Characterization Investigation of β-FeSi2 Semiconductor by In Situ Ultrahigh-Vacuum Transmission Electron Microscopy

Abstract

In an integrated ultrahigh-vacuum system, a thin Fe layer was deposited on a Si (111) 7×7 surface at room temperature by ultrahigh-vacuum molecular beam epitaxy (UHV-MBE) and annealed at 600°C. The characterization of the as-deposited and annealed specimen for microstructure and electronic structure was investigated using an analytical ultrahigh-vacuum transmission electron microscope (UHV-TEM) and an electron energy-loss spectroscope (EELS). After deposition of a 5 ML Fe layer, an epitaxial Fe layer formed on the Si surface, which suggests that the Si substrate may induce the arrangement of Fe atoms in the thin Fe layer. When annealed at 600°C, epitaxial β-FeSi2 islands with moiré fringes formed on the Si substrate. The Fe 3d occupancy change for as-deposited Fe and β-FeSi2 was calculated by the empirical method after background subtraction by the power law and deconvolution by the Fourier ratio. The calculated results show that there is a 0.95±0.06 electron/atom decrease for Fe 3d occupancy from as-deposited Fe to β-FeSi2. Fe white lines intensity ratios for the two states were calculated from the second derivative spectra, which are 2.89 and 2.51 for as-deposited Fe and β-FeSi2, respectively. The results for the intensity ratio show that the higher intensity ratio is related to stronger magnetism.