In situ gas cell for the analysis of adsorption behavior on surfaces using x-ray spectroscopy

TL;DR

This paper introduces a versatile in-situ gas cell designed for X-ray spectroscopy to analyze VOC adsorption on surfaces, demonstrated through experiments with ethanol at a synchrotron facility.

Contribution

The development of a flexible, high-versatility gas cell enabling simultaneous surface and gas-phase XAFS measurements for VOC adsorption studies.

Findings

Successful detection of VOCs like ethanol using the cell.

Effective comparison of gas-phase and surface-adsorbed spectra.

Validation of the cell's capability for monitoring adsorption processes.

Abstract

A gas cell for in-situ measurements of Volatile Organic Compounds (VOCs) and their adsorption behavior on different surfaces by means of X-Ray Fluorescence (XRF) and X-ray Absorption Fine-Structure (XAFS) spectroscopy has been developed. The cell is especially designed to allow for the efficient excitation and detection of low-Z elements such as carbon, oxygen or nitrogen as main components of VOCs. Two measurement modes are available. In the surface mode, adsorption on a surface can be studied using XAFS by fluorescence detection under shallow angles of incidence. The transmission mode enables the simultaneous investigation of gaseous samples via XAFS in transmittance and fluorescence detection modes. Proof-of-principle experiments were performed at the PTB plane grating monochromator beamline for soft x-ray radiation at the synchrotron radiation facility BESSY II. The flexible design and high versatility of the cell are demonstrated with the investigation of ethanol (EtOH) as one of the most abundant VOCs. The comparison of Near-Edge X-ray Absorption Fine-Structure (NEXAFS) spectra under transmission and fluorescence detection in the gas phase with measurements of adsorbed molecules on a Si-wafer surface both at the C and O-K absorption edges proves the applicability of the cell for the monitoring of adsorption processes.