Machine learning molecular dynamics simulation of CO-driven formation of Cu clusters on the Cu(111) surface.

The behavior of adsorbate-induced surface transformation can be clearly understood given the mechanical aspects of such phenomenon are well described at the atomic level. In this study, we provide the atomic-level description on the formation of Cu clusters on the Cu(111) surface by performing set of molecular dynamics simulations driven by machine-learning force-field. The simulations at 450 K-550 K show clusters are formed within a hundred of ns when the Cu surface is exposed with CO. On the other hand, no cluster is formed within the same time interval on the clean Cu surface even at 550 K, which signifies the importance of CO exposure to the surface transformation. The effect of temperature to the formation of clusters is also investigated. The CO-decorated Cu clusters ranging from dimer to hexamer are detected within a hundred of ns at 450 K. Lowering the temperature to 350 K does not result in the formation of clusters within a hundred ns due to the scarce detachments of adatom, while raising the temperature to 550 K results in the formation of more clusters, ranging from dimer to heptamer, but with shorter lifetimes. The clusters can be formed directly through instantaneous detachment of a group of step-atoms, or indirectly by aggregation of wandering Cu monomers and smaller clusters on the surface terrace. The preference to the indirect mechanism is indicated by the higher frequency of its occurrence. Set of nudged elastic band calculations has been performed to confirm the promotion of CO adsorptions to the detachment of Cu step-atoms by lowering the detachment barrier.

Theoretical study of CO2 hydrogenation on Cu surfaces.

CO2 reduction has attracted extensive attentions for its wide applications in chemical engineering and green chemistry. As one of major commercial catalysts, Cu have been widely studied considering its low price and high catalytic efficiency. However, previous studies were mostly focused on the Cu(111) surface, while other surfaces were rarely studied. In this work, we employed the density functional theory calculations to fully investigate the adsorption of all intermediates and products of CO2 hydrogenation on three low-index surfaces as Cu(111), Cu(100), and Cu(110), which have been reported as the main facets of Cu nanoparticles under reaction conditions. Besides, the reaction pathways were also discussed. Our results indicated CO2 hydrogenation is preferred to adopt formate pathways on the Cu surfaces, while the COOH pathway is least favorable. Moreover, Cu(100) and Cu(110) surfaces have the comparable (even better) catalytic activities compared with Cu(111) surface. This study provides the fundamental data for the adsorption and reaction of CO2 hydrogenation, which will be helpful for the design of Cu-based nanocatalysts.

Applicable Superamphiphobic Ni/Cu Surface with High Liquid Repellency Enabled by the Electrochemical-Deposited Dual-Scale Structure.

Until now, scalable fabrication and utilization of superamphiphobic surfaces based on sophisticated structures has remained challenging. Herein, we develop an applicable superamphiphobic surface with nano-Ni pyramid/micro-Cu cone structures prepared by cost-effective electrochemical deposition. More importantly, excellent dynamic wettability is achieved, exhibiting as ultralow sliding angle (∼0°), multiple droplets rebounding (13 times), and a total rejection. The supportive cushions trapped within the dual-scale micro/nanostructures is proved to be the key factor contributing to such high liquid repellency, whose existence is intuitively ascertained at both solid-air-liquid and water-solid-oil systems in this work. In addition, the enduring reliability of the wetting performance under various harsh conditions further endows the surface with broader application prospects.

Preparation of Ultra-Smooth Cu Surface for High-Quality Graphene Synthesis.

As grown graphene by chemical vapor deposition typically degrades greatly due to the presence of grain boundaries, which limit graphene's excellent properties and integration into advanced applications. It has been demonstrated that there is a strong correlation between substrate morphology and graphene domain density. Here, we investigate how thermal annealing and electro-polishing affects the morphology of Cu foils. Ultra-smooth Cu surfaces can be achieved and maintained at elevated temperatures by electro-polishing after a pre-annealing treatment. This technique has shown to be more effective than just electro-polishing the Cu substrate without pre-annealing. This may be due to the remaining dislocations and point defects within the Cu bulk material moving to the surface when the Cu is heated. Likewise, a pre-annealing step may release them. Graphene grown on annealed electro-polished Cu substrates show a better quality in terms of lower domain density and higher layer uniformity than those grown on Cu substrates with only annealing or only electro-polishing treatment.

Two-Dimensional Excitonic Photoluminescence in Graphene on a Cu Surface.

Despite having outstanding electrical properties, graphene is unsuitable for optical devices because of its zero band gap. Here, we report two-dimensional excitonic photoluminescence (PL) from graphene grown on a Cu(111) surface, which shows an unexpected and remarkably sharp strong emission near 3.16 eV (full width at half-maximum ≤3 meV) and multiple emissions around 3.18 eV. As temperature increases, these emissions blue shift, displaying the characteristic negative thermal coefficient of graphene. The observed PL originates from the significantly suppressed dispersion of excited electrons in graphene caused by hybridization of graphene π and Cu d orbitals of the first and second Cu layers at a shifted saddle point 0.525(M+K) of the Brillouin zone. This finding provides a pathway to engineering optoelectronic graphene devices, while maintaining the outstanding electrical properties of graphene.