Impact of Amorphous-C/Ni Multilayers on Ni-Induced Layer Exchange for Multilayer Graphene on Insulators

Abstract

Layer exchange growth of amorphous carbon (a-C) is a unique technique for fabricating high-quality multilayer graphene (MLG) on insulators at low temperatures. We investigated the effects of the a-C/Ni multilayer structure on the quality of MLG formed by Ni-induced layer exchange. The crystal quality and electrical conductivity of MLG improved dramatically as the number of a-C/Ni multilayers increased. A 600 °C-annealed sample in which 15 layers of 4-nm-thick a-C and 0.5-nm-thick Ni were laminated recorded an electrical conductivity of 1430 S/cm. This value is close to that of highly oriented pyrolytic graphite synthesized at approximately 3000 °C. This improvement is likely related to the bond weakening in a-C due to the screening effect of Ni. We expect that these results will contribute to low-temperature synthesis of MLG using a solid-phase reaction with metals.

Metal-induced layer exchange of group IV materials

“…The Ge grain size approached the mm range, which can be called pseudo-single crystals for many thin film devices. This multilayer technique is also useful for the LE in materials other than Ge [130]. In such a system capable of obtaining a large grain size, single crystals can be obtained at arbitrary positions by limiting the area of the initially prepared film [49,[131][132][133].…”

Layer exchange synthesis of multilayer graphene

“…Therefore, multilayer structures containing thin a-C or metals can induce LE, resulting in the formation of a uniform MLG layer molded on the initial thick Ni layer (figures 10(a) and (b)). This phenomenon was originally discovered in the LE of semiconductors [107][108][109] and has also been demonstrated for Niinduced LE of carbon [110,111]. Inserting a 1 nm thick a-C underlayer between Ni and the substrate promotes the supersaturation of carbon atoms in Ni and then accelerates the nucleation (figure 10(a)) [110].…”

“…The thickness of the a-C underlayer is important: LE will occur at both the top and bottom sides if the a-C layer is too thick (>5 nm). The a-C/Ni laminated structure also results in uniform MLG as long as the laminated Ni layer is sufficiently thin (figure 10(b)) [111]. The crystal quality of MLG improves dramatically as the number of a-C/Ni multilayers increases: 15 laminated layers of 4 nm thick a-C and 0.5 nm thick Ni result in high G/D intensity ratio in the Raman spectra (figure 10(c)).…”