TABLE 1 Main feature of the XPS system at the Solid State Physics Laboratory of the University of Torino
x-ray source	Model	VSW TA10 Mg Ka (1253.6 eV) Al Ka (1486.6 eV) (non monochromatic twin anode source)	Thermo Scientific XR5 microfocus monochromatic x-ray source Al Ka (1486.6 eV)
	Spot size	≈1 cm^2	≈500 µm^2
	Spectral resolution	DE = 1.2 eV ( Mg anode ) DE = 1.0 eV ( Al anode )	DE = 0.55 eV ( Al anode )
Electron energy analyser	Model	VSW HA100 Hemispherical analyser (mean radius = 100 mm)
	Fixed Analyser Transmission mode	Pass energy: 10, 22, 44, 90 eV
	Fixed Retarded Ratio mode	Ratio: 5, 10, 50, 100
Working pressure		Of the order of 10^-7Pa
Sample cleaning		Annealing at 150°C by means of an external halogen lamp
		Ar ion (500-3000 eV) sputtering (PSP ISIS3000 ion gun)
Charge compensator		NO

The instrument is based on a VARIAN VT-114 14" UHV system which includes: A 14" ID ss vacuum cylinder, nine 2 ¾" Conflat ports, poppet isolation valve and a new ss bell jar with Wheeler flange. 

A Varian SH-100 Dry Scroll and a turbo-molecular pump Varian V-70LP are used to achieve high vacuum conditions. 
Pumping equipment for UHV includes 6 triode ion pumps (VARIAN model 911-503) with a total pumping speed of 220 l/s, multi-filament titanium sublimation source, cryo panel and a supplementary 20 l/s Varian VacIon Plus 20 Star Cell diode pump located next to the x-ray source. 
Heating resistors are used to bake-out the UHV chamber. 
The working pressure is of the order of 10^-7 Pa.

The XPS apparatus is equipped with two loading pre-chambers to allow a fast and easy sample transferring in and out of the vacuum system. 
The sample holder is charged in the first pre-chamber, which is pumped down up to a pressure of 10^-5 Pa by means of a Varian SH-100 Dry Scroll and a Varian V-70LP turbo-molecular pump. 
The pre-heating treatment of the sample up to a temperature of 150°C can be performed in this pre-chamber by means of the sample irradiation produced by a halogen lamp (100 W) located externally to the pre-chamber, in front of a window-flange. 
Moreover, this first pre-chamber is equipped with a PSP ISIS3000 Ion Source for cleaning of sample surfaces under UHV by means of the bombardment of Ar ions with energies in the 100-3000 eV range. 
A linear magnetic drive connects, through a gate valve, the first and the second pre-chamber,which is maintained at a working pressure of 10^-6 Pa by a Varian 8 l/s VacIon Plus ion pump. 
Finally, the sample holder is driven into the UHV analysis chamber by means of a second linear magnetic drive.

The apparatus is equipped with the following two x-ray sources:

• A VSW TA10 x-ray source with twin anodes (Al and Mg) with independent filaments to provide two separate excitation energies for XPS.
• A Thermo Scientific XR5 microfocus monochromatic x-ray source Al.

The electron energy analyser is a VSW CLASS 100 hemispherical analyser with a mean radius of 100 mm, with five selectable entrance slits / apertures.

The analyser can operate both in Constant Pass Energy mode, with selectable pass energies of 10,22,44,90 eV or in Constant Retard Ratio mode with selectable ratios of 5,10,50,100.