Patent Application
20150246847
The present invention relates to an ion exchange substrate, metalized product and method for producing them.
Glasses and other dielectrics containing metal nanoparticles are of interest due to their unique linear and nonlinear optical properties. These properties are dominated by the strong surface plasmon resonances (SPRs) of the metal nanoparticles. The spectral position and shape of these SPRs can be designed within a wide spectral range throughout the visible and near infrared spectra regions of the electromagnetic spectrum by selection of the metal and the dielectric matrix or by manipulation of the size, shape and spatial distribution of the metal clusters. Therefore, these compound materials are promising candidates for many applications in the field of photonics.
Glass with embedded nanoparticles has traditionally been fabricated using chemical ion-exchange techniques. These processes have been the subject of basic and applied research for the potential exploitation of new dopants in the preparation of passive and active glasses. In the process metal dopants are usually introduced into the glass by immersing the matrix in a molten salt bath containing the dopant ions. For instance, soda-lime float glass (72.2 SiO2, 14.2 Na2O, 0.71 K2O, 6.5 CaO, 4.42 MgO, 1.49 Al2O3, 0.13 Fe2O3, 0.4 SO3, in wt. %) is a preferred substrate for the Ag+—Na+ ion-exchange process.
For the ion-exchange process, a glass substrate is placed in a mixed melt of AgNO3 and KNO3 (or AgNO3 and NaNO3) at 400° C. The metallic ions are driven into the glass due to the chemical potential gradient and they replace alkali ions of the matrix that are released into the melt. In this way, metal concentration values well beyond the solubility limits may be achieved without clustering. The thickness of the glass substrate, time of the ion-exchange process, and weight concentration of AgNO3 in the melt determine the concentration and distribution of Ag+ ions in the glass.
Thermal annealing of the ion-exchanged glass in a H2 reduction atmosphere (or air), typically at 400-650° C. (depending on the process), then results in the reduction of silver ions and formation of spherical silver nanoparticles. For glass containing iron ions (Fe2+ and Fe3+), and for annealing in a non-reducing atmosphere (air) the following two thermo-reducing reactions have been considered:
Fe2+→Fe3++e− a)
and
Ag++e−→Ag0 b)
Thermal-assisted ion exchange has proven to be an ineffective technique when dealing with multivalent ion species, as is the case of cobalt and gold. Multivalent ions come to substitute mono valent alkali ions (mostly Na) of the matrix, requiring structural modifications that come to depend crucially on the local composition of the glass.
Recently, dry fabrication of silver nanocomposites glasses using solid-state field-assisted diffusion process and post-annealing were reported by:
Y. Ma, et al in, “Preparation of Ag nanocrystals embedded silicate glass by field-assisted diffusion and its properties of optical absorption,” Solid State Sci. 12(8), 1413-1418 (2010); and
J. Sancho-Parramon, et al, “Optical and structural properties of silver nanoparticles in glass matrix formed by thermal annealing of field assisted film dissolution,” Opt. Mater. 32(4), 510-514 (2010).
In both cases, the authors successfully produced silver nanocrystals embedded in glass. However, these techniques produce clusters (islands) of inhomogeneously distributed nanoparticles.
Further processing of silver ion exchange glasses using laser or electron beam or X-Ray energy is reported in a number of publications. For example, Blondeau et al. in, “Influence of Pulsed Laser Irradiation on Precipitation of Silver Nanoparticles in Glass” in Journal of Crystal Growth 311 (2008) 172-184 which reports that the irradiation of the glass samples by the laser pulse promotes precipitation of the nanoparticles in a multiphoton process and the formation of nanoaggregates.
A number of similar publications on the processing of glass containing metallic ions using laser or electron sources all led to the formation of metallic nanoparticles.
It is an object of the present invention to produce an ion exchange substrate which has improved large area ion-exchange and nanoparticle homogeneity.
It is another object of the present invention to produce an ion exchange substrate in which the shape and thickness of the layer(s) containing the nanoparticles is better controlled.
It is another object of the present invention to improve the optical properties of the material and the controllability of the optical properties.
It is another object of the present invention to create a metalized substrate.
