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.

FEDER funds through the program COMPETE—Programa Operacional Factores de Competitividade; Karlsruhe Nano Micro Facility (KNMF), a Helmholtz Research Infrastructure at KIT; ELETTRA Synchrotron Radiation Center for the measurements at the SAXS beamline; European COST Actions MP0901-NanoTP;

This work is sponsored by FEDER funds through the program COMPETE - Programa Operacional Factores de Competitividade - and by national funds through FCT – Fundação para a Ciência e a Tecnologia-, under the projects PEst-C/FIS/UI607/2013, PEst-C/CTM/LA0025/2013 and PEst-C/EME/UI0285/2013. The authors would like also to thank the support by: (i) Karlsruhe Nano Micro Facility (KNMF), a Helmholtz Research Infrastructure at KIT; (ii) ELETTRA Synchrotron Radiation Center for the measurements at the SAXS beamline; (iii) European COST Actions MP0901-NanoTP and (iv) European Community as an Integrating Activity 'Support of Public and Industrial Research Using Ion Beam Technology (SPIRIT project)' under EC contract no. 227012. M.B. acknowledges support from the Croatian Ministry of Science, Higher Education and Sport, (project number 098-0982886-2895).