Mechanism of rectification and negative differential resistance in single-molecule junctions with asymmetric anchoring groups: a DFT study

CONTEXT

This study aims to investigate the electronic transport properties of tetracene molecule connected to gold (Au) electrodes with asymmetric anchoring groups. More specifically, we investigate the effect of asymmetric electrode coupling on the rectification ratio of tetracene-based molecular device. To introduce coupling asymmetry in these junctions, one end of the tetracene molecule is terminated with thiol (-SH) or isocyanide (-NC) while the other end with amine (-NH2) or nitro (-NO2) anchoring group. The results indicate that the electronic transport behavior is affected by the nature of molecule-electrode coupling, and the rectification ratio can be modulated by a proper choice of the anchoring groups. We reveal that the tetracene molecule when connected with isocyanide and amine combination exhibits remarkable rectifying performance (with a rectification ratio of 74) in contrast with other configurations. Furthermore, a prominent negative differential resistance (NDR) feature is observed when the molecule is connected with thiol as one of the anchors. Our present findings with excellent rectifying performance and negative differential resistance pave a new roadmap for designing multifunctional molecular devices.

METHODS

By applying non-equilibrium Green's function (NEGF) formalism combined with density functional theory (DFT) Atomistic Tool Kit software package, the electronic transport properties of tetracene molecule connected to gold electrodes with asymmetric anchoring groups have been investigated. The calculations were performed using the Perdew-Burke-Ernzerhof (PBE) parameterization of DFT within generalized gradient approximation (GGA) exchange-correlation functional. To improve calculation precision and save computational efforts, the molecule and anchor groups were double-ζ (DZ) polarized, while single-ζ (SZ) polarized basis set was used for gold electrodes.

Tuning the transport properties of tetracene-based single-molecule junctions with chemical or structural variation of side and anchoring groups

CONTEXT

This study aims to tune the transport properties of tetracene single-molecule junctions with the proper choice and placement of side and anchoring groups. For the operationalization of the molecule that was anchored with thiol or isocyanide groups, two different side groups, amine and nitro, in two different positions, were taken into consideration. For unperturbed tetracene molecule, a prominent negative differential resistance (NDR) feature at 1.8 V was observed with the isocyanide anchoring group while the thiol anchoring group exhibits a plateau region over a bias voltage of 2.2 to 3.2 V. At a bias voltage that is dependent on the chemical or structural change of side or anchoring groups, NDR feature of varying degree was seen in all configurations. Results show that the current flowing through the thiol-anchored molecule perturbed with the amine group at S' position is relatively larger than other configurations because of the smaller HOMO-LUMO gap and broader transmission peaks resulting in a peak to valley current ratio (PVCR) of 1.22. In addition, multiple NDR regions were realized in nitro-perturbed isocyanide-anchored molecule at S position. These results suggest their promising applications in switches, logic cells, and storage devices.

METHODS

The modeling and simulation of side-group mediated anchored tetracene molecule through two electrodic systems were studied using density functional theory (DFT) combined with non-equilibrium Green's function (NEGF) in Virtual NanoLab-AtomistixToolkit (ATK). The electron transport properties were calculated using Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) exchange-correlation function. To optimize computing time, gold electrodes were single zeta polarized whereas the molecule, anchor groups, and side groups were double zeta polarized.

Rise of silicene and its applications in gas sensing

Reviewing a subject is done to provide an insight into theoretical and conceptual background of the study. Looking back into the history of an emerging field and summarizing it in a few pages is a herculean task. Anyway, it was imperative to write a few words about the rise of silicene, its properties, and its applications as gas sensors. Currently, silicene is a growing field of interest. It is probably one of the most studied materials nowadays and scientists and researchers are studying it because of its intriguing electronic properties and potential applications in nanoelectronics. Various experimental and theoretical investigations are going on worldwide to explore the various aspects of this field. It is essential to review the literature based on investigations by various scientists in this field.

First principles investigation on armchair zinc oxide nanoribbons as uric acid sensors

A study is done to check the sensing functionality of armchair zinc oxide (ZnO) nanoribbon towards uric acid. The main focus of the research is to observe the change in the electronic properties (adsorption energy, bandstructure and density of states) and transport properties (current-voltage characteristics) of nanoribbon on adsorption of uric acid. In this work, two armchair ZnO nanoribbons of width, N = 4 and 6 atoms are used, and additional variations are created in the nanoribbon by introducing defect and doping agent. Manganese is used as a dopant. The work reveals that chemisorption occurs only in the case of doping for both widths of nanoribbons, and there is an enormous increase in the conductivity of defective armchair ZnO nanoribbon with width, N = 6 as compared to others on adsorption of uric acid. All calculations are carried out using density functional theory (DFT) and non-equilibrium Green's function (NEGF). Graphical abstract.