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We report our transport studies in quasi one-dimensional (1D) conductors -helical polyacetylene fibers doped with iodine and the data analysis for other polymer single fibers and tubes. We found that at 30 K < T < 300 K the conductance and the current-voltage

A field-effect transistor (FET) with a channel length of ∼100 nm was constructed from a small number of individual V2O5 fibers of the cross section 1.5 nm×10 nm. At low temperature, the conductance increases as the gate voltage is changed from negative to positive values, characteristic of a FET with n-type enhancement mode. The carrier mobility, estimated from the low-field regime, is found to increase from 7.7×10−5 cm2/V s at T=131 K to 9.6×10−3 cm2/V s at T=192 K with an activation energy of Ea=0.18 eV. The nonohmic current/voltage dependence at high electric fields was analyzed in the frame of small polaron hopping conduction, yielding a nearest-neighbor hopping distance of ∼4 nm.

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Owing to the strong dependence of the resistivity on the dopant concentration, nonuniformity across the thickness of a sample leads to an apparent anisotropy in the resistivity (measured parallel to and perpendicular to the plane of the film). Thus the magnitude of the apparent anisotropy (for nonoriented samples) offers a convenient means for quantifying the degree of dopant nonuniformity in trans-(CH)". This technique is used to evaluate the uniformity achieved in [CH(AsF5)r]"by conventional vapor-phase doping as compared with the slow-doping technique developed earlier for susceptibility studies. Using samples which have been demonstrated in this manner to be uniform, we reexamine the semiconductor-metal transition. From the transport data, we find that the better the uniformity in the distribution of dopant, the more abrupt is the transition at y,~. 002. A generalized soliton picture, involving delocalized carriers, appears to be implied by the combination of optical, magnetic, and transport data.

Temperature-dependent current–voltage (I–V) characteristics of a molecule, 1,4-benzenedimethanethiol, was measured for 30K&lt;T&lt;300K by a method of contact made by the electrochemical deposition of a platinum electrode in a lateral configuration. The I–V characteristics are nonlinear and asymmetric in the entire temperature range and the current decreases with decreasing temperature down to 40K. Below 40K, the I–V characteristics become temperature independent. The asymmetric I–V characteristics can be understood as arising from a better contact on one side (made by the self-assembled monolayer) than on the other side (made by the electrochemically deposited Pt electrode). The activation energy of thermally activated conduction for T&gt;100K is typically 0.11eV. For T&lt;40K, the observed temperature independent I–V characteristics are fitted to the Fowler–Nordheim tunneling expression with barrier height of 1–2eV depending on the contact strength of samples.

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