Matteo Ferroni

Screen-printed perovskite-type thick films as gas sensors for environmental monitoring

Abstract Thick films of LaFeO 3 and SmFeO 3 were fabricated by screen-printing technology on alumina substrates with comb-type Au electrodes. The perovskite-type oxide powders used for the preparation of the thick films have been prepared by the thermal decomposition at 700°C of hexacyanocomplexes, Ln[Fe(CN) 6 ] ·  n H 2 O. These powders are ultrafine, homogeneous, and free of intragranular pores. The films have been fired at different temperatures in the 750–1000°C range, in N 2 and air atmospheres. The gas-sensitive electrical response of the thick films have been tested in laboratory, in environments with different gases (CO and NO 2 ) in dry and wet air. For field tests, the prototype sensors have been placed beside a conventional station for environmental monitoring. The electrical response of the thick films has been compared with the results of the analytical instruments for environmental monitoring. The same trend was observed for both systems, with very promising results.

NANOSTRUCTURED PURE AND NB-DOPED TIO2 AS THICK FILM GAS SENSORS FOR ENVIRONMENTAL MONITORING

Abstract Thick films of nanostructured TiO 2 and Niobium-doped TiO 2 have been fabricated by screen-printing technology starting from pure Titania and Niobium-doped Titania powders; the powders were prepared by laser pyrolysis method which provides nanosized particles. The laser powders are crystalline with anatase structure and an average specific surface area of approximately 100 m 2 g −1 ; their grain size ranges from 10 up to 25 nm, the particles are spherical monocristalline and without internal porosity. In this work we evidentiated that TiO 2 -based thick film sensors exhibit a suitable sensitivity to atmospheric environmental monitoring provided that the microstructural properties of the materials are suitably correlated to the required electrical features. Moreover nanostructured particles were obtained at high firing temperature by adding a proper metal ions to inhibit the grain sintering. Finally, prototype sensors based on pure titania sensing film have been prepared and tested in field for environmental monitoring application.

MoO3-based sputtered thin films for fast NO2 detection

Abstract The authors report about preparation and characterization of thin films of MoO3 as a material for gas-sensing applications. Structural investigation of the films is carried out by electron microscopy and X-ray diffraction techniques. The sensing behavior of the MoO3 films was tested to NO2, showing capability to detect a few ppm of NO2 with considerably short response time.

Characterization of a molybdenum oxide sputtered thin film as a gas sensor

We report about preparation and characterization of sputtered MoO3 thin film as sensing layer for gas detection. We show its capability to detect CO concentrations lower than 10 ppm in wet air, a feature that allows direct usage of this material for environmental monitoring. The research also highlights some criteria for selecting a suitable material and shows which features are important for a thin film to be a good candidate as a chemical sensor.

Characterization of a nanosized TiO2 gas sensor

Abstract Thin films were obtained by r.f. reactive sputtering from a Ti.1W.9 target onto a Si substrate followed by annealing in air at 800 °C. The thermal treatment results in a nanosized TiO2 thin film with high surface-to-volume ratio. The nanosized structure, its stability, together with the ease of preparation, make this material suitable as a gas sensor. The sensing layer proved capable to detect 20 ppm of NO2 at a temperature suitable for monitoring of exhaust gases of engines. Its high sensitivity suggests use of this sensor for environmental purposes.

Nanostructured mixed oxides compounds for gas sensing applications

Abstract We present some recent trends about research on gas sensors based on semiconducting thin films based on Ti, W, and Mo mixed oxides. The structural, electrical and gas-sensing properties of these films, deposited by rf reactive sputtering from composite targets of W–Mo, Ti–W and Ti–Mo at different abundance, were investigated through electron microscopy and volt-amperometric techniques. All of these layers showed sensing capability toward CO, NO2 or ethanol. The thin films obtained were able to detect CO, NO2, and ethanol below the concentration limit for environmental-monitoring and breath-analysis application.

Preparation and Characterization of Nanostructured Titania Thick Films

The extraordinary modification of bulk-material properties provided by nanosized materials, due to magnification of surface effects, has encouraged the scientific community to seek novel methodologies of synthesis. Among these, particular emphasis has been given to the techniques that envisage large-scale production and could improve the present-day technology. Nanostructured titania films possess an immense range of applications, e.g. in the field of optics, electrical insulation, photovoltaic solar cells, electrochromic displays, antibacterial coatings, photocatalytic reactors, high-performance anodes in ion batteries, and for gas sensing. Indeed, the production of nanostructured titania thin films has been recently carried out by several methods. It was also shown that some applications greatly benefited from a nanostructured phase for TiO2. [11]

Near-infrared photoluminescence in titania: Evidence for phonon-replica effect

The photoluminescence of rutile and anatase TiO2 has been investigated in the range of 360–890 nm at several temperatures. An unexpected intense near-infrared (1.53 eV) photoluminescence band was recorded for both phases. At low temperatures, the resulting bands form a substructure of equally spaced peaks irrespective of the phase. The spectra were interpreted in the framework of the single-configuration-coordinate model as the phonon-replica effect, originating from ionization of oxygen vacancies.

Preparation of nanosized titania thick and thin films as gas-sensors

Abstract Nanosized titania thick and thin films were produced and shown to possess sensing capability. Correlation between electrical performance and structural features is inferred, with particular emphasis to the role played by the grain size. The nanostructured nature of the layers allows the films to be operated within a remarkably lower temperature range (350–800°C) with respect to previously existing titania bulk sensors. The films are sensitive to CO and NO2.

Structural characterization of Nb–TiO2 nanosized thick-films for gas sensing application

Abstract Pure and Nb-doped TiO2 thick-films were prepared by screen-printing, starting from nanosized powders. Grain growth and crystalline phase modification occurred as consequence of firing at high temperature. It has been shown that niobium addition inhibits grain coarsening and hinders anatase-to-rutile phase transition. These semiconducting films exhibited n-type behavior, while Nb acted as donor–dopant. Gas measurements demonstrated that the films are suitable for CO or NO2 sensing. Microstructural characterization by electron microscopy and differential thermal analysis (DTA) highlights the dependence of gas-sensing behavior on films properties.