Correlations in Infrared Spectra of Nanostructures

ISSN 1063-7834, Physics of the Solid State, 2015, Vol. 57, No. 12, pp. 2373–2381. © Pleiades Publishing, Ltd., 2015. Original Russian Text © I.A. Averin, A.A. Karmanov, V.A. Moshnikov, I.A. Pronin, S.E. Igoshina, A.P. Sigaev, E.I. Terukov, 2015, published in Fizika Tverdogo Tela, 2015, Vol. 57, No. 12, pp. 2304–2312.

SEMICONDUCTORS

Correlations in Infrared Spectra of Nanostructures Based on Mixed Oxides I. A. Averina, A. A. Karmanova, V. A. Moshnikovb,c, I. A. Pronina, S. E. Igoshinaa, A. P. Sigaeva, and E. I. Terukovd a Penza

State University, ul. Krasnaya 40, Penza, 440026 Russia St. Petersburg Electrotechnical University “LETI,” ul. Professora Popova 5, St. Petersburg, 197376 Russia c Peter the Great St.Petersburg Polytechnic University, Politekhnicheskaya ul. 29, 195251 Russia d Ioffe Physical-Technical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia e-mail: [email protected] b

Received April 30, 2015; in final form, June 1, 2015

Abstract—This paper has presented experimental data on the infrared spectroscopic investigation of nanostructures based mixed oxides. Nanostructures in the form of porous thin films deposited on oxidized singlecrystal silicon substrates have been synthesized by the sol–gel method. The qualitative composition of filmforming sols and the related nanostructures has been examined. Correlations relating the coefficient of transmission of infrared radiation through the materials under investigation and their quantitative composition have been established. The processes occurring during the annealing of the nanostructures in the temperature range from 100 to 600°C have been analyzed. DOI: 10.1134/S1063783415120069

1. INTRODUCTION Currently, nanostructures based on mixed oxides are of great interest for fundamental investigations and technical applications [1, 2]. These materials have found a wide use as photocatalysts, phosphors, sensitive elements of gas sensors and vacuum sensors, functional electronic devices based on acoustic waves, etc. For example, nanostructures based on ZnO–ZnO : Fe homojunctions have been used as new-type thermoelectric gas sensors with the maximum sensitivity observed at low temperatures [3, 4]. Doped oxides of titanium and zinc are promising materials for use as photocatalysts that make it possible to decompose the majority of complex organic pollutants [5]. Nanostructures based on SiO2–SnO2, SiO2–In2O3–SnO2, and SiO2–SnO2–ZnO oxides have been used for the fabrication of sensitive elements of chemoresistive gas sensors [6, 7] and vacuum sensors [8]. Suggestions have been made to increase the efficiency of photovoltaic converters based on Grätzel cells by means of the use of mixed oxides in their design [9]. Nanostructures based on mixed oxides have been prepared using different methods [10, 11], among which special mention should be made of the sol–gel technique [12–15]. This technique makes it possible to synthesize nanomaterials with desired structures and properties and to perform the monitoring of the surface of the material at the early stage of its preparation. Moreover, this method is technologically simple and

ecologically safe. A deterrent factor of broad commercial introduction of the sol–gel method for the manufacture of gas sensors and multi-sensor systems is the lack of advanced techniques for analyzing the composition of submicrophases arising during the formation of a structure in systems of hierarchical pores. Classical methods used for investigating sol–gel-derived systems (atomic force microscopy, X-ray diffractometry, etc.) are not effective for the analysis of nanophases in the bulk of the material. At present, there has been developed a method of internal friction [16, 17], the advantage of which is that it provides a means for determining submicroprecipitates throughout the volume of the formed nanostructured layers. The sol–gel process of formation of nanostructures consists of three main stages [18]: (1) the formation of fragments of the sol; (2) the formation of a chemical structure of the gel based on sol particles; and (3) the formation of a structure of the dried xerogel. In the first stage, primary fragments of the sol are combined into aggregates of fractal nature, and their development can occur up to the gel formation. In the second stage, under the conditions of spinodal decomposition, there arise fractal structures that represent components of a percolation cluster. In the third stage, the gel is subjected to heat treatment, during which it transforms into a xerogel; i.e., the nanostructure is completely formed. Theoretical and experimental data on the formation of nanostructures based on mixed

