Structure of PtRu/Ru(0001) and AgPd/Pd(111) surface alloys: A kinetic Monte Carlo study

Bimetallic surfaces allow tailoring their catalytic activity by modifying their composition and/or structure. However, under operating conditions, catalytically active bimetallic structures are often not stable and change their morphology which might reduce their functionality. Still, catalytically active structures do not necessarily need to be thermodynamically stable and might also be kinetically stabilized. Here we report kinetic Monte Carlo simulations based on density functional theory calculation to address the meta-stability of surface alloy systems. As structural changes can typically only occur via vacancy diffusion in the surface, we first determine the vacancy diffusion barrier as a function of their bimetallic environment. By determining the temporal evolution of the bimetallic surface alloys as a function of temperature, we analyze the factors underlying the stability and structure of the bimetallic surface alloys.

Plasma electrolytic oxidation of Ti - W surface alloys synthetized by PVD-LEHCEB

An innovative approach exploiting PVD-coupled Low-Energy High-Current Electron Beam (LEHCEB) and Plasma Electrolytic Oxidation (PEO) techniques were investigated to obtain photoactive TiO2-WO3mixed films. Ti-W surface alloys containing 14 at.% W were synthetized by PVD deposition of 185 nm thick W films onto Ti substrates, followed by LEHCEB alloying at 30 kV for 50 pulses. The obtained Ti-W surface alloys were treated by PEO in 1.5 M H2SO4 at constant cell voltage ranging from 100 to 200 V. The resulting mixed oxide films were investigated by XRD, SEM and EDS analysis. Photoelectrochemical properties were determined by linear sweep voltammetry in dark and under UV-C and UV-VIS irradiation.

Influence of Beam Power on Young’s Modulus and Friction Coefficient of Ti–Ta Alloys Formed by Electron-Beam Surface Alloying

In this study, we present the results of Young’s modulus and coefficient of friction (COF) of Ti–Ta surface alloys formed by electron-beam surface alloying by a scanning electron beam. Ta films were deposited on the top of Ti substrates, and the specimens were then electron-beam surface alloyed, where the beam power was varied from 750 to 1750 W. The structure of the samples was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Young’s modulus was studied by a nanoindentation test. The coefficient of friction was studied by a micromechanical wear experiment. It was found that at 750 W, the Ta film remained undissolved on the top of the Ti, and no alloyed zone was observed. By an increase in the beam power to 1250 and 1750 W, a distinguished alloyed zone is formed, where it is much thicker in the case of 1750 W. The structure of the obtained surface alloys is in the form of double-phase α’and β. In both surface alloys formed by a beam power of 1250 and 1750 W, respectively, Young’s modulus decreases about two times due to different reasons: in the case of alloying by 1250 W, the observed drop is attributed to the larger amount of the β phase, while at 1750 W is it due to the weaker binding forces between the atoms. The results obtained for the COF show that the formation of the Ti–Ta surface alloy on the top of Ti substrate leads to a decrease in the coefficient of friction, where the effect is more pronounced in the case of the formation of Ti–Ta surface alloys by a beam power of 1250 W.

Isolated copper–tin atomic interfaces tuning electrocatalytic CO2 conversion

Direct experimental observations of the interface structure can provide vital insights into heterogeneous catalysis. Examples of interface design based on single atom and surface science are, however, extremely rare. Here, we report Cu–Sn single-atom surface alloys, where isolated Sn sites with high surface densities (up to 8%) are anchored on the Cu host, for efficient electrocatalytic CO2 reduction. The unique geometric and electronic structure of the Cu–Sn surface alloys (Cu97Sn3 and Cu99Sn1) enables distinct catalytic selectivity from pure Cu100 and Cu70Sn30 bulk alloy. The Cu97Sn3 catalyst achieves a CO Faradaic efficiency of 98% at a tiny overpotential of 30 mV in an alkaline flow cell, where a high CO current density of 100 mA cm−2 is obtained at an overpotential of 340 mV. Density functional theory simulation reveals that it is not only the elemental composition that dictates the electrocatalytic reactivity of Cu–Sn alloys; the local coordination environment of atomically dispersed, isolated Cu–Sn bonding plays the most critical role.

Tuning adlayer-substrate interactions of graphene/h-BN heterostructures on Cu(111)–Ni and Ni(111)–Cu surface alloys

The evolution of the interface and interaction of h-BN and graphene/h-BN (Gr/h-BN) on Cu(111)–Ni and Ni(111)–Cu surface alloys versus the Ni/Cu atomic percentage on the alloy surface were comparatively studied by DFT-D2, including critical long-range van der Waals forces.