STANDARD TEST DATA FOR XPS - 12 August 1996
J. M. Conny, C. J. Powell, and L. A. Currie
Surface and Microanalysis Science Division, National Institute of Standards
and Technology, Gaithersburg, MD 20899
Standard test data (STD) are simulations of analytical instrument responses
that can be used to assess data analysis algorithms for extracting relevant
information from analytical data.  The STD on these disks are well-
defined data sets for testing procedures that operators would choose for
detecting, locating, and measuring the intensities of overlapping peaks in
a doublet as measured by x-ray photoelectron spectroscopy (XPS).  The STD
are constructed to simulate a range of analytical situations that are
encountered in practice, such as varying degrees of peak overlap, varying
relative peak intensities, and varying levels of random noise.  We aim
first to determine the variability in peak parameters as determined by a
single operator using his or her software and a particular set of data-
analysis procedures. Second, we seek to determine the variability in peak
parameters that might be obtained from different operators with different
software systems and different data-analysis procedures for the same set of
analytical situations.  This initial set of STD for XPS is being sent to a
small number of volunteers as a pilot study to assess the usefulness of the
STD design described below.
The STD were constructed from selected carbon 1s spectra of polymers that
were measured on a Scienta XPS instrument and supplied by courtesy of Dr.
D. Briggs.  Each of the selected spectra had a single "main" carbon 1s peak.
These spectra were smoothed and then fitted with fifth-degree spline
functions.  In most cases, the STD were constructed by adding the spectra
for two polymers according to the design summarized below to simulate a
spectrum that might be measured from a specimen consisting of two separate
phases; that is, the carbon 1s peaks for the two component materials
overlap.  Different pairs of polymer spectra were used to represent
different types of binary specimens, and adjustments were made in the energy
scales so that the peak positions would not necessarily be the same from one
binary specimen to another.  For a spectrum with a given set of peak
parameters, random (Poisson) noise was then added in replicate to simulate
multiple experimental measurements of the same specimen.  Although the STD
have been derived from experimental data, the peak locations and intensities
in each data set do not now correspond to the parent materials.
This set of STD for XPS is based on the following factorial design which was
developed following a workshop held last year and later suggestions from a
number of users:
	Factor 1:  Separation of component peaks in the doublet
	(a)  No shoulder present in spectrum (based on the numerical second
	     derivative).
	(b)  Shoulder present in the spectrum (based on the numerical second
	     derivative).
	(c)  Valley present in the spectrum (based on the numerical first
	     derivative).
	Factor 2:  Relative intensities of peaks in the doublet
	(a)  Weaker peak on the high binding-energy side of the doublet
	(b)  Approximately equal peak intensities
	(c)  Stronger peak on the high binding-energy side of the doublet
	Factor 3:  Absolute intensity (level of Poisson noise)
	(a)  High intensity (low fractional noise)
	(b)  Low intensity (high fractional noise)
This factorial design gives 18 combinations.  In addition, two spectra with
a single carbon 1s peak serve as null cases for factors 1 and 2.  For these
null cases, spectra were generated at the same two intensity levels.  There
is thus a total of 22 different combinations.  Ten replicates were made for
each combination (that is, different distributions of random noise to
simulate repeated measurements for a given set of peak parameters) to give
a total of 220 spectra in the STD set.
We also provide two reference spectra for a single polymer so that
participants can, if they wish, investigate a typical carbon 1s lineshape.
One reference spectrum contains the measured data, and the other is the
spline-modeled spectrum without noise for the same polymer.
DIRECTORY STRUCTURE AND FILE FORMATS
The 220 STD spectra and the two reference spectra each contain 261
intensity values that span the same binding-energy range, 294.45 eV to
281.45 eV in steps of 0.05 eV.  The enclosed high-density disk (PC
formatted) contain the following files with the indicated formats:
\REF\
  RAW.REF      	Reference spectrum of measurements.
  MODEL.REF    	Reference spectrum of spline-modeled data.
               	For each reference file, format is ASCII text with three
		header lines followed by spectral data as energies and
		intensities (counts), tab delimited, in pairs (columns)
		on separate rows.  There are 264 rows in each file.
\SEPARATE.STD\
  FILE001.DAT ...  FILE220.DAT
               	ASCII text with three header lines followed by the spectral
		data as energies and intensities (counts), tab delimited,
		in pairs (columns) on separate lines.  Each of the 220
		spectra is in a separate file.  There are 264 rows in each
		file.
