Interphase-engineering by atomic layer deposition of nacre-inspired alumina composites

Nacre, also known as mother of pearl, is a layered brick-and-mortar structure composed of hard mineral platelets and soft organic protein. Found in the inner shells of certain mollusks, this natural architecture has evolved to optimize mechanical properties for the protection of the organism. The unique structured design of nacre and its exceptional mechanical performance have inspired the development of synthetic nacre-like materials. In this work, we introduce a novel approach for fabricating nacre-inspired ceramic composites using atomic layer deposition (ALD) to engineer the interphase, or “mortar”, between aligned alumina platelets. ALD, known for its sub-nanometer thickness control and conformal coating capabilities, enables uniform tuning of the interphase thickness from 30 nm up to 120 nm, offering a significant advantage in tailoring the mechanical properties of ceramic-ceramic composites. Our results reveal a direct correlation between ALD-deposited aluminum oxide thickness and enhanced mechanical performance, with increased modulus and hardness observed as the mortar thickens. Three-point bending tests further show that flexural strength is maximized with thicker ALD coatings . In situ micromechanical testing reveals crack initiation at surface defects in micro-cantilevers, with cracks effectively deflected by the nacre-inspired architecture. This resultsin an average flexural strength of approximately 400 MPa, achieved without additional heat treatment or sintering. The precision of ALD in creating conformal interphases is critical to the improved structural integrity and performance of the composite, demonstrating its potential asa powerful technique for fabricating high-performance, bio-inspired ceramic composites.