Periodic Reporting for period 1 - DirectSepa (Direct Separation of Two-Dimensional Materials from the Surface of Liquid Metal Catalysts)
Periodo di rendicontazione: 2021-01-01 al 2021-12-31
However, up to now, none of these promises of graphene have been realized in an everyday device. The main hurdle against practical utilization of graphene and other two-dimensional materials is the deficiency of effective mass-production techniques to satisfy the growing qualitative and quantitative demands for both scientific and technological applications.
The current production process of graphene is via the deposition of a carbon precursor, often methane, on a catalytic surface, often copper. At the copper surface the methane will dissociate, and the carbon atoms will form the graphene layer. However, due to the fact that the carbon atoms will start growing at many places at the catalyst surface simultaneously, the resulting graphene will consist of many different domains, severely deteriorating its quality. A second problem is that the graphene grown at the copper surface will be very strongly attached to it. The only way to release graphene from the copper surface, is by etching away the copper, and thereby often damaging the graphene. The current graphene production process is therefore slow, inefficient, environmentally unfriendly, and resulting in graphene of poor quality.
One solution to overcome these problems, is the growth of graphene on a liquid (molten) copper catalyst. The enhanced atomic mobility, homogeneity, and fluidity of a liquid metal catalyst surface promotes the production of defect-free single domain graphene at high synthesis speeds. The possibility of direct separation of the graphene from the liquid substrate opens up the possibility of using the same substrate material for a continuous production of graphene with virtually unlimited length. So far, it has indeed been shown that graphene can grow on liquid copper. However, the synthesis of graphene was performed, so to speak, in the dark, without being able to observe and investigate its growth. The graphene could only be studied after its growth was finished and the copper surface with graphene on top was cooled down to room temperature and solidified.
In our LMCat project, we were able to observe the growth of graphene on liquid copper while it happens. Thanks to this in situ observation, we were able to tweak graphene growth by changing reaction parameters, resulting in millimeter-size defect-free graphene, with mechanical and electronic properties reaching those of exfoliated graphene.
In the current follow-up project, DirectSepa, we focus on two tracks: 1) the direct separation of graphene from liquid copper without cooling down the catalyst (cooling down often results in the formation of defects) and without etching the copper; 2) in situ investigation of graphene growth on catalysts with lower melting points, thereby hopefully enabling easier separation. For the first track, we are developing a new reactor, that will include measurement techniques for the observation and tailoring of graphene growth on, first, liquid copper, and techniques for the separation of graphene. For the second track, we will make use of the two reactors that we developed and built during the LMCat project.
Simultaneously, experiments on liquid catalysts with lower melting points have been performed, such as copper-tin alloys in several compositions. So far, growing graphene on these catalysts has been proven to be difficult. Additionally, the LMCat reactors are currently being made suitable for the use of gallium, a metal with a melting point at room temperature. Due to its corrosivity, all aluminum parts in the reactor have to be coated.
Finally, theoretical calculations are being performed to understand the strength of graphene on liquid copper, and its strength when being separated from copper. These are important processes that need to be understood for successful separation of graphene.
The framework created in this project could well be applicable to other 2-dimensional materials, such as boron nitride, silicene, molybdenum disulfide of phosphorene.