An original technology for the formation of spatially ordered planar TiO2/Bi2O3 and TiO 2 /CdS  nanosystems is  proposed, which based on the electrochemical anodization of titanium through anodic alumina mask and ionic cyclic  layering of composite films based on Bi2O3 and chemical deposition of CdS on nanostructured TiO 2 surface. Comprehensive studies of multicomponent composites with three-dimensional architecture specified for practical use  have been carried out, and prospects for the creation of effective photovoltaic and sensoric devices on their basis have been determined

Fedosenko, V. S.

Gorokh, G. G.

Iji, М. M.

Lozovenko, A. A.

Горох, Г. Г.

Лозовенко, А. А.

Федосенко, В. С.

Iji, M.M.

Belarusian State University of Informatics and Radioelectronics Repository

161Modern nanomaterials and nanotechnologies(Figure 2 (b)), synchronous fluctuations of the voltage and current density values were observed, which can be associated with a change in the working area during the transition between the layers. Such current surges lead to a change in the deposition rate and uniformity of pore filling. The current-voltage characteristics of indium antimonide nanowires, shown in Fig. 4, showed that the right branch of the I-V characteristic of the InSb structure represents the beginning of the I-V characteristic of a typical semiconductor, that is, the beginning of a parabola. In this case, the shape of the forward branch of I-V characteristic does not differ from the reverse one. This means that a complex InSb nanostructure of this kind does not yet possess either special electrical properties or the property of current rectification. Nevertheless, it can be noted that the I-V characteristic of the structure is reproducible at different points. In the future, accurate modeling of a complex structure and its properties (such as the number of layers, their sequence, thickness, etc.) can make it possible to create a structure with properties promising for practical application.   Figure 4. I-V characteristics of InSb nanowires with variable pore diameters  Conclusion Techniques for the formation of nanoporous membranes from anodic alumina with alternating pore sizes have been developed and investigated, and are adapted for the deposition of metals and semiconductors. Manufactured membranes were tested in the electrochemical deposition of copper and indium antimonide. Electron microscopic studies of the formed nanosystems have been carried out and a pore filling mechanism has been proposed. The current-voltage characteristics of arrays of nanowires with a variable diameter are investigated. The data obtained make it possible to determine the technological parameters in order to reproduce and controllably obtain arrays of nanowires with variable morphology. Acknowledgment The State Program of Scientific Research of the Republic of Belarus «Convergence-2021» supported this work. Conflict of interest: The authors declare that they have no conflict of interest. References: [1] G.G. Gorokh [et al.] Techn. and design in electronic equipment. 1 (2015) 3–12. [2] G.G. Gorokh [et al.] Semiconductors. 51 (2017) 850–853. [3] I.A. Obukhov [et al.] Nanoindustry. 77 (2017) 96–108.    Synthesis of matrix nanostructures from oxides and sulfides of transition metals  G.G. Gorokh*, V.S. Fedosenko, A.A. Lozovenko, and М.M. Iji   Belarusian State University of Informatics and Radioelectronics, P.Brovki Str. 6, Minsk 220013, Belarus  * corresponding author e-mail: gorokh@bsuir.by  Abstract  An original technology for the formation of spatially ordered planar TiO2/Bi2O3 and TiO2/CdS nanosystems is proposed, which based on the electrochemical anodization of titanium through anodic alumina mask and ionic cyclic layering of composite films based on Bi2O3 and chemical deposition of CdS on nanostructured TiO2 surface. Comprehensive studies of multicomponent composites with three-dimensional architecture specified for practical use have been carried out, and prospects for the creation of effective photovoltaic and sensoric devices on their basis have been determined. Keywords: ionic cyclic layering, nanostructures, metal oxide nanocomposite, photovoltaics.  