Tuning the work function of stepped metal surfaces by adsorption of organic molecules

Abstract

Understanding the binding mechanisms for aromatic molecules on transition-metal surfaces, especially with defects such as vacancies, steps and kinks, is a major challenge in designing functional interfaces for organic devices. One important parameter in the performance of organic/inorganic devices is the barrier of charge carrier injection. In the case of a metallic electrode, tuning the electronic interface potential or the work function for electronic level alignment is crucial. Here, we use density-functional theory (DFT) calculations with van der Waals (vdW) interactions treated with both screened pairwise (vdW surf ) and many-body dispersion (MBD) methods, to systematically study the interactions of benzene with a variety of stepped surfaces. Our calculations confirm the physisorptive character of Ag(2 1 1), Ag(5 3 3), Ag(3 2 2), Ag(7 5 5) and Ag(5 4 4) surfaces upon the adsorption of benzene. The MBD effects reduce the adsorption energies by about 0.15 eV per molecule compared to the results from the DFT + vdW surf method. In addition, we find that the higher the step density, the larger the reduction of the work function upon the adsorption of benzene. We also study the effect of vdW interactions on the electronic structure using a fully selfconsistent implementation of the vdW surf method in the Kohn-Sham DFT framework. We find that the self-consistent vdW surf effects increase the work function due to the lowered Fermi level and the increased vacuum level. As a result, the benzene/Ag(2 1 1) system has the lowest work function (3.67 eV) among the five adsorption systems, significantly smaller than the work function of the clean Ag(1 1 1) surface (4.74 eV). Our results provide important insights into the stability and electronic properties of molecules adsorbed on stepped metal surfaces, which could help in designing more appropriate interfaces with low work functions for electron transfer.

Adsorption of Monocyclic Aromatics on Transition Metal Surfaces: Insight into Variation of Binding Strength from First-Principles

“…In fact, the π-conjugated aromatic molecules, particularly benzene (BZ), − and even mono- and polysubstituted aromatic oxygenates of phenolics (e.g., phenol, anisole, and guaiacol) − or halogenated BZ have been employed to study the important role of aromaticity and van der Waals (vdW) interactions in the binding mechanism on metal surfaces including weakly bound systems (e.g., Cu, Ag, and Au) and strongly bound systems (e.g., Rh, Pd, Ir, and Pt); however, their binding strengths calculated using generalized gradient approximation (GGA)-type functionals were severely underestimated with respect to the experimentally measured values. This leads to the employment of nonlocal vdW correlation functionals ,,− (e.g., Perdew–Burke–Ernzerhof (PBE) + vdW surf , optB88-vdW, optB86b-vdW, vdWDF, vdW-DF2, BEEF-vdW, and PBE-dDsC) or other schemes (e.g., random phase approximation) for describing the contributions of vdW-dispersion interactions in chemisorbed systems.…”

Apparent tunneling barrier height and local work function of atomic arrays

“…The work function of a metal surface [1], the work required at temperature T = 0 K to move an electron from the metal to infinity, is relevant for, e.g.,the behavior of electronic devices [2], the energetics of molecules at surfaces [3], including reactions [4–5], and electronic states confined near surfaces [6]. Practical surfaces are finite in size and contain plenty of inhomogeneities that cause local variations of the electrostatic potential.…”

The Role of Steps on Silver Nanoparticles in Electrocatalytic Oxygen Reduction

“…Jiang et al investigated the benzene adsorption on stepped Ag(211), (533), (322), (755), and (544) surfaces. They found that the work function change of the surface was strongly related to the density of the steps [23]. In addition, the adsorption energy of benzene on the Ag(322) surface was found to be the strongest among all the considered systems, which was 9% stronger than that on Ag(111).…”

“…In this study, the ORR mechanism of the Ag(322) surface was investigated using the SCAN-rVV10 method. The Ag(322) surface was selected since it is a stable stepped surface with high reactivity [23,40], which can be reflective of the features of nanoparticles. The results showed that the dissociative pathway was energetically preferred for ORR on Ag(322).…”