In accordance with a first aspect of the invention there is provided a method for metalizing a substrate, the method comprising the steps of:
creating an as-diffused substrate which is suitable for metalization by:
heating and applying a voltage across an ion exchange substrate to embed metallic ions from the metallic layer within the ion exchange substrate by a process of ion exchange to create an as-diffused substrate in which the metallic ions are distributed substantially homogeneously across the substrate;
metalizing the as-diffused substrate by:
applying a pulsed laser beam to a surface of the as-diffused substrate at or near a high concentration of metallic ions such that the energy of the laser causes the conversion of the metallic ions in the as-diffused substrate into metal atoms at or near the point at which the laser pulse is incident upon the as-diffused substrate.
Preferably, the method further comprises creating the ion exchange substrate by annealing a substrate having a suitable concentration of alkali ions and a metallic layer on a surface thereof.
Preferably, the metal is contained in a mixed or percolated metal-dielectric layer.
Preferably, the step of annealing occurs at between 250° C. and 350° C.
More preferably, the step of annealing occurs at 300° C.
Optionally, the step of annealing occurs for between 20 and 40 minutes.
Preferably, the step of heating the ion exchange substrate occurs at a temperature of between 100° C. and 350° C.
More preferably, the step of heating occurs at 300° C.
Preferably, the applied voltage is between 10V and 2 kV.
Optionally, the applied voltage is 1 kV.
Preferably, the process further comprises introducing a conducting layer between an electrode and the substrate to improve the electrical contact between them.
Preferably, the process further comprises introducing a receiving layer which captures ion exchange material removed from the substrate during the ion exchange process.
Preferably, the conducting layer and the receiving layer comprise a graphite layer. The graphite layer may be a graphite foil.
Preferably, the substrate is a glass.
More preferably, the substrate is a soda lime glass.
Preferably, the metallic layer comprises ions of a noble metal.
Preferably, the noble metal is silver.
Optionally, the noble metal is gold or copper.
Preferably, the process further comprises post annealing the as-diffused substrate to convert the metal ions into metal atoms which form metal nanoparticles.
Preferably, the step of post annealing occurs in air.
Preferably, the step of post annealing occurs at between 400° C. and 650° C.
More preferably, the step of post annealing occurs at around 550° C.
Preferably, the step of post annealing occurs in air.
Preferably, the pulsed laser is a nanosecond or picosecond pulse laser.
Preferably, the pulsed laser may operate at wavelengths from 355 nm to 1064 nm.
Preferably, the pulsed laser may have energy fluence up to a 5 J/cm2.
Preferably, the as-diffused samples may be processed at speeds of up to a 50 mm per second.
In accordance with a second aspect of the invention there is provided a method for creating an ion exchange substrate which is suitable for metalization, the method comprising the steps of:
creating an as-diffused substrate which is suitable for metalization by:
heating and applying a voltage across an ion exchange substrate to embed metallic ions from the metallic layer within the ion exchange substrate by a process of ion exchange to create an as-diffused substrate in which the metallic ions are distributed substantially homogeneously across the substrate.
Preferably, the method further comprises creating the ion exchange substrate by annealing a substrate having a suitable concentration of alkali ions and a metallic layer on a surface thereof.
Preferably, the step of annealing occurs at between 250° C. and 350° C.
More preferably, the step of annealing occurs at 300° C.
Optionally, the step of annealing occurs for between 20 and 40 minutes.
Preferably, the step of heating the ion exchange substrate occurs at a temperature of between 100° C. and 350° C.
More preferably, the step of heating occurs at 300° C.
Preferably, the applied voltage is between 10V and 2 kV.
Optionally, the applied voltage is 1 kV.
Preferably, the process further comprises introducing a conducting layer between an electrode and the substrate to improve the electrical contact between them.
Preferably, the process further comprises introducing a receiving layer which captures ion exchange material removed from the substrate during the ion exchange process.
Preferably, the conducting layer and the receiving layer comprise a graphite layer. The graphite layer may be a graphite foil.
Preferably, the substrate is a glass.
More preferably, the substrate is a soda lime glass.
Preferably, the metallic layer comprises ions of a noble metal.
Preferably, the noble metal is silver.
Optionally, the noble metal is gold or copper.
Preferably, the process further comprises post annealing the as-diffused substrate to convert the metal ions into metal atoms which form metal nanoparticles.
Preferably, the step of post annealing occurs in air.
Preferably, the step of post annealing occurs at between 400° C. and 650° C.
More preferably, the step of post annealing occurs at around 550° C.
Preferably, the step of post annealing occurs in air.
