Synthesis of Graphene on Electrochemical Nickel for MEMS Industry (2016)

Graphene, thanks to its novel properties, has proved to be a very good material for electronics applications, spacing from MEMS to biosensing technology. In the last few years chemical vapor deposition of organic precursors onto transition metal supports revealed to be a trustworthy method for high quality graphene deposition, thanks to catalytic properties of the already cited metals. In this work, we selected nickel as the suitable transition metal substrate for graphene growth via chemical vapor deposition, which has been carried out starting from a gaseous methane and hydrogen process stream. In fact, nickel-carbon interaction mechanisms are well known and suitable for the effort of controlling the quantity of organic material that is able to grow onto the metal surface. Obtained samples were analyzed by Raman spectroscopy; spectra pointed out a total absence of the D peak, whose presence is generally accounted for graphene bad transport properties due to many domain boundaries; on the other side, Raman study revealed a higher than one intensity ratio between G peak and 2D band. The succeeding step consisted in the application of the so developed methodology in order to produce graphene coated devices. We based our approach on already existing works [1,2] but tried to exploit the properties of the galvanic displacement process in order to cover monocrystalline silicon wafers with a thin nickel film. First, we tuned the displacement process in order to fit our needs, performing the plating at different times, fixing our attention to film compactness and adhesion to silicon. Then chemical vapor deposition was employed and samples were analyzed to understand the degree of reproducibility of the process. Again, Raman spectroscopy, AFM, SEM and XPS were employed in order to understand graphene quality achieved. Raman spectra were very similar to those of the freestanding nickel foils, while XPS performed onto the same substrate yielded some coherent results: in those points were the nickel signal was higher, and so carbon signal was lower, we ended up with 1.3 nm few layered graphene thickness. Recollecting graphite interplanar distances, which was roughly 0.34 nm, 3 to 4 graphene sheets were deposited. By atomic force microscopy we were able to highlight graphene sheets stacked onto the sample surface. Microstructured, polycrystalline, silicon wafer were coated by the carbonaceous layer using the same chemical vapor deposition process already explained. Raman spectroscopy was again the main characterization technique used to gather information about the deposit: the intensity ratio I(G)/I(2D) was higher than one. In conclusion, we managed to deposit good quality, few layered, graphene onto silicon substrate by using a transition metal thin film as a buffer layer for the growth. A first attempt has been made to understand if graphene layers were grown also between the metal film and silicon; this would represent a first concern towards a very cost efficient and reproducible graphene coated semiconductors. [1] D.Q. McNerny et al.; Sci. Rep. 4, 5049; DOI:10.1038/srep05049 (2014). [2] Yu Yao et al. / Energy Procedia 38 ( 2013 ) 807 – 815.