Investigation of tunable work function, electrostatic force microscopy and band structure of TiO₂ nanoparticles using Kelvin probe force microscopy

The tunable work function of titanium dioxide (TiO₂) nanoparticles of various sizes was measured using the Kelvin Probe Force Microscopy (KPFM) technique. The analysis of the Contact Potential Difference (CPD) across TiO₂nanoparticles of different sizes revealed a clear relationship between nanoparticle size and work function. The study observed work function values ranging from 4.49 eV to 4.57 eV for particle sizes between 3 nm and 85 nm, which were higher than those of bulk TiO₂likely due to quantum confinement effects. Additionally, electrostatic force microscopy (EFM) measurements showed significant charge-trapping behavior within TiO₂nanoparticles under different applied bias voltages. The UV–visible absorption analysis of TiO₂ nanoparticles revealed an energy band gap of 3.35 eV, which larger that of bulkTiO₂. Photoluminescence spectroscopy exhibited two distinct emission peaks at 383 nm, which attributed to near-band-edge excitonic emissions, and 403 nm, corresponding to defect-related states. Investigation on the positions of the conduction band (CB) and valence band (VB) of TiO₂ nanoparticles has been carried by considering the work function and band gap information. The investigation revealed that as the particle size increased, the CB energy shifted slightly toward lower values, and the VB energy shifted slightly toward lower values. Conversely, smaller nanoparticles exhibit larger band gaps and higher work functions.