Development of Experimental Techniques for Thermoelectric Properties Characterization of Low-Dimensional Structures
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Development of Experimental Techniques for Thermoelectric Properties Characterization of Low-Dimensional Structures Claudiu L. Hapenciuc1, Fazeel J. Khan1, Theodorian Borca-Tasciuc1,* and Gwo-Ching Wang2 1 Mechanical and Aerospace Engineering Department, Rensselaer Polytechnic Institute 2 Department of Physics, Rensselaer Polytechnic Institute Troy, NY 12180, U.S.A.
ABSTRACT This work reports current efforts in developing experimental techniques applicable for thermoelectric properties characterization at micro and nanoscale. A one-dimensional transport model was used to asses the effects of heat leakage, non-symmetric boundary conditions, and electrical contact resistance, on thermoelectric properties measurements performed by transient Harman method. If the above effects are important, the thermoelectric figure of merit cannot be extracted directly from the ratio between the Seebeck voltage and the resistive voltage drop across the sample. On the other hand, measurements of both thermal conductivity and Seebeck coefficient can be performed if the temperature drop across the sample is acquired simultaneously with the voltage drop. The theoretical model and the experimental technique are validated by measurements performed on bulk calibration samples. Furthermore, this work shows that the spatial resolution of thermoelectric properties characterization methods can be enhanced by using scanning probe based techniques. Preliminary results are presented for Seebeck coefficient measurements of p-type or n-type calibration samples performed using an AFM probe instrumented with a temperature sensor.
INTRODUCTION Low-dimensional structures may demonstrate a large enhancement of the thermoelectric figure of merit [1], hence measurements of their thermoelectric properties is of high interest. Harman method [2] may provide a fast and reliable way to screen large numbers of samples for high thermoelectric figure of merit ZT. However, implementation of the Harman method for thermoelectric properties characterization of low-dimensional systems must consider several issues: (1) enhanced spatial and temporal resolution is needed as dimensions of the samples may range from a few microns (e.g. across the thickness of a thermoelectric film), to a few nanometers (the diameter of a nanowire); (2) nanostructures may be subjected to significant heat losses during the measurement (e.g. heat sinking effect for film-on-substrate systems, and also due to relatively large size of the electrodes); (3) electrical and thermal contact resistance between the sample and electrodes may become important. This work investigates the effect of heat leakage, non-symmetric boundary conditions, and electrical contact resistance on the Harman based characterization. Moreover, it reports preliminary results on the implementation of scanning probe techniques for thermoelectric properties measurements. A theoretical model was developed and validated by measurements *
Corresponding author. Electronic address: [email protected].
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