Hybrid Sol Gel Films Research Articles

Direct laser writing of electro-optic waveguide in chromophore-doped hybrid sol–gel

To overcome the influence of chromophore absorption and degradation in the ultraviolet spectral range for direct photopatterning of electro-optic devices, a blue laser writing technique operating at 405nm has been used to fabricate electro-optic waveguides from side-chain disperse red-1 doped photosensitive hybrid sol–gel films. The waveguide has good optical confinement and shows an electro-optic coefficient of about 9.0±0.4pm∕V and high temporal stability. The results indicate that the hybrid sol–gel a promising matrix for chromophores, and this technique can find applications in direct patterning of electro-optic devices from nonlinear chromophores-doped photosensitive materials including sol–gels and polymers.

Active organic–inorganic sol gel with high thermal stability for nonlinear optical applications

Second-harmonic generation and thermal stability of hybrid photosensitive sol-gel films doped with a side-chain electro-optic chromophore have been studied. Nonlinear optic coefficient d33 has been derived for the cross-linked and noncross-linked sol-gel films. The d33 of the cross-linked hybrid sol-gel film shows high stability at elevated temperature. No evident degradation in d33 was observed at 110 °C and only 20% of d33 decayed in 15 min at 180 °C. The results indicate that the film can meet the long-term stability requirement for optical components.

Tissue-derived cell growth on hybrid sol–gel films

Hybrid sol–gel films were developed for tissue-derived cell growth. Specifically, Buffalo green monkey kidney cells were grown on hydrophobically modified silica sol–gel thin films and on such films in which poly-L-lysine (PLL) was entrapped in order to affect surface positive charge density. Intermediate hydrophobicity was found optimal for the cell growth. The PLL-modified films enabled drastic reduction of the needed amount of serum. The developed films function better than the commonly used cell-culture polystyrene dishes.

Evaluation of mechanical properties of sol-gel inorganic-organic hybrid films with indentation contact

Evaluation of mechanical properties of sol-gel inorganic-organic hybrid films with indentation contact

Simple fabrication of diffraction gratings by two-beam interference method in highly photosensitive hybrid sol-gel films

Sol-gel hybrid materials containing a large quantity of photoactive molecules exhibited large changes in both refractive index and volume by UV exposure. The materials were used for the fabrication of diffraction gratings using the two-beam interference method. With this technique, we could simply fabricate the diffraction gratings and easily control the grating periods. The diffraction effects and efficiencies of gratings rely heavily on the UV doses and the fabricated diffraction gratings showed a good diffraction performance.

Thick UV-patternable hybrid sol-gel films prepared by spin coating

We report on the fabrication and characterization of thick UV-patternable hybrid sol-gel films by spin coating using a modified sol-gel process. Thick coatings of 25 microns with crack-free surfaces can be produced by one spin coating step. Characterization using different techniques including atomic force microscopy, scanning electron microscopy and profilometry show both a smooth surface of optical quality and precise patterning with sharp vertical walls. Refractive index measurements by prism coupling and using a spectroscopic ellipsometer indicate high reproducibility of coating optical properties prepared by this procedure. Large refractive differences can be obtained by varying the process conditions, allowing the preparation of channel waveguide structures.

A comparative FTIR study of thermal and photo-polymerization processes in hybrid sol–gel films

Controlling the organic polymerization in organic–inorganic hybrids is a key point in the development of new materials with high homogeneity of the nanostructure. The main difficulty is related with the achievement of a simultaneous control of the organic and inorganic network formation. Thermal and photocuring represent the main routes to form the organic chains when polymerizable organic groups are present in the hybrid materials. In the present work hybrid organic–inorganic films were synthesized from 3-methacryloxypropyltrimethoxysilane (MPTMS) cohydrolyzed with tetraethylorthosilicate (TEOS) and N-[(3-trimethoxysilyl)propyl]ethylenediamine (TMESPE) or 3-(triethoxysilyl)-propylamine (TESPA). This an example of basic catalyzed hybrid material with a polymerizable methacrylate functionality whose micro-structure is modified by the amine groups. FTIR spectroscopy was used to compare the effects of thermal or photo-induced polymerization on the materials. TESPA and TMESPE showed a different catalytic effect on the condensation of the inorganic network, with TMESPE the more efficient one. The presence of a more extended silica backbone reduced the curing efficiency in TMESPE derived samples. UV curing was also very effective in catalyzing the inorganic condensation of un-reacted species still present in the film after the deposition. A photo-induced polymerization of the inorganic side was observed in the hybrid films. Thermal polymerization in TMESPE films induces the reaction between the secondary amine and CO bonds in MPTMS, this reaction is, instead, not observed in films cured by UV radiation.

