Modification Of Glass Research Articles

Effect of ultrashort laser-induced surface flaws on architectural glass strength

The present study gives a new insight into the use of laser ablation technology as a robust tool for fracture mechanical and strength examination of scratched architectural glass (soda-lime silica glass). Previously, mechanical tools such as indenters have been used for this purpose; however, artificial scratches produced with such instruments are accompanied by cracks and chippings, which degrade the accuracy of the results. Here, an ultra-short laser with picosecond pulse duration is employed to achieve highly controlled artificially applied flaws. Since most research on laser ablation has been done in the field of optics and electronics and is focused on non-structural/architectural glass, e.g. borosilicate, aluminosilicate, and fused silica, there is no detailed study on laser parameter optimization of soda-lime silica glass. Therefore, laser parameters have been optimized in view of achieving minimal cracks and chippings, along the laser-ablated flaw. The artificial flaws were thoroughly characterized in terms of depth, edge quality and reproducibility using several microscope inspection techniques. Subsequently, highly accurate laser-induced artificial flaws in the range of 42 μm to 123 μm were realized and four-point bending tests were performed to assess the impact of flaw depths on the glass strength and to illustrate the accuracy of the method. Remarkably low standard deviations of the strength values for the laser-modified (LM) specimens were obtained. It is shown that 81 μm difference between the maximum and minimum laser-induced flaw depths results in a glass strength difference of 41.4%. This well-controlled modification of architectural glass can pave the way for further surface modifications applicable to building industry and help in experimentally validating fracture mechanic theories.

Femtosecond laser induced thermophoretic writing of waveguides in silicate glass

Here in, the fs-laser induced thermophoretic writing of microstructures in ad-hoc compositionally designed silicate glasses and their application as infrared optical waveguides is reported. The glass modification mechanism mimics the elemental thermal diffusion occurring in basaltic liquids at the Earth’s mantle, but in a much shorter time scale (108 times faster) and over a well-defined micrometric volume. The precise addition of BaO, Na2O and K2O to the silicate glass enables the creation of positive refractive index contrast upon fs-laser irradiation. The influence of the focal volume and the induced temperature gradient is thoroughly analyzed, leading to a variety of structures with refractive index contrasts as high as 2.5 × 10–2. Two independent methods, namely near field measurements and electronic polarizability analysis, confirm the magnitude of the refractive index on the modified regions. Additionally, the functionality of the microstructures as waveguides is further optimized by lowering their propagation losses, enabling their implementation in a wide range of photonic devices.

Raman spectra study on modifications of BK7 glass induced by 1030-nm and 515-nm femtosecond laser

The direct femtosecond laser writing has been proved to be one of the most efficient techniques for micro-structuring of transparent materials, which can induce refractive index modifications to construct waveguide structures. In this work, laser-induced tracks with single-line configuration are formed inside the BK7 glass by using inscription of femtosecond laser pulses with 1 MHz repetition rate at wavelength of 1030 nm and 515 nm, respectively. The high-resolution confocal Raman spectra are obtained in the track regions to investigate the physical mechanisms of the modification. The results indicate that the specified regions inside the tracks induced by 1030-nm femtosecond laser expand and squeeze the adjacent area under certain writing conditions, leading to a refractive index increase in the core region. The 515-nm femtosecond laser brings out relatively more severe damage in comparison to the 1030-nm laser irradiation. A directional coupler structure has been fabricated by using the optimized writing parameters, showing a nearly balanced output with a ratio of 49.7:50.3 and an insertion loss of 1.36 dB for the single-line waveguide at 1064 nm.

Modification of soda-lime silicate glass under corona poling in air and nitrogen atmosphere

Modifications of a soda-lime silicate glass under thermal poling in corona discharge (CDP) in air and in dry nitrogen is studied with micro Raman technique to evaluate the possibility of glass structuration using poling in nitrogen. It is shown that CDP in dry nitrogen, contrary to CDP in atmospheric air, increases the concentration of silicon-oxygen tetrahedra bound into three-member rings in the subsurface region of the glass. The formation of the three-member rings is accompanied by the release of molecular oxygen.

