T. Abukawa

Surface electronic structure of a single-domain Si(111)4×1-In surface : a synchrotron radiation photoemission study

The electronic structure of a Si(111)4 × 1-In surface has been studied by angle-resolved photoelectron spectroscopy (ARPES). Using a 1.1° off-axis Si(111) wafer as substrate, a single-domain Si(111)4 × 1-In surface has been prepared in order to determine the dispersion of surface state (SS) without the obscurity arising from multi-oriented 4 × 1 domains. Three SSs that cross the Fermi level have been found. Thus, the Si(111)4 × 1-In surface is concluded to be metallic. The dispersions of the metallic SS appeared to be almost one-dimensional, suggesting one-dimensional metallic bonds among In atoms. Completely occupied SSs have been also found. The characteristics of SSs are discussed in relation to the existing structural models for the Si(111)4 × 1-In surface.

Photoelectron diffraction and low energy electron diffraction studies of Cs, K/si(001) surfaces

Abstract X-ray photoelectron diffraction patterns of Cs 3d core levels for the full-Cs-coverage Si(001)-2 × 1-Cs surface have been measured and analyzed kinematically. It is found from the analysis that one monolayer of Cs, i.e., Cs/surface-Si ratio of unity, is present over the substrate forming a double-layer (upper and lower) array of atoms. The arrangement of Cs atoms in the double layer is essentially the same as the K double layer for the Si(001)2 × 1-K surface. New surface orders are reported that can be formed by the deposition of Cs or K atoms onto an annealed Si(001) substrate.

Angle-scanned photoelectron diffraction

A brief survey is given on the current state-of-the-art of this surface structural technique based on photoelectron spectroscopy, with particular emphasis on the progress that has been made recently by routinely measuring full-hemispherical intensity distributions. We limit the discussion to the photoelectron forward focusing regime, which is attained at electron kinetic energies of a few hundred eV. Surface bond directions are directly revealed as pronounced maxima in the angular distributions from subsurface atoms, while characteristic interference features are observed for surface species. For both cases the dependence on the atomic type is weak enough so that these features provide a fingerprint of the local bonding geometry. For surface and near-surface species, this may then serve as a starting point for a structure refinement using single-scattering cluster calculations. Selected examples are given for illustrating these procedures.

Low energy electron diffraction and X-ray photoelectron diffraction study of the Cs/Si(001) surface: dependence on Cs coverage

Cs adsorption on a wide-terrace single-domain Si(001) surface has been studied by low-energy electron diffraction (LEED) and X-ray photoelectron diffraction (XPD) as a function of Cs coverage (θ) and substrate temperature (TS). For TSs of ~ 110 and ~ 320 K, several surface periodicities are found which have not been reported before for this system. Azimuthal Cs3d XPD patterns have been measured for most of the ordered surfaces. An XPD structure analysis is made for a streak × 3 surface at θ = 16 ML, in which a dilute arrangement of Cs atoms is deduced. An XPD structure analysis is made for the surfaces at θ = 13 ML taking into account a reversible transition between 2 × 6 and 2 × 3 for TSs of ∼ 110 and ∼ 320 K, respectively. A Cs dimer model is deduced in which a modulation of atomic positions into a 2 × 6 surface is averaged in the 2 × 3 surface but is fixed in a regular way in the 2 × 6 surface.

Initial stage growth of In and A1 on a single-domain Si(001)2 × 1 surface

Abstract Initial stage growth of In and A1 on a wide-terrace single-domain Si(001)2 × 1 surface has been studied by low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy. Several submonolayer phases that were not reported on double-domain Si(001)2 × 1 substrates are observed, in addition to those already reported. The resulting sequences of two-dimensional (2D) phases for In and A1 coverages of ≤ 0.5 ML can be interpreted based on an order-disorder transition of arrays of 1D metal-dimer chains. The results show close resemblance to the initial growth of Ga on Si(001) and thus indicate that there is a general mode of growth for the Group-III metals on a Si(001)2 × 1 surface below 0.5 ML. Growth for coverages greater than 0.5 ML and the onset of 3D growth are also discussed.

