rus
Issue #8/2013
I.Babkina, K.Gabriyels, O.Zhilova, Yu.Kalinin, A.Sitnikov
Electric and Magnetic Properties of a Multilayered Nanocomposite
Electric and Magnetic Properties of a Multilayered Nanocomposite
Control of a state of environment demand inexpensive, economical and reliable sensors of toxic and explosive gases. High-sensitivity materials with the given properties are necessary for their development. Active scientific and technological research of various gas sensors are stimulated, in particular, by development of environmental monitoring and automated control of technological processes.
Теги: environmental monitoring sensors of toxic and explosive gases sensory layers датчики токсичных и взрывоопасных газов сенсорные слои экологический мониторинг
Creation of gas sensors on the basis of metal-oxide semiconductors is the most perspective. In spite of that 40 years passed from the moment of opening of a principle of their action, manufacturing techniques of these products are still not fulfilled and physical principles of their work are not fully studied. At the heart of the last developments lies adsorption of molecules of oxygen by a surface of metal-oxide heated up to 200–400°С with formation of ions O2–, O–, and O2– that leads to increase in electric resistance of the sensors. At existence in a gas mix of restoring components, for example, CO and CH4, ions of oxygen enter into reaction with them, and electric resistance of a sensor decreases. Seeming simplicity hides serious problems of fundamental physics and manufacturing techniques of the sensors.
One of such problems is selectivity. Sensors react to a large number of restoring reagents that complicates definition of components of a gas mix. To define them it is possible from optimum temperature of Tр corresponding to the maximum gas sensitivity. Introduction of additives in the quantities considerably exceeding level of an alloying of semi-conductor materials is also possible.
Important issue of materials science is research of new magnetoresistive materials for sensors of a magnetic field and other devices of nanoelectronics [1, 2]. Development of nanocomposites with magnetoresistive effect, sensitive to various gases, is even more actual, as will allow to connect two sensors in one device. In this regard the great interest is caused by structures with semi-conductor nanometer layers. If the composite at percolation threshold is used as a magnetic layer, the system at critical thickness of a layer and specific resistance of a film becomes magnetically ordered [3]. This effect did not receive a sufficient theoretical explanation yet. Now there is an accumulation of the experimental facts which will help to explain such ordering of the magnetic moments of granules at the room temperature.
In the present article results of research of the new multilayered composite–semiconductor structures, study of their magnetic and electric properties, and also gas sensitivity of a multilayered film, in which the layers of ferromagnetic–dielectric (Co0,41Fe0,39B0,20)0,34(SiO2)0,66 in superparamagnetic condition are divided by a semi-conductor (dielectric) layer In0,36Y0,04O0,60, are considered.
Obtaining and research methods
Structures {(Co0,41Fe0,39B0,20)0,34(SiO2)0,66/[In0,36Y0,04O0,60]}93 were proluced by ion-beam method on original installation on the basis of vacuum evoporation post UVN-2M [4–6]. For a spraying of multilayered structure were used a target from In0,36Y0,04O0,60 allow with fifteen hinge plates of SiO2 evenly distributed on a surface and a target of structure of In0,36Y0,04O0,60. The V-shaped screen, allowing in a wide range to regulate thickness of a layer was set up between a semi-conductor target and a substrate at a spraying.
A series from five glass-ceramic substrates was fixed on the holder parallel to the target plane along its long part. Due to the chosen parameters, simultaneous dispersion of two targets was carried out.
A separate films from different targets have been sprayed for assessment of layer and interlayer thickness. The thickness of the film was measured at various sites after some hours of drawing it on substrates, rotating with the set speed by means of the interferometer MII-4. The measurement points of thickness were fixed concerning to a substrate and target arrangement. The measured thickness of a film were approximated depending on distance to the substrate edge. Taking into account time of dispersion and the period of rotation of a roundabout, the thickness of the film received for one turn was calculated. The thickness of a layer of the second phase of structure was similarly defined.
The element structure of films was defined on a power dispersive x-ray detachable device Oxford INCA Energy 250 to a scanning electronic microscope JEOL JSM-6380 LV. Electric resistance was investigated on the automated universal measuring complex. High-frequency magnetic properties (valid μ/ and imaginary μ// parts of a complex magnetic permeability) were measured on frequency of 50 MHz by a technique [7].
