Aerosol-assisted Chemical Vapor Deposition of Metal Oxide Structures: Zinc Oxide Rods

Abstract

Whilst columnar zinc oxide (ZnO) structures in the form of rods or wires have been synthesized previously by different liquid- or vapor-phase routes, their high cost production and/or incompatibility with microfabrication technologies, due to the use of pre-deposited catalyst-seeds and/or high processing temperatures exceeding 900 °C, represent a drawback for a widespread use of these methods. Here, however, we report the synthesis of ZnO rods via a non-catalyzed vapor-solid mechanism enabled by using an aerosol-assisted chemical vapor deposition (CVD) method at 400 °C with zinc chloride (ZnCl2) as the precursor and ethanol as the carrier solvent. This method provides both single-step formation of ZnO rods and the possibility of their direct integration with various substrate types, including silicon, silicon-based micromachined platforms, quartz, or high heat resistant polymers. This potentially facilitates the use of this method at a large-scale, due to its compatibility with state-of-the-art microfabrication processes for device manufacture. This report also describes the properties of these structures (e.g., morphology, crystalline phase, optical band gap, chemical composition, electrical resistance) and validates its gas sensing functionality towards carbon monoxide.

ZnO Structures with Surface Nanoscale Interfaces Formed by Au, Fe2O3, or Cu2O Modifier Nanoparticles: Characterization and Gas Sensing Properties

“…The SEM images display the ZnO structured films with uniform rod-like morphology and the presence of equally distributed NPs due to the incorporation of Au NPs. XRD of the Au@ZnO films ( Figure 1 b) displays diffraction patterns connected with the hexagonal ZnO phase, in agreement with our previous observations [ 17 ], and an absence of Au diffraction peaks. This is probably connected with the high dispersion of the Au NPs over the film, their small size, and their low amount in the film.…”

“…The aerosol-assisted chemical vapor deposited ZnO films were characterized by a greyish color that uniformly covered the substrates. The morphological, structural, and chemical characteristics of these films were consistent with those observed in our previous work on ZnO [ 17 ]. Specifically, SEM images of the films displayed quasi-aligned rods (NRs) with lengths of approximately 1.5 μm and an average diameter of 200 nm.…”

“…ZnO rod structures were synthesized at 400 °C on Si/SiO 2 tiles (40 mm × 40 mm) and Si-based transducing platforms (40 mm × 40 mm) via the AACVD of ZnCl 2 (50 mg, ≥98.0%, Sigma–Aldrich, St. Louis, MO, USA) dissolved in ethanol (5 mL, ≥99.9%, PanReac, Chicago, IL, USA), as described earlier [ 17 ]. The transducing platforms contained 100 pairs of Cr/Au (40/200 nm thick) interdigitated electrodes (5 × 2000 μm) with an electrode gap of 5 μm isolated from the Si substrate by a SiO 2 layer.…”

“…Recently, we developed a method to deposit ZnO by aerosol-assisted chemical vapor deposition (AACVD), which offers significant advantages over other CVD techniques, including atmospheric pressure and relatively low-temperature process, as well as the possibility of tuning the material morphology and structure [ 15 , 16 ]. This method allowed the formation of crystalline rod-like ZnO structures and their direct integration into microsensors [ 17 ]. The surface modification of MOX structures with second-phase constituents can also be achieved by different methods [ 7 ]; amongst them, AACVD [ 18 , 19 , 20 ] and impregnation [ 21 , 22 ] methods proved effective to modify structures with both metals and MOXs.…”

Cerium Oxide-Tungsten Oxide Core-Shell Nanowire-Based Microsensors Sensitive to Acetone

“…Tungsten oxide (non-modified nanowires), cerium oxide (non-modified porous films), and cerium oxide-tungsten oxide core-shell nanowires were grown directly onto micromachined transducing platforms (Figure 2a) [18] using the AACVD system described previously [19]. AACVD is a variant of the conventional CVD technique, which uses aerosol to transport dissolved precursors to a heated reaction zone.…”