which highly differs from the standard type I modification and allows the inscription of a “new type” of wave- guides. First, we characterized the fluorescent photo-induced structures using a confocal microscope, then we investigated the dependence of ∆n as a function of the irradiation conditions. Following this, 7 mm long wave- guides were written inside the glass where the waveguiding aspects such as morphology, ∆n profile, near field mode profile, simulated mode profile and propagation losses were investigated. For the sake of brevity, only one single mode waveguide is presented in detail in this paper. Indeed, all modification traces exhibit rather similar waveguiding aspects. However, it should be noted that increasing ∆n results in multimode waveguides which will not be addressed in this paper. Next, a 50–50 beam splitter was successfully fabricated to illustrate the potential of this new writing process. Finally, the waveguiding properties were transposed from bulk samples to ribbon-shaped fibers both made of the same photosensitive silver-containingzincphosphateglasses.
demonstrate that luminescence properties of the native glass are preserved after the shaping
process. Furthermore we establish that the unique fiber's flat geometry allows for the convenient,
accurate Laser writing of complex luminescent silver clusters patterns within the glass matrix.
We believe the drawing of silver-containingzinc-phosphateglasses could lead to a decisive
III.2. Type I modification in phosphate – zincphosphateglasses
More specifically, phosphateglasses exhibit some challenges in the understanding of the laser-glass interaction and its control. This is due to the presence of several components in the glass composition that could affect the laser-glass interaction. As mentioned before in section II.3.8, network modifiers are added to the glass composition to stabilize the glass matrix and/or to dope the glass with high concentrations of rare earth metals. Two writing regimes exist, athermal and thermal (section I.3.4). While writing in the athermal regime i.e. generally low repetition rate and pulse energy in the microjoule (µJ) scale, it was reported that several laser passages switch the ∆n from positive to negative in a phosphate Kigre QX glass . In the thermal regime, positive and negative ∆n were observed for the same photo-induced structures where in the latter case no waveguiding could occur . Generally for the thermal regime, most of the ∆n observed were negative ones making the writing of optical waveguides complicated . Moreover, a self-organizing feature and ripple structures were observed by many research groups [49, 176] in phosphateglasses following DLW, which makes the writing of low loss waveguides nearly impossible. This indicates that the writing window of type I smooth waveguides in the thermal regime is really narrow in phosphateglasses. Moreover, it has been reported that the photo-induced ∆n in phosphate and zincphosphateglasses highly depends on the glass composition as well as the laser parameters [49, 62, 132, 173]. Fletcher et al. investigated the effect of the ratio O/P in zincphosphateglasses and found that a ratio O/P=3.25 is the ideal one for having positive ∆n and writing smooth waveguides [62, 132]. To sum up, creating smooth type I modifications exhibiting positive ∆n in phosphate – zincphosphateglasses is complicated due to the multicomponent nature of the glass and requires a fine optimisation of the laser parameters and/or the glass composition.
