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Deposition of Au nanoparticles (NPs) through UV ultra-short-pulse laser ablation in vacuum is a methodology suitable for obtaining high purity supported plasmonic NPs with a superb adherence to both planar and patterned substrates. Furthermore, the peculiarity that upon sub-picosecond laser irradiation NPs form directly within the target leads to narrow and controlled size-distribution. While extensive literature theoretically models phase changes and pressure relaxation of metal targets under sub-picosecond irradiation, the evolution of the nanostructured deposit through different ablation regimes is poorly documented experimentally. In this paper, besides modeling the temporal evolution of electron and lattice temperature following sub-picosecond laser pulse irradiation of Au bulk at the threshold ablation fluence (0.1 J/cm2), we report an accurate statistical, morphological and structural characterization of the AuNP distributions as a function of the laser fluence tuned from 0.1 to 3 J/cm2 to drive the target through two ablation regimes. The occurrence of photomechanical spallation and phase explosion at low and high fluence, respectively, is correlated with the evolution of the NP deposits, which are discussed by providing a physical insight in the interplay between fluence-driven ablation regimes of the target, arrangement kinetics of the deposited species (NPs and vapour species) and (crystalline or amorphous) phase of the NPs. This knowledge is key for controlling the surface plasmon resonance response of AuNPs depending on the designed application.

A cheap nanofabrication process for titania (TiO2) polycrystalline nanowire array for gas sensing applications with lateral size ranging from 90 to 180 nm, and gas sensing characterizations are presented. Alternatively to typical pattern transfer techniques for submicron fabrication, authors focused on a standard 365 nm UV photolithographic process able to fabricate sol–gel nanostructured titania nanowires from a solid thin film. Main aim of present work is the experimental validation of enhanced gas sensing response of nanopatterned metal oxide thin film sensors. Two different kinds of gas sensor with nanopatterned sensitive area have been realized onto silicon substrates and tested towards different EtOH concentrations; experimental tests have been carried out with a contemporary output signals collection from a nanowires-based gas sensor and a second device with solid sensitive film without patterning, in order to validate effects of nanomachining on sensitive material response.

Organic–inorganic nano-hybrids, synthesized by supersonic molecular beams of TiO2 clusters and copper-phthalocyanine (CuPc) molecules, have been used to develop gas-sensing devices. This approach allows tailoring the properties of the synthesized materials and the interface between clusters and organic molecules so that new functional materials with interesting sensing properties are obtained. Two-layer hybrid devices with different architectures have been realized on alumina substrates with gold interdigitated electrodes. The hybrid films show an increase in conductivity up to a factor 6 compared to the pure CuPc depending on the architecture used. The response in terms of changes in conductivity towards non-oxidizing (methanol) species has been tested at different working temperatures. The hybrids show much higher sensitivity and stability with respect to CuPc grown with the same technique and they are already quite responsive at temperatures (75 °C) where the nanostructured TiO2 sensors are not at all functional. We ascribe these promising performances to the contribution coming from the n-TiO2–CuPc interfaces generated by the deposition process and we envisage the ability of the supersonic beam approach to produce novel classes of nano-hybrids in a variety of functional nanostructures.

Gas sensors research moves nowadays towards new applications of traditional metal oxide gas sensors into new fields like food quality, security applications and combustion control. Besides an implementation of this kind of transducers requires often a reduction of sensor dimensions, introduction of mature silicon technology substrates and fabrication methods. This work focuses on results obtained about implementation of reliable, selective, subtractive processes to perform high resolution patterning of different metal oxide films, deposited by cheap sol–gel technology onto oxidized silicon wafer or provided with thin layers of sputtered silicon nitride. Main innovations in this paper deal with an experimental evaluation of different methods to perform etching processes for three different sol–gel metal oxide materials deposited on standard dielectric layers, and evaluation of photoresist mask chemical inertness.

Cereals contaminated by toxigenic fungi can be analysed by detecting and quantifying the related mycotoxins by using complex extraction procedures and analytical techniques. In this work, we studied the complex headspace of wheat samples contaminated by Fusarium poae fungi by SPME-GC-MS, searching the presence of non-grain volatile metabolites due to fungi contamination and their temporal evolution after inoculation. The chemical information on the headspace composition of fungi-contaminated wheat samples were used for the analysis by an electronic nose, evaluating its discrimination ability among differently contaminated samples.

Nanocrystalline SnO2, In2O3 and In2O3–SnO2 thin films have been prepared by modified sol–gel methods making use of no-standard precursors and a suitable surfactant. The oxide thin films have been used as gas-sensing layers in chemoresistive gas sensors and their performances in the detection of nitrogen dioxide (2–20 ppm in dry air) have been analysed by electrical characterization in controlled atmosphere. The samples have been structurally and morphologically characterized by X-ray diffraction and SEM, respectively. Good gas-sensing responses towards NO2 have been found for all the prepared samples with improved performances for the In2O3–SnO2 based sensor. The performances of the sensors have been discussed according to the surface chemical reactions between the gas phase and the semiconductor.

