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Conference materials UDC 546.05; 538.975
DOI: https://doi.org/10.18721/JPM.153.352
Surface and electrophysical properties study of thin TiO2-SnO2 nanocomposite films
I. A. Gulyaeva 1H, A. P. Ivanishcheva \ M. G. Volkova 2, E. M. Bayan 2, V. V. Petrov 1
1 Research and Education Centre "Microsystem technics and multisensor monitoring systems", Southern Federal University, Taganrog, Russia; 2 Southern Federal University, Rostov-on-Don, Russia H [email protected]
Abstract. Thin nanocomposite films based on pure tin dioxide with a low content of titanium oxide (0, 1, 3, and 5 mol %) were obtained by solid-phase low-temperature pyrolysis. The thickness of the films obtained was up to 200 nm. The particle size of the TiO2-SnO2 nanomaterial lies in the range of 7—13 nm. Atomic force microscopy (AFM) showed that the films have a granular structure with a height difference of 11—114 nm. The surface of the film with a Ti concentration of 5 mol.% has a higher roughness compared to other samples. Force microscopy with a Kelvin probe (KPFM) revealed a surface potential, indicating the existence of a strong surface electric field. A small addition of titanium dioxide (1%) to the tin dioxide structure leads to the appearance of peak values of the surface potential, the value of which reaches 1325 mV. Studies of the temperature dependences of the obtained samples showed that the pure SnO2 film has the maximum resistance values and high nonlinearity. However, with a small addition of titanium dioxide (1%) to tin dioxide, the electrical resistance of the nanosized material sharply decreases and has indicators 4—5 orders of magnitude lower than those of pure SnO2 films.
Keywords: nanomaterials, thin films, pyrolysis, tin dioxide, titanium dioxide, surface potential, electrical properties
Funding: This work was financially supported by the RFBR, project No. 20-07-00653 A.
Citation: Gulyaeva I. A., Ivanishcheva A. P., Volkova M. G., Bayan E. M., Petrov V. V., Surface and electrophysical properties study of thin TiO2-SnO2 nanocomposite films. St. Petersburg State Polytechnical University Journal. Physics and Mathematics, 15 (3.3) (2022) 265-270. DOI: https://doi.org/10.18721/JPM.153.352
This is an open access article under the CC BY-NC 4.0 license (https://creativecommons. org/licenses/by-nc/4.0/)
Материалы конференции УДК 546.05; 538.975
DOI: https://doi.org/10.18721/JPM.153.352
Исследование поверхностных и электрофизических свойств тонких нанокомпозитных пленок состава TiO2-SnO2
И. А. Гуляева 1Н, А. П. Иванищева 1, М. Г. Волкова 2, Е. М. Баян 2, В. В. Петров 1
1 Научно-образовательный центр «Микросистемная техника и мультисенсорные системы мониторинга», Южный федеральный университет, Таганрог, Россия;
2 Южный федеральный университет, Ростов-на-Дону, Россия н [email protected]
Аннотация. Методом твердофазного низкотемпературного пиролиза были получены тонкие нанокомпозитные пленки на основе чистого диоксида олова с низким содержанием оксида титана (0, 1, 3 и 5 мол. %). Атомно-силовой микроскопией (АСМ) показано, что пленки имеют зернистую структуру с перепадом высот 11-114 нм. Методом Кельвин-зондовой силовой микроскопии (КЗСМ) на поверхности TiO2-SnO2
© Gulyaeva I. A., Ivanishcheva A. P., Volkova M. G., Bayan E. M., Petrov V. V., 2022. Published by Peter the Great St.Pe-tersburg Polytechnic University.
пленок с мольным соотношением Ti:Sn равным 1:99 обнаружен высокий поверхностный потенциал потенциала (Vb = 1325 мВ), показывающий существование сильного поверхностного электрического поля.
Ключевые слова: наноматериалы, тонкие пленки, пиролиз, диоксид олова, диоксид титана, поверхностный потенциал, электрофизические свойства
Финансирование: Работа выполнена при финансовой поддержке РФФИ, проект № 20-07-00653 А.
