Bottom-up formation of robust gold carbide

A new phenomenon of structural reorganization is discovered and characterized for a gold-carbon system by in-situ atomic-resolution imaging at temperatures up to 1300 K. Here, a graphene sheet serves in three ways, as a quasi transparent substrate for aberration-corrected high-resolution transmission electron microscopy, as an in-situ heater, and as carbon supplier. The sheet has been decorated with gold nanoislands beforehand. During electron irradiation at 80 kV and at elevated temperatures, the accumulation of gold atoms has been observed on defective graphene sites or edges as well as at the facets of gold nanocrystals. Both resulted in clustering, forming unusual crystalline structures. Their lattice parameters and surface termination differ significantly from standard gold nanocrystals. The experimental data, supported by electron energy loss spectroscopy and density-functional theory calculations, suggests that isolated gold and carbon atoms form – under conditions of heat and electron irradiation – a novel type of compound crystal, Au-C in zincblende structure. The novel material is metastable, but surprisingly robust, even under annealing condition

Atomic-scale understanding of oxidation mechanisms of materials by computational approaches: A review

The urgent requirement of minimising the worldwide cost of corrosion, accompanied by the increasingly pivotal role of advanced oxide materials, highlights the importance of understanding the mechanisms of material oxidation at the atomic level, which could help us to precisely control the oxidation processes. Nowadays, we are able to model and predict how the surface structures of materials evolve during oxidation based on the cross-fertilisation of various computational techniques. This review first overviews the state-of-the-art first-principles and force-field-based approaches for modelling surface reactions. Then, classical theories and recent advances in understanding the atomic-scale oxidation of bulk materials are introduced, from the initial solid-gas interactions to the subsequent oxide film growth. Defect-promoted oxidation mechanisms will be discussed in detail. Finally, distinct oxidation mechanisms of nanomaterials are discussed, including nanoparticles, nanowires, and two-dimensional materials, which are significantly different from their bulk counterparts and could result in novel oxide nanostructures with unique properties. This review provides a systematic overview of the central role of computational techniques in probing the atomic-scale oxidation mechanisms, which could further guide the synthesis of oxide-based cutting-edge materials such as ultra-thin oxide films and hollow oxide nanostructures

Ab-Initio and Molecular Dynamics Simulations Capturing the Thermodynamic, Kinetics, and Thermomechanical Behavior of Galvanized Low-Alloy Steel

A seven-element Modified Embedded Atom Method (MEAM) potential comprising Fe, Mn, Si, C, Al, Zn, and O is developed by employing a hierarchical multiscale modeling paradigm to simulate low-alloy steels, inhibition layer, and galvanized coatings. Experimental information alongside first-principles calculations based on Density Functional Theory served as calibration data to upscale and develop the MEAM potential. For calibrating the single element potentials, the cohesive energy, lattice parameters, elastic constants, and vacancy and interstitial formation energies are used as target data. The heat of formation and elastic constants of binary compounds along with substitutional and interstitial formation energies serve as binary potential calibration data, while substitutional and interstitial pair binding energies aid in developing the ternary potential. Molecular dynamics simulations employing the developed potentials predict the thermal expansion coefficient, heat capacity, self-diffusion coefficients, thermomechanical stress-strain behavior, and solid-solution strengthening mechanisms for steel alloys comparable to those reported in the literature. Interfacial energies between the steel substrate, inhibition layer, and surface oxides shed light on the interfacial nanostructures observed in the galvanizing process