Non-scattering technique of ion-implantation into vibrated micro-powders by using a negative-ion beam

A non-scattering technique for vibrated powder particles by negative-ion implantation is presented and compared with the case of positive-ion implantation. Scattering of powders during conventional positive-ion implantation without any charge compensation results from a very high charging voltage which nearly reaches the implantation voltage for an insulator. Taking account of the forces acting on one particle in the top layer (the Coulomb repulsive force and attractive forces to other particles in the layer just below, such as gravity and van der Waals force), the threshold charging voltage for scattering was derived for a stationary state and a vibrated state. The experimentally obtained threshold voltage for scattering by Ar+ implantation into spherical powders at various diameters of 5-1000 mu m agrees with the predicted value, and scattering for 115 mu m glass beads in a vibrated state at 120 Hz was found to take place at a charging voltage of 500 V, which is less than the 1 kV for the stationary state. In contrast, no scattering was observed in negative-ion implantation of C-, BO- and Cu- with ion energies of 20-30 keV in the vibrated state or in the stationary state. This non-scattering is due to the slightly low charging voltage of the surface in negative-ion implantation. (C) 1998 Elsevier Science S.A.