Atomically resolved phonon and photon spectroscopies of 2D material stackings

该项目涉及双层石墨烯以及石墨烯和六方氮化硼（h-BN）在金属表面的堆叠- Ru(0001), Rh（111）和Pt（111）。第一个目标是用表面科学的方法制备双层结构，以确保在堆叠的二维材料之间存在不同扭曲角度的畴。二维晶格之间的旋转角度将通过电子衍射和扫描隧道显微镜对产生的莫尔条纹进行分析来推断。第二个目标是利用扫描隧穿光谱研究这些堆叠杂化材料的电子特性、声子和光子激发。重点是上述性质对扭转角的潜在依赖性。计划的方法允许直接比较本地声子和光子的激励与电子结构。此外，由于在同一样品上存在扭转角域，实验将在不改变样品的情况下识别量子特性对扭转角的依赖。扫描隧道显微镜的独特机会，探索双层石墨烯中声子的范霍夫奇点的重要性。一个可能的能量减少的特定声子模式，由于一个增强的电子-声子相关方面的科恩异常将被仔细审查。关于范霍夫奇点在双层石墨烯光子发射中的作用存在争议，奇点和由奇点引起的强束缚激子之间的光学跃迁相互竞争。隧穿势垒的局部光子发射随摩尔晶格位置和扭转角的变化将阐明这一争论。利用氩离子轰击法制备了石墨烯上h-BN晶格的单缺陷，以研究其作为色心的光学性质。为此，将对注入的隧穿电流引起的局部电致发光进行光谱分析。

The project addresses double-layers of graphene and stackings of graphene and hexagonal boron nitride (h-BN) on metal surfaces – Ru(0001), Rh(111) and Pt(111). The first aim is the preparation of the bilayer structures in a surface science approach in order to ensure the presence of domains with different twist angles between the stacked two-dimensional materials. The rotation angle between the 2D lattices will be inferred from the analysis of the resulting moiré patterns by electron diffraction and scanning tunnelling microscopy. The second target consists in exploring electronic properties, phonon and photon excitations of these stacked hybrid materials with scanning tunnelling spectroscopy. The focus is on the potential dependence of the aforementioned properties on the twist angle. The planned approach allows the direct comparison of local phonon and photon excitations with the electronic structure. In addition, owing to the presence of twist angle domains on one and the same sample, the experiments will identify the dependence of the quantum properties on the twist angle without the necessity to change the sample. The unique opportunities of the scanning tunnelling microscope shall be used to explore the importance of Van Hove singularities for phonons in bilayer graphene. A possible energy reduction of specific phonon modes due to an enhanced electron-phonon correlation in terms of a Kohn anomaly will be scrutinized. There is a debate on the role of Van Hove singularities in the photon emission of bilayer graphene, where ooptical transitions between the singularities and strongly bound excitons induced by the singularitues compete with each other. The local photon emission from the tunnelling barrier depending on the moiré lattice site and on the twist angle shall elucidate the debate. Single defects in the h-BN lattice on graphene will be prepared using argon ion bombardment in order to study their optical properties as colour centers. To this end, spectroscopy of the local electroluminescence induced by the injected tunnelling current will be performed.