials, nonmetallic materials have a thermal resistance; therefore, accurate estimate of the heat flow is difficult in the case of nonmetallic materials. In this study, a precise instrument is developed for measuring the thermal property of insulating materials over a temperature range of 30 K to approximately the room temperature by using a cryocooler. The cold head of the cryocooler is thermally anchored to the thermal link and used to cool the apparatus to a desired temperature. The temperature distribution in specimen is measured with respect to the supplied heating power, from which the thermal conductivity is calculated and compared with published data for accuracy confirmation. The effective thermal conductivity of polypropylene laminated paper (PPLP) is presented and the trend in the behavior of conductivity near liquid nitrogen temperature is also discussed.     

Thermopower detection of single nanowire using a MEMS device

We present a MEMS-based device on a silicon nitride membrane in order to measure the thermoelectric properties of a single nanowire. A temperature gradient along a nanowire was generated by a nanoheater, and the temperature was measured by Pt thermometers. A thermal simulation using a finite element method was conducted to analyze the temperature distribution over the MEMS device. The validity of the MEMS device was established by testing the Pt nanowires which had different symmetry configurations. From the test results of Pt nanowires, a convincing temperature calibration method was proposed and applied to an actual case of Bi₂Te₃ nanowire. We measured a Seebeck coefficient of −53 μV/K and electrical conductivity of 2.23 × 10⁵ S/m for a single Bi₂Te₃ nanowire with a diameter of 70 nm at 300 K. Our solid design for thermoelectric measurements based on a membrane structure enables the fast and high-yield characterization of one-dimensional nanostructures.     

3omega method to measure thermal properties of electrically conducting small-volume liquid

This work presents a method to measure the thermal conductivity and heat capacity of electrically conducting small-volume liquid samples using the 3omega technique. A mathematical model of heat transfer is derived to determine the thermal properties from the 3omega signal considering the device geometry. In order to validate the model, an experimental apparatus has been designed and set up to measure the thermal properties (thermal conductivity and heat capacity) of seven different liquid samples. The results show good agreement with other literature values, demonstrating that the suggested method is effective for measuring the thermal properties of electrically conducting liquids. More importantly, the result with a sample volume of 1 microl demonstrates the resolution of the thermal conductivity as precise as 0.01% which corresponds to a thermal-conductivity change of 10(-4) Wm K in the case of water-based solutions.     

Thermoelectric temperature control device for vapor pressure measurements

The static method of measuring equilibrium vapor pressure requires locating the sample at the coldest part of the apparatus to avoid errors due to evaporation and recondensation elsewhere. This paper describes a device that can hold the sample 1 K below the temperature of the surrounding air without a liquid bath. It comprises a pair of thermoelectric elements and two thermometers attached to an insulated aluminum block. The device can operate as high as 200?°C while controlling the sample with a precision of 0.02 K; below 110?°C, the precision is 2 mK. Also described is a method to measure the small temperature offset due to heat flow between the sample and the surrounding aluminum block. The uncertainty due to the offset is small compared to the 6 mK uncertainty due to the thermometer.     

Radiative heat losses in thermal conductivity measurements: a correction for linear temperature gradients

A method for the quantification of the radiative heat losses in a steady-state thermal conductivity measurement set-up is developed based on the Stefan–Boltzmann radiation law with the assumption of a linear temperature distribution along the specimen. The resulting expression can be applied to any regular-shaped sample with well-defined side surfaces and cross-section. Owing to the quantification of the radiative heat losses the accuracy of the steady-state thermal conductivity measurement method is improved and the measurement range can be extended to higher temperatures. An exemplary application in a commercial device is presented. The results are in an excellent agreement with the independently measured high temperature thermal conductivity.     

Highly sensitive thermal conductivity measurements of suspended membranes (SiN and diamond) using a 3ω-Völklein method

A suspended system for measuring the thermal properties of membranes is presented. The sensitive thermal measurement is based on the 3ω dynamic method coupled to a Vo?lklein geometry. The device obtained using micro-machining processes allows the measurement of the in-plane thermal conductivity of a membrane with a sensitivity of less than 10 nW/K (+∕-5 × 10(-3) Wm(-1) K(-1) at room temperature) and a very high resolution (ΔK/K = 10(-3)). A transducer (heater/thermometer) centered on the membrane is used to create an oscillation of the heat flux and to measure the temperature oscillation at the third harmonic using a Wheatstone bridge set-up. Power as low as 0.1 nW has been measured at room temperature. The method has been applied to measure thermal properties of low stress silicon nitride and polycrystalline diamond membranes with thickness ranging from 100 nm to 400 nm. The thermal conductivity measured on the polycrystalline diamond membrane support a significant grain size effect on the thermal transport.     

