Stabilizing Metastable Polymorphs of van der Waals Solid MoS2 on Single Crystal Oxide Substrates: Exploring the Possible Role of Surface Chemistry and Structure

Abstract

In this work we address the question of growth of thin films of a soft van der Waals solid (2D MoS2) on a hard, crystalline metal oxide substrates. Thus, MoS2 thin films are grown on different single-crystal metal oxide substrates (SrLaAlO4, c-Al2O3, SrTiO3, LaAlO3) by pulsed laser deposition (PLD) and characterized by different techniques to confirm and quantify their phase constitution (2H, 1T′). We observe that, on the SrLaAlO4 (001) substrate, a mixed 1T′+2H phase of MoS2 grows with a dominant (∼75%) 1T′ phase, while on c-Al2O3 (0001) pure 2H phase grows. On the SrTiO3 and LaAlO3 substrates also the mixed phase grows, but with a much lesser component of the 1T′. Higher 1T′ contribution in SLAO and STO points to the chemical role of strontium in the early growth. It is also noted that, with increased film thickness on SrLaAlO4, the contribution of the pure 2H phase is enhanced, indicating the pivotal role of lattice strain in stabilizing the initial layer(s). The mixed 1T′+2H phase in the ultrathin film shows significantly lower room temperature resistivity (∼2 mΩ cm) with respect to that of the pure 2H phase (∼14 mΩ cm). The substrate selective polymorphism with distinct electronic features could invite multiple application interests.