The end stations

The electron analyzer

The electron analyzer is an hemispherical spectrometer characterized by a mean radius of 66 mm.  The collecting system is based on three lenses V1, V2 and V3, while the detection system is based on a 16 channel Multi Channel Plate. The independent electrodes of the analyzer, the two spheres of the hemispherical part and  are polarized by programmable power supply following calibration curves previously obtained by electron trajectories simulation, to set for each point in the analyzed energy range, the optimal working conditions. This scheme ensures a very high flexibility of the apparatus being possible to weakly change the lens characteristic by software. The curves are dependent on the retarding factor R=Ek/Ep.


Transmission

The transmission of the analyzer as a function of the kinetic energy is shown in Fig. 2. The transmission has been determined by measuring the intensity of Au 4f xps spectra, after the data have been normalized taking into the photoemission cross section. Measurement have been done with pass energy 5 eV. The data have then been normalized to the incoming intensity by measuring the flux with a silicon detector diode and taking into account its responsivity. The transmission is well fitted with a 7th degree polynomial curve
T(Ek)= p1·Ek^7+p2·Ek^6+p3·Ek^5  p4·Ek^4+p5·Ek^3+p6·Ek^2+p7·Ek^1+p8 with
p1=-7.9564e-008;p2=0.00022951;p3=-0.26007;p4=142.36; p5=-34583;  p6= 5.4847e+005;  p7=1.0074e+009; p8=-2.2156e+010.

 
 

Instrumental broadening-energy resolution

The spectrometer resolution has been experimentally determined by measuring the broadening of Au 4f 7/2 and 5/2 XPS spectra of a polycrystalline gold sample cleaned with one hour cycle of  ion sputtering. The instrumental broadening has been calculated with a fitting procedure by using the reference ‘P.H. Citrin, “Surface-atom x-ray photoemission from clean metals: Cu, Ag, and Au”, PRB 27-6 (1983)’. The core level spectra have been fitted as the sum of 4 Voigt functions, after a linear subtraction of the background. The 2+2 components are given by the contribution of bulk and surface components, whose intensity ratio is given by the takeoff angle. Measurements have been done in normal emission. The instrumental broadening is given by the width of the Gaussian component of the 4 Voigt functions. The broadening is given by the contribution of the exciting radiation (then from resolution that is given by photon energy and vertical slit aperture) and of the spectrometer (then from the pass energy).

   


 

 

Last Updated on Tuesday, 18 April 2023 11:43