Carbon bonding site in $\text{Si}\left(001\right)c\left(4\times 4\right)$ prepared by hydrocarbon decomposition

We have reexamined the structural models of $\text{Si}\left(001\right)c\left(4\times 4\right)$ induced by carbon, which is important for the initial C incorporation, using high-resolution photoemission. Through a proper thermal treatment after the thermal decomposition of the typical carrier gas molecules of ${\mathrm{C}}_2{\mathrm{H}}_2$ and ${\mathrm{C}}_2{\mathrm{H}}_4$, a well-ordered $c\left(4\times 4\right)$ surface was reproducibly prepared, which exhibits only a single well defined C $1s$ component with a binding energy of $282.8\text{eV}$. This indicates that the $c\left(4\times 4\right)$ surface is made of a unique C bonding configuration in contrast to some structure models. From the angular variation of the C $1s$ photoemission intensity, we confirm that the unique C bonding site corresponds to the incorporation into the subsurface layers rather than a metastable surface adsorption.

Figure 1

C $1s$ photoemission spectra of the C-induced $c\left(4\times 4\right)$ phase on $\text{Si}\left(001\right)$ taken with a photon energy $\left(\mathrm{h}\nu \right)$ of $330\text{eV}$ along the emission angle ${\theta }_e=0°$ (the surface normal). The surfaces of (a) and (c) were prepared by exposing ${\mathrm{C}}_2{\mathrm{H}}_4$ $\left(200\mathrm{L}\right)$ at $700°\mathrm{C}$ and ${\mathrm{C}}_2{\mathrm{H}}_2$ $\left(8\mathrm{L}\right)$ at $600°\mathrm{C}$, respectively. Post-annealing of the surfaces for (a) and (c) at $700°\mathrm{C}$ for $2\min$ changes the spectra into (b) and (d), respectively. For comparison, the C $1s$ binding energies of ${\mathrm{C}}_2{\mathrm{H}}_2$ and ${\mathrm{C}}_2{\mathrm{H}}_4$ molecules or SiC on $\text{Si}\left(100\right)$ are indicated by the vertical lines. (e) Similar C $1s$ spectra for a series of post-annealings of ${\mathrm{C}}_2{\mathrm{H}}_4$ dosed on $\text{Si}\left(100\right)$ at RT.

Figure 2

(a) Polar-angle $\left({\theta }_e\right)$ dependence of C $1s$ photoelectron intensity (the ${\mathrm{C}}_1$ component in Fig. 1) of $\text{Si}\left(001\right)c\left(4\times 4\right)$ prepared by ${\mathrm{C}}_2{\mathrm{H}}_2$ taken with photon energies $\left(\mathrm{h}\nu \right)$ of 330 and $400\text{eV}$. The emission angle is varied towards the [110] axis around $\left[1\overline{1}0\right]$ as illustrated in (b).

Figure 3

Atomic structure models (side view) proposed previouly by (a) Leifeld et al., (b) Simon et al., and (c) Norenberg et al. The open and solid circles denote Si and C atoms, respectively. (d) The structure model of the clean $\text{Si}\left(001\right)2\times 1$ surface for comparison. The arrows indicate the forward scattering (focusing) direction from a subsurface substitutional site.

Figure 4

Si $2p$ photoemission spectra of the C-induced $c\left(4\times 4\right)$ phase on $\text{Si}\left(001\right)$ taken with a photon energy $\left(\mathrm{h}\nu \right)$ of $135\text{eV}$ along the emission angle ${\theta }_e=60°$ for extreme surface sensitivity.