Graziella Malandrino

A novel route to the second-generation alkaline-earth metal precursors for metal-organic chemical vapour deposition: one-step synthesis of M(hfa)2·tetraglyme (M=Ba, Sr, Ca and Hhfa=1,1,1,5,5,5-hexafluoro-2,4-pentanedione)

A one-pot reaction for the synthesis of better performing alkaline-earth precursors for metal-organic chemical vapour deposition (MOCVD) applications, is reported. The reaction of metal hydroxides (Ba(OH)2·8H20, Sr(OH)2·8H2O) or oxide (CaO) with Hhfa and tetraglyme in air yields quantitatively monomeric, water-free, highly stable and volatile M(hfa)2-tetraglyme adducts. All the adducts have been characterized by TGA and DSC. MOCVD capabilities have been tested through depositions of metal fluoride for buffer layer applications and of BaCaCu matrices for HTc TIBaCaCu superconductor thin films.

Dielectric properties of Pr2O3 high-k films grown by metalorganic chemical vapor deposition on silicon

Praseodymium oxide (Pr2O3) thin films have been deposited on Si(100) substrates by metalorganic chemical vapor deposition using praseodymium tris-2,2,6,6-tetramethyl-3,5-heptandionate as source material. Film structural, morphological, and compositional characterizations have been carried out. Dielectric properties have been studied as well by capacitance–voltage and current–voltage measurements on metal-oxide-semiconductor capacitors of several areas. The Pr2O3 films have shown a dielectric constant e=23–25 and a leakage current density of 8.8×10−8 A/cm2 at +1 V.

Fluorinated β-Diketonate Diglyme Lanthanide Complexes as New Second-Order Nonlinear Optical Chromophores: The Role of f Electrons in the Dipolar and Octupolar Contribution to Quadratic Hyperpolarizability

The second-order nonlinear optical (NLO) properties of [Ln(hfac)(3)(diglyme)] (hfac = hexafluoroacetylacetonate; diglyme = bis(2-methoxyethyl)ether; Ln = La, Ce, Pr, Sm, Eu, Gd, Er, Lu) complexes have been investigated by a combination of electric-field second harmonic generation (EFISH) and harmonic light scattering (HLS) techniques, providing evidence for the relevant role of f electrons in tuning the second-order NLO response dominated by the octupolar contribution. These lanthanide NLO chromophores allow a clean valuation of the influence of f electrons on the quadratic hyperpolarizability and on its dipolar and octupolar contributions. Molecular quadratic hyperpolarizability values measured by the EFISH method, beta(EFISH), initially increase rapidly with the number of f electrons, the value for the Gd complex being 11 times that of the La complex, whereas this increase is much lower for the last seven f electrons, the beta(EFISH) value of the Lu complex being only 1.2 times that of the Gd complex. The increase of beta(HLS), which is dominated by an octupolar contribution, is much lower along the Ln series. Remarkably, the good beta(HLS) values of these simple systems, well known for their luminescence properties, are reached at no cost of transparency.

Core–shell Zn-doped TiO2–ZnO nanofibers fabricated via a combination of electrospinning and metal–organic chemical vapour deposition

Zn-doped TiO2 nanofibers shelled with ZnO hierarchical nanoarchitectures have been fabricated combining electrospinning of TiO2 (anatase) nanofibers and metal–organic chemical vapor deposition (MOCVD) of ZnO. The proposed hybrid approach has proven suitable for tailoring both the morphology of the ZnO external shell as well as the crystal structure of the Zn-doped TiO2 core. It has been found that the Zn dopant is incorporated in calcined electrospun nanofibers without any evidence of ZnO aggregates. Effects of different Zn doping levels of Zn-doped TiO2 fibers have been scrutinized and morphological, structural, physico-chemical and optical properties evaluated before and after the hierarchical growth of the external ZnO shell over the electrospun nanofibers. Moreover, doping promotes the incipient transition from the anatase to rutile phase in the core–shell Zn-doped TiO2–ZnO nanostructures at lower temperature than that observed for pure TiO2. Finally, the present core–shell hierarchical nanofibers possess a very large surface to volume ratio and exhibit a marked cathodoluminescence with a strong UV and visible emission.

