Carbon nanotubes exhibit excellent field-emission behavior characterized by low turn-on fields and large current densities. The present work investigates the transport of electrons by field emission and the resulting spatial distribution at the anode surface through simulation of the tunneling process and the trajectory of electrons across the vacuum gap. Beam spreading is characterized by a multidimensional potential, Coulomb interaction, and randomized energy distributions for closed and open single-walled nanotubes. Electron trajectories are determined by Monte Carlo simulation. Results indicate that the electron. beam spreads primarily due to local field curvature,near the emission site and that, for some nanotubes, a ring pattern at the anode is created. The ring diameter at the anode spreads by 1.2 mum per 10 mum of vacuum gap for the low currents (<100 muA) considered in-this work. These results are consistent with experimental observations. 0 2004 American Vacuum Society.