Current synthesis processes for graphene require high temperatures and the use of catalysts. The scientists at the Fraunhofer Institute for Electron Beam and Plasma Technology (FEP), on the other hand, use plasma-assisted processes. For this purpose, they use the Maxi inline coating system, a multifunctional vacuum system. Depending on the development maturity of the process, it offers the possibility of carrying out processes both in sheet-to-sheet mode and in roll-to-roll mode.
Applying the substrate independently of the catalyst
In the first step, the metal strip is coated with a thin layer of a catalyst material - such as copper - in a vacuum. This makes it possible to select the substrate material independently of the suitable catalyst material. Immediately afterwards, the coated metal strip is moved into a process unit with an argon plasma discharge. The argon ions generated there collide with the substrate and heat it highly efficiently in a very short time. By adding a suitable precursor gas - such as methane or acetylene - in the immediate vicinity of the plasma discharge, the molecules can be broken down into their individual components and partially ionized at the same time.
Lower substrate temperatures required
Ideally, the carbon atoms and ions produced in this way are deposited on the substrate in a single-layer, ordered 2D structure, thus creating the desired layer of graphene. By supporting the ions present in the plasma, the formation process can be realized at comparatively lower substrate temperatures than was previously possible with other state-of-the-art processes.
High production throughputs possible
Using the PECVD process, the researchers have already been able to synthesize graphene over a width of 280 mm at process speeds of one metre per minute. The process therefore enables high production throughputs. In addition, the technology allows an expansion of the substrate materials that can be used and therefore a broader range of applications.