Cesium Fermi level

The position < >m of the metal Fermi level versus vacuum level (its work function ) is known experimentally and varies from —2.15 eV for cesium... 

Indeed, the probability of Cesium to form Cs secondary ions is, in the majority of cases, independent of the position of the Fermi edge, which itself is dne to the very low ionization potential of Cesium, i.e. this places the Cesium ionization level well above the Fermi edge of most surfaces. This insensitivity to the position of the Fermi edge can thus explain the trends in Cs secondary ions from most Cs sputtered metal and semiconductor surfaces and why these are seen to increase over the transient region, with the increase simply reflecting the increased Cesium content implanted into the respective snbstrate. 

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