Polarization holographic gratings in hybrid solgel films doped with Disperse Red 1.

Polarization holographic gratings in sp configuration are written at 488 nm in photorefractive organic-inorganic films based on SiO2. The films, prepared by a solgel technique, contain Disperse Red 1, carbazole units, and 2,4,7-trinitro-9-fluorenone. The gratings are characterized by their diffraction efficiency for a 632.8-nm probe. The polarization gratings act as a half-wave plate, and the diffraction efficiency is independent of the polarization direction of the probe.

Photorefractive gratings in DR1-doped hybrid sol–gel films

Abstract Photorefractive gratings have been obtained with 632.8 nm writing beams in organic–inorganic SiO2-based films. The hybrid glass is prepared by a sol–gel technique, starting from organic Si precursors, and contains Disperse Red 1 (DR1), carbazole units and 2,4,7-trinitro-9-fluorenone (TNF). The photorefractive gain, which has been found unexpectedly even without poling field, has been determined through an asymmetric energy exchange by two-beam coupling measurements. The effects of the polarization of the writing beams and of a circularly polarized photoisomerizing radiation during the erasure of the grating have been interpreted in terms of an orientational contribution to the grating formation.

Indirect excitation of Er3+ in sol-gel hybrid films doped with an erbium complex

Transparent sol-gel hybrid films doped with erbium tris 8-hydroxyquinoline were prepared using methyltriethoxysilane, vinyltriethoxysilane, and phenyltrimethoxysilane as precursors. We obtain a strong 1.53-μm Er3+ luminescence with a wide full width at half-maximum and no thermal quenching. Comparison of absorption of the film with the pump wavelength dependence of Er3+ luminescence intensity indicates the presence of an efficient indirect excitation path for Er3+ via organic ligands.

Thickness, Morphology and Structure of Sol-Gel Hybrid Films: I—The Role of the Precursor Solution's Ageing

The physical properties of inorganic-organic sol-gel hybrid films are determined by a large number of processing parameters, as the initial recipe, the catalysis conditions and the film deposition technique. This work focuses on the influence of the precursor solution's ageing on the quality and structure of hybrid silica-polytetrahydrofuran films, prepared by spin coating. The inorganic precursor, tetraethylorthosilicate, was hydrolysed under acid catalysis and using ethanol as co-solvent. The hydrolysis molar ratio (R) was fixed at 4. Different polymer concentrations of two average molecular weights (Mn = 650 and 2900) were added to the initial colloidal solutions. Ageing took place in open containers. The thickness and surface texture parameters of the films were determined by profilometry, and their structures studied by FTIR. It is shown that the films' thickness increases with the ageing of the precursor solution, more steeply for the hybrid films with higher polymer content and higher Mn. The best films obtained, which present the highest thickness and the lowest relative roughness, are those prepared from the most aged solutions. The FTIR results show that the films' porosity increases with the ageing of the precursor solution, and that the distribution of oligomeric species in solution is maintained upon film deposition. Therefore, the structure of the film is essentially determined by the extension of the condensation reactions until the spinning moment.

Thickness, Morphology and Structure of Sol-Gel Hybrid Films: II—The Role of the Solvent