Ссылка при цитировании: Гуляева И. А., Иванищева А. П., Волкова М. Г., Баян Е. М., Петров В. В., Исследование поверхностных и электрофизических свойств тонких нанокомпозитных пленок состава TiO2-SnO2 // Научно-технические ведомости СПбГПУ. Физико-математические науки. 2022. Т. 15. № 3.3. C. 265-270. DOI: https:// doi.org/10.18721/JPM.153.352
Статья открытого доступа, распространяемая по лицензии CC BY-NC 4.0 (https:// creativecommons.org/licenses/by-nc/4.0/)
Introduction
Inorganic oxide nanomaterials based on tin and titanium dioxides are widely used to create electronic devices, photocatalysts, solar cell electrodes and gas sensors [1-3]. Titanium dioxide is the most commonly used as a photocatalyst, but the width of its band gap does not allow it to be used when irradiated with visible light, so various modifying additives are used for this purpose [4]. One of these additives is tin ions (4+), since the close radius allows you to replace titanium in the crystal lattice [5-6]. Tin dioxide has chemical and thermal stability, and due to the combination of high conductivity and high potential for the release of excess oxygen, Electrodes based on SnO2 also contribute to the complete oxidation of organic compounds [7]. Another reason for the combined use of these oxides may be a similar type of crystallization, since both tin dioxide and titanium dioxide can be crystallized in the structure of rutile [8].
Modification of SnO2 films with titanium dioxide allows to improve various properties of the nanocomposite material, including electrophysical [9-10]. For example, the work [11] describes the properties of nanostructures based on Ti-SnO2 films, among the factors that ensure the success of the use of these materials as electrodes are listed: (1) The structure of the core-shell of the Ti-SnO2 network are listed: (1) The structure of the core-shell of the Ti-SnO2 network, consisting of Ti inside a shell of SnO2 nanocrystals, is favorable for the diffusion of lithium ions during cyclic charge-discharge. (2) The Ti in the composite acts as an effective mechanical support for relieving the stress caused by the intercalation-deintercalation of lithium, which can play a crucial role in the excellent lithium storage capacity and the cyclic capacity of the electrode. (3) Mesopores formed by 3D microstructures also contribute to the improvement of the electrochemical characteristics of the electrode, possibly because they facilitate the diffusion of the electrolyte or lithium ions during charge-discharge processes.
The purpose of this work was to study surface (surface morphology and surface electric potential) and electrophysical (temperature dependence of electrical resistance) properties synthesized by solid-phase low-temperature pyrolysis of thin films TiO2-SnO2.
Materials and Methods
To obtain thin film materials TiO2-SnO2 with a ratio of Ti:Sn = 0:100, 1:99, 3:97, 5:95 by the method of solid-phase low-temperature pyrolysis, tin salts (SnCl4-5H) were used as precursors for the synthesis of thin films TiO2-SnO2 and titanium ((C4H9O)4Ti). The resulting salts were dissolved in 1,4-dioxane and applied three times to the prepared silicon and polycore substrates. Each layer was dried in air and in a drying oven at a temperature of 120 °C. The final temperature treatment was carried out in a muffle furnace at a temperature of 600 °C for two hours. The synthesis conditions were selected according to previous studies [12].
According to X-ray phase analysis, the resulting films have a crystal structure of cassiterite, regardless of the concentration of the additives administered. The resulting reflexes are somewhat expanded, which is typical for film nanocrystalline materials. Diffraction maxima of other phases
© Гуляева И. А., Иванищева А. П., Волкова М. Г., Баян Е. М., Петров В. В., 2022. Издатель: Санкт-Петербургский политехнический университет Петра Великого.
are not detected. Synthesized TiO2-SnO2 is characterized by a decrease in both particle sizes from 36 to 22 nm and the degree of crystallization from 68% to 45% with an increase in the concentration of titanium from 0 to 5 mol. %, which may be due to an increase in the concentration of defects and a less "ideal" crystal structure.
The study of the surface morphology and surface potential of the obtained films was carried out using the Ntegra probe nanolaboratory (NT-MDT SI, Russia). For this purpose, the samples were first examined using atomic force microscopy, and then Kelvin-probe force microscopy was used. In the study, the AFM and KPFM methods used the NSG10/Pt cantilever with a force constant of 11.2 N/m (TipsNano, Estonia) and a radius of curvature of about 25 nm.
To process the results of AFM measurements, the Image Analysis (NT-MDT) program was used, with the help of which the roughness parameters were estimated, the root value of roughness (Sq, Root Mean Square) and the maximum height difference (S , Peak-to-peak)). On the basis of the KPFM measurements, the values of the surface potential Vb were determined. To compare the surface potentials on different film samples, the difference between the maximum and minimum values A V was used, the values of which were averaged according to the sample.
Studies of the electrophysical properties of the obtained film samples were carried out on a software and hardware measuring complex that allows measuring the dependence of resistance on temperature [13].
