Density Functional Theory Study of Pd Aggregation on a Pyridine‐Terminated Self‐Assembled Monolayer

Abstract

By using density functional theory calculations, the initial steps towards Pd metal cluster formation on a pyridine‐terminated self‐assembled monolayer (SAM) consisting of 3‐(4‐(pyridine‐4‐yl)phenyl)propane‐1‐thiol on an Au(1 1 1) surface are investigated. Theoretical modelling allows the investigation of structural details of the SAM surface and the metal/SAM interface at the atomic level, which is essential for elucidating the nature of Pd–SAM and Pd–Pd interactions at the liquid/solid interface and gaining insight into the mechanism of metal nucleation in the initial stage of electrodeposition. The structural flexibility of SAM molecules was studied first and the most stable conformation was identified, planar molecules in a herringbone packing, as the model for Pd adsorption. Two binding sites are found for Pd atoms on the pyridine end group of the SAM. The strong interaction between Pd atoms and pyridines illustrates the importance of SAM functionalisation in the metal nucleation process. Consistent with an energetic driving force of approximately −0.3 eV per Pd atom towards Pd aggregation suggested by static calculations, a spontaneous Pd dimerisation is observed in ab initio molecular dynamic studies of the system. Nudged elastic band calculations suggest a potential route with a low energy barrier of 0.10 eV for the Pd atom diffusion and then dimerisation on top of the SAM layer.

Coordination-Controlled Electrodeposition of Palladium/Copper Thin Films onto a Pyridine-Terminated Self-Assembled Monolayer

“…Support for this model comes from a recent computational study which found a preference of the Pd to sit in between rather than on top of the pyridine rings. 14 While this model is tentative it would explain the larger, more protruding particles seen in Figs. 5e and 5g as well as the difference in the number of larger particles and breadth of particle distribution compared to differently prepared samples like the one shown in Fig.…”

“…Imaging conditions and stability were substantially dependent on the details of the deposition. Since Pd and Pd/Cu metal nanoparticles adhere weakly to pyridine-terminated SAMs 14,23,24 isolated particles are easily removed by attachment to the tip. Therefore, the tip-to-sample distance was maximized by applying a high sample bias of ±1-1.5 V and a low current (<5 pA).…”

“…Compared to the well-established approach using chemically inert SAMs, [1][2][3][4][5][6][7] functionalised layers bearing metal coordinating moieties change the paradigm from defect-based electrodeposition to deposition controlled by molecular properties. The different mechanism not only confines deposition to on top of the SAM as first reported by Kolb et al [8][9][10] but the level of control over the deposition process offers new prospects for the design of materials as illustrated by the tuning of electronic properties, [11][12][13][14][15][16] generation of SAM/metal hybrid structures, 17 control of catalytic activity, 12,18,19 the epitaxial growth of Cu films on a cysteine modified Au surface, 20 or the generation of bimetallic nanostructures. 21 Coordination-controlled electrodeposition (CCED) can be accomplished in different ways and the ones employed in the work presented here are illustrated in Fig.…”