title: Molecular depth profiling of sucrose films: a comparative study of C60(n+) ions and traditional Cs(+) and O2(+) ions.
abstract: Depth profiling of sucrose thin films was investigated with time-of-flight secondary ion mass spectrometry (TOF-SIMS) using 10 keV C(60)(+), 20 keV C(60)(2+), and 30 keV C(60)(3+), and 250, 500, and 1000 eV Cs(+) and O(2)(+) as sputtering ions. With C(60)(n+) ions, the molecular ion signal initially decreases and reaches a steady state that is about 38-51% of its original intensity, depending on the energy of the C(60)(n+) ions. In contrast, with Cs(+) and O(2)(+) sputtering, molecular ion signals decrease quickly to the noise level, even using very low-energy (250 eV) ions. In addition, the measured width of the sucrose/Si interface is much narrower using C(60)(+) ions than that using Cs(+) or O(2)(+) ions. To understand the mechanisms of sputtering-induced damage by these ions, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were used to characterize the bottoms of these sputter craters. XPS data show very little chemical change in the C(60)(+) sputter crater, while considerable amorphous carbon was found in the O(2)(+) and Cs(+) sputter craters, indicating extensive decomposition of the sucrose molecules. AFM images show a very flat bottom in the C(60)(+) sputter crater, while the bottoms of the Cs(+) and O(2)(+) sputter craters are significantly rougher. We used the sputtering model developed by Wucher and co-workers to quantitatively analyze our C(60)(1-3+) data. The results show that low energy C(60)(+) ions generate a relatively thin damage layer with a high molecular ion signal, suggesting that low energy C(60)(+) may be the optimal choice for molecular depth profiling of sucrose films.
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA. zihua.zhu@pnl.gov
authors.forename: Zihua
authors.initials: Z
authors.lastname: Zhu
authors.forename: Ponnusamy
authors.initials: P
authors.lastname: Nachimuthu
authors.forename: Alan S
authors.initials: AS
authors.lastname: Lea
mesh_terms: D002586:Cesium / Q000737:chemistry*; D037741:Fullerenes / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D010100:Oxygen / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D012825:Silicon / Q000737:chemistry; D013395:Sucrose / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D037741:Fullerenes; D002586:Cesium; D013395:Sucrose; C069837:fullerene C60; D010100:Oxygen; D012825:Silicon