| Graphene shows many novel properties, such as the giant intrinsic mobility and very high thermal conductivity. Foreign atomic adsorption and replacement is a major means to control the electronic properties of graphene effectively, and the study of the doping process can also lead to deeper understanding of the interaction between nano systems. With the properties of large specific surface area and light weight, graphene is regarded as a potential carrier for adsorption of molecules and metal atoms. It can also be used as hydrogen storage media and catalyst. However, the interaction between pure graphene and hydrogen molecules is too weak to adsorb hydrogen molecules at room temperature. Meanwhile, the aggregation of metal atoms on graphene also limits its application as functional materials. The clustering of metal atom must be avoided, to enhance the adsorption of hydrogen molecules with the metal atom decorated graphene.In the list of many remarkable properties of graphene, its mechanical properties are miraculous. Graphene is able to sustain reversible elastic tensile strain as large as 25%. Strain can change the activity of graphene and thus enhance the binding of atoms or molecules to the graphene, and thus can effectively disperse metal atoms and further modulate the interaction between adsorbed metal atoms and hydrogen molecules. The adsorption in bilayer graphene of metal atoms usually can be enhanced significantly, and the stable sandwich structures may be formed, extending the application of nano electronic devices based on graphene.Hydrogen storage with Ti decorated nano-materials is attributed to the d levels of Ti with unsaturated bonding, whose configuration significantly affects the system’s stability and activity. Using first-principles calculations, we have investigated hydrogen adsorption and desorption on the Ti decorated defective graphene under various strains(from 0% to 15%), in which Ti atoms’ dispersing are energetically stable. According to the phase diagram, we showed that hydrogen uptake can be modulated as a function of chemical potential and strain, since the strain modifies the configuration of d levels, and consequently affects the binding between H2 and Ti atom. Remarkably, Ti decorated defective graphene under 15% strain could be considered as an ideal media of hydrogen storage, in which the temperature of H2 desorption is expected to be ~300K at 0.5 atm. The control of strain is found to be dominant to the H2 uptake, besides the temperature and pressure.Using first-principles calculations, we have predicted various stable structures of high-coverage 3d transition metal(TM) intercalated bilayer graphene(BLG) stabilized by the biaxial strain. Specifically, Sc and Ti can form stable TM-intercalated BLG without strain, while the stabilization of Fe, Co, and Ni intercalated BLG requires the strain of over 7% with respect to the corresponding bulk metal energetically. Under the biaxial strain ranging from 0% to 10%, we found four ordered sandwich structures for Sc with the coverage of 0.25, 0.571, 0.684, and 0.75, in which the Sc atoms are distributed homogenously instead of simply sitting on hollow sites. According to the phase diagram, a homogenous configuration of C8Ti3C8 with the coverage of 0.75 and another inhomogeneous structure with the coverage of 0.692 were found. We have also considered uniaxial strain in bilayer graphene. It is found that the stability for the Ti-intercalated BLG is roughly same as strains applied along armchair and along zigzag, with only the C8Ti3C8 phase shown up. For the Sc-intercalated BLG, the phases with the coverage of 0.571 and 0.684 appear as the strain along armchair, while another phase with the coverage of 0.5 appears as the strain along zigzag. The electronic and magnetic properties as a function of strain are also discussed, showing that the biaxial strain is critical to stabilize the high-coverage TM-intercalated BLG. |
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