Ranges of low-energy, light ions in amorphous silicon

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Abstract
Range profiles of (1-20)-keV Li, B, N, O, F, Na, Mg, and A1 in amorphous Si have been measured by low-energy (≤3 keV) secondary-ion mass spectrometry. Mean projected ranges and standard deviations of these ranges were calculated from the as-measured profiles. In order to correct for bombardment-induced profile distortions, effective broadening parameters were extracted from the experimental data. The broadening parameters turned out to be element specific, varying between about 1 nm or less for Li, B, Na, and A1 and up to ∼ 12 nm for Mg. Corrected mean ranges and standard deviations are compared with tabulated data based upon Lindhard-Scharff-Schiøtt theory. At 10 keV, i.e., the lowest energy covered by tabulations, the experimental and theoretical ranges show very good agreement except for Na and Mg, in which case the measured ranges are 15-20% smaller than predicted. This discrepancy between experiment and theory is attributed to deviations of the projectile-target interaction potential from the assumed universal Thomas-Fermi potential. Range tabulations involving an empirical electronic stopping power, derived by a rigorous scaling and extrapolation of channeling measurements, are shown to be strongly in error in many cases.