Epitaxial Growth of ⟨100⟩-Oriented Ultrathin (∼4 nm) Continuous Pt Films on MgO(001) and SrTiO ₃ (001) Substrates by Radio Frequency Magnetron Sputtering

⟨100⟩-Oriented Pt ultrathin epitaxial films have attracted attention as spin sources. However, Pt readily adopts a ⟨111⟩ orientation even on (001) substrates at low deposition temperatures (≤450 °C). The higher temperatures required for ⟨100⟩ growth hinder two-dimensional growth and coalescence of Pt-islands. Consequently, forming flat ⟨100⟩-oriented Pt films with a thickness below 10 nm is challenging. In this study, approximately 4 nm-thick ⟨100⟩-oriented Pt epitaxial films were demonstrated using two approaches based on radio frequency magnetron sputtering. The first method involved forming Pt-based seed crystals on MgO(001) substrates at high temperatures (≥650 °C), followed by Pt deposition at lower temperatures (≤250 °C) and subsequent postannealing at 450 °C. The second method was applied to SrTiO 3 (001) substrates. This involved first depositing an underlayer of Fe or Pt/Cu using vacuum evaporation at room temperature, followed by Pt sputtering deposition at 450 °C. The longitudinal electrical resistivities at room temperature were also sufficiently low (≤30 μΩ cm).