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 various 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 measurements using a simple deconvolution procedure. Our results reveal that the beams are Gaussian in shape with a constant width, sigma, for energies greater than approximately 75 eV and for all ion species investigated. This width is consistent with that determined from the distribution of oxygen on a Cu(001) crystal after an O+ ion beam deposition, measured using Auger electron spectroscopy. Using the measurement technique outlined in this article, together with the linear relationship between current density and Faraday 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].