RU2804013C1 - Humidity sensor and gas analytical multisensor chip based on the maxene structure of two-dimensional titanium-vanadium carbide - Google Patents

Abstract

FIELD: gas analysis.

SUBSTANCE: devices for detecting gas mixtures and methods for their manufacture. A method for manufacturing a gas sensor of a chemoresistive type is proposed, which includes preparing a suspension of a two-dimensional material based on titanium carbide, applying it to a dielectric substrate in the form of a layer so that the particles of the coating material form percolation paths between the electrodes, and boiling the coated substrate into a housing, containing the number of electrical leads not less than the number of measuring electrodes that are on the dielectric substrate or on the already formed coating, characterized in that as a two-dimensional material based on titanium carbide, maxene Ti_0.2V_1.8C composition is synthesized as follows: powders of titanium, vanadium, aluminum and graphite are mixed in a molar ratio of 0.2:1.8:1.2:0.8, potassium bromide powder is added to the mixture in a mass ratio of 1:1; the resulting mixture of powders is subjected to homogenization; then the mixture is dried at a temperature of 70°C until the mass loss stops and pressed into a billet, which is covered with potassium bromide powder and heat treated in a muffle furnace at a temperature of 1100°C to the formation of a triple precursor Ti_0.2V_1.8AlC after cooling, the resulting product is washed with hot distilled water, dried at a temperature of 120°C until the weight loss stops and treated with a mixture of concentrated hydrofluoric and hydrochloric acids at a temperature of 50°C, taken in a volume ratio of 3:2, until the formation of multilayer structures of titanium-vanadium carbide Ti_0.2V_1.8C which are then washed from by-products with distilled water and filled with a 12% aqueous solution of tetramethylammonium hydroxide N(CH₃)₄(OH) so that the concentration of Ti_0.2V_1.8C is 20 g/l in it, after which the reaction medium is subjected to ultrasonic treatment for 20 min, the precipitate is isolated and washed with distilled water, and then with absolute ethanol; to the resulting delaminated maxene Ti_0.2V_1.8C alcohol is added so that the concentration of maxene Ti_0.2V_1.8C is 10 g/l, the resulting mixture is homogenized in an ultrasonic bath for 15 minutes until a suspension is formed, a suspension of delaminated maxene Ti_0.2V_1.8C is applied to a dielectric substrate by microplotter printing; before the stage of boiling, the resulting coating is dried at a temperature of 70°C in vacuum until the mass loss stops.

EFFECT: creation of gas sensors of a chemoresistive type, sensitive to humidity, functioning at room temperature, based on two-dimensional titanium and vanadium carbide.

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Description

The present invention relates to the field of gas analysis, namely to devices for detecting gas mixtures and methods for their manufacture.

