Robust Hydrophobic Materials by Surface Modification in Transition-Metal Diborides

Exploring the hydrophobicity of robust conductors is significant for electronic devices to simultaneously be used in a wet environment and extreme conditions. However, a combination of conductivity, strong mechanical properties, and hydrophobicity in one material is hindered by the inherent features of the materials. A new kind of robust hydrophobic conductor is designed in transition-metal diborides (TMdBs: TiB₂, ZrB₂, and HfB₂) to break through this challenge. The results calculated by density functional theory indicate that high hardness comes from high shear and bulk modulus, which is consistent with experimental results (TiB₂, 25.0 GPa; ZrB₂, 17.5 GPa; HfB₂, 21.5 GPa). The theoretical calculated results reveal that edge sides have a lower surface energy than basal plane (001) in TMdBs. Hence, the edge sides are exposed with a needle-like morphology in TMdBs. Moreover, needle-like surfaces exhibiting hydrophobicity have water contact angles of 132.0° (TiB₂), 116.8° (ZrB₂), and 114.0° (HfB₂). The hydrophobicity arises from a lower surface free energy of edge sides in TMdBs and a rough surface that reduces the contact area of water and a solid. This work develops a new kind of robust functional material in TMdBs.