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					                                                                                                       From Graphite to carbon nanotubes. A guide for its
                                                                                                        applications on nanoscience and nanotechnology
                                                                                                                                                                                                      Juan Salvador Arellano Peraza

                                                                                                             Área de Física Atómica Molecular Aplicada, Universidad Autónoma Metropolitana Azcapotzalco, C.P. 02200, México D.F., México


                                                                                                                                                                                                                                2mev/atom: energy difference between graphite and graphene
                                                                                                      Motivation
                                 * Graphene, has been obtained (year 2004). This is a 2D and only one atom thick material.
                                 It can be converted to 0D buckyballas, 1D nanotubes or stacked in the best known 3D
                                 graphite. See Figure 1.
                                 * Graphite is formed by weakly interacting parallel planar carbon layers. Atoms and
                                 molecules can be intercalated between those layers giving rise to a variety of intercalated                                                                                                                                                                                               AB stacking, is the most abundant form
                                 compounds.                                                                                                                                                                                                                                                                                of graphite (circles)
                                                                                                                                            rDensity Functional                                                                                                                                                            AA stacking (two adjacent graphene
                                                                                                                                            Formalism: FHI96MD code                                                                                                                                                        layers), present in the intercalated
                                                                                                                                             rExchange-Correlation                                                                                                                                                         compounds (triangles)
                                                                                                                                            functional: Local Density
                                                                                                                                            Approximation                                                                                                                                                                 [3]
                                                                                                                                             rNonlocal norm-conserving
                                                                                                                                                                                                                                                                                                             LiC6          [3]

                                                                                                                                            pseudopotential of Hamman et
                                                                                                                                            al. for Carbon (4 valence                                                                                                                                       It is the richest Li compound existing at normal pressure
                                                                                                                                            electrons)
                                                                                                                                                                                                                                                                                                            Stage-1 compound
                                                                                                                                             rAll electron description of
                                                                                                                                            Lithium for all the lithium                                                                                                                                     AA stacking of the graphene layers
                                      Figure 1                           [1]                      Figure 2       [2]
                                                                                                                                            intercalated compounds.                                                                                                                                         The Li atoms are placed midway between two parallel
                                                                                                                                                                                                                                                                                                            hexagons, above the center of the hexagon
                                                                                                                                                                                                                            [2]                                                                             Only one third of those positions are occupied by Li
                                                               Hydrogen molecule adsorption on nanotube
                                                                                                                                                                                                                                                                                                               LiC2          [3]

                                                                                                                                                                                                                                                           This compound forms only by high pressure synthesis
                                                                                                                                                                                                                                                           Experimental phase: AA stacking of the graphene layers
                                                                                                                                                                                                                                                           The Li atoms are placed midway between two parallel hexagons, above the center of the hexagon


                                                                                                                                                                                                                                                                                circles: AA stacking
                                                                                                                                                                                                                                                                                stars: AB stacking



                                                                                                                                                                                                                                                                                                                                               circles: AA stacking
                                                                                                                                                                                                                                                                                                                                               stars: AB stacking




                                                  Pb difussion along the /6,6) carbon nanotube                                                                                                                                                                                                              LiC3
                                                                                                                                                                                 -49.22                                                                    Superdense compound formed by ball-milling; it is stable under ambient pressure
ENERGÍA POTENCIAL TOTAL (u.a.)




                                 -140.70
                                                                                                                                                ENERGÍA POTENCIAL TOTAL (u.a.)




                                                                                                                                                                                                                                                           The X-ray diffraction pattern indicates Li atoms at ± 0.83 au from the medium plane between
                                                                                                                                                                                 -49.24


                                 -140.72                                                                                                                                         -49.26


                                                                                                                                                                                 -49.28
                                                                                                                                                                                                                                                           the graphene layers
                                 -140.74
                                                                                                                                                                                 -49.30
                                                                                                                                                                                                                                                                                                                                     Li midway between graphene layers
                                 -140.76                                                                                                                                         -49.32
                                                                                                                                                                                                                                                                                                                                     Li up and down the middle
                                                                                                                                                                                 -49.34                                                                                                                                              relaxed Li positions
                                                                                                                                                                                          2    4       6       8       10      12      14       16
                                 -140.78
                                                                                                                                                                                 DISTANCIA (u.a.) DE LA HOJA DE GRAFENO (CELDA 2X2) AL ÁTOMO DE PLOMO
                                             0          5          10         15          20
                                      DISTANCIA (u.a.) DEL EJE DEL NANOTUBO (6,6) AL ÁTOMO DE PLOMO




                                                                                                             Pb atom adsorption on a graphene layer. The
The binding energy for the                                                                                   figure shows there are 8 carbon atoms per one
Pb atom on the (6,6)                                                                                         Pb atom. The atom is adsorbed at a distance
                                                                                                             of 4.8 a.u., a little less than the equilibrium
carbon nanotube axis is                                                                                      distance for the hydrogen molecule above the
0.27 eV.                                                                                                     graphene layer, 5.07 a.u. These result was
                                                                                                             reported on reference [4].                                                                                                                                                          Conclusions
The initial calculations for
                                                                                                              [1] A. K. Geim and K.S. Novoselov. Nature materials, Vol. 6,                                                                              rAdequate description of graphite (AB packing, cohesion, compressibility) by DFT-LDA calculations
the difussion of the Pb                                                                                       March 2007, p. 183.
                                                                                                                                                                                                                                                        rLi intercalation changes the stacking of C layers from AB in graphite to AA in Li compounds
atom along the carbon                                                                                         [2] J. S. Arellano, L.M. Molina, A. Rubio, M.J. López and J. A.
                                                                                                                                                                                                                                                        rThe distance between graphene layers increases and the uniaxial compressibility decreases in
                                                                                                              Alonso. J. Chem. Phys. Vol. 117, No. 5, 1 August 2002, p. 2281-
nanotube axis shows that                                                                                      2288.                                                                                                                                     LiC6 with respect to pure graphite
                                                                                                              [3] Juan Salvador Arellano Peraza, L. M. Molina, M. J. López, A.
this could be and easy                                                                                        Rubio y J. A.. Alonso. “Resultados para litio intercalado en grafito,
                                                                                                                                                                                                                                                        rDFT underestmates the expansion of the lattice and the uniaxial compressibility of LiC2 as
                                                                                                              LiC2 y LiC6 usando teoría de funcionaled de la densidad”.                                                                                 compared to the experimental values. Assuming AB stacking, we recover the experimental expansion of the
process, that is, without                                                                                     Memoria de la XIV Semana de la Docencia e Investigación en                                                                                lattice but the value of the uniaxial compressibility is similar (small) to that obtained with AA stacking
                                                                                                              Química. Universidad Autónoma Metropolitana-Azcapotzalco,                                                                                 rDFT calculations do not predict separation of the Li atoms from the medium plane between
barrier energies.                                                                                             año 2001,p.113-123.
                                                                                                                                                                                                                                                        graphene layers in the LiC3 compounds
                                                                                                              [4] J. S. Arellano, L.M. Molina, A. Rubio, and J. A. Alonso. J.
                                                                                                              Chem. Phys. Vol. 112, Number 18, 8 May 2000, p. 8114-8119.                                                                                rIt has been given a brief scope of the possible applications of the graphene, graphite and
                                                                                                                                                                                                                                                        carbonaceous materials as can be the design of new lithium batteries or the hydrogen storage.
                                                                                                                                                                                                                                                        ¡There are many more applications under development!