Smiley Edward J, Winograd Nicholas, Garrison Barbara J
Department of Chemistry, 104 Chemistry Building, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Anal Chem. 2007 Jan 15;79(2):494-9. doi: 10.1021/ac061531u.
Emission of benzene molecules by 5-keV cluster bombardment of a range of carbon projectiles from C6H6 to C180 is studied by a coarse-grained molecular dynamics (MD) technique. This approach permits calculations that are not feasible using more complicated potential energy functions, particularly as the interesting physics associated with the ion impact event approaches the mesoscale. These calculations show that the highest ejection yields are associated with clusters that deposit their incident energy 15-20 A below the surface. The highest yield for the projectiles is produced by the C20 and C60 projectiles. The results from the MD simulations are also compared favorably to an analytical model based on fluid dynamics to describe the energy deposition. The analytical model is then utilized to extend the range of the calculations to higher incident energies. The issue of the relative amount of chemical fragmentation and intact molecular desorption is also examined for the benzene crystal. These results show that damage accumulation at high-incident fluence should not be problematic and that it should be possible to perform molecular depth profiling via secondary ion mass spectrometry experiments. In general, the approach presented here illustrates the power of combining a simplified MD method with analytical strategies for describing a length scale that is difficult to achieve with traditional MD calculations.
采用粗粒度分子动力学（MD）技术研究了5千电子伏特的团簇轰击从C6H6到C180的一系列碳抛射体时苯分子的发射情况。这种方法允许进行使用更复杂的势能函数无法实现的计算，特别是当与离子撞击事件相关的有趣物理现象接近中尺度时。这些计算表明，最高的喷射产率与在表面以下15 - 20埃处沉积其入射能量的团簇相关。抛射体的最高产率由C20和C60抛射体产生。MD模拟的结果与基于流体动力学描述能量沉积的解析模型相比也很有利。然后利用该解析模型将计算范围扩展到更高的入射能量。还研究了苯晶体化学碎片化和完整分子解吸的相对量问题。这些结果表明，在高入射通量下的损伤积累应该不是问题，并且应该可以通过二次离子质谱实验进行分子深度剖析。一般来说，这里提出的方法展示了将简化的MD方法与解析策略相结合的力量，用于描述传统MD计算难以达到的长度尺度。
