Abstract
Gold cluster ions in the m z range of 10 4−2 × 10 6 u were produced by bombarding a thin film of gold with 252Cf-fiss fragments. The gold covering a CAl substrate formed islets having a mean diameter of 44 Å. Their size- and mass-distribution was determined by means of electron microscopy. The main task was to measure the m z distribution of the cluster ions ejected from the sample surface. For this purpose we built a time-of-flight (TOF) mass spectrometer, which could be used as a linear TOF instrument or, alternatively, as a tandem-TOF instrument being equipped with an ion-to-ion converter. Combining the results obtained in both modes, it turned out that the linear TOF instrument equipped with micro-channel plates had a mean detection efficiency for 20 keV cluster ions of about 40%. In the tandem mode, the cluster ions hit a CsI converter with energies of 40 z keV ( z = charge state), from where secondary ions - mainly Cs + and (CsI) n Cs + cluster ions — were ejected. These ions were used to measure the TOF spectrum of the gold cluster ions. The detection efficiency of the cluster ions was found to vary in the available mass range from 99.7% to 96.5%. The complete mass distribution between 4 × 10 4 and 4 × 10 6 u was determined and compared with the corresponding mass distribution of the gold islets covering the substrate.
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