Field-assisted Ion Exchange Research Articles

Field-assisted solid state doping of glasses for optical materials

Field-assisted solid-state ion-exchange (FASSIE) allows the doping of surface glass layers with multivalent ions which could not diffuse into the glass matrix by the usual thermal ion-exchange process in molten salt baths. This paper presents preliminary spectroscopic investigation of the diffusion of chromium in silicate glasses, with the aim at improving the procedures for the production of Cr-doped optical waveguides. Metallic chromium films deposited onto the glass substrates by the rf-sputtering technique were used as metal ions source. The environment of diffused chromium ions into the glass matrix was investigated by means of micro-Raman spectroscopy.

Erbium environment on Er-doped silica and alumino-silicate glass films: An EXAFS study

Er-doped dielectric films are characterized by the emission of a photoluminescence signal at λ = 1.54 μm, the main used in the optical telecommunications. The efficiency of the radiative emission is strongly related to the characteristics of the Er 3+ environment. Er-doped SiO 2 films (synthesized by rf-magnetron co-sputtering) and 87SiO 2:10Al 2O 3:3Na 2O silicate glass films doped with 0.5 mol% of Er (prepared by sol–gel route and subsequently doped with silver by Ag + ↔ Na + field-assisted solid-state ion exchange) were studied by extended X-ray absorption fine structure spectroscopy performed at Er L III-edge (Italian beamline GILDA of the ESRF). In the silica samples the Er coordinates about 4.5 O atoms at a short distance ( R = 2.07–2.13 Å), similar to the one observed in Er-doped glasses when the preparation conditions are far from the thermodynamical equilibrium. In alumino-silicate samples the first shell of atoms is formed of 5.5–7.5 O atoms at a distance of about 2.31 Å, showing a local structure similar to other Er-doped sol–gel glasses and glass–ceramics. A comparison between the first shell structure around Er ions and the different intensity of the photoluminescence emission suggests that the increase of the radiative emission upon thermal annealing is mainly related to the decrease of the defects number in the glass structure as a consequence of the annealing.

A Solid-State Route for the Synthesis of Metal Nanocluster Composite Glasses

A field-assisted solid state ion exchange (FASSIE) approach is used to dope silicate glasses with mono- and/or multivalent ions, in which the diffusion of ions coming from a film deposited onto the glass surface is driven by an external electric field. Metal precipitation to form nanoparticles may take place during the ion exchange, depending on the process parameters, or it can be induced by irradiation with high power laser beams. Characterization of silicate glass samples doped with either gold or silver is performed by optical absorption and transmission electron microscopy.

Doping of silicate glasses with erbium by a field-assisted solid-state ion exchange technique

A field-assisted solid-state ion exchange technique is used for the first time to dope surface layers of silicate glasses with erbium at the concentration of the order of a few 1020 Er cm−3. Rutherford backscattering spectrometry, extended x-ray absorption fine structure spectroscopy and photoluminescence spectroscopy are used to characterize the samples treated after erbium oxide films were formed on soda-lime glass slides.

Electro-diffusion equations of monovalent cations in glass under charge neutrality approximation for optical waveguide fabrication

Two improvements of the usual three-dimensional partial differential equations that model ion-exchanged optical devices in glass under charge neutrality approximation are proposed. First, they are rigorously generalised for both non-ideal cation behaviour and concentration-dependent self-diffusion coefficients. Secondly, the Faraday equation is imposed in the derivation instead of the Ohm law. Accordingly, the current density distribution is not governed by the electric field but by the gradient of an effective electrical potential instead. On the other hand, the boundary conditions of those equations are obtained from standard electrolyte theory, which results in contact potentials at interfaces between glass and molten salt, silver film or metallic cathode. Therefore, typical arrangements for field-assisted ion exchange must be considered as electrochemical cells, and thus a correction term must be added to the applied voltage to get a proper modelling. This term can be neglected in some typical cases but it must be retained in others. Finally, it is predicted that the electrochemical cell effect can be used to diffuse cations from a silver film without need for an external applied field. This suggests a new simple method to fabricate integrated optical components by ion exchange in glass.

Mapping method for the comparison of mode data from field assisted ion diffused guides

It is shown that the mode data of field assisted ion exchange profiles in glass can be mapped onto one another when the refractive index profiles are shifted versions of each other, i.e. of the form n( x + s) where s is a shift distance. This allows the mode data of shallow guides to be compared with data of deeper guides. The mapping has utility in that the shallow guide may not support a sufficient number of modes in order for a refractive index profile reconstruction to be made.

