ResPES post-processing

ResPES spectra processing

Overview

The raw ResPES spectra must be first carefully normalized, aligned and calibrated before more extensive analysis. These pages will walk you through the most important data processing steps and basic tools for this purpose which are available at the beamline.

Some of the software tools are not easy to use out of the beamline. It is hence recommanded to complete the basic data processing (especially data aligning) during your beamtime. Most of the processing will be done in Wavemetrics Igor Pro.

Objective

Aligning spectra

Introduction

In order to subtract an off-resonace spectrum properly and to analyze CIS profiles, all ResPES spectra must be aligned on the binding/kinetic energy axis. They can be aligned to the first spectrum in the sequence, for instance. For this purpose, a reference wave with binding energy offsets for each spectrum is required. Once the reference wave is ready, the spectra can be aligned easily using BRIXIAS package procedures as shown below.

How it works

1. Prepare the reference wave. The built-in algorithms in Matrix operation panel (see below) might be sufficiently good in some cases but more accurate results are generally reached using KolXPD multi-peak fitting functions.
2. In Igor Pro, select menu XPS utilities -> Matrix operations -> General matrix operation panel...
3. In Matrix operation panel, select your ResPES wave A.
4. In Operations panel, select Align from the Task ring button B.
5. Select your reference wave C in Load Ref. wave... (The name of the reference wave will remain Ref_aling. Don'w worry about that, the wave you selected will be used.
6. Press Align! button D.
7. Save the aligned ResPES group using Store Image button E.

 

Making Reference wave for aligning

Introduction

Automatic peak fitting in KolXPD software is the most accurate way to prepare the reference wave for aligning ResPES spectra. The reference wave can be created from the peak positions of a core-level which was acquired simultaneously with the valence band region after each photon energy step.

Tips and tricks

• If the core-level was not measured, an analogous procedure can be applied on a shallow core-level in the valence band region or on the Fermi edge. Energy range borders must be adjusted accordingly in such cases.
• In some cases, a sufficienlty accurate reference wave can be easily created using the Calculate reference built-in function of the Matrix operations panel (Igor Pro, XPS utilities menu)
• The reference wave can be also created using the Wavemetrics built-in Batch Curve Fitting... package (Analysis -> Packages).

How it works

1. In KolXPD, open txt file with your ResPES spectra.
2. Select a core level region which was acquired simultaneosly with the valence band region after each photon energy step.
3. Select all core level spectra A and choose Fit all items... C from the Menu ring button B.

 

4. Make a reasonably good fit, then try to fix as much fitting parameters as possible, D. apart from the background, amplitudes and one peak position. If you have more than one peak, fix the relative peak positions to the one peak position, which will be left free.
5. Copy fit to other regions and press Fit all button E.

 

6. Then click on the peak position parameter which was left free F and choose Export selected parameter... G from the Menu ring button.
7. When save dialog window appears save the fitted peak positions as an itx file, which will be used as the reference wave for the aligning.