The finite-size effect on the transport properties in edge-modified graphene nanoribbon-based molecular devices

Lateral scaling and positioning effects of top-gate electrodes on single-molecule field-effect transistors

Molecular electronics aims at integrating controllable molecular devices into circuits or machines to realize certain functions. According to device configuration, molecular field-effect transistors with top-gate electrodes have great advantages for integration. Nevertheless, from technical aspects, it is difficult to control lateral scale and position of a top-gate electrode precisely. Therefore, one problem arises in how lateral scaling and positioning effects of a top-gate electrode affect device performance. To solve this problem, the electronic transport properties of single-molecule field-effect transistor configurations modulated by a series of partial-scale top-gate electrodes with different lateral scales and positions are studied by using non-equilibrium Green's function in combination with density functional theory, and compared with those of the full gate electrode (can be considered as a bottom gate electrode). The results show that lateral scaling and positioning effects indeed have a great impact on electronic transport properties of single-molecule field-effect transistor configurations. For [Formula: see text]-saturated 1,12-dodecanedithiol devices, larger lateral scale of a partial-scale top-gate electrode obtains larger amplification coefficient [Formula: see text] (ratio of device conductances with/without a gate electrode), and even larger [Formula: see text] than that of the full gate electrode. While lateral positioning effect has little influence on this device. For [Formula: see text]-conjugated 1,3,5,7,9,11-dodehexaene-1,12-dithiol devices, performance of a partial-scale top-gate electrode mainly depends on locations of its two edges, i.e. the number of [Formula: see text] bonds that it breaks. These results will provide theoretical directions in device designing and manufacturing in the future.

Tuning of the Electronic Properties of Armchair Graphene Nanoribbons through Functionalization: Theoretical Study of (1)Δg O2 Border Addition

We report the results of a DFT study of the border oxidation by (1) Δg O2 of molecular models of armchair graphene nanoribbons (a-GNRs). The aim of this work is to propose a new method, as an alternative or complementary method to the tuning of the size, to modify the electronic properties of a-GNRs. Here, we investigate modification of the HOMO and LUMO energies, which are some of the most important parameters to be controlled in the design of organic electronic devices. We study the oxidation reaction mechanism of medium-size polycyclic aromatic hydrocarbons, mimicking the stiffness and reactivity of a-GNRs. Thermodynamics and kinetics indicate that the reaction should bring about a decoration of the borders with vicinal dialdehyde groups. We also study the effect of this oxidation on the HOMO and LUMO energies of two series of molecular models of a-GNRs with increasing lengths. The results suggest that the oxidized a-GNRs should present LUMO energies lowered by 0.3-0.5 eV with respect to the original material, whereas the HOMO energies are barely lowered.