Characterization of silicate glasses doped with gold by solid-state field-assisted ion exchange

The doping of silicate glasses with transition metals (with the possibility to induce the formation of metallic nanoparticles by suitable post-exchange treatments) attracts a great attention for its potential in light waveguides technology, ultrafast nonlinear optics, luminescent and magnetic materials. Moreover, the control of the metal distribution inside the glass is a central issue for both the understanding of the incorporation process and for the definition of useful preparation protocols. In the presented experiment, gold-containing silicate glasses were prepared by solid-state field-assisted ion exchange. A metallic film of gold was deposited onto two different glass substrates by sputtering. Then, the substrates were heat-treated under intense electric field to induce diffusion of gold inside the glass network. Structural and compositional characterizations were performed by different techniques: secondary ion mass and Rutherford backscattering spectrometries, and optical absorption spectroscopy.

Tapered Waveguides Produced by Ion Exchange in Glass With a Nonuniform Electric Field

A method of manufacturing waveguides that are tapered in depth and formed by an electric field assisted ion exchange technique in glass is presented. The method relies on the creation of a nonuniform electric field distribution within the glass during the exchange process. This is achieved by creating a large number of narrow strip electrodes, which form the cathode during the field-assisted exchange process. All of the cathode electrodes are at the same potential during the exchange, which makes the manufacturing process particularly simple. Both planar and channel tapered waveguides can be formed by this technique and are characterized by prism coupling and interferometer measurements, respectively. A model for the taper, which is based on conformal mapping calculations for the nonuniform electric field, is developed and compared with measurements. The method allows for the manufacture of both tapered and uniform guides on the same substrate

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

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.

Field-assisted ion diffusion of transition metals for the synthesis of nanocomposite silicate glasses

Field-assisted ion diffusion of metals was realized for the controlled doping of silicate glasses. Metallic films deposited onto the substrates by the rf-sputtering technique were used as the metal ions source. In particular, cobalt was, for the first time, introduced into a soda-lime glass by field-assisted ion exchange, giving rise to diffusion profiles that were observed to depend on the preparation parameters, namely, temperature and electric field intensity across the samples. This technique, which allowed to dope the glass matrix with high metal concentration values, can be used as the first step in combined methodologies for the preparation of nanostructured glass composites. The shape of the measured Co diffusion profiles indicates that the migration process depends not only on the experimental parameters but also on the behavior of alkali ions within the glass. Chemical phenomena occurring at the metal/glass interface also play a significant role in the penetration of the Co ions. The possibility of doping the glass with two different metal species was also investigated, with the aim to create the condition for the formation of core-shell or alloy nanoclusters. In particular, preliminary results on Co + Au field-assisted co-diffusion are presented.

Modeling of ion-exchanged glass waveguide structures

Glass waveguide devices fabricated by ion exchange have evolved to the point where conventional assumptions of waveguide symmetry and mutual independence are no longer valid. We describe a modeling tool that allows for the presence of an arbitrary, nonhomogeneous electric field distribution during the ion exchange process. An asymmetric waveguide produced by selective field-assisted burial is modeled and discussed. A directional coupler fabricated by field-assisted thermal ion exchange and subsequent field-assisted burial is modeled, and it is shown that a proximity effect exists in which the waveguides exert a mutual influence upon each other during processing.

Electrochemistry and microsystems

Electrochemistry takes a key position in products and manufacturing processes of microtechnology, which has established a multi-billion dollar market with applications in information, entertainment, medical, automotive, telecom and many other technologies. In combination with microlithographic pattern generation electrochemical deposition processes are applied in manufacturing CDs and DVDs, nozzle plates for ink jet printers, read–write heads for hard magnetic disks and solder bumps for flip-chip technology. Three-dimensional microstructures with extremely high precision and aspect ratio are manufactured by means of LIGA technology, which combines deep lithography, electroforming and moulding process steps. Field assisted etching processes with ultra-short voltage pulses, anodization of silicon and field assisted ion exchange in glass have been successfully used for generating microstructures. Meanwhile, there are a huge number of microdevices, which utilize electrochemical phenomena. ISFETs and ion sensitive electrodes are standard components in the field of microsensors, microfuel cells will become high-performance power supply systems for mobile IT and entertainment products. In communication technology electrophoresis-based on electronic ink displays will become more and more important products. The most challenging development is dealing with so-called labs-on-a-chip which utilize electrochemical phenomena like electrophoresis, isoelectric focussing and electroosmosis to create a novel platform for ultra-miniaturized analytics in life sciences, medical diagnosis, environmental technologies and many other areas of modern development.