2373

2374

AVERIN et al.

oxides by means of the sol–gel method, which were obtained using different methods, often have not been systemized and even have been contradictory [19]. Therefore, the investigation of the synthesis of nanostructures within a unified experimental approach is an important problem. In this work, the qualitative and quantitative compositions of the materials at different stages of the synthesis, as well as the processes occurring during the annealing of the samples, have been investigated using infrared (IR) spectroscopy [20]. 2. SAMPLE PREPARATION AND EXPERIMENTAL TECHNIQUE Nanostructures of the compositions SnO2–SiO2 and SiO2–SnO2–In2O3 were prepared from sols based on tetraethoxysilane (TEOS) hydrolyzed in an acidic medium. The tin salt SnCl4 ⋅ 5H2O and the indium salt In(NO3)3 ⋅ 4.5H2O were used as modifying additives. Ethyl alcohol served as the solvent. The sol was deposited on oxidized single-crystal silicon substrates (5 × 5 mm in size) by spinning at a table rotation speed of 3000 min–1. The annealing was performed in the temperature range from 100 to 600°C for 30 min in air. The qualitative and quantitative compositions of the film-forming sols with different mass fractions of SnO2 and the related nanostructures were investigated using IR spectroscopy. It was assumed that, during the heat treatment, the quantitative composition of nanostructures remains unchanged. This assumption is consistent with the results obtained in [21] using X-ray photoelectron spectroscopy. In that work, it was shown that the molar ratios of tin dioxide and silicon dioxide in the annealed films correspond to those of the materials in the sol. The IR transmission spectra of the sols containing from 0 to 90 mass % SnO2 were measured on an FSM 1201 Fourier transform infrared (FTIR) spectrometer (OOO Infraspek, Russia) using

an MNPVO36 attachment (with a ZnSe prism)) for frustrated total internal reflection spectroscopy. 3. EXPERIMENTAL RESULTS AND DISCUSSION In the IR transmission spectra of the studied sols (Fig. 1), there are absorption bands that are characteristic of both the products of TEOS hydrolysis (795, 880, 970 cm–1) and the products of TEOS polycondensation (1045, 1080 cm–1), which indicates an incompleteness of the hydrolytic polycondensation reaction. The absorption lines observed at frequencies of 1170, 1275, 1320, 1380, and 1455 cm–1 suggest that the sol contains ethyl alcohol and water. The copolycondensation of TEOS and hydroxides of the modifying compounds, i.e., Sn(OH)4, apparently is indicated by a weak absorption band with the maximum at a frequency of 1420 cm–1, which characterizes vibrations of oxygen atoms in the Si–O–Sn bonds [22]. The results obtained from the analysis of the IR transmission spectra of the TEOS-based film-forming sols containing the modifying compounds are presented in Table 1. The absorption peaks at a frequency of 970 or 1080 cm–1 are used to determine the quantitative composition of the studied sols [23, 24]. The absorption band with the maximum at 1420 cm–1 is ignored because of the weak intensity. The analysis of the absorption peaks makes it possible to determine the concentration of silicon dioxide (c) formed upon the thermal decomposition of orthosilicic acid during the annealing of the sol deposited on the surface of the substrates. The concentration of tin dioxide (x) formed upon the thermal decomposition of Sn(OH)4 can be found for sols according to the following equation:

c + x = 100%.

(1)

Transmission, arb. units

1.0 0.8

90 mass % SnO2

0.6 0.4

O

0.2 0 700

0 mass % SnO2 900

1100 1300 Wavenumber, cm1

1500

1700

Fig. 1. IR transmission spectra of film-forming sols with different mass fractions of tin dioxide. The SnO2 content changes from 0 to 90 mass % with a step of 10 mass %. PHYSICS OF THE SOLID STATE

Vol. 57

No. 12

2015

CORRELATIONS IN INFRARED SPECTRA Table 1. Interpretation of the IR transmission spectra of the film-forming sols with different mass fractions of tin dioxide Position of the absorption lines, cm–1

