Sampling Depths, Depth Shifts, and Depth Resolutions for Bin+ Ion Analysis in Argon Gas Cluster Depth Profiles
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- 作者：R. Havelund ; M. P. Seah ; I. S. Gilmore
- 刊名：Journal of Physical Chemistry B
- 出版年：2016
- 出版时间：March 10, 2016
- 年：2016
- 卷：120
- 期：9
- 页码：2604-2611
- 全文大小：434K
- ISSN：1520-5207
文摘
Gas cluster sputter depth profiling is increasingly used for the spatially resolved chemical analysis and imaging of organic materials. Here, a study is reported of the sampling depth in secondary ion mass spectrometry depth profiling. It is shown that effects of the sampling depth leads to apparent shifts in depth profiles of Irganox 3114 delta layers in Irganox 1010 sputtered, in the dual beam mode, using 5 keV Ar2000+ ions and analyzed with Biq+, Bi3q+ and Bi5q+ ions (q = 1 or 2) with energies between 13 and 50 keV. The profiles show sharp delta layers, broadened from their intrinsic 1 nm thickness to full widths at half-maxima (fwhm’s) of 8–12 nm. For different secondary ions, the centroids of the measured delta layers are shifted deeper or shallower by up to 3 nm from the position measured for the large, 564.36 Da (C33H46N3O5–) characteristic ion for Irganox 3114 used to define a reference position. The shifts are linear with the Binq+ beam energy and are greatest for Bi3q+, slightly less for Bi5q+ with its wider or less deep craters, and significantly less for Biq+ where the sputtering yield is very low and the primary ion penetrates more deeply. The shifts increase the fwhm’s of the delta layers in a manner consistent with a linearly falling generation and escape depth distribution function (GEDDF) for the emitted secondary ions, relevant for a paraboloid shaped crater. The total depth of this GEDDF is 3.7 times the delta layer shifts. The greatest effect is for the peaks with the greatest shifts, i.e. Bi3q+ at the highest energy, and for the smaller fragments. It is recommended that low energies be used for the analysis beam and that carefully selected, large, secondary ion fragments are used for measuring depth distributions, or that the analysis be made in the single beam mode using the sputtering Ar cluster ions also for analysis.