Unité de Physico-Chimie et de Physique des Matériaux, Université catholique de Louvain, Louvain la Neuve, Belgium.
J Am Soc Mass Spectrom. 2009 Dec;20(12):2294-303. doi: 10.1016/j.jasms.2009.08.022. Epub 2009 Sep 3.
This article investigates the influence of the organic film thickness on the characteristic and molecular ion yields of polystyrene (PS), in combination with two different substrates (Si, Au) or gold condensation (MetA-SIMS), and for atomic (Ga+) and polyatomic (C60+) projectile bombardment. PS oligomer (m/z approximately 2000 Da) layers were prepared with various thicknesses ranging from 1 up to 45 nm on both substrates. Pristine samples on Si were also metallized by evaporating gold with three different thicknesses (0.5, 2, and 6 nm). Secondary ion mass spectrometry was performed using 12 keV atomic Ga+ and C60+ projectiles. The results show that upon Ga+ bombardment, the yield of the fingerprint fragment C7H7+ increases as the PS coverage increases and reaches its maximum for a thickness that corresponds to a complete monolayer (approximately 3.5 nm). Beyond the maximum, the yields decrease strongly and become constant for layers thicker than 12 nm. In contrast, upon C60+ bombardment, the C7H7+ yields increase up to the monolayer coverage and they remain constant for higher thicknesses. A strong yield enhancement is confirmed upon Ga+ analysis of gold-metallized layers but yields decrease continuously with the gold coverage for C60+ bombardment. Upon Ga+ bombardment, the maximum PS fingerprint ion yields are obtained using a monolayer spin-coated on gold, whereas for C60+, the best results are obtained with at least one monolayer, irrespective of the substrate and without any other treatment. The different behaviors are tentatively explained by arguments involving the different energy deposition mechanisms of both projectiles.
本文研究了有机膜厚度对聚苯乙烯（PS）特性和分子离子产率的影响，结合了两种不同的衬底（Si、Au）或金冷凝（MetA-SIMS），以及原子（Ga+）和多原子（C60+）射弹的情况。在两种衬底上，通过蒸发不同厚度（0.5、2 和 6nm）的金，将 PS 低聚物（m/z 约 2000Da）层制备成各种厚度，范围从 1nm 到 45nm。Si 上的原始样品也通过蒸发金进行金属化。使用 12keV 的原子 Ga+和 C60+射弹进行二次离子质谱分析。结果表明，在 Ga+轰击下，随着 PS 覆盖率的增加，指纹碎片 C7H7+的产率增加，并在对应于完整单层（约 3.5nm）的厚度处达到最大值。超过最大值后，产率强烈下降，并在厚度大于 12nm 的层中保持恒定。相比之下，在 C60+轰击下，C7H7+的产率在单层覆盖率下增加，并在更高的厚度下保持恒定。在 Ga+分析金金属化层时，确认了强烈的产率增强，但在 C60+轰击时，产率随金覆盖率的增加而连续下降。在 Ga+轰击下，使用单层旋涂在金上可以获得最大的 PS 指纹离子产率，而对于 C60+，无论衬底如何，至少需要一层，并且无需任何其他处理，就可以获得最佳结果。不同的行为通过涉及两种射弹不同能量沉积机制的论点来解释。
