Using XPSPEAK Version 4.1

November 2000

Contents Page Number

XPS Peak Fitting Program for WIN95/98 XPSPEAK Version 4.1 .............. 1

Program Installation ......................................................................................................... 1

Introduction ...................................................................................................................... 1

First Version ............................................................................................................................................ 1

Version 2.0 .............................................................................................................................................. 1

Version 3.0 .............................................................................................................................................. 1

Version 3.1 .............................................................................................................................................. 2

Version 4.0 .............................................................................................................................................. 2

Version 4.1 .............................................................................................................................................. 2

Future Versions ....................................................................................................................................... 2

General Information (from R. Kwok) ........................................................................................................ 3

Using XPS Peak ........................................................................................... 3

Overview of Processing ................................................................................................... 3

Appearance ..................................................................................................................... 4

Opening Files .................................................................................................................. 4

Opening a Kratos (*.des) text file ............................................................................................................ 4

Opening Multiple Kratos (*.des) text files ................................................................................................ 5

Saving Files ..................................................................................................................... 6

Region Parameters .......................................................................................................... 6

Loading Region Parameters .................................................................................................................... 6

Saving Parameters .................................................................................................................................. 6

Available Backgrounds .................................................................................................... 6

Averaging................................................................................................................................................. 7

Shirley + Linear Background ................................................................................................................... 7

Tougaard ................................................................................................................................................. 8

Adding/Adjusting the Background .................................................................................... 8

Adding/Adjusting Peaks ................................................................................................... 9

Peak Types: p, d and f. .......................................................................................................................... 10

Peak Constraints ................................................................................................................................... 11

Peak Parameters ................................................................................................................................... 11

Peak Function ........................................................................................................................................ 12

Region Shift ................................................................................................................... 13

Optimisation ................................................................................................................... 14

Print/Export .................................................................................................................... 15

Export .................................................................................................................................................... 15

Program Options............................................................................................................ 15

Compatibility .................................................................................................................. 16

File I/O ................................................................................................................................................... 16

Limitations ................................................................................................. 17

Cautions for Peak Fitting .......................................................................... 17

Sample Files: ............................................................................................. 17

gaas.xps ................................................................................................................................................ 17

Cu2p_bg.xps ......................................................................................................................................... 18

Kratos.des.............................................................................................................................................. 18

ASCII.prn ............................................................................................................................................... 18

Other Files ............................................................................................................................................. 18

XPS Peak Fitting Program for WIN95/98 XPSPEAK

Version 4.1

Program Installation

XPS Peak is freeware. Please ask RCSMS lab staff for a copy of the zipped

3.3MB file, if you would like your own copy

Unzip the XPSPEA4.ZIP file and run Setup.exe in Win 95 or Win 98.

Note: I haven’t successfully installed XPSPEAK on Win 95 machines unless they have been running Windows 95c – CMH.

Introduction

Raymond Kwok, the author of XPSPEAK had spent >1000 hours on XPS peak fitting when he was a graduate student. During that time, he dreamed of many features in the XPS peak fitting software that could help obtain more information from the XPS peaks and reduce processing time.

Most of the information in this users guide has come directly from the readme.doc file, automatically installed with XPSPEAK4.1

First Version

In 1994, Dr Kwok wrote a program that converted the Kratos XPS spectral files to ASCII data. Once this program was finished, he found that the program could be easily converted to a peak fitting program. Then he added the dreamed features into the program, e.g.

A better way to locate a point at a noise baseline for the Shirley

background calculations

Combine the two peaks of 2p3/2 and 2p1/2 Fit different XPS regions at the same time

Version 2.0

After the first version and Version 2.0, many people emailed Dr Kwok and gave additional suggestions. He also found other features that could be put into the program.

Version 3.0

The major change in Version 3.0 is the addition of Newton’s Method for optimisation

Newton’s method can greatly reduce the optimisation time for multiple

region peak fitting.

