Electron-Beam-Induced Disordering of the $\mathrm{Si}(001)\mathrm{\text{−}}c(4\times 2)$ Surface Structure

An electron beam (EB) irradiation effect on the $\mathrm{Si}(001)\mathrm{\text{−}}c(4\times 2)$ surface was investigated by using low-energy electron diffraction. Quarter-order spots become dim and streaky by EB irradiation below $\sim 40\mathrm{K}$, indicating a disordering in the $c(4\times 2)$ arrangement of buckled dimers. A quantitative analysis of decreasing rates of the spot intensity at various conditions of beam current, beam energy, and substrate temperature leads to a proposal for a mechanism of the disordering in the buckled-dimer arrangement in terms of electronic excitation, electron-phonon coupling, and carrier concentration.

Figure 1

Change of LEED pattern of double-domain $c(4\times 2)$ induced by EB irradiation ($0.7\mu \mathrm{A}$, 50 eV) at 24 K. (a) A $c(4\times 2)$ pattern immediately after the irradiation. (b) A streaky pattern observed 50 s after (a). (c) and (d) are top views of structure model of the Si(001) surfaces corresponding to (a) and (b), respectively. The buckled dimer is symbolized by a pair of open and small solid circles, and zigzag lines connecting buckled-down Si atoms are depicted for emphasizing the arrangement of buckled-dimer rows.

Figure 2

Normalized $\{3/4,1/2\}$ spot intensity changes against irradiation time. (a) Current dependence at 50 eV and 24 K. (b) Energy dependence at 50 nA and 24 K. In (a), normalized intensity change is also shown at 80 K.

Figure 3

Normalized $I_{\mathrm{EB}}$ is plotted against irradiation time for various temperatures. (b) Direct evidence for thermal recovering to $c(4\times 2)$. A cycle of closing and opening was repeated twice in each measurement. See text in detail. In curve at 31 K in (a) and (b), fitted curves are shown with gray bold lines.

Figure 4

(a) Beam current, (b) beam energy, and (c) substrate temperature dependences of the EB induced intensity attenuation rate constant ($k$). Experimental condition is shown in each figure.