In the Eigler group, we focus on three topics in general:

A) Chemistry of graphene, inparticular oxo-chemistry.
B) Synthesis of molecular π-systems, which may interact with 2D materials or are attractive dyes or even emissive dyes.
C) Fabrication of transistor-type devices to determine the charge transport properties of 2D materials and assemblies.

A) Graphene – a single layer of graphite – Oxo-chemistry of graphene

While the chemistry and even regiochemistry of fullerenes, such as C60 is well understood, the chemistry of other carbon allotropes are less studied. Graphene chemistry is just developing and controlling the reactivity of the basal plane of graphene is the next challenge. Analytical and synthetic methods are developed. Stabilizing single layer of graphene is one of the main tasks. Chemists must face the hurdles and challenges of this young discipline of science.

Graphene becomes accessible on the gramm-scale and more by oxidizing graphite to a soluble material, termed as graphene oxide. We learned to control this oxidation process not to over-oxidize the carbon framework. Thus, we can study the on-plane chemistry. Consequently, spectroscopic results and changes stem from the surface chemistry and not from defect-sites. However, defects in graphene can also be studied with controlling the formation of defects.

The heterogeneous materials class graphene oxide, or better termed as oxo-functionalized graphene, may be synthesized now with control over the density of lattice defects, size of holes, type of oxo-groups, such as hydroxyl-, epoxy-groups or organosuflate groups. In addition, the size of particles can be controlled and enriched by centrifugation. Also the degree of functionalization can be controlled to direct e.g. the assembly with other molecules.

B) Molecular synthesis and photonics

Fluorescence dyes find applications in various fields of research, including light harvesting or biomarkers. An additional high dipole moment gives further access to nonlinear optics and redox activity allows to switch the molecular properties.
We combine tailored fluorescence with high dipole moments and redox activity.

Interaction of molecular structures with graphene

Controlling the morphology of functional molecules on 2D surfaces leads to hybride materials with altered physical properties, such as the band-gap and interaction with environmental molecules. This approach enables the realization of novel sensors concepts, displays and solar cells.

Here, we focus on the interaction of graphene, MoS2 or WS2 with high dipole molecules (HDM). Questions, such as doping, molecular order and real dipole moment on the surface will be answered.

C) Fabrication of devices and measurement of transport properties

Atomically thin graphene-based materials suffer significant mobility degradation due to charged impurities and photo scattering induced by silicon oxide-covered silicon (SiO2/Si) substrates. However, within devices those properties can be determined. Up to now, the influence of chemical modification on the transport properties are difficult to predict. Control of doping, tuning of resistance and the interaction with environmental molecules can be evaluated. Therefore, we set-up the technology to make devices from single flakes of 2D materials in general and chemically prepared flakes of graphene in particular.

Device structures can be seen in the figure from flakes, or overlapping flakes to the measureable device. Typical I-V curves are shown on the right side.

In the future we will focus on the fabrication of 2D architectures to further control interactions with molecules to understand sensing applications.