Effect of laser plasma parameters on epitaxial growth of β-FeSe/SrTiO­­­­₃ heterostructures

The combination of different materials in heterostructures often enables phenomena that are impossible to achieve in a single compound. A now-classic example is the interface-enhanced superconductivity of monolayer β-FeSe on (001)-oriented SrTiO₃ (STO). Plasma-synthesized heterostructures based on this system are suitable for the creation of quantum materials configurations to study interface-enhanced processes, magnetic/superconducting proximity effects, and control of quantum properties via electrostatic gating. In this work, we show how tuning the laser-produced plasma of pulsed laser deposition can alter the structure and interface of β-FeSe/STO heterostructures. Langmuir probe diagnostics and thin film x-ray diffraction were utilized. Laser plasmas with electron density (n_e) below ~5×10¹⁹ m^-3 and electron temperatures (T_e) of 0.1-0.2 eV lead to epitaxial c-axis oriented β-FeSe/STO with clear thickness fringes in dynamical x-ray diffraction (Pendellösung oscillations), indicating high crystal quality and sharp interface. On the other hand, plasmas with n_e ~10²⁰ m^-3 and T_e ≈ 0.5-0.6 eV result in β-FeSe with a mixture of two epitaxial orientations, less defined interface, and a greater degree of mosaicity or defects. We will describe how adjusting the laser plasma parameters may allow further control in plasma-mediated growth of β-FeSe/STO such as spatial modulation of nucleation sites, modification of island growth patterns, and activation of plasma-enhanced surface reactivity.