Sergio Nicoletti

The sensitivity and selectivity of micromachined gas sensors strongly depend on the temperature of the heating element; therefore an accurate determination of this temperature is required. In this paper, a simple analytical model of the thermal behavior of a heating element placed onto a thermally insulated dielectric membrane is presented. It is demonstrated that simple resistance vs. power measurements are sufficient for a precise determination of the sensor temperature. These measurements performed "once and for all" at the wafer-level on the statistically relevant number of heaters, allowed us to determine a "universal" temperature vs. power curve.

The heating characteristic of a microheater element, placed onto a thermally insulated dielectric membrane, define the sensitivity and selectivity of a micromachined gas sensor. Therefore an accurate determination of its temperature is required. In this paper, we describe a new four-point probe heating element configuration together with a simple analytical model of its thermal behavior.

ABSTRACT Al2O3 thin films were fabricated by pulsed laser deposition (PLD) on Si3N4/Si, to improve the thermal and electrical isolation of gas sensing devices. The microstructure of the films is analyzed as a function of the deposition conditions (laser fluence, oxygen pressure, target-substrate distance and substrate temperature). X-ray analysis shows that only a sharp peak that coincides with the corundum (116) reflection can be observed in all the films. But, when they are annealed at temperatures above 1,200°C, a change in the crystalline structure of some films occurs. The stoichiometry and morphology of the films with and without thermal treatment are compared using environmental scanning electron microscopy (SEM) and EDAX analysis.Se depositaron películas delgadas de Al2O3 por ablación láser sobre Si3N4/Si para utilizarlas como aislante térmico y eléctrico en dispositivos sensores de gases. Se analiza la microestructura de estas películas en función de las condiciones de la deposición (densidad de energía del láser, presión de oxígeno, distancia blanco-substrato y temperatura del substrato). Los estudios de difracción de rayos X, utilizando geometría de ángulo rasante, muestran que sólo puede observarse la reflexión coincidente con la (116) del corundum. Cuando las películas se tratan térmicamente a temperaturas superiores a 1.200°C sufren un cambio en su cristalinidad que depende de las condiciones de la deposición. Utilizando microscopía electrónica de barrido (SEM) y análisis por EDAX, se comparan la estequiometría y la morfología de las películas con y sin tratamiento térmico.

Silicon doping by high fluence pulsed laser irradiation in BC13 and PC13 atmospheres has been performed giving rise to shallow heavily doped junctions. The doped layers are free from extended defects, nevertheless a reduction of carrier mobility has been evidenced. Point defects originated by the fast solidification of the molten surface are responsible for the degradation of the transpOrt properties in the doped layer. The strain profile, originated from the point defect distribution, have been measured for different irradiation conditions. It was evidenced that the defective region is mostly limited inside the doped layer. A remarkable reduction of point defects is obseved when the laser irradiation takes place on samples kept at 400°C. At this temperature the speed of the solidification front is reduced of about 40%, thus limiting the number of quenched point defects.

... Sintered Silicon Nitride Ceramic Imran Khan, M. Zulfequar* Department of Physics, Jamia Millia Islamia, New Delhi, India. ... The values of ε′ and " ε from room tempera-ture to ( 625K) remain almost independent of tempera-ture. As the temperature are increases, ε′ and " ε in-...

This study presents a new type of Monte Carlo simulation method which allows us to investigate film growth under conditions comparable with experiments. To represent either beam-assisted deposition or thermal processing the method combines assumptions used in collisional physics and in growth kinetics phenomena. Furthermore the physics is based on the analysis of the bonding in simple structures formed by cells of YBa2Cu3O7. For this analysis a semiempirical calculation of the extended Debye-Hückel approximation has been used. The results of the calculations are generally in agreement with experiments. Furthermore they show that the temperature dependence, which is peculiar to the YBCO growth, can be understood at least in qualitative terms, as a special form of growth kinetics. intermediate between Lifshitz-Slyozov and percolation theory.

