High transparent polyimide/titania multi-layer anti-reflective hybrid films

In this study, polyimide-titania hybrid thin films (6FDA-6FpDA-4ABA/TiO₂, PIT) were prepared from soluble fluorine-containing polyimide and titanium butoxide. The soluble polyimide with carboxylic acid terminal groups (6FDA-6FpDA-4ABA-COOH) was synthesized from the precursor s 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 4,4′-(hexafluoroisopropylidene) dianiline (6FpDA), and 4-aminobenzoic acid (4ABA). Such end groups undergo a condensation reaction with titanium butoxide to provide organic-inorganic bonding and thus prevent macrophase separation. The titania content in the hybrid films was varied from 0 to 90 wt.% (PIT0-PIT90). The effects of TiO₂ content on the hybrid film properties and the optimum operating conditions were also investigated. TGA and DSC analysis showed that the decomposition temperature of polyimide was about 468 °C. T_d increased as the titania content in hybrid thin films increased. HRTEMM and XRD results indicated the formation of nanocrystalline-titania domains of around 4-11 nm in the hybrid films. AFM, SEM, TEM, and XRD results indicated the formation of well-dispersed nanocrystalline-titania. FTIR spectra indicated that the amidization was complete and that a cross-linked Ti-O-Ti network had formed. UV-vis and n&k analysis showed that the prepared hybrid films had high refractive index (1.931) and good optical properties. Moreover, the prepared polyimide/titania hybrid thin films were further applied to develop a three layer antireflective (AR) coating on glass and PMMA substrates. The results showed that the average reflectance of the AR coating on the glass and PMMA substrates was 0.5% and 0.8%, respectively. The transparency at 550 nm was greater than 90% for both AR coatings.     

Synthesis of soluble polyimide/silica–titania core–shell nanoparticle hybrid thin films for anti-reflective coatings

In this study, researchers prepared polyimide/silica–titania core–shell nanoparticle hybrid thin films (PI/SiO₂–TiO₂) from soluble fluorine-containing polyimide, colloidal silica, and titanium butoxide. The soluble polyimide with carboxylic acid end groups (6FDA–6FpDA–4ABA–COOH) could condense with titanium butoxide to provide organic–inorganic bonding, and thus prevent macrophase separation. TGA and DSC analysis showed that the decomposition temperature of hybrid materials increased with an increase in the content of silica–titania nanoparticles within the hybrid films. FTIR spectra indicated that the imidization was complete and the cross-linking Ti–O–Ti network formed. HRTEM and HRSEM images showed that the size of the core–shell nanoparticles were 18–20 nm. The thickness of titania shell on the silica is about 2.5 nm. The n&k and UV–Vis analysis showed that the prepared hybrid films had good optical properties and a high refractive index of 1.735. Researchers applied the prepared PI/SiO₂–TiO₂ hybrid thin films to develop a three layer antireflective (AR) coating on the glass and PMMA substrate. Results showed that the reflectance of the AR coating on the glass and PMMA substrate at 550 nm was 0.356 and 0.495%, respectively. The transparency was greater than 90% for both AR coatings on the glass and PMMA substrates.     

Synthesis,properties, and anti-reflective applications of new colorless polyimide-inorganic hybrid optical materials

We report the synthesis, properties and anti-reflective applications of new colorless polyimide-inorganic hybrid thin films prepared from 1,4-bis(3,4-dicarboxyphenoxy)-2,5-di-tert-butylbenzene dianhydride (DDBBDA)/oxydianiline (ODA) with silica or titania precursors. The experimental results suggest that the prepared hybrid films have good thermomechanical properties, excellent transparence, tunable refractive indices of 1.550–1.847, and low optical birefringence. The nanocrystalline titania domain size analyzed form TEM and XRD is in the range of 10–20 nm in the hybrid materials. Three-layer anti-reflective films on glass or polymer substrates processed from the hybrid precursors have a relatively low reflection of less than 0.5% in the visible range. These results indicate that the newly prepared colorless polyimide-inorganic hybrid materials have potential applications for optical devices.     

