Substrate-mediated interactions of Pt atoms adsorbed on single-wall carbon nanotubes: Density functional calculations

In this study, we perform density functional calculations to investigate the interplay between single-wall carbon nanotube (SWNT) supports and adsorbed Pt atoms. We found that adsorption of Pt atoms on SWNTs is found to depend heavily on the curvature of SWNTs. The supporting SWNTs mediate and enhance the range of interactions between Pt adatoms. The long-range interactions originate from the structural deformation of the tube and the complex electronic states formed during the adsorption. Furthermore, these SWNT-mediated interactions significantly modify the diffusion barriers of Pt adatoms on the tube surface.

Figure 1

(Color online) (a) Adsorption configurations of a Pt atom at $A$ and $A^{\ast }$ bridge sites of (10, 0) SWNT and at $B$ and $B^{\ast }$ bridge sites of (5, 5) SWNT. (b) The curvature dependence of the adsorption energy of single Pt atom on bridge sites of carbon nanotube supports. Open and solid squares are for $A$ sites and $A^{\ast }$ sites in the $\left(n,n\right)$ carbon nanotubes; open and solid circles are for $B^{\ast }$ sites and $B$ sites in the $\left(n,n\right)$ carbon nanotubes. Insets show the curvature-induced pyramidalization and misalignments of $\pi$ orbitals of carbon networks in SWNTs. (c) Displacement of C atoms in (5, 5) and (10, 0) SWNTs due to the adsorption of a Pt atom, visualized by gOpenMol (Refs. 25, 26). The lengths of the arrows are 10 times the actual displacement of the C atoms.

Figure 2

(Color online) (a) Dependence of binding energy on Pt-Pt distance. Open and solid circles indicate the Pt atoms aligned linearly and helically, respectively, along the axes of the (5, 5) SWNT. Open and solid squares indicate the Pt atoms aligned linearly and helically, respectively, along the axes of the (10, 0) SWNT. Open triangles indicate the nonadsorbed Pt atoms. (b) Structural models of the supercells of SWNTs with Pt adatoms and aligning paths of two Pt atoms used in the calculation.

Figure 3

(Color online) Difference in charge densities of single Pt adatoms on (5, 5) and (10, 0) SWNTs at a ${10}^{-4}\text{a}\text{.u}\text{.}$ isosurface value. Red/gray and blue/dark gray colors indicate the positive and negative charged areas, respectively, and the charge flows from the red/gray areas into the blue/dark gray areas.

Figure 4

(Color online) d-projected PDOS of Pt adatoms aligned along path 1 on the (5, 5) SWNT at different interatomic distances: (a) $19.67\text{Å}$ and $14.76\text{Å}$; (b) $7.38\text{Å}$ and $4.92\text{Å}$. [(c), (d)] The molecular orbitals [at $E-E_f=-0.93\text{eV}$ and at $E-E_f=-1.48\text{eV}$ correspond to the arrows in (a)] of the system in which the interatomic distance is $14.76\text{Å}$.

Figure 5

(Color online) (a) Illustrations of pathways between adsorption sites. (b) Curvature dependence of the diffusion barrier of a Pt atom adsorbed on SWNTs. The open and solid squares indicate the $A\to A^{\ast }$ and $A^{\ast }\to A$ pathways, respectively, in the $\left(n,0\right)$ SWNTs. Open circles, solid circles, and circles with a dot indicate the $B^{\ast }\to B$, $B\to B^{\ast }$, and $B^{\ast }\to B^{\ast }$ pathways, respectively, in the $\left(n,n\right)$ SWNTs.