Silica Glass Films Research Articles

Ultrafast laser nanostructuring in transparent materials for beam shaping and data storage [Invited

We review recent progress in femtosecond laser anisotropic nanostructuring of transparent materials, including silica glass and thin films. With different writing parameters, oblate nanopores, single lamella-like structures and nanoripples are demonstrated, which can be used in geometric phase optical elements, space variant polarization converters and multiplexed optical data storage.

Residual stress of glass and crystalline oxide thin films responding to humidity

Here, we demonstrate that oxide thin film devices could be affected by humidity in their in-plane stress and in substrate curvature. We prepared silica glass and ceria crystalline thin films on Si(100) wafers by the sol-gel method. Both films had “tensile” in-plane residual stress. We cycled the relative humidity between ca. 20% and 80% in the square wave and monitored the substrate curvature in situ, from which in-plane stress was calculated. The increase and decrease in humidity resulted in a decrease and an increase in tensile stress, respectively. In situ ellipsometric measurements during humidity cycles showed that both thickness and refractive index increase and decrease on the increase and decrease in humidity, respectively. This guarantees that the volume expansion and shrinkage caused by water molecule adsorption/absorption and desorption, respectively, are the origins of the response of the stress to humidity. Responding to the change in humidity, thicker silica glass films with low porosities of 1%–3% showed more sluggish change in stress, suggesting absorption/desorption of water via diffusion in siloxane network in such dense films. Silica glass films with a larger porosity showed more quick response to humidity, indicating adsorption/desorption on the pore wall as the primary cause of the response. “Compressive” stress in a silica glass film with ca. 1% porosity exhibited very slight response in stress to humidity, which was attributed to the hard diffusion of water in compressed siloxane network.

Tracking the optical constants of porous vanadium dioxide thin films during metal–insulator transition: Influence of processing conditions on their application in smart glasses

Vanadium dioxide (VO2) is widely recognized as a thermochromic material with great potential for application in smart glazing for energy-efficient buildings. The monoclinic (M1) VO2 phase undergoes a first-order reversible phase transition from the semiconductor to the rutile metallic state. In this study, an M1 VO2 porous film was synthesized via a polymer-assisted sol-gel route. Processing parameters, such as drying and reduction temperatures, were varied to evaluate their influence on the thermochromic behavior of VO2 and to determine the necessary trade-off between a significant thermochromic effect and high luminous transmittance. Film–silica glass–film systems with luminous transmittance close to 80% and IR solar modulation ability as large as 20% were prepared. By tracking the optical constants of the films during the thermochromic process, the changes produced at the microscopic level in the material could be correlated with its macroscopic behavior when used as an energy-saving material.

Picosecond laser writing of [formula omitted] nanocomposite nanogratings for optical filtering

In this article, we propose a novel approach for dielectric nanograting fabrication by direct laser patterning. Possibilities of a well-controlled ultra-short laser recording of Ag-SiO2 nanocomposite gratings and their optical properties are examined. The mechanisms of laser processing involve silver nanoparticle growth in nanoporous silica glass films and laser interference-based formation of a periodic grating-like nanorelief. It is shown that laser energy should stay below the surface ”grooves” formation threshold for laser-inscription of the interference-based grating. Otherwise, another periodic structure oriented parallel to the incident laser polarization appears to erase the interference pattern. The parameter windows required for the controlled fabrication of the obtained structures are determined. The required threshold decay with the number of applied laser pulses is explained by a similarity in the roles of the nanoparticle absorption and surface defect accumulation typically leading to such dependencies. The optical properties of the obtained gratings are shown to depend on the angle between the incidence plane and the grating direction. When these directions coincide, a signal enhancement with a period-dependent blue-shift is revealed in the diffuse scattering spectra. When these directions are perpendicular, the signal is less enhanced, and a red shift is observed. The observed results are promising in short laser fabrication of different optical components, such as reflective optical filters.