Interpretation

795

Group sensitive to hydrolysis Si– O–C2H5, O2–Si–OH

880

O3–Si–OH

970

1170 1275 1320

Si–OH symmetric stretching vibrations Si–O–Si symmetric stretching vibrations Asymmetric vibrations of bridging oxygen atoms in the Si–O–Si bonds C–O stretching vibrations R–O–OH bending vibrations CH3 symmetric bending vibrations

1380

CH3 asymmetric bending vibrations

1420 1455

Si–O–Sn CH2 scissoring vibrations

1650

O–H bending vibrations

1045 1080

of the spectra shown in Fig. 2 demonstrates that an increase in the mass fraction of silicon dioxide with respect to tin dioxide leads to a decrease in the fraction of the radiation transmitted through the studied sol. This indicates a change in the concentration of bonds corresponding to symmetric stretching vibrations of the Si–OH bonds and to asymmetric stretching vibrations of bridging oxygen atoms in the Si–O–Si bonds, respectively. Based on the experimental data, we obtained the dependence of the coefficient of transmission of the infrared radiation through the studied sols (T) on the mass fraction of silicon dioxide for the absorption peaks at frequencies of 970 (Fig. 3a) and 1080 cm–1 (Fig. 3b). The data presented in Fig. 3 are fairly accurately described within the framework of the Bouguer– Lambert–Beer law using the following exponential relationships:

T1(c) = 4.421exp(− 1.172 × 10 −3 c) − 3.741,

(a)

(b)

0.30


0.6

0.25

0.5

0.20

0.4

0.15

0.3

0.10

0.2

0.05

90 mass % SnO2

0 mass % SnO2

0 mass % SnO2 920

940 960 980 1 Wavenumber, cm

1000

1020

1040

1060 1080 1100 1 Wavenumber, cm

1120

Fig. 2. IR transmission spectra of the studied sols in the spectral ranges of (a) 900–1000 and (b) 1020–1120 cm–1. The SnO2 content changes from 0 to 90 mass % with a step of 10 mass %. PHYSICS OF THE SOLID STATE

Vol. 57

No. 12

2015

(4)

(5) x = 100 + 122.07 ln(5.464T2 + 0.336). These relationships allow us to calculate the quantitative composition of film-forming sols with different mass fractions of tin dioxide and, consequently,

90 mass % SnO2

0.1 900

(2)

T2(c) = 0.183 exp(− 8.192 × 10 −3 c) − 0.067, (3) Taking into account formula (1), expressions (2) and (3) can be represented in the form x = 100 + 853.242 ln(0.226T1 + 0.846),

Let us consider the IR transmission spectra of the studied sols in the spectral ranges of 900–1000 (Fig. 2a) and 1020–1120 cm–1 (Fig. 2b). The analysis

0.7

2375

2376

AVERIN et al.

0.7

0.12 (a)

1

0.6

(b) 0.10

2

0.08 T2, arb. units

T1, arb. units

0.5 0.4 0.3 0.2 0.1

0.06 2 0.04

1

0.02 0

20

40 60 C, mass %

80

100

0

20

40 60 C, mass %

80

100

Fig. 3. Coefficient of transmission of the infrared radiation through the studied sols as a function of the SiO2 mass fraction for absorption peaks at frequencies of (a) 970 and (b) 1080 cm–1: (1) experimental data and (2) approximation.

the composition of the related nanostructures. The quantitative composition of multicomponent sols, which are used to obtain nanostructures of complex composition (for example, SiO2–SnO2–In2O3), can also be determined within the approach described above. However, the solution of this problem is beyond the scope of the present study. Infrared spectroscopy makes it possible to investigate the qualitative and quantitative compositions of not only film-forming sols but also the corresponding nanostructures based mixed oxides in the form of porous thin films deposited on the surface of oxidized single-crystal silicon substrates. Figure 4 shows the IR transmission spectra of the nanostructures based on the mixed SiO2–SnO2 and SiO2–In2O3–SnO2 oxides after the annealing at temperatures in the range from 100 to 600°C. For comparison, this figure also shows the IR transmission spectra of the substrates. The IR transmission spectra shown in Fig. 4 contain a number of characteristic absorption bands and peaks, which allow us to determine not only the qualitative composition of the nanostructures based on mixed oxides but also the processes occurring during the annealing of the samples. The results obtained from the analysis of the specific features of the IR transmission spectra of the nanostructures under investigation are summarized in Table 2. The qualitative composition of the nanostructures under investigation can be judged from the presence of absorption bands with maxima at frequencies of 615, 670, 805, 970, 1110, and 1450 cm–1. The absorption peaks at 615 and 805 cm–1 are characteristic of oxidized single-crystal silicon substrates, whereas the specific features observed at 670, 970, and 1450 cm–1 correspond to the nanostructure formed on their surface. Intense vibrations in the region of 1110 cm–1 are

