Phase interface atom structure in Hf-based oxide film

Significant progress has been made in studying the microscopic mechanism of ferroelectricity in HfO₂ thin films. However, there is still insufficient research on the atomic arrangement and underlying principles of domain and phase boundaries. The atomic structure near the interface boundary can provide insights into the formation principles of phase boundaries, enabling a better understanding of phase stability, domain switching, and phase transformation. In this study, the aberration-corrected scanning transmission electron microscope is used to investigate the atomic structure of HfO₂ materials at the boundaries. The study reveals the formation of orthorhombic phase (O phase)/monoclinic phase (M phase) interfaces throughout the entire grain, with both coherent interface and incoherent interfaces. By examining the atomic structure at these boundaries, we explain the strain and the structure of atoms at different phase boundaries. In a coherent interface, 90° charged domain walls and 90° uncharged domain walls is found, where charged domain walls have positively charged (oxygen-ion diminishing) and negatively charged (oxygen-ion accumulating) interfaces due to the presence of polarized charges. In addition, the O phase/M phase coherent interface possesses transition region between the O phase and M phase, but there is a stepped phase boundary structure in the O phase/M phase incoherent interface, due to the high mismatch stress. These studies provide favorable assistance for the microstructure of phase stability and the evolution laws of phase transitions.