Self-assembly of correlated (Ti, V)O2 superlattices with tunable lamella periods by kinetically enhanced spinodal decomposition

Abstract

Spinodal decomposition, the spontaneous phase separation process of periodic lamellae at the nanometer scale, of correlated oxide ((Ti, V)O2) systems offers a sophisticated route to achieve a new class of mesoscale structures in the form of self-assembled superlattices for possible applications using steep metal–insulator transitions. Here, we achieve the tunable self-assembly of (Ti, V)O2 superlattices with steep transitions (ΔTMI < 5 K) by spinodal decomposition with accurate control of the growth parameters without conventional layer-by-layer growth. Abrupt compositional modulation with alternating Ti-rich and V-rich layers spontaneously occurs along the growth direction because in-plane lattice mismatch is smaller in this direction than in other directions. An increase in the film growth rate thickens periodic alternating lamellae; the phase separation can be kinetically enhanced by adatom impingement during two-dimensional growth, demonstrating that the interplay between mass transport and uphill diffusion yields highly periodic (Ti, V)O2 superlattices with tunable lamellar periods. Our results for creating correlated (Ti, V)O2 oxide superlattices provide a new bottom-up strategy to design rutile oxide tunable nanostructures and present opportunities to design new material platforms for electronic and photonic applications with correlated oxide systems.