typical of both the substrate and the nanostructures of the compositions SiO2–SnO2 and SiO2–SnO2–In2O3. However, in the latter case, these vibrations are the most pronounced due to the formation of the silica network (matrix). It should be noted that the absorption band at 670 cm–1, most likely, corresponds to the formation of SnO2 clusters. Their incorporation into Table 2. Interpretation of the IR transmission spectra of nanostructures based on the mixed SiO2–SnO2 and SiO2– SnO2–In2O3 oxides Position of the absorption lines, cm–1 615 670 685 740 805 970

Interpretation Si–Si symmetric stretching vibrations Sn–O–Sn symmetric stretching vibrations Sn–O–Sn asymmetric stretching vibrations C–O–H bending vibrations Si2O torsional vibrations

1650 2360

Si–OH symmetric stretching vibrations Asymmetric vibrations of bridging oxygen atoms in the Si–O–Si bonds Asymmetric vibrations of bridging oxygen atoms in the Si–O–Si bonds H–O–H bending vibrations Atmospheric CO2

2970

CH3 asymmetric stretching vibrations

3100–3700

O–H symmetric stretching vibrations

1110 1450

PHYSICS OF THE SOLID STATE

Vol. 57

No. 12

2015

CORRELATIONS IN INFRARED SPECTRA

2377

0.8 (a)


5

6

7

0.6 1

4

0.4

3

0.2

2 0 4350

3950

3550

3150

2750

2350

1950

1550

1150

750

Wavenumber, cm1 (b)


0.8 6

1

7

0.6 5 0.4

4 3

0.2

2 0 4350

3950

3550

3150

2750 2350 1950 Wavenumber, cm1

1550

1150

750

Fig. 4. IR transmission spectra of the nanostructures based on (a) SiO2–SnO2 and (b) SiO2–SnO2–In2O3 oxides after annealing at different temperatures T = (2) 100, (3) 200, (4) 300, (5) 400, (6) 500, and (7) 600°C. Curves 1 show the IR spectra of the Si substrate.

the matrix is indicated by a weak absorption band with the maximum at a frequency of 1450 cm–1, which characterizes asymmetric stretching vibrations of the Si–O–Sn bonds. This is confirmed by the experimental data obtained by other methods, for example, atomic force microscopy [25]. It is known that the annealing of nanostructures based on mixed oxides is accompanied by various physicochemical processes, which determine their final composition and structure [26]: (i) evaporation of a solvent, (ii) thermal decomposition of the corresponding hydroxides, (iii) transition of some of the formed oxides from the amorphous state to the crystalline state; (iv) changes in the total porosity and the average size of pores in the film; (v) collapse of fractal aggregates; etc. Infrared spectroscopy also makes it possible to track the occurrence of the majority of the aforemenPHYSICS OF THE SOLID STATE

Vol. 57

No. 12

2015

tioned processes. In particular, the evaporation of a solvent can be judged by analyzing a change in the intensity of the IR absorption lines at frequencies of 740, 1650, 2970, and 3100–3700 cm–1. These lines indicate the presence of ethyl alcohol and water in the studied films. The analysis of the IR transmission spectra shown in Fig. 4 demonstrates that the nanostructures based on the mixed SiO2–SnO2 oxides are characterized by an almost complete evaporation of H2O and C2H5OH at a temperature of 400°C. The presence of diffuse vibrations of weak intensity in the spectra at frequencies of 3500–3700 cm–1, most likely, corresponds to the adsorption of atmospheric moisture on the films. The nanostructures based on the mixed SiO2–SnO2–In2O3 oxides are characterized by the spectra containing the absorption band in the range of 3100–3700 cm–1 even at a temperature of 600°C. This fact has two possible explanations: either,

2378

AVERIN et al.

