Gibson Asumani Boakye

Topic

Mechanochemical fabrication of ZnO nanoparticle inks for eco- friendly low-cost thin film environmental sensors

Department of Electrical & Computer Engineering

Date & location

• Friday, May 15, 2026

• 1:30 P.M.

• Engineering Office Wing

• Room 230

Reviewers

Supervisory Committee

• Dr. Chris Papadopoulos, Department of Electrical and Computer Engineering, University of Victoria (Supervisor)

• Dr. Tao Lu, Department of Electrical and Computer Engineering, UVic (Member) 

External Examiner

• Dr. David Leitch, Department of Chemistry, University of Victoria 

Chair of Oral Examination

• Dr. Aditya Mojumdar, Department of Biochemistry and Microbiology, UVic 

Abstract

The increasing demand for low-cost, scalable, and energy-efficient sensing technologies has driven significant interest in nanomaterial-based thin film sensors. This thesis presents the fabrication and characterization of zinc oxide (ZnO) nanoinks via a low processing temperature mechanochemical planetary ball milling (PBM) approach for the fabrication of eco-friendly, flexible, and low-cost gas sensors. The study focuses on establishing a low input energy, simple and scalable solution-based process that enables the direct conversion of bulk ZnO powder into functional nanoinks suitable for thin film deposition. ZnO nanoinks were prepared through wet ball milling under varying conditions, including milling speed (200 rpm to 800 rpm), time (10 minutes to 120 minutes), and solvent type (DI water, ethylene glycol and Isopropyl alcohol), to investigate their influence on nanoparticle size, morphology, and dispersion. Thin films were subsequently fabricated by deposited the nanoinks onto a wide range of low-cost substrates including glass slide, filter, plain and lined paper, plastic polymer, foil, ceramic and flexible materials using an adjustable blade applicator technique to form films with controlled thickness (15 μm to 50 μm) and uniformity. The versatility of substrate selection highlights the potential for low-cost and f lexible sensor fabrication. Material characterization was conducted using techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Raman spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy, and energy dispersive X-ray spectroscopy (EDX), confirming the formation of nanoscale ZnO. Variations in milling conditions were observed to affect particle size (~ 10 to 500 nm), dispersion, and film morphology with wurtzite crystal structure and desirable optical and morphological properties. Initial gas sensing measurements of the fabricated ZnO thin films on different substrates was evaluated under various conditions, including different gas species (Hydrogen, dry air and argon), gas concentrations (low and high), and different flow systems (static and continuous flow) at room temperature. The sensors demonstrated measurable and reproducible responses, with sensitivity which can be affected by particle size, porosity, and film thickness with response magnitude increasing with increasing target gas concentration (~ 50 to 500 sccm). These results represent a proof-of-concept for low-temperature sensing using solution-processed ZnO films and the sensing mechanism may be attributed to surface adsorption and desorption processes involving oxygen species, which modulate charge carrier concentration and electrical conductivity upon exposure to target gases. This work demonstrates that PBM-fabricated ZnO nanoinks enable low-cost, scalable fabrication of flexible thin film gas sensors. The preliminary gas sensing results provide insight into how processing conditions influence material properties and sensing behavior, highlighting potential for environmental, industrial, and wearable sensing applications.