1,720,968 research outputs found
Direct imaging of the core-shell effect in positive temperature coefficient of resistance-BaTiO(3) ceramics RID A-3737-2012 RID C-5307-2009
No full textMOCVD of CeF3 films on Si(100) substrates: synthesis, characterization and luminescence spectroscopy
No full textMOCVD synthesis of perovskite CaCu3Ti4O12 films
No full textThe results of a recent study on the deposition of calcium copper titanate, CaCu3Ti4O12 (CCTO), thin films on lanthanum alluminate, (001) LaAlO3, substrates by metal-organic chemical vapor deposition (MOCVD) are reported. A molten precursor mixture, consisting of the Ca(hfa)2 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; i-Opr = isopropoxide] precursors, has been employed. The one step route, carried out in the 800-900°C deposition temperature range, has been found unsuited to the formation of the desired CCTO phase, while a two-step MOCVD process leads to the formation of epitaxial CCTO thin films. Film structural and morphological characterization has been carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM)
A novel approach to synthesizing calcium copper titanate thin films with giant dielectric constants
No full textThe in-situ metal-organic chemical vapor deposition (MOCVD) growth of Calcium Copper Titanate Oxide (CCTO) films was analyzed using molten multimetal source. Investigations show that the perfect stoichiometry of the CCTO films pointed to the satisfactory behavior of the liquids. The results show the in-situ deposition of CCTO films on LaAlO3 substrates with the help of X-ray and electron transmission diffraction patterns
Influence of oxide substrates on monolayer graphene doping process by thermal treatments in oxygen
Full text linkThe structural and the electronic properties of monolayer graphene made by chemical vapor deposition and transferred on various oxide substrates (SiO2, Al2O3, and HfO2)are investigated by Raman Spectroscopy and Atomic Force Microscopy in order to highlight the influence of the substrate on the features of p-doping obtained by O2 thermal treatments. By varing the treatment temperature up to 400 °C, the distribution of the reaction sites of the substrates is evaluated. Their total concentration and the consequent highest doping available is determined and it is shown that this latter is linked to the water affinity of the substrate. Finally, by varing the exposure time to the gas up to 2 h, the kinetics of doping is investigated. The doping process is found to be better described by a diffusion limited kinetic model, ascribable to the diffusion of O2 in the interstitial space between graphene and the substrate. After this step, the doping process is completed by a faster redox reaction between O2 adsorbed to graphene and interstitial H2O
Aluminum oxide nucleation in the early stages of atomic layer deposition on epitaxial graphene
Full text linkThe nucleation and growth mechanism of aluminum oxide (Al2O3) in the early stages of atomic layer deposition (ALD) on monolayer epitaxial graphene (EG) on silicon carbide (4H–SiC) has been investigated by atomic force microscopy (AFM), conductive-atomic force microscopy (C-AFM) and Raman spectroscopy. Differently than for other types of graphene, a large and uniform density of nucleation sites was observed in the case of EG and ascribed to the presence of the buffer layer at EG/SiC interface. The deposition process was characterized by Al2O3 island growth in the very early stages, followed by the formation of a continuous Al2O3 film (∼2.4 nm thick) after only 40 ALD cycles due to the islands coalescence, and subsequent layer-by-layer growth. The electrical insulating properties of the deposited ultrathin Al2O3 films were demonstrated by nanoscale current mapping with C-AFM. Raman spectroscopy analyses showed low impact of the ALD process on the defect's density of EG. The EG strain was also almost unaffected by the deposition in the regime of island growth and coalescence, whereas a significant increase was observed after the formation of a compact Al2O3 film. The obtained results can have important implications for device applications of epitaxial graphene requiring ultra-thin high-k insulators
Temperature and time dependent electron trapping in Al2O3 thin films onto AlGaN/GaN heterostructures
No full textIn this article, the charge trapping phenomena in Al2O3 thin films grown by atomic layer deposition (ALD) on AlGaN/GaN heterostructures have been studied by time-dependent capacitance–voltage (C-V) measurements as a function of temperature. In particular, monitoring the transient of the capacitance enabled us to estimate the maximum depth of the insulating layer interested by the negative charge trapping effect under our bias stress conditions and to determine a charge traps density in the bulk Al2O3 in the order of 3 × 1019 cm−3. A temperature dependent C-V analysis up to 150 °C demonstrated the presence of two competitive mechanisms that rule the electron capture and emission in the Al2O3 film, characterized by activations energies of 22 and 88 meV respectively. Photoluminescence analyses revealed the presence of oxygen-related point defects in the insulator with a concentration in the order of ∼1020 cm−3 envisaging that only a fraction of them is electrically active. The results are useful to establish the thermal stability of the trapping phenomena, and the possible application in real devices
Perovskite CaCu3Ti4O12 thin films for capacitive applications: From the growth to the nanoscopic imaging of the permittivity
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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