Electric properties
On fig.1 dependence of specific electric resistance ρ from thickness of a layer In0,36Y0,04O0,60 for considered multilayered structure is presented. Its look in systems with Si, C, Cu, Te3Bi2 is similar to dependence for system [(Co0,45Fe0,45Zr0,10)0,35(Al2O3)0,65/α-Si:H]30 [8]. In the considered case there is a range of thickness of a layer in which considerable change of ρ(h) is observed.
The multilayered structure of a composite-semiconductor is the difficult heterophase system, one of which key parametres is thickness of a semi-conductor layer (h). At thickness of InIn0,36Y0,04O0,60 less than 0.4 nanometers, the phase of the semiconductor has an island structure and owing to minimisation of internal energy of a growing film at self-organizing (fig.2a) concentrates on metal granules. Such morphology essentially does not affect electrotransfer in composite layers. At h from 0.5 to 1.2 nanometers the low-impedance channels of conductivity are formed. At smaller thickness of the semiconductor, the electrotransfer according to the scheme can prevail: metal granule – semiconductor – dielectric - metal granule (fig.2b). In process of h increase, the contribution to conductivity of such transitions will increase, and at 1.2 nanometers the resistance is completely defined by carrying-out channels (fig.2c). The further increase of h leads to increase of a distance between the metal granules and to increase of ρ.
The temperature dependences of electric resistance (R)
of samples were investigated for confirmation of the assumption on change of channels of transfer of a charge in multilayered heterogeneous structures {(Co0,41Fe0,39B0,20)0,34
(SiO2)0,66/[In0,36Y0,04O0,60]}93 with increase in thickness of a layer. Thermal processing of complicated heterogeneous system should be accompanied by nuclear reorganization and lead to emergence of energy of activation of electric conductivity. The assessment of energy of activation of electric conductivity (Ea) was carried out on dependences of lnR from 1/T after annealing at various temperatures. The temperature dependence of electric resistance of considered multilayered heterogeneous structure at thickness of a composite of h1 = 4.4 nm and thickness of a semiconductor of h2 = 1.4 nm is presented as an example on fig.3.
When heating in a wide interval of temperatures and cooling after heating to 480°С, the electric resistance has a linear site in lnR co-ordinates from 1/T in a range 40–138°С. Therefore, temperature dependence of electric resistance can be described by Arrenius’s equation
ρ= ρ0·exp(–EaR/kT),
where ρ0 – constant; EaR – energy of activation of electric conductivity; k – Boltsman constant; T – absolute temperature. The equation also allows to estimate energy of activation of conductivity.
On fig.4 temperature dependences of electric resistance of multilayered heterogeneous structures are presented at various h1 and h2 values: a) 2.9 and 0.4 nanometers; b) 4.7 and 0.8 nanometers; c) 5.1 and 1.1 nanometers; d) 4.4 and 1.4 nanometers. By arrows on schedules is specified energy of activation of electrotransfer at temperatures above room after the corresponding annealing.
The analysis of temperature dependences of electric resistance after consecutive heatings showed that change of R(T) for heterogeneous systems with various thickness of a semi-conductor layer is accompanied by insignificant growth of energy of activation of electrotransfer at increase of annealing temperature. An exception is the multilayered structure at h1 = 2.9 nanometers and
h2 = 0.4 nanometer in which after annealing above 600°С the energy of activation of electrotransfer made
1.1 electron volts that is much higher, than for heterogeneous structures with thickness of a layer from 0.8 to 1.4 nanometers after similar heat treatment.
Nonmonotonicity of increase of electric resistance is shown when heating from 300 to 600°С in a range of a layer thickness of 0.8–1.1 nanometers. It can be connected with change of structure of heterogeneous system or structure and concentration of defects. All these features are shown at those thickness of a layer, when its role in conductivity is essential. It is possible to believe that the reason of nonmonotonic increase of electric resistance is existence of a quasitwo-dimensional percolation grid In0,36Y0,04O0,60. Besides, the energy of activation of electrotransfer after annealing above 600°С is much lower, than in a case with h1 = 2.9 nanometers and h2 = 0.4 nanometers, that also confirms the given guesses.
