The effects of micro and macro structure on electronic properties of bismuth oxyiodide thin films

Abstract

Bismuth oxyiodide (BiOI) thin film was deposited using successive ionic layer adsorption and reaction (SILAR) technique under the same molar ratio of bismuth (III) nitrate pentahydrate (Bi(NO3)5H2O) and potassium iodide (KI). The effects of micro and macro structures due to the post-annealing treatment has been studied towards the improved electronic properties of BiOI films. BiOI thin film was perfectly coated without any cracks or pinholes. The as-deposited BiOI film displayed small flakes with flower shape microstructure. The flakes size has increased from ∼0.8 μm to ∼3.2 μm upon annealing at 350 °C, thenceforth shattered with increasing annealing temperature. BiOI films annealed at 350 °C showed a sharper band edge slope with an energy bandgap ∼1.61 eV compared to others annealing temperatures. The single crystalline BiOI film has transformed from tetragonal to tetragonal-orthorhombic polycrystalline with mix Bi5O7I3 and Bi7O9I3 phases after being annealed ≥450 °C. Electronic properties of BiOI were studied in terms of average resistance and conductivity measured using four-probe hall effect measurement. The conductivity value has reached the maximum for sample annealed at 350 °C, owing to the formation of ordered phase in material structure, higher crystallinity, larger flakes sizes, as well as reduction of defects and grain boundaries resistance. When the annealing temperature exceeded 450 °C, the electrical conductivity decreased due to the particle aggregation, sublimation of materials, formation of mix-phase and polycrystalline structure that generated grain boundaries and provided more resistance for electrons flow. The work has demonstrated a better understanding of material issues and some clues on the effect of the thickness, microstructure and structural properties on the electronic properties of BiOI thin film.

Enhancing the Conductivity and Dielectric Characteristics of Bismuth Oxyiodide via Activated Carbon Doping

“…Importantly, the Bi 4f peak centered at 159.58 eV of all carbon-doped samples slightly shift compared to BiOI (1C/BiOI, 0.8 eV; 5C/BiOI, 1.3 eV; and 10C/BiOI, 0.2 eV), while the peak at 164.68 eV shows a shift (1C/BiOI, 0.9 eV; 5C/BiOI, 1.5 eV; and 10C/BiOI, 0.2 eV), demonstrating how the interaction between carbon and BiOI is modifying the surface chemical environment of Bi [28][29][30]. The peak of Bi 4f 7/2 (or 4f 5/2 ) peak could be decomposed into two bimodal peaks (Figure 6A [36,37] and the absence of two peaks in the Bi 4f spectrum at ≈ 157 and 162 eV [38,39], respectively, indicating that there is no Bi-C bond. On increasing carbon content, the C 1s peaks of 5C/BiOI shift to 284.89 and 285.96 eV and 287.8 eV and of 10C/BiOI shift to 284.42 and 285.85 eV and 289.29 eV, indicating the surface chemical environment changing of Bi due to the strong interaction between carbon and BiOI [40,41].…”

“…The binding energies at 285.86, 287.65, and 290.95 eV correspond to C-C, C-O, and C=O. The absence of a minor peak in the C 1s spectrum at a lower binding energy of roughly ≈ 281-283 eV[36,37] and the absence of two peaks in the Bi 4f spectrum at ≈ 157 and 162 eV[38,39], respectively, indicating that there is no Bi-C bond. On increasing carbon content, the C 1s peaks of 5C/BiOI shift to 284.89 and 285.96 eV and 287.8 eV and of 10C/BiOI shift to 284.42 and 285.85 eV and 289.29 eV, indicating the surface chemical environment changing of Bi due to the strong interaction between carbon and BiOI[40,41].…”

Potential application of bismuth oxyiodide (BiOI) when it meets light

“…These values could be highly susceptible to the nanostructure and thickness of the BiOI film. 43 The electric properties of BiOI are suitable for its application in electronic devices-related applications. Indeed, compared to the optical properties, there are few reports on the electrical properties of BiOI, which need intensive investigation in the future from the aspects of experiment and calculations.…”

“…The conductivity and resistivity of BiOI could also be highly altered by structural engineering. 43 In addition, BiOI is also impossible to possess magnetic behavior. Nevertheless, by proper modification, we can modify BiOI having magnetic properties.…”