A single layer of graphene with dimensions of 20 mm × 20 mm was grown directly on an insulating substrate by chemical vapor deposition using Ga vapor catalysts. The graphene layer showed highly homogeneous crystal quality over a large area on the insulating substrate. The crystal quality of the graphene was measured by Raman spectroscopy and was found to improve with increasing Ga vapor density on the reaction area. High-resolution transmission electron microscopy observations showed that the synthesized graphene had a perfect atomic-scale crystal structure within its grains, which ranged in size from 50 nm to 200 nm.
Although the formation of graphene nuclei conventionally requires high temperature of ∼1050 °C in the first growth stage, the presence of the graphene nuclei allowed for low-temperature edge growth, and this peripheral area continued growing even when the temperature was reduced to 300 °C in the second growth stage. The graphene grown at the second stage was a single layer with fewer defects. The Raman map showed high homogeneity with a 2D/G ratio >2 over the entire contact area of molten gallium, and the hole mobility was 600 cm2 V−1 s−1.
Carbon nanotube/zinc oxide (CNT/ZnO) composite films were fabricated by electrodeposition with aqueous solution of ZnCl2 and water-soluble CNTs prepared using a high-speed vibration milling technique. The experimental results of secondary ion mass spectroscopy and Raman scattering spectroscopy clearly showed that the CNTs were embedded in the ZnO films. The field electron emission was observed from selectively-etched CNT/ZnO composite films.
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