Chanyong Hwang

Breakdown of continuum mechanics for nanometre-wavelength rippling of graphene

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.

Mapping the electronic properties of individual graphene grain boundaries

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.

Revealing the grain structure of graphene grown by chemical vapor deposition

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.

Exfoliation of large-area transition metal chalcogenide single layers

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.

Bulk-sensitive photoemission spectroscopy of A 2 FeMoO 6 double perovskites ( A = Sr , Ba )

The electronic structures of

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

{\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}

Synthesis and hydrogen gas sensing properties of ZnO wirelike thin films

(SFMO) and

Magnetic bubblecade memory based on chiral domain walls

{\mathrm{Ba}}_{2}{\mathrm{FeMoO}}_{6}

Electronic transport through ordered and disordered graphene grain boundaries

(BFMO) double perovskites have been investigated using Fe

Vibrational Properties of h-BN and h-BN-Graphene Heterostructures Probed by Inelastic Electron Tunneling Spectroscopy

2\stackrel{\ensuremath{\rightarrow}}{p}3d