ORALS

Graphene is a perfect 2D crystal of covalently bonded carbon atoms and forms the basis of all graphitic structures with superior properties [1] that can be exploited in many research areas. Nevertheless, these structures cannot have significant impact until efficient production techniques develop to harvest their unique properties in global applications and devices. Chemical Vapor Deposition (CVD) is the most well-known method of graphene growth [2]. The fabrication process is rather complex, as it involves multiple steps such as hydrocarbon decomposition, carbon adsorption and subsequently, diffusion on the catalytic substrate, the generation of the nucleation point and finally, the growth. As the nucleation happens at random places on the surface, this method by default results in micro-meter sized multi-domain layers. Moreover, the separation and transport steps add further defects and contaminations, which further impair the ideal physical properties of these materials. In contrast to a solid catalytic substrate, graphene growing on Liquid Metal Catalysts (LMCat) might be a solution for the production of defect-free single graphene domains at high synthesis speeds due to the enhanced atomic mobility, homogeneity, and fluidity of a LMCat. In-situ monitoring of such a complex procedure is of paramount importance for the control of graphene growth and the understanding of growing kinetics. Among other optical techniques, Raman spectroscopy has been used extensively for studying nanomaterials in general and graphene in particular. Performing in situ Raman spectroscopy at high temperatures, however, needs special considerations, otherwise the weak Raman signal could be easily dominated by the intense thermal radiation. In our case, a UV laser line at 405 nm was used to reduce the black body radiation effect. Raman spectra were acquired on liquid Cu during growth and it verified the existence of graphene even at its primary stages. This result is of paramount importance since it is the first time that a chemically sensitive technique like Raman spectroscopy was implemented for the in-situ monitoring of graphene growth. Beside Raman spectroscopy, a novel metrology system based on reflectance spectroscopy for the in-situ monitoring of surface changes during graphene growth by taking advantage of reflectance variations was developed. Simultaneously, reflectance fluctuations on the surface of copper are monitored and analyzed. The results indicated that the growth rate of graphene can be estimated from the measured differential reflectance. We will present processing strategies for the production of macro-scale CVD-graphene/polymer nanolaminates based on the combination of ultra-thin casting, wet transfer and floating deposition [3, 4]. These composites possess excellent mechanical and electrical properties and can be employed as coatings for EMI shielding or electro-active displays in a variety of applications. This can assist in the protection of membranes, art objects and particularly paintings. Finally, the use of large transparent graphene veils for the protection of art works will also be covered in this presentation.

References:
[1] Novoselov K. S. et al., Proc. Natl. Acad. Sci., 102, 10451, 2005
[2] Bae S. et al., Nat. Nanotechnology, 5, 574, 2010
[3] Vlassiouk I et al., ACS Appl Mater Interfaces, 20, 10702, 2015
[4] Pavlou Ch. al, submitted