Fig. 3: Microscopic oxidation mechanisms with simulated reaction paths and derived band alignment.
From: Oxidation kinetics and non-Marcusian charge transfer in dimensionally confined semiconductors
a Dependence of r1L on photon energy (left vertical axis) and absorption spectrum of WS2 (right vertical axis). Yellow and blue shaded areas: subthreshold and active regimes of reaction, respectively. Horizontal dashed line and gray shaded area: limit of detection and regimes below. Green and blue symbols: data recorded at AH levels of 16.8 and 19.6 g/m3, respectively. Error bar: Standard deviation. b Two alternative reaction paths for defect-free WS2 with molecular O2 and activated O2-. c Two alternative reaction paths for defective WS2 containing sulfur vacancies with O2 and O2-. In b, c, the blue and red lines represent the energy levels of the initial state (IS), transition state (TS), intermediate state (MS), and final state (FS) during the oxidation reaction. Simulated atomic configurations during different reaction states are shown below. d Ultraviolet photoelectron spectroscopy spectrum for 1 L WS2 collected under electrostatic charge compensation mode. The position of valence band can be estimated from the difference of excitation energy (hν = 21.22 eV) and spectral width (W = 15.44 eV). Inset of d: zooming in near the Fermi edge. EV valence band, EVac vacuum energy level. e Charge-transfer mechanism within the framework of Marcus-Gerischer theory for oxidation reaction by considering the carrier equilibrium and band bending between 1 L WS2 and water/oxygen redox couple. EC conduction band, EF Fermi level, EF,redox redox potential of aqueous oxygen, Dred density of states of reduced species, Dox density of states of oxidized species.
