Dependene of Focused Ion Beam Intensity Profile on Ion Species at Several Orders of Magnitude below the Peak Intensity

We have estimated the current intensity distribution of focused Be and Si ion beams emitted from a Au-Si-Be liquid metal ion source down to several orders of magnitude below the peak intensity. The distributions are indirectly measured from implantation-induced damage configurations formed on a GaAs by the ion beams. The diameters of the intensity distributions are more or less larger than the Gaussian profile, and they increase to several microns at six orders of magnitude below. Since the spread depends on ion species, charge, and ion emission current, the prevailing tail of velocity distribution of the FIB must be involved.