High electrical conductivity and n-type thermopower from double-/single-wall carbon nanotubes by manipulating charge interactions between nanotubes and organic/inorganic nanomaterials

Single- and double-wall carbon nanotubes were decorated with organic or inorganic nanomaterials in order to obtain desired electrical transport properties such as a high electrical conductivity or an n-type thermopower. For instance, the electrical conductivity of double-wall carbon nanotubes (DWCNTs) decorated with tetrafluoro-tetracyanoquinodimethane (F₄TCNQ) was increased up to 5.9 × 10⁵ S/m, and single-wall carbon nanotubes (SWCNTs) were converted from p-type to n-type with a large thermopower (−58 μV/K) by using polyethyleneimine without vacuum or controlled environment. When inorganic nanoparticles made of Fe and Cu were used for decorating nanotubes, the electrical conductance of the nanotube films was decreased with an enlarged thermopower. On the other hand, Au decorations yielded higher electrical conductances with lower thermopowers. The thermoelectric power factors were improved by ∼180% with F₄TCNQ on DWCNTs and ∼140% with Fe on SWCNTs. We believe these transport property changes can be attributed to charge interactions resulted from the difference between the work functions/reduction potentials of nanotubes and nanomaterials. This study shows a first step toward the synthesis of both n-type and p-type conductors with carbon nanotubes, which are essential to thermoelectric energy conversion applications.