In accordance with a third aspect of the present invention there is provided an as-diffused substrate obtained by the process described in the second aspect of the invention.
Preferably, the the noble metal is silver and having a surface plasmon resonance with peak absorption at around 470 nm.
In accordance with a fourth aspect of the invention there is provided an as-diffused substrate in which the metallic ions are distributed substantially homogeneously across the substrate.
Preferably, the substrate is a glass.
More preferably, the substrate is a soda lime glass.
Preferably, the metallic layer comprises ions of a noble metal.
Preferably, the noble metal is silver.
Optionally, the noble metal is gold or copper.
In accordance with a fifth aspect of the invention there is provided a method for metalizing an as-diffused substrate by applying a pulsed laser beam to a surface of the as-diffused substrate at or near a high concentration of metal ions such that the energy of the laser causes the conversion of the metal ions in the as-diffused substrate into metal atoms at or near the point at which the laser pulse is incident upon the as-diffused substrate.
Preferably, the metal is contained in a mixed or percolated metal-dielectric layer.
Preferably, the pulsed laser is a nanosecond pulse laser.
Preferably, the pulsed laser may operate at wavelengths from 355 nm to 1064 nm.
Preferably, the pulsed laser may have energy fluence up to a 5 J/cm2.
Preferably, the as-diffused samples may be processed at speeds of up to a 50 mm per second.
Preferably, the as-diffused substrate is a glass.
More preferably, the as-diffused substrate is a soda lime glass.
Preferably, the metallic layer comprises ions of a noble metal.
Preferably, the noble metal is silver.
Optionally, the noble metal is gold or copper.
This process leads to a controllable formation of percolated metallic films with tailored properties internis of volume filling factor etc., which will then in turn affect the optical and electronic properties of the composite material.
In accordance with a sixth aspect of the present invention there is provided a metalized as-diffused substrate obtained by the process described in the fifth aspect of the invention.
In accordance with a seventh aspect of the invention there is provided a metalized as-diffused substrate in which metal atoms form a mixed or percolated metal-dielectric layer in which the atomic characteristic of the metal is apparent.
Preferably, the as-diffused substrate is a glass.
More preferably, the as-diffused substrate is a soda lime glass.
Preferably, the metallic layer comprises ions of a noble metal.
Preferably, the noble metal is silver.
Optionally, the noble metal is gold or copper.
In accordance with an eighth aspect of the invention there is provided a Glass metal composite obtained by a process defined in the first aspect of the invention wherein the metal ions are silver ions and the as diffused substrate has a surface plasmon resonance with a peak absorption at around 350 nm
In accordance with a ninth aspect of the invention there is provided an apparatus for creating an as-diffused substrate by ion exchange, the apparatus comprising:
a positive electrode and a negative electrode separated by a sample space, the sample space being adapted to receive a substrate with a metal coating wherein the negative electrode is provided with a mask a receiving layer which captures ion exchange material removed from the substrate during the ion exchange process.
Preferably, the conducting layer fills voids which would otherwise exist between the substrate and the negative electrode
Preferably, the conducting layer is highly planar and malleable such that it fills voids which would otherwise exist between the relatively uneven surface of the glass substrate and the electrode.
Preferably, the conducting layer and the receiving layer comprise a graphite layer.
Preferably, the apparatus further comprises a heat source.
Preferably, the heat source is an oven within which the electrodes are contained.
The present invention will now be described by way of example only, with reference to the accompanying drawings in which:
a is an image of a silver-ion doped glass annealed in air,
a is a series of microscope images of the slices,
a to 10d show scanning electron microscope images of a glass-silver composite in accordance with the present invention.
The present invention provides methods and apparatus for the creation of an as-diffused material in which ions of a metallic element are exchanged into an ion exchange substrate in place of alkali ions contained in the substrate in a dry fabrication technique which involves a solid state field assisted diffusion process. The present invention further processes the as-diffused material to create a metallized layer at or near the surface of the substrate. In another embodiment of the invention, the as diffused substrate is annealed to create a substrate which has nano-particle clusters.
In the first stage, an ion exchange substrate is created by providing a substrate 7 having a suitable concentration of alkali ions and a metallic layer on a surface of the substrate. The substrate is then annealed 9 in order to create an ion exchange substrate. The ion exchange substrate is placed between the positive and negative electrodes of an electric circuit inside an oven to apply a voltage across the substrate 13 whilst heating the substrate 11. This process embeds metallic ions from the metallic layer within the ion exchange substrate by a process of ion exchange to create an as-diffused product 15 in which the metallic ions are distributed substantially homogeneously across the substrate.