(a)

(b) 1

1


0.5

7 6

7 6

0.50

5 0.4

5

4

4

0.40

0.3

0.2 3

0.30

3 0.1 2

0.20 650

660

670

2 680

690

0 850

910

(c)

970

1030

1090

1150

(d)

0.47

0.47 1 1

0.43

7

0.43


6 0.39 0.39

5 0.35

4

7 6 5 4

0.35 0.31

3 0.31

0.27

3 2

2 0.27 650

0.23 670 680 660 690 Wavenumber, cm1

790

960

1000 1120 Wavenumber, cm1

1200

Fig. 5. Characteristic regions of the IR transmission spectra of the nanostructures based on (a, b) SiO2–SnO2 and (c, d) SiO2– SnO2–In2O3 oxides after annealing at different temperatures T = (2) 100, (3) 200, (4) 300, (5) 400, (6) 500, and (7) 600°C. Curves 1 show the IR spectra of the Si substrate.

during the annealing, the solvent is incompletely evaporated, which is highly improbable, or the studied films have a high porosity, and, consequently, a large amount of water is adsorbed on the surface and in the bulk of the film. A high porosity of the studied material is indirectly indicated by a relatively high intensity of the absorption peak at 2360 cm–1, which characterizes the stretching vibrations of the C=O bonds in atmospheric carbon dioxide.

The thermal decomposition of the corresponding hydroxides (Si(OH)4, Sn(OH)4, and In(OH)3) and the transition of some of them from the amorphous state to the crystalline state are indicated by a change in the intensity of the absorption bands with maxima at 670, 970, and 1110 cm–1 (Fig. 5). The analysis of the IR transmission spectra of the nanostructures based on mixed oxides (Figs. 5a and


Vol. 57

No. 12

2015


5c) demonstrates that the thermal decomposition of tin hydroxide occurs already at a temperature of 100°C. This process is responsible for the appearance of a weak absorption band at 670 cm–1 in the spectra, which correspond to symmetric stretching vibrations of the Sn–O–Sn bonds. It seems likely that tin dioxide in the crystalline state is formed at a temperature of 400°C. This corresponds to the appearance of an absorption peak at 685 cm–1, which characterizes the asymmetric stretching vibrations of the Sn–O–Sn bonds. It should be noted that the presented data are completely consistent with the results of the measurements by alternative methods, including the thermogravimetric analysis. For example, in [27], it was shown that the primary decomposition of tin hydroxide occurs at a temperature of approximately 343 K with the formation of α-stannic acid SnO2 ≤ xH2O (1 < x ≤ 2). The subsequent heating of the sample results in a gradual removal of water, the formation of β-stannic acid (x < 1) at 619 K, and a further gradual dehydration of the material. The crystallization of tin dioxide begins to occur at temperatures below 670 K, whereas typical crystallites of SnO2 with the tetragonal structure are formed at a temperature of 823 K. The general scheme of the thermal decomposition of tin hydroxide has the following form: 343 K Sn(OH) 4 ⎯⎯⎯⎯ → SnO 2 ⋅ x H 2O(1 < x ≤ 2) 619 K 670 K ⎯⎯⎯⎯ → SnO 2 ⋅ x H 2O( x < 1) ⎯⎯⎯⎯ →(SnO 2 ) cr . (6) When considering the process of thermal decomposition of silicon hydroxide, it should be taken into account that the formation of the sol is accompanied not only by the hydrolysis of TEOS but also by its polycondensation. These processes result in the formation of an ultra-fine silica network formed by silicon–oxygen bonds. In turn, this leads to the fact that, in the IR transmission spectra of the studied nanostructures (Figs. 5b and 5d), which were annealed at different temperatures, there appears a broad strong absorption band with the maximum at a frequency of approximately 1110 cm–1. The presence of a weak absorption peak at 970 cm–1 in the spectra of porous thin films heat-treated at temperatures in the range from 100 to 200°C indicates an incomplete polycondensation of Si(OH)4. The disappearance of this peak at temperatures above 300°C characterizes the termination of the decomposition of the silicon hydroxide. The annealing of the material is accompanied by changes in the width and intensity of the absorption band at 1000–1200 cm–1, most likely, due to a partial collapse of fractal aggregates, which results in changes of the concentration and the angle between the atoms involved in the Si–O–Si bonds of the cage-like structure [28]. As in the case of thermal decomposition of tin hydroxide, the experimental data obtained using IR spectroscopy are completely consistent with the results of the thermogravimetric analysis. For exam-


