Catalyst-Free Growth of ZnO Nanowires Based on Topographical Confinement and Preferential Chemisorption and Their Use for Room Temperature CO Detection

Two novel approaches for patterned growth of ZnO nanowires (NWs) based on the selective deposition of zinc acetate (ZA) solution precursors are presented and compared. The first is using the topographical confinement within a photoresist pattern on Si/SiO2 substrates (type I), and the second is using preferential chemisorption on self-assembled monolayer modified Au electrodes on Si/SiO2 substrates (type H). In both approaches, the ZnO seeds from the ZA solution form crystallites without severe defects over a large area via annealing at 350 degrees C. These seed layers were used to grow ZnO NWs via a catalyst-free vapor-phase deposition method using temperatures of up to 900 degrees C. The presented method is effective for realizing NW growth on both Si and Au electrodes by preserving the electrode configuration even at such high temperatures used for NW growth, which is a novelty and crucial for future sensor applications. As a result NWs connected through metal contact pads or electrodes have been realized in very simple and effective way. As a test of principle the resulting configurations were used to demonstrate a highly sensitive room temperature CO sensor. A CO concentration as low as 120 ppb was detected using both types of sensors. The type II sensor exhibited enhanced sensing properties compared to that of type I.