N.G. Mathews; E.J. Frankberg; V. Devulapalli; C. Kumar; B. Putz; A. Lambai; S. Khakalo; M. Cabrioli; B.H. Christensen; J.-P. Niemelä; A.M. Müller; F. Di Fonzo; I. Utke; E. Levänen; G. Mohanty
arXiv:2605.01917 (2026)
In this work, the microscale bending plasticity and fracture behavior of amorphous alumina (a-Al₂O₃) films were studied systematically as a function of deposition method and defect structure. Experiments were performed at room temperature using in situ microcantilever bending tests on a-Al₂O₃ films deposited by pulse laser deposition (PLD), atomic layer deposition (ALD), and sputter deposition (SD), followed by fracture toughness evaluation using notched microcantilevers. The results show substantial bending plasticity in PLD a-Al₂O₃ films, with total strains exceeding 10% without fracture, while ALD films exhibited mixed brittle and plastic responses depending on the defect distribution within the tested volume. In contrast, SD a-Al₂O₃ films showed elastic brittle failure, attributed to their columnar growth microstructure. Notched microcantilever bending tests showed brittle fracture in all three films with a similar fracture toughness of 3.1 ± 0.2 MPa·m⁰·⁵, effectively ruling out localized crack-tip plasticity. Our findings help in the understanding of the relationship between deposition route, defect structure, and microscale mechanical behavior in amorphous alumina films for the development of damage-tolerant amorphous oxides.