Tunneling rules for electronic transport in 1-D systems

Abstract

Carbynes have gained highlight due to their unique properties and applications in molecular electronics exhibiting resonant tunnel effect. We studied the electronic transport through a molecular tunnel junction composed of two polyyne-type carbynes separated by distance (4 Å ≥ dn ≥ 2.1 Å) higher than bond length (dn > dC–C ) ranging from 0.1 Å based on Density Functional Theory/Non-Equilibrium Green’s Function (DFT/NEGF). The frontier molecular orbitals and bond lengths of the polyyne (dC–C ≈ 1.36 Å, dC ≡C ≈ 1.26 Å) at 0.0 V become equal to those in cumulene-type carbynes (dC= C ≈ 1.28 Å) at 0.9 V occurring a semiconductor–metal transition for dn < 4 Å. I–V (dI/dV–V) curve presents switching behaviour up to 0.6 V and after a diode behaviour favoured as dn decreases, that is, to 4.0 Å is 3.3 nA (5 nS) while for 2.1 Å is 3750 nA (1500 nS) showing metallic nature. The log(I)–V [log(dI/dV)–V] curve exhibits the behaviour for low bias voltage while the I–dn curve is exhibited for high bias voltage. The exponential expression for G(d) fits perfectly with the Gmax result obtained with DFT/NEGF calculations. Transition Voltage Spectroscopy (TVS) confirms rectangular barrier and direct tunneling for Vd–s < ϕB /e playing a tunneling rule for electronic transport of these 1-D systems.