Adhesion Behavior between Multilayer Graphene and Semiconductor Substrates
Q Zhang and X Ma and YL Zhao, APPLIED SCIENCES-BASEL, 8, 2107 (2018).
A high bonding strength between graphene and a semiconductor surface is significant to the performance of graphene-based Micro-Electro Mechanical Systems/Nano-Electro Mechanical Systems (MEMS/NEMS) devices. In this paper, by applying a series of constant vertical upward velocities (V-up) to the topmost layer of graphene, the exfoliation processes of multilayer graphene (one to ten layers) from an Si semiconductor substrate were simulated using the molecular dynamics method, and the bonding strength was calculated. The critical exfoliation velocities, adhesion forces, and adhesion energies to exfoliate graphene were obtained. In a system where the number of graphene layers is two or three, there are two critical exfoliation velocities. Graphene cannot be exfoliated when the V-up is lower than the first critical velocity, although the total number of graphene layers can be exfoliated when the V-up is in the range between the first critical velocity and second critical velocity. Only the topmost layer can be exfoliated to be free from the Si surface if the applied V-up is greater than the second critical velocity. In systems where the number of graphene layers is four to ten, only the topmost layer can be free and exfoliated if the exfoliation velocity is greater than the critical velocity. It was found that a relatively low applied V-up resulted in entire graphene layers peeling off from the substrate. The adhesion forces of one-layer to ten-layer graphene systems were in the range of 25.04 nN-74.75 nN, and the adhesion energy levels were in the range of 73.5 mJ/m(2)-188.45 mJ/m(2). These values are consistent with previous experimental results, indicating a reliable bond strength between graphene and Si semiconductor surfaces.
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