High thermal stability quasi-free-standing graphene on silicon carbide through Platinum functionalization
In short: Graphene grown on silicon carbide substrates provide solutions for high frequency electronics operating at high temperatures. However, a major obstacle is that the electrons are substantially slowed down due to the first carbon layer formed on the silicon carbide. Here we report on quasi-free-standing graphene layers with potentially fast electrons even at very high temperatures (1200°C), achieved by letting Platinum penetrate into the graphene-silicon carbide interface.
Graphene, one monolayer of graphite, has demonstrated its outstanding electronic and mechanical properties, which makes it one of the most promising candidate materials for a new generation of electronic devices. Graphene grown on silicon carbide substrates by thermal graphitization provides a potential solution for wafer-scale production of graphene based electronic devices operating at high frequencies, temperatures and voltages.
However, the electron mobility is substantially deteriorated due to the first carbon layer, so called buffer layer, formed on silicon-terminated silicon carbide which is a major obstacle for graphene based electronic devices. To intercalate atoms at the interface is one effective way to eliminate this buffer layer, and as a result, this carbon buffer layer is converted into a quasi-free-standing graphene layer, and the mobility was reported to increase dramatically after intercalation. Nevertheless, so far none of quasi-free-standing graphene achieved via intercalation is stable above ca. 800°C which limits operation temperature of the graphene based SiC device. Platinum has a high melting point which could provide the possibility to endure high temperature. We therefore performed detailed studies of the effects induced by Platinum deposited on graphene grown on silicon carbide, and after subsequent annealing at different temperatures.
Monolayer graphene was prepared by heating the (0001) crystal surface of silicon carbide (polytype 4H) at a temperature of 1300 °C for a few minutes under ultra-high vacuum. Platinum was then deposited on the sample kept at room temperature by using an electron beam evaporator. Influences induced by Platinum deposited on graphene are investigated by photoelectron spectroscopy (PES), selected area Low Energy Electron Diffraction (μ-LEED) and angle resolved photoelectron spectroscopy (ARPES) techniques at the MAX Laboratory.
The initial monolayer graphene sample shows a linear dispersion energy-momentum relation, as illustrated in figure (a). No noticeable change in the energy-momentum relation and no chemical reactions are induced by deposited Platinum until after annealing the sample at ~700°C. When the temperature is raised above 700°C, Platinum starts to penetrate into the graphene-silicon carbide interface. And the initial single layer graphene is converted into bi-layer like electronic properties, see figure (b), with significantly reduced electron doping of the graphene layers. This quasi-free-standing bilayer graphene is stable up to 1200°C, as seen in figure (c).
Details of the research are described in Carbon 79, 631 (2014)
- European Science Foundation, within the EuroGRAPHENE (EPIGRAT).
- Swedish Research Council (VR).
- Linnaeus Grant at LiU.
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Last updated: 11/17/14