Thermal and Structural Modification in Transparent and Magnetic Gallogermanate Glasses Induced by Gd <sub>2</sub>O <sub>3</sub>

Thermal and Structural Modification in Transparent and Magnetic Gallogermanate Glasses Induced by Gd <sub>2</sub>O <sub>3</sub>

Synthesis of Silver Modified Bioactive Glassy Materials with Antibacterial Properties via Facile and Low-Temperature Route

There is an increasing clinical need to develop novel biomaterials that combine regenerative and biocidal properties. In this work, we present the preparation of silver/silica-based glassy bioactive (ABG) compositions via a facile, fast (20 h), and low temperature (80 °C) approach and their characterization. The fabrication process included the synthesis of the bioactive glass (BG) particles followed by the surface modification of the bioactive glass with silver nanoparticles. The microstructural features of ABG samples before and after exposure to simulated body fluid (SBF), as well as their ion release behavior during SBF test were evaluated using infrared spectrometry (FTIR), ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD), electron microscopies (TEM and SEM) and optical emission spectroscopy (OES). The antibacterial properties of the experimental compositions were tested against Escherichia coli (E. coli). The results indicated that the prepared ABG materials possess antibacterial activity against E. coli, which is directly correlated with the glass surface modification.

Preparation and applications of wettability-controlled fluoroalkyl end-capped oligomer/cellulose nanofiber composites

Sol-gel reaction of two fluoroalkyl end-capped vinyltrimethoxysilane oligomer [RF-(CH2CHSi(OMe)3)n-RF; RF = CF(CF3)OC3F7; n = 2, 3: RF-(VM)n-RF] in the presence of cellulose nanofiber (CNF) under non-catalytic conditions was found to provide the corresponding fluorinated oligomeric silica/CNF composites [RF-(VM-SiO3/2)n-RF/CNF]. The obtained composites were applied to the surface modification of glass to give a good oleophobic/superhydrophobic characteristic on the composite surface due to the fabrication of the roughness architecture. The RF-(VM-SiO3/2)n-RF/CNF composites were also applied to the surface modification of poly(ethylene terephthalate) [PET] fabric swatch, affording a superoleophilic/superhydrophobic characteristic on the modified fabric surface. Modified PET fabric swatch thus obtained was applicable to not only the separation membrane to separate the mixture of oil/water but also the perfect adsorption of oil droplets spread on water interface. In addition, we have prepared the RF-(VM-SiO3/2)n-RF/CNF composites films by casting homogeneous aqueous methanol solutions containing the corresponding composites. Pristine CNF film afforded the superoleophilic property on the surface; however, it was demonstrated that the obtained transparent colorless CNF composite films can supply highly oleophobic characteristic on the surface.

Efficiency enhancement in blue phosphorescent organic light emitting diode with silver nanoparticles prepared by plasma-assisted hot-filament evaporation as an external light-extraction layer

The uniform growth of silver (Ag) nanoparticles in large areas is important for improving the flat panel devices, mainly organic light emitting diodes (OLED). In this work, two dimensional (2D) arrays of Ag nanoparticles were grown on glass surface substrates via plasma-assisted hot-filament evaporation technique at different plasma environments: no plasma, plasma cleaning (PC), plasma deposition (PD) and PC&PD, which were utilized as an external light-extraction layer for blue phosphorescent OLED device. The surface morphology of the Ag nanoparticles revealed the formation of spherical-like shapes of uniform size which ranged from 7 to 14 nm at different plasma conditions. X-ray diffraction showed that the nanoparticles were mainly single crystals and their crystallinity was significantly enhanced by employing plasma process in PC&PD. The localized surface plasmon resonance peaks of Ag nanoparticles were located at around 380–430 nm which suggests a dependency on diameter and interparticle spacing. The variation of refractive index of Ag nanoparticles 2D array in the visible wavelength from 1.9 to 2.4 plays a key role in high performance OLED. The light-extraction of the OLED device with Ag nanoparticles at PC&PD condition appeared to increase by 82.5% the luminance efficiency compared to that of a reference device without the Ag nanoparticle layer. The effects of the plasma environment on the morphological, structural and optical properties of Ag nanoparticles layer are discussed in the following sections by taking into consideration the effects of glass modification by these Ag nanoparticles on OLED performance.