The chemical etching is occurring in our case in the whole exposed area with a maximum in the center of the structure, except in the location of the luminescent ring structure. A correlation between the silver concentration and the etching rate has been first considered. Recently, the solu- bility in de-ionized water of unexposed zinc-phosphate glass has clearly shown that the presence of silver tends to increase the solubility of the glass in water and acid. 15 In the present case, the lowering of the silver concentration in the center of femtosecond exposed area is not related to a reinforcement of the glass with respect to water etching. Other phenomena have to be taken into account, like stress-induced effects reported in silica which can modify the etching rate. 6 In phosphate glass, the influence of femtosecond laser has been mainly investigated for refractive index modification. Using 1 kHz repetition rate laser, Bhardwaj et al. reported that neg- ative refractive index variation was observed in SCHOTT IOG-1 phosphate glass without a clear etching rate change. 17 Ehrt et al. demonstrated in fluoro-phosphateglasses that im- portant positive refractive index variation can be obtained. It is attributed in this particular case to a change of connectiv- ity between fluorine and phosphate groups. 18 High repetition rate laser can favor ionic migration like in potassium-lantha- num-phosphate glass, where positive index variation was observed following the fluctuations of (K, La) local concen- tration. In the present investigation, the generation of hole/ electron pairs leads to the formation of Ag 2þ and Ag 0 species mainly. Most of the electron traps are gathered in the ring structure to form silver clusters Ag m xþ while the chemical
3. Results and discussion 3.1. Morphology comparison
Using two different laser setups both type I and type A waveguides were inscribed in the same glass substrate. First, we start by characterizing the type I waveguides. Series of type I waveguides were written typically 160 µm below the glass surface of a silvercontainingzincphosphate glass (see Experimental method section) while changing the laser parameters. The pulse energy was varied from 0.5 µJ to 1 µJ while the writing speed between 1 mm/s and 25 mm/s. For the sake of brevity, only one single mode (SM) type I waveguide is fully characterized and compared to a SM type A waveguide. Type I SM waveguide is obtained using a pulse energy of 0.65 µJ and a writing speed of 5 mm/s. Under white light (WL) illumination, the top view of type I SM waveguide reveals a single smooth line of modification that is typical of type I modification (Fig. 1 (a.i)). From the side view, a white colored triangular shape waveguide was observed that is surrounded by a dark ring as shown in Fig. 1 (a.iii). Such waveguide morphology was also observed by other research groups in Eagle 200 glasses [ 37 – 39 ]. Under blue excitation, a very weak-fluorescence (compared to type A structures) was observed to surround the waveguide under high camera exposure time (Figs. 1 (a.ii) - (1.iv)). The weak fluorescence indicates the formation of only few silver clusters following laser inscription. Knowing that the laser writing process is performed using a relatively low repetition laser (250 kHz compared to 9.8 MHz the laser used to create type A waveguides) and high writing speeds, the ideal conditions for the creation and aggregation of silver clusters Ag m x+ were not met.
We report on dual-color control of femtosecond direct laser writing (DLW) in a non commercial silver-containingzincphosphate glass, thanks to an additional illumination with a cw (continuous wave) UV laser either after the femtosecond irradiation or simultaneously. By tuning the cw UV power, we demonstrate the tunable control and inhibition of the production efficiency of laser-induced fluorescent silver clusters, leading up to 100% inhibition for simultaneous co- illumination when the laser writing is performed close enough to the permanent structuring threshold. The role of the cw UV illumination is discussed in terms of inhibition of the silver cluster precursors or of dissolution of the laser-induced silver clusters. These results show the ability of laser writing inhibition in our photosensitive silver-containingphosphate glass, which is a necessary step to further develop super-resolution laser writing approaches such as STED-like DLW either of fluorescent silver clusters or of silver metallic nanoparticles with plasmonic properties.
acid groups of PMMA would then be responsible for the acidolysis of PC and formation of graft copolymer through mixed aliphatic–aromatic ester bond ( Eq. (2)).
PMMA–COOH+PC–O–CO–O–PC PMMA–COO–PC+PC–OH+CO 2 (2)
This reaction does not however occur significantly below 240°C, thus at the blending temperature of PC and PVDF (235°C). This situation might be improved by bypassing the first step of the grafting reaction (partial PMMA hydrolysis), which takes place at substantially high temperature (300°C). For this purpose, a random copolymer of methyl methacrylate (MMA) and acrylic acid (AA) could be substituted for PMMA. Further, neutralization of the carboxylic acid groups by metal cation could contribute to the catalysis of the acidolysis reaction. Zinc cation known for coordinative interaction with electron donating heteroatoms (N, O,…) is worth being considered. Therefore, random copolymer of MMA and 6 mol% AA will be synthesized and neutralized by Zn cations to different extents. The reaction of these copolymers with PC will be studied in benzophenone at 240°C and in the melt at 235°C. Under these conditions, no degradation of PC and PMMA occurs . Finally, the question will be addressed to know whether the compatibility between PC and PVDF is improved when the random copolymer of methyl methacrylate and 6 mol% of acrylic acid is used rather than neat PMMA in the blending process. The effect of the (partial) neutralization of the acrylic acid co-units by Zn cations will also be studied, since the formation of the PC-g-PMMA copolymer at the interface is expected to be more favorable.
