Adsorption Properties Of Graphene Modified By Transition Metal

Graphene is a two-dimensional honeycomb crystal that carbon atoms form thesp2orbital hybrid. Due to the special two-dimensional crystal structure and thenanoscale dimension, bring about graphene a large number of excellent physicalproperties. Graphene has a low Johnson noise, super large surface area, high thermalstability, fast electron transfer rate and lot of excellent characteristics and is widelyused as an ideal absorbent material. After adsorption of other substances, the originalelectronic structure of graphene is changed. So, the changed electronic structure isused to explore graphene-based electronic devices. In this paper, our calculations wereperformed using first-principles density functional theory to calculate the adsorptionproperties of transition metals Fe, Co, Ni adsorption graphene and Fe atoms modifiedgraphene adsorbed NH3molecule, those works provide a theoretical basis toapplication of graphene based nano-materials and NH3molecular sensors.All calculations were performed with DMol3package of Materials Studiosoftware to complete with exchange-correlation function of local densityapproximation (LDA) and Perdew and Wang form. Fully electronic spin-restrictedKohn-Sham non-symmetric wave function on the local atomic orbital basis vectorscommenced numerical basis functions with double numerical plus polarization(DNP).Three high-symmetry positions H, B and T site, where H is the hex-center site, Bis the bond-top site and T is the atom-top site, were selected in transition metaladsorption graphene system. After completely optimization, H site is the most stableadsorption positions for Fe, Co and Ni atom. The adsorption energy of Fe atoms isstronger than that of Co and Ni atom. Based on the fully optimization, the electronicproperties have been calculated. When adsorption the transition metal, the density ofstates dramatically changed near the Fermi energy and the Dirac point disappears,electronics tend to occupy low-level energy, peaks move toward to the left. The partial density of states (PDOS) show that the occupied4s orbit becomes the unoccupiedstate and the transition metal atoms lose electron. As to the charge condition,redistribution of charge occurs, the electron transition from the transition metal atomto the graphene plane. Carbon atoms that the nearest adsorption atom has themaximum charge transition and other carbon atoms charge transfer is less than0.006e.The charge transfer of Fe atom is larger than Co and Ni atom.Two kinds of adsorption configurations were chosen for intrinsic grapheneabsorption NH3molecular. One is the nitrogen atom and another is three hydrogenatoms of NH3molecular close to graphene plane. The adsorption energy is0.240eVand0.191eV corresponding to above two kinds of adsorption configurationsrespectively. The small adsorption energy indicates that there are no chemical reactionbetween NH3molecules and graphene plane. The adsorption configuration of nitrogenatom close to graphene plane is more stable than that of hydrogen atom. Theconfiguration of adsorbed NH3molecule for graphene modified by Fe atom is thesame as intrinsic graphene. After fully structural optimization, the configuration ofthree hydrogen atoms close to Fe modifying graphene plane break symmetricalposition and rotation180°to N atom close to the adsorption plane. This result may bedue to the introduction of Fe atom resulting in the configuration of H atom close to Femodifying graphene plane unstable. In both of the stable adsorption configurations,the adsorption energies of introducing or not Fe atom are1.791eV and0.240eVrespectively. The adsorption energy is significantly strengthened by introducing Featom in graphene. Strong hybridization between Fe3d state and nitrogen2p state isevident from the prominent peaks in the local density of states. This shows that stronginteractions occurred between NH3molecule and Fe atom. After introducing Fe atom,the mulliken charge redistribution, electron of the Fe atom transfer to both grapheneplane and the nitrogen atom in NH3molecule. Fe atom has the interaction with both Catom and N atom, which is the reason of the adsorption strengthen.