Synchronizing gas injections and time-resolved data acquisition for perturbation-enhanced APXPS experiments

An experimental approach is described in which well-defined perturbations of the gas feed into an Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS) cell are fully synchronized with the time-resolved x-ray photoelectron spectroscopy data acquisition. These experiments unlock new possibilities for investigating the properties of materials and chemical reactions mediated by their surfaces, such as those in heterogeneous catalysis, surface science, and coating/deposition applications. Implementation of this approach, which is termed perturbation-enhanced APXPS, at the SPECIES beamline of MAX IV Laboratory is discussed along with several experimental examples including individual pulses of N₂ gas over a Au foil, a multi-pulse titration of oxygen vacancies in a pre-reduced TiO₂ single crystal with O₂ gas, and a sequence of alternating precursor pulses for atomic layer deposition of TiO₂ on a silicon wafer substrate.