V. Brinzari

Influence of surface Pd doping on gas sensing characteristics of SnO2 thin films deposited by spray pirolysis

Abstract In this article the analysis of steady state and transient gas sensing characteristics of undoped and Pd surface doped SnO2 films, deposited by spray pyrolysis, is described. The influence of parameters such as air humidity (2–50% RH), operation temperature (25–500 °C) and Pd surface concentration (0–1% ML Pd) on gas response to CO and H2 (0.1–0.5%), response time, shape of sensitivity S(T) curves and activation energy of τ(1/kT) dependencies are discussed. A mechanism based on a chemisorption model is proposed to explain how Pd influences the gas sensing characteristics of SnO2 films.

Factors influencing the gas sensing characteristics of tin dioxide films deposited by spray pyrolysis: understanding and possibilities of control

Abstract The main structure and electronic parameters of SnO2 thin films are considered from the point of view of optimization gas sensor characteristics. The results of phenomenological modeling and their comparison with experiments are used for choosing the correct film parameters and modes of deposition for the processing of SnO2 films by the spray pyrolysis method. Optimal deposition conditions were found, allowing one to obtain films with improved sensitivity, selectivity, low temperature sensitivity maximum position and low response times without additional doping by metal catalysts.

Grain Size Effects in Sensor Response of Nanostructured SnO2- and In2O3-Based Conductometric Thin Film Gas Sensor

Based on the experimental results, obtained by studying both structural and gas-sensing properties of the SnO2 and In2O3 films deposited by the spray pyrolysis method, we analyzed the influence of crystallite size on the parameters of the SnO2- and In2O3-based thin film solid-state gas sensors. For comparison, the behavior of ceramic-type gas sensors was considered as well. In particular, we examined the correlation between the grain size and parameters of conductometric-type gas sensors such as the magnitude of sensor signal, the rate of sensor response, thermal stability, and the sensitivity of sensor signal to air humidity. Findings confirmed that that grain size is one of the most important parameters of metal oxides, controlling almost all operating characteristics of the solid state gas sensors fabricated using both the ceramic and thin film technologies. However, it was shown that there is no single universal requirement for the grain size, because changes in grain size could either improve, or worsen of operating characteristics of gas sensors. Therefore, the choice of optimal grain size should be based on the detailed consideration of all possible consequences of their influence on the parameters of sensors designed.

Possibilities of aerosol technology for deposition of SnO2-based films with improved gas sensing characteristics

Abstract Advantages of aerosol technology for deposition of nano-scaled (5–50 nm) undoped and Pd-doped metal oxide films for gas sensor applications are discussed in this report. Using SnO2-based film deposition as a case study, it has been shown that this technology has great potential for controlling the structure, the electrophysical, and gas sensing properties of metal oxides.

Morphological rank of nano-scale tin dioxide films deposited by spray pyrolysis from SnCl4·5H2O water solution

The morphology and some principal details of the crystallographic grain structure of tin dioxide thin (20–300 nm) films obtained from SnCl4·5H2O water solution by spray pyrolysis deposition were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) methods. Direct correlation between the pyrolysis temperature and several fundamental nanoscale grain shapes and crystallographic features successively replacing each other with Tpyr was shown. These were: (I) separate crystallites with a sphere-like shape (spherulites), existing at 300–350 °C; (II) agglomerated spherulites at T=350–410 °C; and (III) nanocrystals with regular crystal faceting at T=410–530 °C. In turn, the nanocrystals can be subdivided into three types of crystal habit: needle or long prismatic, prismatic and pyramidal habits, each of which corresponds to its own temperature range in increasing order. XRD study and crystallographic form analysis of the cassiterite phase allowed us to suggest identification of the grain facets observed in our experiments. An explanation is also suggested for the gas-sensing properties of such films, which are strongly dependent on the crystallographic grain habit {hkl} and may be attributed to surface orientation effects.

Conductometric gas sensors based on metal oxides modified with gold nanoparticles: a review

AbstractThis review (with 170 refs.) discusses approaches towards surface functionalizaton of metal oxides by gold nanoparticles, and the application of the resulting nanomaterials in resistive gas sensors. The articles is subdivided into sections on (a) methods for modification of metal oxides with gold nanoparticles; (b) the response of gold nanoparticle-modified metal oxide sensors to gaseous species, (c) a discussion of the limitations of such sensors, and (d) a discussion on future tasks and trends along with an outlook. It is shown that, in order to achieve significant improvements in sensor parameters, it is necessary to warrant a good control the size and density of gold nanoparticles on the surface of metal oxide crystallites, the state of gold in the cluster, and the properties of the metal oxide support. Current challenges include an improved reproducibility of sensor preparation, better long-term stabilities, and a better resistance to sintering and poisoning of gold clusters during operation. Additional research focused on better understanding the role of gold clusters and nanoparticles in gas-sensing effects is also required. Graphical AbstractThe Figure illustrates the growth in the number of publications devoted to the analysis of gas-sensitive properties of metal oxides modified by gold nanoparticles and shows SEM image of SnO2 films modified with gold nanoparticles.

Crystallographic characterization of In2O3 films deposited by spray pyrolysis

Abstract Results of a detailed structural characterization of In2O3 films, deposited by spray pyrolysis from InCl3–water solutions, are presented in this paper. The influence of technological parameters such as precursor concentration in sprayed solution, pyrolysis temperature, and film thickness on morphology, crystallite sizes, texturing, and strains were analyzed. SEM, TEM, XRD, AFM, HRTEM, and laser ellipsometry methods were applied for these purposes. An explanation of observed regularities is also given.

In2O3- and SnO2-Based Thin Film Ozone Sensors: Fundamentals

The paper considers SnO2 and In2O3 thin films as materials for the design of solid-state conductometric ozone sensors in depth. In particular, the present review covers the analysis of the fundamentals of SnO2- and In2O3-based conductometric ozone sensor operation. The main focus is on the description of mechanisms of ozone interaction with metal oxides, the influence of air humidity on sensor response, and processes that control the kinetics of sensor response to ozone.

Synthesis by successive ionic layer deposition (SILD) methodology and characterization of gold nanoclusters on the surface of tin and indium oxide films

Abstract The ability of successive ionic layer deposition (SILD) technology to synthesize gold clusters on the surface of tin(IV) oxide and indium(III) oxide films is discussed. It was shown that during the process, concentration of active sites that are capable of absorbing gold ions, and the size of the gold particles thus formed, may be controlled by both concentration of the solutions used and the number of SILD cycles. Thus, SILD methodology, employing separate and multiple stages of adsorption and reduction of adsorbed species, has considerable potential for customizing the properties of the deposited metal nanoparticles. In particular, it is shown that during the deposition of gold nanoparticles on the surface of tin(IV) oxide and indium(III) oxide films by SILD methodology, conditions can be realized under which the size of gold nanoclusters may be controllably varied between 1–3 nm and 50 nm. A model is proposed for the formation of gold clusters during the SILD process.

Distinguishing feature of metal oxide films' structural engineering for gas sensor applications

The different methods of structural engineering, used for improvement of solid state gas sensors parameters are reviewed in this paper. The wide possibilities of structural engineering in optimization of gas sensing properties were demonstrated on the example of thin tin dioxide films deposited by spray pyrolysis.