A technique for accurate measurements of ion beam current density using a Faraday cup

We have performed measurements of the spatial distribution of current in va rious alkali and reactive ion beams over the energy range 5-600 eV using a Faraday cup. Ion beam current densities have been extracted from these meas urements using a simple deconvolution procedure. Our results reveal that th e beams are Gaussian in shape with a constant width, sigma, for energies gr eater than approximately 75 eV and for all ion species investigated. This w idth is consistent with that determined from the distribution of oxygen on a Cu(001) crystal after an O+ ion beam deposition, measured using Auger ele ctron spectroscopy. Using the measurement technique outlined in this articl e, together with the linear relationship between current density and Farada y cup current, it is possible to determine the beam current density using a single current measurement. (C) 2000 American Institute of Physics. [S0034 -6748(00)03309-8].