S. Capone

Monitoring of rancidity of milk by means of an electronic nose and a dynamic PCA analysis

Abstract This paper reports the use of a semiconductor thin films based electronic nose to recognise the rancidity of two different kinds of milk (UHT and pasteurised) during their ageing days. The employed sensor array consists of five different SnO 2 thin films prepared by means of the sol–gel technology. The data coming from the response of the sensors have been elaborated by principal component analysis (PCA) in order to obtain a classification of the data clusters related to different milk ageing days and so track the dynamic evolution of milk rancidity. The obtained results could lead to industrial applications in dairying for the quality control of starting milk and the rancidity check during the different stages of production.

Analysis of vapours and foods by means of an electronic nose based on a sol–gel metal oxide sensors array

Abstract In this paper, a novel electronic nose based on a metal oxide gas sensors array, prepared by means of the sol–gel method in the form of thin films, is described, including the fabrication process. Two different configurations of the array were developed: one consisting of sensors with the same sensing layer (SnO2) but different geometry and material for the electrical electrodes, and another consisting of chemically modified SnO2 thin films. Examples of application to the analysis of air pollutants (CO, NO2, CH4, C2H5OH and CH3OH) and different foods (oil, milk, tomato, wine, ground coffee). Recognition of different air contaminants and of the aroma of foods is achieved by using the principal component analysis (PCA). Good discrimination among the clusters has been obtained indicating promising results for the application of our sensor array as electronic nose, in particular in the food industry for the classification of different olive oils.

A novel gas sensor based on SnO2/Os thin film for the detection of methane at low temperature

Abstract Osmium-doped tin oxide thin films were prepared by means of sol–gel technique. Their methane sensing properties were studied and compared to undoped SnO 2 thin films. The good sensitivity to methane at a low working temperature makes them very attracting active materials to be used in domestic CH 4 leak-detectors.

AIR QUALITY MONITORING BY MEANS OF SOL-GEL INTEGRATED TIN OXIDE THIN FILMS

Abstract Sol–gel pure and Pd-doped SnO2 thin films on integrated substrates were developed to detect NO2 and CO. PdO particles are included in the film matrix and their presence enhances the CO gas sensitivity and response time. Measurements of electrical conductivity showed that these films have a response variation higher than 1000% for NO2 at temperatures in the range of about 200°C with a detection limit near 0.1 ppm, good for air quality monitoring. The response to CO is below 100% of the electrical variation but also in this case the sensor can detect very low concentration level.

A comparison between V2O5 and WO3 thin films as sensitive elements for NO detection

Abstract Vanadium oxide (V2O5) and tungsten oxide (WO3) thin films were investigated with the aim to obtain information about their physical and gas sensing properties. The analysis in the presence of different NO concentrations have shown that both materials are able to detect nitrogen oxide, but their responses exhibit different characteristics. In particular, tungsten oxide was found to be more suitable to be used in the field of application for detecting low concentrations. In addition, a mechanism of detection has been considered.

Metallophthalocyanines thin films in array configuration for electronic optical nose applications

Abstract The interaction between some ambient reactive compounds and organic or inorganic thin layers can cause variations in the physical properties of the chemically interactive layers. Molecules in the gas phase, which are adsorbed onto the surface or absorbed in the bulk of the thin layer, generally modify the electrical or optical or mass properties of the gas-sensitive material giving rise to a number of different kinds of chemical sensors based on different working principles. This work reports and discusses the experimental results obtained with optical absorbance measurements in UV-Vis spectral range onto these optical sensitive layers in controlled atmosphere containing vapours. In particular, very interesting results have been obtained by optical absorption measurements carried out in the region of the typical Q band of phthalocyanines and a selectivity toward different vapours, depending both on the metal and the peripheral substituents of the macrocycle, was found. The as-manufactured sensors have been arranged in an array configuration and examples of applications for “electronic optical nose” to the analysis of some volatile organic compounds (VOC) which are of interest in food analysis are reported in this work.

Sprayed SnO2 thin films for NO2 sensors

Abstract SnO 2 thin films as NO 2 sensor in low concentration range have been obtained by chemical spray deposition technique. The AFM analysis showed that the as-deposited films are constituted of islands of rectangular shape and elongated in the same direction. The electrical characterisation results and their variations in the presence of the NO 2 gas mixed in low concentration with dry air are reported. The electrical response to NO 2 gas was studied in order to find the optimum detection temperature. The results have shown a resistance change of about 6000% at a working temperature of 350°C in the presence of 500 ppm of NO 2 toxic gas and a sensitivity threshold of about 5 ppm at the same working temperature.

SnO2 sol–gel derived thin films for integrated gas sensors

Abstract In this paper, we present for the first time the compatibility of sol–gel method for SnO2 thin film preparation with the silicon technology for integrated gas sensor microfabrication. An integrated circuit (IC) compatible test structure of medium power consumption equipped with boron-doped silicon heater and Au/W metallization is developed. The acid composition of the (liquid) sol phase, the thermal budget of sensing layer structuring, selective wet etching of SnO2 sensing film, thickness uniformity and step coverage of SnO2 sol–gel films are fitted with the requirement of above test structure where metal layer is deposited before SnO2 film. Nanometric grain sizes of undoped and antimony doped polycrystalline SnO2 films are obtained, as revealed by XRD investigations. The AFM measurements of SnO2 thin films deposited on existing Au/W metallization shown the excellent step coverage and morphology of SnO2 films used for gas sensing applications. Low temperature gas sensing properties of our SnO2 sol–gel derived thin films in reducing (CH4, CH3COOH) and oxidizing (NO2) are preliminary reported by using our integrated test structure.

In2O3 Thin Films Obtained Through a Chemical Complexation Based Sol-Gel Process and Their Application as Gas Sensor Devices

A new approach is presented for preparing In2O3 thin films starting from inorganic precursors, based on a very simple but effective modification of the usual precipitation-peptization process. Indium nitrate was dissolved in methanol and In3+ ions were chelated with acetylacetone before adding concentrated base to the resulting solution. Such a route allowed obtaining long-term stable sols, from which films could be deposited on glass substrates by spin-coating. Furthermore, the films exhibited a very good adhesion and uniformity, without any need for adding additives to the solution. The modification of the In precursor was confirmed by thermal analysis, while XRD studies revealed that the films prepared with the modified route result in smaller In2O3 grains compared to the traditional precipitation-peptization process. Optical reflectance measurements on the films further highlighted the difference between the two processes. Gas-sensing tests carried out on the films deposited onto alumina substrates in the temperature range between 100 and 400°C showed that faster responses are obtained at temperatures higher than 250°C. The response value (R/R0, where R is the electrical resistance of the sensor in the test gas and R0 that in dry air) to 100 ppb ozone is remarkably high: it is equal to 1500 for In2O3 with a response time of about 1 minute. The recovery time is about 10 minutes.

Recognition of olive oils by means of an integrated sol–gel SnO2 Electronic Nose

In this paper, we report a specific application of a semiconductor thin films based sensor array for the discrimination of different olive oils. The active elements of the sensor array were undoped and Ni, Pd, Pt, Os-doped SnO thin films prepared by 2 sol–gel technique. Olive oil samples were randomly selected. They included commercial olive oils of different qualities (extravirgin, virgin and husk oils) and non-commercial local olive oils (deriving from different zone of the Salento region in Apulia) with different degrees of acidity. The sensor array coupled with a principal component analysis allows discrimination between different olive oils. In particular good separation between commercial and local products was obtained. 2002 Elsevier Science B.V. All rights reserved.