Currently, metal oxides in the form of thick or thin films that operate at elevated temperatures up to 400°C are widely used to create chemoresistive gas sensors. In order to reduce the operating temperature and increase sensitivity, other materials are also used in sensors of this type. Thus, relatively recently, so-called two-dimensional materials have begun to actively develop, the appearance of which is due to the study of monatomic carbon layers called graphene [Novoselov KS et al. Two-dimensional atomic crystals // Proceed. Natl. Acad. Sci. USA 2005, 102, 10451-10453]. The lack of actual “volume” in these structures leads to the fact that the material is a surface that directly changes its electrical characteristics during chemisorption of gases and other environmental changes. It is assumed that such structures can be used for the development of ultrasensitive gas sensors [Schedin F. et al. Detection of individual gas molecules adsorbed on graphene // Nature Materials. 2007, 6, 652-655]. From the literature there are many examples of the development of sensors based on such structures (for example, Russian patents for the invention RU 2522735, RU 2646419, RU 2659903; US patents US 2018328874, US 2018136157; Korean patents KR 20180095463, KR 20180107491; China patents CN 108241008, CN 108181355; Japanese patent JP 2018091699). However, carbon structures, including carbon nanotubes, have significantly lower chemoresistive response values compared to oxides, so a search is underway for other two-dimensional materials suitable for the development of gas sensors, among which the most famous are sulfides and selenides [Dral A.R. et al. 2D metal oxide nanoflakes for sensing applications: review and perspective // Sensors and Actuators B. 2018, 272, 369-392; Donarelli M. et al. 2D materials for gas sensing applications: a review on graphene oxide, MoS ₂ , WS ₂ and phosphorene // Sensors. 2018, 18, 3638; Lee E. et al. Two-dimensional transition metal dichalcogenides and metal oxide hybrids for gas sensing // ACS Sensors. 2018, 3, 2045-2060; Anichini C. et al. Chemical sensing with 2D materials // Chemical Society Reviews. 2018, 47, 4860-4908; Choi S.-J. et al. Recent developments in 2D nanomaterials for chemiresistive-type gas sensors // Electronic Materials Letters. 2018, 14, 221-260; Liu X. et al. Two-dimensional nanostructured materials for gas sensing // Advanced Functional Materials. 2017, 27, 1702168; Yang S. et al. Gas sensing in 2D materials // Applied Physics Reviews. 2017, 4, 021304], as well as nitrides and carbides of transition metals (maxenes). In the latter case, it is shown that it is possible to create a sensor based on a macene layer, in which, when the gas environment changes, the electrical characteristics change at room temperature [Lee E. et al. Room temperature gas sensing of two-dimensional titanium carbide (MXene) // ACS Applied Materials & Interfaces. 2017, 9, 37184-37190; Chertopalov S. et al. Environment-sensitive photoresponse of spontaneously partially oxidized Ti ₃ C ₂ MXene thin films // ACS Nano. 2018, 12, 6109-6116; Kim SJ et al. Metallic Ti ₃ C ₂ T _x MXene gas sensors with ultrahigh signal-to-noise ratio // ACS Nano. 2018, 12, 986-993].

It should be noted that control of atmospheric humidity is important for many processes and applications, therefore the structures of maxenes in the form of Ti ₃ C ₂ T _x have also been studied to the effects of H ₂ O vapor and have demonstrated high sensitivity [Yang Z. et al. Improvement of gas and humidity sensing properties of organ-like MXene by alkaline treatment // ACS Sensors. 2019, 4, 1261-1269].

The disadvantage of sensors based on macenes is that the resulting gas response is relatively small and comparable to the response of carbon structures, and therefore, to improve the performance, attempts have been made to create sensors based on modified macenes. One of the ways to change gas-sensitive characteristics is to create heterostructures. In [He T. et al. MXene/SnO ₂ heterojunction based chemical gas sensors // Sensors and Actuators B: Chemical. 2021, 329, 129275] it was demonstrated that the addition of SnO ₂ to Ti ₃ C ₂ T _x can improve the chemoresistive response of the sensor compared to pure macenes, as well as improve its stability.

Another way to change the chemoresistive characteristics of macenes is to replace the transition metal [Gogotsi Y. et al. MXenes: two-dimensional building blocks for future materials and devices // ACS Nano. 2021, 15, 5775-5780]. For example, it is assumed that the use of vanadium in the structure of macenes can improve the gas response of sensors to humid air [Xu X. et al. Vanadium doped tin oxide porous nanofibers: Enhanced responsivity for hydrogen detection // Talanta. 2017, 167, 638-644; Wang YT et al. Hollow V ₂ O ₅ nanoassemblies for high performance room-temperature hydrogen sensors // ACS Appl. Mater. Interf. 2015, 7, 8480-8487], which was confirmed in [Lee E. et al. Two-dimensional vanadium carbide MXene for gas sensors with ultrahigh sensitivity toward nonpolar gases // ACS Sensors. 2019, 4, 1603-1611].