After formation of a continuous semi-conductor layer (h = 1.4 nanometers) at 300–600°С, R(T) changes almost on three orders that much more, than in multilayered structures with smaller thickness of a layer. It is necessary to note, that in system with h1 = 4.4 nanometers and
h2 = 1.4 nanometers, energy of activation of electric resistance after annealing at 550°C more than after processing at 700°C that was not observed in structures with smaller thickness of a layer.
Research of temperature processing of metal-dielectric nanocomposites showed that when heating to temperatures which are not leading to essential structural changes, electric resistance in structures raises to percolation threshold [9, 10]. In compound In0,36Y0,04O0,60 annealing to 300°С lead to increase in conductivity [11, 12]. On fig.5 presented dependences of specific electric resistance on thickness of a layer In0,36Y0,04O0,60 for considered multilayered structures in an initial condition (1) and after annealing are at 300°С (2–4). At h < 1 nanometers the ρ of annealed samples increases, and at h > 1.1 nanometers it decreases rather nase values. This is one more proof of change of the phases involved in electrotransfer with increase in thickness of a layer.
Research of structure and gas sensitivity of a semi-conductor film In0,36Y0,04O0,60 showed that in an initial condition it has amorphous structure, and at annealing above 400°С it crystallises. Sensing properties in oxide are observed only in a crystalline state, and at addition of restoring gases electric resistance of films goes down [13–15].
For considered heterogeneous multilayered structure influence of hydrogen on electric resistance is investigated. It is established that at annealing above 400°С the structure of the gas environment influences on electric conductivity of samples, if thickness of a layer more than 0.83 nanometers. Thus considerable influence of hydrogen on ρ films is observed at h > 1 nanometer (fig.6, 7). Such regularities testify to course of crystallisation of oxide In0,36Y0,04O0,60 when heating above 400°С that can be shown as increase of electric resistance on dependences of R(T) (fig. 4 b–4d).
Change of a sign of influence of hydrogen on electric resistance of samples at various temperature of processing (fig.6) is an interesting feature of this multilayered heterogeneous structure. So, if the sample was annealed at 400°С, the regenerative gas lowers R, and after heat treatment at 600°С, electric resistance raises that is not difinitive for this semi-conductor material. Change of a sign of gas sensitivity is possible at change of conductivity type of the the semiconductor.
The electronic theory of chemical sorption and catalysis, based on superficial electronic conditions of semiconductors [13] is used for explanation of changes of electroconductivity of multilayered structure at contact with the gas environment of various structures. Molecules adsorbed on a surface of oxide of gas can give electrons (donors) or attach them to themselves from oxide (acceptors). As at heat treatment of multilayered structure for 10 minutes at 400°С the temporary dependence of electric resistance, typical for the n-type semiconductor (fig.6a) is observed, adsorption of molecules of an acceptor leads to creation of the on-surface areas poor by electrons and reduction of an electrical conductivity at introduction of argon and air. It testifies to dominating influence on conductivity of semi-conductor layers of In0,36Y0,04O0,60. At adsorption of molecules of donor type, the outer layer on oxide of n-type enriched with electrons that increases a structure electrical conductivity at hydrogen adsorption is being created.
At the increased temperature it is necessary to consider diffusion between composite and semi-conductor layers. B possesses the greatest factor of diffusion, proceeding from film structure. Probably, introduction of its atoms into structure of the semiconductor changes its electric conductivity from n-type to p-type and reaction to the adsorbed gases (fig.6b). The temperature of annealing at which the sign of gas sensitivity changes, correlates with maximum temperature on R(T) dependences. Besides, for the studied film at h1 = 4.4 nanometers and h2 = 1.4 nanometers energy of activation of electrotransfer went down when heated from 580 to 700°С that also can be connected with introduction of atom of boron in a crystal lattice of In0,36Y0,04O0,60 layers.
