Hydrogen implantation in lanthanum thin films for ambient pressure hydride formation

Near room temperature superconductivity of metal superhydrides has been shown both theoretically and experimentally at high pressures ($>100$ GPa). Taking advantage of room temperature superconductivity for engineering applications requires decreasing the pressure of formation while retaining the superconducting hydride phase. We implanted lanthanum thin films with various doses of hydrogen ions at ambient pressure in order to form a lanthanum hydride phase. We found evidence for granular superconductivity below 5 K consistent with the phase coexistence of lanthanum hydride and lanthanum. As the H${}^{+}$ dose increased, $T_C$ decreased from 4.6 K to 3.2 K with broader superconducting transitions. Transmission electron microscopy showed increased substrate damage with increased ion dose and confirmed the granular structure of the films. Although a superhydride phase requires a higher H${}^{+}$ dose than what was attained in this work, we have demonstrated that ion implantation at ambient pressure is a feasible technique for superconducting lanthanum hydride formation.