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Efficient thermoelectric energy conversion on quasi-localized electron states in diameter modulated nanowires.

Zianni X - Nanoscale Res Lett (2011)

Bottom Line: It is known that the thermoelectric efficiency of nanowires increases when their diameter decreases.We showed that the electron thermoelectric properties depend strongly on the geometry of the diameter modulation.It is demonstrated that quasi-localized states can be formed that are prosperous for efficient thermoelectric energy conversion.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Applied Sciences, Technological Institution of Chalkida, Psachna, 34400 Evia, Greece. xzianni@teihal.gr.

ABSTRACT
It is known that the thermoelectric efficiency of nanowires increases when their diameter decreases. Recently, we proposed that increase of the thermoelectric efficiency could be achieved by modulating the diameter of the nanowires. We showed that the electron thermoelectric properties depend strongly on the geometry of the diameter modulation. Moreover, it has been shown by another group that the phonon conductivity decreases in nanowires when they are modulated by dots. Here, the thermoelectric efficiency of diameter modulated nanowires is estimated, in the ballistic regime, by taking into account the electron and phonon transmission properties. It is demonstrated that quasi-localized states can be formed that are prosperous for efficient thermoelectric energy conversion.

No MeSH data available.


Related in: MedlinePlus

The electron thermal conductance κe versus EF at T = 5 K (red), 10 K (blue) and 50 K (green).
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Figure 5: The electron thermal conductance κe versus EF at T = 5 K (red), 10 K (blue) and 50 K (green).

Mentions: The transmission coefficient deviates from the symmetric-Lorentzian function because the transmission resonance R is not perfectly isolated. Due to coupling between R and the neighbouring transmission states, T(E) is asymmetric. At low temperatures, the asymmetry of T(E) has small effect on the conductance G and the thermopower S. G has a symmetric peak form, S is antisymmetric around the peak of G and S2GT has a double-peak form [2,4]. The asymmetry of T(E) has a more significant effect on the electron thermal conductance κe that is also asymmetric with a peak shifted towards higher energies with respect to the zero of S2GT (Figure 5). κe is sensitive to the shape of T(E) across the propagation resonance because the off-resonance states mainly contribute to it. The electron thermal conductance κe would be zero for a single energy level with zero broadening (Γ = 0), as it has been shown for a single delta-like level of a quantum dot [2]. Due to the asymmetric κe, ZT0 is also asymmetric (Figure 3). At elevated temperatures, Equation 9 is not a good approximation for ZT0, because then the electron distribution is thermally broadened and effects of coupling to neighbouring states become important.


Efficient thermoelectric energy conversion on quasi-localized electron states in diameter modulated nanowires.

Zianni X - Nanoscale Res Lett (2011)

The electron thermal conductance κe versus EF at T = 5 K (red), 10 K (blue) and 50 K (green).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211351&req=5

Figure 5: The electron thermal conductance κe versus EF at T = 5 K (red), 10 K (blue) and 50 K (green).
Mentions: The transmission coefficient deviates from the symmetric-Lorentzian function because the transmission resonance R is not perfectly isolated. Due to coupling between R and the neighbouring transmission states, T(E) is asymmetric. At low temperatures, the asymmetry of T(E) has small effect on the conductance G and the thermopower S. G has a symmetric peak form, S is antisymmetric around the peak of G and S2GT has a double-peak form [2,4]. The asymmetry of T(E) has a more significant effect on the electron thermal conductance κe that is also asymmetric with a peak shifted towards higher energies with respect to the zero of S2GT (Figure 5). κe is sensitive to the shape of T(E) across the propagation resonance because the off-resonance states mainly contribute to it. The electron thermal conductance κe would be zero for a single energy level with zero broadening (Γ = 0), as it has been shown for a single delta-like level of a quantum dot [2]. Due to the asymmetric κe, ZT0 is also asymmetric (Figure 3). At elevated temperatures, Equation 9 is not a good approximation for ZT0, because then the electron distribution is thermally broadened and effects of coupling to neighbouring states become important.

Bottom Line: It is known that the thermoelectric efficiency of nanowires increases when their diameter decreases.We showed that the electron thermoelectric properties depend strongly on the geometry of the diameter modulation.It is demonstrated that quasi-localized states can be formed that are prosperous for efficient thermoelectric energy conversion.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Applied Sciences, Technological Institution of Chalkida, Psachna, 34400 Evia, Greece. xzianni@teihal.gr.

ABSTRACT
It is known that the thermoelectric efficiency of nanowires increases when their diameter decreases. Recently, we proposed that increase of the thermoelectric efficiency could be achieved by modulating the diameter of the nanowires. We showed that the electron thermoelectric properties depend strongly on the geometry of the diameter modulation. Moreover, it has been shown by another group that the phonon conductivity decreases in nanowires when they are modulated by dots. Here, the thermoelectric efficiency of diameter modulated nanowires is estimated, in the ballistic regime, by taking into account the electron and phonon transmission properties. It is demonstrated that quasi-localized states can be formed that are prosperous for efficient thermoelectric energy conversion.

No MeSH data available.


Related in: MedlinePlus