The influence of the solvent on the thickness, morphology and structure of silica-polytetrahydrofuran hybrid films, prepared by spin coating, has been analysed. The inorganic precursor, tetraethylorthosilicate, was hydrolysed under acid catalysis, the hydrolysis molar ratio being 4. Polymers of average molecular weight (M n ) 650 and 2900 were incorporated in the initial colloidal solutions, in a low concentration (organic/inorganic molar ratio 0.01). Two solvents were compared: ethanol, protic, and tetrahydrofuran, aprotic and a little less polar. The thickness and surface texture parameters of the films were determined by profilometry, their morphology characterized by SEM and their structure studied by FTIR. It is shown that the solvent has no effect on the molecular structure of the films, but strongly influences the surface texture and the morphology of both pure silica and hybrid films. The solutions prepared in tetrahydrofuran present shorter gelation times (t G ) and allow the deposition of good quality films almost up to the gelation point (to a reduced time, t/t G , of ∼0.9). The films are thinner than those prepared from corresponding ethanolic solutions at the same reduced ageing times. For pure silica films, tetrahydrofuran is the best choice, since it reduces the fractured region on the edge of the substrate. For hybrid films, this effect is achieved by the polymer and tetrahydrofuran is responsible for a higher arithmetical mean roughness. Therefore, ethanol becomes the preferable solvent.

Effects of composition and catalyst on the optical properties of ZrO 2-based Ormosil films

FTIR spectroscopy measurements were performed to investigate zirconia-based Ormosil thin films. Samples synthesized with a sol–gel technique were prepared starting from 3-glycidoxypropil-trimethoxysilane (GLYMO) and zirconium(IV)-propoxide (Zr–OPr). Acetic or nitric acid were used as a catalyst. The effects induced by the Zr content and the catalyst type on the mid-infrared spectra of the sol–gel hybrid films were studied and a detailed assignment of the vibrational absorption bands is presented. The thermal evolution of the hybrid systems was also followed by monitoring the release of the organic groups, the thickness, and refractive index changes by means of FTIR, diffuse reflectance spectroscopy, and ellipsometry.

Experiments for inorganic–organic hybrid sol–gel films for micro- and nano-photonics

Inorganic–organic hybrid materials can offer multifunctionality and allow properties tailoring from subnanometer (atomic) to submillimeter (mesoscopic) length scales. That is why these films could play a significant role in the field of micro- and nano-photonic devices (waveguids, emitting devices, quantum dot devices, photonic band gaps and holographic materials).The organic groups can modify the inorganic backbone by reducing the connectivity of the gel network allowing thick film deposition and lessening the processing temperature. In order to follow the sol–gel chemistry in the case of the substituted alkoxides that influence the molecular species presented in solution at the moment of deposition, model systems based on tetraethoxysilane (TEOS), methyltriethoxysilane (MTEOS) and vinyltriethoxysilane (VTEOS) were investigated. The hybrid organic–inorganic sol–gel-based photonic components were realized with phenyltriethoxysilane (PTEOS).The composition and the process were optimized to allow a better control of the optical parameters (losses, refractive index, transmission), to reduce the processing temperature and to improve photosensitivity.

Photopatternable sol-gel for compound semiconductor processing

A simple technique using hybrid organic–inorganic sol-gel films for compound semiconductor processing is proposed and demonstrated. The dual organic and inorganic nature of the hybrid sol-gel films allows high quality photopatternability and robust masking for the dry-etching process. The sol-gel channels on GaAs and InP are fabricated and high-aspect-ratio dry etching of semiconductors is shown. In addition, the potential of the hybrid sol-gel as a planarizing layer on deep-etched InP with overcut and undercut profiles is demonstrated.

One-step transfer of diffractive structure from a designed pattern to a replica by use of a hybrid solgel film

A one-step method for microfabrication of a diffractive lens mold with continuous relief, including a solgel process for replication, is presented. The mold is fabricated by focused ion beam milling (FIBM) on a substrate of bulk silicon and is then used directly for replication of the diffractive structure by means of a hybrid solgel glass stamping process. The surface roughness of the replica, Ra, is 4 nm over a 5 m x 5 m area. The measured diffraction efficiency is 86% and is influenced by accumulated mold geometry and solgel process errors. The demonstrated process of direct stamping by use of the master fabricated by FIBM offers the potential for mass production at very low cost.

