Martha Es-Souni

Multiferroic BiFeO3 thin films processed via chemical solution deposition : Structural and electrical characterization

Polycrystalline BiFeO3 thin films were fabricated on (111)Pt∕Ti∕SiO2∕Si substrates via Bi-acetate- and Fe-acetylacetonate-based chemical solution deposition and spin-coating techniques. The processing parameters were optimized in order to obtain films with high resistivity. The optical properties (refractive indices and extinction coefficients) were measured by means of ellipsometry (HeNe laser, λ=632.8A). Microstructure characterization was made by means of atomic force microscopy, grazing incidence x-ray diffractometry (XRD), and texture analysis. Additionally, powders prepared from a stoichiometric precursor were investigated by means of thermogravimetric and differential thermal analyses and XRD. It is demonstrated that the formation of perovskite-type BiFeO3 is accompanied by the appearance of bismuth oxide at low temperatures which then transforms into Bi36Fe2O57. For the films it was found that annealing in oxygen leads to higher indices of refraction, lower roughness, and smaller grain size. Compl...

Effects of rare earth manganites on structural, ferroelectric, and magnetic properties of BiFeO3 thin films

The results of structural studies of pure-phase perovskite thin films of BiFeO3–10% RMnO3 (R=La, Eu, Gd, Tb, and Dy) are presented. Raman scattering studies show line broadening similar to what is reported for RMnO3; they were attributed to Jahn–Teller distortion and orthorhombic structural change. Evidence of an anomaly of the orthorhombic distortion at GdMnO3 could be obtained. Interestingly the addition of GdMnO3 leads to a substantial increase in magnetization, combined with moderate ferroelectric polarization. All other compositions are characterized by higher ferroelectric polarization but almost no magnetization.

On the properties of two binary NiTi shape memory alloys. Effects of surface finish on the corrosion behaviour and in vitro biocompatibility

The present paper compares the transformation behaviour and mechanical properties of two orthodontic wires of close chemical compositions. The effects of surface topography and surface finish residues on the potentiodynamic corrosion behaviour and biocompatibility are also reported. The cytotoxicity tests were performed on both alloys in fibroblast cell cultures from human gingiva using the MTT test. It is shown that the surface finish and the amounts of surface finish residues affect dramatically the corrosion resistance. Bad surface finish results in lower corrosion resistance. The in vitro biocompatibility, though not affected to the extent of corrosion resistance, is also reduced as the surface roughness and the amounts of residues increase. This is thought to be due to surface effects on corrosion and metallic ions release.

On the transformation behaviour, mechanical properties and biocompatibility of two NiTi-based shape memory alloys:: NiTi42 and NiTi42Cu7

The transformation behaviour, mechanical properties and cytotoxicity of a binary NiTi42 and a ternary NiTi42Cu7 alloy have been investigated. The transformation temperatures were determined via differential scanning calorimetry, the mechanical properties have been investigated in 3-point bending tests in the temperature range between 6 and 60 degrees C. The cytotoxicity tests were performed on both alloys in cultured epithelial cells from human gingiva. The cytotoxicity investigations included both MTT tests and morphological observations. It is shown that although the ternary alloy is characterised by a narrower hysteresis and superior mechanical properties, including fatigue resistance, its cytotoxicity is higher than that of the binary alloy. This is thought to arise from the release of copper ions in the medium, which upon atomic absorption spectroscopy measurements amount to approximately 2.8 microg cm(-2) for an incubation period of 7 days.

Thick film polymer-ceramic composites for pyroelectric applications

Thick films of 0-3 composites of lead-zirconate-titanate ceramic and polyvinylidene-trifluorethylene copolymer have been produced by spin coating on gold-coated silicon wafers. The dielectric properties were investigated as a function of ceramic volume fraction and temperature. Pyroelectric measurements were undertaken by temperature modulation with a Peltier element. Additionally, the pyroelectric response has been investigated up to 3000Hz using a modulated laser. The piezoelectric response of the composites obtained by using a laser vibrometer are also reported. It is shown that the dielectric constant increases with increasing volume fraction of ceramic and that it reaches a maximum at a temperature in the range of 65–70°C due to the ferroelectric-paraelectric phase transition of the polymer matrix. The pyroelectric coefficient increases to 92μCm−2K−1 at a ceramic volume fraction of 20%. Furthermore the effective piezoelectric charge coefficient d33 of the composite almost vanishes at this composition...

