Papers by Author: Maurizio Passacantando

Abstract: Multi-walled carbon nanotubes (MWCNTs) have been grown, simultaneously at different temperatures (600 °C, 700 °C, 725 °C, and 750 °C), by thermal chemical vapour deposition (CVD) of acetylene (C2H2) gas, in ammonia (NH3) atmosphere. The samples have been characterized morphologically by scanning electron microscopy (SEM) and a structurally by Raman spectroscopy. These analyses show that, when the temperature of substrate increases, the CNT average diameter and the density distribution decrease, and the CNTs are less defective. However there is a temperature limit (725 °C) for CNT growth. We have grown CNTs onto Si3N4/Si substrates with Pt electrodes, in order to realize the gas sensing devices. The CNTs grown at 725 °C, exhibit a fast response and a high sensitivity to NO2 gas.

Abstract: We present an extensive theoretical and experimental study of the Mn-Ge dilute magnetic semiconductor, a material which - due to its high integrability with mainstream Si technology - may hold good promises for spintronic applications. Ab-initio calculations on several different systems containing isolated Mn impurities as well as small clusters (up to three Mn impurities) show that Mn has a tendency to segregate into the Ge matrix and to stabilize occupation of interstitial sites if these are coordinated with other Mn occupying substitutional sites nearby. Several different experimental characterizations (HRTEM, XRD, UPS, MOKE) performed on Mn ion-implanted systems are analyzed and discussed: a close comparison betweeen experimental evidences and density functional calculations allows a full understanding of the sample properties and to disentagle the contributions coming from the diluted and segregated phases. The complexity of this system shows that much has to be done still to understand the physics of these materials and to undisclose all their possible applications.

Abstract: The microstructural characterization of r.f. magnetron sputtered ZnO thin films deposited on 6H-SiC is presented with a comprehensive investigation of their properties as a function of annealing temperature and film thickness. These structures, with some modifications, are utilised as Schottky diode hydrogen gas sensors and Surface Acoustic Wave (SAW) devices.