EXPERIMENTAL-OBSERVATION OF PARTICLE ENTRAPMENT AND TRANSPORT IN AN INTENSE ION-BEAM

An experiment is described in which 1.5- to 3.0-mu-m-diam gold spheres are injected into the central region of a nearly square 27.4-keV, 9-mA argon ion beam with a cross-sectional area of approximately 3.3 cm2, and the results compared to theory. In the experiment, silicon wafers located 30 and 50 cm from the point of introduction served as targets to collect the particles. After injection, large numbers of gold-filled craters were found throughout and surrounding the central implant region on the wafers. Gravity and axial momentum transfer acting alone generate trajectories that would place all the particles well below the horizontal centerline of the implanted area. Consequently, particles landing above the central impact region can only be explained by the presence of an electrostatic confining force. Theoretical calculations based on an electrostatic trapping model predict particle distributions on the target that are in remarkable agreement with our experimental results. Thus, these observations provide conclusive evidence in support of beam particle entrapment and transport, phenomena that have heretofore remained unconfirmed.