The second important aspect of gas sensors is selectivity to analytes. To date, all available chemoresistive type sensors have low selectivity. To solve this problem, sensors are combined into sets or multisensory lines, the combined signal of which is selective with the appropriate selection of sensor elements [Gardner JW A brief history of electronic noses // Sensors & Actuators B. 1994, 18, 211-221]. At the same time, for the task of mass production and miniaturization, multisensor lines are formed on a separate chip [Sysoev V.V., Musatov V.Yu. Gas analytical devices “electronic nose” // Saratov: Sarat. state those. univ. 2011, 100 pp]. Thus, a multisensor chip for recognizing oxygen-containing gases is known (US patent US 5783154), which includes a set of sensor segments made of a metal-oxide layer deposited on a substrate and segmented by coplanar electrodes. The measuring signal is a set of resistances read between each pair of electrodes. A variation of this approach is the development of a chip in which not the resistance distribution is measured, but the distribution of the electrical potential applied to the metal-oxide layer (RF Patent RU 2392614). A set of such chemoresistive elements having internal or externally induced differences in physicochemical properties, which is combined into a line of multisensor chip, generates a combined signal that turns out to be specific for each individual type of test gas mixture. Analysis of this multidimensional signal using pattern recognition technologies allows identification and analysis of the type of gas or gas mixture. Similar structures of the gas analytical chip are also known, chemoresis elements in which are metal-oxidal nanocons (US Patent US 8443647, Korea KRA 20140103816), potassium titanate (RF Patent RU2625543), Titan dioxide nano polls (Patent of the Russian Federation RU 2641 017) or a layer of oxide tin (RF patent RU 2626741), cobalt oxide (RF patent RU 2677093), manganese oxide (RF patent RU 2677095), nickel oxide (RF patent RU2682575), zinc oxide (RF patent RU 2684423), synthesized by electrochemical deposition, as well as nanoviscosity kerov titanium trisulfide (RF patent RU 2684429). In all of these multisensor chip designs, either quasi-one-dimensional materials (nanotubes and nanofibers) or a nanostructured oxide layer with volumetric geometric dimensions are used as a gas-sensitive material. The design of such a chip based on oxidized titanium carbide was recently shown Where (RF patent RU 2709599, prototype), in which the highest gas sensitivity of the sensors, comparable to known oxide chemoresistive elements, was achieved when heated to 350°C. However, the task of creating a gas sensor that operates efficiently at room temperature requires further technical solutions.

Based on a review of modern scientific and technical literature, it can be concluded that the two-dimensional structures of titanium-vanadium carbide of the composition (maxena) for the formation of gas sensors sensitive to humidity, as well as suitable for creating a multisensor line or multisensor chip, have not been used and are promising.

The technical result of the invention is the creation of gas sensors of a chemoresistive type, sensitive to humidity, including in the form of a multisensor chip, operating at room temperature, based on two-dimensional titanium carbide and vanadium composition (maxena).

The technical result is achieved by proposing a method for manufacturing a chemoresistive type gas sensor, which includes preparing a suspension of a two-dimensional material based on titanium carbide, applying it to a dielectric substrate in the form of a layer so that particles of the coating material form percolation tracks between the electrodes, and boiling the substrate coated in a housing containing a number of electrical leads not less than the number of measuring electrodes that are located on a dielectric substrate or on an already formed coating, characterized in that maxene composition is synthesized as a two-dimensional material based on titanium carbide as follows: mix titanium, vanadium, aluminum and graphite powders in a molar ratio of 0.2:1.8:1.2:0.8, add potassium bromide powder to the mixture in a mass ratio of 1:1; the resulting mixture of powders is subjected to homogenization; then the mixture is dried at a temperature of 70°C until weight loss stops and pressed into a billet, which is filled with potassium bromide powder and heat treated in a muffle furnace at a temperature of 1100°C until a triple precursor is formed after cooling, the resulting product is washed with hot distilled water, dried at a temperature of 120°C until weight loss stops and treated with a mixture of concentrated hydrofluoric and hydrochloric acids at a temperature of 50°C, taken in a volume ratio of 3:2, until multilayer structures of titanium-vanadium carbide are formed which are then washed from by-products with distilled water and filled with a 12% aqueous solution of tetramethylammonium hydroxide so that the concentration was 20 g/l in it, after which the reaction medium is subjected to ultrasonic treatment for 20 minutes, the precipitate is isolated and washed with distilled water and then with absolute ethanol; to the resulting delaminated macene add alcohol so that the concentration of maxene it contained 10 g/l, homogenize the resulting mixture in an ultrasonic bath for 15 minutes until a suspension is formed, a suspension of delaminated macene applied to a dielectric substrate using microplotter printing; Before the boiling stage, the resulting coating is dried at a temperature of 70°C in a vacuum until weight loss stops.

