Revealing the role of interfacial heterogeneous nucleation in the metastable thin film growth of rare-earth nickelate electronic transition materials.

Although rare-earth nickelates (ReNiO 3 , Re ≠ La) exhibit abundant electronic phases and widely adjustable metal to insulator electronic transition properties, their practical electronic applications are largely impeded by their intrinsic meta-stability. Apart from elevating the oxygen reaction pressure, heterogeneous nucleation is expected to be an alternative strategy that enables the crystallization of ReNiO 3 at low meta-stability. In this work, the respective roles of high oxygen pressure and heterogeneous interface in triggering ReNiO 3 thin film growth in the metastable state are revealed. ReNiO 3 (Re = Nd, Sm, Eu, Gd and Dy) thin films grown on a LaAlO 3 single crystal substrate show effective crystallization at atmospheric pressure without the necessity to apply high oxygen pressure, suggesting that the interfacial bonding between the ReNiO 3 and substrates can sufficiently reduce the positive Gibbs formation energy of ReNiO 3 , which is further verified by the first-principles calculations. Nevertheless, the abrupt electronic transitions only appear in ReNiO 3 thin films grown at high oxygen pressure, in which case the oxygen vacancies are effectively eliminated via high oxygen pressure reactions as indicated by near-edge X-ray absorption fine structure (NEXAFS) analysis. This work unveils the synergistic effects of heterogeneous nucleation and high oxygen pressure on the growth of high quality ReNiO 3 thin films.