Laser material processing with tightly focused cylindrical vector beams

We demonstrate a comprehensive modification study of silica glass, crystalline silicon, and amorphous silicon film, irradiated by tightly focused cylindrical vector beams with azimuthal and radial polarizations. The evidence of the longitudinal field associated with radial polarization is revealed by second harmonic generation in z-cut lithium niobate crystal. Despite the lower threshold of ring-shaped modification of silicon materials, the modification in the center of single pulse radially polarized beam is not observed. The phenomenon is interpreted in terms of the enhanced reflection of longitudinal component at the interface with high-index contrast, demonstrating that the longitudinal component is inefficient for the flat surface modification. Enhanced interaction of the longitudinal light field with silicon nanopillar structures produced by the first pulse of double-pulse irradiation is also demonstrated.

Optical Degradation of Colloidal Eu-Complex Embedded in Silica Glass Film Using Reprecipitation and Sol-Gel Methods.

A reprecipitation method has been investigated for fabricating colloidal nanoparticles using Eu-complex. Herein, we investigated optical degradation characteristics of (1,10-phenanthroline)tris [4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato]europium(III) colloidal nanoparticles, which were embedded into a silica glass film fabricated by a conventional sol-gel process. At first, we tried several types of good solvents for the reprecipitation method, and dimethyl sulfoxide (DMSO) is found to be a suitable solvent for realizing the small diameter and the high long-term stability against the ultraviolet irradiation even though the boing point of DMSO is higher than that of water used as a poor solvent. By optimizing the good solvent and the concentration of Eu-complex, the relative photoluminescence intensity of 0.96 was achieved even though the ultraviolet light was continuously irradiated for 90 min. In addition, the average diameter of 106 nm was achieved when DMSO was used as a good solvent, resulting in the high transmittance at a visible wavelength region. Therefore, we can achieve the transparent emissive thin film with a center wavelength of 612 nm, and the optical degradation was drastically reduced by forming nanoparticles.

Preparation of silica glass films on the surface of polypropylene microporous membrane separators by dip coating with polysilazane and their application in lithium-ion batteries

Preparation of silica glass films on the surface of polypropylene microporous membrane separators by dip coating with polysilazane and their application in lithium-ion batteries

Improved Photobleaching for (1,10-phenanthroline)tris[4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato]europium(III) Particle Embedded in Sol-Gel Derived Glass Film

In this research, we investigated improved photobleaching characteristics of (1,10-phenanthroline)tris[4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato]europium(III) by forming nano-particles embedded into a sol-gel derived silica glass film by a conventional sol-gel process. The relative photoluminescence intensities after the UV irradiation for 90 min were 88, 76, and 67% for nano-particles in the sol-gel derived glass film, powders in the sol-gel derived glass film, and raw powders, respectively. This result indicates that the phtobleaching of this Eu-complex can improved by forming nano-partcile structures by a reprecipitation method and embedding in the sol-gel derived silica glass.

Sensing Behaviour of Some Nanocomposite Systems

Silver nanoparticles of diameters 3.4 to 13.2 nm grown at the interfaces between silicate glass and some oxide crystallites exhibited about six orders of magnitude reduction in resistivity for a relative humidity change from 25% to 80%. Sn-SnO2 nano core-shell structure prepared within a gel-derived silica glass film by electrodeposition technique followed by heat treatment showed large change in resistivity as a function of humidity. The resistivity also changed due to gas flow of CO2, C2H5OH and NO2, respectively. The latter arose because of reduction/oxidation of Sn4+/Sn2+ species present at the shell layer of the nanostructures. Nickel nanosheets of thickness ~0.6 nm grown within the interlayer spaces of Na-4 mica crystallites showed a change of dielectric permittivity (5%) for an applied magnetic field of 1.2 Tesla. An inhomogeneous model was used to explain this behavior. Two dimensional CuO phase was grown within the channels of diameter ~5 nm of mesoporous SiO2 structure. A magnetodielectric (MD) parameter M.D. of 4.4% was obtained in this case. BaTiO3 nanoparticles of diameter ~25 nm having pores with diameter 10 nm showed multiferroic behavior which arose due to the presence of oxygen vacancies as a result of large surface area present. An M.D. parameter of 11% was found. Similarly mesoporous LiNbO3 of 10 nm diameter showed an M.D. parameter of ~4.5% at a magnetic field 1 Tesla. A giant magnetocapacitance effect with a value of 44% at 1.5 T was observed in nickel zinc ferrite (NZF) impregnated mesoporous silica. A magnetocapacitance of 51% at magnetic field 1.7 T was found in the case of nanocomposites comprising of iron ion containing silica based nanoglass and mesoporous silica. In the last two examples the behavior was explained on the basis of Catalan model of space-charge polarization with extracted values of magnetoresistance of the NZF and nanoglass phases being 58%.

