Direct Synthesis of Layer-Tunable and Transfer-Free Graphene on Device-Compatible Substrates Using Ion Implantation Toward Versatile Applications

Direct synthesis of layer-tunable and transfer-free graphene on technologically important substrates is highly valued for various electronics and device applications.State of the art in the field is currently a two-step process:a high-quality graphene layer synthesis on metal substrate through chemical vapor deposition(CVD)followed by delicate layer transfer onto device-relevant substrates.Here,we report a novel synthesis approach combining ion implantation for a precise graphene layer control and dual-metal smart Janus substrate for a diffusion-limiting graphene formation to directly synthesize large area,high quality,and layer-tunable graphene films on arbitrary substrates without the post-synthesis layer transfer process.Carbon(C)ion implantation was performed on Cu-Ni film deposited on a variety of device-relevant substrates.A well-controlled number of layers of graphene,primarily monolayer and bilayer,is precisely controlled by the equivalent fluence of the implanted C-atoms(1 monolayer~4×10^(15)C-atoms/cm^(2)).Upon thermal annealing to promote Cu-Ni alloying,the pre-implanted C-atoms in the Ni layer are pushed toward the Ni/substrate interface by the top Cu layer due to the poor C-solubility in Cu.As a result,the expelled C-atoms precipitate into a graphene structure at the interface facilitated by the Cu-like alloy catalysis.After removing the alloyed Cu-like surface layer,the layer-tunable graphene on the desired substrate is directly realized.The layer-selectivity,high quality,and uniformity of the graphene films are not only confirmed with detailed characterizations using a suite of surface analysis techniques but more importantly are successfully demonstrated by the excellent properties and performance of several devices directly fabricated from these graphene films.Molecular dynamics(MD)simulations using the reactive force field(ReaxFF)were performed to elucidate the graphene formation mechanisms in this novel synthesis approach.With the wide use of ion implantation technology in the microelectronics industry,this novel graphene synthesis approach with precise layer-tunability and transfer-free processing has the promise to advance efficient graphene-device manufacturing and expedite their versatile applications in many fields.

Modelling thermodynamics of nanocrystalline binary interstitial alloys

Grain boundary （GB） segregation in nanocrystalline alloys can cause reduction of GB energy, which leads to thermodynamic stabilization of nanostructures. This effect has been modelled intensively. However, the previous modelling works were limited to substitutional alloy systems. In this work, thermodynam- ics of nanocrystalline binary interstitial alloy systems was modelled based on a two-sublattice model proposed by Hillert [M. Hillert, et al. Acta Chem. Scand., 24 （1970） 3618] and an atomic configuration for nanocrystalline systems proposed by Trelewicz and Schuh LI.R. Trelewicz, et al. Physical Review B, 79 （2009） 094112]. The modelling calculations agree with the reported experimental data, indicating that the current thermodynamic model is capable of accounting for the alloying effect in the nanocrystalline binary interstitial alloys.