Iron 원자 흡착에 의한 Si(111)-7x7 표면의 원자배치구조 연구

Abstract

We have investigated the changes of atomic arrangement induced by the adsorption of iron (Fe) on the Si(111)-7x7 surface. The formation of iron silicide on the Si(111)-7x7 surface becomes quite complicated depending on the various growth conditions. We observed a number of stable Fe silicide phases by varying Fe coverage and annealing temperature. We have identified the atomic arrangement of those phase by using LEED (low-energy electron diffraction) and the electrical properties by PES(photoelectron spectroscopy) measurements and provided a phase diagram of the Fe silicides formed on the Si(111)-7x7 surface in the Fe coverage range from 0.3 ML to 3.0 ML and the temperature range from 0 to 800℃.At room temperature, we find that the 6-fold symmetry of the clean Si(111)-7x7 surface becomes a 1x1 structure of a 3-fold symmetry when the Fe coverage becomes 1ML (monolayer). The surface becomes a phase of amorphous Fe-Si film for coverage beyond 1.0 ML. By annealing the amorphous Fe silicide at 100℃, the surface recovers the 3-fold 1x1 symmetry again. We find another ordered phase of a 2x2 structure when the surface annealed at temperature between at 200℃ and 600℃ before it returns to the 7x7 symmetry of the clean surface when annealed beyond 600℃. The PES spectra obtained from the Fe-induced ordered phases reveal new characteristic peaks, of which the peak position changes with atomic arrangement. We also observe that the work function change induced by Fe adsorption grows almost linearly with Fe coverage in sharp contrast with the decreasing trend caused by the adsorption of other metallic atoms indicating the opposite direction of the dipole moment induced by Fe compared to that of others. Such a tendency of the increasing work function change by Fe adsorption becomes modified at 1.0 ML as the surface shows another atomic structure. We discuss a possible growth mechanism Fe silicide based on the phase diagram determined.