It is advisable that the application of measuring electrodes on top of the resulting coating of delaminated macene carried out by cathode or magnetron sputtering using shadow masks and other microelectronic production methods.

It is also advisable that, to form a suspension, delaminated maxene dispersed in ethylene glycol, ethanol, n-propanol, isopropanol, n-butanol.

Dielectric substrate onto which a suspension of delaminated macene is applied can be made of oxidized silicon, glass, sapphire, ceramics, quartz, Si ₃ N ₂ , polymer, and the material of the measuring electrodes deposited on the dielectric substrate can be platinum, gold or other metal having ohmic contact with maxene

Conditions for the formation of macene determined experimentally. The molar ratios of 0.2:1.8:1.2:0.8 were established as a result of preliminary experiments and are determined by the need to minimize the formation of by-products, for example, titanium and vanadium carbides. Potassium bromide is necessary for synthesis in its melt, which protects from oxygen in the surrounding atmosphere. The specified ratio provides the required amount of salt to form a protective layer. Heat treatment in a muffle furnace at a temperature of 1100°C leads to the formation of a ternary precursor subsequent processing of which in a mixture of acids makes it possible to obtain agglomerated two-dimensional titanium-vanadium carbide (maxene) due to selective chemical etching of aluminum. As a result, selective removal of aluminum layers located between the layers occurs and aggregates of multilayer structures of titanium-vanadium carbide are formed Delamination of the resulting macene aggregates carried out under certain experimental conditions by treatment with tetramethylammonium hydroxide and ultrasonic exposure. Synthetic conditions for the formation of a suspension of delaminated macene are caused by the need to obtain functional ink suitable for application to a dielectric substrate in the form of a special coating using microplotter printing, and were determined experimentally. The specified variants of alcohols for preparing the suspension, types of substrates and electrode materials are standard and correspond to samples known from the current state of technology.

The essence of the invention lies in the fact that as a result of the method, a chemoresistive type gas sensor is obtained, in which a layer of the composition is used as a gas-sensitive material (maxena), placed on a dielectric substrate between the measuring electrodes, whose resistance at room temperature changes under the influence of humidity and organic vapors in the surrounding air. The number of measuring electrodes on the dielectric substrate can be more than three, on top of which or under which a layer of two-dimensional carbide of the composition is applied (maxena) of various densities; in this case, the layer enclosed between each pair of electrodes forms a gas sensor (or sensor), and the combination of such sensors forms a multisensor chip of the chemoresistive type. The design of the sensor differs from the design of a multisensor chip only in the number of measuring electrodes - for a sensor the number of measuring electrodes is two, and for a multisensor chip the number of measuring electrodes exceeds three.

When placing a sensor manufactured in the described manner - a sensor or a multi-sensor chip based on two-dimensional titanium-vanadium carbide composition In the initial air atmosphere (dry air) at room temperature, oxygen is adsorbed on the surface of the macene, which determines the localization and transport of electrons in the layer, and, consequently, the initial resistance of the material. When water vapor appears in the surrounding atmosphere, adsorption of H ₂ O molecules occurs on the surface of macene, as a result of which the localization of electrons near the adsorbed molecules increases, and the mobility of electrons decreases due to the presence of new local scattering centers, which leads to an increase in the resistance of the layer of two-dimensional carbide structures titanium-vanadium. These processes constitute the physicochemical nature of the chemoresistive effect in this material towards water vapor, which determines the function of a humidity sensor operating at room temperature. A similar change in resistance also occurs upon adsorption of macene structures and other molecules, including organic ones, on the surface.

