First-principles insights into N 2 H 4 -assisted exfoliation of Cu x TiSe 2

The atomistic mechanisms governing solvent-mediated exfoliation of transition metal dichalcogenides remain poorly understood, limiting the rational design of scalable synthesis strategies. Here we investigate the role of hydrazine (${\mathrm{N}}_{2}{\mathrm{H}}_{4}$) in the liquid-phase exfoliation of ${\mathrm{TiSe}}_{2}$ and copper-intercalated ${\mathrm{TiSe}}_{2}$ (${\mathrm{Cu}}_{x}{\mathrm{TiSe}}_{2}$), is investigated combining density functional theory (DFT) calculations with experimental solvothermal synthesis under subcritical conditions. ${\mathrm{N}}_{2}{\mathrm{H}}_{4}$ is found to physisorb on pristine ${\mathrm{TiSe}}_{2}$ but chemisorb on ${\mathrm{Cu}}_{x}{\mathrm{TiSe}}_{2}$, driven by the formation of an N-Cu bond. This enhanced chemical affinity, rather than a simple geometric expansion of the interlayer spacing, is identified as the primary driver of the selective, copper-promoted exfoliation observed experimentally. ${\mathrm{N}}_{2}{\mathrm{H}}_{4}$ intercalation further increase the equilibrium interlayer separation and reduces the exfoliation energy. AFM characterization confirms the synthesis of monolayer ${\mathrm{Cu}}_{x}{\mathrm{TiSe}}_{2}$ sheets. These results reveal the key interactions that enable ${\mathrm{N}}_{2}{\mathrm{H}}_{4}$-assisted exfoliation of ${\mathrm{TiSe}}_{2}$ and its copper-intercalated analogs.