Supersonic cluster beam deposition (SCBD) is used for fabrication of microsensors based on nanostructured titania layers. With a simple one-step post-deposition thermal treatment it is possible to modify the structural and electrical properties of the sensitive layers. Morphological, structural, and electrical characterisations are shown. The obtained sensors have very good performances in term of dynamic response to the exposure to methanol.

Herein we report the preparation of hybrid Co porphyrin-SnO2 thin films by sol-gel technique and a study of their sensing properties. The porphyrin structure bears a carboxylic group to improve its stabilization into the oxide matrix. SEM characterization of the spin-coated thin films deposited onto alumina substrates showed a homogeneously morphology. These CoTCPP-SnO2 sensors showed fast and reversible responses towards the detection of methanol vapors and highest responses were obtained at the working temperature of 250 degreesC. Optical characterization of the heated CoTCPP-SnO2 thin films indicated that the metalloporphyrin is still present after heating up to 320 degreesC, while it was completely decomposed after thermal treatment at 400 degreesC. These results support the presence of a catalytic effect of the CoTCPP at lower temperature, which induces a significant increase in the sensor responses at 250 degreesC, while at higher temperature, where the porphyrin is thermally decomposed, the hybrid CoTCPP-SnO2 sensors behave similarly to pure SnO2 devices. On the contrary, no significant differences in the sensor responses where observed in the case of CO detection, showing that metalloporphyrins can be used to modify the selectivity of SnO2 sensors.

This paper reports on the preparation, surface and electrical characterisation of titanium dioxide thin-films for highly selective gas sensor devices. Seeded supersonic beam deposition technique was used to prepare nanostructured thin films for gas sensors application. Two different typologies of sensors, prepared under different deposition conditions, were investigated. They showed gas-sensing properties comparable to most of the TiO 2 films realised with other more conventional techniques.

In this paper, a sensors array based on pure and doped SnO 2 sol–gel thin films used for the discrimination of different Mediterranean salami is presented. Principal component analysis (PCA) results have shown good discrimination of the clusters when applied to three different measurements typologies: (a) among different salami, (b) among samples of the same salami with different ripening and (c) among salami produced by male and female swine. Microbiological analyses, regarding micrococcaceae and lactobacilli growth, are, also, reported. Moreover, preliminary results obtained by static headspace/gas chromatography/mass spectrometry (SHS/GC/MS) analysis are shown.

In this work we show the capability of a sol–gel based electronic nose to be used in qualitative and quantitative analysis with the aim to recognize common volatile compounds usually present in the headspace of foods. Acetone, hexanal and 2-pentanone were chosen for this kind of measurements, performed both in dry air and in mixture of 50% humidity, just to simulate the experimental set-up in real applications. Moreover, different mixtures of 2-pentanone and hexanal at low concentration were investigated. We show how linear technique, such as principal component analysis (PCA) algorithm can be used for inspecting data distribution in simple cases like cluster discrimination. Moreover, non-linear techniques for difficult regression problems, such as artificial neural networks (multi-layer perceptron (MLP) and radial basis function (RBF)) are needed in particular for the prediction of different concentrations.

In this paper we present the study on gas sensing properties of TiO2 thin films grown by seeded supersonic beam of cluster oxides. Supersonic cluster beams, produced by a pulsed micro-plasma cluster source have been successfully used to prepare nanocrystalline thin films of TiO2. The obtained gas sensor devices, prepared by using different deposition parameters, were suitable for the use in a gas sensor array for electronic nose. Sensors showed a quite good response to ethanol, methanol and propanol. Principal component analysis was used as method for testing the array capability in discrimination and recognition of the volatile compounds.

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.

Pure and Ni-, Pt-, Pd-, Os-doped tin oxide and pure and Fe-doped indium oxide thin films have been prepared by the sol‐gel process. The microstructural properties of the as-prepared films have been investigated by means of X-ray diffraction (XRD). All the samples showed a polycrystalline structure that resulted to be dependent on the presence of the particular doping element. Integrated gas microsensor devices based on both pure and doped sol‐gel thin films of these two different metal oxides (SnO2 and In2O3) were realized. They were linked in an array configuration and exposed to the volatile compounds of different commercial olive oils samples in order to test the application of the array in an electronic nose for the discrimination among different commercial olive oils. The differently modified sensitive materials showed different sensing characteristics to the headspace of the olive oil, hence modulating the selectivity of the array. PCA analysis was performed on the array responses and the results showed the capability to discriminate olive oils of different quality. # 2002 Elsevier Science B.V. All rights reserved.

Gas sensors based on hybrid ZnPc–TiO 2 nanostructures, produced by molecules and clusters both deposited by supersonic beams, demonstrate enhanced properties in terms of sensitivity, stability and recovery times with respect to pure ZnPc. The hybrid sensors produced by successive deposition of the molecules and the TiO 2 clusters show the ability to detect reducing gases, such as methanol, to which the response of metal-phthalocyanines is quite poor. A mechanism based on the formation of chemical bonding, activated by the kinetic energy of the molecules and the strong reactivity of the inorganic clusters, is proposed as being at the basis of electron transfer occurring between the inorganic nanostructure and the molecule. This mechanism would explain the rise of new gas sensing properties of this novel class of nano-hybrid materials.