The magnitude of the chemoresistive response S of a sensor based on two-dimensional titanium-vanadium carbide composition is defined as the relative change in resistance in the test gas R _g - a mixture of the analyte with dry air, relative to the resistance in the reference atmosphere (dry air) R _b as a percentage:

Despite the fact that the magnitude of the chemoresistive response of the sensor based on two-dimensional titanium-vanadium carbide of the composition in relation to water vapor exceeds, for example, the response to organic vapor, such a sensor, like other chemoresistive sensors, does not have absolute selectivity to humidity. Therefore, in order to increase the selectivity of the device in conditions of uncertainty of a priori knowledge about the composition of the ambient air, it is more advisable to use a multisensor chip. For its manufacture, a layer of two-dimensional structures of titanium-vanadium carbide of the composition applied to a substrate containing more than three measuring electrodes. In this case, a line consisting of at least three sensors is formed on the substrate, forming in the general case a multisensory line of elements, resistance or chemoresistive response which are components of the vector or different for different test gases. In this case, the layer enclosed between each pair of electrodes forms a sensor, and the entire set of sensors on the substrate forms a multisensor chip of the chemoresistive type. The vector signal of a multisensory ruler when exposed to different gases or gas mixtures is processed by pattern recognition methods within the framework of a multisensory approach [Sysoev V.V., Musatov V.Yu. Gas analytical devices “electronic nose” // Saratov: Sarat. state those. univ. 2011, 100 pp.] and identify the test gas.

For gas measurements and calibration, a fabricated sensor or multi-sensor chip based on two-dimensional structures of titanium-vanadium carbide composition placed in a chamber equipped with gas flow inlet and outlet, and exposed to test gases. The resistance of a layer of two-dimensional structures of titanium-vanadium carbide of the composition is used as a measuring signal between the measuring electrodes, which is recorded using standard circuits using a divider or using a Winston bridge, using an appropriate electrical measuring unit.

The invention is illustrated by the following figures.

Fig. 1. Diffraction patterns: (a) composition phases and the phase of two-dimensional titanium-vanadium carbide obtained from it by chemical etching (b) composition

Fig. 2. Optical photograph of a working sample of a multisensor chip coated with a delaminated two-dimensional titanium-vanadium carbide composition

Fig. 3. Change in the resistance of a gas sensor (sensor) coated with a delaminated two-dimensional titanium-vanadium carbide composition when exposed to vapors of ethanol, ammonia, isopropanol, methanol, humid air in concentrations of 500-16000 ppm (particle-per-million) mixed with dry air at room temperature.

Fig. 4. Chemoresistive responses of sensors of a working sample of a multisensor chip coated with a delaminated two-dimensional titanium-vanadium carbide composition when exposed to vapors of ethanol, ammonia, isopropanol, methanol, humid air in concentrations of 16,000 ppm. The given scatters correspond to the distribution of the chemoresistive response across sensors in a multisensor chip at room temperature.

Fig. 5. Comparative diagram of the coefficient of gas sensitivity to water vapor, calculated as the ratio of the chemoresistive response S to the gas concentration C, for a gas sensor coated with a delaminated two-dimensional titanium-vanadium carbide composition and other prototypes of gas sensors based on macenes known from the literature The numbering in the figure corresponds to the following sources:

[1] Muckley E.S. et al. Multimodality of structural, electrical, and gravimetric responses of intercalated MXenes to water // ACS Nano. 2017, 11, 11118-11126.

[2] Liu L.-X. et al. Flexible and multifunctional silk textiles with biomimetic leaf-like MXene/silver nanowire nanostructures for electromagnetic interference shielding, humidity monitoring, and self-derived hydrophobicity // Adv. Funct. Mater. 2019, 29, 1905197.