Metal phosphates have received much attention because of their versatile applications, mainly as catalysts, molecular sieves, optical materials and anticorrosive pigments. 1–3 Among these materials, zinc phosphates (amorphous phases, hopeite) have also been shown to be interesting materials in dentistry applications as luting cements owing to their strong adhesion, biocompatibility and low solubility in aqueous and biological environments. 4,5 In this context, the antibacterial properties of freshly prepared zincphosphate cements have been demon- strated against Streptococcus mutans bacteria. 6–9 These were attributed to the release of zinc and were greatly reduced aer the cement hardened. 10–12 Moreover, materials based on zinc– calcium phosphates have been shown to promote bone regen- eration in medical applications thanks to the essential function of zinc in bone tissue development. 6,7,13 However, to the best of our knowledge, no study of environmental applications of porous zinc phosphates has been reported, yet zinc is an element with low toxicity to humans and the environment in comparison with other metals found in metal phosphates. 11 They also have interesting properties for corrosion preven- tion. 12 –14 Both features are assets for use in the elds of biomedicine and water treatment.
zektzerite there is just enough alkali ions to compensate all (ZrO 6 ) 2- entities and just
enough SiO 2 to enable to these entities to be connected to 6 SiO 4 units (Si/Zr = 6). This
result suggests that similar connectivity of Zr with the surrounding silicate network should be found in our glasses. Similar results were obtained by McKeown et al. on their Zr-rich borosilicate glasses by comparison with zektzerite EXAFS data . The presence of a small fraction of B or Al as second neighbors of Zr can also be envisaged .
Na + ions and the decrease of NBOs amount in glasses of the ZrxNd series. Indeed, if we consider that Nd 3+ ions are mainly located in Na + , Ca 2+ and NBOs-rich regions (i.e. in depolymerized regions (DR), see Fig. 18 in ) of glass structure, the addition of ZrO 2
in the composition is expected to drain mainly Na + ions and thus to induce a decrease of the Na + /Ca 2+ ratio in the environment of Nd 3+ ions (indicated by arrows in Fig. 18 in ). This relative enrichment in Ca 2+ ions thus raises the mean bond valence between the oxygen atoms of Nd-O-Si bonds and the charge compensating cations (Na + + Ca 2+ ) because Ca 2+ cations are doubly charged. As a response, to avoid the overbonding of oxygen atoms connecting Nd and Si, the Nd-O mean distance adjusts itself (it increases as shown by EXAFS, Fig. 4).
ded in the amorphous phase) was formed. The proportion of the crystalline phase increased with an increase in the Ca/Pyrophos- phate ratio in the batch solution. It was demonstrated that the for- mation of the glassy material is not thermodynamically but rather kinetically driven and that the evolution of a transient amorphous phase toward a crystalline phase could be avoided by the washing step. The amorphous state of nuclei of glasses could be explained by i) the ionic strength of the initial solution, ii) the structural degrees of freedom of pyrophosphate entities and iii) the inhibi- tory effect of orthophosphate ions on calcium pyrophosphate phase crystallisation. Even if the different mechanisms involved in the formation of such materials (chemical, structural, and mor- phological evolution during the synthesis steps) are still to be investigated in detail, the synthesis of these new monolithic cal- cium pyrophosphate glasses in water-based solvent and at a low temperature opens up many perspectives to develop the chemistry of low-temperature calcium pyrophosphate-based materials for various applications. In the field of materials for bone substitution, these novel materials and their synthesis process should be partic- ularly well-suited to the preparation of hybrid organic-inorganic biomaterials, involving delicate biomolecules such as enzymes or growth factors.
