Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144, USA.
Applied Physics, Division of Materials Science, Department of Engineering Sciences and Mathematics, Luleå University of Technology, SE-971 87 Luleå, Sweden.
J Chem Phys. 2017 Feb 28;146(8):084308. doi: 10.1063/1.4976832.
We present the first data on emission of C60- stimulated by single impacts of 50 keV C602+ on the self-assembled molecular layer of C deposited on free standing 2 layer graphene. The yield, Y, of C60- emitted in the transmission direction is 1.7%. To characterize the ejection and ionization of molecules, we have measured the emission of C60- from the surface of bulk C (Y = 3.7%) and from a single layer of C deposited on bulk pyrolytic graphite (Y = 3.3%). To gain insight into the mechanism(s) of ejection, molecular dynamic simulations were performed. The scenario of the energy deposition and ejection of molecules is different for the case of graphene due to the confined volume of projectile-analyte interaction. In the case of 50 keV C602+ impacts on graphene plus C, the C atoms of the projectile collide with those of the target. The knocked-on atoms take on a part of the kinetic energy of the projectile atoms. Another part of the kinetic energy is deposited into the rim around the impact site. The ejection of molecules from the rim is a result of collective movement of the molecules and graphene membrane, where the membrane movement provides the impulse for ejection. The efficient emission of the intact molecular ions implies an effective ionization probability of intact C. The proposed mechanism of ionization involves the tunneling of electrons from the vibrationally exited area around the hole to the ejecta.
我们呈现了第一个关于 C60- 发射的实验数据，这些数据是由 50keV 的 C602+ 对沉积在独立双层石墨烯上的自组装分子层的单次冲击所激发的。在传输方向上发射的 C60- 的产率 Y 为 1.7%。为了表征分子的发射和电离，我们测量了来自大块 C 的 C60- 的发射（Y = 3.7%）和来自沉积在大块热解石墨上的单层 C 的 C60- 的发射（Y = 3.3%）。为了深入了解发射机制，我们进行了分子动力学模拟。由于靶分析物相互作用的受限体积，对于石墨烯的情况，能量沉积和分子发射的场景是不同的。在 50keV 的 C602+ 对石墨烯加 C 的冲击情况下， projectile-atom 与目标原子相互碰撞。被敲出的原子获得了一部分 projectile-atom 的动能。另一部分动能则沉积在冲击点周围的边缘。分子从边缘的发射是分子和石墨烯膜集体运动的结果，其中膜的运动为发射提供了冲量。完整分子离子的有效发射意味着完整 C 的有效电离概率。所提出的电离机制涉及电子从孔周围的振动激发区域到喷射物的隧道。