[3] Muckley ES et al. Multi-modal, ultrasensitive, wide-range humidity sensing with film // Nanoscale. 2018, 10, 21689-21695.

[4] Li N. et al. High-performance humidity sensor based on urchin-like composite of MXene-derived TiO ₂ nanowires // ACS Appl. Mater. Interfaces 2019, 11, 38116-38125.

[5] Yang Z. et al. Improvement of gas and humidity sensing properties of organ-like MXene by alkaline treatment // ACS Sensors. 2019, 4, 1261-1269.

[6] Zhao X. et al. Smart Ti ₃ C ₂ T _x MXene fabric with fast humidity response and Joule heating for healthcare and medical therapy applications // ACS Nano. 2020, 14, 8793-8805.

[7] An H. et al. Water sorption in MXene/polyelectrolyte multilayers for ultrafast humidity sensing // ACS Appl. Nano Materials. 2019, 2, 948-955.

Fig. 6. Dependence of the chemoresistive response S of sensors of a working sample of a multisensor chip coated with a delaminated two-dimensional titanium-vanadium carbide composition on the concentration of vapors of ethanol, ammonia, isopropanol, methanol, humid air at room temperature. The given scatters correspond to the distribution of the chemoresistive response across the sensors in the multisensor chip.

Fig. 7. The result of processing by linear discriminant analysis (LDA) of the vector signal of an operating sample of a multisensor chip coated with a delaminated two-dimensional carbide composition when exposed to vapors of ethanol, ammonia, isopropanol, methanol, humid air, with a concentration of 16,000 ppm mixed with dry air, when the chip is operating at room temperature. The axes show the first and second LDA components (LDA 1, LDA 2), used as features in this pattern recognition method.

Achievement of the stated technical result is confirmed by the following examples. The examples illustrate but do not limit the proposed technical solution.

Example 1.

Powders of titanium (99%, LANHIT company, Russia), vanadium (99%, LANHIT company, Russia), aluminum (99%, LANHIT company, Russia) and graphite (99%, Technocarb company) were mixed. , Russia) in a molar ratio of 0.2:1.8:1.2:0.8. Then potassium bromide powder (99.99%, Rushim company, Russia) was added to the resulting mixture in a mass ratio of 1:1 and homogenized by co-grinding in a planetary ball mill. The resulting mixture was dried at a temperature of 70°C until weight loss stopped and pressed into a dense billet, which was placed in an alundum crucible, covered with a protective layer of KBr powder and subjected to heat treatment in a muffle furnace at a temperature of 1100°C until a ternary precursor was formed the diffraction pattern of which is presented in Fig. 1a. After cooling, the resulting product was washed from potassium bromide with hot distilled water and dried at a temperature of 120°C until weight loss stopped. Then the powder were treated with a mixture of concentrated hydrofluoric and hydrochloric acids at a temperature of 50°C, taken in a volume ratio of 3:2. After chemical etching, the product was repeatedly washed to remove reaction by-products in distilled water by centrifugation. Obtained aggregates of multilayer structures of titanium-vanadium carbide the diffraction pattern of which is presented in Fig. 1b were delaminated into separate two-dimensional structures. To do this, a 12% aqueous solution of tetramethylammonium hydroxide was added to them (Technic company, France), while the concentration of maxene was 20 g/l, after which the reaction medium was subjected to ultrasonic treatment for 20 minutes. The resulting product was isolated from the mother liquor by centrifugation, washed with distilled water and absolute ethanol, and then added to delaminated maxene ethylene glycol (Spektr-Khim company, Russia) was added so that the concentration of maxene it was 10 g/l. The resulting mixture was homogenized to form a suspension in an ultrasonic bath for 15 minutes.

A set of 39 coplanar Pt strip electrodes, 50×1 µm in size, with an interelectrode gap of 50 µm, was deposited onto a dielectric substrate made of oxidized silicon using magnetron sputtering, according to a pre-formed photolithographic pattern. Each measuring electrode contained at the end a contact pad measuring about 0.036 mm ² for further welding into the housing.

