Study of the electrical behavior of nanostructured Ti–Ag thin films, prepared by glancing angle deposition

Aiming at biosignal acquisition for bioelectrodes application, Ti-Ag thin films were produced by GLAD, in order to tailor their electromechanical properties. The electrical behaviour of the sculptured Ti-Ag thin films was studied with increasing annealing temperatures. The results revealed a good correlation with the set of morphological features displayed. With the increase of the vapour flux angle, a more defined structure was obtained, as well as a more porous morphology, which increased the electrical resistivity of the coatings. An important point consists in the recrystallization of Ti-Ag intermetallic phases due to the temperature increase (between 558 K and 773 K), which resulted in a sharp decrease of the electrical resistivity values.

Modelação, simulação e implementação de agitação acústica para aplicações em microfluídica

Tese de Doutoramento (Programa Doutoral em Engenharia Biomédica)

Evolution of the surface plasmon resonance of Au:TiO2 nanocomposite thin films with annealing temperature

This paper reports on the changes in the structural and morphological features occurring in a particular type of nanocomposite thin-film system, composed of Au nanoparticles (NPs) dispersed in a host TiO2 dielectric matrix. The structural and morphological changes, promoted by in-vacuum annealing experiments of the as-deposited thin films at different temperatures (ranging from 200 to 800 C), resulted in a well-known localized surface plasmon resonance (LSPR) phenomenon, which gave rise to a set of different optical responses that can be tailored for a wide number of applications, including those for optical-based sensors. The results show that the annealing experiments enabled a gradual increase of the mean grain size of the Au NPs (from 2 to 23 nm), and changes in their distributions and separations within the dielectric matrix. For higher annealing temperatures of the as-deposited films, a broad size distribution of Au NPs was found (sizes up to 100 nm). The structural conditions necessary to produce LSPR activity were found to occur for annealing experiments above 300 C, which corresponded to the crystallization of the gold NPs, with an average size strongly dependent on the annealing temperature itself. The main factor for the promotion of LSPR was the growth of gold NPs and their redistribution throughout the host matrix. On the other hand, the host matrix started to crystallize at an annealing temperature of about 500 C, which is an important parameter to explain the shift of the LSPR peak position to longer wavelengths, i.e. a red-shift.

High-temperature polymer based magnetoelectric nanocomposites

The use of polymer based magnetoelectric materials for sensing and actuation applications has been the subject of increasing scientific and technological interest. One of the drawbacks to be overcome in this field is to increase the temperature range of application above 100 ºC. In this way, a nanocomposite material composed by a mixture of two aromatic diamines, 1,3-Bis-2-cyano-3-(3 aminophenoxy)phenoxybenzene (diamine 2CN) and 1,3-Bis(3-aminophenoxy)benzene (diamine 0CN) and CoFe2O4 (CFO) nanoparticles was designed, fabricated and successfully tested for high temperature magnetoelectric applications. Results revealed that CFO nanoparticles are well distributed within the 0CN2CN polymer matrix and that the addition of CFO nanoparticles does not significantly alter the polyimides structure. The magnetization response of the composite is determined by the CFO nanoparticle content. The piezoelectric response of the 0CN2CN polymer matrix (≈11 pC.N-1) and the maximum α33 value (0.8mV.cm-1.Oe-1) are stable over time and decrease only when the composite is subjected to temperatures above 130 ºC. Strategies to further improve the ME response are also discussed.