PhD thesis defense: Designing hybrid superlattices via molecular intercalation in van der Waals materials

Layered van der Waals (vdW) materials offer an atomically precise platform where electronic properties are governed as much by interlayer coupling as by in-plane chemistry. This thesis advances intercalation – the insertion of guest species (atoms, ions or molecules) into the vdW gap – as a materials-by-design route to engineer structural, electronic, magnetic properties and correlated behaviors beyond the interface-limited reach of electrostatic/ionic gating, surface functionalization and proximity effects in heterostructures. Intercalation generates compositionally defined hybrid phases in which three intertwined – (i) structural (interlayer spacing, stacking, polymorphism), (ii) electronic (doping, carrier density), and (iii) supramolecular/chemical (guest–host hybridization, induced ordering) levers – jointly determine the electronic and magnetic structure of the intercalation compound (IC), giving rise to emergent properties absent in either component alone. We first use two antiferromagnetic hosts, NiPS3 and MnPS3, as testbeds, mapping their electrochemistry/chemistry to steer them toward ferri- and ferromagnetic ground states via established intercalation routes, revealing how process parameters, reaction pathways and rational guest choice dictate IC architecture and magnetism. Because micrometre-scale devices are essential for integration and transport measurements yet conventional electrochemical setups are complex and the process often damaging, we develop a bias-free galvanic route that decouples the electron source from the molecular guest via sacrificial anodes. Insertion proceeds under intrinsic kinetics, producing highly crystalline superlattices from bulk crystals down to few-layer flakes. In particular, intercalation into TMDCs (2H-TaS₂, 2H-NbSe2) devices and into α-RuCl3 and CrSBr bulk crystals rebalances CDW/superconductivity and converts antiferromagnets into ferri-/ferromagnets, respectively. Collectively, these results elevate intercalation from a chemical/electrochemical process to a materials-by-design toolkit, providing actionable design rules and a scalable, device-ready platform to program spacing, doping and host-guest interactions – and thus superconductivity, magnetism and competing orders – in vdW materials.