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Characterization of carbon nanostructures in Al and Ag covetic alloys

Jaim, H.M. Iftekhar, Cole, Daniel P., Salamanca-Riba, Lourdes G.
Carbon 2017 v.111 pp. 309-321
Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, alloys, aluminum, atomic force microscopy, electric current, energy, graphene, image analysis, nanomaterials, oxidation, silver, thermal properties, transmission electron microscopy
Electrocharging assisted process is a method for the incorporation of carbon in molten metals under high electric current which results in the formation of networks of carbon nanostructures inside the metal matrix, and gives the new material improved mechanical, electrical and thermal properties. Alloys produced with this method are called covetics. In our previous works, different characterization techniques such X-ray photoelectron spectroscopy (XPS), Raman, X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) confirmed the presence of sp2 crystalline graphene nanoribbons and sheets in Ag and Al-covetic samples. Here, we report on detailed Raman mapping and characterization of Al-6061, Al-7075 and Ag covetics to further investigate the fraction of sp2/sp3 bonding, strain, defects, degree of oxidation, and crystalline sizes of the graphene nanoribbons. Gradual changes of strain are observed in regions with sp2 bonding and some degree of amorphous carbon is revealed by Raman scattering. Different degrees of oxidation of the carbon nanostructures with mostly sp2 bonding are evident by EELS spectrum imaging. Atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) also reveal the presence of graphene ribbons and sheets with different lengths and conductivity.