Existence of a stable intermixing phase for monolayer Ge on Si(001)

Abstract A monolayer adsorption of Ge on a single-domain Si(001)2 × 1 surface has been investigated by X-ray excited Auger electron diffraction (AED) and scanning tunneling microscopy. Contrary to the common belief, a significant intermixing of Ge down to at least the fourth layer is identified. This intermixing is found to progress to a stable interface alloy phase that develops fully for annealing at 500–600°C. A possible reason for the alloy phase is discussed to be an elastic interaction from the Si(001) surface.

Mg-induced Si(111)3 × 1 structure studied by photoelectron spectroscopy

Abstract By means of angle resolved photoelectron spectroscopy using synchrotron radiation, we have measured the valence band and surface sensitive Si 2p core-level spectra for the Si(111)3 × 1Mg surface. The dispersion of the valence band shows the fact that this surface has a semiconducting property and two surface states in the projected bulk band gap at the K point. From the fitting results of the Si 2p core-level spectra, we find that the two surface shifted core-level components, S′1 and S′2 stem from the Si atom with single dangling bond and the Si atom bonding to the Mg atom, respectively. From experimental observations we suggest that the Si(111)3 × 1Mg structure is formed by ordering of Mg atoms on the ideal Si(111)1 × 1 surface, not by reconstruction of Si atoms of the substrate.

Initial interface formation study of the Mg/Si(111) system

The initial interface and silicide formation induced by Mg adsorption on the Si(111)7×7 surface have been studied using low‐energy electron diffraction, x‐ray photoelectron spectroscopy, and synchrotron radiation photoelectron spectroscopy. At room temperature, it is found that Mg atoms are preferably adsorbed on top sites of Si adatoms and rest atoms on the Si(111)7×7 surface and with increasing of Mg deposition, a Mg2Si epitaxial layer is formed and the surface structure transforms from the diffuse (1×1) phase into the (2/3√3×2/3√3)R30°. After growing up to a critical thickness, the Mg film grew in a disordered phase on the epitaxial layer. The Fermi level of the Mg2Si film is positioned at 0.51±0.05 eV above the valence band maximum. On the other hand, at 300 °C the Mg2Si epitaxial layer was formed in the (1×1) phase on the Si(111)7×7 and grew up to a critical thickness in the initial stage. For the successive evaporation, the Mg film grew in a disordered phase on the Mg2Si(111)1×1 surface.

Real-time monitoring of the Si carbonization process by a combined method of reflection high-energy electron diffraction and Auger electron spectroscopy

The carbonization process of a preferential-domain Si(001)2×1 surface with ethylene was investigated by a combined method of reflection high-energy electron diffraction and Auger electron spectroscopy. It is found that the carbonization process during the so-called incubation time is the Si1−xCx alloy formation before the nucleation of 3C–SiC grains. A reaction model for the Si1−xCx alloy formation and for the 3C–SiC grain growth is proposed for substrate temperatures of 600–750 °C. From the model, we postulate that the external supply of Si and C should be started just at the completion of the lateral 3C–SiC grain growth at temperatures of 600–650 °C in order to obtain thick 3C–SiC layers with a flat surface morphology.

Core-level photoemission study of the Si(111)4×1-In surface

Abstract In 4 d and Si 2 p photoemission spectra for the Si(111)4x1-In surface have been measured. It is found that the In 4 d spectra consist of mainly two components and that no significant surface core level shift is present on Si 2 p . The latter finding suggests that the substrate is almost ideally terminated by a one-to-one bonding with In atoms. It is also found that the In 4 d spectra are asymmetric in shape while Si 2 p spectra are symmetric. This shows that In atoms form a metallic over-layer with covalent bondings to a semiconducting Si substrate.