Design of photoinduced relief optical devices with hybrid sol–gel materials

Photosensitive organic–inorganic compounds appear as an alternative option for the design of new optical devices since they combine the characteristics of both glasses and photopolymers and improve the properties of the final material. These hybrid materials consisted of methacryloxypropyltrimethoxysilane, titanium isopropoxide, methacrylic acid and a photoinitiator. The hybrid sol–gel film was obtained via hydrolysis–condensation reactions and coating on a substrate. Spatially controlled UV irradiation induced the polymerization of the organic parts 1, thus, leading to structural changes and relief generation. Due to the characteristics of the sensitive material, no further etching is required to reveal the surface corrugation. These new innovative advanced materials, open up new vistas in the field of optical devices. Hybrid glasses, in which the organic and inorganic phases are blended at the sub-micrometric scale, are transparent and with low optical loss. In addition, they are harder than organic polymers but less brittle than silica. Hybrid sol–gel glasses generated by this self-developing process are shown to be suitable for generation of optical components such as diffraction gratings.

Silicon-containing polymers for non-linear optics

A variety of novel poly[ethynediyl-arylidene-ethynediyl-silylene]s (PEAES), including those containing hypercoordinate silicon atom as well as donor and acceptor groups, has been synthesized. The presence of hypercoordinate silicon favours high values of fast Kerr-type non-linearities, and the incorporation of amide groups gives rise to good optical quality nanocomposites in a silica matrix. The inorganic-organic hybrid sol-gel film incorporating 5–14 mass% of the polymer containing pentacoordinate silicon showed Reχ (3) = −9.5 ×10−11 esu. The predominant role of the electron nonlinear mechanism has been demonstrated by using test beams with linear and circular polarizations. The photorefractive properties of composites based on PEAES as optical chromophores, poly(9-vinylcarbazole) as photoconductor, N-ethylcarbazole and phenyltrimethoxysilane as plasticizer, and fullerenes as charge generators have been investigated. The nonlinear optical effects, including four-wave mixing and two-beam coupling were studied at 633 nm without preliminary electric poling. The photorefractive origin of the refractive index changes was confirmed by the high two-beam gain under an externally applied electric field. Refractive index gratings affording two-beam gain can also be written under zero field conditions. To explain this unique property of the materials it is suggested that chromophore orientation asymmetry arises either during film formation or is induced by the longitudinal intensity gradient.

Structural changes induced by the catalyst in hybrid sol–gel films: a micro-Raman investigation

The effect of acid catalysts on the structure and properties of zirconia-based hybrid organic–inorganic thin films obtained by sol–gel, starting from γ-glycidoxypropyl-trimethoxysilane (GLYMO) and zirconium n-propoxide Zr(C 3H 7) 4, is studied by means of micro-Raman spectroscopy. The kind of network formed during the polymerisation process depends on the catalyst: this modifies the reactivity of the organic moiety of the GLYMO and a glass former behaviour is obtained only when the epoxy ring of the GLYMO is cleaved. Unopened epoxy rings, on the other hand, may protect the guest luminescent molecules, like the azo-dyes, to acid attacks. Nitric and acetic acids are reported as examples.

The defect structure of sol–gel-derived silica/polytetrahydrofuran hybrid films by FTIR

The structural perturbations induced by polytetrahydrofuran (PTHF) on sol–gel hybrid films were identified by Fourier-transform infrared (FTIR) spectroscopy. The films were prepared by spin-coating, from aged solutions containing tetraethylorthosilicate (TEOS) as the inorganic precursor and different concentrations of PTHF. All the spectra reveal a set of bands that may be associated with structural defects of the silica network. The hybrid films show an additional `defect' band at 560 cm −1 , assigned to a skeletal vibration of 4-fold siloxane rings, whose intensity grows as the polymer content or molecular weight increases. The relative intensity of two components of the ν asSi–O–Si mode (resolved by deconvolution of the band at ∼ 1080 cm −1 ) grow accordingly. They were thus assigned to the longitudinal (LO) and transverse optical (TO) modes of that vibration in 4-fold siloxane rings. Simultaneously, the bands assigned to the νSi–O − mode and to the νSi–O(H) mode of unreacted silanol groups (obtained by deconvolution of the band at ∼ 950 cm −1 ) increase. These conjugated observations lead to the conclusion that the polymer hinders the condensation reactions, being responsible for a more porous structure, with retention of a larger proportion of 4-fold siloxane rings. For high concentrations of high molecular weight PTHF, the defect structure of the films indicates that a partial segregation of the polymer occurs.