Electrochromism in thin film composites

Author(s)

Fabio Furlan Ferreira

• Document type: Doctoral Thesis
• Press: São Paulo. , gráficos, ilustrações, tabelas.
• Institution: Universidade de São Paulo (USP). Instituto de Física (IF/SBI)
• Defense date: 2003-02-07

Examining board members

Marcia Carvalho de Abreu Fantini; Mônica Alonso Cotta; Antonio Domingues dos Santos; Jair Scarmínio; Manfredo Harri Tabacniks

• Advisor: Marcia Carvalho de Abreu Fantini
• Field of knowledge: Physical Sciences and Mathematics - Physics
• Indexed in: Banco de Dados Bibliográficos da USP-DEDALUS
• Location: Universidade de São Paulo. Biblioteca do Instituto de Física; IF/TIFUSP; F383e D

Abstract

In this work we initially calculated the optical properties of cermet films of Me-NiO and Me-CoO, being the metals Me = Au, Ag, Cu, Ni, Pd and Pt, by means of the Maxwell Garnett effective medium theory. This theoretical study allowed evaluating the viability to obtain, experimentally, a colored material in the visible spectrum region, with selective absorption in a narrow range of wavelengths. The results showed that the ideal candidate for such goal is the Au cermet. Looking at this result, the growth of Au-NiO and Au-CoO thin films was initiated using different experimental strategies: (i) deposition by reactive DC magnetron sputtering, (ii) deposition of the NiO, film by reactive DC magnetron sputtering and Au by the sol-gel and dip coating methods and (iii) deposition of both films, NiOxHy and Au, by sol-gel and dip coating. The films grown by sputtering showed a small selectivity (-5-10%), due to the atomistic character of this type of technique. It leads to the formation of small clusters of Au (smaller than -3 nrn), instead of aggregates with sizes of the order of some tenths of nanometers, easily obtained by the sol-gel method. Better selectivity, around 15%, is obtained in films deposited as multilayers. Post thermal annealing of the cermet films grown by sputtering induces the agglomeration of Au, but destroys the electrochromic properties. In the case of Au films grown by sol-gel, the spectral selectivity increases, due to the presence of Au, going from 15% to 20% in films deposited on the oxide matrix, deposited by sputtering and sol-gel, respectively. Under electrochemical processes, the NiOxHy films grown by sol-gel and dip coating presented the highest transmission variation (70%), due to larger porosity of these films. (AU)