Levente Tapasztó

Tailoring the atomic structure of graphene nanoribbons by scanning tunnelling microscope lithography

The practical realization of nanoscale electronics faces two major challenges: the precise engineering of the building blocks and their assembly into functional circuits. In spite of the exceptional electronic properties of carbon nanotubes, only basic demonstration devices have been realized that require time-consuming processes. This is mainly due to a lack of selective growth and reliable assembly processes for nanotubes. However, graphene offers an attractive alternative. Here we report the patterning of graphene nanoribbons and bent junctions with nanometre-precision, well-defined widths and predetermined crystallographic orientations, allowing us to fully engineer their electronic structure using scanning tunnelling microscope lithography. The atomic structure and electronic properties of the ribbons have been investigated by scanning tunnelling microscopy and tunnelling spectroscopy measurements. Opening of confinement gaps up to 0.5 eV, enabling room-temperature operation of graphene nanoribbon-based devices, is reported. This method avoids the difficulties of assembling nanoscale components and may prove useful in the realization of complete integrated circuits, operating as room-temperature ballistic electronic devices.

Tuning the electronic structure of graphene by ion irradiation

Mechanically exfoliated graphene layers deposited on

Breakdown of continuum mechanics for nanometre-wavelength rippling of graphene

{\text{SiO}}_{2}

Mapping the electronic properties of individual graphene grain boundaries

substrate were irradiated with

Revealing the grain structure of graphene grown by chemical vapor deposition

{\text{Ar}}^{+}

Exfoliation of large-area transition metal chalcogenide single layers

ions in order to experimentally study the effect of atomic scale defects and disorder on the low-energy electronic structure of graphene. The irradiated samples were investigated by scanning tunneling microscopy and spectroscopy measurements, which reveal that defect sites, besides acting as scattering centers for electrons through local modification of the on-site potential, also induce disorder in the hopping amplitudes. The most important consequence of the induced disorder is the substantial reduction in the Fermi velocity, revealed by bias-dependent imaging of electron-density oscillations observed near defect sites.

The intrinsic defect structure of exfoliated MoS2 single layers revealed by Scanning Tunneling Microscopy.

It is known that graphene exhibits natural ripples with characteristic lengths of around 10 nm. But when it is stretched across nanometre-scale trenches that form in a reconstructed copper surface, it develops even tighter corrugations that cannot be explained by continuum theory.

Characterizing the global dispersion of carbon nanotubes in ceramic matrix nanocomposites

Grain boundaries, the characteristic topological defects of chemical vapor deposition grown graphene samples, are expected to substantially alter the electronic properties of the unperturbed graphene lattice. However, there is very little experimental insight into the underlying mechanisms. Here, we systematically map the electronic properties of individual graphene grain boundaries by scanning tunneling microscopy and spatially resolved tunneling spectroscopy measurements. The tunneling spectroscopy data reveal that the conductivity inside the boundaries is markedly suppressed for both electron and hole-type charge carriers. Furthermore, graphene grain boundaries can give rise to n-type inversion channels within the p-doped graphene sheets, forming p-n junctions with sharp interfaces on the nanometer scale. These properties persist for grain boundaries of various configurations and are robust against structural disorder.

Nanomesh-Type Graphene Superlattice on Au(111) Substrate.

The physical processes occurring in the presence of disorder: point defects, grain boundaries, etc. may have detrimental effects on the electronic properties of graphene. Here we present an approach to reveal the grain structure of graphene by the selective oxidation of defects and subsequent atomic force microscopy analysis. This technique offers a quick and easy alternative to different electron microscopy and diffraction methods and may be used to give quick feedback on the quality of graphene samples grown by chemical vapor deposition.

Polarized light microscopy of chemical-vapor-deposition-grown graphene on copper

Isolating large-areas of atomically thin transition metal chalcogenide crystals is an important but challenging task. The mechanical exfoliation technique can provide single layers of the highest structural quality, enabling to study their pristine properties and ultimate device performance. However, a major drawback of the technique is the low yield and small (typically < 10 μm) lateral size of the produced single layers. Here, we report a novel mechanical exfoliation technique, based on chemically enhanced adhesion, yielding MoS2 single layers with typical lateral sizes of several hundreds of microns. The idea is to exploit the chemical affinity of the sulfur atoms that can bind more strongly to a gold surface than the neighboring layers of the bulk MoS2 crystal. Moreover, we found that our exfoliation process is not specific to MoS2, but can be generally applied for various layered chalcogenides including selenites and tellurides, providing an easy access to large-area 2D crystals for the whole class of layered transition metal chalcogenides.