Book/Dissertation / PhD Thesis

FZJ-2017-07304

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png The influence of the substrate on the structure and electronic properties of carbon-based 2D materials

Sforzini, J. (Corresponding author)FZJ*

2017
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-255-9

Please use a persistent id in citations: http://hdl.handle.net/2128/16138  urn:nbn:de:0001-2017120701

Abstract: The exploration of two-dimensional (2D) materials, such as graphene, has become the hottest research of interest in recent years because they offer the possibility to create more efficient, smaller and cost-effective nano-devices. In order to realize potential applications of 2D materials in the areas of electronics and optoelectronics, there are many challenges associated with their electronic and structural behavior, which require the understanding of the interactions at 2D materials interfaces. With this in mind, the goal of this thesis was to assess interactions between various 2D layers and substrates, of interest for both fundamental studies and industrial applications, by studying the modification of the layer electronic and structural properties in relation to the supporting substrate using different surface science techniques. In particular, interactions residing at graphene/6H-SiC(0001) interfaces were considered. At first, a new approach used to gauge the strength of these interactions was presented based on the determination of the graphene adsorption height with respect to the H-intercalated SiC substrate. By comparing this value with the graphene vertical distance of different graphene/substrate systems, we found H-intercalated graphene (H-QFMLG) free of interactions besides van der Waals, indicating that the effect of the underlying H-intercalated SiC on graphene was almost non existent. The influence of this substrate on the structural and electronic properties of graphene was further investigated upon nitrogen doping in comparison to the carbon buffer layer terminated SiC in epitaxial graphene (EMLG). The outcome was that both graphene layers showed a similar n-type carrier increase but a dissimilar concentration and variety of dopants substituted into the graphene layers leading to the main conclusion that the effective doping of graphene was surprisingly dependent on the supporting material. In the case of H-QFMLG, the nitrogen dopants were found partially replacing the hydrogen intercalation at the interface, which in turn became N-doped contributing to the graphene doping (’proximity doping’) but degrading the graphene layer in terms of buckling and interface interactions. On thecontrary, the buffer layer in EMLG was found inert allowing a multicomponent substitution of the nitrogen dopants into graphene. Howver, ths was not the case for boron-doped EMLG, for which boron was found in one chemical configuration and in both buffer layer and graphene. In the last part of the thesis, the focus was laid on the study of physical phenomena that occur at organic/metal interfaces. Specifically, the molecular symmetry reduction (from the D4h symmetry group) via degeneracy lifting of the platinum- and palladium-phthalocyanine/Ag(111) complexes was investigated using vibrational spectroscopy. Because of the presence of an interfacial dynamical charge transfer, some vibrational peaks showed a Fano-type line shape. By their assignment to vibrational modes which were infrared active only in the C$_{2v}$ symmetry group, we proved that a preferential charge transfer from the Ag surface into one of the originally doubly degenerate lowest unoccupied molecular orbitals took place, i.e. the electronic degeneracy was lifted and the molecule-surface complex acquired the twofold symmetry.

Note: RWTH Aachen, Diss., 2017

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Contributing Institute(s):

1. Funktionale Nanostrukturen an Oberflächen (PGI-3)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

Appears in the scientific report 2017

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