Metalization of the ion exchange substrate 1 is achieved by applying a pulsed laser beam 17 to a surface of the as-diffused substrate such that the energy of the laser causes the conversion of the metal ions in the as-diffused substrate into metal atoms at or near the point at which the laser pulse is incident upon the as-diffused substrate to convert silver ions into silver atoms and form a mixed or percolated metal-dielectric layer.
Metal-dielectric mixtures consisting of metallic inclusions in an insulating matrix present a peculiar optical behavior that allows their use in different applications, both in linear and non-linear optics (diffraction gratings, surface enhanced Raman spectroscopy, second harmonic generation etc.). The optical properties of these composites are mainly dominated by the surface plasmon resonance of the free electrons of the inclusions and the effects of the percolation among inclusions. Thus, the optical behavior of these mixtures may depend on a large number of parameters, like the size, shape and distribution of the metallic inclusions, the interaction among them and the nature of the dielectric matrix. A widely used approach for modeling the optical properties consists of using effective optical constants for the composite, calculated in terms of the optical constants of the mixing materials (effective medium approximations).
When metallic nanoparticles are contained in, for example, a glass matrix the material is known as a glass with embedded metallic nanoparticles or a metal-glass nanocomposite. But if we have a mixture of metallic atoms in a substrate for example, silver with glass is created with a layered structure then this is known as a percolated layer of glass and silver.
In one example of the creation of the as-diffused material in accordance with the present invention a substrate Schott B270 super-white soda-lime glass of 1 mm thickness weighing 2.6026 g. One side of the glass (a circular area with a diameter of 18 mm) has a coating of a fast drying silver suspension (Agar 301: very fine silver flakes dispersed in isopropanol).
Step I of Fabrication:
The sample is annealed at 300° C. for ˜30 minutes. The substrate comprises a coated silver layer formed a homogeneous stable solid film of beige colour and with a thickness of ˜15 μm which is annealed to form the ion exchange substrate. After coating and annealing, the weight of the sample had increased by 29.1 mg. The thickness and weight increase after annealing indicated the formation of silver oxide (Ag2O with density of 7.14 g/cm3).
Step II of Fabrication:
The sample is then pressed between two metal electrodes which in this example are circular in shape and with a diameter of 18 mm. In order to improve the contact a piece of graphite foil was inserted between the glass and the negative electrode. This has also the advantage that the substances coming out of the glass do not pollute the electrodes. Also graphite forms a non-blocking cathode since it accepts alkali ions. The electrodes with the samples are placed inside an oven and connected to a high-voltage power supply, with the positive voltage connected to the Ag side.
The foil 32 is positioned between the glass and the negative electrode and acts to receive ions which are moving out of the glass preventing them from polluting the electrodes. In addition the layer is highly planar and malleable such that it fills voids which would otherwise exist between the relatively uneven surface of the glass substrate and the electrode. This assists in drawing the Na ions from the glass substrate at a more even rate across the surface of the substrate which in turn improves the homogeneity of the ion exchange process such that Ag ions are drawn into the glass in a substantially homogeneous manner. Other materials with similar functional properties such as graphene may be used for a similar purpose
In Step II of the fabrication the current is ionic and is caused by the silver ions moving into the glass from the anode and alkali and alkaline ions moving out of the glass at the cathode. The current-time dynamics described in the present invention is in contrast to the previous works where Step I, namely annealing of the silver film in air before field-assisted diffusion, has not been performed. This led to the observation in
It has been suggested earlier that the amounts of metallic ions penetrating into the glass matrix depend on the applied voltage and temperature. This allows control of the doping process. Here, the current after an hour became nearly constant. For the purpose of this embodiment of the present invention, after an hour the voltage was disconnected and the residual silver film was removed from the anode surface. The sample was transparent. Transmission spectra of the original glass sample and of the as-diffused sample indicate that after Step II the silver is predominantly in ionic state.
