MONITORING OF THE ION ENERGY AND CURRENT-DENSITY AT THE SURFACE OF FILMS GROWN BY EXCIMER-LASER ABLATION

A simple and easy to implement, ion time-of-fight (TOF), detection sys tem has been developed and used to monitor the ions ejected during pul sed excimer laser ablation of solid and molten Si and Ge targets. The setup employs a Faraday cup (FC) detector with a high gain-bandwidth p reamplifier and an adjustable voltage electrostatic barrier. The FC is capable of very long time, undisturbed, operation even with significa nt deposition of material on it. The analysis of the TOF ion signal an d its modification by the barrier potential yields valuable quantitati ve information about the ion flux and kinetic energy at the surface of the growing film. The technique is capable of resolving atomic/cluste r components of different charge to mass ratios. High ion fractions an d ion energies are observed, in all cases studied, when the laser flue nce is clearly above the ablation threshold. (C) 1998 American Institu te of Physics, [S0021-8979(98)05914-3].