Effect of doping and defects on t he electro nic struct ure of graphane:A first principle study

Although graphene is considered as a pri me candidate for many applications, the absence of a band gap is a worrisome feature for the application to solid st ate electronic devices. I n the past, several studies have bee n proposed to open a band gap [۱, ۲]. The most interesting one is the recent discov ery of a completely hydrogenated graphene sheet nam ed as graphane. Graphane was first predicted by Sofo et al [۳] through the first principle total energy calculation and re cently, Elia s et al [۴] through exp osing grap hene under hydrogen plasma surroundings have sensitized the graphane sheet.The density functional the ory (DFT) calculations were pe rformed using QUANTUM ESPRESSO [۵] w ith an ultrasoft pseudopotential [۶ ]. For the e xchange correlation ter m, we used the generalized gradient approximation (GGA) with Perdew -Burke-Ernzerhof (PBE ) [۷]. Kohn Sham wave functions ar e truncated at energy cu toff of ۶۰۰ eV. Geometry structure, were relaxed until the force on eac h atom was less than ۰. ۰۱ eV/A° an d the convergence criteria for energ y was ۱۰-۷ eV. The break up for th e graphane layers in the supercell was set at ۱۵ A°, to avoid spurious interlayer fundamental inte ractions.Upon hydrogen passivation, the electronic band str ucture of graphane pro duces remarkable changes as comp ared to the pristine grap hene. Our calculations showed tha t the direct band gap at the ī point s approximately is ۳.۴ e V, which is close to prev ious works [۳].However, we analyze the effe cts of dopi ng on graphane with nitrogen and boron. In the case study of doping, w e replaced one nitrogen or boron at om with a carbon atom. Our calcul ations showed that bon d and angle length in doped grap hane close to pristine graphane. Since nitrogen has one more valen ce electron than carbo n, it acts a s an electr on donor a nd its presen ce makes t he sheet more reactive. It also makes the material an n-type conductor and raises the Fermi energy. Boron, in contras t to nitroge n, serves as an electron acceptor, in duced the em ptying of electronic sta te below the Fermi ene rgy for pristine grapha ne, and creates p-type graphane. After doping graphane with nitrogen, boron is the first atom th at comes to mind as a dopant, becau se it is located in the sa me row of the periodic table as nitrogen and ca rbon, and bo ron is readily available in nature.The Stone-Wales (SW) defect is a typical topological defect in the carbon nanostructures and is com prised of two pairs of five-mebered and seven-membere d rings. From band stru cture and DOS calculat ions, we found that graphane with SW defect ha s a direct b and gap of ۲.۵ eV in ī point and as compared w ith pristine graphane, t his defect ca uses that Fe rmi level s hift to conduction bond.The structural and electronic properties of pristine graphane, B-doped, N-do ped and def ective graph ane were calculated using density f unctional t heory. We realized that boron (nitrogen) has a p-type(n-ty pe) effect. F urthermore, effect of SW and vac ancy defect on the electronic struct ure are same as n-type. These chan ges have significant effe ct on the electronic stru cture as co mpared with pristine gra phane. The maximum change on energy gap i s occure in single vacancy defect an d only this defect has an indirect band gap. Our calculations showe d that doped unlike defect has a small effect on geometery.

کلیدواژه ها:

Graph ane ، Electro nic Structur e ، Boron-D oped ، Nitrog en-Doped ، Defect.