T. A. Pisarenko

Growth of Fe3O4 films on the Si(111) surface covered by a thin SiO2 layer

Magnetite polycrystalline films are grown by variously oxidizing a Fe film on the Si(111) surface covered by a thin (1.5 nm) SiO2 layer. It is found that defects in the SiO2 layer influence silicidation under heating of the Fe film. The high-temperature oxidation of the Fe film results in the formation of both Fe3O4 and iron monosilicide. However, the high-temperature deposition of Fe in an oxygen atmosphere leads to the growth of a compositionally uniform Fe3O4 film on the SiO2 surface. It is found that such a synthesis method causes [311] texture to arise in the magnetite film, with the texture axis normal to the surface. The influence of the synthesis method on the magnetic properties of grown Fe3O4 films is studied. A high coercive force of Fe3O3 films grown by Fe film oxidation is related to their specific morphology and compositional nonuniformity.

Study of ultrathin iron silicide films grown by solid phase epitaxy on the Si(001) surface

Ultrathin films of iron silicide have been grown by high-temperature annealing of 0.14-to O.5O-nm-thick Fe films deposited on the Si(001) surface at room temperature. It has been found that annealing leads to the formation of nanoislands of iron silicide on the surface, so that their type depends on the thickness of the Fe film. High-energy electron diffraction and atomic force microscopy measurements have revealed that the deposition of Fe films less than 0.32 nm thick on the Si(001) surface stimulates epitaxial growth of both three-dimensional β-FeSi2 and two-dimensional γ-FeSi2 islands. It has been found that, for Fe coverages of more than 0.32 nm thick, a complete transition to solide phase epitaxy is observed only for two-dimensional β-FeSi2 islands. The effect of prolonged annealing at 850°C on the morphology of the surface of the iron silicide film has been investigated.

Effect of oxygen pressure on the texture of a magnetite film grown by reactive deposition on a SiO2/Si(001) surface

Magnetite films (Fe3O4) 75 nm thick were grown on an oxidized Si(001) surface using reactive iron deposition in an oxygen atmosphere. Iron oxide films were grown under different O2 pressures. The structure of the films was controlled during their growth by the reflection high-energy electron diffraction (RHEED) method. It was established that the growth of magnetite films with a texture occurs only in a specific range of O2 pressures. A decrease in oxygen pressure led to the growth of a Fe3O4 film without a texture, while reactive deposition under pressures above the upper limit of the aforementioned range resulted in the formation of hematite crystallites (α-Fe2O3) in the Fe3O4 film.

The effect of synthesis temperature on structural and magnetic properties of Fe3O4 films grown on the SiO2/Si(001) surface

Magnetite (Fe3O4) films have been deposited on a SiO2/Si(001) surface at various temperatures by reactive sputtering of iron in oxygen. The influence of the synthesis temperature on the structure and magnetic properties of Fe3O4/SiO2/Si(001) samples have been studied by the methods of reflection high-energy electron diffraction, atomic force microscopy, Raman spectroscopy, and vibrating sample magnetometry. An optimum substrate temperature for the formation of polycrystalline films with the best magnetic characteristics has been determined.

Influence of defects in a silicon dioxide thin layer on the processes of silicidation in the Fe/SiO2/Si(001) system

The kinetics of the evolution of the structure and phase composition of the Fe/SiO2/Si(001) system under different conditions for deposition of the iron layer and subsequent annealing is considered. It is established that the SiO2 thin layer (∼1 nm) is not destroyed during iron deposition over a wide temperature range from 20 to 650°C. As a result, iron films with different morphologies are formed on the surface of the oxide. Annealing leads to the destruction of the SiO2 layer at defect sites. This brings about the interaction of iron atoms with the silicon substrate and subsequent formation of iron silicides.

Thin magnetite films on an oxidized silicon surface: Raman spectroscopy study

Polycrystalline films of magnetite (Fe3O4) formed by the reactive sputtering of iron in oxygen on Si(001) substrates covered by thin (1.4 nm) or thick (1200 nm) SiO2 layers have been studied by Raman spectroscopy. It is established that (i) the α-Fe2O3 phase is formed due to the laser-induced heating in magnetite films synthesized on thick SiO2 layers and (ii) the formation of α-Fe2O3 phase depends on the thickness of the buffer SiO2 layer.

Evolution of the structural and magnetotransport properties of magnetite films depending on the temperature of their synthesis on the SiO 2 /Si(001) surface

The methods of transmission and reflection electron diffraction have been used to investigate the structure of Fe3O4 films depending on the temperature of their synthesis on an Si substrate coated with an ultrathin layer of SiO2. The thus-grown polycrystalline films of magnetite had a texture, the axis of which was perpendicular to the surface of the SiO2 film. It has been revealed that, with an increase in the growth temperature, a structural rearrangement occurs which is characterized by an increase in the volume fraction of grains with the preferred (311) orientation. A study of the magnetotransport properties of the films has shown that the magnitude of their magnetoresistance increases with an increase in the temperature of their synthesis. It has been established that in the Fe3O4/SiO2/Si system with a tunneling-thin layer of SiO2 the magnetoresistance decreases as a result of the flow of an electric current through the silicon substrate.

The Influence of Seed Layer on Growth of Magnetite Films on the SiO2/Si (001) Surface

Polycrystalline magnetite films with the thickness of 50 nm were grown on SiO2/Si(001) surface by the reactive deposition of Fe in O2 atmosphere using various preparation ways of the formation of iron oxide seed layer. The seed layers were formed by the deposition and oxidation of 3 nm Fe layer at different thermal conditions. It was found that polycrystalline magnetite films grown with the use of seed layer have [110] texture and are characterized by increase of the squareness of magnetic hysteresis loop. Structural analysis of magnetite films and predeposited seed layers was studied by RHEED.

Comparative Study of the Lateral Photovoltaic Effect in Fe3O4/SiO2/n-Si and Fe3O4/SiO2/p-Si Structures

The results of a comparative study of the lateral photovoltaic effect in Fe3O4/SiO2/n-Si and Fe3O4/SiO2/p-Si structures are presented. The lateral photovoltage reaches its maximum near the measurement contacts in both structures, but the signs of this voltage differ. As the light spot moves away from the contacts, the photovoltage varies linearly in Fe3O4/SiO2/n-Si and decreases exponentially in Fe3O4/SiO2/p-Si. It is found that interface states at the SiO2/Si interface induce the photovoltage polarity inversion associated with a change in the conductivity type of silicon. An extreme thickness dependence of the photovoltage with an optimum Fe3O4 film thickness of ~50 nm is observed in both structures.

RHEED Study of the Texture in Polycrystalline Films of Magnetite Grown on Oxidized Silicon Surface

Polycrystalline films of magnetite (Fe3O4) with thickness of 75 nm were grown on SiO2/Si (001) surface by reactive deposition of Fe in O2 atmosphere. The growth of Fe3O4 films was conducted with the different oxygen pressures. The structure of films was monitored by reflection high-energy electron diffraction (RHEED) during the film growth. It was found that there is a range of oxygen pressure in which the growth of only textured Fe3O4 film takes place. Reactive deposition of Fe at lower oxygen pressure results in a growth of Fe3O4 film without a texture. In contrast at the deposition with higher oxygen pressure the texture in the Fe3O4 film remains but the appearance of hematite (α-Fe2O3) is observed.