RESUMO
Memristors are expected to be one of the key building blocks for the development of new bio-inspired nanoelectronics. Memristive effects in transition metal oxides are usually linked to the electromigration at the nanoscale of charged oxygen vacancies (OV). In this paper we address, for Pt/TiOx/TaOy/Pt devices, the exchange of OV between the device and the environment upon the application of electrical stress. From a combination of experiments and theoretical simulations we determine that both TiOxand TaOylayers oxidize, via environmental oxygen uptake, during the electroforming process. Once the memristive effect is stabilized (post-forming behavior) our results suggest that oxygen exchange with the environment is suppressed and the OV dynamics that drives the memristive behavior is restricted to an internal electromigration between TiOxand TaOylayers. Our work provides relevant information for the design of reliable binary oxide memristive devices.
RESUMO
Magnetite superparamagnetic nanoparticles (MNP) are becoming one of the firsts nanocommodity products. MNP find a number of applications and they are been produced at relatively large scale. The co-precipitation method presents many technical and economical advantages among alternative processes. However, the relationships between physical and chemical reaction conditions during the co-precipitation process and the resulting properties of obtained MNP are not yet fully understood. The novelty of this contribution is the establishment of the cross-dependency effects of the main physical and chemical parameters of the co-precipitation reaction on the properties of resulting MNP. The conditions were varied by following an experimental design. The crystallite size, particle size and magnetization of the MNP and the Z-potential and size of their aggregates were selected as main response properties. A set of equations in the form of 4D surface responses in the space of co-precipitation process variables was obtained and analyzed in terms of the resulting properties. The set of equations is useful to predict, optimize and tailor very precisely the properties of resulting MNP as a function of reaction conditions.