Ta. Dang et al., ADVANTAGES OF A HIGH-FREQUENCY SQUARE-WAVE IN A SPUTTERED NEUTRAL MASS-SPECTROMETRY STUDY OF INSULATING MATERIALS, Surface and interface analysis, 24(2), 1996, pp. 86-90
The direct bombardment mode (plasma sputtering) of d.c.-voltage sputte
red neutral mass spectrometry (SNMS) achieves better depth profile res
olution than ion gun sputtering by minimizing the conic structures and
preferential sputtering associated with ion gun sputtering. However,
when applied to insulating materials, d.c. SNMS allows a charge to bui
ld up on the surface; this charging causes sample decomposition and de
grades the depth resolution. This problem can be eliminated by applyin
g a high-frequency square-wave voltage to the target. The negative pha
se of the square wave produces positive ion bombardment, while the pos
itive phase attracts electrons to the sample surface to neutralize the
accumulated positive charge. The analysis of insulators is particular
ly enhanced by this method.