| 1. |
- Könemann, Fabian, et al.
(author)
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Imaging the Thermalization of Hot Carriers after Thermionic Emission over a Polytype Barrier
- 2020
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In: Physical Review Applied. - 2331-7019. ; 13:5
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Journal article (peer-reviewed)abstract
- The thermalization of nonequilibrium charge carriers is at the heart of thermoelectric energy conversion. In nanoscale systems, the equilibration length can be on the order of the system size, leading to a situation where thermoelectric effects need to be considered as spatially distributed, rather than localized at junctions. The energy exchange between charge carriers and phonons is of fundamental scientific and technological interest, but their assessment poses significant experimental challenges. We address these challenges by imaging the temperature change induced by Peltier effects in crystal phase engineered InAs nanowire (NW) devices. Using high-resolution scanning thermal microscopy (SThM), we study current-carrying InAs NWs, which feature a barrier segment of wurtzite (WZ) of varying length in a NW of otherwise zincblende (ZB) crystal phase. The energy barrier acts as a filter for electron transport around the Fermi energy, giving rise to a thermoelectric effect. We find that thermalization through electron-phonon heat exchange extends over the entire device. We analyze the temperature profile along a nanowire by comparing it to spatially dependent heat diffusion and electron thermalization models. We are able to extract the governing properties of the system, including the electron thermalization length of 223±9nm, Peltier coefficient and Seebeck coefficient introduced by the barrier of 39±7mV and 89±21μV/K, respectively, and a thermal conductivity along the wire axis of 8.9±0.5 W/m K. Finally, we compare two ways to extract the elusive thermal boundary conductance between the NW and underlying substrate.
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| 2. |
- Könemann, Fabian, et al.
(author)
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Nanoscale Scanning Probe Thermometry
- 2018
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In: THERMINIC 2018 - 24th International Workshop on Thermal Investigations of ICs and Systems, Proceedings. - 9781538667590
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Conference paper (peer-reviewed)abstract
- We present further development and application examples of a thermometry approach capable of producing real-space temperature maps of operating nanoscale devices with sub-10nm resolution. The technique relies on scanning thermal microscopy with a resistive element coupled to a cantilevered tip. The resistive element acts both as integrated heater and as sensing element. A modulated temperature field is generated in the sample by exciting the device under investigation with an electrical AC bias. A map of the sample's temperature response due to different physical effects, such as Joule heating and thermoelectric effects, can be inferred from the demodulated sensor signal. As application examples, we demonstrate the investigation of thermoelectric heating/cooling at crystal phase heterostructures in InAs nanowires and Joule self-heating of individual multi-walled carbon nanotubes.
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