I have developed the XPS and XAS data analysis suite (so-called "EX3ms") for the synchrotron radiation (SR) soft x-ray beamline users to calibrate the energy and intensity in photons and electrons and analyze the peak composition and shape in the background subtracted profile. The code in the suite works in the Visual Basic for Applications (VBA) on the Windows Microsoft© Excel 2007 or later version utilizing the Solver Add-In for curve-fit optimisation. Excel 2016 on Mac or later version is also partly supported. Users easily handle and share the XPS and XAS data on Excel spread-sheet, and analyze it into the publications with your collaborators. Users immediately identify the atomic elements and its chemical shifts in their measured XPS and XAS spectra during the beamtime without annoying the calibration of energy and intensity at the SR beamline. The relative sensitivity factor and photo ionization cross section are taken into account to evaluate the atomic and chemical ratios. The various fitting functions in both peak and background are available to optimize the variables under certain constraints. User-defined function is also easily implemented by VBA scripting to untangle the spectral complexities in the sample characterization.
The VBA code is installed through VBE as the Personal Workbook Macro, and assigned with a short-cut key assignment in the macro called "PERSONAL.XLSB!CLAM2" listed at the top of sub procedures. Solver Add-in also needs to be deployed in Excel Add-ins and referenced in VBE to activate Solver Add-in for VBA code. Any data analysis sequence runs from the Option of Macro menu "PERSONAL.XLSB!CLAM2" or the short-cut key assigned on the worksheet in the workbook. The VBA code works differently on either what worksheet is active or what syntax is specified in active worksheet.
- Windows Excel 2007 https://youtu.be/tWpcnDjkHzo
- Windows Excel 2016 https://youtu.be/VAENRwzYRXk
- macOS Excel 2016 https://youtu.be/geoulV1kGx8
Any data placed in the Excel spreadsheet with specified formats can be analyzed in the VBA code. First of all, "KE/eV" is typed in the A1 cell for the spectrum with the kinetic energy scale. The kinetic energy data are in the first column below A2 and their corresponding intensities in the second column below B2. "BE/eV" at the A1 cell corresponds to the binding energy scale of spectrum, "PE/eV" the photon energy, and "ME/eV" any other scales. ISO (VAMAS) format is also acceptable, but the element and transition name is used for block identifier, so one vamas should be created from one set of spectra on one sample. The name of workbook has to be careful because it is also used for the name of worksheet contained the spectral data called the Data sheet, and the other processing worksheets for graphing (Graph sheet), fitting (Fit sheet). The length of workbook name is also limited within 19 characters other than the extension characters after a dot, because the VBA code adds the initial identifiers (6 characters as maximum) of each worksheet name prior to the worksheet name of the Data sheet, even though the name of Excel worksheet is limited within 25 characters.
The short-cut key is used to run the code on the Data sheet, and you can specify the photon energy and atomic elements in the dialogue boxes appeared during the processing. Eventually, the Graph and Fit sheets are generated from the Data sheet to tidy the data before the fitting process. Graph sheet is used to calibrate the energy and intensity, identify the peaks and chemical shifts, and compare the spectra reading from the other workbooks. The short-cut key is used to update the plots in the Graph and Fit sheets after the revisions of the parameters for calibrations and peak identification. Fit sheet is used to initiate the optimization of the background subtraction and peak fitting either in sequential or simultaneous. The parameters of fitting can be adjustable and constrained in the range after the first fitting sequence, and optimized repeatedly by using the short-cut key.
You can compare the spectral data with one after another in the Graph and Fit sheets. In the Graph sheet, the short-cut key is used with syntax "comp" in the D1 cells to open the dialogue for selection of the workbooks to be compared. You can also add or replace the data one after another to use "comp" in every 3 columns after D1 cell like G1, J1, and so on. In the Fit sheet, the short-cut key is used with syntax "ana" in the D1 cell only to open the dialogue for selection of the workbooks to be compared, and produces the Cmp sheet. Compared spectra normalized and calibrated in Graph and Cmp sheets are easily exported into the Exp sheet by the short-cut key with syntax "exp" in A1 cell to be used for the other programs.
Energy calibration is required to correct the energy scale for each spectrum, because the photon energy from the beamline is slightly deviated by the heat-load conditions and the electron energy from the sample is shifted by the charging or work function of instrument. It is difficult to evaluate the absolute photon and electron energies during the limited beamtime. However, the standard sample spectrum leads to the correct binding energy without evaluating the absolute energies, because the energies measured in the standard sample are well-known in the database or literature. It is also noted that the photon energy is used to evaluate the XPS sensitivity factors, so the roughly estimated photon energy is still required. In the Graph sheet, even though the photon energy, work function, and charging factor are adjustable parameters for binding energy correction, the calibration of binding energy is finalized in the charging factor.
The offset and multiple factors are also available to subtract baseline and scale spectral intensity for data comparison. To compare the multiple spectra at a glance, both ends of spectral intensity are automatically subtracted to be zero and scaled to be unity with the short-cut ley with the syntax of "auto" at A1 cell in Graph sheet. To specify the energy ranges for spectral offset and multiple scaling, "auto[x0,x1:x2,x3]" can be used in a way that the spectral range between x0 and x1 is averaged to be 0 (offset) and the range between x2 and x3 is averaged to be 1 (multiple). If either x0/x2 or x1/x3 is null, nothing happens to be scaled in the corresponding range. The original data scales for offset and multiple factors are 0 and 1 respectively, and easily reset at these values by syntax "auto0". After the energy calibration, you can also repeat the previous scaling with syntax "autop". It should be noted that the fitting process is performed on the original data only.
