Graphene samples can have a very high carrier mobility if influences from the substrate and the environment are minimized. Embedding a graphene sheet into a heterostructure with hexagonal boron nitride (hBN) on both sides was shown to be a particularly efficient way of achieving a high bulk mobility [1]. Nanopatterning graphene can add extra damage and drastically reduce sample mobility by edge disorder [2][3][4]. Preparing etched graphene nanostructures on top of an hBN substrate instead of SiO2 is no remedy, as transport characteristics are still dominated by edge roughness [5]. Here we show that etching fully encapsulated graphene on the nanoscale is more gentle and the high mobility can be preserved. To this end, we prepared graphene antidot lattices [6] where we observe magnetotransport features stemming from ballistic transport. Due to the short lattice period in our samples we can also explore the boundary between the classical and the quantum transport regime.In single layer graphene the charge carriers are completely exposed to the environment, which limits their mobility. Placing graphene on hexagonal boron nitride (hBN) was shown to improve the carrier mobility [7], allowing the observation of ballistic transport or the fractional quantum Hall effect in bulk graphene [8]. Recently, a dry stacking technique was introduced, which allows complete encapsulation of graphene into layers of hBN and excludes any contamination from process chemicals such as electron beam resist [1]. To obtain graphene nanodevices, chemically prepared graphene nanostructures [9-11] are a potential route for certain applications, however, the high flexibility of a top down patterning approach is extremely desirable. Graphene antidot lattices can help circumventing the problem of the missing band gap in transistor applications [12], and were even predicted to serve as the technological basis for spin qubits [13]. Clearly, for advanced graphene nanodevices, not only the bulk mobility has to be improved, but the nanopatterning has to be optimised.Here we present experiments on graphene antidot lattices [6,14,15] etched into hBN/graphene/hBN heterostructures with lattice periods going down to a = 50 nm. Magnetotransport on those samples shows commensurability features stemming from ballistic orbits around one or several antidots. This allows us to prove that the high carrier mobility is preserved in the nanopatterning step even though the zero field resistance is dominated by scattering on the artificial nanopattern, giving an apparent reduction of the mobility. The small feature size of our samples also allows us to approach the region where the classical picture of cyclotron orbits no longer applies. This classical to quantum crossover is governed by the ratio between the Fermi wavelength λ F of the carriers and the dimensions of the nanopattern.To obtain embedded graphene samples, hBN/graphene/hBN stacks were prepared using the dry stacking technique, patterned into Hall bar shape, and contacted using Cr/Au [1]. In hBN/graphene/h...

One-dimensional diffusion of Co adatoms on graphene nanoribbons has been induced and investigated by means of scanning tunnelling microscopy (STM). To this end, the nanoribbons and the Co adatoms have been imaged before and after injecting current pulses into the nanoribbons, with the STM tip in direct contact with the ribbon. We observe current-induced motion of the Co atoms along the nanoribbons, which is approximately described by a distribution expected for a thermally activated one-dimensional random walk. This indicates that the nanoribbons reach temperatures far beyond 100 K, which is well above the temperature of the underlying Au substrate. This model system can be developed further for the study of electromigration at the single-atom level.

Chemically synthesized "cove"-type graphene nanoribbons (cGNRs) of different widths were brought into dispersion and drop-cast onto exfoliated hexagonal boron nitride (hBN) on a Si/SiO 2 chip. With AFM we observed that the cGNRs form ordered domains aligned along the crystallographic axes of the hBN. Using electron beam lithography and metallization, we contacted the cGNRs with NiCr/Au, or Pd contacts and measured their I-V -characteristics. The transport through the ribbons was dominated by the Schottky behavior of the contacts between the metal and the ribbon.

A reliable method is proposed for measuring specific contact resistivity (ρ C ) for graphenemetal contacts, which is based on a contact end resistance measurement. We investigate the proposed method with simulations and confirm that the sheet resistance under the metal contact (R SK ) plays an important role, as it influences the potential barrier at the graphene-metal junction. Two different complementary metal-oxide-semiconductor-compatible aluminum-based contacts are investigated to demonstrate the importance of the sheet resistance under the metal contact: the difference in R SK arises from the formation of insulating aluminum oxide (Al 2 O 3 ) and aluminum carbide (Al 4 C 3 ) interfacial layers, which depends on the graphene pretreatment and process conditions. Auger electron spectroscopy and X-ray photoelectron spectroscopy support electrical data. The method allows direct measurements of contact parameters with one contact pair and enables small test structures. It is further more reliable than the conventional transfer length method when the sheet resistance of the material under the contact is large. The proposed method is thus ideal for geometrically small contacts where it minimizes measurement errors and it can be applied in particular to study emerging devices and materials.

We investigate the interplay of two highly localized, nearly degenerate electronic states, namely, a zero-energy edge mode in a graphene nanoribbon on the one hand and an Abrikosov-Suhl resonance located at a Kondo impurity on the other. On-surface synthesis of the ribbon structures in combination with intercalation of singleatom Kondo impurities by atomic manipulation in a scanning tunneling microscope junction offer full control of the atomic geometry of the system. Density functional theory provides the microscopic description to scrutinize the electronic features observed in experiment. We find the interaction of the two localized states and the resulting signatures of Kondo physics to be very sensitive to the placing of the atom, suggesting its use as a laboratory to study the interplay of the Kondo effect with other zero-bias anomalies as well as to tailor these states by controlling the atomic-scale coupling.