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A conductive atomic force microscopy (C-AFM) study on a positive temperature coefficient of resistance (ptcr) BaTiO3 thermistor is reported. The method provides imaging of the dielectric properties with a lateral resolution on the nanometer scale. Measurements were carried out in the temperature range of 25-250 C to study the conduction mechanisms below and above the ferroelectric-paraelectric transition at similar to 130 C. The effective thickness of the barrier regions associated with the grain-shell and grain boundaries is similar to 450-550 nm and is similar to 10% of the volume fraction of the grains. The C-AFM results therefore confirm previous impedance spectroscopy studies that show the ptcr-effect to be associated with both the grain boundaries and outer grain-shells of individual grains.

Chemical Vapor Deposition (CVD) uses one or more gaseous species (precursors) to form on a substrate, solid phase materials through an activated process. While today a large variety of precursors is known and rather complex deposition routes are involved, a user-friendly classification of precursor compounds as well as a viable discussion of their physical and chemical characteristics can be useful to MOCVD practitioners. In this Chapter, an overview of both the exploitation and challenges of MOCVD fabrication of praseodymium oxides will be highlighted from different points of view, including the more suited precursors, the synthesis of thin films and their stability on silicon substrates.

Citato 156 volte in letteratura internazionale (Fonte: www.scopus.com). Citato 143 volte in letteratura internazionale (Fonte: apps.webofknowledge.com). Citato 212 volte in letteratura internazionale (Fonte: http://scholar.google.com/) Studio multicentrico. I membri dei vari centri sono indicati singolarmente in quota al proprio dipartimento universitario/centro di appartenenza nel paragrafo "Acknowledgment". Abstract Summary Background Data: The epidemiology of venous thromboembolism (VTE) after cancer surgery is based on clinical trials on VTE prophylaxis that used venography to screen deep vein thrombosis (DVT). However, the clinical relevance of asymptomatic venography-detected DVT is unclear, and the population of these clinical trials is not necessarily representative of the overall cancer surgery population. Objective: The aim of this study was to evaluate the incidence of clinically overt VTE in a wide spectrum of consecutive patients undergoing surgery for cancer and to identify risk factors for VTE. Methods: @RISTOS was a prospective observational study in patients undergoing general, urologic, or gynecologic surgery. Patients were assessed for clinically overt VTE occurring up to 30 ± 5 days after surgery or more if the hospital stay was longer than 35 days. All outcome events were evaluated by an independent Adjudication Committee. Results: A total of 2373 patients were included in the study: 1238 (52%) undergoing general, 685 (29%) urologic, and 450 (19%) gynecologic surgery. In-hospital prophylaxis was given in 81.6% and postdischarge prophylaxis in 30.7% of the patients. Fifty patients (2.1%) were adjudicated as affected by clinically overt VTE (DVT, 0.42%; nonfatal pulmonary embolism, 0.88%; death 0.80%). The incidence of VTE was 2.83% in general surgery, 2.0% in gynecologic surgery, and 0.87% in urologic surgery. Forty percent of the events occurred later than 21 days from surgery. The overall death rate was 1.72%; in 46.3% of the cases, death was caused by VTE. In a multivariable analysis, 5 risk factors were identified: age above 60 years (2.63, 95% confidence interval, 1.21-5.71), previous VTE (5.98, 2.13-16.80), advanced cancer (2.68, 1.37-5.24), anesthesia lasting more than 2 hours (4.50, 1.06-19.04), and bed rest longer than 3 days (4.37, 2.45-7.78). Conclusions: VTE remains a common complication of cancer surgery, with a remarkable proportion of events occurring late after surgery. In patients undergoing cancer surgery, VTE is the most common cause of death at 30 days after surgery. Copyright © 2005 by Lippincott Williams & Wilkins.

MOCVD fabrication of ferroelectric SrBi2Ta2O9 (SBT) films using Sr(hfac)(2)center dot tetraglyme, Bi(C6H5)(3), and Ta(OC2H5)(5) precursors is reported. The SBT phase has been reproducibly obtained adopting a two-step procedure, namely, the deposition of a fluorine-containing Sr-Bi-Ta-O(F) matrix followed by the annealing step at 800 degrees C. The multicomponent deposition process was optimized by tuning the overall process to individual kinetics associated with each singled-out precursor, to film morphologies and microstructures, and finally to film properties. Particular attention has also been focused on the annealing process of the deposited Sr-Bi-Ta-O(F) matrix aimed at an efficient crystallization step of the SBT phase as well as on an efficient elimination of fluorine phases associated with decomposition of the fluorinated Sr precursors.