Version 3.1

1. Removed all the run-time errors that were reported

2. A Shirley + Linear background was added

3. The Export to Clipboard function was added as requested by a user Some other minor graphical features were added

Version 4.0

Added:

1. The asymmetrical peak function. See note below

2. Three additional file formats for importing data

A few minor adjustments

The addition of the Asymmetrical Peak Function required the peak function to be changed from the Gaussian-Lorentzian product function to the Gaussian-Lorentzian sum function. Calculation of the asymmetrical function using the Gaussian-Lorentzian product function was too difficult to implement. The software of some instruments uses the sum function, while others use the product function, so both functions are available in XPSPEAK. See Peak Function, (Page 12) for details of how to set this up.

Note:

If the selection is the sum function, when the user opens a *.xps file that was optimised using the Gaussian-Lorentzian product function, you have to re-optimise the spectra using the Gaussian-Lorentzian sum function with a different %Gaussian-Lorentzian value.

Version 4.1

Version 4.1 has only two changes.

1. In version 4.0, the printed characters were inverted, a problem that was

due to Visual Basic. After about half year, a patch was received from Microsoft, and the problem was solved by simply recompiling the program

2. The import of multiple region VAMAS file format was added

Future Versions

The author believes the program has some weakness in the background subtraction routines. Extensive literature examination will be required in order to revise them. Dr Kwok intends to do that for the next version.

General Information (from R. Kwok)

This version of the program was written in Visual Basic 6.0 and uses 32 bit processes. This is freeware. You may ask for the source program if you really want to. I hope this program will be useful for people without modern XPS software. I also hope that the new features in this program can be adopted by the XPS manufacturers in the later versions of their software.

If you have any questions/suggestions, please send an email to me. Raymund W.M. Kwok

Department of Chemistry

The Chinese University of Hong Kong

Shatin, Hong Kong

Tel: (852)-2609-6261

Fax:(852)-2603-5057

email: rmkwok@cuhk.edu.hk

I would like to thank the comments and suggestions from many people. For the completion of Version 4.0, I would like to think Dr. Bernard J. Flinn for the routine of reading Leybold ascii format, Prof. Igor Bello and Kelvin Dickinson for providing me the VAMAS files VG systems, and my graduate students for testing the program. I hope I will add other features into the program in the near future.

R Kwok.

Using XPS Peak

Overview of Processing

1. Open Required Files

See Opening Files (Page 4)

2. Make sure background is there/suitable

See Adding/Adjusting the Background, (Page 8)

3. Add/adjust peaks as necessary

See Adding/Adjusting Peaks, (Page 9), and Peak Parameters,

(Page 11)

4. Save file

See Saving Files, (Page 6)

5. Export if necessary

See Print/Export, (Page 15)

Appearance

XPSPEAK opens with two windows, one above the other, which look like this:

The top window opens and displays the active scan, adds or adjusts a background, adds peaks, and loads and saves parameters. The lower window allows peak processing and re-opening and saving

data

Opening Files

Opening a Kratos (*.des) text file

1. Make sure your data files have been converted to text files. See the back

of the Vision Software manual for details of how to do this. Remember, from the original experiment files, each region of each file will now be a separate file.

2. From the Data menu of the upper window, choose Import (Kratos)

Choose directory

Double click on the file of interest

The spectra open with all previous processing INCLUDED

Opening Multiple Kratos (*.des) text files

You can open up a maximum of 10 files together.

1. Open the first file as above

Opens in the first region (1)

2. In the XPS Peak Processing (lower) window, left click on 2 (second

region), which makes this region active

3. Open the second file as in Step 2, Opening a Kratos (*.des) text file,

(Page 4)

Opens in the second region (2)

You can only have one description for all the files that are open. Edit

with a click in the Description box

4. Open further files by clicking on the next available region number then

following the above step.

You can only have one description for all the files that are open. Edit

with a click in the Description box

Description

Box

2

To open a file that has already been processed and saved using

XPSPEAK, click on the Open XPS button in the lower window. Choose directory and file as normal

The program can store all the peak information into a *.XPS file for later use. See below.

