Lots of spectroscopy are available but to calculate surface atomic concentration Auger spectra will be used.
People are familiar with X-Ray photoelectron spectroscopy as they are sensitive technique to the surface.
The problem is not yet refined what to take in Auger spectra whether to intensity or peak to peak amplitude or to take peak area.
How to calculate the peak area.
One way to do so is to to plot a integral spectra and calculate the area under the peak by using any standard software like CASAXPS.
Another to take HALF OF THE PEAK HEIGHT and FWHM
the you have to multiply h into square of w where w is width of peak divided by 2. and you will get area under peak in differential format if plot is and it will give the same result as integral plot.