Phonon Assisted Transport in Nanowire Quantum Dot
(2025) PHYM01 20251Solid State Physics
Department of Physics
- Abstract
- Nanowire quantum dots have shown promise as energy filters in thermoelectric applications. However, anomalous effects in the thermocurrent have been observed when heat is applied in close proximity to the quantum dot. This work began as an experimental investigation but transitioned to a data analysis project due to hardware failure. Using previously acquired experimental data, we compare the measured thermocurrent and compare it to theoretical expectations. The deviations from the theoretical thermocurrent, along with the properties of the anomalies, suggest a mechanism involving phonon-assisted electron transport through the quantum dot. A phenomenological model based on this interpretation is developed and used to reproduce key features... (More)
- Nanowire quantum dots have shown promise as energy filters in thermoelectric applications. However, anomalous effects in the thermocurrent have been observed when heat is applied in close proximity to the quantum dot. This work began as an experimental investigation but transitioned to a data analysis project due to hardware failure. Using previously acquired experimental data, we compare the measured thermocurrent and compare it to theoretical expectations. The deviations from the theoretical thermocurrent, along with the properties of the anomalies, suggest a mechanism involving phonon-assisted electron transport through the quantum dot. A phenomenological model based on this interpretation is developed and used to reproduce key features of the observed thermocurrent. Although the model captures several aspects of the experimental results, some features remain unexplained, indicating that additional mechanisms may be at play, or that the proposed model is not correct. Based on our findings, we propose a set of follow-up experiments using identical or similar devices to further investigate the role of phonon-electron interactions in thermoelectric transport through nanowire quantum dots. (Less)
- Popular Abstract
- When nanowire quantum dots are used to turn thermal energy into electricity, some unexplained effects were observed in a previous study. In this Thesis, a possible picture of how vibrations in the nanowire lattice can produce these effects is proposed.
As you might know, temperature differences can be turned into motion using heat engines. If you have some stored thermal energy but not a steam engine, and want to charge your phone, there is the field of thermoelectrics which is about converting temperature gradients into electricity. For an efficient conversion of thermal- to electrical energy, energy filtering is useful. This is where nanowire quantum dots come in.
A nanowire is an extremely thin wire (around 40 nm in this work)... (More) - When nanowire quantum dots are used to turn thermal energy into electricity, some unexplained effects were observed in a previous study. In this Thesis, a possible picture of how vibrations in the nanowire lattice can produce these effects is proposed.
As you might know, temperature differences can be turned into motion using heat engines. If you have some stored thermal energy but not a steam engine, and want to charge your phone, there is the field of thermoelectrics which is about converting temperature gradients into electricity. For an efficient conversion of thermal- to electrical energy, energy filtering is useful. This is where nanowire quantum dots come in.
A nanowire is an extremely thin wire (around 40 nm in this work) made of semiconductor material. Quantum mechanics tells us that all things have both particle and wave properties and that the smaller something is, the more wavelike it is. Electrons are very small, and at low energies their wavelength is of a size comparable to the nanowire dimensions. By introducing barriers into this nanowire by negatively biasing parts of it, you get a very small dot where electrons can be. Just as only some frequencies resonate in a flute, only some energies of electrons have the correct energy to exist in this dot. The possible electron states are quantized. Hence, this is known as a quantum dot.
Using your thermal energy to heat one side of the nanowire, the electrons there receive higher energy than on the cold side. By then adjusting your quantum dot in a way that these high-energy electrons can be inside it but not the cold ones, it is possible for the high-energy electrons to tunnel through the dot to the cold side on the other side of the nanowire. This is a thermocurrent. By adjusting the quantum dot so that lower energies are allowed, it is possible to get electron transport from the cold side to the hot side instead. In a previous study, one such nanowire quantum dot device was studied and showed some promise in filtering the correct energies. However, when the heat was applied close to the quantum dot, the resulting current did not match the theoretical predictions. If you want to use this device for anything, it is of course important to understand what is going on. Therefore, this thesis focuses on trying to explain the underlying physics of these deviations from the theory. The idea which is explored in the thesis is one of phonon-electron interaction. Phonons are vibrations in the nanowire lattice structure, and they can interact with electrons, giving them energy. The result of the thesis is a model of phonon-electron interaction which shows how phonons could give their energy to electrons in order for the electrons to then create a current resembling the one in the measurements. However, this model does not explain all the effects seen in the measurements, and more experiments are needed before we know how to make the electrons behave. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9206327
- author
- Granfors, Jakob LU
- supervisor
-
- Adam Burke LU
- organization
- course
- PHYM01 20251
- year
- 2025
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- Quantum Dots, Thermoelectrics, Nanowire, Phonon Assisted Transport
- language
- English
- id
- 9206327
- date added to LUP
- 2025-06-27 10:21:42
- date last changed
- 2025-06-27 10:21:42
@misc{9206327,
abstract = {{Nanowire quantum dots have shown promise as energy filters in thermoelectric applications. However, anomalous effects in the thermocurrent have been observed when heat is applied in close proximity to the quantum dot. This work began as an experimental investigation but transitioned to a data analysis project due to hardware failure. Using previously acquired experimental data, we compare the measured thermocurrent and compare it to theoretical expectations. The deviations from the theoretical thermocurrent, along with the properties of the anomalies, suggest a mechanism involving phonon-assisted electron transport through the quantum dot. A phenomenological model based on this interpretation is developed and used to reproduce key features of the observed thermocurrent. Although the model captures several aspects of the experimental results, some features remain unexplained, indicating that additional mechanisms may be at play, or that the proposed model is not correct. Based on our findings, we propose a set of follow-up experiments using identical or similar devices to further investigate the role of phonon-electron interactions in thermoelectric transport through nanowire quantum dots.}},
author = {{Granfors, Jakob}},
language = {{eng}},
note = {{Student Paper}},
title = {{Phonon Assisted Transport in Nanowire Quantum Dot}},
year = {{2025}},
}