The field-assisted diffusion process may be understood as an electro-chemical process in a solid-state cell. At the applied temperature (300° C.) the cations in the glass, mainly Na+, K+, Ca2+, become mobile (sodium is particularly known to be mobile at elevated temperatures. The applied direct current (dc) electric field leads to an ionic current flow and depletion of alkali and alkaline ions under the anode. This results in a space-charge region with a strong electric field, which drives silver into the glass. Here, the oxidized silver film under anode acts as a source for silver ions. Cations are moving towards the cathode where they are neutralized, leaving negative voids near the anode. This paves the way for silver ions (Ag+) to start migrating into the glass matrix and fill the voids left by the alkali ions. For instance and in the case of sodium, it is known that the covalent character of Ag—O bond is higher than that of Na—O bond. Therefore, the force constant for Ag—O is higher. This causes the force constant for Si—O to be lower for Ag—Si—O NBO (non-bridging oxygen) than for Na—Si—O NBO.
The amount of cations in the glass matrix is limited and they will deplete after a period. Close to the anode a large part of the current is carried by silver anions. The total charge transfer of 2.01 A.s/cm2 is equivalent to the charge of 2.24 mg/cm2 of Ag+ ions. After the diffusion process, the residual silver film is mechanically removed from the surface.
Step III of fabrication is a step included where the end point of the process is to create large sized silver nanoparticles within the substrate by applying heat. The as-diffused sample is annealed in air at 550° C. for 48 hours. Post annealing of the sample in air for 48 hours and at 550° C. provides a change of colour of the treated area. Therefore, as a result of the post-annealing process silver ions (Ag+) are further reduced to silver atoms)(Ag0), which then in turn form silver nanoparticles with larger sizes. For annealing in air and given the considerable coloration observed the electrons required for silver reduction may be extracted from atoms that are intrinsic to the glass, namely non bridging oxygen (NBO) atoms.
Making a thin slice of the sample and examining the profile of the nanoparticle containing layer provides the means for further optical analysis.
Here, due to the high absorption, the SPR (Surface Plasmon Resonances) band is mostly cut off making it very difficult to register the exact peak position and its small red shift caused by the spill-out effect of the nanoparticles. The spill-out effect of the electrons will lead to the volume-average mean electron density decreasing and consequently peak position red shifting. It is more prominent with decreasing the particle size.
The width of the plasmon band shows the decay time of the coherent motion of the electrons constituting the plasmon upon external excitation. Previously, it has been shown that in the vicinity of an SPR band of silver nanoparticles (due to the small imaginary part of their interband susceptibility), the plasmon band at its FWHM (Full Width Half Maximum) has the same value as the frequency of electron collisions. Therefore, decrease in particle size can result in the increase of the frequency of electron collisions and hence broadening of the plasmon band.
This embodiment of the present invention shows the formation of larger particles with lower number density closer to the surface and smaller nanoparticles with higher number density in the deeper layers. The dc electric field-assisted fabrication of homogenous (island-free) silver-doped nanocomposites glass in air and via a three-step technique was demonstrated which allows for the formation of larger particles with lower number density closer to the surface and smaller nanoparticles with higher number density in the deeper layers.
The amount of ions penetrating into the glass matrix and shape of the diffusion profile is dependent on the process parameters such as applied voltage and temperature. In addition annealing parameters (such as temperature and duration) create the condition for metal-based nanocluster formation.
In another embodiment of the present invention, an as-diffused substrate is created in a process similar to that described above but with certain improved novel features.
Silver ions (Ag+) are introduced into a soda-lime glass by a solid-state field-assisted diffusion process which used an external electric field to assist the migration of the silver ions into the substrate, making it possible to perform ion exchange with even multivalent ions that are driven by the gradient in the electrochemical potential. In this configuration, the metal dopant supplier is a metallic film directly deposited on the glass matrix. This technique prevents interdiffusion between the ionic species as in this case the dopant ions coming from the film replace the alkali ions of the glass substrate matrix.
The process for creating an as-diffused substrate is as follows:
Step 1: One side of a piece of glass was coated with a fast drying silver suspension or paste to create the ion exchange substrate.
Step 2: The sample was then pressed between two metal electrodes. In order to improve the contact a piece of graphite foil was inserted between the glass and the negative electrode. This has also the advantage that the substances coming out of the glass do not pollute the electrodes. Graphite also formed a non-blocking cathode since it accepts alkali ions. The electrodes with the ion exchange substrate were placed inside an oven and connected to a high-voltage power supply, with the positive voltage connected to the Ag site. The experimental setup for field-assisted diffusion apparatus is shown in
The current-time dynamics of the process were monitored throughout the experiment. After the diffusion process, the residual silver film was mechanically removed from the surface. The as-diffused glass sample then contained silver ions and was transparent. The existence of silver ions in the as-diffused glass can be confirmed by annealing which leads to the formation of silver nanoparticles in the glass matrix.
