Neutral clusters beam analysis

For the more volatile (alkali) metals it has been possible since the late 1970s to create a beam of cold, naked clusters of 1 < n < 100, where n is the number of atoms per cluster 348, 349). Metal vapor is produced in an oven and then cooled by expansion. The clusters are separated in a time-of-flight mass spectrometer (TOFMS). Later it became possible to handle less volatile (transition) metals through vaporization by a laser beam 347, 350-352). For the mass analysis the neutral clusters are photoionized by a suitable UV laser. 

The control of materials purity and of environmental conditions requires to implement physico-chemical analysis tools like ESC A, RBS, AUGER, SEM, XTM, SIMS or others. The principle of SIMS (Secondary Ion Mass Spectroscopy) is shown in Eig. 31 an ion gun projects common ions (like 0+, Ar+, Cs+, Ga+,. ..) onto the sample to analyze. In the same time a flood gun projects an electron beam on the sample to neutralize the clusters. The sample surface ejects electrons, which are detected with a scintillator, and secondary ions which are detected by mass spectrometry with a magnetic quadrupole. 

Static Secondary Ion Mass Spectrometry (S-SIMS) is a more sensitive (sensitivity of 10 atoms/cm ) surface analysis technique than X ray Photoelectron Spectroscopy (10 atoms/cm ) [6,18]. Under primary bombardment with a focused ion beam the solid surface emits secondary particles. As illustrated in Fig. 5, the bom bardment with primary ions such as Ga, Ar, or other molecular ion sources like SF5 [19-21] or C0O [22], which should enhance molecular ion formation at high masses vs fragmentation, provokes the emission of neutral, positively, or negatively charged fragments and clusters. 

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