The resulting suspension was applied to a dielectric substrate with 39 measuring platinum electrodes, made of oxidized silicon, using microplotter printing in such a way that the particles of delaminated macene in the coating were located in the form of a single layer and formed percolation paths between the electrodes. The resulting coating was dried at a temperature of 70°C in vacuum until weight loss stopped. As a result, a coating was formed on the surface of the substrate, completely covering all the measuring electrodes, as shown in the photograph (Fig. 2) taken using an optical microscope on a working sample of the multisensor chip. The layer located between each pair of electrodes of the multisensor chip consists mainly of particles 75-300 nm in size and forms the basis of a separate sensor.

After coating, the substrate was welded using an ultrasonic station (WEST Bond 747677E, USA) with an Au wire with a diameter of 38 μm into a ceramic body with applied conductive multi-tracks and equipped with a 50-pin connector with a pitch of 1.27 mm (ERNI Electronics, Germany) for further pairing of the chip with external reading electronic circuits.

Example 2.

According to example 1, characterized in that the number of measuring electrodes was two, and they were applied to a ready-made coating of delaminated macene by cathode sputtering method.

Next, the chemoresistive responses of both individual sensors (for example, obtained according to example 2) and sensors as part of a multisensor chip were analyzed.

To calibrate the signal of the resulting gas sensor to the effects of humidity and other analytes in the gas phase, the sample was placed in a chamber equipped with a gas flow inlet and outlet. The analytes used were vapors of alcohols (isopropanol, ethanol, methanol), ammonia and water mixed with dry air, emitted by bubbling air through the corresponding liquids in the range of 500-16000 ppm. The flow rate of 400 cm ³ /min was controlled by high precision mass flow controllers (Bronkhorst, The Netherlands). Dry air was generated using a suitable generator (Peak Scientific Instruments, UK). The resistance of the maxene layer was used as the measuring signal of the sensors between the measuring electrodes using an electrical measuring unit (RF Patent for utility model No. 182198). Sensor measurements were carried out at room temperature.

In FIG. Figure 3 shows typical chemoresistive responses - changes in the resistance of the resulting sensor at room temperature to vapors of ethanol, ammonia, isopropanol, methanol, humid air, with a concentration of 500-16000 ppm, mixed with dry air. It can be seen that when exposed to analytes, the sensor resistance increases and decreases reversibly when the analytes are removed in an atmosphere of clean air. The chemoresistive response is stable, reproducible and significantly exceeds the noise value, which allows us to consider this sensor as suitable for practical use.

In FIG. Figure 4 shows that the magnitude of the chemoresistive response of the multisensor chip sensors to water vapor significantly exceeds the response to other test analytes at the same concentration, for example equal to 16000 ppm. Moreover, the value of the gas sensitivity coefficient, calculated as the ratio of the chemoresistive response S to the water vapor concentration C, varies for a given sensor, as shown in Fig. 5, in range which exceeds the values of detected concentrations known from the literature for humidity sensors based on macenes which are also shown in Fig. 5:

The main characteristic of the gas sensor - the dependence of the chemoresistive response S on the concentration of analyte C, is presented in Fig. 6 for the resulting multisensor chip based on two-dimensional structures of titanium-vanadium carbide composition (maxena). The dependence S(C) is shown using the example of all test analytes - ethanol, ammonia, isopropanol, methanol and water vapors. The sensor response to analytes obeys the function in accordance with the Freundlich adsorption isotherm. The exponent n varies between 0.38-0.61 for different analytes and corresponds to a value of 0.61±0.03 in the case of humidity.

