The formation of iron silicide nanocrystals (NCs) and their embedding into monocrystalline silicon was studied. Solid phase epitaxy of 0.4 nm Fe at 630 °C resulted in formation of NCs consisted of β-FeSi2 and ε-FeSi phases. Annealing of NCs at 750 °C for 90 min led to transformation of β-FeSi2 and ε-FeSi into α-FeSi2. On the other hand, silicon layer growth over as-formed NCs, at the same temperature, resulted in formation of single phase NCs consisted of β-FeSi2. Silicon deposition rate proved to be the crucial point for a full embedding of NCs. The rate of 1 nm/min resulted in emersion of NCs to the surface during silicon overgrowth irrespective of Si cap layer thickness, while the rate of 8 nm/min led to the full embedding of β-FeSi2 NCs. Both incompletely and fully embedded β-FeSi2 NCs have epitaxial relationship and stress favorable for an indirect to direct band-gap transition at Y point.
A robotic laser technological complex has been used for the laser powder fusing (LPF) of samarium (Sm) and iron (Fe) powders on stainless steel (SS) substrate in argon flow conditions for the creation of thick (1.0–1.5 mm) ferromagnetic coatings. The formation of Fe–Sm–Ni–Cr and Fe–Cr–Sm alloys was demonstrated on SS substrate due to intensive diffusion of Fe, Cr and Ni atoms from the substrate. A magnetic field (0.2 T) during LPF on the SS substrate resulted in crystallisation of single grains (5–20 microns) of the Fe–Cr–Sm alloy with mutually perpendicular orientation, which were embedded in the Sm–Fe–Ni–Cr alloy matrix and formed a mesh structure in the fused layer. When the additional magnetic field was absent during LPF the larger part of Sm atoms were located in near-surface sample area and around elongated grains, as well as in small grains of spherical form, but dissolution of Sm was blocked in elongated grains. The fused layers from Sm and Fe powders on SS substrates with and without magnetic field had a low coercivity (20–100 Oe), near zero residual magnetisation and high saturation magnetisation (110–112 emu/g) at 300 K. The maximum coercivity (100 Oe) was observed for coating fused with magnetic field, corresponding to mutually perpendicular orientation of ferromagnetic Fe–Cr–Sm grains. The cooling of samples to 4 K resulted in magnetic ordering with a Curie temperature of 50 K and with small changes in coercivity.
Optimization of growth parameters has permitted to create monolithic nanocomposites with buried nanocrystals (NCs)
of iron and chromium disilicides and polycrystalline nanocomposites with buried Mg2Si NCs (3-40 nm) on the base of
reactive deposition epitaxy (RDE), solid phase epitaxy(SPE) and molecular beam epitaxy (MBE), which demonstrated
wonderful thermoelectrical properties and the possibility of strong light emission with wavelength of 1.2 - 1.6 microns
in the mesa-diode structures with p-n junction at direct and back bias. Doping process of Mg2Si nanocrystals inside
nanocomposite layers was developed on the base of ordered surface phases of metals on a silicon substrate.
Nanocomposite layers with n- and p-type conductivity have been successfully grown. The huge increase of Zeebeck
coefficient in the Si-p/β-FeSi2 NCs/Si-p and Si/Mg2Si NCs/Si nanocomposites has been found.
Growth and magnetism of thin iron films on the surfaces Si(100), Si(111) and Si(111)-4° are studied by in situ SMOKE and ex-situ AFM methods. Comparison of growth modes for slow and ultra-fast deposition is given. Design of the pulse-type ultra-fast evaporator is described.
The morphology and optical properties of Si samples implanted by low-energy Fe+ ions with different fluencies (1×1015
- 1.8×1017 cm-2) and further subjected to pulsed ion-beam treatment (PIBT) have been studied by atomic force
microscopy and optical reflectance spectroscopy. It was proved that the iron disilicide ( β-FeSi2) crystallites have been
formed on the surface of Si substrate as a result of ion implantation and PIBT. The method of ultrahigh vacuum and low-temperature
(Τ = 850°C) cleaning of Fe+-implanted Si samples has been used for the first time. It was found that it is
possible to form smooth epitaxial Si films with reconstructed surface and thickness up to 1.7 μm by molecular beam
epitaxy (MBE) on the surface of Si samples implanted at a fluence of up to 1×1016 CM-2. Further increasing implantation
fluence results into disruption of epitaxial Si growth and strong increase of surface relief roughness due to 3D silicon
growth mechanism. Preservation of β-FeSi2 precipitates inside Si matrix after the formation of a cap epitaxial Si layer
has been confirmed by optical spectroscopy data. Low temperature photoluminescence measurements in the range of
1400-1700 nm showed that light emission of the Si/ β-FeSi2/Si heterostructures formed is due to contributions from β-
FeSi2 precipitates and dislocations.
