Figure 4. The top panel gives orthorhombic lattice parameters ao, bo, and co as a function of He dose.

The orthorhombic c axis is clamped to the substrate and remains constant, while ao and bo increase upon strain doping. The bottom panel shows the evolution of the pseudocubic out-of-plane parameter cpc and orthorhombic distortion (ao − bo) of the films as a function of He dose. Increasing the He dose allows for fine and continuous control over octahedra rotation and tetragonality.