Verkhoturov Stanislav V, Geng Sheng, Czerwinski Bartlomiej, Young Amanda E, Delcorte Arnaud, Schweikert Emile A
Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144, USA.
Institute of Condensed Matter and Nanosciences-Bio and Soft Matter (IMCN/BSMA), Université Catholique de Louvain, 1 Croix du Sud, B-1348 Louvain-la-Neuve, Belgium.
J Chem Phys. 2015 Oct 28;143(16):164302. doi: 10.1063/1.4933310.
We present the first data from individual C60 impacting one to four layer graphene at 25 and 50 keV. Negative secondary ions and electrons emitted in transmission were recorded separately from each impact. The yields for C(n)(-) clusters are above 10% for n ≤ 4, they oscillate with electron affinities and decrease exponentially with n. The result can be explained with the aid of MD simulation as a post-collision process where sufficient vibrational energy is accumulated around the rim of the impact hole for sputtering of carbon clusters. The ionization probability can be estimated by comparing experimental yields of C(n)(-) with those of C(n)(0) from MD simulation, where it increases exponentially with n. The ionization probability can be approximated with ejecta from a thermally excited (3700 K) rim damped by cluster fragmentation and electron detachment. The experimental electron probability distributions are Poisson-like. On average, three electrons of thermal energies are emitted per impact. The thermal excitation model invoked for C(n)(-) emission can also explain the emission of electrons. The interaction of C60 with graphene is fundamentally different from impacts on 3D targets. A key characteristic is the high degree of ionization of the ejecta.
我们展示了单个C60在25 keV和50 keV能量下撞击一至四层石墨烯的首批数据。对透射过程中发射出的负二次离子和电子分别进行了记录。对于n≤4的情况，C(n)(-)团簇的产率高于10%，它们随电子亲和势振荡，并随n呈指数下降。该结果可借助分子动力学模拟解释为一种碰撞后过程，即撞击孔边缘积累了足够的振动能量以溅射碳团簇。通过将C(n)(-)的实验产率与分子动力学模拟得到的C(n)(0)产率进行比较，可以估算出电离概率，其中电离概率随n呈指数增加。电离概率可以用热激发（3700 K）边缘的喷射物来近似，该喷射物会因团簇碎裂和电子脱离而衰减。实验得到的电子概率分布类似泊松分布。平均而言，每次撞击发射出三个热能电子。用于解释C(n)(-)发射的热激发模型也能解释电子的发射。C60与石墨烯的相互作用与对三维靶材的撞击有根本不同。一个关键特征是喷射物的高度电离。
