A. Chiodoni

Optical and structural properties of SiC layers grown by an electron cyclotron resonance CVD technique

Abstract Large area microcrystalline and polycrystalline SiC thin films have been grown by electron cyclotron resonance CVD over (100) silicon wafers. The samples have been characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), micro-Raman and photo luminescence spectroscopy. Stoichiometric SiC films containing 3C–SiC crystals with orientation close to that of Si substrate and lateral grain dimension up to 1400 A were obtained under suitable deposition conditions. They also exhibit blue photoluminescence at room temperature in the range of 400–450 nm with features dependent on their structure.

Electrodynamics of Superconducting YBCO Films with Confined Correlated Nanodefects

We study the modification of local electrodynamical properties induced into microsized regions patterned by high energy gold ions into as-grown YBa2Cu3O7-x; film matrix. Two complementary cases of radiation-induced micro-channels on strip-shaped films are considered. In the first one the micro-channel is aligned perpendicular to the main supercurrent flow direction (transverse geometry). In the second one the micro-channel is parallel to the main supercurrent flow direction (longitudinal geometry). Quantitative magneto-optical analysis provides local imaging of magnetic field and current density redistribution over the modified film surface. A preliminary study of the local forces responsible for the not-local reorganization of screening current within the two previously mentioned landmark-geometries is presented.

R.F. SPUTTERING DEPOSITION OF BUFFER LAYERS FOR Si/YBCO INTEGRATED MICROELECTRONICS

The aim of the present work is the optimization of the Si/buffer-layer/YBCO multilayer deposition process so as to grow superconducting films of quality suitable for device applications. The structural properties of the Si/CeO2 system, obtained by RF magnetron sputtering of CeO2 targets in Ar atmosphere, have been studied. More than 50 films have been deposited and some of them submitted to post-deposition annealing treatments both in N2 and O2 atmospheres. The presence of an unwanted amorphous SiO2 layer at the Si/CeO2 interface compromises the YBCO c-axis orientation, and therefore the sharpness of the R versus T transition. A newly designed deposition system has been realized: it has been specially conceived for obtaining bi- and tri-layers, adopting two targets in YSZ and CeO2, respectively. Results on YSZ/Si and CeO2/YSZ/Si systems obtained with the new machine are presented and discussed: (100) oriented YSZ films with nominal thickness of 40 nm have been obtained. The CeO2 film subsequently deposited has the desired (100) orientation. The YBCO film, in the final YBCO/YSZ/CeO2/Si configuration, is c-axis oriented.

Proton irradiation induced effects on YBCO films analysed by magneto-optics

In this paper we present a quantitative magneto-optical analysis on c-axis oriented YBCO thin films, as grown and irradiated with 3.5 MeV protons at three different fluences. Magneto-optical measurements were performed over the temperature range 5–70 K and at magnetic fields up to 150 mT. The local current density values were obtained from the field maps by means of the Biot-Savart law inversion. The critical current density (Jc) is locally defined as the current density where the maximum pinning efficiency is reached. This procedure allows obtaining Jc independently of dissipation threshold criteria or critical state model. A Jc enhancement emerges for irradiation at the lowest fluence ( Ф +2.5⋅1015 cm−2) in the whole investigate temperature range. On the contrary at increasing the irradiation dose a temperature-dependent crossover from an enhancement to a worsening of Jc is exhibited.

Quantitative magneto-optical analysis of superconductors

A magneto-optical equipment has been set up and carefully calibrated. In this paper, we shortly review the main characteristic of this equipment, then we focus on the analysis to be performed in order to extract from magneto-optical images the local values of magnetic induction and electrical current density along the superconducting sample. This implies the numerical inversion of the Biot-Savart law. A detailed analysis modeling the interaction of the spontaneous magnetization across the indicator film with the magnetic fields in the specimen region has been performed. In particular, we take into account the generally disregarded interaction of the indicator film with in-plane magnetic fields, i.e. with the component parallel to the indicator surface. A set of experimental data on YBCO films is presents to show the actual impact of the new analysis method, for what concerns both the local values of the magnetic induction and the electrical current density evaluation. A critical comparison of the new obta...

Structural properties of 3C-SiC layers grown on Si substrates by Electron Cyclotron Resonance CVD Technique

In this work we mainly report on the analyses of polycrystalline silicon carbide films grown by Electron Cyclotron Resonance Chemical Vapor Deposition (ECR-CVD) on Si (100) and Si (111) substrates. Structural properties of the films have been analyzed by X-ray diffractometry, transmission electron microscopy and micro-Raman spectroscopy. Samples deposited with optimized deposition conditions, show a polycrystalline columnar structure with lateral crystal dimensions ranging from 300 up to 1400 A and an orientation close to that of the Si substrates.