Development of ion jelly thin films for electrochemical devices

Dissertação para obtenção do Grau de Doutor em Química Sustentável

Effect of different dopant elements on the properties of ZnO thin films

Vacuum, Vol. 64

Development of copper and nickel based oxide thin-films: design and fabrication of thin-film transistors

Dissertação para obtenção do Grau de Doutor em Nanotecnologia e Nanociência

VO2 thin films and nanoparticles for energy-saving applications in architectural elements

Vanadium dioxide (VO2) is a promising material with large interest in construction industry and architecture, due to its thermochromic properties. This material may be used to create "smart" coatings that result in improvements in the buildings energy efficiency, by reducing heat exchanges and, consequently, the need for acclimatization. In this work, VO2 thin films and coatings were produced and tested in laboratory, to apply in architectural elements, such as glass, rooftop tiles and exterior paints. Thin films were produced by RF magnetron sputtering and VO2 nanoparticles were obtained through hydrothermal synthesis, aiming to create "smart" windows and tiles, respectively. These coatings have demonstrated the capability to modulate the transmittance of infrared radiation by around 20%. The VO2 nanoparticle coatings were successfully applied on ceramic tiles. The critical temperature was reduced to around 40ºC by tungsten doping. Ultimately, two identical house models were built, in order to test the VO2 coatings, in real atmospheric conditions during one of the hottest months of the year, in Portugal – August.

High-performance flexible hybrid field-effect transistors based on cellulose fiber paper

IEEE Electron Device Letters, VOL. 29, NO. 9,

Influence of the deposition pressure on the properties of transparent and conductive ZnO: Ga thin-film produced by r.f. sputtering at room temperature

Thin Solid Films, vol. 427, nº 1-2

Engineering of metal oxide nanoparticles for application in electrochemical devices

The growing demand for materials and devices with new functionalities led to the increased inter-est in the field of nanomaterials and nanotechnologies. Nanoparticles, not only present a reduced size as well as high reactivity, which allows the development of electronic and electrochemical devices with exclusive properties, when compared with thin films. This dissertation aims to explore the development of several nanostructured metal oxides by sol-vothermal synthesis and its application in different electrochemical devices. Within this broad theme, this study has a specific number of objectives: a) research of the influence of the synthesis parameters to the structure and morphology of the nanoparticles; b) improvement of the perfor-mance of the electrochromic devices with the application of the nanoparticles as electrode; c) application of the nanoparticles as probes to sensing devices; and d) production of solution-pro-cessed transistors with a nanostructured metal oxide semiconductor. Regarding the results, several conclusions can be exposed. Solvothermal synthesis shows to be a very versatile method to control the growth and morphology of the nanoparticles. The electrochromic device performance is influenced by the different structures and morphologies of WO3 nanoparticles, mainly due to the surface area and conductivity of the materials. The dep-osition of the electrochromic layer by inkjet printing allows the patterning of the electrodes without wasting material and without any additional steps. Nanostructured WO3 probes were produced by electrodeposition and drop casting and applied as pH sensor and biosensor, respectively. The good performance and sensitivity of the devices is explained by the high number of electrochemical reactions occurring at the surface of the na-noparticles. GIZO nanoparticles were deposited by spin coating and used in electrolyte-gated transistors, which promotes a good interface between the semiconductor and the dielectric. The produced transistors work at low potential and with improved ON-OFF current ratio, up to 6 orders of mag-nitude. To summarize, the low temperatures used in the production of the devices are compatible with flexible substrates and additionally, the low cost of the techniques involved can be adapted for disposable devices.