In another example of the present invention, an as-diffused substrate in accordance with the present invention was metallized using the apparatus shown in
The as-diffused substrate containing silver ions may be irradiated using a range of pulsed laser systems at various available wavelengths (from 355 nm to 1064 nm) and various values for energy fluence—up to a few J/cm2.
The use of a sufficiently intense and energetic laser source to irradiate the substrate provides a mechanism whereby electrons become available within the substrate for the conversion of Ag+ to Ag0. This release of electrons from the glass matrix and their capture by silver ions constitutes the reduction of silver from ionic state to the metallic state as a result of irradiation. The Silver has been observed to form a glass silver composite or percolated layer of metallic silver on the surface of the glass where the laser irradiation was incident. This allows the creation of this product in a reproducible and scalable manner, making it useful for many applications.
In the embodiment of the present invention, glass was doped with silver ions and silver-doped nanocomposites glasses were created using the above described solid-state field-assisted diffusion process to produce a substantially transparent piece of silver ion doped percolated (SID) glass.
In that process, the combined action of the applied electric field and temperature increased the mobility of alkali metal ions, such as sodium cations (Na+), which are particularly mobile at elevated temperatures. The process leads to an ionic current flow and depletion of alkali ions under the anode resulting in a space-charge region with a strong electric field which makes cations move toward the cathode where they are neutralized. It also leaves negative voids near the anode and paves the way for silver ions to migrate into the glass matrix and fill the voids. The diffusion process is also assisted by the thermal relaxation of the surface tensile stress during the ion exchange process, caused by the size difference between Ag+ (with ionic radius of about 1.26 Å), and Na+ (with ionic radius of about 1.02 Å). This process results in the formation of Ag—Si—O NBO (nonbridging oxygen) in the glass matrix.
Annealing of the substrate at 550° C. for 48 hours resulted in a strong change of colour in the material due to the formation of embedded spherical silver nanoparticles as is shown in
Therefore the annealing process results in the silver ions (Ag+) being further diffused into the glass matrix and being reduced to silver atoms)(Ag0), which then in turn formed silver nanoparticles with larger sizes. The electrons required for silver reduction are extracted from the non-bridging oxygen (NBO) atoms that are intrinsic to the glass.
The concentration of silver ions in the substrate and its temperature due to the annealing process play a fundamental role in the formation and aggregation of silver atoms. During this process, more Ag—O bonds are broken to form neutral silver atoms that become the dominant state. The development of appreciable colour (as can be seen in
Metal particles exhibit different optical properties compared to bulk metals making dielectrics mixed with noble metal particles the subject of intensive research efforts across the globe. When a metal particle is smaller than the wavelength of light, the light reflected from it is replaced by light scattering, which is particularly strong at the resonance frequencies of its collective electron excitations—surface plasmon resonances (SPRs). Therefore, the present invention provides a way of controlling the size of the nanoclusters by controlling the extent to which the SID sample is annealed when the SID is created with a substantially homogeneous distribution of silver ions using the above described process.
In the following embodiment a SID sample was cut into five pieces, and the pieces were annealed in air at 550° C., each for a different duration as follows: 1 h, 2 h, 4 h, 8 h, 48 h. This resulted in the formation of silver nanoparticles inside the glass, changing the colour of the glass to dark yellow for short annealing times and brown for longer times. The glass substrate used here (B270) is known to have a very low concentration of Iron, which is often considered as a reducing agent for silver during annealing process. Thin slices of the cross sections allowed visualization of their depth profile. The resin cures at room temperature. Each section has been polished on both sides and providing slide thicknesses in the range of 30-33 μm.
a) shows microscope images of the thin slices. These are the cross sections of the generated silver nanoparticle-containing layers.
