This suggests that SWCNTs can exhibit good power factor ( PF) which indicates the generated power per unit temperature difference and is expressed as PF = σS 2, where σ and S are the electrical conductivity and Seebeck coefficient, respectively. SWCNTs exhibit high electrical conductivity and high Seebeck coefficient 10, 11, 12. Recently, SWCNTs have been considered for application to thermoelectric generators, which produce electricity from ambient thermal energy. Thus, significant progress has been observed in electronics applications such as thin-film transistors, fuel cells, and lithium-ion batteries 7, 8, 9. In particular, various electronic characteristics appear depending on the chirality and diameter of the SWCNTs 5, 6. Owing to their unique structure, they exhibit excellent electronic, thermal, and mechanical properties 2, 3, 4. Single-wall carbon nanotubes (SWCNTs) are novel polyaromatic molecules with small diameters (~ 4 nm) and large length scales (~ 10 μm) 1. Therefore, SWCNT films exhibited n-type thermoelectric properties when the interaction between the sodium atoms and the SWCNTs was larger than that between the oxygen molecules and the SWCNTs. The water molecules, oxygen, and sulfur atoms did not affect the Fermi level. The calculations showed that sodium atoms and oxygen molecules moved the Fermi level closer to the conduction and valence bands, respectively. The electronic band structure and density of states of SWCNTs with oxygen atoms, oxygen molecules, water molecules, sulfur atoms, and sodium atoms were analyzed using first-principles calculations.
In x-ray photoelectron spectroscopy, SWCNT films with SDBS surfactant exhibited a larger amount of sodium than oxygen on the SWCNT surface. In particular, SWCNT films with sodium dodecylbenzene sulfonate (SDBS) surfactant heated to 350 ☌ exhibited a longer retention period, wherein the n-type Seebeck coefficient lasted for a maximum of 35 days. Several types of anionic surfactants were employed to fabricate SWCNT films via drop-casting, followed by heat treatment at various temperatures. We investigated the origin of n-type thermoelectric properties in single-wall carbon nanotube (SWCNT) films with anionic surfactants via experimental analyses and first-principles calculations.
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