Faculty of Physics

Carbon Compounds

The work in the field of synthesising nanocrystalline, boron-doped diamond layers as a model system for thermoelectric applications has been continued. This has involved the construction of an apparatus to determine the thermal conductivity of thin layers and layer systems. The measuring principle is based on the 3-Omega method and is applicable over a wide temperature range of up to 850 degrees Celsius. In addition to thermal conductivity, which can be determined both in parallel and perpendicular to the layer plane, information about the density and heat capacity of the layer can also be obtained by spectroscopic interference measurement of thermal waves.

Graphene: The work on the synthesis of graphene by the means of CVD microwave plasma was continued; as an excellent proton conductor and ultra-thin barrier material to other ions and molecules with excellent mechanical stability, for example, the nanomaterial graphene qualifies as an ideal membrane component. To this end, the initial groundwork has already been carried out using the PECVD method for the synthesis of high-quality graphene. Graphene layers were deposited on metal substrates, allowing excellent control to be exerted over the structural properties of the graphene in the material. The monolayer polycrystalline graphene layers were then transferred to SiO2 and Nafion for electrochemical investigations.

Carbon Nano Walls (CNWs): Argon was used as carrier gas for the precursor Al(acac)3 carbon nanowall layers on aluminium, stainless-steel, nickel and silicon substrates. By varying substrate temperature and BIAS voltage, layers of different morphologies could be deposited. A potential growth mechanism was discussed on the basis of the knowledge acquired.

Spin (NV) centres in high-purity diamond: A further research focus of the AG is the cooperation project for the ‘Production and investigation of near-surface spin centres in high-purity diamond,’ which is funded by MERCUR within the framework of the UAR. The spin centre investigated in this project is the nitrogen imperfection, whose spin with coherence times of up to 1.8 ms at room temperature represents a promising, technically usable quantum system. The investigation also addresses the influence of the distance to the surface on the properties – in particular the coherence time. The advantages over other technical quantum systems in use can be found in the comparatively simple preparation and manipulation. Monocrystalline diamonds with significantly better purity than commercially available electronic grades (N <5 ppb) have already been produced.

Surface modification of bipolar plates containing carbon: Bipolar plates of carbon and polypropylene, for use in fuel cell technology, have markedly improved properties with regard to contact resistance when it comes to plasma treatment. In addition to the plasma etching of the polypropylene, the change in the graphite is mainly due to the removal of nanocrystalline structures, which improves conductivity due to the reduced number of grain boundaries. The best results were achieved here with oxygen-containing gases.