How to sensitively measure the rate of neutral free radical production by photo-deionization of negative ion beams

Abstract

Two measurement methods to determine the rate of neutral free radical production by the photo-deionization of negative ion beams ( PDINIB ) are introduced. These methods, namely, photoelectron-current measurement by low-frequency electro-modulation probe ( PMMP ) and measurement of decrease in the negative-ion beam current ( DNIC ) were employed to evaluate the production rate in a trial surface-processing apparatus developed in the author's laboratory utilizing a steady-flux refined beam of neutral free radicals produced by the PDINIB procedure. A 63Cu negative ion beam of kinetic energy E, varied up to 15 keY was irradiated with a 514.5 nm visible light beam from a 25 W CW Ar ion laser. The detection limit of the production rate by the PMMP setup was as high as 6x109 Is under the condition that E, = 15 keV, the negative ion beam current I = 4 j.tA, and the laser power P = 6 W. The DNIC method is simpler but less reliable than the PMMP method owing to larger uncertainty resulting from the fluctuation of the negative-ion beam current.