G. Korotcenkov

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.

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.

Structural characterization of SnO2 gas sensing films deposited by spray pyrolysis

Abstract The results of SnO 2 thin film structure characterization using X-ray diffraction, scanning electron microscopy, and Auger electron spectroscopy are presented in this report. We discuss the influence of film deposition conditions and modes of heat treatment in the range of temperatures (400–900°C) on crystallite size and predominant orientation. It was determined that SnO 2 films, deposited by spray pyrolysis, are textured polycrystalline films. The crystallite sizes in the films could be controlled over a range from 9 to 25 nm by varying the film thickness, deposition method, and post-deposition annealing temperature. The structure of these SnO 2 films was very stable in an oxygen-containing atmosphere. It was found that crystallite orientation, in addition to crystallite size, plays a major role in determining the gas sensitivity of SnO 2 films. Crystallites with crystallographic (110) and (200) planes parallel to substrate are predominant in the films. The relative amounts of crystallites with a (110) and (200) orientation depend on film thickness and deposition mode.

Successive ionic layer deposition (SILD) as a new sensor technology: synthesis and modification of metal oxides *

In this paper, we have discussed both peculiarities and advantages of successive ionic layer deposition (SILD) methods for the synthesis and modification of metal oxides. For these purposes, the results of research into the design of SILD technology suitable for preparing porous nanostructure SnO2 films and the surface modification of SnO2 films deposited by spray pyrolysis have been analysed. It has been shown that this new method can be used for the deposition of metal oxides and for noble metals. A great deal of interest in the SILD method may be generated by the methods simplicity, cheapness, and ability to deposit thin nanostructure films on rough surfaces. The SILD method essentially consists of successive treatments of both conductive and dielectric substrates by solutions of various salts, which form poorly soluble compounds at the substrate surface. It has been found that SILD technology is an effective method for improving gas sensor parameters. For example, it has been established that surface modification by Pd and Ag using SILD technology improves the gas response of SnO2-based sensors to reducing gases, and depresses their sensitivity to oxidizing gases.

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.

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.

Successive ionic layer deposition: possibilities for gas sensor applications

In this paper we discuss results of research related to design of successive ionic layer deposition (SILD) technology for both preparing porous nano-structured SnO2 films, and surface modification of SnO2 films deposited by spray pyrolysis. This new method of metal oxide deposition has exited high interest, because of this method simplicity, cheapness, and ability to deposit thin nano-structured films on rough surfaces. Method of successive ionic layer deposition (SILD) consists essentially of repeated successive treatments of the conductive or dielectric substrates by solutions of various salts, which form on the substrate surface poorly soluble compounds. It was shown that SILD technology is effective method for above mentioned purposes.

Processes controlling the rate of In/sub 2/O/sub 3/ thin film gas sensor's response

The kinetics of gas response to reducing and oxidizing gases of In/sub 2/O/sub 3/-based thin film gas sensors is analyzed in this report. The influence of operating temperature, air humidity and film thickness (d from 20 to 400 nm) on both the E/sub act/ and time constants of gas response is reviewed. Model conceptions allowing to explain specific character of In/sub 2/O/sub 3/ interaction with reducing and oxidizing gases are proposed.