IMPROVED HYDROGEN AND DEUTERIUM DEPTH PROFILING IN POLYMERS USING LOW-ENERGY FORWARD RECOIL SPECTROMETRY

We demonstrate that the hydrogen and deuterium depth resolution of for ward recoil spectrometry (FRES) is greatly improved by utilizing 1.3 M eV He-4 ions and sample tilting. The near-surface depth resolution is measured on samples of alternating deuterated and protonated polystyre ne layers, each ca 250 angstrom thick. The depth resolution at the sur face is dramatically improved (from 800 angstrom to 250 angstrom) as t he incident beam energy decreases from 3.0 to 1.3 MeV. We call this te chnique low-energy FRES (LE-FRES) to differentiate it from standard FR ES, which uses 3 MeV He-4 ions incident at theta = 75-degrees. Further more, by using a glancing incident or exit geometry, the LE-FRES depth resolution is improved to ca 125 angstrom, which is comparable to the resolution of secondary ion mass spectrometry and nuclear reaction an alysis. Measurements of the energy and glancing angle dependence of th e depth resolution are in quantitative agreement with theoretical pred ictions. The probing depth of LE-FRES is found to have a maximum at th eta almost-equal-to 71-degrees and decreases at glancing exit and inci dent angles. A contour plot illustrates the relationship between depth resolution and probing depth and provides guidance for future users o f LE-FRES.