The microstructure, composition, and electrical and gas-sensitive characteristics of sensors based on thin nanocrystalline SnO2 films with various catalysts deposited on the surface (Pt/Pd, Au) and introduced into the bulk (Au, Ni, Co) are investigated in the modes of constant and pulse heating. Atomic force microscopy and laser Raman spectroscopy are used to study micromorphology and structural defects depending on the composition of nanosized films. It is shown that sensors with Au and Co additives introduced into the volume make it possible to detect vapors of liquid hydrocarbons (on the example of aviation kerosene) at a concentration level of 5 ppm (0.1 of permissible exposure limit) and are characterized by increased stability of parameters during testing under prolonged exposure to vapors, as well as in conditions of varying humidity. Sensors with Au and Co additives in volume and deposited onto the film surface ultrathin two-layer Pt/Pd catalysts demonstrate the fastest response after testing.

The electrical and gas-sensitive characteristics of sensors based on thin nanocrystalline SnO2 films with various catalysts deposited on the surface (Pt/Pd, Au) and introduced into the bulk (Au, Ni, Co) are studied in the modes of constant and pulsed heating. Atomic force microscopy and laser Raman spectroscopy were used to study the micromorphology and structural defects depending on the composition of nanoscale films. it is shown that sensors with au and co additives introduced into the volume can detect liquid hydrocarbon vapors (for example, aviation kerosene) at a concentration level of 5 ppm (0.1 permissible exposure limit) and are characterized by increased stability of parameters during testing under prolonged exposure to vapors, as well as in conditions of changing humidity. Sensors with Au and Co additives in bulk and ultrathin Pt/Pd catalysts applied to the surface of the films are characterized by the highest performance after testing.

In this work, novel semiconductor sensors were developed for detecting high pre-explosive concentrations of H-2 (0.1-2.5 vol%) with high selectivity and stability. The sensors were based on thin (similar to 100 nm) nanocrystalline SnO2 films produced by magnetron sputtering of dispersed Pt and Pd layers deposited on the surface and addition of 13-14 at% Pt in the bulk. Studies on their nanostructure, composition, electrical properties, and gas-sensitive characteristics were carried out. X-ray photoelectron and Raman spectroscopies revealed that in the process of stabilizing annealing in Pt/Pd/SnO2:Sb,Pt film platinum introduced into the bulk segregates on the surface of the SnO2 microcrystals in the form of Pt degrees metal clusters and dispersed Pt2+ ions. The dispersed Pt2+ ions form bonds with lattice oxygen and contribute to the overlap of conduction channels. In the sensor subjected to annealing at T-an(1) = 723 K and T-an(2) = 873 K, the optimal situation is realized when under the action of low (n < 0.1 vol%) H-2 concentrations, the condition 2d(0) = d(M) is satisfied and G(1)/G(0) = 9-12. In the range of 0.1-2.5 vol% H-2, narrowing of the space-charge region favors the formation of a conducting layer, and at 2d(0) <= d(M) there is a sharp increase in the values of the responses to G(1)/G(0) = 220-250 at 2.5 vol%.

The paper presents a comparison of the responses of sensors to ammonia in continuous heating and thermal cycling modes, and also shows the dependence of the response time of the sensors on the content NH3. Thin films of tin dioxide were obtained using RF magnetron sputtering, and then annealed in air at a temperature of 425 degrees C for 24 hours. In thermal cycling, the temperature of the heating cycle remains constant 400 degrees C (duration of the heating cycle was 8 s). The temperature of the cooling cycle changes in the range 200 degrees C - 100 degrees C, but duration of cooling of the cooling cycle was remained constant of 5 s. It was shown that the thermal cycling mode has several advantages over the constant heating mode. The experiments showed that sensors based on SnO2:Sb have short response times - less than 3 seconds.

The effect of temperature modulation on the response of ammonia sensors based on tin dioxide films was studied. Samples were obtained by RF-magnetron sputtering of a SnO2: Sb target on sapphire substrates with pre-deposited Pt-electrodes and a heater. Varying the duration of the heating cycle and lowering the temperature in the cooling cycle can increase the response by one to two orders of magnitude. The results are explained by a change in the density of chemically adsorbed oxygen on the surface of the SnO2: Sb film depending on the temperature mode.

