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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 total figure of merit ZT versus EF. The curves are for : a uniform nanowire 10 nm thick (black) with κph = 1.5 κ0, and nanowires modulated by one dot (red) with κ ph = 0.5 κ0 and by five dots (dark green) with κ ph = 0.1 κ0, at T = 10 K.
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Figure 7: The total figure of merit ZT versus EF. The curves are for : a uniform nanowire 10 nm thick (black) with κph = 1.5 κ0, and nanowires modulated by one dot (red) with κ ph = 0.5 κ0 and by five dots (dark green) with κ ph = 0.1 κ0, at T = 10 K.

Mentions: At R, ZT is found much smaller than ZT0 (compare Figures 3 and 7). This is explained by that: (i) the power factor S2GT is small (Figure 4), and (ii) the reduction of κph is expected to be smaller than the reduction of κe. In diameter modulated wires, wave interference effects result in reduction of the thermal conductance for both electrons and phonons. The significant reduction of κe is due to the formation of transmission resonances for electrons and the energy selectivity provided by the Fermi distribution. Such transmission resonances have not been found for phonons [17-19]. More than one phonon modes contribute to the phonon conduction. Each mode has its own T(E) and energy selectivity is not provided by the phonon distribution. It is, therefore, unlike that, in diameter modulated nanowires, κph could be reduced as much as κe at R. This remains, however, to be further explored.


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

Zianni X - Nanoscale Res Lett (2011)

The total figure of merit ZT versus EF. The curves are for : a uniform nanowire 10 nm thick (black) with κph = 1.5 κ0, and nanowires modulated by one dot (red) with κ ph = 0.5 κ0 and by five dots (dark green) with κ ph = 0.1 κ0, at T = 10 K.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: The total figure of merit ZT versus EF. The curves are for : a uniform nanowire 10 nm thick (black) with κph = 1.5 κ0, and nanowires modulated by one dot (red) with κ ph = 0.5 κ0 and by five dots (dark green) with κ ph = 0.1 κ0, at T = 10 K.
Mentions: At R, ZT is found much smaller than ZT0 (compare Figures 3 and 7). This is explained by that: (i) the power factor S2GT is small (Figure 4), and (ii) the reduction of κph is expected to be smaller than the reduction of κe. In diameter modulated wires, wave interference effects result in reduction of the thermal conductance for both electrons and phonons. The significant reduction of κe is due to the formation of transmission resonances for electrons and the energy selectivity provided by the Fermi distribution. Such transmission resonances have not been found for phonons [17-19]. More than one phonon modes contribute to the phonon conduction. Each mode has its own T(E) and energy selectivity is not provided by the phonon distribution. It is, therefore, unlike that, in diameter modulated nanowires, κph could be reduced as much as κe at R. This remains, however, to be further explored.

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