Enabling Photoemission Electron Microscopy in Liquids via Graphene-Capped Microchannel Arrays

Abstract

Photoelectron emission microscopy (PEEM) is a powerful tool to spectroscopically image dynamic surface processes at the nanoscale but is traditionally limited to ultra-high or moderate vacuum conditions. Here, we develop a novel graphene-capped multichannel array sample platform that extends the capabilities of photoelectron spectro-microscopy to routine liquid and atmospheric pressure studies with standard PEEM setups. Using this platform, we show that graphene has only a minor influence on the electronic structure of water in the first few layers and thus will allow for the examination of minimally perturbed aqueous-phase interfacial dynamics. Analogous to microarray screening technology in biomedical research, our platform is highly suitable for applications in tandem with large-scale data mining, pattern recognition, and combinatorial methods for spectro-temporal and spatiotemporal analyses at solid-liquid interfaces. Applying Bayesian linear unmixing algorithm to X-ray induced water radiolysis process, we were able to discriminate between different radiolysis scenarios and observe a metastable “wetting” intermediate water layer during the late stages of bubble formation.

2D Material Membranes for Operando Atmospheric Pressure Photoelectron Spectroscopy

“…Therefore Kolmakov et al introduced an alternative approach of using an array of microchannels which are covered with graphene on one end (working electrode), filled with a liquid electrolyte, and with the other end capped with an adhesive sealant that if conductive (e.g. solidified Ga) can also serve as the counter electrode [97,98]. Given that the size of an individual graphene covered aperture is limited by the area over which graphene can be reliably suspended (typically of the order of micrometres), this array of holes provides a larger total active area for measurement meaning that a less-focussed X-ray beam can be used whilst still detecting a sufficient photoelectron signal.…”

Graphene Microcapsule Arrays for Combinatorial Electron Microscopy and Spectroscopy in Liquids

“…The latter allows for the study of the complex spectro-temporal and spatiotemporal behaviors at liquid-solid interfaces. Finally, this platform is not limited to SEM metrology but can be used in laboratory stand-alone or synchrotron based X-ray photoelectron spectroscopy (XPS) 45 , photoelectron emission microscopy (PEEM) 32 , and low energy electron microscopy (LEEM) setups. We also successfully applied a variety of scanning probe microscopy techniques to the MCA liquid sample platform, which will be reported in forthcoming publications.…”

LEEM and PEEM as Probing Tools to Address Questions in Catalysis

“…In this case, the authors used a three-electrode cell with a solid electrolyte and were able to indirectly follow in real time the changes on a Pt surface due to the reaction of a specie generated electrochemically. On the other hand, it has been also reported the possibility of measuring with PEEM a liquid-solid interphase by using a graphene-capped microchannel array [69]. The idea behind this approach is to isolate the imaging components of LEEM/PEEM microscopes from the high pressure environment at which the samples are submitted in order to avoid technical problems with the high voltages typically used (15-20 kV).…”