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 (C ₆₀ ⁺ ) projectile bombardment. PS oligomer (m/z ∼ 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 C ₆₀ ⁺ projectiles. The results show that upon Ga⁺ bombardment, the yield of the fingerprint fragment C₇H ₇ ⁺ increases as the PS coverage increases and reaches its maximum for a thickness that corresponds to a complete monolayer (∼3.5 nm). Beyond the maximum, the yields decrease strongly and become constant for layers thicker than 12 nm. In contrast, upon C ₆₀ ⁺ bombardment, the C₇H ₇ ⁺ 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 C ₆₀ ⁺ bombardment. Upon Ga⁺ bombardment, the maximum PS fingerprint ion yields are obtained using a monolayer spin-coated on gold, whereas for C ₆₀ ⁺ , 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.

本文研究了有机薄膜厚度对聚苯乙烯 (PS) 的特性和分子离子产率的影响，结合两种不同的基材 (Si、Au) 或金缩合 (MetA-SIMS)，以及原子 (Ga ⁺ )和多原子（C ₆₀ ⁺）弹丸轰击。PS低聚物（m/z ∼ 2000 Da）层在两个基板上制备，厚度范围从 1 到 45 nm。Si 上的原始样品也通过蒸发三种不同厚度（0.5、2 和 6 nm）的金进行金属化。使用12 keV 原子Ga ⁺和C ₆₀ ⁺射弹进行二次离子质谱分析。结果表明，在 Ga ⁺ 轰击时，指纹片段 C ₇ H ₇ ⁺的产率随着 PS 覆盖率的增加而增加，并在对应于完整单层（~3.5 nm）的厚度下达到最大值。超过最大值后，产率急剧下降，并且对于厚度超过 12 nm 的层变得恒定。相比之下，在 C ₆₀ ⁺轰击时，C ₇ H ₇ ⁺产率增加到单层覆盖并且它们在更高的厚度下保持恒定。对金金属化层的Ga ⁺分析证实了强大的产率提高，但产率随着 C ₆₀ ⁺轰击的金覆盖率不断降低。加盖⁺ 在轰击中，使用旋涂在金上的单层获得最大的 PS 指纹离子产率，而对于 C ₆₀ ⁺，使用至少一个单层获得最佳结果，与基材无关且没有任何其他处理。通过涉及两种射弹的不同能量沉积机制的论点，初步解释了不同的行为。