The total vector signal of the resulting sample of a multisensor chip based on two-dimensional structures of titanium-vanadium carbide composition (maxene) to the test analytes was processed using the linear discriminant analysis (LDA) method, see, for example, [Sysoev VV et al. The temperature gradient effect on gas discrimination power of metal-oxide thin-film sensor microarray // Sensors. 2004, 4, 37-46). In FIG. Figure 7 shows a two-dimensional projection of a 4-dimensional LDA phase space in which the vector signals of the chip to analytes of equal concentration (16000 ppm) are located. The axes show the first and second LDA components, which are calculated in this method in such a way as to optimize (maximize) the ratio of the variation between classes (in this case, responses to different analytes) of data to the intraclass variance (in this case, responses to the same same analyte) [Bolch B. Multivariate statistical methods for economics / B. Bolch, K. J. Huan; lane from English HELL. Plitman and ed. S.A. Ayvazyan. - M.: Statistics. 1979, 318 pp]. These signals are clustered into groups depending on the analyte with centers of gravity located significantly from each other, which makes it possible to technically separate them and selectively determine them. This allows not only to detect these gases, i.e. perform the function of a sensor, but also identify them, i.e. perform the function of a gas analyzer and, in particular, separate the effects of water vapor from the effects of other organic vapors.

Thus, as a result of implementing this method, gas sensors are obtained based on two-dimensional titanium-vanadium carbide of the composition (maxena), operating at room temperature, namely a sensor or multisensor chip of the chemoresistive type, having a selective response to humidity with a detection limit above a concentration of 10 ppm and organic vapors in concentrations from hundreds of ppm.

Claims (5)

1. A method for manufacturing a chemoresistive-type gas sensor, which includes preparing a suspension of a two-dimensional material based on titanium carbide, applying it to a dielectric substrate in the form of a layer so that particles of the coating material form percolation tracks between the electrodes, and boiling the coated substrate into the body , containing a number of electrical leads not less than the number of measuring electrodes that are located on a dielectric substrate or on an already formed coating, characterized in that maxene of the composition is synthesized as a two-dimensional material based on titanium carbide as follows: mix titanium, vanadium, aluminum and graphite powders in a molar ratio of 0.2:1.8:1.2:0.8, add potassium bromide powder to the mixture in a mass ratio of 1:1; the resulting mixture of powders is subjected to homogenization; then the mixture is dried at a temperature of 70°C until weight loss stops and pressed into a billet, which is filled with potassium bromide powder and heat treated in a muffle furnace at a temperature of 1100°C until a triple precursor is formed after cooling, the resulting product is washed with hot distilled water, dried at a temperature of 120°C until weight loss stops and treated with a mixture of concentrated hydrofluoric and hydrochloric acids at a temperature of 50°C, taken in a volume ratio of 3:2, until multilayer structures of titanium-vanadium carbide are formed which are then washed from by-products with distilled water and filled with a 12% aqueous solution of tetramethylammonium hydroxide so that the concentration was 20 g/l in it, after which the reaction medium is subjected to ultrasonic treatment for 20 minutes, the precipitate is isolated and washed with distilled water and then with absolute ethanol; to the resulting delaminated macene add alcohol so that the concentration of maxene it contained 10 g/l, homogenize the resulting mixture in an ultrasonic bath for 15 minutes until a suspension is formed, a suspension of delaminated macene applied to a dielectric substrate using microplotter printing; Before the boiling stage, the resulting coating is dried at a temperature of 70°C in a vacuum until weight loss stops. 2. The method according to claim 1, characterized in that the application of measuring electrodes on top of the resulting coating of delaminated macene carried out by cathode or magnetron sputtering using shadow masks and other microelectronic production methods. 3. The method according to claim 1, characterized in that to form a suspension, delaminated macene dispersed in ethylene glycol, ethanol, n-propanol, isopropanol, n-butanol. 4. The method according to claim 1, characterized in that the dielectric substrate on which a suspension of delaminated macene is applied made of oxidized silicon, glass, sapphire, ceramics, quartz, polymer. 5. The method according to claim 1, characterized in that the material of the measuring electrodes deposited on the dielectric substrate is platinum, gold or another metal having ohmic contact with maxene