Introduction In modern photovoltaic, sensor and thermoelectric devices, multicomponent metal oxides and sulfides of transition metal metal oxides are widely used [1], while the use of combined oxide and sulfide layers can significantly increase their functional properties [2]. Previously, the methods of deposition of Sn, Mo, W, Bi oxides using the processes of local chemical and ionic coprecipitation of the corresponding components on the prepared nanoporous templates were studied and developed [3]. This article describes an original technology for the formation of multicomponent composites based on oxides and sulfides, using electrochemical anodizing of titanium through an anodic alumina mask and successive ionic layer adsorption and reaction (SILAR method) of composite films based on Bi2O3 and CdS on the island surface of TiO2. The SILAR method is based on cycle treatment of substrates in ion-containing solutions such as metal chlorides, nitrates, and acetates. As a result of reaction between adsorbed metal cations and anions, a nanolayer of hard-to-dissolve compound is formed on the substrate surface [4]. Combination of the SILAR method with the nanostructured matrices allows to create the systems which properties depend on their morphology and composition. So, investigations of the metaloxide and sufide films formation on the film of TiO2 nanoislands by the SILAR method are especially interesting nowadays. Experimental To create a template with TiO2 island nanostructures, a two-layer Ti/Al thin-film system (Ti – 200 nm, Al – 1 μm), deposited on a silicon substrate, was used. Anodizing of two-layer Ti/Al composition was carried out in 0.4 M H3PO4 in a combined mode: first, the layer of porous anodic alumina (PAA) was formed at a constant current density of 6 A/cm2; when the anodizing front reached the titanium sublayer, the voltage was stabilized at 120 V. During this period, the formation of the PAA matrix was completed, and through its pores, local oxidation of the titanium sublayer and the formation of TiO2 nanoislands, accompanied by a sharp drop in the current, began. The anodizing process was stopped after the anodic current decreased to 60 μA/cm2. Then, the formed PAA was etched away in a 50% orthophosphoric acid solution at 50°C. As a result, a structure 162Actual Problems of Solid State PhysicsIХ International Scientific Conferenceremained on the silicon wafer, which was the titanium layer with the nanostructured film of TiO2 nanoislands. The process of layer-by-layer deposition of bismuth oxide on island nanostructures of titanium oxide, as in the case of ionic deposition on PAA matrices [5], included surface preparation, consisting in boiling the initial workpiece in distilled water for 30 minutes at a temperature of 100°C. An aqueous solution of 0.1 M Bi(NO3)×5H2O was used as a cationic solution. Heated distilled water was used as an anionic solution. Composite multioxide films were obtained by ionic layer-by-layer cyclic deposition by sequential processing of the initial samples in cationic and anionic solutions for 30 s. at temperature of 30°C. One deposition cycle included treatment in cationic and anionic solutions with intermediate washings in distilled water for 5 s. to remove ions weakly bound to the surface. The total of 150 cycles were carried out. The CdS compound was obtained by preparing two intermediate solutions and mixing them. First, the 2 g of ammonia was added to 1 g of CdSO4 and gradually mixed until a homogeneous mass was obtained. Then, the 1 g of thiourea was dissolved in the 10 ml of distilled water. The resulting compositions were mixed in 1:2 ratio. The resulting mass was placed in a water bath and intensively stirred at temperature of 30°C for 5-10 minutes until complete dissolution and obtaining the homogeneous solution. Then the resulting solution was applied to heated substrate with the nanostructured TiO2 film with 2 ml dispenser and centrifuged at 1000 rpm for 30 s. The resulting film was dried in a SNOL 3.2/1100 muffle furnace under air at 70°C for 30 min. and 150°C for 60 min. The surface morphology and cross-sections of the PAA with metal oxides films were examined in a Hitachi S-806 scanning electron