Temperature-driven local rearrangement in the Er environment of Er-doped silica glass films prepared by rf-cosputtering deposition

In this paper, an experimental study is presented on Er:SiO2 films prepared by an rf-cosputtering deposition technique, and then annealed in the 100–1200°C range. Samples were characterized by spectrally resolved cathodoluminescence, UV–VIS photoluminescence and Rutherford Backscattering Spectrometry (RBS). Strong optical modifications with temperature were observed, connecting the peculiar features of the Er luminescence activity to those of the silica matrix, namely, the density of nonbridging oxygen hole centers, oxygen-deficient sites and OH groups. In general, a complex phenomenology was observed, involving major local rearrangements of the Er environment. RBS data allowed to evidence migration phenomena, resulting in a compositional change of the films, thus indicating the progressive modification of the system as well as the possible formation of Er nanoclusters for high temperatures.

Subterahertz hypersound attenuation in silica glass studied via picosecond acoustics

We report picosecond acoustic measurements in silica-glass films grown by wet thermal oxidation on a $(111)$ silicon substrate. The longitudinal acoustic phonons are observed over the range from 150 to 300 GHz using an infrared pump and a second harmonic blue probe. The transducer is an aluminum thin film deposited on top. Multiple interference effects are analyzed and fully taken into account. They lead to a signal presenting rapid oscillations as a function of the sample thicknesses. The latter are determined by separate interferometry. Our remarkably precise acoustic attenuation results are found to follow rather well a model combining thermally activated relaxations and anharmonicity. New values for the optical absorption of silicon in the 400-to-500-nm region of the spectrum are obtained as a by-product.

Plasmonic nano lithography with a high scan speed contact probe

We demonstrate plasmonic lithography with an optical contact probe to achieve high speed patterning without external gap distance control between the probe and the photoresist. The bottom surface of the probe is covered with a 10 nm thickness silica glass film for the gap distance control and coated with self-assembled monolayer (SAM) to reduce friction between the probe and the photoresist. We achieve a patterning resolution of ~50 nm and a patterning speed of ~10 mm/s. We obtain the quality of line patterning comparable to that in conventional optical lithography.

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.

Improved Durability of Eu Chelate Encapsulated by Silica Glass Film Prepared by Sol-Gel Method

We demonstrated an improved durability of Eu(HFA)3(TPPO)2 [tris(hexafluoroacetylacetonato)- europium(III) 1,2-phenylenebis(diphenylphosphine oxide)] encapsulated by a sol-gel derived silica glass film. The film was constructed using phenyltrimethoxysilane and diethoxy- dimethylsilane as a starting solution. Unlike cases in which conventional tetramethoxysilane is used, no decrease in internal quantum efficiency was observed at room temperature. We further improved the thermal and long-term stability of Eu(HFA)3(TPPO)2 inside the transparent glass film at elevated annealing temperatures when compared to the Eu(HFA)3(TPPO)2 powder itself: The photoluminescence quantum efficiency of the transparent film was 60% at 160℃ and 32% at 20℃. Properly prepared glass networks protect the Eu chelate from free oxygen and water in the transparent glass film, which is promising for future practical applications.

Optical properties of sol–gel fabricated Co/SiO 2 nanocomposites

Cobalt nanoparticles were grown in silica glass and silica film on silicon substrate by annealing of the sol–gel prepared porous silicate matrices doped with cobalt nitrate. Annealing of doped porous silicate matrices was performed at various conditions that allowed to obtain the nanocomposite glasses with various content of metallic Co. The absorption and photoluminescence spectra of Co/SiO 2 glasses were measured. In the absorption spectra at 285 nm (4.34 eV) we observed the band corresponding to the surface plasmon resonance in Co nanoparticles. The spectra proved the creation of Co 2+ ions in tetrahedral and octahedral coordinations in silica glass as well. The formation of nanoparticles of cobalt oxides at annealing in air was revealed by XRD and absorption measurements. The measured reflection spectra of Co/SiO 2 film also demonstrate the surface plasmon resonance in Co nanoparticles.