Synthesis and characterization of polyimide-based hybrid thin films from a novel colloidal core-shell nanocomposite particles

In this study, poly(4,4-(hexafluoroisopropylidenediphthalic anhydride)-co-oxydianiline) (6FDA-ODA) and a novel core-shell nanoparticle consisting of a core (SnO2/TiO2) and a shell (ZrO2/Sb2O3) with the composition (SnO2:TiO2:ZrO2:Sb2O3 = 18:5:3:4) were used to prepare polyimide/nanoparticles hybrid thin films. The resultant hybrid thin films were investigated by FTIR, TGA, DSC, TEM, SEM, AFM, alpha-step, UV-Vis, and n&k analyses. The results show that the prepared hybrid thin films had a good thermal stability. The size of nanoparticles was effectively controlled in the range of 8-10 nm in the hybrid thin films. These nanoparticles were evenly distributed across the hybrid thin films and no phase separation occurred. In terms of the optical properties, the prepared hybrid thin films had good transparency in the range of visible light. The cutoff wavelength had a blue shift as the content of the nanoparticles increased. The refractive index of prepared hybrid thin films increased with corresponding increases in nanoparticle content. Moreover, the prepared polyimide/core-shell nanoparticle hybrid thin films displayed excellent film formability and planarity.     

Synthesis and characteristics of polyimide/titania nano hybrid films

Polyimide/titania (PI/TiO₂) nano hybrid films are synthesized by sol-gel technology. [4,4′-(4,4′-Isopropylidenediphenoxy) bis (phthalic anhydride)] (IDPA), 4,4′-diaminodiphenyl ether (ODA) and 3-aminopropyltrimethoxysilane (APrTMOS) mixed entirely and reacted at room temperature to form the polyamic acid (PAA). Tetraethyl orthotitanate (Ti(OEt)₄) and actylacetone, the latter one is used as chelating agent, are then added to the polyamic acid. After imidization at high temperature, PI/TiO₂ hybrid films with different block chain length, 5000 of PAA and 15000 g mol^− 1, and a cross-linked structure are formed. The resulting hybrid films, containing relatively small amounts of titania, exhibit higher transparency and flexibility. Moreover, as compared with pure PI, the hybrid film formed from APrTMOS has better ability to form a film with a higher titania content. Due to the high and low refractive index (RI) of TiO₂ and APrTMOS, their introduction may lead to the change of the RI of hybrid films. From the transmission electron microscope (TEM) images; the particle size of titania decreases with increasing APrTMOS content. Thermal decomposition temperatures (T_d), with a 5% weight loss, are in the range of 400-540 °C. The dynamic mechanical thermal analysis showed a systematic increase of glass transition temperature, along with a broader and weaker tan δ peak with increasing titania content.     

Transparent high refractive index nanocomposite thin films

This work reports the preparation of acetic acid-modified TiO₂ nanoparticles by sol–gel synthesis method. The nanoparticles can be incorporated directly into the polymer matrix to form transparent high refractive index nanocomposite thin films. The result shows that increasing the titania content in the hybrid nanocomposite thin films can significantly increase the refractive index. Hybrid nanocomposite thin film with refractive index value of 2.38 had been prepared. All prepared films also exhibit excellent optical transparency in the visible region.     

Synthesis and optical properties of photosensitive polyimide/silica hybrid thin films

In this study, the photopatternable fluorinated polyimide/silica hybrid materials were synthesized by 4,4′-hexafluoroisopropylidenediphthalic anhydride (6FDA), oxydianiline (ODA), aminopropyltriethoxysilane (APrTEOS), and 12 nm colloidal silica with a coupling agent. The monodispersed colloidal silica was used to form a silica domain instead of alkoxysilanes in the conventional process. The coupling agents used were 3-methacryloxypropyl trimethoxysilane (MPTMS) or (4-vinylphenethyl)trimethoxysilane (VPTMS). The coupling agent and the silica domain were designed to reduce the volume shrinkage and enhance the thermal properties, respectively. The retention of 2-methyl acrylic acid 2-dimethylamino-ethyl ester (MDAE) in the prepared hybrid films was supported by X-ray photoelectron spectroscopy (XPS) and thickness variation during the curing process. The particle size of silica in the hybrid materials based on SEM analysis was in the range of 10–25 nm. The prepared hybrid materials also exhibited a reduced refractive index after increasing the silica content. The SEM diagram suggested the prepared photosensitive hybrid materials could obtain lithographical patterns with a good resolution. These results indicate that the newly prepared photosensitive polyimide/silica hybrid materials may have potential applications for optical devices.     