Continuous very thin (2.5-3.0 nm) and thin (16-18 nm) ytterbium suicide films with some pinhole density (3•107- 1•108 cm-2) have been formed on Si(111) by solid phase epitaxy (SPE) and reactive deposition epitaxy (RDE) growth methods on templates. The stoichiometric ytterbium suicide (YbSi2) formation has shown in SPE grown films by AES and EELS data. Very thin Yb suicide films grown by RDE method had the silicon enrichment in YbSi2 suicide composition. The analysis of LEED data and AFM imaging has shown that ytterbium suicide films had non-oriented blocks with the polycrystalline structure. The analysis of scanning region length dependencies of the root mean square roughness deviation (σR(L)) for grown suicide films has shown that the formation of ytterbium suicide in SPE and RDE growth methods is determined by the surface diffusion of Yb atoms during the three-dimensional growth process. Optical functions (n, k, α, ε1, ε2, Im ε1-1, neff, εeff) of ytterbium silicide films grown on Si(1 1 1) have been calculated from transmittance and reflectance spectra in the energy range of 0.1-6.2 eV. Two nearly discrete absorption bands have been observed in the electronic structure of Yb silicide films with different composition, which connected with interband transitions on divalent and trivalent Yb states. It was established that the reflection coefficient minimum in R-spectra at energies higher 4.2 eV corresponds to the state density minimum in Yb suicide between divalent and trivalent Yb states. It was shown from optical data that Yb silicide films have the semi-metallic properties with low state densities at energies less 0.4 eV and high state densities at 0.5-2.5 eV.
The method of Differential Reflection Spectroscopy (DRS) have been applied to study thin iron films during the process of growth on Si (111) or Si(100) surfaces at room temperature. Some details on the Dynamic Standard method in DRS method are presented. Magnetic properties of as-grown films have been demonstrated by the SMOKE method. Dependence ofdielectric functions of the films on the deposit amount is given.
Processes of β-FeSi2 nanosize islands growth on Si(111)7x7 surface and Si(111)-Cr surface phases (SP) and silicon overgrowth atop β-FeSi2 nanosize islands have been studied by LEED, in situ Hall temperature measurements and ex situ AFM and optical spectrscopy methods. It was established, that Si(111)7x7-Cr surface phase appears the influence on β-FeSi2 island orientation and crystalline structure, but island density does not change as compared with Si(111)7x7 surface. It was shown that Si(111)√3x√3/30°-Cr SP results in reduction of iron disilicide island density and their repeated nucleation on the free modified silicon surface. The optimal growth temperature (800 °C) for molecular beam epitaxy (MBE) of silicon layer atop of β-FeSi2 nanosize islands on different substrate has been determined. It was revealed, that iron disilicide clusters, grown on Si(111)7x7-Cr surface phase, appear the minimal influence on crystal structure of the silicon layer. It was observed the closed concurrence of electric parameters of silicon with buried iron disilicide clusters and atomically clean silicon that testifies to the minimal carrier scattering on these clusters and can confirm them epitaxial burying in the silicon crystal lattice. From optical spectrscopy data two direct interband transitions at 0.75 eV and 1.10 eV were observed in silcon samples with buried β-FeSi2 nanosize clusters.
Morphology, optical properties, crystal and electronic structure of monocrystal silicon after plasma processing,
depending on initial voltage of magnetoplasma compressor (MPC), have been studied. It was shown that periodic surface
structures are formed on silicon only in the short range ofinitial MPC voltages (2.8-3.2 kV), but at higher initial voltages
(3.4-3.6 kV) the formation of "crater" and carrying out of the part of material on its periphery till the moment of
crystallization is observed without the formation of surface structures. The decrease of the silicon lattice constant has
been observed after plasma processing at all initial voltages that correlates with the decrease of band-gap energy by data
of optical spectroscopy. Changes in crystal lattice and electronic structure of silicon modified by compression plasma
flow have confirmed by red shift of 4.5 eV peak in reflectance spectra and decrease of its amplitude.
