The team explains that in silicon-based electronics, the upper temperature threshold that the components can withstand upon graphene integration is around 400 °C. The threshold is even lower for plastic semiconducting devices, which can only withstand up to 100 °C during the graphene growing process. Under traditional conditions, graphene growth occurs at around 1000 °C and has not been suitable for the direct integration into such electronic devices.
This new method could change that situation though, as the team managed to grow CVD-graphene onto sapphire and polycarbonate substrates with the help of a molten gallium catalyst and dilute methane atmosphere. The gallium catalyst was chosen as it was a proven catalyst in recent graphene growth methods and can be easily removed by a gas jet after the graphene has been synthesized. The methane was diluted to 5% by mixing the atmospheric gas with a nitrogen and argon mixture.
The Researchers inspected the quality of the grown graphene using Raman spectroscopy (RAMANplus, Nanophoton Corporation), scanning electron microscopy (SEM, S-4800, Hitachi High-Technologies Corporation) and high-resolution transmission electron microscopy (HR-TEM, JEM-ARM200F, JEOL Ltd).
The new CVD process was able to create high quality graphene at near room temperature (relatively speaking), with graphene being grown onto sapphire substrates at 50 °C and at 100 °C on polycarbonate substrates.
The low-temperature synthesis was made possible through carbon attachment to island edges of pre-grown graphene nuclei islands and resulted in no damage to the substrate or surrounding components. The pre-existing nuclei island themselves were produced through conventional CVD processes or by a special nuclei transfer technique using a mixture 12C and 13C at low temperatures.