Continuous Band‐Filling Control and One‐Dimensional Transport in Metallic and Semiconducting Carbon Nanotube Tangled Films

Abstract

Field‐effect transistors that employ an electrolyte in place of a gate dielectric layer can accumulate ultrahigh‐density carriers not only on a well‐defined channel (e.g., a two‐dimensional surface) but also on any irregularly shaped channel material. Here, on thin films of 95% pure metallic and semiconducting single‐walled carbon nanotubes (SWNTs), the Fermi level is continuously tuned over a very wide range, while their electronic transport and absorption spectra are simultaneously monitored. It is found that the conductivity of not only the semiconducting but also the metallic SWNT thin films steeply changes when the Fermi level reaches the edges of one‐dimensional subbands and that the conductivity is almost proportional to the number of subbands crossing the Fermi level, thereby exhibiting a one‐dimensional nature of transport even in a tangled network structure and at room temperature.

Thermoelectric Detection of Multi‐Subband Density of States in Semiconducting and Metallic Single‐Walled Carbon Nanotubes

“…The multi‐subband feature is clearly seen in the plot of the transconductance defined as the absolute value of the derivative of the drain–source current I D with respect to V G , as shown in Figure b. Two peaks were observed, suggesting that the Fermi level enters the second subband, as reported in a previous study . Figure c shows the V G dependence of S (the same data as Figure ).…”

“…With decreasing V G from V CNP , G started to increase at V G − V CNP ≈ −0.5 V, as indicated by the solid red line. As we further decreased V G , we observed an additional enhancement of G at V G − V CNP ≈ −1.7 V. It has been reported that this two‐step enhancement of G is due to the multi‐subband formation in semiconducting SWCNTs, and that the onsets of the enhancement correspond to the first and second subband edges, respectively. The multi‐subband feature is clearly seen in the plot of the transconductance defined as the absolute value of the derivative of the drain–source current I D with respect to V G , as shown in Figure b.…”

“…This is partly because of the difficulty of systematically controlling the carrier doping level by the chemical doping method. Another approach is to control the Fermi level using an electric field . In particular, the ionic gating has been shown to be a powerful tool for systematic control of the Fermi level over a wide range of carrier densities; this technique would enable us to deduce the multi‐subband nature of the Seebeck effect, which is the most fundamental thermoelectric property of SWCNTs.…”

Semiconducting Single‐Walled Carbon Nanotubes or Very Rigid Conjugated Polymers: A Comparison

“…When moving from a single nanotube to arrays or networks, the electrostatic coupling between the nanotubes also has to be taken into account. [222,227] Compared to the extensive knowledge about charge transport in long or short, individual and pristine semiconducting nanotubes, and also compared to semiconducting polymers, the understanding of charge transport in random networks of SWCNTs is still far from comprehensive. [107] The charge carrier mobility in a single nanotube also strongly depends on the carrier density.…”

Replacing Copper with New Carbon Nanomaterials in Electrical Machine Windings

“…As such, the presently high price of carbon-based conductors should decrease with the growth of industrial applications and commercial use. At present, the price of copper is in the range of 10 €/kg and its density is about six times the density of CNT yarn conductor material [25]. It is not expected that CNT yarn conductors will soon beat copper conductors.…”