Iron Silicide Structures Research Articles

Iron silicides formation on Si (100) and (111) surfaces through theoretical modeling of sputtering and annealing

The iron silicides formation during epitaxial film grown process on the (100) and (111) silicon surfaces were investigated using molecular dynamics (MD). The iron and silicon atom deposition rate and silicon substrate temperature influence on the formed iron silicide structure and stoichiometric composition were studied in detail. During the growth of iron silicide crystal structure significant diffusion of the substrate atoms into the forming BCC core occurs, this intensifies with the substrate temperature increase, and the ratio of substrate atoms inside the Fe3Si phase reaches nearly 12%. The BCC structure formation is less active on the (100) surface, and at the temperatures as low as 26 °C and 300 °C the iron silicide crystal phase does not form at all. However, with the temperature increase or the deposition rate decrease, the crystal structure formation processes occur more actively in both cases of (100) and (111) surfaces. Thus, the effect of the deposition rate decrease is identical to the temperature growth. It was shown that the formation of the structured B2 phase of iron silicide in buffer layer between the film and the substrate leads to the inhibition of the mutual diffusion of iron and silicon atoms.

Electronic structure and magnetic properties of MnTe from first-principles calculations

Based on density functional theory (DFT) together with the projector augmented wave (PAW) method, we systematically investigate the structural, magnetic and electronic properties of the chalcogenide MnTe in six competing structures: rocksalt (RS), cesiun-chloride (CC), zinc-blende (ZB), wurtzite (WZ), iron-silicide (IS) and nickel-arsenide (NA). The ground state of MnTe is completely determined. And the structural parameters, magnetic properties, bulk modulus, phase transition pressure, and the density of states are studied, too. The density of states shows that MnTe in RS, CC and IS structures are antiferromagnetic conductors, and MnTe in WZ, ZB and NA are antiferromagnetic semiconductors. These results provide us the possibility to apply them to the spintronics of antiferromagnetic systems.

The importance of catalyst oxidation for the growth of carbon nanotubes on Si substrates

Iron catalyst in the form of a thin layer was deposited directly onto silicon wafers in order to grow carbon nanotubes by a chemical vapor deposition process. The chemical and morphological transformations undergone during the process by the iron were monitored in situ by photoelectron spectroscopy and ex situ by SEM. We found that the growth of carbon nanotubes was successful only when the iron catalyst was previously oxidized. Metallic iron transformed to embedded iron silicide structures, unable to initiate nanotube growth. On the other hand, pre-oxidized iron led to the formation of superficial particles and showed only a partial conversion to silicide, which resulted in carbon nanotube growth, even at very low pressures.

Study of Fe deposition onto [formula omitted]-Al/Si(1 1 1) template by scanning tunneling microscopy

The surface dynamics of Fe deposited onto the template surface of 3 × 3 -Al adatom-layer on Si(1 1 1) has been studied using scanning tunneling microscopy (STM). By imaging at both positive and negative sample bias, we identify the locations of Fe, Al and Si atoms by the susceptibility differences of these sites in receiving electrons and holes from the STM tip. When 0.1 ML of Fe atoms are deposited at room temperature, some Fe atoms incorporate themselves into the adlayer as dispersed atoms or small Fe clusters with 2–10 atoms. A smaller amount of Fe atoms choose to sit on the adlayer, once again as dispersed atoms or small Fe clusters. As the Fe coverage increases beyond 0.1 ML, both Fe clusters in and on the adlayer grow into 3-dimensional islands. Raising the growth temperature to 100 °C is enough to enhance the diffusivity of Fe atoms and initiate a small degree of cluster coalescence. However, these clusters still do not show any crystallinity by STM observation until they are annealed. Deposition of Fe atoms at 400 °C or post-deposition annealing above this temperature leads to the formation of iron silicide islands with a 2 × 2 surface lattice and a CsCl-type iron silicide structure, which are surrounded by 3 × 3 -Al/Si(1 1 1) adlayer domains with a depletion of Si atoms near the silicide islands. Most of these islands have a triangular shape, and grow preferentially along the step edges of the Si(1 1 1) surface. The 3 × 3 -Al adlayer appears to passivate the Si surface and enhances the diffusivity of Fe atoms but the passivation is not thermally stable.

