Characterization of Copper Covetic Bulk and Films: Copper with High Carbon Content
Isaacs, Romaine Antonio
Salamanca-Riba, Lourdes G
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Incorporation of carbon nanostructures in metals is desirable to combine the strongly bonded electrons in the metal and the free electrons in carbon nanostructures that give rise to high ampacity and high conductivity, respectively. Carbon in copper has the potential to impact industries such as: building construction, power generation and transmission, and microelectronics. This thesis focuses on the structure and properties of bulk and thin ﬁlms of a new material, Cu covetic, that contains carbon in concentrations up to 16 at.%. X-ray photoelectron spectroscopy (XPS) shows C 1s peak with both sp2 and sp3 bonded C measuring up to 3.5 wt.% (16 at.%). High resolution transmission electron microscopy and electron diffraction of bulk covetic samples show a modulated structure of ≈ 1.6 nm along several crystallographic directions in regions that have high C content suggesting that the carbon incorporates into the copper lattice forming a network. Electron energy loss spectra (EELS) from covetics reveal that the level of graphitization from the source material, activated carbon, is maintained in the covetic structure. Bulk Cu covetics have a slight increase in the lattice constant, as well as <111> texturing, or possibly a different structure, compared to pure Cu. Density functional theory calculations predict bonding between C and Cu at the edges and defects of graphene sheets. The electrical resistivity of bulk covetics ﬁrst increases and then decreases with increasing C content. Cu covetic ﬁlms were deposited using e-beam and pulsed laser deposition (PLD) at different temperatures. No copper oxide or any allotropes of carbon are present in the films. The e-beam films show enhanced electrical and optical properties when compared to pure Cu ﬁlms of the same thickness even though no carbon was detected by XPS or EELS. They also have slightly higher ampacity than Cu metal ﬁlms. EELS analysis of the C-K-edge in the PLD ﬁlms indicate that graphitic carbon is transferred from the bulk into the ﬁlms with uniform carbon distribution. PLD ﬁlms exhibit ﬂatter and higher transmittance curves and sheet resistance two orders of magnitude lower than e-beam ﬁlms leading to a high ﬁgure of merit as transparent conductors.