Influence of Nickel Catalyst Morphology on Layer‐Exchange‐Based Carbon Crystallisation of Ni/a‐C Bilayers

Abstract

Metal‐induced crystallisation with layer exchange is applied on Ni/C bilayer stacks deposited by three PVD techniques on SiO2. The layer stacks were deposited at room temperature by either ion beam sputtering, direct current magnetron sputtering or high‐power impulse magnetron sputtering. The influence of the Ni morphology on the layer exchange degree αLE and the resulting graphitic ordering is studied by atomic force microscopy, Rutherford backscattering spectrometry and Raman spectroscopy. The initial RMS roughness of the Ni top layer varied with the deposition technique by a factor of 20, from 0.3 to 6.1 nm. After annealing in UHV at up to 700 °C, layer exchange was observed for all samples. Still, the layer exchange degree was affected by the roughness of the initial bilayer stack. The highest value of 96% was achieved for magnetron‐sputtered samples, what is by ∼35% higher than for the initially roughest Ni surfaces. Raman spectroscopy showed the formation of graphitic carbon, characterised by a strong 2D line, for all three bilayer stacks. The degree of graphitic ordering increased with decreasing Ni surface roughness.

Cobalt-Activated Transfer-Free Synthesis of the Graphene on Si(100) by Anode Layer Ion Source

“…Similar to the single-step graphene synthesis case, observed results can be explained by competition between the effects of the increased grain size [22] and increased Co surface roughness [36]. The possible additional dissociation of the C-H bonds by Co interlayer results in prevailing the boundary defects alone in graphene synthesized on silicon, as is seen in Figure 6e.…”

“…In the case of the graphene synthesized on SiO 2 by annealing of the amorphous carbon and catalytic metal (Co or Ni) bilayer, the I 2D /I G ratio in all cases was lower than in the case of the graphene synthesized on quartz using PECVD and sacrificial Ni catalytic interlayer (see [7,[9][10][11]18,36], respectively). At the same time, the defects density in graphene synthesized by bilayer annealing in almost all cases was higher ( [7,[9][10][11]18,36]).…”

“…Thus, graphene layer number can decrease with Co film thickness. At the same time, for graphene synthesized on Ni by metal-induced crystallization, increased roughness increased graphene layers number and defects density [36]. Thus, increased Co film thickness can also increase graphene layers' number and defects density.…”

“…Co film can become both smoother [35] and rougher with increased annealing temperature [34]. The increased roughness for graphene synthesized on Ni by metal-induced crystallization resulted in increased graphene layers number and defects density [36]. The increased Co grain size reduces graphene nucleus number and thickness as carbon diffusion mainly occurs via the catalytic metal grains, and fewer carbon atoms can reach the Si surface [22].…”

Study of Ni-Catalyzed Graphitization Process of Diamond by in Situ X-ray Photoelectron Spectroscopy

“…Other recent papers dealt with Ni-enhanced graphitization of amorphous carbon films (a-C) prepared by CVD. − The a-C/Ni films were annealed mainly in a hydrogen atmosphere. It was observed that carbon film exchanges with Ni film and graphitizes at elevated temperature. − Recent theoretical studies explained the graphitization mechanism for RTA: a-C to graphene transformation entails the metal-induced crystallization and layer exchange mechanism. Carbon dissolution in Ni was excluded …”