We aim to enhance the carbon fibre (CF)-matrix interface by synthesizing carbon nanotubes (CNTs) on the surface of the CF, creating a hierarchical composite. A 12 nm thick aluminium oxide film applied by atomic layer deposition (ALD) provides protection of the CF from deterioration during CNT growth in a chemical vapour deposition (CVD) process. However, the adhesion of alumina to CF, grown in classical water/trimethylaluminium ALD is severely diminishing during CNT growth, as detected by interface shear strength (IFSS) measurements. In our approach to improve the CF-alumina adhesion, we employed a pre-treatment of the CF with ozone and entirely replaced water with ozone in the ALD process, to promote the covalent bonding of the alumina to the CF surface. The current results show a new perspective in achieving the CNT synthesis on the CF while successfully mitigating its detrimental effects on the fibre mechanical properties.