Special Session 8 Introduction: Fundamentals to Applications in 2D Materials

Provides an overview of the 2015 Special Session 8 meeting as part of the 11th International Conference on Diffusion in Solids and Liquids, Munich, Germany, June 22-26, 2015

Thickness Estimation of Epitaxial Graphene on SiC using Attenuation of Substrate Raman Intensity

A simple, non-invasive method using Raman spectroscopy for the estimation of the thickness of graphene layers grown epitaxially on silicon carbide (SiC) is presented, enabling simultaneous determination of thickness, grain size and disorder using the spectra. The attenuation of the substrate Raman signal due to the graphene overlayer is found to be dependent on the graphene film thickness deduced from X-ray photoelectron spectroscopy and transmission electron microscopy of the surfaces. We explain this dependence using an absorbing overlayer model. This method can be used for mapping graphene thickness over a region and is capable of estimating thickness of multilayer graphene films beyond that possible by XPS and Auger electron spectroscopy (AES).Comment: 14 pages, 9 figure

Special Session 8 Introduction: Fundamentals to Applications in 2D Materials

Provides an overview of the 2015 Special Session 8 meeting as part of the 11th International Conference on Diffusion in Solids and Liquids, Munich, Germany, June 22-26, 2015

Growth of Low-Dimensional Carbon Nanomaterials

Low dimensional carbon nanostructures, carbon nanotubes (CNTs) and graphene, have attracted significant interest due to promising applications ranging from high-speed electronics to sensing. However, insight into growth mechanisms of low-dimensional carbon nanomaterials remains a challenge. Metal-free nanocarbon/SiC structures offer an excellent platform to gain a fundamental understanding of carbon nano-materials. In this talk, metal-free nanocarbon/SiC structures are used as a platform to gain a fundamental understanding of the growth mechanisms of CNTs and graphene. Specifically, an understanding and control of the SiC surface graphitization process and interface structure needs to be established. In this review, we focus on graphene growth on SiC (0 0 0 1) (Si-face) as a model system in comparison with aligned CNT growth on SiC. The experimental aspects for graphene growth, including vacuum and ambient growth environments, and growth temperature will be presented, then, proposed decomposition and growth mechanisms are discussed. Both thermal and chemical decomposition processes are presented and special emphasis is given to the role of oxygen. The chemical reactions driving the graphitization process and ultimately the carbon nanostructure growth on SiC are discussed. The composition of the residual gases in the growth environment is a critical parameter as well as gas composition at the growth temperature.https://corescholar.libraries.wright.edu/physics_seminars/1005/thumbnail.jp

Adsorption and Diffusion of Oxygen on Single-Layer Graphene with Topological Defects

In this work, effects of oxygen adsorption and diffusion on the stability, morphology, and charge transfer in single-layer graphene with structural point defects were investigated by density functional theory, specifically for the experimentally characterized monovacancy, double-vacancy, 555–777, 5555–6–7777, and Stone-Wales defects. The theoretical analysis demonstrated strengthened oxygen adsorption on defective graphene as compared to pristine graphene, resulting in trapping of the oxygen onto defects. This was accompanied by significant charge transfer of up to 3e, unlike for pristine graphene. At the same time, atomic oxygen diffuses at different rates dependent on the local environment, however with relatively low barriers (mostly <1 eV), lower than for pristine graphene, thus, revealing an interplay between diffusion and adsorption in this case. Addition of a nonempirical correction to the exchange-correlation functional to take into account London dispersion demonstrated that the vdW-DF PBE functional does not change the overall trend in adsorption, structure and diffusion pathways, but the predicted adsorption energies and activation energy barriers are lower. Interestingly, following incorporation of oxygen within defects, the morphology has shown deformation from planarity of the nanostructure, particularly with higher coverage. This could explain, in part, initiation of buckling and possibly the early stage of a “tip”-like structure in carbon nanotube growth on SiC(0001) in the presence of oxygen, as has been observed experimentally. Overall, the calculations on the effects of oxygen or other moiety adsorption on defective graphene provided a quantified basis for engineering defects in single-layer graphene, which are difficult to characterize experimentally