A novel approach based on a molten multicomponent precursor source has been applied for the MOCVD fabrication of high-quality CaCu3Ti4O12 (CCTO) thin films on various substrates. The adopted in situ strategy involves a molten mixture consisting of Ca(hfa)(2)center dot tetraglyme, Ti(tmhd)(2)(O-iPr)(2), and Cu(tmhd)(2)[Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; tetraglyme) 2,5,8,11,14-pentaoxapentadecane; Htmhd = 2,2,6,6-tetramethyl- 3,5-heptandione; O-iPr) isopropoxide] precursors. Film structural and morphological characterizations have been carried out by several techniques [X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM)], and in particular the energy filtered TEM mapping and X-ray energy dispersive (EDX) analysis in TEM mode provided a suitable correlation between nanostructural properties of CCTO films and deposition conditions and/or the substrate nature. Correlation between the nanostructure and optical/dielectric properties has been investigated exploiting spectroscopic ellipsometry.

CeO2 (cubic fluorite) thin films have been deposited on no-rolled Hastelloy C276 substrates by metal-organic chemical vapour deposition (MOCVD) from the Ce(hfa)(3)center dot diglyme [Hhfa 5 1,1,1,5,5,5- hexafluoro- 2,4- pentanedione; diglyme = (CH3O(CH2CH2O)(2)CH3)]precursor. The X-ray patterns of all samples grown in the 350-55 degrees C temperature range point to the formation of < 100 > oriented CeO2 films, while at higher deposition temperatures (650-850 degrees C) random CeO2 films are formed. XRD data indicate that 450 degrees C is the best deposition temperature. Detailed studies of the influence of all deposition parameters ( precursor vaporization temperature, O-2 and Ar gas flows, deposition temperature and time) on the CeO2 film growth have been carried out. There is evidence that the deposition process occurs in a mass transport regime. A suitable rationale for the observed textural changes vs. temperature has been proposed and the present columnar grain morphology, depending upon deposition temperatures, has been related to the zone model proposed by Mochvan and Demchishin for physical vapour deposition processes.

The conduction mechanism in Si/SiO2/PrxSiyOz/Pr2O3 stack deposited by Metal-Organic Chemical Vapour Deposition (MOCVD) has been investigated and correlated to the electrical defects by performing current density-voltage (J-V) measurements at several temperatures (from 100 degrees C to 200 degrees C). The Hill's diagram indicated that at high electric fields the conduction follows the Poole-Frenkel mechanism. Nanoscopic and microscopic properties have been correlated by comparison between capacitance voltage (C-V) measurements on large area MOS devices and measurements carried out at nanometer scale by scanning capacitance microscopy (SCM). A trap density of 4.77 x 10(11) cm(-2) was measured independently of the scale dimension. Finally, the energy levels contributing to the conduction phenomena were determined to be located at the midgap.

Praseodymium-containing thin films have been deposited on Si(001) substrates by metal-organic chemical vapor deposition (MOCVD) from the Pr(tmhd)(3) (H-tmhd = 2,2,6,6-tetramethyl-3,5-heptanedione) precursor. The structural, compositional, and morphological film characterization has been investigated using X-ray diffraction (XRD), angle-resolved X-ray photoelectron spectroscopy (AR-XPS), and transmission electron microscopy (TEM). Detailed studies of the deposition parameters indicate that the MOCVD process is governed by a kinetic regime and that some reactive phenomena occur at the film/substrate interface, forming a praseodymium silicate layer. A possible explanation for interfacial interaction has been proposed, taking into account the diffusion of Si from the substrate towards the bulk and that of oxygen from the film surface toward the substrate/ film interface. Finally, the electrical characterization of the praseodymium silicate layer has been carried out in order to evaluate its potential implementation as an alternative dielectric. Its dielectric constant has been evaluated to be about 8.

Different praseodymium oxide phases have been obtained by varying oxygen partial pressure during the MOCVD process at 750°C on Si(100). Hexagonal Pr2O3 have been obtained under oxygen deficient conditions, while at oxygen partial pressure higher than 0.7 torr oxidized phases, such as Pr6O11 and/or PrO2, are dominant. Transmission electron microscopy (TEM) and energy filtered transmission electron microscopy (EF-TEM) analyses have been used to characterize structural, compositional and morphological features of praseodymium oxide films.