Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via Cozzi 55, 20125 Milano, Italy.
Nanoscale. 2018 May 3;10(17):8014-8022. doi: 10.1039/c7nr08737c.
We compare the ultrafast charge transfer dynamics of molecules on epitaxial graphene and bilayer graphene grown on Ni(111) interfaces through first principles calculations and X-ray resonant photoemission spectroscopy. We use 4,4'-bipyridine as a prototypical molecule for these explorations as the energy level alignment of core-excited molecular orbitals allows ultrafast injection of electrons from a substrate to a molecule on a femtosecond timescale. We show that the ultrafast injection of electrons from the substrate to the molecule is ∼4 times slower on weakly coupled bilayer graphene than on epitaxial graphene. Through our experiments and calculations, we can attribute this to a difference in the density of states close to the Fermi level between graphene and bilayer graphene. We therefore show how graphene coupling with the substrate influences charge transfer dynamics between organic molecules and graphene interfaces.
我们通过第一性原理计算和 X 射线共振光电子能谱比较了生长在 Ni(111)界面上的外延石墨烯和双层石墨烯上分子的超快电荷转移动力学。我们使用 4,4'-联吡啶作为这些探索的原型分子，因为核心激发分子轨道的能级排列允许电子从衬底在飞秒时间尺度上超快注入到分子中。我们表明，从衬底到分子的超快电子注入在弱耦合双层石墨烯上比在外延石墨烯上慢约 4 倍。通过我们的实验和计算，我们可以将这归因于石墨烯和双层石墨烯中接近费米能级的态密度的差异。因此，我们展示了石墨烯与衬底的耦合如何影响有机分子与石墨烯界面之间的电荷转移动力学。
