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

Abstract

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 XPS 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 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.

Aligning time-resolved kinetics (TAP) and surface spectroscopy (AP-XPS) for a more comprehensive understanding of ALD-derived 2D and 3D model catalysts

“…For example, the actual partial pressure of reactants in front of the sample area probed by AP-XPS is usually lower than the nominal pressure measured in the chamber due to the differential pumping through the analyzer. 84 Considerable progress has been made in improving the understanding and control of the gas transport in AP-XPS devices, 14,85–87 and further corrections can be devised for the exposure models in both devices. We envision that these advanced capabilities will enable more robust and flexible transient experiments to be performed in kinetic and spectroscopic devices with eventual data reconciliation in mind from the start of experimental planning and data acquisition.…”

Spiers Memorial Lecture: prospects for photoelectron spectroscopy

“…65 In the last decade, the potential of NAP-XPS to contribute to the understanding of commercially important thin film growth processes has been realised, and although there remain rather few published studies, investments are being made to support these challenging experiments at a number of synchrotron sources, including at the SPECIES and HIPPIE beamlines at MAX-IV. 66,67 The pressure used in atomic layer deposition (ALD) (and the useful range in some chemical vapour deposition (CVD) processes) is typically in the 10 −3 to 20 mbar range, which is well-matched to NAP-XPS. 23 However, there are also formidable challenges.…”

“…It is necessary then to develop a ‘snapshot’ mode capability, where data from many repeated cycles may be summed at the same temporal delay between pulse and spectrum (akin to those developed for some forms of time-resolved pump–probe photoelectron spectroscopy, discussed in Section 4.4). 66 This can then be used to study ‘steady-state’ ALD, when the chemistry is identical for a large number of successive pulses. This capability was realised for a test reaction (CO oxidation on Pd(100)) in 2021.…”

Characterization of model and real catalysts by APXPS

“…Redekop et al have implemented the gas pulse perturbation approach at the Species beamline in Max IV using a time counting, delay-line detector. In this proof-of-concept work, emphasis has been put on the careful characterization of the gas transport within the cell during the pulses, obtaining an estimation of the residence time and of the intrinsic reaction rate constant range that can be accessed [18].…”