Vol. 57

No. 12

2015

2379

ple, in [29], it was shown that the thermolysis of Si(OH)4 is accompanied by two endothermic effects: (i) dehydration of water in the molecular form, which is terminated at a temperature of approximately 700°C; and (ii) destruction of the terminal (silanol) OH groups of the silicon hydroxide polycondensate, which is terminated at a temperature above 250°C. The general scheme of the thermal decomposition of silicon hydroxide has the following form: |

|

− Si−O−Si−OH | 280 °C

|

(7)

700 °C

⎯⎯⎯⎯ → SnO 2 ⋅ x H 2O ⎯⎯⎯⎯ → SiO 2. It should be noted that the process of thermal decomposition of indium hydroxide is investigated in a similar manner using the absorption peak at a frequency of 410 cm–1, which corresponds to vibrations of the In–O bonds. However, this peak is located outside the measurement range of the spectrometer used in our study. Consequently, the decomposition of indium hydroxide upon heating can be analyzed only indirectly using the absorption peak at 1110 cm–1, which is characterized by a small splitting at temperatures in the range from 500 to 600°C (Fig. 5d). It seems likely that this feature can be associated with the formation of Si–O–In bonds. From the data of the thermogravimetric–differential thermal analysis [30], it is known that the decomposition of In(OH)3 occurs at a temperature of 288°C. A further increase in the temperature leads to the dehydration of the formed oxide. The complete removal of water is observed at 600°C. The general scheme of the thermal decomposition of indium hydroxide has the following form: 288 °C 2In(OH)3 ⎯⎯⎯⎯ → In 2O3 ⋅ x H 2O (8) 600 °C ⎯⎯⎯⎯ → In 2O3. Moreover, as part of this work, we investigated the quantitative composition of the nanostructures based on the mixed SiO2–SnO2 oxides in the form of thin films deposited on the surface of oxidized single-crystal silicon substrates (the annealing was performed at a temperature of 600°C). The IR transmission spectra of the films with different mass fractions of tin dioxide are shown in Fig. 6. The spectral range from 1050 to 1170 cm–1 was chosen based on the fact that it includes the absorption peak at 1110 cm–1, which corresponds to asymmetric stretching vibrations of bridging oxygen atoms in the Si–O–Si bonds. The use of the absorption peak at 670 cm–1, which corresponds to stretching vibrations of the Sn–O–Sn bonds, is complicated because of its low intensity. The influence of the silicon substrate on the IR transmission spectra of the nanostructures under investigation was minimized using the method of specular reflection (the measurements were performed with a PZO30 attachment). Based on the results of the analysis of the IR transmission spectra considered above, we plotted the coef-

2380

AVERIN et al.

0.24

0.24 (a)

(b)

0.20

0.22 2

90 mass % SnO2 Transmission, arb. units


0.22

85 0.18 0.16

80 70 60

0.14

50

0.20 0.18 1 0.16 0.14

0.12

0.12

0.10 1050 1070 1090 1110 1130 1150 1170 Wavenumber, cm1

0.10 0

10

20

30 40 c, mass %

50

60

Fig. 6. (a) IR transmission spectra of the nanostructures based on the SiO2–SnO2 oxides. (b) Coefficient of transmission of the infrared light through the studied sols as a function of the SiO2 mass fraction: (1) experimental data and (2) approximation.

ficient of transmission of the infrared radiation through the studied films as a function of the mass fraction of silicon dioxide (Fig. 6b). This dependence within the framework of the Bouguer–Lambert–Beer law is described by the exponential relationship

T3(c) = 0.111exp(− 0.049c) + 0.12.

(9)

The mass fractions of tin dioxide and silicon dioxide in the films based on the SiO2–SnO2 oxides are related by the expression similar to formula (1). Therefore, relationship (9) can be represented in the form

x = 100 + 20.392 ln(9.002T3 − 1.082).

