Dynamics of Molecular Impacts on Soft Materials: From Fullerenes to Organic Nanodrops
Dynamics of Molecular Impacts on Soft Materials: From Fullerenes to Organic Nanodrops
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DOI：
10.1021/ac900746x
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发表时间：
2009-08-15
影响因子：
7.4
通讯作者：
Hamraoui, K.
中科院分区：
文献类型：
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作者：
Delcorte, A.;Garrison, B. J.;Hamraoui, K.
目前的理论研究探索了各种高能分子射束和团簇与模型聚合物表面的相互作用，对表面分析的质谱学具有直接的意义。弹丸大小(高达23 kDa)介于二次离子质谱仪中使用的多原子离子(SF5、C-60)和例如在解吸电喷雾电离中产生的大有机微滴之间。目标是它的无定形聚乙烯模型，已经在以前的研究中使用[Delcorte，A.；加里森，B.J.J.Phys。化学。C 2007年，第111,15312页]。选择的方法依赖于经典的分子动力学(MD)模拟，使用它对高能或长时间计算(20-50ps)的聚合物样品进行粗粒度描述，并对低能或短时间计算(<；1ps)使用完整的原子描述。根据每个核子的入射能量(即有效的速度)，可以观察到两个溅射或脱附区域。该跃迁发生在1 eV/核子附近，通过每核子溅射产额随每核子能量变化曲线的斜率变化来确定。当超过1 eV/核子时，溅射产额只与总的入射能量有关，而与入射的核度无关。在1 eV/核子以下，即在小型弹丸的溅射阈值附近，产额同时受到弹丸能量和核度的影响。在每个核子的最低能量下，也可以观察到完整的分子簇的沉积。溅射曲线的转变与能量沉积机制的改变有关，从原子机制。以及介观过程对流体动力流动的影响。这也与碎片化方面的变化相对应。在1 eV/核子以下，入射粒子不能在样品中引起键断裂。这一分子发射区域具有最小的碎裂，提供了新的分析视角，超出了富勒烯等较小的分子簇的范围。
The present theoretical study explores the interaction of various energetic molecular projectiles and clusters with a model polymeric surface, with direct implications for surface analysis by mass spectrometry. The projectile sizes (up to 23 kDa) are intermediate between the polyatomic ions (SF5, C-60) used in secondary ion mass spectrometry and the large organic microdroplets generated, for example, in desorption electrospray ionization. The target is it model of amorphous polyethylene, already used in a previous study [Delcorte, A.; Garrison, B. J. J. Phys. Chem. C 2007, 111, 15312]. The chosen method relies on classical molecular dynamics (MD) simulations, using it coarse-grained description of polymeric samples for high energy or long time calculations (20-50 ps) and a full atomistic description for low energy or short time calculations (< 1 ps). Two regions of sputtering or desorption are observed depending on the projectile energy per nucleon (i.e., effectively the velocity). The transition, occurring around 1 eV/nucleon, is identified by a change of slope in the curve of the sputtering yield per nucleon vs energy per nucleon. Beyond 1 eV/nucleon, the sputtering yield depends only on the total projectile energy and not on the projectile nuclearity. Below 1 eV/nucleon, i.e., around the sputtering threshold for small projectiles, yields are influenced by both the projectile energy and nuclearity. Deposition of intact molecular clusters is also observed at die lowest energies per nucleon. The transition in the sputtering curve is connected to a change of energy deposition mechanisms, from atomistic. and mesoscopic processes to hydrodynamic flow. It also corresponds to a change in terms of fragmentation. Below 1 eV/nucleon, the projectiles are not able to induce bond scissions in the sample. This region of molecular emission with minimal fragmentation offers new analytical perspectives, out of reach of smaller molecular clusters such as fullerenes.