An experimental and theoretical view of energetic C(60) cluster bombardment onto molecular solids.
An experimental and theoretical view of energetic C(60) cluster bombardment onto molecular solids.
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DOI：
10.1002/sia.5077
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发表时间：
2013-01-01
期刊：
影响因子：
--
通讯作者：
Winograd N
中科院分区：
文献类型：
--
作者：
Brenes DA;Postawa Z;Wucher A;Blenkinsopp P;Garrison BJ;Winograd N
最近的实验测量和分子动力学计算机模拟进行的计算表明，高能C60初级离子轰击分子固体，完整的分子的发射是独一无二的。利用能量和角分辨中性质谱仪结合激光光电离技术，测量了20 keV能量下苯并[a]芘分子的极性角分布 初级离子，并观察到在所有可能的发射能量上积分的偏离正常角度处的峰值。同样，计算机模拟20千电子伏C60射弹轰击粗颗粒苯系统导致几乎相同的极角分布的计算。在解析测量和计算的极角分布时，具有高动能的溅射分子是偏离正常峰的主要贡献者。低动能的分子进行了测量和计算，解吸宽峰的表面正常。计算机模拟表明，从C60碰撞的能量的快速沉积促进了流体流动和溢出型运动的分子发射。偏离正常发射角的特征对于分子是独特的，因为碎裂过程去除了否则将在接近垂直于表面的情况下喷射的分子。20 keV轰击Ni {001}单晶的实验测量 证明没有这个独特的签名。
Recent experimental measurements and calculations performed by molecular dynamics computer simulations indicate, for highly energetic C60 primary ions bombarding molecular solids, the emission of intact molecules is unique. An energy- and angle-resolved neutral mass spectrometer coupled with laser photoionization techniques was used to measure the polar angle distribution of neutral benzo[a]pyrene molecules desorbed by 20-keV primary ions and observed to peak at off-normal angles integrated over all possible emission energies. Similarly, computer simulations of 20-keV C60 projectiles bombarding a coarse-grained benzene system resulted in calculations of nearly identical polar angle distributions. Upon resolving the measured and calculated polar angle distributions, sputtered molecules with high kinetic energies are the primary contributors to the off-normal peak. Molecules with low kinetic energies were measured and calculated to desorb broadly peaked about the surface normal. The computer simulations suggest the fast deposition of energy from the C60 impact promotes the molecular emission by fluid-flow and effusive-type motions. The signature of off-normal emission angles is unique for molecules because fragmentation processes remove molecules that would otherwise eject near normal to the surface. Experimental measurements from a Ni {001} single crystal bombarded by 20-keV demonstrate the absence of this unique signature.