PNNL

Abstract

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been used for elemental depth profiling for over three decades. In recent years, cluster primary ions (principally C60+, Bin+ and Aun+) have been widely available, and can greatly enhance the signal intensity of molecular ions (10 to 1000 times). It is of great interest to know the performance of cluster primary ions for elemental depth profiling for the purpose of allowing normal ToF-SIMS users to easily choose the optimal primary ion beam for their depth profiling work. Presently, however, the experimental data are far from enough and such choices are very difficult to make. In this paper, hydrogen and deuterium depth profiling were studied using six different primary ions (25 keV Bi+, Bi3+, Bi5+, 50 keV Bi32+, 10 keV C60+, and 20 keV C602+). It is found that cluster primary ions do enhance H- and D- yields, but the enhancement is only about 1.5 to 4.0 times when compared to monatomic Bi+ ions. Because the current of monatomic primary ion beam is much stronger than the currents of cluster ion beams for most presently available commercial ToF-SIMS instruments, the monatomic primary ion beam can provide the strongest H- and D- signal intensity, and it may still be the best choice for hydrogen and deuterium depth profiling. Besides H and D, two representative nuclides, 30Si and 18O, were also studied. The results are very similar to that of H and D.