(10)

Using relationship (10) and IR transmission spectra, we can determine the quantitative composition of the nanostructures based on the SiO2–SnO2 oxides. Of particular interest are the films in which the concentration of the conducting phase exceeds the percolation threshold [31], i.e., the SnO2 mass fraction of more than 50 mass %. These films are used as sensitive elements of gas sensors [32] and vacuum sensors of the adsorption type [33].

infrared spectroscopy. It was shown that the absorption peaks at frequencies of 970 and 1080 cm–1, which correspond to symmetric stretching vibrations of the Si–OH bonds and to asymmetric stretching vibrations of bridging oxygen atoms in the Si–O–Si bonds, respectively, make it possible to determine the quantitative composition of the film-forming sols. The processes occurring in the nanostructures based on mixed oxides of the compositions SiO2–SnO2 and SiO2– SnO2–In2O3 during the annealing in the temperature range from 100 to 600°C were investigated. The experimental data on the thermal decomposition of hydroxides of tin, indium, and silicon, as well as the data on the transition of tin dioxide from the amorphous state to the crystalline state, were presented. It was demonstrated that the absorption band with the maximum at a frequency of 1110 cm–1, which corresponds to asymmetric stretching vibrations of bridging oxygen atoms in the Si–O–Si-bonds, makes it possible to determine the quantitative composition of the nanostructures based on the mixed SiO2–SnO2 oxides, where the concentration of the conducting phase exceeds the percolation threshold.

4. CONCLUSIONS The nanostructures based on mixed oxides of the compositions SiO2–SnO2 and SiO2–SnO2–In2O3 were synthesized by the sol–gel method. The qualitative composition of multicomponent film-forming sols and the related nanostructures was studied using

ACKNOWLEDGMENTS This study was supported by the Ministry of Education and Science of the Russian Federation within the framework of the basic part of the state assignment for the Penza State University (project no. 2014/151,


Vol. 57

No. 12

2015


project code 117), the Scholarship from the President of the Russian Federation (grant no. SP-4686.2013, and the Ministry of Education and Science of the Russian Federation within the framework of the project part of the state assignment for the St. Petersburg Electrotechnical University “LETI” (project no. 16.2112.2014/K). REFERENCES 1. G. Sun, F. Qi, S. Zhang, Y. Li, Y. Wang, J. Cao, H. Bala, X. Wang, T. Jia, and Z. Zhang, J. Alloys Compd. 617, 192 (2014). 2. O. G. Ellert, M. V. Tsodikov, and V. M. Novotortsev, Usp. Khim. 79 (8), 758 (2010). 3. I. A. Pronin, D. Tz. Dimitrov, L. K. Krasteva, K. I. Papazova, I. A. Averin, A. S. Chanachev, A. S. Bojinova, A. Ts. Georgieva, N. D. Yakushova, and V. A. Moshnikov, Sens. Actuators, A 206, 88 (2014). 4. L. K. Krasteva, D. Ts. Dimitrov, K. I. Papazova, N. K. Nikolaev, T. V. Peshkova, V. A. Moshnikov, I. E. Gracheva, S. S. Karpova, and N. V. Kaneva, Semiconductors 47 (4), 586 (2013). 5. I. A. Pronin, B. V. Donkova, D. Ts. Dimitrov, I. A. Averin, Zh. A. Pencheva, and V. A. Moshnikov, Semiconductors 48 (7), 842 (2014). 6. S. Majumder, S. Hussain, R. Bhar, and A. K. Pal, Vacuum 81, 985 (2007). 7. I. A. Averin, I. A. Pronin, and A. A. Karmanov, NanoMikrosist. Tekh., No. 5, 23 (2013). 8. I. A. Averin, S. E. Igoshina, V. A. Moshnikov, A. A. Karmanov, I. A. Pronin, and E. I. Terukov, Tech. Phys. 60 (6), 928 (2015). 9. L. Kavan, M. Zukalova, O. Vik, and D. Havlicek, ChemPhysChem 15 (6), 1056 (2014). 10. M. V. Kalinina, V. A. Moshnikov, P. A. Tikhonov, V. V. Tomaev, and I. A. Drozdova, Glass Phys. Chem. 29 (3), 322 (2003). 11. N. N. Vershinin, N. N. Aleinikov, V. A. Bakaev, and O. N. Efimov, Ross. Nanotekhnol. 3 (5–6), 39 (2008). 12. A. A. Ponomareva, V. A. Moshnikov, and G. Suchaneck, in Handbook of Functional Nanomaterials, Ed. by M. Aliofkgazraei (Nova Science, New York, 2008), Vol. 2, Chap. 11, p. 265. 13. I. A. Pronin and M. V. Goryacheva, Surf. Coat. Technol. 235, 835 (2013). 14. I. A. Averin, A. A. Karmanov, V. A. Moshnikov, R. M. Pecherskaya, and I. A. Pronin, Izv. Vyssh. Uchebn. Zaved., Povolzh. Reg., Fiz.-Mat. Nauki, No. 2, 155 (2012).

