Fig. 2. Dielectric constant, band gap, and breakdown field strength of CVD-grown Bi₂SiO₅ nanoflakes.

a Typical Bias-dependent capacitance (C) measurements on CVD-grown Bi₂SiO₅ nanoflake with a common metal-insulator-metal (MIM) device configuration, where the thick graphite and In/Au metals serve as the bottom and top electrodes (inset), respectively. The dielectric constant (ɛ_r) of Bi₂SiO₅ was estimated as ~32.4 at 100 Hz. b Corresponding frequency-dependent capacitance (C–f) characteristics of the MIM device, whose OM image is inset in b. c The thickness-dependent effective permittivity (ε_eff) of Bi₂SiO₅ nanoflakes with a measuring frequency of 100 Hz. The dashed blue curve is a visual guide. d Ultraviolet-visible (UV-vis) absorption spectrum of CVD-grown Bi₂SiO₅ nanoflakes transferred onto quartz substrate with high coverage by mechanical pressing. The inset shows the fitting of its optical band gap (~3.8 eV) by Tauc’s law, where a, h, and ν are the absorption coefficient, Planck constant and frequency, respectively. e Energy band gap versus dielectric constant of representative dielectric materials in literature, showing the coexistence of high dielectric constant and large band gap in Bi₂SiO₅. The dashed line is a visual guide. f Thickness-dependent current-voltage curves of Bi₂SiO₅ nanoplates measured by C-AFM, showing a high breakdown field strength of 9.4 MV/cm (8.2 nm).