Magnetic properties
Transition from a superparamagnetic to ferromagnetic structure at formation of a continuous layer of a semiconductor and to achieve of specific electric resistance of structure about 0.005 Ohm·m [16] for systems {[(Co0,41Fe0,39B0,20)0,34(SiO2)0,66]/
Si]}94, {[(Co0,41Fe0,39B0,20)0,34(SiO2)0,66]/[C]}46, {[(Co0,41
Fe0,39B0,20)0,34(SiO2)0,66]/[Cu]}93 and {[(Co0,41Fe0,39B0,20)0,34
(SiO2)0,66]/[Te3Bi2]}101. Systems investigated by authors of a composite–semiconductor type have higher ρ in all range of thickness of layers (fig.2, 4). However, as measurements of R(T) showed, for studied structure there are intervals of temperatures where considerable reduction of specific resistance is observed. So, for multilayered heterogeneous system with a layer from In0,36Y0,04O0,60 it is an interval from 250 to 350°С. Besides, fall of ρ is possible at annealing in the atmosphere containing hydrogen.
Dependences of valid (μ/) and imaginary (μ//) parts of complex magnetic permeability of the studied structure in an initial and annealed condition are presented on fig.8. The analysis of μ/(h) and μ//(h) revealed that in a range of thickness of a layer of 1.0–1.5 nm maxima of a complex magnetic permeability is observed. The place of a maximum correlates with dependences of electric resistance of the samples (fig.5), however μ/ and μ// remain small. It is possible, this results from the fact that as a result of heat treatment specific electric resistance of heterogeneous structure remained slightly above, than 0.005 Ohm·m. Growth of magnetic permeability of a semi-conductor layer in thickness of 1.2–1.4 nm relates with strengthening of interaction between ferromagnetic granules of composite layers through conductivity electrons.
It should be noted that the carried out research show that the thickness of a layer In0,36Y0,04O0,60 defines the electrotransfer mechanism. At h smaller than 0.5 nm transfer of a charge is defined by a composite (Co0,41Fe0,39
B0,20)0,34(SiO2)0,66, which structure is before percolation threshold. At thickness from 0.5 to 1.2 nm, conductivity redistribution from electrotransfer metal–dielectric–metal to channels metal–semiconductor–metal is observed.
Increase in electric resistance when heating in a range from 300 to 500°С relates to crystallisation of a semi-conductor layer. Change of a sign of gas sensitivity is connected with change its conductivity type, that can be explained by boron diffusion from a composite layer and its introduction into a crystal lattice of a layer In2O3.
It is established that thermal processing for 30 min at 300°С in the hydrogen atmosphere at pressure of 7.8 Torr leads to appearance in multilayered heterogeneous structure of a maximum on dependences μ/(h) and μ//(h)
in a range of thickness of a layer of 1.0–1.5 nm, which situation correlates with dependences of electric resistance of samples on thickness of a semi-conductor layer.
This work was supported by RFFR (project number 13-02-97512-r_tsentr_a).
One of such problems is selectivity. Sensors react to a large number of restoring reagents that complicates definition of components of a gas mix. To define them it is possible from optimum temperature of Tр corresponding to the maximum gas sensitivity. Introduction of additives in the quantities considerably exceeding level of an alloying of semi-conductor materials is also possible.
Important issue of materials science is research of new magnetoresistive materials for sensors of a magnetic field and other devices of nanoelectronics [1, 2]. Development of nanocomposites with magnetoresistive effect, sensitive to various gases, is even more actual, as will allow to connect two sensors in one device. In this regard the great interest is caused by structures with semi-conductor nanometer layers. If the composite at percolation threshold is used as a magnetic layer, the system at critical thickness of a layer and specific resistance of a film becomes magnetically ordered [3]. This effect did not receive a sufficient theoretical explanation yet. Now there is an accumulation of the experimental facts which will help to explain such ordering of the magnetic moments of granules at the room temperature.
In the present article results of research of the new multilayered composite–semiconductor structures, study of their magnetic and electric properties, and also gas sensitivity of a multilayered film, in which the layers of ferromagnetic–dielectric (Co0,41Fe0,39B0,20)0,34(SiO2)0,66 in superparamagnetic condition are divided by a semi-conductor (dielectric) layer In0,36Y0,04O0,60, are considered.