The technology of solid-phase growth of nanosize islands of magnesium suicide on Si (111) 7x7 with narrow distributions of lateral size and height (60 - 80 and 5 - 7 nanometers, respectively) and density of up to 2x 109 sm-2 is proposed. A 20-50 nm thick Si layer has been grown upon these islands. Basing on the data of AES, EELS, AFM and JR spectroscopy, a conclusion is made that the Mg2Si islands remain in depth of the Si layer. The suggestion is made that sizes, density and crystal structure of the buried magnesium suicide clusters preserves. It is shown, that the system of three as-grown layers of buried clusters has smoother surface than the one layer system. The contribution of the Mg2Si clusters into the dielectric function is observed at the energy 0.8-1.2 eV, it is maximal if the clusters are localized on the silicon surface. It is shown, that with increase of the number of Mg2Si cluster layers their contribution increases into the effective number of electrons per a unit cell and effective dielectric function of the sample.
A technology of solid-phase growth of Mg2Si thin films from Mg and Si layers on a pre-fabricated template layer of Mg2Si islands on Si (111) has been developed. The optimum temperature (T=550° C) for growth of epitaxial Mg2Si films on Si (111) has been found. It has been shown from optical spectroscopy data that Mg2Si epitaxial film has a direct fundamental transition with the energy of 0.75-0.76 eV with small combined density of states. It represents transition of small number of valence electrons into Mg-Si bonding states in the conductance band. The strong absorption range (1.9-6.2 eV) corresponds to transitions from bonding to anti-bonding states.
Solid phase multilayer growth technique of magnesium silicide (Mg2Si) films with preliminary formation of templates, allowing to growth the thick (60-100 nm) Mg2Si film, has offered. Optical function data have shown, that thick (60-80 nm) Mg2Si films are the narrow band semiconductor with optical band gap of Egopt = 0.75 eV and two absorption regions with the small state density at 0.75-2.1 eV and large state density at 2.3-6.2 eV on Mg2Si cell, but in the second range about 3.0 electrons on Mg2Si cell participate in formation of electronic structure. The integrated spectra of the dielectric function of Mg2Si have been decomposed into the contributions from four non-interacting harmonic oscillators and the parameters of these oscillators were evaluated. It was established that the third harmonic oscillator (Ep=2.50 eV) with large oscillator strength introduces the main contribution into the dielectric function. The researches of electrical properties of thick magnesium silicide films on silicon also have shown, that they are narrow band semiconductors of p-type conductivity with energy band gap (Egel=0.77 eV), in which the high mobility holes with high rate of their scattering was observed at temperature increase (μ~T-4.0). On temperature dependencies of carrier concentration two activation regions, connected to a generation of carriers through fundamental transition (0.77 eV) and second interband transition with energy 2.78 eV, have been found.
Interface formation in Yb/Si(111) system has been investigated by AES and EELS spectroscopy and in situ Hall measurements at room temperature. It was established that interface formation process may be divided into five stages: 1) 2D growth of Yb (up to two monolayers), 2) intermixing and formation of 2D Yb silicide, 3) formation of 3D silicode islands, 4) growth of Yb on 3D silicide islands, 5) coalescence of 3D Yb-Yb silicide islands and formation of continuous Yb film. We attribute the observed conductivity character in Yb/Si(111) system to the evaluation of morphological and electrical properties of the growing Yb layer (2D Yb, silicide, metal) rather than to the changes within the space charge layer under the surface. Two-layer calculations have shown that holes are majority carriers in the deposited mobility and surface hole concentration within the coverage range below 6 ML where formation of a continuous Yb silicide film completes. Conductivity oscillations are explained by transition from semiconductor-type conductivity at the first growth stage (2D Yb growth) to metal-like conductivity of 2D and 3D Yb silicide films. It was shown that thin continuous Yb film (13 Ml) has the resistivity (16 μΩ-cm) close to the bulk refractory metals.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.