The monolayer FeSe film grown on ${\mathrm{SrTiO}}_3$ has attracted tremendous interest due to its remarkable interface-enhanced high-temperature superconductivity and emergent quantum phenomena. However, achieving controlled growth of monolayer FeSe on the ${\mathrm{SrTiO}}_3$ substrate remains challenging. Here, utilizing an in situ molecular beam epitaxy-scanning tunneling microscopy and spectroscopy combined system, we develop a method to successfully grow monolayer FeSe films on both conductive and insulating ${\mathrm{SrTiO}}_3$ substrates through a two-step deposition approach that involves the deposition of Fe clusters and subsequent selenization. By applying postannealing, we further tune the crystallinity and superconducting properties of the as-grown film, yielding an in situ scanning tunneling spectroscopy gap of ∼15.7 meV and an ex situ macroscopic transition temperature of ∼37.2 K. This work provides a valuable route for the controlled growth of interface-enhanced high-temperature superconductors and could be branched out into growing other similar compound films.

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• Growth
• Superconductivity
• 2-dimensional systems
• High-temperature superconductors
• Iron-based superconductors
• Monolayer films
• Annealing
• Electrical transport techniques
• Molecular beam epitaxy
• Scanning tunneling microscopy
• Scanning tunneling spectroscopy