Ioanna Paloumpa

Novel corrosion-resistant films for Mg alloys

Abstract A novel method for the corrosion inhibition of Mg alloys, based on the formation of a thin polyacrylic–polypyrrole film, is presented. The film was created after simple immersion of the samples in a specially formulated emulsion of polyacrylic and polypyrrole polymers. The synthesis conditions were studied, as well as the resulting corrosion resistance of coated magnesium foils (AZ31) in terms of corrosion rate in neutral aqueous NaCl solutions. The relative ratio of polyacrylic polymer to polypyrrole was found to be important for the film properties. Furthermore, only in situ polymerisation of pyrrole in the polyacrylic emulsion can provide advanced corrosion properties in relatively thin films (2–5 μm). Blending of polypyrrole powder with the polyacrylic emulsion gives rise to thick films (20 μm) with reduced corrosion-inhibition properties. The corrosion rate was only weakly dependent on the film thickness of these novel coatings. We argue that the mechanism of corrosion inhibition is related to the formation of a thin passive layer of chemisorbed polypyrrole polymers or oligomers on the native magnesium oxide of the surface. The structure is further stabilised by polyacrylic polymer chains interacting as dopants of polypyrrole. The method is environmentally friendly: non-toxic chemicals are used, no rinsing is required, etc. The advanced corrosion-inhibition properties of the films, as well as the simple application process on the metal surface, provide significant potential for the industrial application of the method.

A polymer high-k dielectric insulator for organic field-effect transistors

We report on organic field-effect transistors with enhanced gate effects using the soluble copolymer poly(vinylidene fluoride-trifluoroethylene) for the dielectric layer. The layer has a measured relative dielectric constant of about 11 (at 1kHz), which enables operation voltages smaller than for the organic insulator polymethylmetacrylate (e=3.3 at 1kHz).

Selective polypyrrole electrodes for quartz microbalances: NO2 and gas flux sensitivities

Abstract Quartz microbalances were produced which have polypyrrole as a conductive polymer electrode. The polymer layers were operated as both electrode and sensitive material to detect the concentration of toxic gases. Tests with NO2 demonstrated detection limits below the MAK values at room temperature. It was also investigated the response to some other noxious compounds and to the total gas flux. The possible mechanisms associated with the sensor properties are pointed out and discussed.

Electrical investigations on metal/ferroelectric/insulator/semiconductor structures using poly[vinylidene fluoride trifluoroethylene] as ferroelectric layer for organic nonvolatile memory applications

Poly[vinylidene fluoride trifluoroethylene] (P[VDF/TrFE]) is a ferroelectric polymer and a candidate for the application in a ferroelectric field effect transistor, which is considered as a nonvolatile and nondestructive readout memory cell. In this contribution the authors focus on metal/ferroelectric/insulator/semiconductor capacitor structures with P[VDF/TrFE] as ferroelectric layer. Measuring the capacitance of Al/P[VDF/TrFE]/SiO2/Si stacks in dependence of the applied bias and analyzing the oxide capacitance in dependence of the thickness of the ferroelectric layer, they observe a formation of an interfacial nonferroelectric layer. This layer is responsible for reduced values of polarization profound for thinner P[VDF/TrFE] layers in this system. Capacitance-time measurements at such stacks show the possibility to distinguish between a higher and a lower capacitance state for more than 5 days. Long-time measurements revealed imprint and fatigue-like behavior.

Ferroelectric properties of spin-coated ultrathin (down to 10 nm) copolymer films

Spin-cast films of the ferroelectric copolymer poly(vinylidene fluoride-trifluoroethylene) are attractive for various applications. For such films the question arises whether there exists a ferroelectric functionality depending on film thickness. We characterize the ferroelectric properties of ultrathin films down to a layer thickness of 10 nm with spectroscopic and electrical methods (capacitance-voltage). The measurements indicate an extrinsic switching mechanism with a much lower operation voltage than that for a collective intrinsic switching. Both independent methods agree that there is no critical thickness for spin-coated copolymer films down to 10 nm if an adapted system of electrodes is used.

Buffer layer investigations on MFIS capacitors consisting of ferroelectric poly[vinylidene fluoride trifluoroethylene]

In this paper we present capacitance-voltage (CV) measurements on metal-ferroelectric-insulator-semiconductor (MFIS) capacitors with poly[vinylidene fluoride trifluoroethylene] (P[VDF/TrFE] as ferroelectric layer and SiO2, Al2O3 and HfO2 as buffering insulator layer. In order to discuss our data in a quantitative manner we perform fits to the data based on a model proposed by Miller and McWorther. The improvement of the polarization values and subsequently its effect on the hysteresis of the CV curve by the successive shrinking of the buffer layer thickness and the following choice of a high-k buffer material is demonstrated. Our data underline that a saturated polarization of P[VDF/TrFE] cannot be controlled with a SiO2 buffer layer and the insertion of a high-k buffer layer is essential for further improvements of the characteristics of MFIS stacks.