Synthesis of iron silicides starting with Fe/Si multilayers

The iron silicides are considered key materials for silicon integrated optoelectronic devices. This report describes the synthesis of the iron silicides starting with e-beam evaporated multilayered Fe/Si samples. Samples with two chemical wavelengths were studied upon annealing and ion beam mixing. The characterization included X-ray diffraction, CEMS and Rutherford backscattering.     

Local states of iron in iron implanted hematite Fe2O3

Powder samples of⁵⁷Fe₂O₃ and⁵⁶Fe₂O₃ were implanted with⁵⁶Fe and⁵⁷Fe ions, respectively. By the use of Conversion Electron Mössbauer Spectroscopy it was possible to observe the local states of implanted ions (⁵⁷Fe in⁵⁶Fe₂O₃) or the states of iron atoms from the target which were displaced during implantation due to the ballistic processes (⁵⁶Fe in⁵⁷Fe₂O₃). The implanted and displaced iron atoms appear in three different states: (i) in regular substitutional positions of Fe₂O₃, (ii) as magnetite Fe₃O₄-type structures and (iii) paramagnetic FeO_1?x state. The observed fractions of each state agree rather well with the calculated values obtained from the local iron atom enrichment at the surface as well as from the analysis of the equilibrium phase diagram for the binary Fe?O system. However, in⁵⁷Fe implanted samples some enhancement of the FeO_1?x fraction was found in comparison with the⁵⁶Fe implanted hematite.     

Experimental and theoretical positron annihilation studies on bulk nickel silicides

Bulk nickel silicides (NiSi and NiSi₂) have been studied using the experimental positron lifetime and depth-resolved positron beam measurements. Ab-initio calculations of positron lifetime for the silicides have also been carried out using the atomic superposition method. For NiSi phase, it is found that the theoretically computed positron lifetime compares favourably with the experimentally deduced value indicating that NiSi is defect free. However, for NiSi₂, the experimental positron lifetime does not compare well with the theoretical value suggesting that NiSi₂ contains vacancy defects. This is further supported by the positron diffusion lengths deduced from the VEPFIT analysis of the positron beam results.     

Optical characteristics of an epitaxial Fe3Si/Si(111) iron silicide film

The dispersion of the relative permittivity ? of a 27-nm-thick epitaxial Fe₃Si iron silicide film has been measured within the E = 1.16–4.96 eV energy range using the spectroscopic ellipsometry technique. The experimental data are compared to the relative permittivity calculated in the framework of the density functional theory using the GGA-PBE approximation. For Fe₃Si, the electronic structure and the electronic density of states (DOS) are calculated. The analysis of the frequencies corresponding to the transitions between the DOS peaks demonstrates qualitative agreement with the measured absorption peaks. The analysis of the single wavelength laser ellipsometry data obtained in the course of the film growth demonstrates that a continuous layer of Fe₃Si iron silicide film is formed if the film thickness achieves 5 nm.     

FMR studies in Al2+ implanted Fe60Al40 alloy

The Al²⁺ implanted layer (∼ 200 nm) in Fe₆₀Al₄₀ has been investigated by FMR. The magnetization is found to be 6400 G in the absence of anisotropy which agrees well with the value reported on cold worked Fe₆₀Al₄₀. Smaller line width for a sample implanted with the highest fluence of 1×10¹⁵ ion/cm² indicates better chemical and magnetic homogeneities. The g-factor is 2.06.     

Binding energy of silicon 2p electrons in iron silicides

Experimental data for the binding energies of Si 2p electrons in a number of stable and metastable iron silicides are analyzed and generalized. The silicides are applied on the Si(100)2 × 1 and Si(111)7 × 7 reconstructed single-crystal faces with solid-phase epitaxy. Core electron spectra are taken by means of high-energy-resolution photoelectron spectroscopy using synchrotron radiation. It is shown that the binding energies of Si 2p electrons in stable silicides, as well as in the silicon-iron solid solution, increase with increasing silicon content in them, since the role of interatomic relaxation in photoelectron excitation events grows feeble.     

Experimental and theoretical studies of Si/P substituted orthorhombic Fe2P

A Mössbauer spectroscopic study of orthorhombic Fe₂P_1–x Si _x withx 0.35 was performed. A large spread in magnetic hyperfine fields was found at the six Fe positions ranging from 10–26 T at 4.2 K. Small rearrangements in the crystal positions as compared to the hexagonal phase cause large changes in the magnetic field. Large changes in Fe magnetic moments have also been obtained in a spin-polarized LMTO band calculation performed on orthorhombic Fe₂P as compared to a similar calculation of hexagonal Fe₂P.     