X-ray diffraction analyses using symmetrical and asymmetrical reflections were performed on YBa2Cu3O7−x films grown in situ by pulsed laser deposition. Monocrystalline (100) oriented SrTiO3, MgO and YSZ were used as substrates. The measurements allowed the calculation of the film lattice parameters and the determination of the film-substrate epitaxial relationships. The in-plane and out-plane film textures were also studied. The critical current density between 17 K and 87 K was measured in narrow strips patterned by a direct writing laser system. A comparative discussion of the results obtained for the transport properties and the structural characteristics was carried out for films grown on MgO.

ABSTRACT This study presents a Monte Carlo simulation method designed to describe the growth of oxicuprate films. The basic assumption of the simulation is that the deposition process can be divided in a collisional and a thermal phase and that the collisional phase can be treated with the methods used in ion implantation. This assumption allows the extension of the simulations to energies well above the thermal range. In agreement with experimental trends, preliminary results show anisotropic effects in the film growth.

ABSTRACT We report a systematic study of the Hall mobility and the carrier concentration of a conjugated polymer [poly(4,4′-dipentoxy-2,2′bithiophene)] as a function of the electrochemical doping level, over a wide range of the carrier concentration (from ∼ 1015 to ∼ 1019 cm−3). Very high values were obtained for the carrier mobility (from 102 to 10−1 cm2 V−1 s−1), when compared with those reported in the literature for organic materials. Furthermore, an inverse relationship between mobility and carrier concentration was found. © 1998 American Institute of Physics.

The heating characteristic of a microheater element, plated onto a thermally insulated dielectric membrane, define the sensitivity and selectivity of a micromachined gas sensor. Therefore an accurate determination of its temperature is required. In this paper, we describe a new four-point probe heating element configuration together with a simple analytical model of its thermal behavior

... Appl. Supercond. 3 (1993 ) 2349. [ 12 ] S. Matarazzo, S. Barbanera, V. Boffa, R. Bruzzese, F. Ciciulla, U. Gambardella, F. Murtas, S. Pagano, M. Penna and C. Romeo, J. Supercond. 6 (1993) 393. [ 131 A. Di Chiara, F. Lombardi, S. Matarazzo, S. Pagano, B. Ruggiero, M. Russo ...

We report on magneto-transport studies in lithographically patterned InAs 2DEG devices. Electron transport between adjacent current injection and extraction channels was studied as a function of temperature and magnetic field. The mean free path in the quantum well at RT and 5 K in our devices is approximately 280 nm and 980 nm respectively. The spacing between the current tabs

ABSTRACT The occurrence of the Sick Building Syndrome (SBS) inside buildings equipped with Heating Ventilation Air Conditioning (HVAC) Systems can be reduced by controlling the concentration of pollutants in the indoor air. This can be achieved by smart intervening procedures implemented in the HVAC control system, which will be operated on the basis of reliable information about both the indoor and outdoor air quality, aiming to ensure the most appropriate amount of ventilation. Within CLEAN-AIR, we are developing a dedicated, miniaturized, low-cost electronic nose realized using state-of-the-art microsystems/sensors fabrication technologies. This e-nose provides data as input to the specifically implemented smart intervening procedures, which will allow the HVAC system to be operated under demand, rather than by a fixed duty cycle.

A current problem various gas sensors have to deal with is the lack of selectivity against a single gas in the presence of gas mixture. This paper presents the application of a membrane reactor consisting of a permeable, porous silicon membrane combined with an ultra-short packed silicon gas chromatographic column (GCC) to optimize the gas selectivity for a resistive thin

The microstructure of YBa2Cu3O7 thin films grown by pulsed laser deposition on (001)-oriented MgO substrates cut at different angles off-axis was studied by X-ray diffraction and transmission electron microscopy. The films consist of twin-related grain domains with the c axis normal to the surface. The in-plane texture was found to be epitaxially related to the substrate lattice as predicted by the near-coincidence site lattice theory. An increase in the number of grain orientations and their relative populations was observed when the angle at which the substrate was cut off-axis increased, corresponding to a deterioration of the electrical transport properties. Growth of preferred orientations was observed in a sample cut at a high off-axis angle. The bias toward a particular direction has been explained in terms of a constraint induced by surface steps in the grain nucleation.