First-principles study of coadsorption of Cu2+ and Cl- ions on the Cu (110) surface.

Motivated by the importance of Cl- in the industrial electrolytic Cu plating process, we study the coadsorption of Cl- and Cu2+ on the Cu (110) surface using first-principles density functional theory (DFT) calculations. We treat the solvent implicitly by solving the linearized Poisson-Boltzmann equation and evaluate the electrochemical potential and energetics of ions with the computational hydrogen electrode approach. We find that Cl- alone is hardly adsorbed at sufficiently negative electrochemical potentials µ Cl but stable phases with half and full Cl- coverage was observed as µ Cl is made more positive. For Cl- and Cu2+ coadsorption, we identified five stable phases for electrode biases between -2V < U SHE < 2V, with two being Cl- adsorption phases, two being Cl- + Cu2+ coadsorption phases and one being a pure Cu2+ adsorption phase. In general, the free energy of adsorption for the most stable phases at larger |U SHE| are dominated by the energy required to move electrons between the system and the Fermi level of the electrode, while that at smaller |U SHE| are largely dictated by the binding strength between Cl- and Cu2+ adsorbates on the Cu (110) substrate. In addition, by studying the free energy of adsorption of Cu2+ onto pristine and Cl- covered Cu (110), we conclude that the introduction of Cl- ion does not improve the energetics of Cu2+ adsorption onto Cu (110).

Oxygen-Promoted Chemical Vapor Deposition of Graphene on Copper: A Combined Modeling and Experimental Study.

Mass production of large, high-quality single-crystalline graphene is dependent on a complex coupling of factors including substrate material, temperature, pressure, gas flow, and the concentration of carbon and hydrogen species. Recent studies have shown that the oxidation of the substrate surface such as Cu before the introduction of the C precursor, methane, results in a significant increase in the growth rate of graphene while the number of nuclei on the surface of the Cu substrate decreases. We report on a phase-field model, where we include the effects of oxygen on the number of nuclei, the energetics at the growth front, and the graphene island morphology on Cu. Our calculations reproduce the experimental observations, thus validating the proposed model. Finally, and more importantly, we present growth rate from our model as a function of O concentration and precursor flux to guide the efficient growth of large single-crystal graphene of high quality.

Nanostructure Formation by controlled dewetting on patterned substrates: A combined theoretical, modeling and experimental study.

We perform systematic two-dimensional energetic analysis to study the stability of various nanostructures formed by dewetting solid films deposited on patterned substrates. Our analytical results show that by controlling system parameters such as the substrate surface pattern, film thickness and wetting angle, a variety of equilibrium nanostructures can be obtained. Phase diagrams are presented to show the complex relations between these system parameters and various nanostructure morphologies. We further carry out both phase field simulations and dewetting experiments to validate the analytically derived phase diagrams. Good agreements between the results from our energetic analyses and those from our phase field simulations and experiments verify our analysis. Hence, the phase diagrams presented here provide guidelines for using solid-state dewetting as a tool to achieve various nanostructures.

Protein Induces Layer-by-Layer Exfoliation of Transition Metal Dichalcogenides.

Here, we report a general and facile method for effective layer-by-layer exfoliation of transition metal dichalcogenides (TMDs) and graphite in water by using protein, bovine serum albumin (BSA) to produce single-layer nanosheets, which cannot be achieved using other commonly used bio- and synthetic polymers. Besides serving as an effective exfoliating agent, BSA can also function as a strong stabilizing agent against reaggregation of single-layer nanosheets for greatly improving their biocompatibility in biomedical applications. With significantly increased surface area, single-layer MoS2 nanosheets also exhibit a much higher binding capacity to pesticides and a much larger specific capacitance. The protein exfoliation process is carefully investigated with various control experiments and density functional theory simulations. It is interesting to find that the nonpolar groups of protein can firmly bind to TMD layers or graphene to expose polar groups in water, facilitating the effective exfoliation of single-layer nanosheets in aqueous solution. The present work will enable to optimize the fabrication of various 2D materials at high yield and large scale, and bring more opportunities to investigate the unique properties of 2D materials and exploit their novel applications.

High aspect ratio 10-nm-scale nanoaperture arrays with template-guided metal dewetting.

We introduce an approach to fabricate ordered arrays of 10-nm-scale silica-filled apertures in a metal film without etching or liftoff. Using low temperature (<400°C) thermal dewetting of metal films guided by nano-patterned templates, apertures with aspect ratios up to 5:1 are demonstrated. Apertures form spontaneously during the thermal process without need for further processing. Although the phenomenon of dewetting has been well studied, this is the first demonstration of its use in the fabrication of nanoapertures in a spatially controllable manner. In particular, the achievement of 10-nm length-scale patterning at high aspect ratio with thermal dewetting is unprecedented. By varying the nanotemplate design, we show its strong influence over the positions and sizes of the nanoapertures. In addition, we construct a three-dimensional phase field model of metal dewetting on nano-patterned substrates. The simulation data obtained closely corroborates our experimental results and reveals new insights to template dewetting at the nanoscale. Taken together, this fabrication method and simulation model form a complete toolbox for 10-nm-scale patterning using template-guided dewetting that could be extended to a wide range of material systems and geometries.