Thermoelectric Power of Single-Walled Carbon Nanotubes

Abstract

We have measured the temperature-dependent thermoelectric power (TEP) of crystalline ropes of single-walled carbon nanotubes. The TEP is large and holelike at high temperatures and approaches zero as T ! 0. The results argue against the opening of a gap at low temperature in these materials. When derived from a simple band structure picture, the TEP of a single metallic nanotube is significantly lower than the measured TEP, strongly suggesting that the predicted electron-hole symmetry of metallic nanotubes is broken when the tubes self-assemble into ropes. Different models for the symmetry breaking are considered. [S0031-9007(97)05214-9]

Physisorption of molecular oxygen on single-wall carbon nanotube bundles and graphite

“…11 It is, therefore, still discussed controversially which microscopic processes lead to the observed changes in the electronic-transport properties of SWNT's. Apart from the aforementioned chemical doping, 3,4,5,12 it has also been proposed that doping of the tube-metal contacts is responsible for changes in the transport properties. 1,13,14 It also remains unclear whether atomic or molecular oxygen is responsible for the charge transfer that is necessary for doping-let it be at contacts or on the tube surfaces.…”

Giant Seebeck coefficient in semiconducting single-wall carbon nanotube film

“…The S value of mixed SWCNT film is between those for α ~ 0 and 1, and is consistent with those reported for SWCNT samples with a nominal fraction α = 67 %. 3) Figure 2(a) summarizes the α dependence of S at 300 K. The power factor P = S 2 /ρ at 300 K is 33, 6.7 and 3.9 µW/mK 2 for semiconducting, mixed, and metallic SWCNT films, respectively.…”

“…This is due mainly to their high thermal conductivity and low Seebeck coefficient. [3][4][5][6][7][8][9] For example, an S of up to only about 60 μV/K was reported for SWCNT films with an uncontrolled mixture of semiconducting and metallic SWCNTs. An enhanced Seebeck coefficient of 260 μV/K was observed only in a junction between an individual SWCNT and a metal electrode.…”

“…The initial SWCNTs (Arc-SO,), which are mixtures of semiconducting and metallic SWCNTs, 3 were purchased from Meijo-Nanocarbon Co. and dispersed into 2 weight % deoxycholate sodium salt solutions. SWCNTs with a controlled semiconducting ratio were obtained through density gradient ultracentrifugation.…”

Magnetic impurities in nanotubes: From density functional theory to Kondo many-body effects

“…In all other cases, the tiny values of T K make our results difficult to verify experimentally, which is a bit disappointing. There is however a positive implication, namely that, according to these results, the increase in the resistivity observed in nanotubes below 100 K 44-46 as well as the associated peak in the thermopower 44,45 could indeed be caused by magnetic impurities trapped inside the tube. A remarkable magnetic impurity is the single carbon atom vacancy.…”