3.3.3.6. X-ray Absorption Spectroscopy

Introduction

These are a set of contributed definitions to describe X-ray absorption spectroscopy (XAS) experiments, in which the absorption coefficient of a sample is measured as a function of the incident photon energy across one or more absorption edges.

The generic NXxas application definition holds the energy axis and the processed absorption intensity that are common to every XAS experiment. Technique-specific application definitions extend NXxas to capture the detection mode and the metadata that a given technique requires.

Application Definitions

NXxas

Generic application definition for X-ray absorption spectroscopy. It stores the incident photon energy and the processed absorption intensity, and serves as the base that the technique-specific definitions below extend.

NXxas_trans

X-ray absorption measured in transmission, where the absorption coefficient follows the Beer-Lambert law \(\mu(E)\,t = -\ln(I/I_0)\).

Base Classes

NXelement

A chemical element of the periodic table.

NXabsorption_edge

An X-ray absorption edge, which arises from the excitation of an atom to a state with a core vacancy: when the incident photon energy reaches the threshold for this excitation, the absorption spectrum shows a sharp discontinuity.

NXemission_line

An emission line, which arises from the radiative decay of an atom with a core vacancy: an electron from a higher level fills the vacancy and a photon is emitted with an energy characteristic of the element.

NXauger_line

An Auger line, which arises from the non-radiative decay of an atom with a core vacancy: an electron from a higher level fills the vacancy and another electron, the Auger electron, is ejected with a kinetic energy characteristic of the element.