Structural disorder in Fe−Si alloys near Fe3Si composition

Ordered and slightly disordered Fe_1?xSi_x alloys near X=0.25 are studied by means of Mössbauer spectroscopy. Quantitative analysis of the spectra after correction for the thickness effect is presented. The short range order as well as the long range order parameters are calculated from Mössbauer spectra. Distribution of atoms among different sites is determined. A slight disorder for x<0.252 is mainly due to an interchange of Fe atoms from A sites with Si atoms residing at D sites. However, at larger x the B disorder prevails.     

Surface and bulk electrical properties of the hematite phase Fe2O3

Electrical properties of Fe₂O₃ were studied by using several electrical methods such as electrical conductivity, thermopower (Seebeck effect) and work function. The studies were performed at elevated temperatures (1053–1153 K) and under controlled oxygen activity (10²10⁵ Pa). Samples of different thickness varying between 10³ nm and 1 mm were taken for the measurements of both electrical conductivity and thermopower. It has been found that the exponent of the po₂ dependence resulting from the work function measurements (1/n ) is about 1/2. Both thermopower and electrical conductivity data are well consistent with work function data for the thin film (1000 nm) of Fe₂O₃. The charge transport in Fe₂O₃ has been interpreted in terms of small polaron mechanism. Analysis of measured electrical parameters, regarding the thickness of studied specimens, indicates that the near-surface layer of Fe₂O₃ exhibits much higher deviation from stoichiometry than the bulk phase and resulting strong interaction between charge carriers. This effect has been interpreted in terms of segregation of intrinsic lattice defects to the surface, and presumably also to grain boundaries, of Fe₂O₃.     

Electron impact ionization cross-section of C2, C3, Si2, Si3, SiC,SiC2 and Si2C

Total ionization cross-sections for C₂, C₃, Si₂, Si₃, SiC, SiC₂ and Si₂C molecules have been calculated by electron impact. Spherical complex optical potential formalism has been employed for obtaining the inelastic cross-sections for these molecules. Then by applying complex scattering potential-ionization contribution method, total ionization cross-sections are derived. These cross-sections are calculated in the energy range from ionization threshold to 2?keV. There are no measurements available in the literature to the best of our knowledge with which our results can be compared. The results show a linear relationship between maximum ionization cross-section and square root of the ratio of polarizability to ionization potential, depending on its atomicity. This gives a confirmation for the consistency of the data reported here. Present work is a maiden attempt to find electron impact ionization cross-section for these molecules, except for C₂ and C₃.     

Mössbauer spectroscopy study surface structure of Si implanted by57Fe

Mossbauer spectroscopy, RBS and Infrared absorbed spectroscopy (IAS) analysis were carried out for the single crystal Si and amorphous Si both implanted by⁵⁷Fe. Mossbauer spectra were fitted by separated and continuous spectrum for single crystal Si and amorphous Si, respectively. Some interesting information of the chemical characteristics around the implanted ions were obtained.     

Diffusion measurement of implanted Sb into Si,using SiO2 encapsulation

Large, asymmetric atomic relaxations have been shown to play a crucial role in the structure and properties of several point defects in oxide materials. Examples include trapped hole centers in alkaline-earth oxides and E1′ and E4′ oxygen-vacancy centers and peroxy-radical defects in silicon dioxide. Schirmer's “bound small polaron” model, applied in particular to the alkaline-earth oxide defects, and model treatments of the E1′ center in SiO2 by Yip, Griscom and Fowler clearly illustrate the important spectroscopic consequences of such atomic relaxations. In fact, such effects had been incorporated in Lüty's classic model of the Type II FA center in alkali halides. Edwards and Fowler have recently applied MNDO and MINDO/3 quantum-chemistry approaches to the E1′, E4′, and peroxy radical defects in SiO2. These calculations generally corroborate suggested models and bear as well on possible creation mechanisms. Large relaxation effects are likely to be important in many other defects in oxide materials.     

The charge states of iron in insulators implanted with57Co and57Fe

Single crystals of α-Al₂O₃ and LiNbO₃ were implanted with⁵⁷Co (dose: up to 2×10¹⁵ atoms/cm²) and with⁵⁷Fe (dose: 2×10¹⁵ atoms/cm²) ions. The Mössbauer spectra revealed the disordered atomic environment. Fe²⁺ and Fe³⁺ charge states were observed. The spectra were compared to the spectra of crystals doped with⁵⁷Co. It was remarkable that in the doped α-Al₂O₃ Fe³⁺ states with slow spin-spin relaxation have appeared. The CEMS study of the samples implanted with⁵⁷Fe resulted in Fe²⁺ ionic states indicating that a fraction of Co atoms can also be in Co²⁺ state.