Electron Transport in Molecular Wires

Abstract

Numerical simulations have been performed to study the influence of -orbital interactions and molecule-metal coupling strength ( 1 ¼ 2 ¼ i ) on the electronic transport properties of molecular assembly system. The model involves 1,4-dithiolbenzene (DTB) molecules stacked in one dimension ordered structure. The results show that the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) gap (HLG) is reduced when decreasing the intermolecular distance d and increasing the number of DTB molecular units N. The influences of the geometric and couplingstrength parameters d, N, -orbital, and i on the current-voltage (I-V) or the conductance-voltage (G-V) characteristics are investigated. It is found that the conductance gap depends on the HLG. The system in the regime of strong -interactions shows shorter conductance gap. The conductance gap for a wire made of two DTB molecular units decreases by 2.4 V when d changes from 6.9 to 3.3 A ˚, while it sharply decreases by 3.3 V when the molecular structure goes from a single molecule to a wire made of six molecular units. The results indicate also that i is an important factor in determining the current flow. The saturation current for a wire containing four molecular units increases by 150 mA when i changes from 0.2 to 0.4 eV. In fact, the main factors that determine the I-V or G-V characteristics are clearly related to the magnitude of the HLG, i and the position of the energy levels of the molecule relative to the Fermi energy contacts.

Modelling the temperature dependence of the threshold voltage of bis(1,4-dithiolbenzene) molecular assembly system

“…As d decreases from 6.9 to 3.3 Å, the HOMO and LUMO energy levels become closer, which results in the relative reduction of the HLG by about 34.32%. 33) In this molecular configuration, we believe that with face-to-face two-DTB packing, the π electron orbital interactions are the key factor in lowering the HLG. Therefore, we can expect stronger π-coupling interactions with shorter d ≤ 4.8 Å.…”

“…Table I indicates the evolution of the energy levels HOMO, LUMO, and HLG of the molecular wire made of two DTB units. 33) The HLG is estimated to be about 3.41172 eV for d = 6.9 Å. As d decreases from 6.9 to 3.3 Å, the HOMO and LUMO energy levels become closer, which results in the relative reduction of the HLG by about 34.32%.…”

“…We investigate the influence of π-orbital coupling on the electronic and structural properties of the MAS between adjacent DTB molecules by calculating the energy band diagram. The calculations of the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) and the HOMO-LUMO gap (HLG) were performed as a function of the intermolecular spacing d. 33) The one-dimensional (1D) structure of MAS is composed of DTB molecules packed in a parallel geometrical arrangement (Fig. 1).…”

“…At a constant temperature, the smaller the intermolecular distance, the shorter the conductance gap (CG = 2V th ) observed. 33) When the intermolecular distance is less than 6.9 Å, the molecular wire made of two DTB molecules shows a shorter conductance gap than that of a wire with a single DTB molecule. Table I indicates the evolution of the energy levels HOMO, LUMO, and HLG of the molecular wire made of two DTB units.…”

Current-Voltage Characteristics of Bi-dithiolbenzene in Parallel Arrangement

“…In Fig. 3(a) With E f located at HLMG, V th strong π-interactions obtained with larger N or shorter d reduces V and CG change significantly depending on N or d [2]. The system in th.…”