Obtaining and research methods
Structures {(Co0,41Fe0,39B0,20)0,34(SiO2)0,66/[In0,36Y0,04O0,60]}93 were proluced by ion-beam method on original installation on the basis of vacuum evoporation post UVN-2M [4–6]. For a spraying of multilayered structure were used a target from In0,36Y0,04O0,60 allow with fifteen hinge plates of SiO2 evenly distributed on a surface and a target of structure of In0,36Y0,04O0,60. The V-shaped screen, allowing in a wide range to regulate thickness of a layer was set up between a semi-conductor target and a substrate at a spraying.
A series from five glass-ceramic substrates was fixed on the holder parallel to the target plane along its long part. Due to the chosen parameters, simultaneous dispersion of two targets was carried out.
A separate films from different targets have been sprayed for assessment of layer and interlayer thickness. The thickness of the film was measured at various sites after some hours of drawing it on substrates, rotating with the set speed by means of the interferometer MII-4. The measurement points of thickness were fixed concerning to a substrate and target arrangement. The measured thickness of a film were approximated depending on distance to the substrate edge. Taking into account time of dispersion and the period of rotation of a roundabout, the thickness of the film received for one turn was calculated. The thickness of a layer of the second phase of structure was similarly defined.
The element structure of films was defined on a power dispersive x-ray detachable device Oxford INCA Energy 250 to a scanning electronic microscope JEOL JSM-6380 LV. Electric resistance was investigated on the automated universal measuring complex. High-frequency magnetic properties (valid μ/ and imaginary μ// parts of a complex magnetic permeability) were measured on frequency of 50 MHz by a technique [7].
Electric properties
On fig.1 dependence of specific electric resistance ρ from thickness of a layer In0,36Y0,04O0,60 for considered multilayered structure is presented. Its look in systems with Si, C, Cu, Te3Bi2 is similar to dependence for system [(Co0,45Fe0,45Zr0,10)0,35(Al2O3)0,65/α-Si:H]30 [8]. In the considered case there is a range of thickness of a layer in which considerable change of ρ(h) is observed.
The multilayered structure of a composite-semiconductor is the difficult heterophase system, one of which key parametres is thickness of a semi-conductor layer (h). At thickness of InIn0,36Y0,04O0,60 less than 0.4 nanometers, the phase of the semiconductor has an island structure and owing to minimisation of internal energy of a growing film at self-organizing (fig.2a) concentrates on metal granules. Such morphology essentially does not affect electrotransfer in composite layers. At h from 0.5 to 1.2 nanometers the low-impedance channels of conductivity are formed. At smaller thickness of the semiconductor, the electrotransfer according to the scheme can prevail: metal granule – semiconductor – dielectric - metal granule (fig.2b). In process of h increase, the contribution to conductivity of such transitions will increase, and at 1.2 nanometers the resistance is completely defined by carrying-out channels (fig.2c). The further increase of h leads to increase of a distance between the metal granules and to increase of ρ.
The temperature dependences of electric resistance (R)
of samples were investigated for confirmation of the assumption on change of channels of transfer of a charge in multilayered heterogeneous structures {(Co0,41Fe0,39B0,20)0,34
(SiO2)0,66/[In0,36Y0,04O0,60]}93 with increase in thickness of a layer. Thermal processing of complicated heterogeneous system should be accompanied by nuclear reorganization and lead to emergence of energy of activation of electric conductivity. The assessment of energy of activation of electric conductivity (Ea) was carried out on dependences of lnR from 1/T after annealing at various temperatures. The temperature dependence of electric resistance of considered multilayered heterogeneous structure at thickness of a composite of h1 = 4.4 nm and thickness of a semiconductor of h2 = 1.4 nm is presented as an example on fig.3.
When heating in a wide interval of temperatures and cooling after heating to 480°С, the electric resistance has a linear site in lnR co-ordinates from 1/T in a range 40–138°С. Therefore, temperature dependence of electric resistance can be described by Arrenius’s equation
ρ= ρ0·exp(–EaR/kT),
where ρ0 – constant; EaR – energy of activation of electric conductivity; k – Boltsman constant; T – absolute temperature. The equation also allows to estimate energy of activation of conductivity.