The influence of operating modes on the response of ammonia sensors based on tin dioxide films has been studied. Samples have been obtained as a result of high-frequency magnetron sputtering of a SnO2:Sb target on sapphire substrates with predeposited Pt electrodes and a heater. Varying the heating cycle duration and reducing the cooling cycle temperature may increase the response by one or two orders of magnitude. The results are explained as being due to the change in the density of chemically adsorbed oxygen on the surface of the SnO2:Sb film depending on the temperature regime.

Gas-sensitive characteristics of aviation kerosene sensors based on nanocrystalline SnO2 thin films with various catalysts have been studied as a function of the operating temperature and gas concentration in the air. Thin tin dioxide films were grown in magnetron by sputtering of a tin–antimony alloy target in oxygen–argon plasma. It is shown that the sensors are characterized by a high sensitivity to aviation kerosene vapors and by a good stability of parameters during long-term tests and under the variation of humidity.

The results of studies of electrical and gas sensitive characteristics of acetone sensors based on thin nanocrystalline SnO 2 films with various catalysts deposited on the surface (Pt/Pd, Au) and introduced into the volume (Au, Ni, Co) are presented. Films containing impurities of gold and 3d-metals were obtained by the method of magnetron sputtering of mosaic targets. Particular attention was paid to the influence of the longterm tests and humidity level on the properties of sensors. It is shown that the sensors with the deposited dispersed gold layers with Au+Ni and, especially, Au+Co additives introduced into the volume are characterized by the increased stability in the process of testing under prolonged exposure to acetone and also under conditions of varying humidity.

The results of studying electrical and gas sensitive characteristics of H2 sensors based on thin nanocrystalline SnO2 films with the Pt, Pd, and Ag dispersed layers deposited on the surface and Ag, Y, and Ag + Y additives in the volume are presented. It is shown that various combinations of catalysts on the surface and in the volume have a significant effect on the microstructure of films and density of oxygen adsorption sites on the surface of tin dioxide. As a result, the resistance values of sensors in clean air R0, activation energies of the temperature dependences of R0, responses to hydrogen in the concentration range of 50–2000 ppm are different. Studies performed by the method of UV-visible spectroscopy revealed in the absorption spectra of films with a silver addition in the volume a band of surface plasmon resonance of silver indicating that the additive is present in the form of metallic Ag nanoparticles. Particular attention was paid to the influence of long-term tests on the properties of sensors with the listed additives. It was established that the joint introduction of Ag+Y into the volume of films prevents the increase of the resistance and responses during prolonged exposure to hydrogen, which is observed during the operation of all other samples studied. Possible mechanisms for changing the sensors’ properties during testing and the role of additives in their stabilization are considered.

This work presents the results of investigation of the effect of the complex modifiers of Ag + Y introduced into bulk of SnO2 thin films on the properties of hydrogen sensors and the stability of the devices at long-term test. Two types of the films with different deposited on the surface dispersed catalysts Pt/Pd/SnO2:Sb, Ag, Y and Ag/SnO2:Sb, Ag, Y were studied. It is shown that additives of Ag, Y in the presence Pt/Pd on the surface provide the maximum values of the response to hydrogen at the temperature 670 K. In the case of the deposited catalytic Ag the response to hydrogen is considerably lower and the temperature of the maximum response > 713 K. A common feature of two types of the films is the high stability of their properties under the periodical influence of hydrogen in long-term tests.

