Epitaxial Growth of ⟨100⟩-Oriented Ultrathin (∼4 nm) Continuous Pt Films on MgO(001) and SrTiO3(001) Substrates by
Soshi Akita1, Tomohiro Yasuda1, Yuki Sobukawa1
1Degree Programs in Pure and Applied Sciences, Graduate School of Science and Technology, University of Tsukuba, Tsukuba, Ibaraki305-8573, Japan.
Abstract:
⟨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 SrTiO3(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).
