3 Å, as shown by Figure 3b. This result is different from previous results obtained by means of SPE. Within the SPE technique, the well-ordered c (4 × 8) structure can be formed only at a Fe exposure lower than 1.5 ML and after high temperature annealing at about 600°C. 3-Methyladenine cell line The c (4 × 8) silicide phase exists only in the ultrathin film regime with a definite thickness in the

range of 1.4 to 1.9 Å. If the Fe coverage is above 1.5 ML, a different type of silicide, namely, the (2 × 2) phase will grow into islands on top of the c (4 × 8) film [2]. This phenomenon could be attributed to the iron-rich environment of SPE because the c (4 × 8) phase is reported to have a FeSi2 stoichiometry and the Si atoms diffused to the reaction sites are insufficient [2]. The single c (4 × 8) phase and the larger thickness of the c (4 × 8) film obtained by the RDE method can be attributed to the supply of sufficient free Si atoms during the silicide AZD6738 mw reaction. Figure 3 STM image of the homogeneous c (4 × 8) iron silicide thin film and line profile. (a) STM

image (2,000 × 2,000 nm2; V s = 2.0 V; I = 0.2 nA) of the homogeneous c (4 × 8) iron silicide phase grown at 750°C by depositing 1.5 ML of Fe on the Si (111) surface. The largest area of the c (4 × 8) tabular island is up to approximately 1.0 μm2. (b) The line profile along the line in (a) shows that the height of the c (4 × 8) tabular islands is approximately 6.3 Å with respect to the substrate terrace. Previous studies showed that several metastable silicides [1 × 1, 2 × 2, and c (4 × 8) phases] that do not exist in the bulk phase diagram can be grown epitaxially on the Si (111) substrate under the strain from the substrate. The 1 × 1 phase can be assigned to the FeSi with Myosin a CsCl structure, while the 2 × 2 phase can be assigned to the γ-FeSi2 with a CaF2 structure and the FeSi1 + x (0 ≤ x ≤1) with a defect CsCl structure [4]. The FeSi1 + x (0 ≤ x ≤1) can be derived from the CsCl structure by introducing Fe vacancies distributed in a random fashion. The heights observed for the type A islands prove that the 2 × 2 phase is FeSi1 + x (0 ≤ x ≤1) because the corresponding crystal

structure has a spacing of 1.57 Å between equivalent atomic planes. If the 2 × 2 phase is γ-FeSi2 in the CaF2 structure, the heights in multiples of 3.14 Å should be observed [8, 10]. Furthermore, the tunneling current–voltage (I-V) curve measured on top of the type A islands (Figure 2c) exhibits a semiconducting character with a band gap of approximately 0.9 eV, verifying that the 2 × 2 phase is not γ-FeSi2 because γ-FeSi2 is metallic [5, 9]. The c (4 × 8) pattern could result from the formation of periodic defects of vacancies and/or Si 4SC-202 chemical structure substitution on the Fe sites in the buried Fe layers.