Model-based analysis of the silica glass film etch mechanism in CF4/O2 inductively coupled plasma

The analysis of the Er-doped silica glass films (62%SiO2–30%B2O3–8%P2O5 + 0.2 wt%. Er2O3) etch mechanism in the CF4/O2 inductively coupled plasma was carried out using the combination of simplified models for plasma chemistry and etch kinetics. As the O2 mixing ratio in the CF4/O2 plasma increases from 0% to 30%, the etch rate decreases monotonically in the range of 385–190 nm/min that contradicts with the behavior of F atom density and flux. From the model-based analysis, it was found that, at low ion bombardment energies, the etch process followed the formal kinetics of ion-assisted chemical reaction and was controlled by both neutral and ion fluxes.

Optical properties of sol–gel fabricated Mn/SiO 2 nanocomposites: Observation of surface plasmon resonance in Mn nanoparticles

Manganese nanoparticles were grown in silica glass and silica film on silicon substrate by annealing of the sol–gel prepared porous silicate matrices doped with manganese nitrate. Annealing of doped porous silicate matrices was performed at various conditions that allowed to obtain the nanocomposite glasses with various content of metallic Mn. TEM of Mn/SiO 2 glass indicates the bimodal size distribution of Mn nanoparticles with mean sizes of 10.5 nm and 21 nm. The absorption and photoluminescence spectra of Mn/SiO 2 glasses were measured. In the absorption spectra at 300 nm (4.13 eV) we observed the band attributed to the surface plasmon resonance in Mn nanoparticles. The spectra proved the creation of Mn 2+ and Mn 3+ ions in silica glass as well. The absorption spectra of Mn/SiO 2 glasses annealed in air prove the creation of manganese oxide Mn 2O 3. The measured reflection spectra of Mn/SiO 2 film manifest at 240–310 nm the peculiarity attributed to surface plasmons in Mn nanoparticles.

Preparation and characterization of nanocrystalline ZnS/ZnO doped silica inverse opals

ZnS/ZnO doped silica glass inverse opals were prepared by a sol–gel chemistry method via polystyrene colloidal crystals templating. After the infilling precursors were solidified in the void space among polystyrene spheres, the polymer templates were removed by calcinations and the doped silica glass films were generated with long-range order of the inverse replicas of the template arrays. The effective reflective index of the structure and reflective index of the doped silica glass is calculated by Bragg equation using wavelengths of optical stop band and periodicity diameters of the inverse opals. The result is well agreed with mixture rule approximation.

Ge nanoclusters in PECVD-deposited glass after heat treatment and electron-beam irradiation

This paper reports the formation of Ge nanoclusters in silica glass thin films deposited by plasma-enhanced chemical vapor deposition (PECVD). We studied the samples by transmission electron microscopy (TEM) and Raman spectroscopy after annealing. TEM investigation shows that the Ge nanoclusters at two areas were formed by different mechanisms. The Ge nanoclusters formed in a single row along the interface of a silicon substrate and the silica glass film by annealing during high-temperature heat treatment. Ge nanoclusters did not initially form in the bulk of the film but could be subsequently formed by the electron-beam irradiation. The interface between the silicon substrate and the silica glass film was investigated by Raman spectroscopy. The shift of the Raman peaks around 286.8 cm-1 and 495 cm-1 suggests that the interface is a Si1-xGex alloy film and that the composition x varies along the film growth direction.

Effect of boron concentration on the UV photosensitivity of silica glass film for planar lightwave circuit

The photosensitivity dynamics in SiO 2 glass with a composition similar to that of silica planar lightwave circuit (PLC) devices was investigated as a fundamental study prior to device fabrication. Silica bulk glasses with similar composition to the core layer of PLC devices were prepared with various concentrations of B 2O 3. The photosensitivity in boron and germanium co-doped amorphous SiO 2 yields a refractive index change Δ n as high as 10 −3 after irradiation with a KrF UV laser beam. The index modulation disappeared after thermal annealing. The result of annealing experiment and UV absorption/Raman spectra revealed that the molar volume change by UV irradiation is responsible for the index variation in the material.