Yet another graphene advancement has been made by scientists; a collaboration between Sungkyunkwan University Advanced Institute of Nanotechnology and Jae-Hyun Lee at Ajou University in Korea has developed a way to successfully grow affordable graphene at a fraction of the price.
They were able to grow the single-crystalline graphene much quicker by using cheaper polycrystalline substrates. The team led by Dongmok Whang and Hyun Lee spaced out pieces of single-crystal graphene onto a polycrystalline substrate. By using single pieces from the same original sample, the “crystal lattice” faces the same direction. This allows the graphene to grow together without having any grain boundaries.
As Lee explains, this will help drop the cost and purchase price:
“If the synthesis temperature, gas used, etc. are assumed to be similar, the thermal budget and the price of the substrate can be said to be reduced to a quarter.”
As the article in Phys.org points out, the cost of graphene has come down considerably in the past 20 years. What originally cost hundreds of thousands of dollars per kilogram is now less than $50. But, to use graphene for electronics, the crystal quality must be high, without having grain boundaries that will disrupt the electronics’ communication properties.
Which is why this discovery is a big deal: to be able to grow high-quality crystal graphene without grain boundaries. Scientists and engineers will be able to experiment and have much more graphene available to reach new technological breakthroughs.
Lee said they got the idea after reading about a study that highlighted that it takes less energy to grow graphene seeds from the edge than it does from the nucleus. “In other words, it was thought that additional nucleation could be easily suppressed at lower energy conditions (e.g., low concentration of precursor or low growth temperature).”
Luckily, the team had prior experience growing single-crystal graphene, and they had access to a large original sample. They also knew from experience that for a clean bond, the pieces would need to be evenly spaced, and they knew when you grow graphene on a particular facet of single-crystalline germanium, Ge(110), you can transfer it more easily because a hydrogen layer forms between the graphene and the substrate. After running into a few issues with the growth rate, the team reduced the amount of methane during the process, which slowed the growth rate enough that the etch rate could go in first and smooth out any defects.
Next, the team needed to determine what size seed worked best and the correct spacing. The process they used is reported by Phys.org:
They cut “seeds” 10 μm wide from their original single-crystalline graphene sample and transferred them to polycrystalline platinum spaced 50 μm apart. Here, they grew single-crystalline graphene to cover an area of 2 cm x 2 cm.”It was difficult to grow to larger sizes due to the limitations of our CVD system,” says Lee. “But we believe that our approach can be fully applied to large catalyst substrate.”
The polycrystalline platinum the team created can be recycled without losing quality, and the cost is reduced from $2,000 per square cm to around $100. They said it may be possible to grow the seeds on aluminum foil or polycrystalline copper, which would further reduce the cost.
Next up for the team they would like to try and use this approach with 2-D materials. Lee explains:
“There are many variables to consider because of the different solubility and diffusion rates of each element in the catalyst. However, if we use a process that sequentially reacts one precursor and another precursor, such as an atomic layer deposition (ALD) process, which can simplify process parameters, it could be possible to grow a single crystalline monolayer of various 2-D materials.”