Thermal conductivity measurement of thin films by a dc method

A dc method, which needs no complex numerical calculation and expensive hardware configuration, was developed to measure the cross-plane thermal conductivity of thin films in this paper. Two parallel metallic heaters, which were deposited on different parts of the sample, serve simultaneously as the heaters and temperature sensors during the measurement. A direct current was flowed through the same two metallic strips to heat the thin-film sample. The heating power and the heater's temperature were obtained by a data acquisition device, and the thermal conductivity of thin film was calculated. To verify the validity of the dc method, several SiO(2) films with different thicknesses were deposited on Si wafers, respectively, and their thermal conductivities were measured by both the dc method and 3ω method. The results of two methods are in good agreement within an acceptable error, and they are also inconsistent with some of previously published data.     

A method for determining the thermal EMF and thermal conductivity

A method for measuring the thermal emf and thermal conductivity of conducting samples is described. After the temperature and potential differences are measured between the sample’s ends, on which metal contacts are deposited, at a specified direct current, the current is turned off, and instantaneous values of the integral thermal emf are measured directly at the metal contacts. Using the results from measuring the temperature and potential differences during passage of the direct current, the electrical and thermal conductivities of the sample are calculated. A specific feature of this technique is the use of additional thick metal layers being in contact with the surfaces of the metal contacts at the sample’s ends, which are aimed at stabilizing the temperature gradient along the sample when the current source is switched off.     

Multi-layer thermoelectric-temperature-mapping microbial incubator designed for geo-biochemistry applications

We demonstrate a novel, vertical temperature-mapping incubator utilizing eight layers of thermoelectric (TE) modules mounted around a test tube. The temperature at each layer of the TE module is individually controlled to simulate the vertical temperature profile of geo-temperature variations with depth. Owing to the constraint of non-intrusion to the filled geo-samples, the temperature on the tube wall is adopted for measurement feedback. The design considerations for the incubator include spatial arrangement of the energy transfer mechanism, heating capacity of the TE modules, minimum required sample amount for follow-up instrumental or chemical analysis, and the constraint of non-intrusion to the geo-samples during incubation. The performance of the incubator is experimentally evaluated with two tube conditions and under four preset temperature profiles. Test tubes are either empty or filled with quartz sand, which has comparable thermal properties to the materials in the geo-environment. The applied temperature profiles include uniform, constant temperature gradient, monotonic-increasing parabolic, and parabolic. The temperature on the tube wall can be controlled between 20 °C and 90 °C with an averaged root mean squared error of 1 °C.     

An apparatus for simultaneous measurement of electrical conductivity and thermopower of thin films in the temperature range of 300-750 K

An automated apparatus capable of measuring the electrical conductivity and thermopower of thin films over a temperature range of 300-750 K is reported. A standard dc resistance measurement in van der Pauw geometry was used to evaluate the electrical conductivity, and the thermopower was measured using the differential method. The design of the instrument, the methods used for calibration, and the measurement procedure are described in detail. Given the lack of a standard National Institute of Standards and Technology (Gaithersburg, Md.) sample for high temperature thermopower calibration, the disclosed calibration procedure shall be useful for calibration of new instruments.     

Laser flash method for measuring thermal conductivity of liquids-application to low thermal conductivity liquids

A laser flash method developed for the measurement of thermal conductivity of solids was applied to liquids of low thermal conductivity. The sample liquid was sandwiched in between a small thin metal disk and a sample holder. When the laser beam is absorbed in the front surface of the metal disk, the temperature of the disk quickly rises about 2 K and heat then flows downwards through the sample liquid as one-dimensional heat flow. The thermal conductivity of liquid can be obtained from the temperature fall of the disk without employing any reference materials and also without measuring the thickness of the sample liquid layer. Thermal conductivities of water and toluene near room temperature were measured by this method with a mean deviation of 2.6%. This laser flash method may be applied to the measurement of the thermal conductivity of liquids such as molten salts at elevated temperatures.