Spectral intensity is divided (normalized) by the other reference spectrum to compensate the noise or contamination happened during the measurement. Reference data can be added as the second data set with syntax "comp" in the Graph sheet prior to the normalization as mentioned above. The short-cut key with syntax "norm" at A1 cell in the Graph sheet proceeds the normalization of the first data set by the second data set resulting in the third data set in the Norm sheet.
The peaks calibrated and identified by the database in the Graph sheet are analyzed in the Fit sheet based on the least-square regression method. Peak area is evaluated with analytical and numerical ways together with the choice of background subtraction processes. The number of peaks can be chosen with parameters such as curve shape, energy, FWHM width, amplitude etc. All the parameters can be constrained or limited in a specific range. Amplitude ratios and peak energy differences among the peaks are also adjustable in the cells with specified syntax described elsewhere.
- Gaussian (G), Lorentzian (L), and its blended function (GL) with tail parameters for asymmetric peak (TGL) based on the models here
- Shirley and Tougaard backgrounds blended with and without polynomial function
- Constant, linear, quadratic, and cubic for polynomial background
- Polynomial and its blended backgrounds optimized with peak fittings (active mode: "BG" to "ABG")
- Error-function, Arctangent and Victoreen backgrounds for XAS pre-edge subtraction
- Trapezoidal (numerical) integration for peak areas normalized by various sensitivity factors including photoionization cross section, source angle correction, MFP, analyzer transmission function etc.
- User-defined function can be easily implemented in the Visual Basic programming.
Batching process can be customized from the macro called "PERSONAL.XLSB!debugAll".
EX3ms has been used for many users during the experiment and post-data processing to publish the data in the manuscript in peer-reviewed journals in the following.
- http://dx.doi.org/10.1016/j.snb.2013.12.017
- http://dx.doi.org/10.1016/j.apsusc.2016.01.180
- http://dx.doi.org/10.1016/j.carbon.2015.01.018
- http://dx.doi.org/10.1016/j.jenvman.2015.09.036
- http://dx.doi.org/10.1039/C6RA09972F
Database files are available online linked in the following subsections. You can add elements with orbital, binding energy, and sensitivity factor in the UD.xlsx. Cross section for each photon energy can be further evaluated from the data of photoionization cross section in WebCross folder. XAS atomic form factor can also be used for XAS sensitivity based on XAS folder. All the files can be downloaded online specified below except UD.xlsx which has to be handled manually from database.
X-ray data booklet
Values compiled by Gwyn P. Williams (updated Excel file and poster available)
Scofield photoionization cross-section database combined with x-ray booklet binding energy database "Hartree-Slater subshell photoionization cross-sections at 1254 and 1487 eV" J. H. Scofield, Journal of Electron Spectroscopy and Related Phenomena, 8129-137 (1976).
"Calculated Auger yields and sensitivity factors for KLL-NOO transitions with 1-10 kV primary beams" S. Mroczkowski and D. Lichtman, J. Vac. Sci. Technol. A 3, 1860 (1985).
- http://dx.doi.org/10.1116/1.572933
- http://www.materialinterface.com/wp-content/uploads/2014/11/Calculated-AES-yields-Matl-Interface.pdf
(Electron beam energy at 1, 3, 5, and 10 keV for relative cross section and derivative factors)
"X-Ray Interactions: Photoabsorption, Scattering, Transmission, and Reflection at E = 50-30,000 eV, Z = 1-92" B. L. Henke, E. M. Gullikson, and J. C. Davis, Atomic Data and Nuclear Data Tables 54, 181-342 (1993).
Photoionization cross section online database files should be downloaded and placed in this folder.
"Atomic Calculation of Photoionization Cross-Sections and Asymmetry Parameters" J. J. Yeh, Gordon and Breach Science Publishers, Langhorne, PE (USA), 1993.
"Atomic subshell photoionization cross sections and asymmetry parameters: 1 <= Z <= 103" J. J. Yeh and I. Lindau, Atomic Data and Nuclear Data Tables, 32, 1-155 (1985).
Note that database are supposed to be revised and updated locally based on the experiment. All the database files are based on AlKa source energy at 1486.6 eV, and webCross data normalize the RSF. You may also check spectral lines and profiles online below;
The XPS library (database, spectra, analytical procedures etc.)
NIST X-ray Photoelectron Spectroscopy Database
"The NIST X-ray photoelectron spectroscopy (XPS) database" C. D. Wagner, NIST Technical Note 1289 (1991).
The Surface Analysis Society of Japan: Common Data Processing System
Spectroscopy Hub (VAMAS XPS data file)
Harwell XPS GURU (technical detailed in knowledge base)
This repository is public to test the code for general purpose of any curve fitting. In fact, I have developed the bunch of code optimized for BL3.2Ua data format and analysis at SLRI. If you are an user of BL3.2Ua in Siam Photon Laboratory, I will send you a link of the beamline version of code.