The electron transport properties in short polyyne nanochains lying between two semi-infinite cumulene leads are investigated using tight-binding Hamiltonian of the Harrison's model and the Landauer-Buttiker formalism. The presence of all kinds of atomic orbitals occurring in the monatomic system one by one is studied and proven. The effects of dimerization on the density of states, electron transmission and current-voltage characteristics of a linear chain of carbon atoms (carbyne) are discussed. Our results show that the polyyne exhibits a semiconducting behavior because of dimerization. In the absence of dimerization, the carbon nanochain behaves as a conductor. Actually, under mechanical strain due to dimerization, a metal-to-semiconductor transition occurs. Moreover, it is found that the bandgap in polyyne nanochains is never a constant value, but highly depends on bond length alternation. Thereby, a polyyne nanochain via strain can be exploited as a nanodevice with tunable bandgap. The influences of increasing length of the finite polyyne nanochain on the transport properties regarding all atomic orbital types are studied. The nonlinear behavior of the current-voltage curve for different temperatures of the metallic leads is calculated and interpreted. Our theoretical results are in a good overall agreement with the most recent experimental findings.
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