Recently, graphene has attracted significant interest among researchers owing to its excellent properties such as high carrier mobility, high Young’s modulus and high optical transmittance. To this note, the need for high-quality graphene layers has increased resulting in the development of different synthesis techniques. For example, chemical vapor deposition (CVD) technique have been widely used to synthesize graphene. It utilizes copper or nickel catalysts to produce single- or multi-layered graphene respectively. However, it becomes expensive and complicated due to additional transfer processing. As such, researchers have been looking for an alternative technique for graphene synthesis and have identified the growth of graphene directly on an insulating substrate as a promising solution to producing high-quality graphene.
In previously published literature, various approaches have been employed in the direct growth of graphene on substrates using solid carbon sources and gas sources. For instance, using nickel catalyst, graphene has been formed through crystallization of solid-state carbon sources. During the annealing process, carbon diffuses into nickel. During cooling, however, the diffused carbon precipitates to form graphene layers. By adjusting the cooling rate and the source carbon amount, the quality and number of graphene layers can be effectively controlled. Unfortunately, it is difficult to control the location of graphene formation during the process. Basically, the formation of graphene layers can occur on top of nickel surface, at the interface or in both at the same time.
Researchers Dr. Ki-Ju Kim, , Dr. Hyun-Mi Kim and Professor Ki-Bum Kim at Seoul National University in collaboration with Dr. Seong-Yong Cho at University of Illinois at Urbana-Champaign developed a method for synthesizing graphene on dielectric substrate trough solid-state crystallization of amorphous carbon. They utilized nickel as a catalyst and titanium as a carbon diffusion barrier. They calculated and compared the energy balances of the different graphene formation structures to determine the preferential location for the formation of graphene. Their main aim was to synthesize high-quality graphene layers on dielectric substrates at favorable temperatures. Their research work is published in Journal of Vacuum Science & Technology B.
The authors observed the formation of graphene layers on top of the dielectric substrate. Also, they confirmed the transformation of the titanium layer to TiC layer which had a consequence of reducing the diffusion flux of carbon. Furthermore, they noted that the kinetic graphene nucleation and growth led to its formation on the nickel surface.
The demonstrated method led to a successful synthesis of high-quality graphene on the dielectric substrate especially at a temperature of about 6000 °C and Raman Signal D to G peak intensity ratio of approximately 0.29. This was attributed to the possibility of controlling the location of graphene formation by introducing titanium as a diffusion barrier for carbon. Thus, during annealing process, carbon diffused into nickel to form TiC layer at the interface hence impeding further carbon diffusion. Consequently, during cooling, the reaming carbon in the nickel layer precipitated resulting in the formation of multilayered graphene. Formation temperature is a key consideration for good graphene quality. The developed synthesis technique will advance the growth of graphene directly on dielectric substrates.
Kim, K., Cho, S., Kim, H., & Kim, K. (2018). Direct formation of graphene on dielectric substrate: Controlling the location of graphene formation adopting carbon diffusion barrier. Journal of Vacuum Science & Technology B, 36(2), 021802.Go To Journal of Vacuum Science & Technology B