Low-temperature deposition of meta-stable β-MoO3(011) epitaxial thin films using step-and-terrace substrates

• Meta-stable β-MoO3(011) thin films are fabricated using dc magnetron sputtering.
• Depositions on step-and-terrace substrates realize the β-MoO3(011) epitaxy.
• The step-and-terrace structure is a key to control the growth behavior.

We demonstrated the epitaxial growth of meta-stable β-MoO3(011) thin films on SrTiO3(100), NdGaO3(110), and NdGaO3(001) substrates, using dc reactive magnetron sputtering. Low-temperature deposition at ~ 200 °C resulted in the suppression of the formation of thermodynamically stable α-MoO3, and we observed the growth of a β-MoO3 phase with mixed orientation. In contrast, depositions on substrate surfaces with a step-and-terrace structure resulted in uniaxially oriented β-MoO3(011) epitaxial thin films. The step-and-terrace structures were found to play an important role in controlling the epitaxial growth behavior of β-MoO3 thin films.