Solute-adsorption enhanced heterogeneous nucleation: the effect of Cu adsorption on α-Al nucleation at the sapphire substrate

Interfacial adsorption of solute atoms is a promising means to tune heterogeneous nucleation. In this study, a new method has been established to theoretically evaluate the effect of solute addition on the nucleation potency of heterogeneous nucleation interfaces. The evaluation consists of three steps: (1) analyzing the solute adsorption behavior; (2) determining the nucleation mode; and (3) evaluating the effect of solute adsorption on nucleation potency using the solute-adsorbed interface model. A combination of the ab initio and molecular dynamics methods together with the two-phase thermodynamic model was used to evaluate a prototype Al-Cu/(0001) sapphire interface. It is found that solute Cu atoms adsorb at the interface between the melt and (0001) sapphire interface. The adsorption is driven by the strengthening of the Cu-Al bonds as revealed by the Bader charge analysis which is demonstrated to reduce interfacial energy. Furthermore, it is revealed that the interfacial adoption of Cu results in the formation of an Al-Cu adsorption layer, which enhances the interfacial chemical affinity thus enlarging the nucleation driving force. Meanwhile, the lattice mismatch between the sapphire substrate and the primary Al (α-Al) nucleus is decreased by Cu addition, which lowers the barrier for nucleation. The above two effects together increase the nucleation potency of the studied interface, which is in good agreement with previous experiments. It is proposed that the effect of solute adsorption shall be considered in the search for effective substrates for tuning the nucleation.

Effects of B on the Segregation Behavior of Mo at the Fe–Cr(111)/Cr2O3(0001) Interface: A First-Principles Study

The addition of B can inhibit the precipitation of σ phases at the grain boundary to improve the hot workability and corrosion resistance for super austenitic stainless steel with high Cr and Mo content. This study focused on the interaction between B and Mo at the Fe–Cr(111)/Cr2O3(0001) interface and its effect on interfacial adhesion by employing the first-principles method, especially the effect of B on the segregation behavior of Mo. The most stable O-terminated Fe/Cr2O3 interface was chosen as the basic configuration. The segregation energy and the work of separation were calculated for the metal/chromia interface with Fe–Cr as the substrate. It has been demonstrated that B can promote the diffusion of Mo atoms into the oxide layer to increase the content of Mo in the passive film. In addition, the interfacial adhesion is higher at the most segregated sites. However, it is more difficult for two or more Mo atoms than a single Mo atom to diffuse into the oxide part with the effect of B, indicating that B can only improve the Mo content of the passive film to a small extent. The electronic properties were also further discussed to analyze the interactions and the binding characters between doped atoms and their surrounding atoms and to explain the underlying reasons for the variation of interfacial adhesion.

Effects of dopants on the adhesion and electronic structure of a SnO2/Cu interface: a first-principles study

Doping has been adopted as a versatile approach for tuning the adhesion of metal oxide/metal interfaces. Understanding the mechanism of doping at the interface adhesion on the atomic and electronic scale is crucial for the rational design and optimization of metal oxide/metal composites. In this work, we have investigated the effects of dopants on the adhesion of SnO2/Cu interfaces through first-principles calculations. Firstly, O-terminated a SnO2(110)/Cu(111) interface (denoted as I) was considered and the work of separation values of the interfaces with various dopants (Mo, Sb, Ti, Zn and Cu) were calculated to evaluate the interface adhesion strength. It was demonstrated that low-valence dopants (Zn2+ and Cu2+) enhance the adhesion strength of interface I, while high-valence dopants (Mo6+ and Sb5+) play the opposite role. Secondly, the strengthening effects of low-valence dopants were further verified in four candidate interfacial models with different atomic structures (denoted as II-V). The work of separation values indicated that the adhesion of all of the interfaces involved could be enhanced by low-valence doping. The electronic structure of the interface was demonstrated through density of states, charge density and charge density difference analyses. The results revealed that upon low-valence doping, the holes facilitate charge transfer between Cu and SnO2, which generates strong covalent bonds across the interface and thus significantly enhances the interface adhesion. This work not only provides insight into rational doping to enhance the adhesion of SnO2/Cu composites but can also be expanded upon for the design of other metal oxide/metal composites with strong interface adhesion.

Alloying effects of Ag on grain boundaries and alumina interfaces in copper: a first principles prediction

The mechanical properties of oxide dispersion-strengthened copper are largely dictated by its internal interfaces, i.e. the oxide interfaces and the grain boundaries (GBs).

On the Reliability of Pure and Hybrid DFT Methods for the Evaluation of Halogen, Chalcogen, and Pnicogen Bonds Involving Anionic and Neutral Electron Donors

In this article, we report a comprehensive theoretical study of halogen, chalcogen, and pnicogen bonding interactions using a large set of pure and hybrid functionals and some ab initio methods. We have observed that the pure and some hybrid functionals largely overestimate the interaction energies when the donor atom is anionic (Cl(-) or Br(-)), especially in the halogen bonding complexes. To evaluate the reliability of the different DFT (BP86, BP86-D3, BLYP, BLYP-D3, B3LYP, B97-D, B97-D3, PBE0, HSE06, APFD, and M06-2X) and ab initio (MP2, RI-MP2, and HF) methods, we have compared the binding energies and equilibrium distances to those obtained using the CCSD(T)/aug-cc-pVTZ level of theory, as reference. The addition of the latest available correction for dispersion (D3) to pure functionals is not recommended for the calculation of halogen, chalcogen, and pnicogen complexes with anions, since it further contributes to the overestimation of the binding energies. In addition, in chalcogen bonding interactions, we have studied how the hybridization of the chalcogen atom influences the interaction energies.