Tuning the electron transport of molecular junctions by chemically functionalizing anchoring groups: First-principles study

Abstract

In this first-principles study, we present density-functional calculations of the electronic structures and electron transport properties of organic molecular junctions with several anchoring groups containing atoms with different electronegativities, i.e., benzenediboronate (BDB), benzenedicarboxylate (BDC), and dinitrobenzene (DNB) molecular junctions sandwiched between two Cu(110) electrodes. The electronic-structure calculations exhibit a significant difference in the density of states not only at the anchoring groups but also at the aromatic rings of the molecular junctions, suggesting that the electron transport is specific for each system. Our transport calculations show that the BDB and DNB molecular junctions have finite electron transmissions at the zero-bias limit while the BDC molecular junction has a negligible electron transmission. Moreover, for the BDB and DNB systems, the electron transmission channels around the Fermi energy reveal fingerprint features, which provide specific functionalities for the molecular junctions. Therefore, our theoretical results demonstrate the possibility to precisely tune the electron transport properties of molecular junctions by engineering the anchoring groups at the single-atom level.

Systematic chemical functionalization of hybrid molecule–surface interfaces

“…a) even though no second electrode is present in the latter case (for a proper comparison see Fig. 4 in ()). On the contrary, for the BDB molecular junction a small electron transmission at is observed (0.02 ) and even a larger transmission (0.2 ) for the DNB junction.…”

“…Similarly to the above theoretical part, all details of the experimental setup employed in our molecule-Cu(110) related studies are described in the same set of Refs. [45][46][47][48][49][50][51].…”

Real-space finite-difference calculation method of generalized Bloch wave functions and complex band structures with reduced computational cost

“…Here I r denotes the identity matrix of the order r. We would like to emphasize that this generalized eigenvalue problem (32) has much smaller dimension than that mentioned in previous subsection [see Eqs. (11)- (13)], but these two generalized eigenvalue problems are exactly equivalent to each other mathematically. By taking advantage of the block form of the reduced matrix 2 , we can easily obtain the inverse of the matrix 2 analytically.…”

“…However, we have to be very careful about unphysical influence brought by the approximation, such as undesirous scattering at the interface between a jellium part and an atomic structure [17] and unexpected charge transfer between them [16]. In our previous work on the electron transport through molecular junctions, we have pointed out the unphysical influence on the electronic structure originating from the jellium approximation of the interiors of the electrodes [13]. Fujimoto and Hirose have also showed for a gold atomic chain that employing the ideal distance between the surface of a jellium electrode and the attaching Au (100) layer, the half of the interlayer distance in the [100] direction, the conductance calculated is ≈5% less than that calculated with crystalline electrodes [7].…”

“…The OBM method is based on the realspace finite-difference formalism [10] within the framework of the density functional theory [11] and enables us to treat realistic models of the semi-infinite electrodes made up of atoms easily, instead of approximating the electrodes with an uniform background (jellium) model [12]. The jellium approximation has been still employed for electron transport calculations frequently [6,[13][14][15], because the boundary conditions of scattering wave functions are analytically determined due to the structureless charge distribution. Besides this, it is also well known that the jellium approximation of electrodes forms an artificial interface to atomic structures, which may cause unphysical scattering of electron flow and charge transfer affecting the electron transport properties [16,17].…”