Gerardo Algara-Siller

Chemistry on Graphene

Day of Ph.D. defence: 08.12.2014 (TU Ilmenau)



State-of-the-art transmission electron microscopes (TEMs) are capable to achieve sub-Angstrom resolution. Therefore matter can be studied at the atomic level, i.e., with a TEM the atomic structures and processes can be observed, consequently physical and chemical properties can be derived. In this work, graphene, one atom thick material with outstanding physical and chemical properties, has been thoroughly characterised by different TEM techniques. The structural description of graphene allowed us to compare graphene samples fabricated by different methods and to assess their quality. Furthermore, graphene has been used as a substrate, protective layer, raw material, surface template and nano-confiner.Graphene substrates were used to support nano-objects which were designed for biological applications. Treatments of the graphene substrates prior to sample deposition as well as sample deposition techniques provided the means to obtained samples suitable for TEM investigations. The TEM studies in nano-objects (Au NCs, QDs, nanodiamond with NV centres), deposited on graphene, resulted in the characterisation of their structure, size and dispersion. DNA deposited on graphene was also investigated by TEM. The results showed that the approach of using graphene as substrate can be used to image the structure biological samples. It is presented also in this thesis that graphene can protect radiation sensitive materials such as C3N4 and MoS2 from the electron beam, allowing imaging these materials in their pristine state. By using the electron beam to nano-engineer bilayer graphene it was possible to create single-walled carbon nanotubes. In another experiment, graphene served as surface template where an adlayer graphene grew from residual contamination during imaging. Experiments with water trapped between graphene layers (nano-confinement) resulted in the detection, observation and characterisation of a new form of ice at room temperature, i.e. square ice. Additionally, atomically clean graphene was obtained by the development of a new cleaning method using adsorbents - dry-cleaning -.

Ph.D. thesis