INSTRUCTIONS FOR ANALYSIS OF STD
We ask that you analyze as many of the 220 spectra as possible using
procedures that you believe are suitable for the data.  The first 22
spectra contain an example of each of the 22 combinations adopted in the
design, the second 22 spectra contain other examples (with different noise
distributions) for each of the 22 combinations (in a different random
order), and so on.  Repeated analyses of spectra with the same peak
parameters but with different distributions of random noise will enable us
to determine the uncertainties in the peak parameters obtained by each
participant for each of the 22 combinations.  Comparisons of the mean peak
parameters determined by each participant for a particular combination with
those determined by other participants will enable us to determine the
variability in measurements based on different data-analysis procedures for
each combination.
For each spectrum, we wish to know:
	1.  The number of component peaks in each spectrum,
	2.  The binding energies for the identified peaks, and
	3.  The intensities (areas) of the identified peaks.
This information can be tabulated in an ASCII file or otherwise
using the Excel 4.0 worksheet (ANALYSIS.XLS) on Disk 1.  Hardcopy of
the worksheet is also provided.  In addition, as indicated on the Data
Return Form enclosed in this file and in hardcopy, we ask for information
on the software you used, all steps of your data analysis procedure, the
reasons for your precedure choices and uncertainty estimates.  We wish
particularly to know the fitting function you used and the type of
background and end points if a background was subtracted.  It would be
useful if you could send several figures illustrating typical fits to
representative spectra; the figures should show the background function
and the end points.  We would also be interested in any comments you may
have on the STD design and on your experiences.  The completed forms (or
the completed files on the disk) should be returned to us by mail.
Please report your results to either Joe Conny or Cedric Powell (to whom
questions can also be addressed).  We will then report back to you on the
variability in your peak parameters for each combination in the design.
After a sufficient number of returns have been received, we will report
back to you on the variability in the peak parameters determined by
different participants for each combination.  We expect to prepare a report
for publication on our findings, but the individual results will not be
identified with the corresponding participants.
We thank you for your cooperation in advance and look forward to hearing
from you.
Joe Conny
Chemistry B-364
National Institute of Standards and Technology
Gaithersburg, MD 20899
Phone: 301-975-3932
Fax: 301-216-1134
Email: jconny@enh.nist.gov
Cedric Powell
Chemistry B-248
National Institute of Standards and Technology
Gaithersburg, MD 20899
Phone: 301-975-2534
Fax: 301-926-6689
Email: cpowell@enh.nist.gov
____________________________________________________________________________
STANDARD TEST DATA FOR XPS  --  Data Return Form
Name:     __________________________________________________________________
Address:  __________________________________________________________________
          __________________________________________________________________
          __________________________________________________________________
Phone:    _______________  Fax:  _______________  E-Mail: __________________
Type of software used for data analysis.  Give vendor and version number.
____________________________________________________________________________
By what means did you decide whether there were one or two peaks in a
spectrum (e.g., visual inspection, statistical test - please specify, etc.)?
____________________________________________________________________________
____________________________________________________________________________
Please give details of all steps of the data analysis procedure, e.g., type
of background and end points if a background was subtracted, type of fitting
function, etc.  Please attach figures with backgrounds showing typical fits
for several representative spectra.
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
What means did you use to determine the quality of the fit?
____________________________________________________________________________
____________________________________________________________________________
What is a typical statistical uncertainty in your determination of:
Peak position (eV)  _________________________________________
Intensity (high intensity data)  ____________________________
          (low intensity data)   ____________________________
How were the uncertainty estimates obtained (e.g., visual inspection,
statistical tests - please specify, etc.)?
____________________________________________________________________________
____________________________________________________________________________
Did you find the analyses easy, straightforward or hard? ___________________
Other comments on your   ___________________________________________________
experiences in the
analysis of the STD      ___________________________________________________
____________________________________________________________________________
____________________________________________________________________________
Other comments on the    ___________________________________________________
design of the STD set
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
Do you think it would be useful to have additional STD for other XPS
conditions (e.g., different analyzer pass energies or no x-ray
monochromator) to simulate measurements with different energy resolutions or
different types of instruments?  Would it be useful to have STD for other
purposes (e.g., assessment of detection limits) or for other techniques of
surface analysis?
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________