STM/STS Studies of Self-Organized Growth of Iron Silicide Nanocrystals on Vicinal Si(111) Surface

The evolution of iron silicide structure grown by solid state epitaxy on Si(111) vicinal surface was investigated by scanning tunnelling microscopy. The reactions, which occur on the surface, are compared for two various Fe coverages: 0.33 and 2 monolayers. The annealing at 250°C does not enable substantial recovery of the surface ordering, deteriorated by Fe deposition at room temperature. The onset of 2 x 2 surface reconstruction is observed upon annealing at 400°C. A three-dimensional growth tendency of iron silicide crystallites on a bare Si(111) 7 x 7 surface was found at 700°C. In the case of 2 monolayer coverage crystallites nucleate along the edges of substrate terraces forming a regular array of nanometer size dots. Basing on atomically resolved spectroscopic effects and statistical considerations, structure of iron silicide nanocrystallites as well as Schottky-like character of the barrier at the interface between metallic crystallite and semiconducting substrate is deduced.

RHEED-STM study of iron silicide structures on Si(1 1 1)

Structures of the initial stage of Fe silicide grown on Si(1 1 1) by reactive deposition epitaxy method are studied by reflection high-energy electron diffraction and scanning tunneling microscopy. At the beginning, triangular two-dimensional Fe silicide islands of a 2×2 structure appear. During iron deposition, they grow and part of them stick to each other, while their flatness and periodic structure remain unchanged. At multilayer coverage, a diffraction pattern due to three-dimensional islands appears. This is considered to be a new Fe silicide phase as a precursor of β-FeSi 2.

Microdisperse Iron Silicide Structures Produced by Implantation of Iron Ions in Silicon

Iron implanted and subsequently annealed n-type Si(111) was studied by conversion electron Mossbauer spectroscopy for phase analysis and Auger electron spectroscopy for sputter depth profiling and element mapping. During implantation (200 keV, 3 × 1017 cm−2, 350°C) a mixture of β- and α-FeSi2 is firmed and after the subsequent annealing (900°C for 18 h and 1150°C for 1 h) a complete transition to the β- and the α-phase can be detected. The as-implanted profile has Gaussian shape and is broadening during annealing at 900°C to a plateau-like profile and shows only a slight broadening and depth depending fluctuations of the iron concentration after the 1150°C annealing. With scanning Auger electron spectroscopy the lateral iron and silicon distribution were investigated and show for the sample annealed at 900°C large separated β-FeSi2 precipitates which grow due to the process of Ostwald ripening. At 1150°C additionally coalescence of the precipitates occur and a wide extended penetration α-FeSi2 network structure is formed.

High-pressure phases of magnesium selenide and magnesium telluride

The electronic structure, the charge density, and the total energy of MgSe and MgTe in the rocksalt (B1), cesium chloride (B2), zinc blende (B3), wurtzite (B4), nickel arsenide (${\mathrm{B}8}_{1}$ ), and iron silicide (B28) structures are studied using first-principles self-consistent local-density calculations in a large plane-wave basis employing soft nonlocal pseudopotentials. Experimentally for MgSe a transition was observed from the rocksalt to the iron silicide structure at 107 GPa. We find this transition between the same structures at 160 GPa. For MgTe the experimental ground state is the wurtzite structure, while the nickel arsenide structure obtained at 1--3.5 GPa persists after unloading to normal pressure. Up to 60 GPa no other transition was observed. Theoretically we find a nickel arsenide ground state and a transition to the cesium chloride structure at 69.6 GPa. The wurtzite and nickel arsenide structures are energetically very close. The difference at the minimal energy in these two structures is only 20.3 meV per atom.