Vertical optical directional coupler

A method for fabricating optical directional couplers by combining thermal and field assisted ion exchange processes is presented. Modeling, design, fabrication, and test methods are discussed. Thi...

Comparative study of Ag–Na thermal and field-assisted ion exchange on Er-doped phosphate glass

Abstract Silver–sodium ion-exchanged waveguides on a new erbium-doped phosphate glass have been fabricated and characterized. Thermal diffusion and field-assisted ion exchanges have been investigated and compared. A simple yet effective method to reconstruct the refractive index profile from the measured effective indexes, obtained by the m -lines spectroscopy with prism-coupling technique, has been successfully adopted. The optical parameters describing the waveguide properties, namely the refractive index variation, the diffusion coefficient and, for the field-assisted ion exchanges, the drift velocity, have been calculated and correlated with the fabrication parameters. Thermal diffusion is more reproducible while the field-assisted process provides a step-like index and better confinement by an appropriate control. Straightforward guidelines have been outlined for choosing appropriate diffusion time, temperature and melt composition to fabricate active waveguides compatible with optical fibers.

H-ROD: A new and versatile microoptical component

Abstract We present the semi cylindrical H-ROD element as a new and versatile microoptical component. With field assisted ion exchange semi cylindrical index distributions can be integrated in a planar glass substrate. By combination of two identical elements an integrated GRIN ROD lens can be realized. Furthermore a semi cylindrical element can also be utilized for imaging by using internal reflection (H-ROD). Aside of this the H-ROD provides direct access to the filter plane, which offers a wide range of applications.

Modeling of the microlens fabrication in glasses by field-assisted ion exchange: The space charge effects

Effects of the space charge on the microlens formation in glasses using the electric-field-assisted ion exchange process have been analyzed by numerical methods. It is shown that the electric field strength in the substrate is inhomogeneously distributed and decreases with time. Since the field-assisted migration velocity depends on the field strength, these factors slow down the ion exchange rate and decrease the microlens diameter below the values calculated assuming a homogeneous field strength distribution in the substrate.

Effect of Concentration-Dependence on Ion-Exchanged Channel Waveguide Profile

An accurate simulation model of ion-exchange processes for fabricating channel glass waveguides is presented. The simulation results are in good agreement with the experimental results because the simulation takes the concentration-dependent diffusion coefficient into account and applies the cubic-interpolation pseudoparticle (CIP) method for electromigration which can treat a sharp interface with a few grids. The simulation is then used to study optimum process conditions for a buried single-mode channel waveguide. It is demonstrated that an annealing process following field-assisted ion-exchange is useful in reducing the coupling loss to a single-mode optical fiber.

Planar waveguides prepared by K+–Na+ field-assisted ion exchange in different types of silicate glass

The goal of this work was to address the technological problems associated with waveguide preparation by thermal- and electric-field–assisted K+–Na+ ion exchange in two types of soda-lime glass: common FTD and special pure GIL49. The number of modes, depth, profile, and the change in refractive index were measured for waveguides prepared at temperatures between 250 and 410 °C and electric-field values between 0 and 50 V/mm. Although the influence of some admixture content inside the glass was relatively high, all of these parameters were controlled accurately and repeatedly by the electric field.

Effects of annealing electric field assisted - ion exchanged soda-lime glass guides

Soda-lime glass samples have been subjected to either a thermal or an electric field assisted ion exchange. The effective refractive indices of the modes supported by the guides have been measured using a prism coupler before and after annealing and refractive index profiles have been reconstructed from the data. The effective refractive indices of the modes for guides produced by electric field assisted exchange exhibit an unusual evolution with annealing time. The area under the refractive index profiles produced from the measurements shows a significant reduction with annealing time. These features are not present in samples prepared by thermal ion exchange. The results are attributed to a relaxation mechanism operative only within regions of the glass that have been subjected to field assisted ion injection.

Simulation of field-assisted ion exchange for glass channel waveguide fabrication: effect of nonhomogeneous time-dependent electric conductivity

Nonhomogeneous time-dependent electric conductivity distribution during field-assisted ion exchange in glass is taken into account in the numerical modeling of optical waveguide fabrication. As an example, the influence of the nonhomogeneous conductivity on a buried channel waveguide is studied in detail. It is shown that there is a substantial variation of electric current density during the process, particularly in the waveguide region. The main difference in comparison to the previous more approximative models is seen to be a smaller refractive index increase for the waveguides.