Computational Appraisal of Silver Nanocluster Evolution on Epitaxial Graphene: Implications for CO Sensing

Abstract

Early stages of silver nucleation on a two-dimensional (2D) substrate, here, monolayer epitaxial graphene (MEG) on SiC, play a critical role in the formation of application-specific Ag nanostructures. Therefore, it is of both fundamental and practical importance to investigate the growth steps when Ag adatoms start to form a new phase. In this work, we exploit density functional theory to study the kinetics of early-stage nuclei Ag n (n = 1–9) assembly of Ag nanoparticles on MEG. We find that the Ag1 monomer tends to occupy hollow site positions of MEG and interacts with the surface mainly through weak dispersion forces. The pseudoepitaxial growth regime is revealed to dominate the formation of the planar silver clusters. The adsorption and nucleation energies of Ag n clusters exhibit evident odd–even oscillations with cluster size, pointing out the preferable adsorption and nucleation of odd-numbered clusters on MEG. The character of the interaction between a chemisorbed Ag3 cluster and MEG makes it possible to consider this trimer as the most stable nucleus for the subsequent growth of Ag nanoparticles. We reveal the general correlation between Ag/MEG interaction and Ag–Ag interaction: with increasing cluster size, the interaction between Ag adatoms increases, while the Ag/MEG interaction decreases. The general trend is also supported by the results of charge population analysis, according to which the average charge per Ag adatom in a Ag n cluster demonstrates a drastic decrement with cluster size increase. 2D–3D structural transition in Ag n clusters was investigated. We anticipate that the present investigation is beneficial by providing a better understanding of the early-stage nucleation of Ag nanoparticles on MEG at the atomic scale. Specific interaction between odd-numbered Ag clusters preadsorbed onto the MEG surface and carbon monoxide (CO) as well as clusters’ stability at 300 K is discussed in terms of sensing applications.

Size-Dependent Adsorption and Adhesion Energetics of Ag Nanoparticles on Graphene Films on Ni(111) by Calorimetry

“…Density functional theory (DFT) calculations of the diffusion barrier for Ag/C(0001) from the literature report a diffusion barrier between 0.3 and 7.6 kJ/mol. 24,50,70 The value for E diff reported here falls within this range.…”

“…51 Another study found an energy change of −224 to −229 kJ per mole of Ag atoms for n × Ag(gas) → Ag n (adsorbed) with n = 7−9 for pseudoepitaxial growth of 2D Ag on graphene/SiC(0001) (up from only −35 and −111 kJ/mol at n = 1 and 2, respectively). 50 These can be compared with the measured heats of adsorption in the first pulses of our experiments where the first pulse at 300 K forms clusters of ∼26 atoms (on average) and an average heat of adsorption of 230 kJ/mol, and the first two pulses at 100 K form clusters of ∼9 and ∼30 atoms, respectively, with heats of adsorption of 223 and 207 kJ/mol, respectively. The differences between our experimental results and those calculations could be attributed to any of the following reasons: (1) the larger cohesive energy for the larger particles we studied, (2) stabilization of particles in our experiments by defect sites in the first pulse at 100 K, (3) stabilization of particles in our experiments due to longrange attractive interactions with the underlying Ni(111) substrate, or (4) intrinsic errors in their DFT calculations or our experiments.…”

Oxidation at the sub-nanoscale: oxygen adsorption on graphene-supported size-selected Ag clusters

“…30,66 We found an adsorption energy of the cluster on the Gr/Ru substrate of 2.32 eV, in agreement with the energy obtained for similar Ag clusters on a graphene/SiC substrate. 67 We used the calculated core-electron binding energies to t the spectrum in Fig. 2(a) with a Doniach-Šunjić lineshape obtaining a Lorentzian (L) to Gaussian (G) width ratio of 0.3 : 0.7, a value consistent with a similar study on Ag nanoparticles with diameters below 2 nm, 57 and an asymmetry parameter a ¼ 0.09.…”

Water Diffusion Effects at Gold–Graphene Interfaces Supporting Surface Plasmon Polaritons

“…This case can be, to some extent, referred to as water intercalation beneath graphene. We employed double-ζ polarized (DZP) basis set with an energy shift of 200 meV to perform geometric optimization.As was shown in previous work, − the DZP basis set is good enough to provide reasonable results for graphene-based systems, including metal–graphene interface. Force tolerance was set to 0.02 eV/Å.…”