Preparation of fluoroalkyl end-capped vinyltrimethoxysilane oligomer/micro-sized silica composites possessing superoleophilic/superhydrophobic characteristic: application to selective removal of aromatic compounds from aqueous methanol solution by using these composites

Fluoroalkyl end-capped vinyltrimethoxysilane oligomer [RF-(CH2–CHSi(OMe)3)n-RF; n = 2, 3; RF = fluoroalkyl group: RF-(VM)n-RF] was found to undergo the sol–gel reaction in the presence of micro-sized silica particles under alkaline conditions to afford the corresponding fluorinated oligomer/micro-sized silica composites [RF-(VM-SiO3/2)n-RF/μ-SiO2]. The obtained composites were applied to the surface modification of glass to reveal a superoleophilic/superhydrophobic characteristic on the modified surface. In contrast, fluoroalkyl end-capped vinyltrimethoxysilane oligomer/silica nanocomposites [RF-(VM-SiO3/2)n-RF/n-SiO2], which were prepared in the presence of nanometer-sized silica particles under similar sol–gel reactions, provided an oleophobic/superhydrophobic property on the surface. RF-(VM-SiO3/2)n-RF/μ-SiO2 composites were applied to the solid-phase extraction sorbent to isolate the transparent colorless oil from water-in-oil (W/O) emulsion. These composite powders were also applicable to the effective removal of traditional organic dyes, such as rhodamine B, acid red 289, and fluorescein from aqueous methanol solution. Of particular interest, it was demonstrated that RF-(VM-SiO3/2)n-RF/μ-SiO2 composites, of whose micro-sized silica gel is surface-functionalized with amino units, can exhibit a similar superoleophilic/superhydrophobic characteristic on the composite surface, giving the selective removal of fluorinated phenol-type aromatic compounds from aqueous methanol solutions, although the removal ability for the corresponding non-fluorinated ones was not observed at all under similar conditions.

Thermal and structural modification in transparent and magnetic germanoborate glasses induced by Gd2O3

A series of new transparent and magnetic germanoborate glasses in the system (100-x)[60GeO2–25B2O3–10Na2O–4Al2O3–1PbO] – (x) Gd2O3, with x = 0, 1, 2, 5, 10, 15 and 20 mol%, was prepared and studied with respect to their thermal and structural changes in the presence of Gd2O3. Based on Differential Scanning Calorimetre (DSC) analysis, a glass with 5% of Gd2O3 showed a high thermal stability, which progressively decreases for samples with higher content of Gd2O3. By the analysis of Raman and Fourier Transform Infrared (FTIR) spectra, it was possible to identify that by increasing the amount of Gd2O3, a progressive depolymerization of 6-membered Ge[IV] rings is promoted, concomitant with an increase of Ge[IV] tetrahedra units with non-briding oxygens. The structural analysis through the local-sensitive techniques EXAFS (Extended X-ray Absorption Fine Structure) and XANES (X-ray Absorption Near Edge Structure) showed that the short-range structural modification around the elements Ge and Gd3+ does not change with the addition of Gd2O3 and the presence of germanium four-fold coordination [GeIV] and Gd3+ states, respectively. A simulation of the coordination number (N), the interatomic distance (R) of Ge–O and Gd–O bonds and the Debye-Waller factor was also carried out. The microstructure, after crystallization, of the sample with 15 mol% of Gd2O3 was evaluated using optical and electron microscopes. Finally, the paramagnetic behaviour and ion probe quantification of Gd3+ ions were obtained based on magnetic susceptibility measurements.

Fabrication of Uniform Phase Structures in the Bulk of a N-BK7 Glass Using Ultrashort Laser Pulses

We study the possibility of application of direct laser writing technique for the fabrication of large-size uniform phase structures in the bulk of the borosilicate glass N-BK7. The morphology and the type of modifications induced by the sub-picosecond (500 fs) pulses are studied depending on the energy dose of irradiation. We show that with moderate focusing and at pulse energies below the threshold of self-focusing effects, it is possible to choose writing regimes (the scanning speed, the repetition rate of pulses) which allow the fabrication of extended structures with flat modification of the glass refractive index in the layer-by-layer scanning mode. At higher peak intensities of the laser, the Kerr nonlinearities affect the pulse propagation and the dynamics of the relaxation processes, and the resulting structures are essentially inhomogeneous with the alternating sign of refractive index change. To validate the approach, a buried phase structure with large dimensions was fabricated showing a rather uniform refractive index change over the entire processed range.

Void and micro-crack generation in transparent materials with high-energy first-order vector Bessel beam

In this work, we present efficient generation of a high-quality vector Bessel beam using an S-wave plate (radial/azimuth polarization converter) together with an ordinary glass axicon. We examine laser-induced modifications in glass with different pulse durations. We achieve material cracking and observe dominant crack propagation directions caused by the generated beam’s intensity asymmetry. By translating the beam, we demonstrate potential application of vector Bessel beams and their transverse polarization components for microprocessing of transparent materials using ultra-short pulses.

