Metal nanoparticles embedded into mesoporous thin films: synthetic strategies, full characterization and their electrical and optical properties

G. J. A. A. SOLER-ILLIA; E. D. MARTINEZ; M. C. FUERTES; A. WOLOSIUK; M. L. MARTÍNEZ-RICCI; M. BELLINO; L. GRANJA

Honolulu

Congreso; PACIFICHEM 2010; 2010

The rational design of nanocomposite made up of metallic nanoparticles (MNP) confined within a matrix holds a promise for obtaining integrated devices. Mesoporous oxide thin films (MOTF) represent attractive template matrices for the inclusion of MNP. The nano-derived properties of these systems are due to the metal NP dimensions, confinement, interfacial effects and the possibilities to combine the accessibility of the mesopore system and the electronic or surface properties of the MOTF matrix. In addition, optical quality NP-MOTF nanocomposites present unique potential applications in catalysis, electronic and photonic devices, data storage and sensors. An accurate chemical control of MNP size and pore filling is needed in order to master size-derived effects such as electron transfer, surface plasmon resonance (SPR), fluorescence enhancement or surface-enhanced Raman scattering (SERS). In this work, we present the chemical strategies leading to the reproducible preparation of gold and silver MNP-MOTF nanocomposites by electroless reduction of metal ions in contact with a mesoporous silica, titania, zirconia or mixed oxide matrix. Gold and silver loading in the mesopores was followed by crossing X-Ray Reflectometry and EDS. The conditions required for efficient pore loading depend on the metallic precursor, the mesoporous matrix, and its state of surface charge; transition metal oxides lead to faster reduction kinetics. Optimizing these factors lead to efficient loadings and tuned Plasmon bands (i.e., absorption and band position), as a consequence of controlling the size and interconnectivity of the MNP, and the refractive index of the surrounding MOTF walls. The photocatalytic properties of mesoporous titania can be advantageously used for producing arbitrary micronic patterns of silver NP in the mesoporous channels by lithography. Nanocomposite “wires” become conductive after a critical MNP pore loading is reached, as assessed by conductive AFM.