servations. By scaling τ rec by a given factor, the same scaling
on all rates of kinetic reactions and D e leaves the distributions
In case of departure from this scaling law, that do not cor- respond to our experimental observations but which may be appropriate for other conditions (glasses, metal ions, thermal treatment), the system evolution regime may be dramatically dif-
List of figures
Figure 1.1 : Pathogens associated with four of the most common HAIs in intensive care unit surveillance, 2003 (adapted from ). Gram-negative bacterial species are shown in color, gram-positive species are shown in black and white.......................... 4 Figure 1.2: Persistence of relevant pathogens on environmental surfaces (adapted from ). The estimated survival time, in months, is based on the average life of infective strains on dry, inanimate surfaces at room temperature. The reported persistence for Klebsiella pneumoniae (30 months) and Salmonella typhimurium (50 months) are not shown to their full extent in the graph. .......................................... 8 Figure 1.3: The multiplication of pathogen reservoirs and infection transmission routes due to contaminated surfaces (adapted from ). ................................................ 8 Figure 1.4: Cell wall structure of Gram-negative and Gram-positive bacteria (from ) ............................................................................................................... 11 Figure 1.5 : Model of the development of biofilms from planktonic cells and dispersal of bacteria from a mature biofilm . ................................................................... 12 Figure 1.6: Genetic and biochemical mechanisms of the development of bacteria resistance to biocidal metals (from ). ............................................................ 13 Figure 1.7: Mechanisms of action of silver against bacteria (from ) ................... 15 Figure 1.8: High-angle angular dark-field scanning TEM (HAADF STEM) images showing the interactions of silver nanoparticles with bacteria: (left) E. coli, (middle) S. typhus, (right) P. aeruginosa (adapted from )............................................................ 16 Figure 1.9: Maxwellian energy distribution of
The thermal evolution of samples was checked by TGA-DTA.
Fig. 5 shows the TGA and DTA curves respectively, of PYG-00,
PYG-03 and PYG-06. The TGA curves exhibit two distinct regions of mass loss for PYG-00 and PYG-03 and an almost continuous curve for PYG-06. The mass losses can be attributed to the release of water either adsorbed or associated with the mineral structures (in particular the first mass loss associated to an endothermic event before 150 °C). The final mass losses (plateau after 600 °C) were 14.3%, 13.0% and 12.3% for PYG-00, PYG-03 and PYG-06, respectively. We recall here that PYG-00 was found to be purely amorphous and PYG-06 to be composed of crystalline and amor- phous phases. The beginning of the plateau (around 150 °C) corre- sponds to an exothermic event followed by a sharp endothermic peak. Complementary investigations by XRD on samples heated at 200 °C ( Supplementary material, S2 ) indicate the formation of monetite and apatite crystals. The Raman spectra show a shift of the line assigned to orthophosphate toward higher wavenumbers corresponding to calcium phosphate apatite, however monetite could not be clearly identified. These data suggest the crystallisa- tion of orthophosphate moieties present in the glass into apatite and monetite phases. The formation of additional orthophosphate ions could also result from the endothermic hydrolysis of pyrophosphate ions into orthophosphate (Eq. (1)), as reported for other hydrated calcium pyrophosphates.