Luminescent Studies on Germanate Glasses Doped with Europium Ions for Photonic Applications.

Glass and ceramic materials doped with rare earth (RE) ions have gained wide interest in photonics as active materials for lasers, optical amplifiers, and luminescent sensors. The emission properties of RE-doped glasses depend on their chemical composition, but they can also be tailored by modifying the surrounding active ions. Typically, this is achieved through heat treatment (including continuous-wave and pulsed lasers) after establishing the ordering mechanisms in the particular glass–RE system. Within the known systems, silicate glasses predominate, while much less work relates to materials with lower energy phonons, which allow more efficient radiation sources to be constructed for photonic applications. In the present work, the luminescent and structural properties of germanate glasses modified with phosphate oxide doped with Eu3+ ions were investigated. Europium dopant was used as a “spectroscopic probe” in order to analyze the luminescence spectra, which characterizes the changes in the local site symmetries of Eu3+ ions. Based on the spectroscopic results, a strong influence of P2O5 content was observed on the excitation and luminescence spectra. The luminescence study of the most intense 5D0→7F2 (electric dipole) transition revealed that the increase in the P2O5 content leads to the linewidth reduction (from 15 nm to 10 nm) and the blue shift (~2 nm) of the emission peak. According to the crystal field theory, the introduction of P2O5 into the glass structure changes the splitting number of sublevels of the 5D0→7F1 (magnetic dipole) transition, confirming the higher polymerization of fabricated glass. The slightly different local environment of Eu3+ centers the results in a number of sites and causes inhomogeneous broadening of spectral lines. It was found that the local asymmetry ratio estimated by the relation of (5D0→7F2)/(5D0→7F1) transitions also confirms greater changes in local symmetry around Eu3+ ions. Our results indicate that modification of germanate glass by P2O5 allows control of their structural properties in order to functionalize the emissions for application as luminescent light sources and sensors.

Boson band mapping: revealing ultrafast laser induced structural modifications in chalcogenide glass.

The formation of femtosecond laser direct-written waveguides in gallium lanthanum sulfide (GLS) chalcogenide glass with a peak index contrast of Δnmax=0.023 and an average positive refractive index change of Δnwaveguide=0.0049 is explained for the first time, to the best of our knowledge. Evidence of structural change and ion migration is presented using Raman spectroscopy and electron probe microanalysis (EPMA), respectively. Raman microscopy reveals a frequency shift and a change in full-width at half maximum variation of the symmetric vibration of the GaS4 tetrahedra. The boson band is successfully used to identify and understand the material densification profile in a high refractive index glass waveguide. EPMA provides evidence of ion migration due to sulfur, where the observation of an anion (S2-) migration causing material modification is reported for the first time. These results will enable optimization of future mid-infrared and nonlinear integrated optical devices in GLS glass based on femtosecond laser written waveguides.

Ultrafast internal modification of glass by selective absorption of a continuous-wave laser into excited electrons.

The internal modification of glass using ultrashort pulse lasers has been attracting attention in a wide range of applications. However, the remarkably low processing speed has impeded its use in the industry. In this study, we achieved ultrafast internal modification of glass by coaxially focusing a single-pulse femtosecond laser and continuous-wave (CW) laser with the wavelength that is transparent to the glass. Compared with the conventional method, the processing speed increased by a factor of 500. The observation of high-speed phenomena revealed that the CW laser was absorbed by the seed electrons that were generated by the femtosecond laser pulse. This technique may help expand the applications of femtosecond lasers in the industry.

Enhanced electrical properties and energy storage performances of NBT-ST Pb-free ceramics through glass modification

Abstract In the current study, a strategy incorporating with glass addition has been employed to enhance the energy storage performance of 0.5(Na0.5Bi0.5TiO3)-0.5SrTiO3 Pb-free bulk ceramics through a traditional electroceramic processing route. The strategy is to introduce liquid sintering to dielectric ceramics, and hence lower the sintering temperature, finally resulting in refined grains and enhanced electrical properties. The detailed impacts of different additive contents on the phases, microstructure, electrical properties and energy storage and release of NBT-ST specimens were deeply and systemically studied. The results indicate as the glass content increases, the grains of NBT-ST-xBBZ ceramics are remarkably refined, and the dielectric constant and loss decrease. After glass addition, the breakdown strength of ceramics is nearly doubled. When the doping content of the glass is 1 wt%, the energy density reaches 1.67 J/cm3 under an electric field strength of 200 kV/cm. After further testing of NBT-ST-0.01BBZ ceramic, it exhibits good temperature (from 30 to 150 °C), frequency (0.2–100 Hz) and cycle (104) stability.