Saving Files

1. To save a file click on the Save XPS button in the lower window

2. Choose Directory

3. Type in a suitable file name

4. Click OK

Everything that is open will be saved in this file The program can also store/read the peak parameter files (*.RPA) so

that you do not need to re-type all the parameters again for a similar spectrum.

Region Parameters

Region Parameters are the boundaries or limits you have used to set up the background and peaks for your files. These values can be saved as a file of the type *.rpa.

Note that these Region Parameters are completely different from the mathematical parameters described in Peak Parameters, (Page 11) Loading Region Parameters

1. From the Parameters menu in the upper window, click on Load Region

Parameters

2. Choose directory and file name

3. Click on Open button

Saving Parameters

1. From the Parameters menu in the XPS Peak Fit (Upper) window, click

on Save Region Parameters

2. Choose directory and file name

3. Click on the Save button

Available Backgrounds

This program provides the background choices of

Shirley

Linear

Tougaard

Averaging

Averaging at the end points of the background can reduce the time to

find a point at the middle of a noisy baseline

The program includes the choices of None (1 point), 3, 5, 7, and 9

point average

This will average the intensities around the binding energy you

select.

Shirley + Linear Background

1. The Shirley + Linear background has been added for sloping

backgrounds

The "Shirley + Linear" background is the Shirley background plus a

straight line with starting point at the low BE end-point and with a slope value

If the slope value is zero, the original Shirley calculation is used

If the slope value is positive, the straight line has higher values at

the high BE side, which can be used for spectra with higher background intensities at the high BE side

Similarly, a negative slope value can be used for a spectrum with

lower background intensities at the high BE side

2. The Optimization button may be used when the Shirley background is

higher at some point than the signal intensities

The program will increase the slope value until the Shirley

background is below the signal intensities

Please see the example below - Cu2p_bg.xps - which shows

background subtraction using the Shirley method (This spectrum was sent to Dr Kwok by Dr. Roland Schlesinger).

A shows the problematic background when the Shirley background

is higher than the signal intensities. In the Shirley calculation routine, some negative values were generated and resulted in a non-monotonic increase background

B shows a "Shirley + Linear" background. The slope value was input

by trial-and-error until the background was lower than the signal intensities

C

was obtained using the optimisation routine

A slope = 0

B slope = 11 C slope = 15.17

Note: The background subtraction calculation cannot completely remove the background signals. For quantitative studies, the best procedure is "consistency". See Future Versions, (Page 2).

Tougaard

For a Tougaard background, the program can optimise the B1 parameter by minimising the "square of the difference" of the intensities of ten data points in the high binding energy side of the range with the intensities of the calculated background.

Adding/Adjusting the Background Note: The Background MUST be correct before Peaks can be added. As with all backgrounds, the range needs to include

as much of your peak as possible and as little of anything else as possible.

1. Make sure the file of interest is open and the appropriate region is active

2. Click on Background in the upper window

The Region 0 box comes up, which contains the information about

the background

3. Adjust the following as necessary. See Note.

High BE (This value needs to be within the range of your data) Low BE (This value needs to be within the range of your data) NOTE: High and Low BE are not automatically within the range of your data. CHECK CAREFULLY THAT BOTH ENDS OF THE BACKGROUND ARE INSIDE THE EDGE OF DATA. Nothing will happen otherwise.

No. of Ave. Pts at end-points. See Averaging, (Page 7)

Background Type

Note for Shirley + Linear:

To perform the Shirley + Linear Optimisation routine:

a) Have the file of interest open

b) From the upper window, click on Background

c) In the resulting box, change or optimise the Shirley + Linear

Slope as desired

Using Optimize in the Shirley + Linear window can cause problems. Adjust manually if necessary

3. Click on Accept when satisfied

Adding/Adjusting Peaks Note: The Background MUST be correct before peaks can be added. Nothing will happen otherwise. See previous section.