Morphological and structural control of nanostructured oriented CeO2 films grown on random metallic substrates

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·diglyme [Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; diglyme = (CH3O(CH2CH2O)2CH3)] precursor. The X-ray patterns of all samples grown in the 350–550 °C temperature range point to the formation of oriented CeO2 films, while at higher deposition temperatures (650–850 °C) random CeO2 films are formed. XRD data indicate that 450 °C is the best deposition temperature. Detailed studies of the influence of all deposition parameters (precursor vaporization temperature, O2 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.

Breakdown kinetics of Pr2O3 films by conductive-atomic force microscopy

The dielectric breakdown (BD) kinetics of praseodymium thin films has been determined by comparison between current-voltage measurements on large-area (up to 78.54μm2) metal-oxide-semiconductor structures and conductive-atomic force microscopy (C-AFM). C-AFM clearly images the weak BD single spots under constant voltage stresses. The stress time on the single C-AFM tip dot was varied from 2.5×10−3 to 8×10−2s. The density of BD spots, upon increasing the stress time, exhibits an exponential trend. The Weibull slope and the characteristic time of the dielectric BD have been determined by direct measurements at nanometer scale.

Study of the Thermal Properties of Pr(III) Precursors and Their Implementation in the MOCVD Growth of Praseodymium Oxide Films

A praseodymium adduct, Pr(hfa) 3 .diglyme [(H-hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentandione, diglyme = CH 3 O(CH 2 CH 2 O) 2 CH 3 )] has been synthesized. It has been applied as a Pr source for the metallorganic chemical vapor deposition (MOCVD) of praseodymium containing films on silicon substrate and compared with Pr(tmhd) 3 [(H-tmhd = 2,2,6,6-tetramethyl-3,5-heptandione)] precursor. Physical and thermal properties of both Pr(hfa) 3 .diglyme and Pr(tmhd)3 precursors have been fully analyzed and their efficacy as MOCVD precursors for the growth of praseodymium oxide films have been fully tested. Depending on the oxygen partial pressure (p O2 ), different praseodymium oxide phases have been obtained.

Epitaxial NiO gate dielectric on AlGaN/GaN heterostructures

This letter reports on epitaxial nickel oxide (NiO) films grown by metal-organic chemichal vapor deposition on AlGaN/GaN heterostructures. The grown material was epitaxial, free from voids and exhibited a permittivity of 11.7, close to bulk NiO. This approach is advantageous with respect other methods such as the thermal oxidation of Ni films due to a better reproducibility and film quality. A reduction of the leakage current in Schottky diodes with an interfacial NiO layer has been observed and described using the metal-insulator-semiconductor Schottky model. The results indicate that these films are promising as gate dielectric for AlGaN/GaN transistors technology.

From micro- to nanotransport properties in Pr2O3-based thin layers

In this paper, the conduction mechanisms in Si/SiO2/PrxSiyOz/Pr2O3/Au metal-insulator-semiconductor capacitors have been investigated. The dielectric stack has been produced by metal-organic chemical-vapor deposition. Nanoscopic and microscopic capacitance properties have been correlated. The capacitance-voltage (C-V) characteristics of 25-μm-radius metal-oxide-semiconductor capacitors have been evaluated and compared to the measurements performed by scanning capacitance microscopy (SCM). The study of the SCM images allows us to confirm the value of interface state density (Dit≈1012cm−2eV−1) obtained by C-V investigation excluding any defect or grain-boundary contribution in the capacitance phenomena. The conduction mechanisms have been investigated by current-density–voltage (J-V) measurements performed at different temperatures (from 100 to 200 °C). At low electric fields, a slight dependence of J-V characteristics in function of both temperature and electric field has been observed, while a relatively ...

Silver nanowires by a sonoself-reduction template process

An effective approach based on a sono-assisted self-reduction template process from a suitable silver precursor (Ag(hfa)tetraglyme) is reported for preparing metallic silver nanowires.