Results of investigation of the effect of the complex modifiers of silver and yttrium introduced into bulk of tin dioxide thin films with disperse layers of Pt/Pd on the surface on the properties of hydrogen sensors are presented in this work. The thin films of tin dioxide were obtained by magnetron sputtering of tin-antimony alloy target at the direct current. The influence of humidity on the electrical and gas-sensitive characteristics of the hydrogen sensors based on these films was investigated. The long-test stability of the investigated samples was researched. It is shown that additives silver and yttrium in the presence of Pt/Pd on the surface provide the maximum values of the response to hydrogen at 670 K. In the cases of the deposited catalytic silver the response to hydrogen is considerably lower. In according with the results of the experiments, the characteristics of the films with additions of silver+yttrium in the bulk have weaker dependence on humidity changes. A common feature of samples with modifiers of silver and yttrium is the high stability of their properties under the periodical influence of hydrogen in long-term tests. Analysis of results shown that the complex modifiers of silver+yttrium interact with lattice atoms of tin and oxygen contribute to the emergence of deep centers in the semiconductor, and these additives prevent the process of reduction of tin dioxide at hydrogen adsorption and ensure the stability of the parameters of the sensors in operation.

Time dependences in the thermo-cyclic mode of the conductivity of CO sensors, constructed in a traditional four-electrode and a planar three-electrode design on the basis of thin nanocrystalline tin dioxide films, are analyzed. The analysis showed that the use of the Pt/Pd/SnO2:Sb sensors in a planar design in the thermocyclic mode with a long cooling cycle makes it possible to detect smoldering products at a significant reduction of power consumption.

Analysis of the results of studying electrical and gas sensitive characteristics of the molecular hydrogen sensors based on thin nanocrystalline SnO2 films coated with dispersed Au layers and containing Au+Ni and Au+Co impurities in the bulk showed that the characteristics of these sensors are more stable under the prolonged exposure to hydrogen in comparison with Au/SnO2:Sb, Au films modified only with gold. It has been found that introduction of the nickel and cobalt additives increases the band bending at the grain boundaries of tin dioxide already in freshly prepared samples, which indicates an increase in the density Ni of the chemisorbed oxygen. It is important that during testing, the band bending eφs at the grain boundaries of tin dioxide additionally slightly increases. It can be assumed that during crystallization of films under thermal annealing, the 3d-metal atoms in the SnO2 volume partially segregate on the surface of microcrystals and form bonds with lattice oxygen, the superstoichiometric tin atoms are formed, and the density Ni increases. If the bonds of oxygen with nickel and cobalt are stronger than those with tin, then, under the prolonged tests, atomic hydrogen will be oxidized not by lattice oxygen, but mainly by the chemisorbed one. In this case, stability of the sensors’ characteristics increases.

The electrical and gas-sensitive characteristics of sensors based on nanocrystalline SnO2 thin films with noble metals (Pt, Pd, Au) and 3d-transition metals (Co, Ni) additives in the bulk and on the surface have been studied. Thin (~100 nm) tin dioxide films were grown in magnetron by DC sputtering of a tin–antimony alloy target in oxygen–argon plasma. It was shown that the obtained sensors can detect acetone and ethanol vapors at 1 ppm level. The detecting of acetone vapors needs higher temperatures than detecting of ethanol. In a temperature range T < 650 K, responses to ethanol exceed responses to acetone for all studied samples. For higher operating temperatures T > 700 K, the sensors with deposited Pt, Pd catalysts on the surface as well as the sensors with Ni and Co additives in the bulk are characterized by a higher sensitivity to acetone than to ethanol. The use of different operating temperatures allows detecting selectively acetone and ethanol vapors.

The effect of hydrogen sulfide in the concentration range of 0–100 ppm on the characteristics of thin films of tin dioxide and tungsten trioxide obtained by the methods of magnetron deposition and modified with gold in the bulk and on the surface is studied. The impurities of antimony and nickel have been additionally introduced into the SnO2 bulk. An optimal operating temperature of sensors 350°C was determined, at which there is a satisfactory correlation between the values of the response to H2S and the response time. Degradation of the sensor characteristics is investigated in the long-term (~0.5–1.5 years) tests at operating temperature and periodic exposure to hydrogen sulfide, as well as after conservation of samples in the laboratory air. It is shown that for the fabrication of H2S sensors, the most promising are thin nanocrystalline Au/WO3:Au films characterized by a linear concentration dependence of the response and high stability of parameters during exploitation.