microscope (SEM) operated at 15 kV of accelerated voltage. Investigations of formed structures elemental compositions were performed by the electron-probe X-ray spectral microanalysis (EDX) using add-on "Bruker" for scanning electron microscope. Results and discussion Figure 1 shows SEM images of the formed nanocomposites TiO2/Bi2O3. The deposition of Bi2O3 films occurred uniformly over the entire surface of the TiO2 island matrix, filling the space between the oxidized titanium regions. The bismuth oxide film with thickness of about 400 nm is an accumulation of grains in the form of plates. The grain length was about 250 nm, and the width was up to 40 nm.    а б Figure 1. SEM images of the surface (a) and cleavage (b) of TiO2 matrix with deposited Bi2O3 film   163Modern nanomaterials and nanotechnologiesThe results of EDX studies of formed structures are shown in Figure 2. The EDX spectrum contains all elements of the studied system with a predominance of Bi. The atomic ratio of Bi, Ti, and O, taking into account all the elements that make up the films, was 31.46% Bi: 3.78% Ti: 51.05% O.   Figure  2. The electron-probe X-ray spectral microanalysis of TiO2 island matrix with deposited Bi2O3 film formed after 150 SILAR cycles  Sulfide compounds of CdS were also deposited on the nanostructured surface of titanium oxide. Figure 3 shows micrographs of the formed TiO2/CdS composites. The CdS film is granular formation with the grain size of about 20 nm, the thickness of the film is about 3 µm, and the total thickness of titanium and its oxide is about 265 nm. The formed CdS films are characterised by high level of agglomeration and small grain size [6].     а б Figure 3. SEM images of the surface (a) and cross-section (b) of TiO2 matrix with deposited CdS film  164Actual Problems of Solid State PhysicsIХ International Scientific ConferenceFigure 4 shows the results of EDX studies of a nanostructured TiO2 film with a CdS film deposited on it. The formed structure is dominated by cadmium and sulfur, which confirms the formation of the CdS compound; in addition to cadmium sulfide and titanium oxide, the film contains nitrogen and carbon atoms. Probably, these are the reaction products when two initial solutions are combined. As a result, CO, (NH4) 2SO4, 4NH3 were formed.   Figure 4. The electron-probe X-ray spectral microanalysis of TiO2 island matrix with deposited CdS film  Conclusion The composite TiO2/Bi2O3 and TiO2/CdS layers were formed by SILAR method of Bi–O-containing films and chemical deposition of CdS on the island TiO2 films. The Bi2O3 film with thickness of about 400 nm was an accumulation of grains in the form of plates. The grain length was about 250 nm, and the width was up to 40 nm. According to elemental analysis, an atomic ratio of elements was 31.46% Bi: 3.78% Ti: 51.05% O. The CdS film was granular formation with the grain size of about 20 nm, the thickness of the film was about 3 µm, and the total thickness of titanium and its oxide was about 265 nm. The electrochemical and chemical methods allows to form nanostructured multicomponent oxides consisted of two or three metal components. The formed multicomponent films have great potential to applicate in high-sensitivity gas sensors, photovoltaic and thermoelectric devices. Acknowledgment  The Belarusian Republican Foundation for Fundamental Research supported this work by grant № F20RА-020. Conflict of interest: The authors declare that they have no conflict of interest. References:  [1] Y. Deng, Semiconducting Metal Oxides for Gas Sensing. Springer Nature Singapore Pte Ltd. (2019) 253. [2] M. Punginsang, Mater. Sci. Semicond. Process. 90 (2019) 263–275. [3] G. Gorokh [et al.] Phys. Status Solidi B. 257 (2020) 1900283-1900291. [4] G. Gorokh [et al.] Sensors. 21 (2021) 4169-4183. [5] N.S.Kozhevnikova [et al.] Russ. chem. Revi. 84 3 (2015) 225-250. [6] A.Zakhlebayeva [et al.] Mater. Today: Proc. 37 (2021) 4064-4070. 

Synthesis of matrix nanostructures from oxides and sulfides of transition metals

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Synthesis of matrix nanostructures from oxides and sulfides of transition metals

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