Ghenadii Korotcenkov

Silicon Porosification: State of the Art

This review is devoted to the analysis of the problems related to fabrication of the Si porous layers. The review was motivated by a great interest to Si-based porous materials from nano- to macro-scale for various applications in electronics, optoelectronics, photonics, chemical sensors, biosensors, etc. The peculiarities of the silicon porosification and the principles of preparing porous layers are considered in the present article. Various methods used for Si porosification such as chemical stain etching, chemical vapor etching, laser-induced etching, metal-assisted etching, spark processing and reactive ion (plasma) etching were analyzed. However, the main attention was focused on electrochemical porosification of Si. The review discusses in detail the influence of parameters such as electrolyte composition and pH, current density, etching time, temperature, wafer doping and orientation, lighting, magnetic field, and ultrasonic agitation on the process of Si porosification. It was shown that the structure of porous silicon strongly depends on both technological parameters of electrochemical etching and the parameters of the semiconductor subject to treatment. This review also addresses the main properties of porous silicon, porous multilayer and 3D structure formation, oxidation of porous Si, release of the porous layer, drying, storage, etching, filling and surface functionalizing of porous Si. Features of III-V compound porosification are also briefly analyzed.

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.

Porous Semiconductors: Advanced Material for Gas Sensor Applications

The present review article is devoted to the analysis of the problems related to the design of gas sensors based on porous semiconductors (PS). The peculiarities of the semiconductor porosification by anodic etching and the principles of gas sensor design based on porous semiconductors, including gas sensor construction and main operating characteristics, are considered in the article. It is shown that the influence of the surrounding atmosphere on such parameters of porous semiconductors as refractive index, the intensity of photoluminescence, electroconductivity, dielectric constant, and surface potential might be used for gas sensor design. Based on the conducted analysis it is concluded that porous semiconductors have a great potential for the above-mentioned applications. However, the realization of those opportunities is restrained by such factors as bad reproducibility, increased temporal drift of characteristics, low selectivity, and an unsatisfactory level of understanding of the operating mechanism of sensors fabricated on the basis of porous semiconductors.

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.

Handbook of Gas Sensor Materials: Properties, Advantages and Shortcomings for Applications Volume 2: New Trends and Technologies

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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.

Thin Metal Films

Thin metal films have a long history in gas sensor applications since all types of gas sensors include metal films, playing the role of either electrode or sensing material. This chapter describes the approaches which can be used for designing metal film-based gas sensors. Processes responsible for conductivity change in metal films are discussed. The advantages and disadvantages of metal-based gas sensors and approaches to sensor parameters improvement are analyzed as well. The chapter includes 9 figures, 2 tables, and 82 references.

Spray Pyrolysis of Metal Oxides SnO2 and In2O3 as an Example of Thin Film Technology: Advantages and Limitations for Application in Conductometric Gas Sensors

In this paper we present results of structural analysis of SnO2 films deposited by spray pyrolysis and designed for application in conductometric gas sensors. The aim of this analysis was summarizing the results obtained in this field, highlighting a correlation between material structure and its gas sensing properties, and formulating some general regularities typical for metal oxides.

Ultra-low thermal conductivity of nanogranular indium tin oxide films deposited by spray pyrolysis

The authors have shown that nanogranular indium tin oxide (ITO) films, deposited by spray pyrolysis on a silicon substrate, demonstrate ultralow thermal conductivity κ ∼ 0.84 ± 0.12 Wm−1 K−1 at room temperature. This value is approximately by one order of magnitude lower than that in bulk ITO. The strong drop of thermal conductivity is explained by the nanogranular structure and porosity of ITO films, resulting in enhanced phonon scattering on grain boundaries. The experimental results were interpreted theoretically, employing the Boltzmann transport equation approach for phonon transport and filtering model for electronic transport. The calculated values of thermal conductivity are in reasonable agreement with the experimental findings. The presented results show that ITO films with an optimal nanogranular structure may be prospective for thermoelectric applications.