Hydrogen-free PECVD growth of few-layer graphene on an ultra-thin nickel film at the threshold dissolution temperature

Abstract

The synthesis of few-layer graphene sheets on an ultra-thin nickel film-coated SiO₂/Si substrate using hydrogen-free plasma-enhanced chemical vapor deposition (PECVD) with in situ low-temperature carbon dissolution is preliminarily demonstrated. The deposited carbon atoms are initially dissolved into the nickel matrix and subsequently precipitate out onto the nickel film surface. The threshold carbon dissolution temperature for synthesizing few-layer graphene is observed to be as low as 475 °C, and the critical thickness of the host nickel film is at least 30 nm. Due to the ultra-low solubility of the carbon atoms in the nickel film at a threshold temperature of 475 °C, the layer number in few-layer graphene can be precisely controlled. Raman scattering analysis indicates almost identical D and 2D peak intensities for nickel films with different thicknesses, whereas the G peak is enhanced with an increasing layer number of graphene which precipitates from thicker nickel films. Saturation of the G peak for the 50 nm thick nickel film is observed, due to the finite carbon dissolution within a limited deposition time, and results in a stabilized, high quality precipitated few-layer graphene. The linear transmittance of few-layer graphene at 550 nm increases from 83 to 93% when the deposition time is shortened from 600 to 100 s, which corresponds to a decrease of the graphene layer number from 8 to 3 layers. The Raman scattering peak ratio of I_D/I_G decreases from 1.8 to 0.2 and the G-band linewidth shrinks from 67 to 37.2 cm⁻¹, providing strong evidence for the improved quality of few-layer graphene synthesized by hydrogen-free PECVD at the threshold temperature on an ultra-thin nickel host.