Bottom-Up Synthesis of Graphene Monolayers with Tunable Crystallinity and Porosity.

We present a method for a bottom-up synthesis of atomically thin graphene sheets with tunable crystallinity and porosity using aromatic self-assembled monolayers (SAMs) as molecular precursors. To this end, we employ SAMs with pyridine and pyrrole constituents on polycrystalline copper foils and convert them initially into molecular nanosheets-carbon nanomembranes (CNMs)- via low-energy electron irradiation induced cross-linking and then into graphene monolayers via pyrolysis. As the nitrogen atoms are leaving the nanosheets during pyrolysis, nanopores are generated in the formed single-layer graphene.

Proximity-Induced Superconductivity and Quantum Interference in Topological Crystalline Insulator SnTe Thin-Film Devices.

Topological crystalline insulators represent a new state of matter, in which the electronic transport is governed by mirror-symmetry protected Dirac surface states. Due to the helical spin-polarization of these surface states, the proximity of topological crystalline matter to a nearby superconductor is predicted to induce unconventional superconductivity and, thus, to host Majorana physics. We report on the preparation and characterization of Nb-based superconducting quantum interference devices patterned on top of topological crystalline insulator SnTe thin films.

Stop-Frame Filming and Discovery of Reactions at the Single-Molecule Level by Transmission Electron Microscopy.

We report an approach, named chemTEM, to follow chemical transformations at the single-molecule level with the electron beam of a transmission electron microscope (TEM) applied as both a tunable source of energy and a sub-angstrom imaging probe. Deposited on graphene, disk-shaped perchlorocoronene molecules are precluded from intermolecular interactions. This allows monomolecular transformations to be studied at the single-molecule level in real time and reveals chlorine elimination and reactive aryne formation as a key initial stage of multistep reactions initiated by the 80 keV e-beam.

Quantitative separation of the anisotropic magnetothermopower and planar Nernst effect by the rotation of an in-plane thermal gradient.

A thermal gradient as the driving force for spin currents plays a key role in spin caloritronics. In this field the spin Seebeck effect (SSE) is of major interest and was investigated in terms of in-plane thermal gradients inducing perpendicular spin currents (transverse SSE) and out-of-plane thermal gradients generating parallel spin currents (longitudinal SSE). Up to now all spincaloric experiments employ a spatially fixed thermal gradient.

Electron beam controlled covalent attachment of small organic molecules to graphene.

The electron beam induced functionalization of graphene through the formation of covalent bonds between free radicals of polyaromatic molecules and C=C bonds of pristine graphene surface has been explored using first principles calculations and high-resolution transmission electron microscopy. We show that the energetically strongest attachment of the radicals occurs along the armchair direction in graphene to carbon atoms residing in different graphene sub-lattices. The radicals tend to assume vertical position on graphene substrate irrespective of direction of the bonding and the initial configuration.

A universal scheme to convert aromatic molecular monolayers into functional carbon nanomembranes.

Free-standing nanomembranes with molecular or atomic thickness are currently explored for separation technologies, electronics, and sensing. Their engineering with well-defined structural and functional properties is a challenge for materials research. Here we present a broadly applicable scheme to create mechanically stable carbon nanomembranes (CNMs) with a thickness of ~0.