Developments in the Catalytic Graphitisation of Diamond and Silicon Carbide Surfaces

Crynodeb

Graphitisation of diamond and SiC surfaces to produce high-quality epitaxial graphene was developed and investigated using surface sensitive techniques, namely X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), low-energy electron microscopy (LEEM), and X-ray photoemission electron microscopy (XPEEM). The transfer of epitaxial graphene grown by catalytic graphitisation has been achieved and studied using Raman spectroscopy. Above 930 ◦C, the diamond (111) surface undergoes a (2×1) reconstruction with three domains, confirmed by XPS and LEED. Previously acquired angle-resolved photoemission spectroscopy (ARPES) measurements are affirmed by modern density-functional theory (DFT) modelling along the KΓK reciprocal space direction which demonstrates the π-band rising above the Fermi level, indicative of a metallic surface state. Heating the diamond surface above 1000 ◦C produces graphene that co-exists and strongly interacts with the (2 × 1) reconstruction, evidenced by the emergence of Dirac cones along the KgMKg direction in both previously acquired ARPES and DFT modelling. The temperature required to graphitise the diamond (111) surface is catalytically reduced to ∼500 ◦C in the presence of a thin iron overlayer. The purity and crystallography of the iron is vital in producing epitaxial graphene with minimal defects. Real-time electron emission spectroscopy (REES) allowed the detachment, transport, and re-crystallisation of carbon from the diamond surface into graphene to be monitored for a linear temperature ramp to 685 ◦C. A heavily boron-doped diamond was catalytically graphitised at 640 ◦C. Angle-resolved XPS and Raman measurements reveal that boron is transported through the iron and forms a boron-doped graphitic structure with a boron content of ∼5 % and p-type characteristics. Patterned graphene is fabricated directly on the 6H-SiC (0001) surface using catalytic graphitisation. LEEM, XPEEM, and Raman spectroscopy mapping confirm that graphitised regions adhere perfectly to the catalyst pattern with a step edge <50 nm. An acid-free delamination transfer technique using a polyvinyl alcohol scaffold was developed in order to move graphene, catalytically-grown on SiC, onto silicon dioxide. This improved transfer heralds an order-of-magnitude improvement in the post-transfer defect density of graphene when compared to acid-etch transfer techniques, as well as significantly reducing polymer residues and contamination. Raman spectra with the characteristic graphene Raman peaks (D, G, and 2D) have been measured for the first time on catalytically-grown graphene from diamond

Dyddiad Dyfarnu	2020
Iaith wreiddiol	Saesneg
Sefydliad Dyfarnu	Prifysgol Aberystwyth
Goruchwyliwr	Andrew Evans (Goruchwylydd) & Rachel Cross (Goruchwylydd)