The behavior of single layer van der Waals (vdW) materials is profoundly influenced by the immediate atomic environment at their surface, a prime example being the myriad of emergent properties in artificial heterostructures. Equally significant are adsorbates deposited onto their surface from ambient. While vdW interfaces are well understood, our knowledge regarding atmospheric contamination is severely limited. Here we show that the common ambient contamination on the surface of: graphene, graphite, hBN and MoS₂ is composed of a self-organized molecular layer, which forms during a few days of ambient exposure. Using low-temperature STM measurements we image the atomic structure of this adlayer and in combination with infrared spectroscopy identify the contaminant molecules as normal alkanes with lengths of 20-26 carbon atoms. Through its ability to self-organize, the alkane layer displaces the manifold other airborne contaminant species, capping the surface of vdW materials and possibly dominating their interaction with the environment.

In crystalline solids, the interactions of charge and spin can result in a variety of emergent quantum ground states, especially in partially filled, topological flat bands such as Landau levels or in “magic angle” graphene layers. Much less explored is rhombohedral graphite (RG), perhaps the simplest and structurally most perfect condensed matter system to host a flat band protected by symmetry. By scanning tunneling microscopy, we map the flat band charge density of 8, 10, 14, and 17 layers and identify a domain structure emerging from a competition between a sublattice antiferromagnetic insulator and a gapless correlated paramagnet. Our density matrix renormalization group calculations explain the observed features and demonstrate that the correlations are fundamentally different from graphene-based magnetism identified until now, forming the ground state of a quantum magnet. Our work establishes RG as a platform to study many-body interactions beyond the mean-field approach, where quantum fluctuations and entanglement dominate.

Silver nanoparticles (Ag NPs) play important roles in the development of plasmonic applications. Combining these nanoparticles with graphene can yield hybrid materials with enhanced light–matter interaction. Here, we report a simple method for the synthesis of graphene–silver nanoparticle hybrids on highly oriented pyrolytic graphite (HOPG) substrates. We demonstrate by scanning tunneling microscopy and local tunneling spectroscopy measurements the electrostatic n-type doping of graphene by contact with silver. We show by UV-Vis reflectance investigations that the local surface plasmon resonance (LSPR) of Ag NPs partially covered with graphene is preserved for at least three months, i.e., three times longer than the LSPR of bare Ag NPs. The gradual loss of LSPR is due to the spontaneous sulfurization of non-covered Ag NPs, as revealed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. We show that the Ag NPs completely sandwiched between graphene and HOPG do not sulfurize, even after one year.

A corrugated graphene overlayer can increase the sensitivity and selectivity of local surface plasmon resonance-based vapour sensing with gold nanoparticles.