Multiferroic properties of Bi0.9Gd0.1Fe0.9Mn0.1O3 thin film

Monolithic oxides whose lattice structures exhibit both ferroelectric and magnetic ordering and eventually intrinsic coupling between them are known as multiferroics. The possibility to switch magnetization by an electric field and reciprocally polarization by a magnetic field may allow new applications spanning the fields from new memory devices to medical measuring technology. Until now, the only monolithic oxide that has been shown to exhibit both (weak) magnetism and ferroelectric polarization at room temperature is BiFeO3 (BFO). However, as this material is a line compound, i.e., with sharply defined stoichiometry, its properties largely depend on defects and parasitic phases that could arise during processing. In the present work, we report on a new compound based on the solid solution GdMnO3–BiFeO3 (GdMBFO) that exhibit a fairly high magnetization coupled with moderate ferroelectric polarization at room temperature. Using conductive-tip atomic force microscopy, we show the highly electrically homog...

LaMnO3 effects on the ferroelectric and magnetic properties of chemical solution deposited BiFeO3 thin films

Thin films of the BiFeO3–LaMnO3 solid solution were processed on (111)‐Pt∕Ti∕SiO2∕Si substrates via spin coating. Microstructure, and leakage current, ferroelectric and magnetic properties are reported. It is shown that the addition of 5mol% LaMnO3 substantially improves the properties. Leakage currents that are several orders of magnitude lower than those of pure BiFeO3 were obtained. The leakage currents follow the Poole-Frenkel mechanism, and a trap depth of 0.94eV was obtained. The addition of LaMnO3 resulted in saturated polarization hysteresis loops with a high remnant polarization 2Pr of 88μC∕cm2. Finally, LaMnO3 also leads to higher coercive fields but smaller saturation magnetization.

Self-poled Pb(Zr,Ti)O3 films with improved pyroelectric properties via the use of (La0.8Sr0.2)MnO3/metal substrate heterostructures

Pb(Zr,Ti)O3 (PZT) thin films were deposited on different substrate heterostructures including platinized silicon, stainless steel and Ni-based alloy foils. A buffer layer of (La0.8Sr0.2)MnO3 (LSMO) between PZT and substrate was used. The pyroelectric coefficients were determined using low frequency sinusoidal temperature waves. It is demonstrated that PZT films deposited on metallic foils exhibit high pyroelectric coefficients of up to 760μC∕Km2 in the unpoled state, whereas the films deposited on platinized substrates were found to have pyroelectric coefficients in the range of 30μC∕Km2. These results are explained in terms of elemental diffusion from the substrate together with stressed states of the films.

On the in vitro biocompatibility of Elgiloy, a co-based alloy, compared to two titanium alloys.