Results and Discussion
Fig. 1 shows AFM scans of studied samples of TiO2-SnO2 films with a Ti:Sn ratio of 0:100, 1:99, 3:97, 5:95 mol.% with a size of 3x3 ^m2.
Table 1 shows roughness (S, nm), maximum elevation differences (S, nm), as well as surface potential values (Vb, mV) and its average values (AFb, mV) for each of the samples obtained.
Table 1
Surface characteristics of TiO2-SnO2 films
Ti:Sn, mol.% S, nm y S, nm q Vb, mV AV mV £r
0:100 11.0 1.4 4 4
1:99 34.3 4.1 1325 141
3:99 60.2 7.4 326 39
5:99 114.6 12.6 126 17
AFM studies have shown that TiO2-SnO2 films have a granular structure, and the roughness of films increases with increasing concentration of titanium dioxide. The least roughness has a film SnO2 (S = 11.0 nm), and TiO2-SnO2 film with a concentration of Ti 5 mol.% has the highest roughness (S =114.6 nm).
Studies of KPFM have shown that the lowest value of the surface potential (Vb = 4 mV) is characteristic of the tin oxide film — Fig. 1, h. This is due to the fact that the contact of two crystallites of tin dioxide contributes to the formation of a low surface potential. However, a small addition (1 mol.%) of titanium dioxide to the structure of tin dioxide leads to the appearance of peak values of the surface potential, the value of which reaches 1325 mV. It is known that the electron output work of titanium dioxide (4.7 eV) [14] is somewhat less than that of tin oxide (4.8-4.9 eV). [15, 16].
When the crystallites TiO2 and SnO2 come into contact, electrons will pass from titanium dioxide to tin dioxide, and regions with large local surface potential values of Vb should arise. The latter indicates the existence on the surface of such a film of a strong (up to 107 V/cm) electric field, which can significantly affect the transfer of charge carriers in it and the processes occurring on its surface [17].
Fig. 2 shows the dependence of electrical resistance on inverse temperature.
Pure SnO2 film has maximum resistance values and high nonlinearity. However, with a small addition of titanium dioxide (1%) to tin dioxide, the electrical resistance of the nanoscale material is sharply reduced and has indicators 4-5 orders of magnitude lower than pure SnO2 films. This may also be a consequence of the presence of a high surface electric field in TiO2-SnO2 films
a)
b)
0 200 400 600 800 1000 X, am
c)
d)
f- ; , i . i fit J Yi
^ f r '
• 7ju- »
• - fw 21 af # V^J
Fig. 1. AFM elevation scans (a, c, e) and their corresponding surface potential distribution (b, d, f over the surface TiO2-SnO2 films with a Ti:Sn mole ratio of 0:100 (a, b), 1:99 (c, d), 3:97 (e, f and
5:95 (g, h) mol. %
Fig. 2. Dependence of R on 1000/T for TiO2-SnO2 films with a molar ratio of Ti:Sn equal to 0:100 (curvel), 1:99 (curve 2), 3:97 (curve 3) and 5:95 (curve 4) mol. %
with a Ti:Sn molar ratio of 1:99. A higher content of titanium dioxide additives (3 and 5%) shows a higher resistance than that of sample c (1%). At the same time, the dependence of electrical resistance on the reverse temperature for the resulting films is close to linear.
Conclusion
Nanoscale films of TiO2-SnO2 composition with controlled thickness were formed by solidphase low-temperature pyrolysis. The KPFM method detected a surface potential on their surface, showing the existence of a high surface electric field. The resulting TiO2-SnO2 films can be used as solar cell electrodes and gas-sensitive materials for gas sensors.
Acknowledgments
We would like to express our gratitude to the staff of the Laboratory for Technology of Functional Nanomaterials of the Institute of Nanotechnology, Electronics and Equipment Engineering of the Southern Federal University for their help in conducting AFM and KFM studies.
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THE AUTHORS
GULYAEVA Irina A.
ORCID: 0000-0001-9364-1007
BAYAN Ekaterina M.
[email protected] ORCID: 0000-0002-8445-9139
IVANISHCHEVA Alexandra P.
[email protected] ORCID: 0000-0002-3779-8242
[email protected] ORCID: 0000-0003-3725-6053
PETROV Victor V.
VOLKOVA Maria G.
ORCID: 000000019483162X
Received 13.07.2022. Approved after reviewing 25.07.2022. Accepted 26.07.2022.
© Peter the Great St. Petersburg Polytechnic University, 2022
