Adsorption structures of phenol on the $\text{Si}\left(001\right)\text{−}\left(2\times 1\right)$ surface calculated using density functional theory

Several dissociated and two nondissociated adsorption structures of the phenol molecule on the $\text{Si}\left(001\right)\text{−}\left(2\times 1\right)$ surface are studied using density functional theory with various exchange and correlation functionals. The relaxed structures and adsorption energies are obtained and it is found that the dissociated structures are energetically more favorable than the nondissociated structures. However, the ground state energies alone do not determine which structure is obtained experimentally. To elucidate the situation core level shift spectra for $\text{Si}2p$ and $\text{C}1s$ states are simulated and compared with experimentally measured spectra. Several transition barriers were calculated in order to determine, which adsorption structures are kinetically accessible. Based on these results we conclude that the molecule undergoes the dissociation of two hydrogen atoms on adsorption.

Figure 1

(Color online) Locally stable adsorption structures for phenol on the $\text{Si}\left(001\right)\text{−}\left(2\times 1\right)$ surface.

Figure 2

(Color online) Simulated $\text{C}1s$ core level binding energy spectra for structures C, D, E, and F. The energy zero is the core level binding energy averaged over the $s{p}^2$-bonded, benzenelike carbon atoms. The model function is based on the measured spectrum in Ref. 4.

Figure 3

(Color online) $\text{Si}2p$ core level shifts for the $\text{Si}\left(001\right)\text{−}\left(2\times 1\right)$ surface. (a) The XPS data from Ref. 4 for various phenol concentrations. (b) Fit of the DFT data to the experimental data for the clean surface. (c) DFT curves for structures D, E, F, and H and the clean surface.

Figure 4

Transition barriers (in eV) between the considered adsorption structures. Thick arrows represent probable reactions, whereas thin arrows represent unlikely ones.

Figure 5

(Color online) A sketch of the minimum energy path for molecule adsorption. The final states are structures (a) D, (b) B, and (c) C. Gas-phase states, precursor states, transition states and an intermediate, locally stable state are marked as GP, PS, TS, and IS, respectively. The numbers indicate the activation energies in eV.

Figure 6

(Color online) A sketch of the minimum energy path for reactions $\text{A}\to \text{E}$, $\text{E}\rightleftarrows \text{D}$, and $\text{D}\to {\text{F}}^{\prime }$. Transition states are labeled TS. The numbers indicate the activation energies in eV.