fig2

Figure 2. (A) Schematic of the electron depletion layer theory. Mechanistic representation of acetone sensing by an n-type MOS sensor (A₁); Initial electronic levels (A₂); Changes in the electronic levels of n-type MOS upon exposure to oxygen (A₃) and target gases (A₄). Figure 2A is quoted with permission from Panigrahi et al.^[37]; (B) Core-shell configuration of p-type MOS in vacuum and air (B₁); Interaction of p-MOS in the presence of reducing gas CO (B₂) and in oxidizing NO₂ (B₃). Figure 2B is quoted with permission from Kaur et al.^[38]; (C) Schematic illustration of gas diffusion processes at different pore sizes; (D) Schematic representation of gas diffusion processes within hollow tin dioxide microspheres at different temperatures. Figure 2C and D is quoted with permission from Wang et al.^[34]. MOS: Metal oxide semiconductor.