Abstract.Aim: The aim of the present investigation was to contribute to an understanding of the effects of surface topography and chemical composition on the corrosion behavior and thus the biocompatibility of Elgiloy® (RMO, Denver, CO, USA), a common Co-based alloy. Material and Methods: The results are compared with those obtained for a binary NiTi alloy, Neo Sentalloy™ (GAC, Central Islip, NY, USA) and a β-III-Ti alloy, TMA® (Ormco, Glendora, CA, USA). In the present study, the surface topography and the chemical composition of two different grades of Elgiloy®, Blue Elgiloy® (soft) and Yellow Elgiloy® (ductile), were examined by means of scanning electron microscopy (SEM) and energy-dispersive spectroscopy analysis (EDS). Their corrosion behavior in half-strength Ringer solution and in an artificial saliva solution according to Barrett [1] was investigated using potentiodynamic corrosion testing (PDC). The photometry-based PAN method was used to quantify the released Ni and Co ions. The in vitro biocompatibility of the two grades of Elgiloy® was tested in three different cell cultures: in L929, a commercially available mouse fibroblast cell line, and in primary human epithelial cells and fibroblasts. Results: The results of the corrosion testing showed satisfactorily high pitting corrosion potentials but lower repassivation potentials and a strong increase in current density once pitting had occurred. The photometric results revealed the release of Ni and Co ions in both tested electrolytes. The tested native surfaces exhibited numerous grinding and polishing grooves, inclusions and inhomogeneities of the microstructure. After corrosion testing the same surfaces displayed numerous signs of corrosion, especially in areas with microstructural inhomogeneities. In vitro biocompatibility testing showed a substantially reduced dehydrogenase activity in the presence of Elgiloy®. The reduced quality of surface finish resulting from the manufacturing process led in the case of the tested Elgiloy® types to decreased corrosion resistance with consequently reduced in vitro biocompatibility. Conclusions: In this context it is also conceivable that patients with a proven allergy to nickel, cobalt or chromium may react sensitively to the deployment of this alloy, at least in the surface quality tested by us. From this aspect, the introduction of a binding standard for the surface quality of materials used in orthodontic appliances is urgently recommended.Zusammenfassung.Ziel: Ziel der Studie ist es, den Zusammenhang zwischen der chemischen Zusammensetzung, Oberflächenmikrostruktur und der Korrosionsbeständigkeit sowie der daraus folgenden In-vitro-Bioverträglichkeit einer gängigen Kobaltbasislegierung in zwei unterschiedlichen Härtegraden von Elgiloy® (RMO, Denver, CO, USA), Blue Elgiloy® (soft) and Yellow Elgiloy® (ductile), herzustellen. Material und Methoden: Zum Vergleich werden die Ergebnisse einer Nickeltitanlegierung, Neo Sentalloy™ (GAC, Central Islip, NY, USA), und einer Titanlegierung, TMA® (Ormco, Glendora, CA, USA), herangezogen. Die Oberflächenbeschaffenheit und chemische Zusammensetzung wurden mittels Rasterelektronenmikroskopie (REM) und energiedispersiver Röntgenspektroskopie (EDS) untersucht. Ihr Korrosionsverhalten in halbstarker Ringer-Lösung und in einer Speichelersatzlösung nach Barrett [1] ist in potentiodynamischen Korrosionsversuchen (PDK) ermittelt worden. Die im Korrosionstest freigesetzten Ni- und Co-Ionen sind photometrisch nach der PAN-Methode erfasst worden. Die In-vitro-Bioverträglichkeit beider Elgiloy®-Sorten ist mittels MTT-Test in drei Zellkulturen – L929, eine Mausfibroblastenlinie sowie primären humanen Fibroblasten und Epithelzellen – ermittelt worden. Ergebnisse: Die Ergebnisse der Korrosionsuntersuchungen zeigen zwar zufriedenstellend hohe Lochfraßpotentiale, aber niedrigere Repassivierungspotentiale sowie einen starken Anstieg der Stromdichte nach Beginn der Lochfraßkorrosion. In photometrischen Untersuchungen der verwendeten Elektrolyte konnten freigesetzte Ni- und Co-Ionen nachgewiesen werden. Die untersuchten nativen Oberflächen weisen zahlreiche Schleif- und Polierspuren, Einschlüsse sowie Inhomogenitäten in der Mikrostruktur auf. Die den Korrosionsversuchen ausgesetzten Oberflächen lassen zahlreiche Korrosionserscheinungen erkennen, die bevorzugt in Bereichen intermetallischer Phasen auftreten. In-vitro-Bioverträglichkeitsuntersuchungen zeigen in Anwesenheit von Elgiloy® eine deutlich herabgesetzte Dehydrogenaseaktivität. Eine durch den Herstellungsprozess bedingte herabgesetzte Güte der Oberflächenqualität führt im Fall der untersuchten Elgiloy®-Sorten zu einer verminderten Korrosionsresistenz. Dieses wiederum ist die Ursache für einen Rückgang der In-vitro-Bioverträglichkeit. Schlussfolgerungen: In diesem Zusammenhang ist es auch denkbar, dass Patienten mit nachgewiesener Ni-, Co- oder Cr-Allergie empfindlich auf den Einsatz dieser Legierung, zumindest in der uns vorliegenden Oberflächengüte, reagieren können. Es liegt daher nahe, eine verbindliche Norm für die Oberflächenbeschaffenheit der in der Kieferorthopädie eingesetzten Materialien zu fordern.

On the interaction of polyacrylic acid as a conditioning agent with bovine enamel

In the present paper, the effects of polyacrylic acid (PAA) conditioning on the morphology and chemistry of bovine enamel surface and the resulting interfacial reactions are being investigated using photometric, microscopic (SEM, AFM), electron spectroscopic (XPS) and staining methods (neutral red dye). The results are compared to two reference surfaces obtained by simple grinding and by etching with a phosphoric acid solution. It is shown that PAA conditioning leads to the leaching of calcium and phosphorus ions, to the smoothening of the surface and probably to the formation of a polymeric film at the surface. A mechanism by which a preliminary PAA conditioning of the enamel leads to the reported higher bonding strength between enamel and glass ionomer cements is proposed.