Reza Mohammadi

Metal diborides typically contain transition metals in between the graphene-like boron sheets. High entropy enables the incorporation of the main group metalloid silicon and overcomes chemical coordination preferences.

Rhenium diboride (ReB₂) exhibits high differential strain due to its puckered boron sheets that impede shear deformation. Here, we demonstrate the use of solid solution formation to enhance the Vickers hardness and differential strain of ReB₂. ReB₂-structured solid solutions (Re_0.98Os_0.02B₂ and Re_0.98Ru_0.02B₂, noted as “ReOsB₂” and “ReRuB₂”) were synthesized via arc-melting from the pure elements. In-situ high-pressure radial x-ray diffraction was performed in the diamond anvil cell to study the incompressibility and lattice strain of ReOsB₂ and ReRuB₂ up to ∼56 GPa. Both solid solutions exhibit higher incompressibility and differential strain than pure ReB₂. However, while all lattice planes are strengthened by doping osmium (Os) into the ReB₂ structure, only the weakest ReB₂ lattice plane is enhanced with ruthenium (Ru). These results are in agreement with the Vickers hardness measurements of the two systems, where higher hardness was observed in ReOsB₂. The combination of high-pressure studies with experimentally observed hardness data provides lattice specific information about the strengthening mechanisms behind the intrinsic hardness enhancement of the ReB₂ system.

Silver nanovines, prepared at ambient pressure and temperature, were grown in solution using eutectic gallium‐indium (EGaIn) seeds. In this process, EGaIn serves both as an effective reductant and heterogeneous nucleation center enabling the selective growth of silver nanovines from aqueous silver nitrate solutions. This process is a versatile route towards grafted silver nanostructures performed under ambient conditions with non‐toxic reagents.

The present study investigates the impact and freezing behavior of the droplets of surfactant solutions on non-wettable coatings at very low temperatures of −10 to −30 °C. Our goal is to elucidate the critical role of concentration, molecular weight, and ionic nature of surfactants on these phenomena. To achieve this goal, we used sodium dodecyl sulfate (anionic), hexadecyltrimethylammonium bromide (cationic), and n-decanoyl-n-methylglucamine (nonionic) at four concentrations ranging from 0 to 2 × CMC (critical micelle concentration). We captured the impact-freezing of the droplets on superhydrophobic alkyl ketene dimer coatings using a high-speed camera at 5000 frames per second. The results show that the ability of the droplets to spread and retract on the coatings is a function of concentration, ionic nature, and molecular weight of the surfactants, as well as the temperature-dependent viscosity of the solutions. Additionally, surfactant-laden droplets generally demonstrated an accelerated freezing compared to pure water. This might be due to the fact that the presence of surfactants can promote both heterogeneous ice nucleation from within the liquid and a larger solid–liquid interfacial area by filling the air pockets of the surface, leading to enhanced heat transfer. The behavior of the cationic surfactant at certain concentrations was, however, an exception leading to a freezing delay, for which a mechanism will be proposed.

Due to their unique mechanical, tribological, thermal, and anticorrosion properties, nickel-tungsten (Ni-W) alloy films have become indispensable for many industrial applications. The present study investigates the impact of W content on the microstructure and mechanical properties of Ni-W thin films. By co-sputtering of Ni and W on silicon wafers coated with a thin buffer layer (∼20 nm) of titanium (Ti), six Ni-W coatings were fabricated, ranging from pure Ni to pure W. The samples were characterized using energy dispersive spectroscopy, x-ray diffraction, scanning electron microscopy, atomic force microscopy, and microindentation. The results show that hardness of the Ni-W films is primarily a function of the W content, which changes the microstructure and surface morphology of the samples. When W concentration is smaller than 40 at. %, the Ni-rich samples have a face-centered cubic structure and the hardness increases with the W content. For the samples having 40 < W < 55 at. %, the sensitivity of the hardness to the W content becomes markedly low, which could be due to the presence of an amorphous phase. Finally, the impact of W addition on the hardness of the samples containing 55–80 at. % W is two times greater than that of W < 40 at. %. The extra hardening effect could be attributed to the dominancy of a solid solution hardened body-centered cubic W phase and electronic interaction between two transition metals. This sharp increase in the hardness leads to obtaining a high hardness of 21.9 ± 2.0 GPa for the Ni-79 at. % W film. The findings of this study show that solid solution strengthening could be considered the main hardening mechanism of these films.