Tailoring the Surface Properties of ZnO Nanowires by ALD Deposition

Innovative research on metal-oxide gas sensors involves nanostructuring and surface modification as key elements to tailor sensitivity and selectivity. This work addresses a ZnO nanowire-based sensing device obtained by coupling a lithographically prepared substrate with hydrothermal ZnO growth, to align and interconnect the nanowires between two electrical contacts. Furthermore, conformal coating by atomic layer deposition technique allows functionalization of the surface of the nanowires with sub-monolayers of Al₂O₃ and TiO₂. A detailed analysis is carried out from a morphological and structural point of view with photoluminescence and Raman spectroscopy and electron microscopy. The material characterization results are analyzed in comparison with the functional characterization in gases toward reducing (NO₂) and oxidizing (H₂S) gases. Unparalleled sensing enhancement with Atomic Layer Deposition functionalization is obtained for NO₂ detection. The passivation role of surface states is discussed combining information from experimental techniques with a proposed model.