G. Micocci

Physical and structural characterization of tungsten oxide thin films for NO gas detection

Abstract Tungsten trioxide (WO3) thin films were rf sputtered from a WO3 target in various oxygen/argon (O2/Ar) atmospheres and at different total pressures. A detailed structural and morphological investigation has been carried out on all obtained films by high resolution electron microscopy and nanodiffraction methods. Optical and electrical properties have been studied as function of deposition parameters. In addition, all obtained films were tested in controlled atmosphere in order to investigate their response to NO in the interval 2–100 ppm in dry air. The sputtering parameters were optimized in order to obtain the maximum sensitivity to NO gas. Finally, a close dependence between sputtering conditions, morphological features and physical properties was observed.

Properties of vanadium oxide thin films for ethanol sensor

Thin films of vanadium oxides for ethanol sensor applications were been prepared by means of rf reactive sputtering from a vanadium pentoxide target in an Ar–O2 atmosphere. Films with the best sensitivity and selectivity were obtained with 15% oxygen at a working temperature between 280 and 300 °C. These films show a very low sensitivity to CO, CO2, and CH4 and total insensivity to NH3.

Optical absorption and photoconductovity in amorphous indium selenide thin films

Abstract Optical absorption coefficient and photoconductivity measurements were performed on amorphous indium selenide thin films produced by vacuum evaporation. The dependence of the absorption coefficient α on the photon energy ħω at the edge of the absorption band is well described by the relation α h ω = B( h ω - E opt ) 2 where B is a quality factor and Eopt is the optical band gap. The steady state photoconductivity as a function of the temperature and light intensity is tentatively interpreted in terms of a simple kinetic model proposed by Weiser et al.

Structural and electrical properties of sputtered vanadium oxide thin films for applications as gas sensing material

A detailed structural and morphological investigation has been carried out by conventional transmission electron microscopy, high resolution electron microscopy and nanodiffraction methods on vanadium oxide films obtained by reactive rf sputter at a high power discharge (1000 W) and different O2/Ar ratio. Electrical characterization has been also performed in controlled atmosphere in order to investigate the influence of NO2 oxidizing gas on the material conductance as a function of deposition parameters. A strict relation between structure, morphology and resistance variation in controlled atmosphere has been observed.

ELECTRICAL PROPERTIES OF N-GASE SINGLE CRYSTALS DOPED WITH CHLORINE

Hall-effect and space-charge-limited-current (SCLC) measurements were performed on Cl-doped GaSe single crystals grown by the Bridgmann–Stockbarger method. The temperature dependence of the free electron density shows the characteristics of a partially compensated n-type semiconductor. The electrical properties are dominated by a deep donor level at about 0.57 eV below the conduction band. An electron trapping level between 0.56 and 0.62 eV below the conduction band has been observed by SCLC measurements. The trapping level concentration depends on the amount of dopant. Finally, the conduction band density-of-states effective mass was estimated to be 1.1 m0.

SEM-EDS investigation on PM10 data collected in Central Italy: Principal Component Analysis and Hierarchical Cluster Analysis

BackgroundPrincipal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) were applied on PM10 particle data in order to: identify particle clusters that can be differentiated on the bases of their chemical composition and morphology, investigate the relationship among the chemical and morphological parameters and evaluate differences among the sampling sites. PM10 was collected in 3 different sites in central Italy characterized by different conditions: yard, urban and rural sites. The concentration of 20 chemical parameters (C, O, Na, Mg, Al, Si, P, Cd, Cl, K, Ca, Sn, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn) were determined by Scanning Electron Microscopy – Energy Dispersive X-ray Spectroscopy (SEM-EDS) and the particle images were processed by an image analysis software in order to measure: Area, Aspect Ratio, Roundness, Fractal Dimension, Box Width, Box Height and Perimeter.ResultResults revealed the presence of different clusters of particles, differentiated on the bases of chemical composition and morphological parameters (aluminosilicates, calcium particles, biological particles, soot, cenosphere, sodium chloride, sulphates, metallic particles, iron spherical particles). Aluminosilicates and Calcium particles of rural and urban sites showed a similar nature due to a mainly natural origin, while those of the yard site showed a more heterogeneous composition mainly related to human activity. Biological particles and soot can be differentiated on the bases of the higher loads of Fractal Dimension, which characterizes soot, and content of Na, Mg, Ca, Cl and K which characterize the biological ones. The soot of the urban site showed higher loadings of Roundness and Fractal Dimension than the soot belonging to the yard and rural sites, this was due to the different life time of the particles. The metal particles, characterized mainly by the higher loading of iron, were present in two morphological forms: spherical and angular particles. The first were generated by a fusion process at high temperature, while the second one had crustal origin (those characterized by typical terrigenous elements) and also human origin.ConclusionIn this work a protocol for the morphological-chemical characterization of single particles has been developed. SEM analysis allows to classify particles in 10 different families and PCA and HCA have provided information about the sources of PM and similarities and differences among the sites.

Gas-sensing properties of porphyrin dimer Langmuir-Blodgett films

Abstract Langmuir–Blodgett films of a 1:4 mixture of meso,meso′-buta-1,3-diyne-bridged Ni(II) octaethylporphyrin dimer and arachidic acid have been deposited onto various substrates. The isotherm at the air/water interface and absorbance measurements using polarised light are consistent with a planar statistical orientation of the porphyrin dimers which are probably prone onto the arachidic acid tails. The presence in the dimer of the acetylenic linking group allows the formation of a large and highly conjugated molecular structure; this has suggested the use of the films in gas sensing apparatus. Electrical characterisation in controlled atmosphere and with the simultaneous presence of interfering gaseous species, such as C2H5OH, NH3, and CO, suggest that this porphyrin dimer is a promising selective NO gas sensing material.

SnO2 thin films for gas sensor prepared by r.f. reactive sputtering

Abstract SnO2 thin films have been grown by means of the r.f. reactive sputtering method in order to be used as gas sensors. The films are deposited onto heated alumina substrates in an Ar-O2 atmosphere starting from an SnO2 target. We have optimized the growth parameters in order to achieve the best thin-film properties. The surface structure and the composition of the prepared films are investigated by X-ray diffraction and X-ray photoelectron spectroscopy. The effect on the gas-sensing characteristics of dispersing platinum onto the film surface by sputtering from a Pt target followed by a suitable thermal annealing, has also been studied. In particular, Pt-added SnO2 thin films show a high sensitivity to carbon monoxide gas at temperatures of about 170°C. This temperature is lower than the optimum operating temperature (about 350°C) of SnO2 samples without platinum.

CO sensing characteristics of reactively sputtered SnO2 thin films prepared under different oxygen partial pressure values

Abstract Thin films of tin oxide (SnO2) have been deposited by means of RF sputtering from a pure SnO2 target onto alumina substrates in an Ar O 2 mixture. Different oxygen contents in the sputtering atmosphere were used, in order to achieve the best thin films properties for CO detection. Films with the best sensitivity were obtained with 30% oxygen. The optimum operating temperature of the realized devices was about 270 °C.

Characteristics of reactively sputtered Pt–SnO2 thin films for CO gas sensors

SnO2 thin films were prepared by the rf reactive sputtering method from a target of the same compound in order to be used as gas sensors. Dynamic response characteristics of the electrical conductance to different CO concentrations in dry air are presented for pure films and for films activated with a suitable amount of metallic Pt deposited by sputtering onto a SnO2 surface. The sensitivity, the response, and recovery times as a function of temperature were analyzed. In particular, the Pt–SnO2 films show relatively high sensitivity to CO gas and good stability at an operating temperature of about 170 °C.