Synthesis and Characterization of Tin(IV) Oxide Obtained by Chemical Vapor Deposition Method

Nagirnyak et al. Nanoscale Research Letters (2016) 11:343 DOI 10.1186/s11671-016-1547-x NANO EXPRESS Open Access Synthesis and Characterization of Tin(IV) Oxide Obtained by Chemical Vapor Deposition Method Svitlana V. Nagirnyak*, Victoriya A. Lutz, Tatiana A. Dontsova and Igor M. Astrelin Abstract The effect of precursors on the characteristics of tin oxide obtained by chemical vapor deposition (CVD) method was investigated. The synthesis of nanosized tin(IV) oxide was carried out with the use of two different precursors: tin(II) oxalate obtained using tin chloride(II) and oxalic acid; tin(II) oxalate obtained using tin chloride(II); and ammonium oxalate. The synthesized tin(IV) oxide samples were studied by electron microscopy, X-ray diffraction and optical spectra. The lattice parameters of tin(IV) oxide samples were defined, the bandgap of samples were calculated. Keywords: Tin(IV) oxide, Tin(II) oxalate, CVD method, X-ray diffraction, Bandgap Background Metal oxides are the basis of modern diverse smart and functional materials and devices because physical and chemical properties of these oxides can be tuned. Functional properties of metal oxides depends on many chemical and structural characteristics such as chemical composition, various kinds of deficiencies, morphology, particle size, surface-to-volume ratio, etc. By varying either of these characteristics, the electrical, optical, magnetic, and chemical properties can be regulated, giving the possibility of fabricating smart devices. Such unique characteristics make oxides the most diverse class of materials, with properties covering almost all aspects of materials science and physics in areas such as semiconductivity, superconductivity, ferroelectricity, and magnetism [1–4]. It is known that the reversible chemisorption of reactive gases on the surface of the oxide semiconductor is accompanied by reversible changes in conductivity. This makes semiconductors the most attractive materials for the manufacture photosensitive electronic converters based on them. Conductivity of semiconducting oxides caused by deviations from stoichiometry and also defects such as interstitial cation or anion vacancies. Depending on type of determinate impurity (electron acceptor or electron donor) and conduction type (n- or p-type), the * Correspondence: Department of Chemistry, National Technical University of Ukraine “KPI”, Kyiv 03056, Ukraine resistance of the sensitive layer of the sensor is increased or decreased. Oxidizing gases or electron acceptors such as NO2 produce a decrease in the conductance of n-type semiconducting materials (i.e., electrons are the major carriers, such as ZnO, SnO2, In2O3) and an increase in the conductance of p-type semiconducting materials (i.e., holes are the major carriers, such as CuO); reducing gases or electron donors such as H2S, CO, H2 and water vapor act in a reverse manner [5, 6]. Metal oxides SnO2, ZnO, In2O3, and CdO are widebandgap n-type semiconductors and the most frequently used as a sensitive material for the gas sensors. They belong to a class of transparent conductive oxides due to a number of unique functional properties, of which the most important are the electrical conductivity, the visibility in a wide spectral range, and high reactivity of the surface [7, 8]. Metal oxide-based gas sensors are widely used due to its high sensitivity to harmful for human health or hazardous gases (such as CO, NO, NO2, H2, etc.) in conjunction with easy fabrication methods and low manufacturing costs. Tin(II) oxide is the promising sensor material among a wide set of semiconducting metal oxides [9–11]. It is known that nanocrystalline materials characterized the largest values of sensor response due to high surface-tovolume ratio and, therefore, higher absorption capacity [6]. To obtain nanocrystalline, SnO2 uses different methods: sol-gel method [12], chemical vapor deposition [13], © 2016 The Author(s). Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Nagirnyak et al. Nanoscale Research Letters (2016) 11:343 hydrothermal [14], thermal evaporation [15]. Among a large number of approach methods of chemical vapor deposition (CVD), which is implemented of vapor-liquidsolid mechanism (VLS), deserves special attention. This method allows obtaining particles of very diverse morphology with a high degree of crystallinity [1, 16, 17]. In the articles [18–20], SnO2 nanowires and nanoribbons (doped and pure) have been successfully synthesized using such precursors as Sn and SnO2 powders. Also known to use other precursors for synthesis of SnO2 nanowires are SnO powder, and a mixture of carbon powder and SnO2 powder. However, from our point of view, it is interesting to research also other precursors, as has long been known that precursors have a significant impact on the final physicochemical properties of materials. In this paper, we investigate the effect of new precursor SnC2O4 (obtained from different reagents) on the characteristics of tin oxide obtained by CVD. Methods of synthesis Tin(II) oxalate was obtained by sol-gel method from different precursors: in the first case tin chloride(II) and oxalic acid; in the second case – tin chloride(II) and ammonium oxalate. In both cases, hot oxalic acid (ammonium oxalate) solution was added to hot aqueous solutions of SnCl2 · 2H2O in a molar ratio of 1:1.5, respectively. The resulting solution was cooled. The precipitate formed was filtered, washed with distilled water while ions Cl− detected by reaction with AgNO3 and dried in an oven at 378 K for 2 h. Thus, there were two obtained samples of tin oxalate: sample A – using oxalic acid and sample B – using ammonium oxalate (Table 1). For tin(IV) oxide weighed tin(II) oxalate was loaded in an alumina boat, which was placed at the center of a quartz tube in a horizontal-type furnace. The furnace was heated to 1123, 1223, and 1323 K and kept in an inert atmosphere for 1 h. The inert atmosphere was implemented by nitrogen with 0.005 % oxygen impurity. The overall reaction of tin(II) oxalate decomposition: SnC2 O4 → SnO2 þ 2CO Page 2 of 7 Table 2 Obtained SnO2 samples Sample Precursors Treatment temperature, K Sample 1 Sample A 1123 Sample 2 Sample A 1223 Sample 3 Sample A 1323 Sample 4 Sample B 1123 Sample 5 Sample B 1223 Sample 6 Sample B 1323 Results and Discussion Electron Microscopy The particle sizes of the obtained samples were determined with a transmission electron microscope TEM 100-01. Figure 1 displays TEM images of the obtained tin(II) oxalate samples. The figure shows that sample A has a wire-like form, while pa (...truncated)