Facilitated glass separation by asymmetric Bessel-like beams.

The modification of transparent materials is enabled by focused ultrashort laser pulses. Single pass processing up to several millimeters can be achieved by the usage of elongated beam profiles. We studied the mechanical separability in dependence of the material thickness. As simulations show, asymmetric beam profiles can cause modifications with preferential direction reducing the necessary breaking force. Pump-probe microscopy is implemented to examine the laser-matter-interaction. We present a measured 3D-reconstruction of the transient interaction inside the material and elucidate the desired crack formation. We demonstrate beam shaping concepts to create a new, efficient and robust class of Bessel-like beams, which can be used to achieve a preferred crack direction. We verify the concept by modification and separation of silicate glasses.

Laser-fabricated axicons challenging the conventional optics in glass processing applications.

Laser-based fabrication can be an alternative technology to mechanical grinding and polishing processes. However, the performance of these elements in real applications still needs to be validated. In this paper, we demonstrate that the subtractive fabrication technology is able to produce high-quality axicons from fused silica, which can be efficiently used for glass processing. We comprehensively investigate axicons, fabricated by ultrashort pulsed laser ablation with subsequent CO2 laser polishing, and compare their performance with commercially available axicons. We show that laser-fabricated axicons are comparable in quality with a precision commercial axicon. Furthermore, we demonstrate the intra-volume glass modification and dicing, utilising mJ-level laser pulses. We show that the tilting operation of the laser-fabricated axicons results in the formation of directional transverse cracks, which significantly enhance the 1 mm-thick glass dicing process.

Ultralow-loss geometric phase and polarization shaping by ultrafast laser writing in silica glass

Polarization and geometric phase shaping via a space-variant anisotropy has attracted considerable interest for fabrication of flat optical elements and generation of vector beams with applications in various areas of science and technology. Among the methods for anisotropy patterning, imprinting of self-assembled nanograting structures in silica glass by femtosecond laser writing is promising for the fabrication of space-variant birefringent optics with high thermal and chemical durability and high optical damage threshold. However, a drawback is the optical loss due to the light scattering by nanograting structures, which has limited the application. Here, we report a new type of ultrafast laser-induced modification in silica glass, which consists of randomly distributed nanopores elongated in the direction perpendicular to the polarization, providing controllable birefringent structures with transmittance as high as 99% in the visible and near-infrared ranges and >90% in the UV range down to 330 nm. The observed anisotropic nanoporous silica structures are fundamentally different from the femtosecond laser-induced nanogratings and conventional nanoporous silica. A mechanism of nanocavitation via interstitial oxygen generation mediated by multiphoton and avanlanche defect ionization is proposed. We demonstrate ultralow-loss geometrical phase optical elements, including geometrical phase prism and lens, and a vector beam convertor in silica glass.

Controlling the visibility of embedded silicon solar cells in building-integrated photovoltaic windows using surface structure modification and metal-oxide back coating

In this paper, we demonstrate a simple and effective method to control the visibility of embedded silicon solar cells in building-integrated photovoltaic (BIPV) windows by surface structure modification and metal-oxide back coating. The surface structure modification by etching the front glass in BIPV modules and the use of a thin niobium pentoxide (Nb2O5) film as a back coating enable the silicon solar cells to be hidden from view without a serious loss in the power efficiency. By employing the etched front glass and Nb2O5 back coating, silicon solar cells embedded in the BIPV module exhibited power conversion efficiency of 15.23% and fill factor of 65.05%. We also investigate the origin of the improved photovoltaic performance of the solar cells in the BIPV modules. The surface modification of the front cover glass of the BIPV windows enhances the light absorption in the solar cells, which results in the improved photovoltaic performance degraded by a metal-oxide back coating. We believe that the proposed surface modification which induces light trapping and anti-reflection into the cover glass of the BIPV modules with a metal-oxide back coating film is a promising and practical solution for the successful integration of BIPV windows with high efficiency and invisibility.