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 digitally synchronized with time-resolved XPS data acquisition with a Delay Line Detector (DLD). 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 (1) individual pulses of N2 gas over 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 (ALD) of TiO2 on a silicon wafer substrate.