Fast Direct Growth of Self-Crystallized Graphene-from Controllable Growth to Material Characterization and Device Applications

Graphene, one of the most attractive research topics in modern science owing to its fascinating electrical properties, has been attracted much attention. Its unique structure, two-dimensional honeycomb carbon lattice, enables high conductivity and transparency. This material is thus potentially expected to become a transparent conductive layer in optoelectrical applications and thus stimulates a lot of studies on the synthetic growth methods to requisitely develop high uniformity with high quality and simple process for industrial manufactory.

   Common process for the synthesis of the graphene is typically based on heat chemical vapour deposition (CVD), for which carbon sources such as methane and acetylene are as precursors with metal-catalytic layers such as Cu or Ni foils. However, an additional complex transferred processes of the graphene layer on an insulator substrate from the metal-mediated layer are imperative steps for the device application, containing spinning coating of protective layer, etching of mediated layer, fishing of graphene layer, and removal of protective layer. Defects, such as cracks, wrinkles, and chemical residuals (Fe³⁺, polymer…etc.) can be readily formed during transferred processes, resulting in decease of electron mobility due to scattering behaviours by defects, thereby degrading device performance. Many transfer-free processes had been investigated to prevent these problems. The concept of back-side segregation by bulk or boundary diffusion had been applied to achieve the segregated graphene at interface between the substrate and the metal-mediated layer.  

   In this talk, a directly self-crystallized graphene layer with transfer-free process on arbitrary insulator by Ni vapor-assisted growth at growth temperatures between 950 to 1100 ºC via conventional chemical vapor deposition (CVD) system was developed and demonstrated. Domain sizes of graphene were confirmed by Raman spectra from ~12 nm at growth temperature of 1000 ºC to ~32 nm at growth temperature of 1100 ºC, respectively. Furthermore, the thickness of the graphene is controllable, depending on deposition time and growth temperature. In addition, we also develop a new method to synthesize graphene and highly oriented graphite via Ni-catalyzed solid phase segregation using amorphous carbon as a resource by the rapid microwave heating process (RMHP) in air. By controlling input powers of the microwave, the annealing temperature could be controlled, enabling this synthesis to dissolve the carbon atoms into catalyst layer. With annealing under an adequate temperature in air, the carbon solute in the Ni will retard the formation of the NiO film on the surface by reduction process.