Study of graphene layer growth on dielectric substrate in microwave plasma torch at atmospheric pressure

Abstract

The initial stage of graphene layer deposition on silicon oxide substrate by ethanol decomposition in dual-channel microwave plasma torch at atmospheric pressure was studied in dependence on precursor flow rate and delivered microwave power. Depending on ethanol flow rate and substrate temperature, horizontally or vertically aligned graphene nanosheets with various density could be prepared directly on dielectric substrate. In the regime with high microwave power, above 400 W, mixture of amorphous carbon particles and graphene sheets was deposited on the substrate. Prepared layers were analyzed by scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The microwave plasma diagnostics was carried out using optical emission spectroscopy (OES). The sample analysis showed increasing density of horizontally aligned carbon nanosheets with increasing ethanol flow rate and their delamination and transition into vertically aligned graphene sheets with increasing substrate temperature. The Raman spectroscopy analysis of layers showed presence of D (1345 cm−1), G (1585 cm−1) and 2D (2685 cm−1) peaks with 2D/G ratio of 1.59 and full width at half maximum (FWHM) of 2D peak was 42 cm−1, corresponding to few layer graphene structure. In case of amorphous nanoparticles deposition, the D* peak at 1210 cm−1 and D** at 1500 sccm−1 was observed in Raman spectra with D/G ratio of 1.19 and C1s XPS spectra of carbon contained 20.4 at.% of sp3 carbon phase in comparison to 8.3 at.% in case of graphene nanosheets layer. High D/G ratio, up to 3.5, and low intensity 2D band was characteristic for vertically aligned graphene nanosheets layers. The possibility to influence density and size of graphene nanosheets on substrate represents promising alternative for future deposition of graphene on arbitrary substrate.