Abstract
Ambient-pressure photoelectron spectroscopy (APPES) and microscopy are at the frontier of modern chemical analysis at liquid-gas, solid-liquid and solid-gas interfaces, bridging science and engineering of functional materials. Complementing the current state-of-the art of the instruments, we survey in this short review several alternative APPES approaches, developed recently in the scanning photoelectron microscope (SPEM) at the Elettra laboratory. In particular, we report on experimental setups for dynamic near-ambient pressure environment, using pulsed-gas injection in the vicinity of samples or reaction cells with very small apertures, allowing for experiments without introducing additional differential pumping stages. The major part of the review is dedicated to the construction and performance of novel environmental cells using ultrathin electron-transparent but molecularly impermeable membranes to isolate the gas or liquid ambient from the electron detector operating in ultra-high vacuum (UHV). We demonstrate that two dimensional materials, such as graphene and derivatives, are mechanically robust to withstand atmospheric - UHV pressure differences and are sufficiently transparent for the photoelectrons emitted from samples immersed in the liquid or gaseous media. There are many unique opportunities for APPES using X-rays over a wide energy range. We show representative results that illustrate the potential of these 'ambient-pressure' approaches. Combined with the ca 100 nm lateral resolution of SPEM, they can overcome the pressure gap challenges and address the evolution of chemical composition and electronic structure at surface and interfaces under realistic operation conditions with unprecedented lateral and spectral resolution.
Highlights
Fundamental understanding and control of processes occurring at surfaces and interfaces can guide the design and optimization of catalysts and materials used in chemical industry, energy and electronic devices and will respond to many open questions in biomedical research
The major part of the review is dedicated to construction and performance of novel environmental cells, where ultrathin electron-transparent but molecularly impermeable membranes are used to isolate the gas or liquid ambient from the electron detector operated in ultra-high vacuum (UHV)
We demonstrate that two-dimensional materials, such as graphene and derivatives, are mechanically robust to withstand atmospheric—UHV pressure differences and are sufficiently transparent for the photoelectrons emitted & Andrei Kolmakov andrei.kolmakov@nist.gov & Sebastian Gunther sebastian.guenther@tum.de
Summary
Fundamental understanding and control of processes occurring at surfaces and interfaces can guide the design and optimization of catalysts and materials used in chemical industry, energy and electronic devices and will respond to many open questions in biomedical research. More than two decades ago, the demand to characterize the materials at their natural length scales has pushed the development of two major types of X-ray photoelectron microscopies operated with synchrotron light [22,23,24,25] and it is appealing to adapt such instruments for working at ‘ambient’ pressures. Such adaptation is practically impossible for the. The membrane-based approaches suitable for all type of instruments with electron detection are extensively discussed, including information on the recent progress in membrane characterization and fabrication technology
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