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Aluminum nitride (AlN) thin films were deposited by sputtering on Ti bottom electrodes and integrated on a kapton substrate for flexible and stretchable electronics. The aim of this work was to find the best combination of Ti underlayer sputtering conditions and AlN over-growth to obtain the (002) nitride orientation, fundamental requirement for the piezoelectric response of the material in piezoelectric devices. Flexible electronics represent today’s cutting-edge electronic technologies thanks to their low cost and easy fabrication scalability.

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.

Nanocrystalline NiO thin films were deposited by dc reactive magnetron sputtering in a mixture of oxygen and argon and subsequently coated by Au on a NiO film surface. Very thin Au overlayers with a thickness of about 1 and 7 nm have been prepared by magnetron sputtering. Then, the surface modified NiO films have been analysed by TEM, EDX and SEM. NiO thin films showed a polycrystalline structure with the size of nanocrystals ranging from a few nanometers to 10 nm. Electrical responses of NiO-based structure towards hydrogen have been measured.

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.

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.

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 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.

A cheap nanofabrication process for Titania (TiO2) polycristalline 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 kind 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 nano-machining on sensitive material response.

Fast and cheap nanofabrication process of titania (TiO2) nanowires array with lateral dimensions width ranging from 90 to 180 nm and 1.4 mm in length is presented. In spite of typical pattern transfer techniques for submicron fabrication, this work focused on a 365 nm UV photolithographic process to obtain long nanowires of sol-gel nanostructured titania onto silicon oxide mesa. TiO2 nanostrips-based array was electrically connected by sputtered platinum electrodes and tested towards different gases. A performance comparison within micromachined and solid thin film gas sensor was carried out.

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).

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 TO-12 socket, of 8 different signals coming from a WO3 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 WO3 film deposed by RF-sputtering. Preliminary tests of gas sensing showed good responses to the target analytes for the specific application (1-heptanol, 3-methyl butanol, 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 the fabrication of libraries of nanostructured TiO2 films with a gradient in nanoparticle crystalline phase and dimensions. By supersonic cluster beam deposition it is possible to produce rutile nanoparticles with a diameter smaller than 10 nm and to spread them into a co-deposited amorphous titania matrix. Upon thermal annealing rutile nanocrystals act as growth seeds of a film with a spatially controlled rutile/anatase ratio. Films with controlled crystalline phase variation have been deposited on micropatterned substrate to produce arrays of chemoresistive sensors of volatile organic compounds. Devices with different nanocrystalline structures and performances are obtained by a simple one-step thermal treatment after deposition.

Thin films in the SnO2-In2O3 system, with relative concentrations of the two oxides ranging from 2% to 98% (molar percentage of the oxide), were deposited by sol-gel and solution processes. The films for the physical characterizations were deposited onto oxidized silicon substrates, while the films for the gas-sensing tests were deposited onto alumina. The starting solutions were characterized by FTIR spectroscopy, while the films on silicon, heated at various temperatures, were characterized by X-ray diffraction and SEM observations. The interaction between the two systems is particularly evident in the case of the system described by a 50% In2O3-50% SnO2 nominal composition. The crystallization on In2O3 during the film heat-treatment hinders the crystallization of SnO2, thus Sn is dispersed as an n-dopant in the In2O3 lattice, indeed showing a current signal, in the gas-sensing test, two orders of magnitude higher than the pure film. The response of the mixed-oxide based device to NO2 is better than pure In2O3. On the other hand, the response (relative resistance change) of pure SnO2 to low (from 0.1 to 1 ppm) NO2 concentrations ranges from 150 to 300, a result that can be correlated with the nanostructure of the film, which, from SEM and XRD results, seems constituted by very small grains.

Hybrid CoTPP-SnO2 thin films have been obtained by the sol-gel approach coupled with spin coating technique. These films have been deposited onto interdigital electrodes and their performances as chemical sensors have been measured towards the detection of methanol vapors. These CoTPP-SnO2 sensors showed fast and reversible responses towards different concentrations of methanol and best results were obtained at 250 degrees C working temperature, while a sharp decrease was observed at higher temperatures. These results are attributed to the well known catalytic activity of metalloporphyrins, which is not thermally decomposed at 250 degrees C, as confirmed by optical measurements.

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.

In this paper, we present the first sensor ever built using films grown by supersonic beam of cluster oxides as sensing material. Supersonic cluster beams, produced by a pulsed micro-plasma cluster source have successfully used to prepare nanocrystalline thin films of TiO/sub 2/. The sensors, prepared by using different deposition parameters, were suitable for 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 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.

Cluster supersonic beams have been previously shown to be a viable method to produce nanostructures by assembling them on a substrate in a controlled way. Control of precursors properties in the beam efficiently determine morphology, structure of films and their functional properties. Sensors based on cluster assembled TiO/sub 2/ show remarkable properties (sensitivity, response time and selectivity). We expand this approach to organic functionalization of nanostuctured oxides in a co-deposition scheme combining supersonic sources of organics (SuMBE) and of oxides (MPCS). Characterization of the properties of films and of the precursors will be discussed. This opens the perspective of using a co-deposition process combining metal (oxides) clusters and organic molecules to produce hybrid "decorated" nanostructures that could combine the inorganic stability and the molecular selectivity to produce a novel generation of gas sensors. The performance of the first prototype will also be presented.

In this work a fast, cheap and reproducible strategy for the realization of gold nanoparticles (NPs) over large areas is presented and their unique optical properties due to the excitation of Localized Surface Plasmon Resonances (LSPR) investigated. Based on thermal de-wetting of thin metal films, this fabrication method allows the realization of waferscale homogeneous distributions of gold nano-islands on planar substrates, providing an interesting alternative to sequential and very expensive manufacture techniques. Furthermore, a numerical method for the description of the optical and functional properties of the proposed metal nanostructures is proposed. Single and multiple gold nanostructures distributed on planar substrates are studied by exploring their possible application as label-free chemical sensors. The proposed analytical method is applied in particular for the study of possible interactions between plasmonic NPs and resonant organo-metallic molecules deposited in form of thin films on the metal nanostructures. The key factors determining the performances of this hybrid plasmonic material as chemical sensor are investigated.