Therefore the exact plasmon band position and height could not be determined, however what has been measured allowed us to make the following conclusions. For longer annealing times the silver spreads out into deeper layers, the nanoparticle containing layer becomes thicker. Near the surface the plasmon band becomes narrower, which fits to the simulated spectra for growing particle sizes. This can either happen by the agglomeration of more silver or by Ostwald ripening (K. Yata and T. Yamaguchi, “Ostwald ripening of silver in glass,” J. Mater. Sci. 27, 101-106 (1992). In this process smaller NPs are dissolved and redeposited onto larger NPs. In the depths where the shorter-annealed samples have wide plasmon band, the width decreases strongly. The plasmon bandwidth at the lowest edge of the profile is slightly lower for longer annealing times. This means that NPs already
A further SID glass sample was irradiated using the third harmonic of a pulsed Nd:YVO4 laser operating at λ=355 nm. Laser processing of the SID glass in air results in a space selective, one-step precipitation of silver particles, leading to the formation of a homogeneously scalable glass-silver composite (GSC). The laser was utilized at an output energy density (laser fluence) of 420 mJ cm−2 per pulse with a repetition frequency of 80 kHz and pulse duration of 8 ns.
c presents an image of the fabricated GSC material, produced by laser irradiation of the SID glass at the laser scanning speed of 14 mms-1. At this scanning speed, approximately 330 pulses per spot were fired into the SID glass. The laser provided a beam with Gaussian intensity profile of an excellent quality (beam quality factor of M2≈1.1) focused to a spot of d≈60 μm in diameter (1/e2 of the central value) on the sample surface leading to the Rayleigh range
of approximately R≈7.2 mm. This large Rayleigh range (the distance from the beam waist of diameter d to the position where it is ✓2d) provides a uniform irradiation trace throughout the experiments. The laser beam was focused using a flat-field scanning lens system, a specialized lens system in which the focal plane of the deflected laser beam is a flat surface which offsets the off-axis deflection of the beam through the focusing lens system. This ensured a precise energy input and a uniform irradiation trace throughout the process.
The SPR band of the GSC is shown in
The SID glass absorbs approximately 65% of the laser light. This is indicated by
As can be seen in
In conclusion, in one aspect, the present invention provides a laser-assisted, fast technique for a one-step precipitation of silver from ionic state to metallic state in glass and spatially selective fabrication of a homogeneously structured composite material: glass-silver composite. The optical and structural properties of such composite material can be designed at will, which could have potential impact on light/plasmon wave and sensing technologies, optoelectronics, and surface enhanced Raman spectroscopy. The structural properties of the material are designed by the parameters of the laser, e.g., laser fluence and the irradiated number of pulses per spot. These properties, that are now subject of our further studies, will facilitate the application of GSC in some areas of optoelectronics and chemistry such as light and plasmon wave technology, circuitry, sensing technology, and surface enhanced Raman spectroscopy.
The elementary composition and scanning electron microscopy of the GSC is shown in
Advantageously, the speed of the processing (laser processing of as-diffused glass) can be as high as a few tens of mm per second. Whilst the formation of nanoparticles (metallic chains) as a result of either laser or even X-ray irradiation and subsequent annealing has been reported, the metallization a substrate in a one step laser assisted process was a wholly unexpected effect and is novel. This process leads to a controllable formation of percolated metallic films with tailored properties in terms of volume filling factor etc., which will then in turn affect the optical and electronic properties of the composite material.
It is noted that, as distinct from the prior art, the present invention provides an area of homogenous silver-ion doped (SID) glass where the homogeneity extends across the whole sample which has been processed in accordance with the present invention. It also provides for the creation of homogenous (island-free) glass containing silver nanoparticles and for the irradiation of a processed sample with a laser leading to the fabrication of homogenous glass-silver composite (metallized area on the glass surface) samples.
It is further noted that the skilled person applying laser irradiation to an ion exchange material would expect to see a gradual change from colourless to yellow to amber to white as reported by blondeau (Journal of Crystal Growth 311(2008) 172-184. IN contrast, the present invention provides a substrate upon which a metal layer is created at or in close proximity to the position upon the substrate at which the laser beam is incident. The optical absorption properties of the substrate and the final metalised material are different from those shown in the prior art as dempnstrated in the above mentioned figures.
The present invention may find application in Technical Marking, Biomedical Applications, Sensors, Embedded Circuits (Optoelectronic circulates and light wave technology), Electro-Optic Materials with tailored nonlinearity, Stimulated Enhanced Raman Scattering (SERS) spectroscopy & related applications (nonlinear optics), and the creation of objects with an aesthetic silver layer.
Improvements and modifications may be incorporated herein without deviating from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1200890.0 | Jan 2012 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2012/000717 | 9/14/2012 | WO | 00 | 8/20/2014 |
