Catalytic decomposition of SiO2 by Fe and the effect of Cu on the behavior of released Si species

Si supply mechanism in the spontaneous formation of SiO2 pattern on a Cu foil, which was previously reported to enable the selective growth of graphene in no direct contact with organic materials, was investigated. Upon annealing at 1000 °C and atmospheric pressure, SiO2 in the Fe-coated SiO2/Al2O3 template covered by a Cu foil was found to be severely decomposed by Fe droplets. No signature of reaction between SiO2 and Fe droplets suggested that Si species, which contributed to the spontaneous formation of SiO2 pattern on a Cu foil, originated from SiO2 catalytically decomposed by Fe droplets. In the absence of a Cu foil covering an Fe-coated SiO2/Al2O3 template, the catalytic activity of Fe droplets was significantly suppressed because of the encapsulation of Fe droplets by a 2-nm-thin-Fe3O4 layer. Furthermore, a part of the Fe film on SiO2/Al2O3 without a Cu foil turned into nanodroplets and assisted the formation of SiO2 nanowires. These results reveal that a Cu foil made an intriguing role in preventing Fe from being encapsulated by Fe3O4, so the catalytic role of Fe droplets was not terminated until SiO2 was fully decomposed. Our experimental results provided insights into better understanding of these intriguing behaviors of Fe and Cu on SiO2 at high temperature and at atmospheric pressure.