15. C. J. Brinker and G. W. Scherer, Sol–Gel Science: The Physics and Chemistry of Sol–Gel Processing (Academic, San Diego, California, United States, 1990). 16. A. S. Il’in, A. I. Maksimov, V. A. Moshnikov, and N. P. Yaroslavtsev, Semiconductors 39 (3), 281 (2005). 17. Yu. N. Andreev, M. V. Bestaev, D. Ts. Dimitrov, V. A. Moshnikov, Yu. M. Tairov, and N. P. Yaroslavtsev, Semiconductors 31 (7), 714 (1997). 18. I. E. Gracheva, V. A. Moshnikov, and E. V. Abrashova, Materialovedenie, No. 6, 13 (2013). 19. A. A. Yelwande, M. E. Navgire, D. T. Tayde, B. R. Arbad, and M. K. Lande, Bull. Korean Chem. Soc. 33 (6), 1856 (2012). 20. I. A. Averin, A. P. Sigaev, A. A. Karmanov, I. A. Pronin, S. E. Igoshina, and A. A. Kudashov, in Proceedings of the International Symposium “Reliability and Quality,” Penza State University, Penza, May 26–June 1, 2014, Vol. 2, p. 133. 21. A. A. Ponomareva, V. A. Moshnikov, and G. Suchaneck, Tech. Phys. Lett. 37 [!](10), 892 (2011). 22. M. Aziz, S. S. Abbas, and W. R. W. Baharom, Mater. Lett. 91, 31 (2013). 23. I. A. Averin, A. A. Karmanov, R. M. Pecherskaya, and I. A. Pronin, in Proceedings of the International Symposium “Reliability and Quality,” Penza State University, Penza, May 21–31, 2012, Vol. 2, p. 181. 24. S. E. Igoshina, A. A. Karmanov, and A. P. Sigaev, Molodoi Uch., No. 8, 41 (2014). 25. I. E. Gracheva, A. I. Maksimov, and V. A. Moshnikov, J. Surf. Invest. [!]3 [!](5), 761 (2009). 26. A. A. Ponomareva, V. A. Moshnikov, and G. Suchanek, Materialovedenie 12, 45 (2011). 27. V. V. Ivanov, I. A. Sidorak, A. A. Shubin, and L. T. Denisova, Zh. Sib. Fed. Univ., Ser. Tekh. Tekhnol. 3 (2), 189 (2010). 28. A. A. Ponomareva, Candidate’s Dissertation (St. Petersburg Electrotechnical University “LETI,” St. Petersburg, 2013). 29. V. V. Avdin, L. Sh. Altynbaeva, and I. V. Krivtsov, Vestn. Yuzhno-Ural. Gos. Univ. 31, 60 (2010). 30. F. V. Motta, R. C. Lima, A. P. A. Marques, E. R. Leite, J. A. Varela, and E. Longo, Mater. Res. Bull. 45, 1703 (2010). 31. I. A. Pronin, I. A. Averin, V. A. Moshnikov, N. D. Yakushova, M. V. Kuznetsova, and A. A. Karmanov, NanoMikrosist. Tekh., No. 9, 15 (2014). 32. RF Patent 2532428 (08 September 2014). 33. RF Patent 2485465 (20 June 2013).

SPELL: OK


Vol. 57

No. 12

2015

2381

Translated by O. Borovik-Romanova