Determining absolute Seebeck coefficients from relative thermopower measurements of thin films and nanostructures

Mason, S. J.; Hojem, A.; Wesenberg, Devin; Avery, Azure D.; Zink, B. L.

doi:10.1063/1.5143447

Cited by 19 publications

(11 citation statements)

References 80 publications

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“…This manipulation of S via geometric constraints has been used to produce single-metal thermocouples (10,11) and is often attributed to the change of the electronic mean free path due to increased surface scattering. The Mott-Jones relation has been used to relate this change of electronic mean free path to the absolute Seebeck coefficient as a function of film thickness in platinum thin films (12) and in Au, AuPd, and Cr/Pt films on silicon-nitride membranes (13). However, recent scanning PTE studies indicate that polycrystalline metal nanowires possessing uniform thickness and width exhibit substantial variation of the local S (14).…”

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confidence: 99%

Thermoelectric response from grain boundaries and lattice distortions in crystalline gold devices

Evans

Yang

Gan

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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The electronic Seebeck response in a conductor involves the energy-dependent mean free path of the charge carriers and is affected by crystal structure, scattering from boundaries and defects, and strain. Previous photothermoelectric (PTE) studies have suggested that the thermoelectric properties of polycrystalline metal nanowires are related to grain structure, although direct evidence linking crystal microstructure to the PTE response is difficult to elucidate. Here, we show that room temperature scanning PTE measurements are sensitive probes that can detect subtle changes in the local Seebeck coefficient of gold tied to the underlying defects and strain that mediate crystal deformation. This connection is revealed through a combination of scanning PTE and electron microscopy measurements of single-crystal and bicrystal gold microscale devices. Unexpectedly, the photovoltage maps strongly correlate with gradually varying crystallographic misorientations detected by electron backscatter diffraction. The effects of individual grain boundaries and differing grain orientations on the PTE signal are minimal. This scanning PTE technique shows promise for identifying minor structural distortions in nanoscale materials and devices.

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mentioning

confidence: 99%

Thermoelectric response from grain boundaries and lattice distortions in crystalline gold devices

Evans

Yang

Gan

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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“…This value inherently includes contributions from the Cr/Pt leads as well as the CNT film, though the contribution from the metal is ≲5 µV K −1 at all T, such that thermopowers presented here are dominated by the CNT film. [32] Figure 1b also indicates two locations where higher magnification shows the density and size of CNT bundles more clearly. Measurement of K B + K film versus T for the HiPCO film is compared in Figure 1f to the SiN background K B (shown as a red line).…”

Section: Resultsmentioning

confidence: 94%

Size‐ and Temperature‐Dependent Suppression of Phonon Thermal Conductivity in Carbon Nanotube Thermoelectric Films

Wesenberg

Roos

Avery

et al. 2020

Adv Elect Materials

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will lead to important applications for power generation and more efficient energy utilization, and could play a vital role in meeting our current global energy challenges. [1-5] The potential of a thermoelectric material is typically assessed using the dimensionless figure-of-merit, ZT = α 2 σT/k, where α is the Seebeck coefficient, σ is the electrical conductivity, k is the thermal conductivity, and T is temperature. ZT determines the overall efficiency of thermoelectric energy generation or cooling (via the Onsager reciprocal Peltier effect where current driven through the material generates a thermal gradient) with larger values of ZT resulting in better thermoelectric devices. Current thermoelectric devices are based on materials with ZT ≈ 1. If this value could be increased to 3-4, the resulting gains in the efficiency will allow broad application of thermoelectric devices for energy generation and refrigeration, [6] though low-cost, flexible materials could see important use in mobile and wearable device applications even at much lower ZT. [7-10] Regardless of the targeted application, the materials properties in ZT are usually determined by the same physics and difficult to separately optimize. Carbon nanomaterials have dramatic and often tunable thermal and electronic properties. [11-13] These range from some of the highest known thermal conductivities observed for individual single-walled carbon nanotubes (CNT), [14-18] or suspended single-layer graphene [19] to the recently observed unconventional superconducting phase of bilayer magic-angle twisted graphene. [20] Despite k reaching in excess of 3000 W m −1 K −1 in single nanostructures, driven by the large contributions from phonons, [12,21] carbon nanotube films can introduce a range of phonon scattering mechanisms that strongly reduce thermal conductivity. [22-24] This allows consideration of such disordered CNT films or mats for thermoelectric energy harvesting applications, and indeed these materials have recently shown promising thermoelectric figure-of-merit. [25,26] This is largely due to realization of theoretically predicted large Seebeck coefficients and large in-plane electronic conductivity when doped, and to dramatic reduction of thermal conductivity. This reduction is

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“…We can then evaluate the Au/Si sample effective Seebeck coefficient to be around 46 ± 1 µV/K. It is not straightforward to compare this value with the Seebeck coefficient of Au layers which is evaluated to be around 2 µV/K [ 37 ] or with the one of Si which, in our case, for the corresponding doping concentration, is evaluated to be around 700 µV/K. A more precise Seebeck model is then needed and is planned to be developed in order to give a more accurate evaluation but also the Seebeck value of the Au layer itself.…”

Section: Resultsmentioning

confidence: 99%

Imaging Thermoelectric Properties at the Nanoscale

et al. 2021

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Based on our previous experimental AFM set-up specially designed for thermal conductivity measurements at the nanoscale, we have developed and validated a prototype which offers two major advantages. On the one hand, we can simultaneously detect various voltages, providing, at the same time, both thermal and electrical properties (thermal conductivity, electrical conductivity and Seebeck coefficient). On the other hand, the AFM approach enables sufficient spatial resolution to produce images of nanostructures such as nanowires (NWs). After a software and hardware validation, we show the consistency of the signals measured on a gold layer on a silicon substrate. Finally, we demonstrate that the imaging of Ge NWs can be achieved with the possibility to extract physical properties such as electrical conductivity and Seebeck coefficient, paving the way to a quantitative estimation of the figure of merit of nanostructures.

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Determining absolute Seebeck coefficients from relative thermopower measurements of thin films and nanostructures

Cited by 19 publications

References 80 publications

Thermoelectric response from grain boundaries and lattice distortions in crystalline gold devices

Thermoelectric response from grain boundaries and lattice distortions in crystalline gold devices

Size‐ and Temperature‐Dependent Suppression of Phonon Thermal Conductivity in Carbon Nanotube Thermoelectric Films

Imaging Thermoelectric Properties at the Nanoscale

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