Effects of alkali metal adsorption on the structural and field emission properties of graphene

Theoretical investigation of structures and energetics of sodium adatom and its dimer on graphene: DFT study

“…Height of the adatom from graphene sheet in present work comes out to be 2.24 Å which is comparable to that calculated in Ref. [28].…”

“…Adsorption energies and structural properties for the three sites considered are summarized in Table 1 and results are compared with the literature available. The results of our calculation show that the preferred site of adsorption is the same as that observed by Qiao et al and Chan et al [2,28] i.e H-site; however, the value reported by [2] is À 0.462 eV and that by [29] is À 0.935 eV. As the value obtained in present calculation is À 0.614 eV, it lies in between the values reported by Qiao et al [2] and Chan et al [28] (also evident from Table 1).…”

“…The adsorption energy, geometry, charge transfer, IP and density of states (DOS) along with PDOS of adatom/ dimer-graphene system are calculated. We found that the adsorption energy of Na on graphene is less than its dimer's adsorption which is in agreement with the previous results [2,28]. Several adsorption sites including hollow, bridge, and top positions were considered for the adatom adsorption on graphene.…”

“…We notice from Mulliken analysis that charge transfer of 0.288e from Na (in its minimized position) to graphene sheet takes place which is less than those calculated in references [18,28]. This difference may be attributed to the two different calculation methods adopted by them.…”

“…The H site being the most favorable for sodium adatom adsorption (see Table 1), we only consider the field emission properties of this configuration. The IP of the pristine graphene in our work is 5.30 eV {(incidentally, this is higher than (4.94 eV) as reported by Qiao et al [28]}. With the Na metal adsorbed on graphene, the IP reduces significantly, i.e.…”