Investigation of solid/vapor interfaces using ambient pressure X-ray photoelectron spectroscopy

Abstract

Heterogeneous chemical reactions at vapor/solid interfaces play an important role in many processes in the environment and technology. Ambient pressure X-ray photoelectron spectroscopy (APXPS) is a valuable tool to investigate the elemental composition and chemical specificity of surfaces and adsorbates on the molecular scale at pressures of up to 130 mbar. In this review we summarize the historical development of APXPS since its introduction over forty years ago, discuss different approaches to minimize scattering of electrons by gas molecules, and give a comprehensive overview about the experimental systems (vapor/solid interfaces) that have been studied so far. We also present several examples for the application of APXPS to environmental science, heterogeneous catalysis, and electrochemistry.

Insights into Electrochemical Reactions from Ambient Pressure Photoelectron Spectroscopy

“…[18][19] A typical instrument (Figure 1) consists of a highpressure cell/chamber, separated from the electron analyzer-which remains in high vacuum-by a differentially pumped electrostatic lens system and series of apertures. [20][21] Such instruments are found at synchrotrons around the world [22][23][24][25][26][27] and are being increasingly used with lab X-ray sources as well, which will further empower the field in the years to come. AP-XPS probes the surface chemistry of catalysts at elevated pressures, 29 identifying and quantifying adsorbates in equilibrium with the gas.…”

UHV and Ambient Pressure XPS: Potentials for Mg, MgO, and Mg(OH)2 Surface Analysis

“…2a). 10 A small aperture close to the sample leads to the first pumping stage where the pressure is about four orders of magnitude lower, while additional pumping stages further lower the pressure before the detector. The signal is maximized by electrostatic focusing onto the apertures between the differential pumping stages.…”

“…41 There are three basic configurations of APXPS measurement chambers as shown in Fig. 2b, c, and d. 10,12 Exposing a sample to a gas in a standard vacuum chamber is the simplest. These chambers typically have large volumes, and a background pressure of the dosed gas remains after the experiment, necessitating a bake-out to restore UHV.…”

A versatile photoelectron spectrometer for pressures up to 30 mbar

“…The majority of today's typical high-pressure photoelectron spectrometers are designed primarily for the study of solid surfaces under a high pressure (HP) gas atmosphere, and incorporate a small-volume "high-pressure" cell 7 or a backfilled analysis chamber 8 as described in more detail in Ref. 9. This concept can be traced back to the pioneering work of Roberts in the late 1970s.…”

“…13,14 While the use of synchrotron light sources has obvious advantages, it severely restricts the widespread use of the technique due to the limited number of synchrotron end stations with HPXPS capabilities. 9,15 Increasing availability is one of the key challenges if HPXPS is to be utilized to its full potential in a wide variety of subject areas, and indeed in the recent years there has been renewed interest in the development of laboratory-based HPXPS instruments utilizing differentially pumped analyzers and focused X-ray sources. 9,16,17 In processes ranging from heterogeneous catalysis 18 and electrochemical reactions in devices such as fuel cells, 19 solar cells, 20,21 and batteries [22][23][24] to environmental chemistry 25 and biomaterials 26 HPXPS is a fast-growing and valuable addition to the suite of advanced characterization techniques available to the scientific community.…”