Synthesis of Crystalline Superlattices by Controlled Crystallization of Modulated Reactants

A series of crystalline superlattice compounds containing an integral number of intergrown transition metal-dichalcogenide layers was prepared through controlled crystallization of Ti/Se/Nb/Se superlattice reactants rather than through epitaxial growth. The component elemental-layer thicknesses and annealing sequence were chosen to favor interfacial nucleation of the component binary compounds. The layered reactants contracted in the c -axis direction during an initial low-temperature anneal as NbSe 2 and TiSe 2 crystallites nucleated and grew along the interfaces, kinetically trapping the desired superlattice structure. The c -axis domain size increased gradually as a function of annealing time and temperature, yielding high-quality c -axis-oriented TiSe 2 /NbSe 2 crystalline superlattices after annealing at 500°C. The large number of observed 00ℓ diffraction orders permitted the average crystal structure of the superlattice in the direction of the c axis to be determined through a Rietveld analysis.