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Gallium clusters from a liquid metal ion source

ABSTRACT Gallium ion clusters Ga+ n with n ranging up to 30 have been measured from liquid gallium ion sources using a time‐of‐flight spectrometric technique. The observations were made as a function of total ion emission current, angle of emission, and temperature of the liquid metal. Under all conditions Ga+ is the overwhelmingly dominate species emitted. The cluster data reveal several remarkable features. First, emission of clusters tends to be very low below 2 μA emission current, to rise steeply with current to 10 or 20 μA and decrease for higher current. Second, within the range examined, clusters with n=8 and 15 have particularly low abundances. Third, the energy distributions of the resolvable clusters are bimodal with characteristic peaks at approximately 30 and 120 eV below the source potential. Fourth, the angular distributions of the clusters are more nearly axial than that of the primary species. The temperature of the liquid metal has no noticeable effect on cluster emission over the range examined. A possible model for cluster formation will be discussed.

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