First-principles calculations of surfactant-assisted growth of polar CaO(111) oxide film: The case of water-based surfactant

Surfactant-assisted growth of polar CaO(111) oxide film in the presence of water-based surfactant is studied by first-principles calculations both from thermodynamic and kinetic points of view. We show that the water molecules not only supply a surfactant by depositing hydrogen on the surface throughout the growth process, but also supply oxygen atoms as an elemental constituent in the film growth with rather small energy barriers, i.e. water oxygen atoms are easily inserted in the top surface layer of the growth film during the wet oxidation process. Adding the water surfactants to conventional synthesis techniques leads to the continuous presence of hydrogen atoms in the surface region during the growth process, which efficiently quenches polarity and dynamically stabilizes the growth of the polar surface, and thus facilitates the growth of defect-free CaO(111) films with arbitrary thickness.

Figure 1

(a) Top view and (b) side view of the OH-terminated CaO(111) surface. In (a) and (b), three possible adsorption sites (A, B, and C) are indicated. The ($1\times 1$) surface unit cell is shown by the black dashed line in (a). Big blue (bright) spheres: Ca, big red (dark) spheres: O, small gray (bright) spheres: H.

Figure 2

Perspective view of the Ca atomic adsorption geometry on (a) A, (b) B, and (c) C sites at the OH-terminated CaO(111) surface. The corresponding binding energies of the Ca atom are also shown, and the binding energy of the most stable configuration is in bold.

Figure 3

Perspective view of optimized surface geometry after deposition of (a) 1/4-, (b) 1/2-, (c) 3/4-, and (d) 1-ML Ca atoms at the OH-terminated CaO(111) surface.

Figure 4

Perspective view of the surface geometries of the H-Ca-terminated CaO(111) surface with hydrogen atom at (a) A, (b) B, and (c) C sites. The corresponding binding energies of surface hydrogen atom are also listed in this picture, and the binding energy of the most stable configuration is in bold.

Figure 5

Perspective view of the water molecule physisorbed geometries (I${}_{\mathrm{A}}$, I${}_{\mathrm{B}}$, I${}_{\mathrm{C}}$) on the H-Ca-terminated CaO(111) surface with the water molecule at (a) A, (b) B, and (c) C sites. (d) Perspective view of the water molecule chemisorbed geometry (F) on the H-Ca-terminated CaO(111) surface. The corresponding binding energies of the water molecule on the surface are also shown.

Figure 6

Different MEP for the water molecule at (a) A, (b) B, and (c) C sites dissociation and water oxygen atom insertion in the H-Ca-terminated surface region during wet oxidation. Insets show the transition states of each reaction pathway.