book of abstracts - IM2NP

A B S T R A C T S FRIDAY, JULY 2 N A N O S E A 2 0 1 0
9H30-9H50
Photochromic silver-containing mesoporous TiO2 films as writable and
rewritable data carriers.
N. Crespo-Monteiro,1 N. Destouches,1 L. Bois,2 F. Chassagneux, 2 S. Reynaud1 (1
Université de Lyon, F-42023 Saint-Etienne, France; CNRS, UMR 5516, Laboratoire Hubert Curien, 18 rue Pr.
Lauras F-42000 Saint-Etienne, France; and Université de Saint-Etienne, Jean-Monnet, F-42000 Saint-Etienne,
France; 2 Laboratoire Multimatériaux et Interfaces, Université Claude Bernard Lyon 1, Bat Berthollet, 69622
Villeurbanne, France).
1 – Introduction
Silver species adsorbed on colloidal titania have been known for a long time to exhibit photochromism [1-2].
They reversibly change their color in response to light exposure. The silver salts are reduced under UV light
leading to silver nanoparticles that are oxidized under visible light. Recently, photochromic Ag/TiO2
nanocomposite films have been studied for holographic data storage and smart glasses [3]. Here, we
demonstrate that silver-containing mesoporous titania films can be used as writable and rewritable data
carriers. We perform both permanent and erasable micro-inscriptions by using continuous lasers at various
wavelengths under different experimental conditions. We also investigate the irreversible and the reversible
mechanisms leading to the non erasable and erasable photoinscriptions, respectively.
2 – Experimental section
The mesoporous titania films were prepared following an evaporation-induced self-assembly route using
non-ionic amphiphilic triblock copolymer P123 as structuring agent and tetrabutylorthotitanate (TBT) as
titanium oxide precursor [4]. The films were deposited by dip-coating on cleaned glass slides. After drying,
the copolymer was extracted with hot ethanol in a Soxhlet apparatus, and the films were soaked in the
aqueous ammoniacal silver solution.
The formation of silver nanoparticles was realized by UV-laser exposures at 244 nm or 325 nm wavelength.
The photo-oxidation of silver nanoparticles was realized by visible laser exposures at 488nm, 514 or 633 nm.
The formation and oxidation of silver nanoparticles was characterized by absorption spectroscopy, scanning
electron microscopy, transmission electron microscopy and optical microscopy (local coloration of the
sample). Raman spectroscopy was used for the characterization of the TiO2 crystallization and atomic
microscopy force for the measurement of the film topography.
3 – Results
The UV wavelengths are used to locally reduce silver salts in the film. These wavelengths are absorbed by
the TiO2 matrix that emits photoelectrons leading to the formation of silver nanoparticles in the film. Under
visible light, the incident photons excite the particle surface plasmon that decays into other electrons
excitations. The photoexcited electrons on Ag are transferred via TiO2 and non-excited Ag nanoparticles to
oxygen molecules, which act as trapping centers. Therefore the silver nanoparticles are oxidized.
We first study the influence of the incident UV-laser intensity on the photochromic behaviour of the film and
evidence that microinscriptions can be reversibly or irreversibly printed in the same material, depending on
the UV-laser intensity. The microinscriptions can be completely erased with a monochromatic visible
illumination and we demonstrate the rewritability of the films by printing several successive
microinscriptions in the same place without change of contrast. We also investigate the effect of a visiblelaser
illumination at different intensities and wavelengths. We demonstrate that, depending on the incident
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