On fig.4 temperature dependences of electric resistance of multilayered heterogeneous structures are presented at various h1 and h2 values: a) 2.9 and 0.4 nanometers; b) 4.7 and 0.8 nanometers; c) 5.1 and 1.1 nanometers; d) 4.4 and 1.4 nanometers. By arrows on schedules is specified energy of activation of electrotransfer at temperatures above room after the corresponding annealing.
The analysis of temperature dependences of electric resistance after consecutive heatings showed that change of R(T) for heterogeneous systems with various thickness of a semi-conductor layer is accompanied by insignificant growth of energy of activation of electrotransfer at increase of annealing temperature. An exception is the multilayered structure at h1 = 2.9 nanometers and
h2 = 0.4 nanometer in which after annealing above 600°С the energy of activation of electrotransfer made
1.1 electron volts that is much higher, than for heterogeneous structures with thickness of a layer from 0.8 to 1.4 nanometers after similar heat treatment.
Nonmonotonicity of increase of electric resistance is shown when heating from 300 to 600°С in a range of a layer thickness of 0.8–1.1 nanometers. It can be connected with change of structure of heterogeneous system or structure and concentration of defects. All these features are shown at those thickness of a layer, when its role in conductivity is essential. It is possible to believe that the reason of nonmonotonic increase of electric resistance is existence of a quasitwo-dimensional percolation grid In0,36Y0,04O0,60. Besides, the energy of activation of electrotransfer after annealing above 600°С is much lower, than in a case with h1 = 2.9 nanometers and h2 = 0.4 nanometers, that also confirms the given guesses.
After formation of a continuous semi-conductor layer (h = 1.4 nanometers) at 300–600°С, R(T) changes almost on three orders that much more, than in multilayered structures with smaller thickness of a layer. It is necessary to note, that in system with h1 = 4.4 nanometers and
h2 = 1.4 nanometers, energy of activation of electric resistance after annealing at 550°C more than after processing at 700°C that was not observed in structures with smaller thickness of a layer.
Research of temperature processing of metal-dielectric nanocomposites showed that when heating to temperatures which are not leading to essential structural changes, electric resistance in structures raises to percolation threshold [9, 10]. In compound In0,36Y0,04O0,60 annealing to 300°С lead to increase in conductivity [11, 12]. On fig.5 presented dependences of specific electric resistance on thickness of a layer In0,36Y0,04O0,60 for considered multilayered structures in an initial condition (1) and after annealing are at 300°С (2–4). At h < 1 nanometers the ρ of annealed samples increases, and at h > 1.1 nanometers it decreases rather nase values. This is one more proof of change of the phases involved in electrotransfer with increase in thickness of a layer.
Research of structure and gas sensitivity of a semi-conductor film In0,36Y0,04O0,60 showed that in an initial condition it has amorphous structure, and at annealing above 400°С it crystallises. Sensing properties in oxide are observed only in a crystalline state, and at addition of restoring gases electric resistance of films goes down [13–15].
For considered heterogeneous multilayered structure influence of hydrogen on electric resistance is investigated. It is established that at annealing above 400°С the structure of the gas environment influences on electric conductivity of samples, if thickness of a layer more than 0.83 nanometers. Thus considerable influence of hydrogen on ρ films is observed at h > 1 nanometer (fig.6, 7). Such regularities testify to course of crystallisation of oxide In0,36Y0,04O0,60 when heating above 400°С that can be shown as increase of electric resistance on dependences of R(T) (fig. 4 b–4d).
Change of a sign of influence of hydrogen on electric resistance of samples at various temperature of processing (fig.6) is an interesting feature of this multilayered heterogeneous structure. So, if the sample was annealed at 400°С, the regenerative gas lowers R, and after heat treatment at 600°С, electric resistance raises that is not difinitive for this semi-conductor material. Change of a sign of gas sensitivity is possible at change of conductivity type of the the semiconductor.
