Experimental Determination of Conduction and Valence Bands of Semiconductor Nanoparticles using Kelvin Probe Force Microscopy

W. Zhang, Y. Chen
Georgia Institute of Technology, US

Keywords: KPFM, conduction band, valence band, Fermi level, work function, contact potential difference


Determination of the band gaps (Eg), positions of conduction and valence bands (Ev and Ec) is critical for the understanding of many photochemical processes (e.g., photocatalyst synthesis for decomposing organic compounds or splitting water for hydrogen harvesting). Our previous work explored the application of Kelvin probe force microscopy (KPFM) in quantifying the local surface potential of engineered nanoparticles. In this study, we further developed an experimental method using KPFM and UV-visible spectroscopy to estimate the energy positions of the conduction and valence band edges of three types of pristine oxide nanoparticles (CuO, TiO2, and ZnO NPs). The experimental measurement of the contact potential difference (CPD) on NPs was converted to the Fermi levels and further used to calculate Ev and Ec. The experimental results reached excellent agreement with literature reported values. This experimental approach opened a unique way of estimating EV and EC of any unknown nanomaterials. In contrast, conventional methods for the determination of EV and EC are based on theoretical calculations (e. g., density-functional theory) are restrained to the simple semiconductor materials (e.g., diatomic compounds) and often requires the thermodynamic information of enthalpy or entropy, which is sometimes unavailable for new nanomaterials.