[Fityk-users] XPS background

[Marcin Wojdyr]

Hi,
I'm sending this reply also to the mailing list, perhaps there are
XPS people there.

On Wed, 25 Jan 2006, Roberto Canteri wrote:

> Hi, I am looking for a fitting XPS data program. Your software is
> very impressive but for that specific task is laking for a Doniach-Sunjic
> peak shape and Shirley or Toogard background.

Adding D-S peak shape is quite easy, so I'll do it.
(Recently I was adding some new functions to Fityk and if someone would
like to have more functions in Fityk, it is a good time to write about it).

Shirley/Toogard backgrounds would be more difficult to implement.
I had only a quick look on some descriptions of XPS backgrounds found
at the web, but if i understand correctly, it's not just an analytical
function, which can be fitted.
As found in CasaXPS manual:
"An alternative approach is to include the background shape as part of the
model". And the reference there is:
Castle J. E. et al, J. Electr. Spectr. Related Phenom,106, 65 (2000)

I haven't read the paper, but having an analytical function as a
background would make the implementation much easier.

But I've also found a paper (Vegh, Surface Science 2005 pp. 220-228),
in which author (i may be wrong, cause i only had a glance at this paper)
says about misunderstanding, misusing etc. in the method of Castle.

So the question is: is there any function, which can model background
in XPS data?

Marcin

--
Marcin Wojdyr | http://www.unipress.waw.pl/~wojdyr/

[JG]

W liście z śro, 25-01-2006, godz. 18:05, Marcin Wojdyr pisze:

I think no because it is an integral of the spectra multiplied by e.q.
Tougaard function. The same rely to Shirley background, it is simpler
but still integral.
Sometimes in XPS background subtraction some person used expotential
background, but it is not very often in serious publications.

Jerzy Goraus

[JG]

One thing more, in fact it is not required to evaluate the integral
from Tougaard background all the time. It is sufficient to add two
parameters (possible to fit ) which will do linear operation to the
array with precomputed integral from T. B.
There are as far as I remebber two paramters for Tougaard function,
and the function is linear with respect to one of them, the second
is usually chosen constant.
It would be good to have a look at
Surface Science 420/1999 (285-294)

Jerzy Goraus