The electronic theory of chemical sorption and catalysis, based on superficial electronic conditions of semiconductors [13] is used for explanation of changes of electroconductivity of multilayered structure at contact with the gas environment of various structures. Molecules adsorbed on a surface of oxide of gas can give electrons (donors) or attach them to themselves from oxide (acceptors). As at heat treatment of multilayered structure for 10 minutes at 400°С the temporary dependence of electric resistance, typical for the n-type semiconductor (fig.6a) is observed, adsorption of molecules of an acceptor leads to creation of the on-surface areas poor by electrons and reduction of an electrical conductivity at introduction of argon and air. It testifies to dominating influence on conductivity of semi-conductor layers of In0,36Y0,04O0,60. At adsorption of molecules of donor type, the outer layer on oxide of n-type enriched with electrons that increases a structure electrical conductivity at hydrogen adsorption is being created.
At the increased temperature it is necessary to consider diffusion between composite and semi-conductor layers. B possesses the greatest factor of diffusion, proceeding from film structure. Probably, introduction of its atoms into structure of the semiconductor changes its electric conductivity from n-type to p-type and reaction to the adsorbed gases (fig.6b). The temperature of annealing at which the sign of gas sensitivity changes, correlates with maximum temperature on R(T) dependences. Besides, for the studied film at h1 = 4.4 nanometers and h2 = 1.4 nanometers energy of activation of electrotransfer went down when heated from 580 to 700°С that also can be connected with introduction of atom of boron in a crystal lattice of In0,36Y0,04O0,60 layers.
Magnetic properties
Transition from a superparamagnetic to ferromagnetic structure at formation of a continuous layer of a semiconductor and to achieve of specific electric resistance of structure about 0.005 Ohm·m [16] for systems {[(Co0,41Fe0,39B0,20)0,34(SiO2)0,66]/
Si]}94, {[(Co0,41Fe0,39B0,20)0,34(SiO2)0,66]/[C]}46, {[(Co0,41
Fe0,39B0,20)0,34(SiO2)0,66]/[Cu]}93 and {[(Co0,41Fe0,39B0,20)0,34
(SiO2)0,66]/[Te3Bi2]}101. Systems investigated by authors of a composite–semiconductor type have higher ρ in all range of thickness of layers (fig.2, 4). However, as measurements of R(T) showed, for studied structure there are intervals of temperatures where considerable reduction of specific resistance is observed. So, for multilayered heterogeneous system with a layer from In0,36Y0,04O0,60 it is an interval from 250 to 350°С. Besides, fall of ρ is possible at annealing in the atmosphere containing hydrogen.
Dependences of valid (μ/) and imaginary (μ//) parts of complex magnetic permeability of the studied structure in an initial and annealed condition are presented on fig.8. The analysis of μ/(h) and μ//(h) revealed that in a range of thickness of a layer of 1.0–1.5 nm maxima of a complex magnetic permeability is observed. The place of a maximum correlates with dependences of electric resistance of the samples (fig.5), however μ/ and μ// remain small. It is possible, this results from the fact that as a result of heat treatment specific electric resistance of heterogeneous structure remained slightly above, than 0.005 Ohm·m. Growth of magnetic permeability of a semi-conductor layer in thickness of 1.2–1.4 nm relates with strengthening of interaction between ferromagnetic granules of composite layers through conductivity electrons.
It should be noted that the carried out research show that the thickness of a layer In0,36Y0,04O0,60 defines the electrotransfer mechanism. At h smaller than 0.5 nm transfer of a charge is defined by a composite (Co0,41Fe0,39
B0,20)0,34(SiO2)0,66, which structure is before percolation threshold. At thickness from 0.5 to 1.2 nm, conductivity redistribution from electrotransfer metal–dielectric–metal to channels metal–semiconductor–metal is observed.
Increase in electric resistance when heating in a range from 300 to 500°С relates to crystallisation of a semi-conductor layer. Change of a sign of gas sensitivity is connected with change its conductivity type, that can be explained by boron diffusion from a composite layer and its introduction into a crystal lattice of a layer In2O3.
It is established that thermal processing for 30 min at 300°С in the hydrogen atmosphere at pressure of 7.8 Torr leads to appearance in multilayered heterogeneous structure of a maximum on dependences μ/(h) and μ//(h)
in a range of thickness of a layer of 1.0–1.5 nm, which situation correlates with dependences of electric resistance of samples on thickness of a semi-conductor layer.
This work was supported by RFFR (project number 13-02-97512-r_tsentr_a).
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