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.
[Show abstract][Hide abstract] ABSTRACT: An ion streak camera has been constructed for measurement of time and angle correlations in ion emission from liquid‐metal ion sources. Emission events are detected with a chevron microchannel plate multiplier (MCP) as a fan of the ion beam is electrostatically deflected across the plate. The intensified images on the phosphor of the MCP are recorded in a digital video camera synchronized with the sweep. The images are then digitized and Fourier transformed to obtain two‐dimensional power spectra in frequency and angular wave number. Experiments have been performed using sweep times of 100 ns to 10 μs. The time behavior of the emission has been examined for low‐current direct current beams and for beams for which the extractor of the source has been driven at 2 MHz. Preliminary results for the power spectra are presented and discussed for these different cases.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 02/1988; 6(1-6):482 - 484. DOI:10.1116/1.584046 · 1.46 Impact Factor
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