Ever since the invention of photoelectron spectroscopy, researchers have attempted to analyze materials under conditions closely resembling their application environment. Near-Ambient Pressure X-ray Photoelectron Spectroscopy is a logical development in this quest, since it allows for analyzing non-vacuum compatible samples in general, and phase boundaries, such as solid|liquid or solid|gas interfaces, in particular. With the development of spectrometer systems compatible with analysis pressures of up to 100 mbar, many novel experimental geometries have been realized since the early 2000s. Since then, experimental capability and variety have further progressed through the proliferation of off-synchrotron laboratory systems, and advanced sample environments to simulate material usage conditions. This progress has, e.g., enabled the performance of operando spectroscopy during catalytic or electrochemical experiments. The present work gives, from an instrumental point of view, a short overview over basic system design considerations and recent developments in the field.
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