To add a peak, from the Region Window, click on Add Peak

The peak window appears

This may be adjusted as below using the Peak Window which will

have opened automatically

In the XPS Peak Processing (lower) window, there will be a list of Regions, which are all the open files, and beside each of these will be numbers representing the synthetic peaks included in that region.

Regions

(files)

Synthetic

Peaks

1. Click on a region number to activate that region

The active region will be displayed in the upper window

2. Click on a peak number to start adjusting the parameters for that peak.

The Processing window for that peak will open

3. Click off Fix to adjust the following using the maximum/minimum arrow

keys provided:

Peak Type. (i.e. orbital – s, p, d, f)

S.O.S (Δ eV between the two halves of the peak)

Position

FWHM

Area

%Lorenzian-Gaussian

See the notes for explanations of how Asymmetry works.

4. Click on Accept when satisfied

Peak Types: p, d and f.

1. Each of these peaks combines the two splitting peaks

2. The FWHM is the same for both the splitting peaks, e.g. a p-type peak

with FWHM=0.7eV is the combination of a p3/2 with FWHM at 0.7eV and a p1/2 with FWHM at 0.7eV, and with an area ratio of 2 to 1

3. If the theoretical area ratio is not true for the split peaks, the old way of

setting two s-type peaks and adding the constraints should be used. The S.O.S. stands for spin orbital splitting.

Note: The FWHM of the p, d or f peaks are the FWHM of the p3/2, d5/2 or f7/2, respectively. The FWHM of the combined peaks (e.g. combination of p3/2 and p1/2) is shown in the actual FWHM in the Peak Parameter Window.

Peak Constraints

1. Each parameter can be referenced to the same type of parameter in

other peaks. For example, for four peaks (Peak #0, 1, 2 and 3) with known relative peak positions (0.5eV between adjacent peaks), the following can be used

Position: Peak 1 = Peak 0 + 0.5eV

Position: Peak 2 = Peak 1 + 0.5eV

Position: Peak 3 = Peak 2 + 0.5eV

2. You may reference to any peak except with looped references.

3. The optimisation of the %GL value is allowed in this program.

A suggestion to use this feature is to find a nice peak for a certain

setting of your instrument and optimise the %GL for this peak.

Fix the %GL in the later peak fitting process when the same

instrument settings were used.

4. This version also includes the setting of the upper and lower bounds for

each parameter.

Peak Parameters

This program uses the following asymmetric Gaussian-Lorentzian sum

The program also uses the following symmetrical Gaussian-Lorentzian product function

Peak Function

Note:

If the selection is the sum function, when the user opens a *.xps file that was optimised using the Gaussian-Lorentzian product function, you have to re-optimise the spectra using the Gaussian-Lorentzian sum function with a different %Gaussian-Lorentzian value.

You can choose the function type you want

1. From the lower window, click on the Options button

The peak parameters box comes up

Select GL sum for the Gaussian-Lorentzian sum function Select GL product for the Gaussian-Lorentzian product function.

2. For the Gaussian-Lorentzian sum function, each peak can have six

parameters

Peak Position

Area

FWHM

%Gaussian-Lorentzian

TS TL

If anyone knows what TS or TL might be, please let me know. Thanks, CMH

3. Each peak in the Gaussian-Lorentzian product function can have four

parameters

Peak Position

Area

FWHM

%Gaussian-Lorentzian

Since peak area relates to the atomic concentration directly, we use it as a peak parameter and the peak height will not be shown to the user.

Note: For asymmetric peaks, the FWHM only refers to the half of the peak that is symmetrical. The actual FWHM of the peak is calculated numerically and is shown after the actual FWHM in the Peak Parameter Window. If the asymmetric peak is a doublet (p, d or f type peak), the actual FWHM is the FWHM of the doublet.

Region Shift

A Region Shift parameter was added under the Parameters menu

Use this parameter to compensate for the charging effect, the fermi level

shift or any change in the system work function

This value will be added to all the peak positions in the region for fitting

purposes.