Undoped and doped microsensors, based on tin oxide, have been prepared by the sol–gel deposition technique. The influence of the ageing of the Ti/Au interdigitated electrical contacts on the responses of the samples has been investigated. In particular, in this paper, are reported the responses of different sensors towards some gases and vapours, discussing the reproducibility, repeatability and the baseline drift during the measurements. SEM and XPS analyses of the samples were performed before and after the working period. The sensors showed a little drift, probably due to the ageing of the electrical contacts that was observed also in the SEM images. Obtained XPS results are in good agreement with SEM images.

The detection of aroma volatile compounds emitted by extra virgin olive oils (EVOOs) is of key importance in the quality control of this product. Physical–chemical techniques (GC, GC/MS, HPLC) and sensory analysis (panel test) are the classical methods used for this purpose, but they are expensive, time consuming, and do not allow on-line measurements. In this paper a new device, an Electronic Nose, that is a sensor array based on pure and doped SnO2 sol–gel thin films used for the discrimination of different Mediterranean “single-cultivar” EVOOs, was presented. To confirm the sensor array responses, analytical technique like headspace-solid phase micro-extraction/gas chromatography/mass spectrometry (HS-SPME/GC/MS) analysis was applied to the analysis of volatiles compounds in EVOOs samples. Moreover sensory analysis on EVOOs was carried out. The obtained GC/MS data were used to identify the particular compounds and characterize the chemical composition of the EVOOs samples. In addition a chemometric pattern recognition technique was used for multivariate data analysis. The variations in the GC/MS fingerprint of the different samples were analysed using principal component analysis (PCA). Statistical analyses were carried out on data obtained from Electronic Nose, GC/MS and sensory analysis. © 2005 Elsevier B.V. All rights reserved.

In this work we describe the design implementation, validated by experimental results, of an innovative gas sensor array for wine quality monitoring. The main innovation of this integrated array deals with the simultaneous outputs, from a single chip on custom SMD socket, of eight different signals coming from a WO 3 thin film structure heated in a linear temperature gradient mode, allowing an overall evaluation of gas sensing properties of the material in a 100 °C-wide window, typically from 300 to 400 °C. The implemented sensitive layer is a WO 3 film deposed by RF-sputtering. Preliminary tests of gas sensing showed good responses to the target analytes for the specific application (1-heptanol, 3-methylbutanol, benzaldehyde and ethyl-hexanoate).

Semiconductor sensors based on nanocrystalline SnO2, In2O3 and In2O3–SnO2 thin films have been investigated for detecting low concentration (2–20 ppm) of nitrogen dioxide in dry air. In this work the gas-sensitive layers were prepared by modified sol–gel methods making use of non-standard precursors and a suitable surfactant. The samples have been structurally and morphologically characterized by X-ray diffraction and SEM, respectively. Good gas-sensing responses towards NO2 have been found for all the prepared samples with improved performances for the In2O3–SnO2 based sensor. The performances of the sensors have been discussed according to the surface chemical reactions between the gas phase and the semiconductor.

We report on the preparation and characterization of titanium dioxide thin film gas sensor devices for application in lambda measurement. The sensor responses to different oxygen concentrations have been analyzed. Moreover, according to a computing software that simulates the composition of exhaust gases for different λ values, we exposed the sensors to different complex mixtures of exhaust gases, calibrating in such a way the sensor for the measurement of lambda.

This work reports on the use of two innovative techniques in the field of gas sensors for preparing nano-structured materials: sol–gel and supersonic cluster beam deposition. By means of sol–gel, nano-structured In 2 O 3 thin films have been prepared and deposited under different deposition parameters on silicon wafer. In this way the results have shown a good compatibility of the method with silicon technology, then potentially suitable to be used in the fabrication of integrated devices. The second technique has been applied for the preparation of nano-structured TiO 2 thin films showing its capability to be used in the fabrication of gas sensor devices, mainly when a good control of the grain dimension is required.

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.

In this paper we report on the deposition and characterization of tin oxide (SnO2) nanoparticle thin films. The films were deposited by the matrix-assisted pulsed laser evaporation (MAPLE) technique. SnO2 colloidal nanoparticles with a trioctylphosphine capping layer were diluted in toluene with a concentration of 0.2 wt% and frozen at liquid nitrogen temperature. The frozen target was irradiated with a KrF (248 nm, tau = 20 ns) excimer laser (6000 pulses at 10 Hz). The nanoparticles were deposited on silica (SiO2) and < 100 > Si substrates and submitted to morphological (high resolution scanning electron microscopy (SEM)), structural Fourier transform infrared spectroscopy (FTIR) and optical (UV-Vis transmission) characterizations. SEM and FTIR analyses showed that trioctylphosphine was the main component in the as-deposited films. The trioctylphosphine was removed after an annealing in vacuum at 400 degrees C, thus allowing to get uniform SnO2 nanoparticle films in which the starting nanoparticle dimensions were preserved. The energy gap value, determined by optical characterizations, was 4.2 eV, higher than the bulk SnO2 energy gap (3.6 eV), due to quantum confinement effects.