metal content silicate glasses, for example, glasses within the ZrO 2 –SiO 2 , HfO 2 –SiO 2 , and La 2 O 3 –SiO 2
systems, have high melting temperatures (>1700 °C) , and their melts tend to demix or crystallize upon quenching . The sol-gel technique is an alternative process to prepare glasses, especially oxyfluoride  and metal-silicate compositions [51,52]. It allows the preparation of novel glasses at a lower temperature compared to the conventional melt-quench process, achieving a wider range of compositions, in particular, a high amount of fluorine in the glass with better dispersion of the components. Additionally, the sol-gel technique is handy, flexible, and quite cheap. (2) The second step in the fabrication of glass- ceramics includes the heat treatment of the starting glasses under specific heating conditions. The heat- treatment can lead to surface and/or volume precipitation of the dielectric crystals (hereinafter just “crystals”), but volume crystallization is desirable for the preparation of transparent GCs. In most of the GCs, this volume crystallization can be favoured by adding nucleation agents. Usually, the heat-treatment is done using a two-step process. During the first heat treatment, the formation of the precursors of the crystalline phases, i.e., nucleation, is happening. The temperature during this step should be high enough to achieve mobility of the ions in the glass matrix, but not too high, to avoid dissolution of the nuclei or extensive growth of the crystals. After, the nucleated glass is heat-treated at a higher temperature so that the nuclei can grow into larger crystals. The temperature during the growth step should be close to the crystallization temperature of the glass, that the heat treatment leads to the precipitation of crystalline particles within the glass matrix. During this step, the nuclei grow continuously, and their volume increases, until they are impeded by neighbouring crystals. Then, secondary growth is observed, resulting in the fusion of smaller crystals to larger ones. The size and concentration of the crystals are determined by the temperature and the duration of the thermal treatments and by the chemical composition of the glass.
cm -1 Raman band relative intensity shows a significant increase after the introduction of 10 mol.% of KNbO 3 . Such effect is expected to be related to the formation of tungsten bronze “crystal motif” .
Our results are in accordance with those on the alkali oxide – Nb 2 O 5 – Ga 2 O 3 ternary system reported
by Fukumi et al. : they stated that the structure consists in a majority of gallium tetrahedral sites which play a glass-former role while the Nb 5+ ions are inserted into the glass skeleton in more or less distorded octahedra. In terms of charge compensation for the GaLaK-5, GaLaK-10 and GaLaK-14 glasses, the same approach used for the GaLaK-0 glass can be considered: all the [GaO 4 ] - gallate units
polymeric insulation is to avoid the accumulation of space charge under electrical and/or thermal stresses which can significantly reduce the component reliability. Injection mitigation in low density polyethylene (LDPE) films by plasma processed silver nanoparticles (AgNPs) containing plasma polymer composites was recently reported through space charge measurements. The barrier effect has been assigned to the creation of permanent deep traps by introducing silver nanoparticles near the polyethylene surface. To substantiate the above findings, current measurements realized on composite layers and on polyethylene films with and without silver nanoparticles have been carried out. It is shown that in the presence of AgNPs in organosilicon layer, polarization/depolarization currents are one order of magnitude lower, transient currents decay faster and are not sensitive to multiple polarization. This can be understood if the AgNPs in the layer are acting as deep traps mitigating further injection with the result to decrease the apparent conductivity of the layer and to increase its breakdown strength. Similar trend is observed in polyethylene tailored by composite layer. These results strengthen the interpretation of the barrier effect based on space charge stabilized by deep traps formed by the AgNPs.
was performed in two-step process: silver sputtering to obtain the single layer of AgNPs followed by plasma polymerization to create the dielectric cover matrix . For both steps, we have used an axially-asymmetric RF (13.56 MHz) capacitively-coupled discharge maintained at low gas pressure .
LAPLACE, Université de Toulouse, CNRS, 118 Route de Narbonne, 31062 Toulouse Cedex 9, France
Under electrical stress, dielectric materials can accumulate electrical charges. This may even lead to a breakdown, i.e. to a system failure [1,2] . To prevent the harmful consequences of this phenomenon, charge trapping by metallic, silver nanoparticles (AgNPs) has been considered  . Even though the space charge build-up mitigation was demonstrated, the underlying mechanisms remain poorly described. To identify the AgNPs influence, their response needs to be probed at relevant scale, i.e. at the nanoscale. Thus, our overall objective is to determine the impact of AgNPs on the charge injection and retention in thin dielectric layers.