An example:

A polymer surface is positively charged and all the peaks are shifted to

the high binding energy by +0.5eV, e.g. aliphatic carbon at 285.0eV shifts to 285.5eV

When the Region Shift parameter is set to +0.5eV, 0.5eV will be added

to all the peak positions in the region during peak fitting, but the listed peak positions are not changed, e.g. 285.0eV for aliphatic carbon.

Note: I have tried this without any actual shift taking place. If someone finds out how to perform this operation, please let me know. Thanks, CMH.

In the meantime, I suggest you do the shift before converting your files from the Vision Software format.

Optimisation

You can optimise:

1. A single peak parameter

Use the Optimize button beside the parameter in the Peak Fitting

window

2. The peak (the peak position, area, FWHM, and the %GL if the "fix" box is

not ticked)

Use the Optimize Peak button at the base of the Peak Fitting

window

3. A single region (all the parameters of all the peaks in that region if the

"fix" box is not ticked)

Use the Optimize Region

menu (button) in the upper window

4. All the regions

Use the Optimize All

button in the lower window

During any type of optimisation, you can press the "Stop Fitting" button

and the program will stop the process in the next cycle.

Print/Export

In the XPS Peak Fit or Region window, From the Data menu, choose Export or Print options as desired

Export

The program can export the ASCII file of spectrum (*.DAT) for making high quality figures using other software (e.g. SigmaPlot) It can export the parameters (*.PAR) for further calculations (e.g. use Excel for atomic ratio calculations) It can also copy the spectral image to the system clipboard so that the

spectral image can be pasted into a document (e.g. MS WORD).

Program Options

1. The %tolerance allows the optimisation routine to stop if the change in

the difference after one loop is less that the %tolerance

2. The default setting of the optimisation is Newton's method

This method requires a delta value for the optimisation calculations You may need to change the value in some cases, but the existing

setting is enough for most data.

3. For the binary search method, it searches the best fit for each parameter

in up to four levels of value ranges

For example, for a peak position, in first level, it calculates the chi^2

when the peak position is changed by +2eV, +1.5eV, +1eV, +0.5eV, -0.5eV, -1eV, -1.5eV, and -2eV (range 2eV, step 0.5eV)

Then, it selects the position value that gives the lowest chi^2

In the second level, it searches the best values in the range +0.4eV,

+0.3eV, +0.2eV, +0.1eV, -0.1eV, -0.2eV, -0.3eV, and -0.4eV (range 0.4eV, step 0.1eV)

In the third level, it selects the best value in +0.09eV,

+0.08eV, ...+0.01eV, -0.01eV, ...-0.09eV

This will give the best value with two digits after decimal

Level 4 is not used in the default setting

The range setting and the number of levels in the option window can

be changed if needed.

4. The Newton's Method or Binary Search Method can be selected by

clicking the "use" selection box of that method.

5. The selection of the peak function is also in the Options window.

6. The user can save/read the option parameters with the file extension

*.opa

The program reads the default.opa file at start up. Therefore, the

user can customize the program options by saving the selections into the default.opa file.

Compatibility

The program can read:

Kratos text (*.des) files together with the peak fitting parameters in

the file

The ASCII files exported from Phi's Multiplex software

The ASCII files of Leybold's software

The VAMAS file format

For the Phi, Leybold and VAMAS formats, multiple regions can be

read

For the Phi format, if the description contains a comma ",", the

program will give an error. (If you get the error, you may use any text editor to remove the comma)

The program can also import ASCII files in the following format:

Binding Energy Value 1 Intensity Value 1

Binding Energy Value 2 Intensity Value 2

etc etc

The B.E. list must be in ascending or descending order, and the

separation of adjacent B.E.s must be the same

The file cannot have other lines before and after the data

Sometimes, TAB may cause a reading error.

File I/O

The file format of XPSPEAK 4.1 is different from XPSPEAK 3.1, 3.0 and 2.0

XPSPEAK 4.1 can read the file format of XPSPEAK 3.1, 3.0 and 2.0,

but not the reverse

File format of 4.1 is the same as that of 4.0.