Investigation of graphene layers on electrodeposited polycrystalline metals

Abstract

Nowadays, many different methods are used to produce graphene. Electrochemical techniques represent a low‐cost and versatile route to deposit metals, although the characterization of graphene grown on electrochemically deposited polycrystalline metals is still in its infancy. In this work, several metal substrates were prepared by electrochemical processes and then covered with graphene layers grown by CVD. Free‐standing foils of Cu and Ni‐Cu alloy (20 wt.% of Cu) were prepared by electroforming, while a pure Ni film was obtained by galvanic displacement on a Si wafer. The thickness of Ni film on Si wafer was about 0.7 µm, whereas the Ni‐Cu foils were much thicker (12 µm). The characterization of the graphene films was performed by using Raman spectroscopy, XPS and AES. Copyright © 2016 John Wiley & Sons, Ltd.

Growth and characterization of ultrathin carbon films on electrodeposited Cu and Ni

“…The shape of C KVV spectra and the values of D parameter were different in diverse samples, as it is illustrated in Figure 4 The most surprising result was obtained for the treated Ni foil (Figure 4 B), where the diamond-like shape of C KVV is observed in the XAES spectrum, whereas in AES case, the same spectrum becomes clearly graphitic, indicating the presence of graphene. 16,19,24 Exactly the same effect was observed also in the AES spectra of the first 2 samples, where also was confirmed the presence of graphene. All the values of the D parameter for diverse samples are reported in Table 2 together with the data for reference samples from refs.…”

“…In the other 2 samples (on Ni/Si and on Ni foil), the spectrum is graphitic with D = 21.2 and 22.0 eV, respectively. The most surprising result was obtained for the treated Ni foil (Figure B), where the diamond‐like shape of C KVV is observed in the XAES spectrum, whereas in AES case, the same spectrum becomes clearly graphitic, indicating the presence of graphene . Exactly the same effect was observed also in the AES spectra of the first 2 samples, where also was confirmed the presence of graphene.…”

“…These differences can be justified by recalling that the analysis area of XPS (approximately 1 mm in diameter) is remarkably larger than the Raman spot with a diameter of 1 μm; therefore, XPS measurements provide an average value of the film thickness, whereas local analysis is given by Raman spectroscopy. In a previous work, CVD carbon films grown on Ni substrates were found to be highly uneven, with coexistence of few‐layer graphene zones and graphite areas. Interrupted cooling applied in the present work improved the film uniformity, although the discrepancy between XPS and Raman data in Table indicates that some local variations in the film thickness still exist.…”

“…In a previous work, 16 CVD carbon films grown on Ni substrates were found to be highly uneven, with coexistence of few-layer graphene zones and graphite areas. Interrupted cooling applied in the present work improved the film uniformity, although the discrepancy between XPS and Raman data in Table 1 indicates that some local variations in the film thickness still exist.…”

“…In the case of much thinner film on Cu, the XPS signal in the VB starts immediately from the Fermi level and contains a very high band of Cu 3d, covering all the features of graphene. It should be noted, that namely the absence of occupied states near to the Fermi level results in the narrower, diamond‐like C KVV spectra of graphene, whereas the presence of C 2p‐π states in the VB is reflected in the wider C KVV line of graphite …”