Synthesis of Crystalline Superlattices by Controlled Crystallization of Modulated Reactants

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Abstract
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 NbSe2 and TiSe2 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 TiSe2/NbSe2 crystalline superlattices after annealing at 500°C. The large number of observed 00 diffraction orders permitted the average crystal structure of the superlattice in the direction of the c axis to be determined through a Rietveld analysis.