The modification of the surface reception properties of nanocrystalline structures is of great interest in environmental, catalysis and energy related applications. For instance, an oxide surface covered with a layer of another oxide opens the possibility of creating the nanosized counterparts of bulk catalytic systems. A relevant example is the TiO2-WO3, which is an active catalysts in a broad range of reactions. The chemical synthesis of the colloidal, nanocrystalline version of such system will first be exposed, by coupling suitable sol-gel chemistry with solvothermal processing. Then, the range of obtained structures will be discussed, ranging from WOx-surface modified TiO2 to TiO2-WO3 heterojunctions. The complex structural evolution of the materials will be discussed, depending on the W concentration. A summary of the acetone sensing properties of these systems will be shown. In particular, the surface activation of the otherwise almost inactive pure TiO2 by surface deposition of WO3-like layers will be highlighted. Addition of the smallest W concentration boosted the sensor response to values comparable to those of pure WO3, ranging over 2-3 orders of magnitude of conductance variation in presence of ethanol or acetone gases. Simple analysis of the sensing data will evidence that the combination of such nanocrystalline oxides results in catalytic activation effects, with exactly opposite trend, with respect to pure TiO2, of the activation energies and best responses.
ZnO@SnO2 multilayered network was deposited on fluorine doped tin oxide (FTO) glass and applied as photoanode in dye sensitized solar cells whose functional performances are compared with single oxide-based photoanodes made of SnO2 nanoparticles and ZnO microparticles. Multi-oxide photoanodes provide for enhanced photoconversion efficiency (3.31%) as compared with bare SnO2 nanoparticles (1.06%) and ZnO microparticles (1.04%). Improved functional performances of the ZnO@SnO2 layered network are ascribable to partial inhibition of back electron transfer from SnO2 to the redox electrolyte, guaranteed by the ZnO, which acts as a capping layer for the underlying SnO2.
We report on the potentiality of the Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique for the deposition of
thin films of colloidal nanoparticles to be used for gas sensors based on electrical transduction mechanisms. The MAPLE
technique seems very promising, since it permits a good thickness control even on rough substrates, generally used to
enhance the active surface for gas adsorption.
TiO2 (with a capping layer of benzyl alcohol) and SnO2 (with a capping layer of trioctylphosphine) colloidal
nanoparticles were diluted in suitable solvents (0.2% concentration), frozen at liquid nitrogen temperature and ablated
with a ArF (λ=193 nm) or KrF (248 nm) excimer laser. The nanoparticle thin films were deposited on silica,
interdigitated alumina and <100> Si substrates and submitted to morphological (SEM-FEG), structural (XRD, FTIR),
optical (UV-Vis transmission) and electrical (sensing tests) characterizations.
A uniform distribution of TiO2 nanoparticles, with an average size of ~10 nm, was obtained on flat and rough substrates.
The deposited TiO2 nanoparticles preserved the anatase crystalline structure, as evidenced by the XRD spectra. FTIR
analysis showed that the SnO2 nanoparticles maintained the capping layer after the laser-assisted transfer process. This
protective layer was removed after annealing at 400 °C. The starting nanoparticle dimensions were preserved also in this
case. Electrical tests, performed on TiO2 nanoparticle films, in controlled atmosphere in presence of ethanol and acetone
vapors, evidenced a high value of the sensor response even at very low concentrations (20-200 ppm in dry air). In
contrast, in the case of SnO2 nanoparticle films, electrical tests to ethanol vapor presence showed poor gas sensing
properties probably due to the small nanoparticle sizes and interconnections.
We developed a novel method to detect the presence of unburned diesel fuel in used diesel fuel engine oil. The method is
based on the use of an array of different gas microsensors based on metal oxide thin films deposited by sol-gel technique
on Si substrates. The sensor array, exposed to the volatile chemical species of different diesel fuel engine oil samples
contaminated in different percentages by diesel fuel, resulted to be appreciable sensitive to them. Principal Component
Analysis (PCA) and Self-Organizing Map (SOM) applied to the sensor response data-set gave a first proof of the sensor
array ability to discriminate among the different diesel fuel diluted lubricating oils. Moreover, in order to get information
about the headspace composition of the diesel fuel-contaminated engine oils used for gas-sensing tests, we analyzed the
engine oil samples by Static Headspace Solid Phase Micro Extraction/Gas Chromatograph/Mass Spectrometer (SHS-SPME/
The aim of this work is the fabrication of a cheap sol-gel Pt-doped TiO2 thin film sensor on silicon substrate, evaluate electrical performances of electrical interconnections and responses of sensitive film in severe environment like exhaust of combustion process. The sensor will be implemented as microsensors for NOx or oxygen detection, while a preliminary investigation on real operative conditions shows that the transducers perform a response time (t90) in real condition smaller than 1 second at 600 °C. Application field of this type of transducer will be evaluated in a real spark ignition engine, to monitor air/fuel ratio and also monitoring the combustion quality in other industrial combustion processes like domestic heating systems. The production process of this devices, and particularly thin film deposition, can be carried out on a 3" silicon wafer and obtaining with a single batch process more than 300 sensors for wafer, 2x2 mm2. The sensors are provided with an integrated heater and a thermometer to perform temperature compensation. Actually this work try to develop an affordable process to integrate cheap sol-gel deposition process with silicon technology; a particular study is devoted to a complete photolithographic patterning of titania sensitive film, that is very difficult to etch after complete annealing, in order to have sensitive film only onto well defined areas of wafer. Same process, with little modification, can be applied to different kind of sensitive film, pure and doped ones. Different strategies on protective coating were evaluated to reduce electrical contacts degradation at high temperatures, obtaining long time stability of overall microsensor.