Diffusion behavior of transition metals in field-assisted ion-exchanged glasses

Abstract

The use of ion-exchange techniques for doping silicate glasses with transition metals has attracted much attention in the last decades for its potential in several applications, namely, light waveguides technology, luminescent materials, and for the possibility to realize systems in which metal nanocluster formation is controlled by suitable post-exchange techniques. In this framework, the control of metal distribution inside the glass is a central issue for both the understanding of the incorporation process and for the definition of effective preparation protocols. In this experiment, metallic films (Ag, Cu, Au, Co) were deposited onto the substrates by the rf-sputtering technique. Metal ions then penetrate to substitute glass alkali by means of field-assisted ion-exchange, realized at different temperature and electric field values. In particular, we present in this paper the Au doping of silicate glasses, successfully realized for the first time with this method. The gold diffusion profiles, as measured by Secondary Ion Mass Spectrometry (SIMS), indicate that the migration depends on the experimental parameters (temperature and electric field), but also on the local structure, as well as on chemical phenomena occurring at the metal/glass interface.

Silver and gold doping of SiO2 glass by solid-state field-assisted diffusion

“…Much work has been done with this technique in the case of the diffusion of monovalent ions into soda-lime and borosilicate glasses [11][12][13][14][15], where the dopant ions replace alkali ions of the glass matrix. Solid-state field-assisted diffusion has also been realized in more recent years for doping silicate glasses with monovalent [16][17][18] as well as multivalent ions [19,20], but much less attention has been dedicated to the possibility of doping a pure silica matrix, where the penetration of foreign ions should actually depend on defects/impurities as well as local re-arrangements of the structure. In this work, preliminary results are presented for both Ag and Au doping.…”

Optical and structural properties of silver nanoparticles in glass matrix formed by thermal annealing of field assisted film dissolution

“…As pointed out in [23], a complete modeling of the ion diffusion process is still lacking. In any case, in the studied samples we showed that by varying the applied electric field, the depth distribution of Ag can be modified, with a concentration maximum at the surface (V EFAD = 0.4 kV), as usual in field assisted film dissolution [24], or at certain depth within the glass (V EFAD = 1.6 kV), that has been previously associated to a lack of local charge neutrality due to structural network modifications upon the formation of a strongly depleted region [14]. Such region can be formed as the applied electric field is higher.…”

“…In this way the oxide layer at the interface can supply Ag + for ion diffusion upon application of electric field [22]. In addition alkali ion migration of native ions inside the glass (basically Na + ) is faster than the diffusion of metal, generating a space-charge distribution inside the glass and modifying the diffusion of metal ions [14]. Thus, the distribution of metal ions inside the glass depends then in a complex way on the physical and chemical phenomena that take place at the metal-glass interface and in the glass.…”

“…Most of these methods consist of a two-step process: i) the inclusion of metal ions into the glass matrix and ii) the formation of clusters upon post-inclusion treatment [13]. The possibility of ion inclusion in glass matrix by the electric field assisted dissolution of a film at moderately elevated temperatures has been recently investigated for transition metals [14]. Formation of metal aggregates upon thermal annealing of glasses in which electric field assisted dissolution of nanoparticles was performed has been also reported [6].…”

Silver doping of glasses

“…In this sense, several spectroscopic investigations have been performed on the structural rearrangements in silicate glasses doped with silver by different non-equilibrium techniques [30][31][32][33] looking on one hand at a deeper understanding of the silver behavior in the matrix, and on the other hand at a comprehensive phenomenological descripition able to provide suitable recipes for the fabrication of glasses with prescribed features. The diffusion behavior of silver in glasses has been also di object of several dedicated studies: the classical phenomenology of the Nernst-Planck equations, as first described for this case by Doremus [34], has been tested for several Ag-glass systems, demonstrating the need to include local effects of both compositional (pseudo mixed-alkali effect) and electrical (local fields build-up) nature [35][36][37][38], In this perspective, the electrical conductivity properties of silverdoped glasses has been also extensively studied [39][40][41][42] for application purposes.…”