Intercalation of Mn in a few layers of NbSe2 by molecular beam epitaxy

Abstract

Modifications of NbSe₂ ultrathin films by intercalation of Mn ions is investigated. The synthesis consists of a two-step approach. First NbSe₂ ultrathin films are grown by van der Waals epitaxy on either graphite (HOPG) or MoS₂ substrates. Optimized growth conditions show that at low growth temperatures of 250 °C phase-pure NbSe₂ is obtained. These films are then modified by a topotactical reaction with small amounts of vapor deposited Mn atoms. It is shown by combination of x-ray photoemission spectroscopy and low energy He-ion scattering spectroscopy that 0.2 to 0.3 monolayer-equivalent amounts of Mn atoms can react with the NbSe₂ and intercalate in between NbSe₂ layers before Mn adsorption occurs at the surface. The intercalation is confirmed by scanning tunneling microscopy (STM). The Mn ions remain disordered in the intercalation layer as evidenced by STM and low energy electron diffraction. Although the Mn²⁺ ions are in a high spin state long range magnetic ordering may be frustrated by the structural disorder. Nevertheless, the demonstration of hetero-TM intercalation into TMD layers is an important step in the synthesis of van der Waals crystals modified by elements with large magnetic moments.