Formation of step-state bands on Si(111) $\sqrt{3}\times \sqrt{3}-$Ag vicinal surfaces

The effects of the step configuration and step density on the surface conductivity of Si(111) vicinal surfaces were investigated using an ultrahigh-vacuum electron microscope equipped with a surface conductivity measurement system. The Si(111)$\sqrt{3}\times \sqrt{3}$-Ag structure, which has a nearly-free-electron-like two-dimensional metallic surface state, was formed on the Si(111) terraces. The conductivity of the samples increased with increasing step density, which cannot be explained by assuming that steps form a barrier to electron conduction through the surface-state bands. The step density can affect the electronic band structure of the system through the formation of step-state bands or by changes in the band bending. The electronic band structure of the Si(111)$\sqrt{3}\times \sqrt{3}$-Ag surface prepared on vicinal surfaces was investigated by angle-resolved photoemission spectroscopy (ARPES) to examine these two possibilities. The ARPES investigation shows that the bulk bands are not modified and step-state bands are created on vicinal surfaces with high step densities. The electronic states of neighboring steps overlap to form step-state bands as the step-step distance is approached on a vicinal surface with high step density.

Figure 1

REM images of surface structures prepared at different sample temperatures of (a) 460 and (b) 600 °C on a 9° off-vicinal surface. The right-hand side is in the $[\overline{1}\overline{1}2]$ direction and the surface steps down to the right. Dark lines are step bands at lower temperature and facets at higher temperature. Round-shaped terraces surrounded by dark lines at lower temperature change to band-shaped terraces at higher temperature.

Figure 2

RHEED patterns of surface structures prepared at different sample temperatures of (a) 460, (b) 500, and (c) 600 °C on a 9° off-vicinal surface. Large arrows indicate reflections from the $\sqrt{3}-\mathrm{Ag}$ structure and small arrows indicate those from the (113) facets.

Figure 3

Schematic diagram showing changes in the surface morphology at several substrate temperatures.

Figure 4

Typical I-V  measurements. The horizontal axis is the electric current applied between the outer probes and the vertical axis is the voltage difference between the inner probes. Green triangles, red circles, and blue crosses indicate the Ag-deposition temperatures of 600, 500, and 460 °C, respectively.

Figure 5

Binding energy–wave vector maps of photoelectron intensity near the Γ point along the $[\genfrac{}{}{0ex}{}{\rightharpoonup }{1}\overline{1}2]$ direction from the (a) 7° and (b) 9° off-vicinal surfaces.

Figure 6

Schematic diagrams showing electronic circuits for the three types of step configuration on the 7° off-vicinal surface.