  Controlling the crystalline structure of Hafnium Zirconate and its epitaxial
relationship to a semiconducting electrode has a high technological interest,
as ferroelectric materials are key ingredients for emerging electronic devices.
Using Pulsed Laser Deposition, a phase pure, ultra-thin film of HfZrO4 is grown
epitaxially on a GaN (0001) / Si (111) template. Since standard microscopy
techniques do not allow to determine with certitude the crystalline structure
of the film due to the weak scattering of oxygen, differentiated differential
phase contrast (DPC) Scanning Transmission Electron Microscopy is used to allow
the direct imaging of oxygen columns in the film. Combined with X-Rays
diffraction analysis, the polar nature and rhombohedral R3 symmetry of the film
are demonstrated.

Materials Science