Preparation and optical properties of organic/inorganic nanocomposite materials by UV curing process

In this study, photo-polymerized poly(acrylic)/silica hybrid thin films were prepared from various acrylic monomers and monodispersed colloidal silica with the coupling agent, 3-(trimethoxysilyl)propyl methacrylate (MSMA). The silica content in the hybrid thin films varied from 0 to 50 wt.%. The experimental results show that the particle size of silica in hybrid films could be effectively controlled at 15–20 nm as the weight ratio of MSMA to colloidal silica is higher than 0.68 and 0.60 for the poly(methyl methacrylate)/silica (US) and poly(ethylene glycol dimethacrylate-trimethylolpropane trimethacrylate)/silica (UDT) hybrid materials, respectively. The polymerization conversion for US and UDT hybrid materials could reach to 100% and 94.5%, respectively. The comparison of surface roughness with the film thickness is less than 0.10%, indicating the excellent surface planarity of the prepared hybrid thin films. Besides, the prepared hybrid films from the crosslinked acrylic polymer moiety show much better film uniformity, thermal stability and mechanical properties than those obtained from poly(methyl methacrylate). The refractive index decreases with increasing the silica content in the hybrid films. Excellent optical transparency is obtained in the prepared hybrid films. These results show that the prepared hybrid thin films have potential applications as passive films for optical devices.     

钛溶胶复合有机硅涂层材料的制备与表征

以钛酸丁酯(TBT)和γ-(2,3-环氧丙氧)丙基三甲氧基硅烷(GLYMO)为原料,通过溶胶-凝胶法制备了一类钛溶胶复合有机硅涂层材料,并采用多种手段对复合涂层的微结构和光学性质进行了表征。结果表明,所得复合涂层材料的表面平整光滑,可见光透过率在91%以上。随着钛含量的增加,涂层的折射率在1.49～1.56(633nm)范围内呈上升趋势。     

Broad band optical characterization of sol-gel TiO2 thin film microstructure evolution with temperature

Titanium dioxide (TiO₂) thin films have been produced by spin coating a titanium isopropoxide sol on silicon wafer substrates. The structural evolution of the thin films in terms of decomposition, crystallization and densification has been monitored as a function of annealing temperature from 100 to 700 °C using optical characterization and other techniques. The effect of annealing temperature on the refractive index and extinction coefficient of these TiO₂ thin films was studied in the range of 0.62 to 4.96 eV photon energy (250-2000 nm wavelength) using spectroscopic ellipsometry. Thermal gravimetric analysis and atomic force microscopy support the ellipsometry data and provide information about structural transformations in the titania thin films with respect to different annealing temperatures. These data help construct a coherent picture of the decomposition of the sol-gel precursors and the creation of dense layers of TiO₂. It was observed that the refractive index increased from 2.02 to 2.45 at 2.48 eV (500 nm) in sol-gel spin coated titania films for annealing temperatures from 100 °C to 700 °C.     

Synthesis and morphology of new functional polyimide/titania nano hybrid materials

The synthesis and full characterization of 3,5-diamino-N-(1-oxo-3-phenyl-1-(phenylamino)propan-2-yl)benzamide (5), as a new diamine monomer containing l-phenylalanine fractions in the structure of pendant group is presented. The stated diamine is employed as a key monomer for the in situ sol–gel fabrication of polyimide/titania nano hybrid thin films containing different titania contents. It is shown that titania particles are created in the size range of 20–80 nm, well-dispersed and enjoy the favorable spherical shapes supposing the constructive organic–inorganic interactions. The superior thermal stabilities of resulted nanocomposite films are confirmed using thermal analysis techniques. Moreover, the UV–Vis spectroscopy has shown the growing up in blocking efficiency along with the increase in titania contents. Predictably, the produced titania nanoparticles have amorphous structures.     

PMMA–SiO2 hybrid films as gate dielectric for ZnO based thin-film transistors

In this paper we report a low temperature sol–gel deposition process of PMMA–SiO₂ hybrid films, with variable dielectric properties depending on the composition of the precursor solution, for applications to gate dielectric layers in field-effect thin film transistors (FE-TFT). The hybrid layers were processed by a modified sol–gel route using as precursors Tetraethyl orthosilicate (TEOS) and Methyl methacrylate (MMA), and 3-(Trimethoxysilyl)propyl methacrylate (TMSPM) as the coupling agent. Three types of hybrid films were processed with molar ratios of the precursors in the initial solution 1.0: 0.25, 0.50, 0.75: 1.0 for TEOS: TMSPM: MMA, respectively. The hybrid films were deposited by spin coating of the hybrid precursor solutions onto p-type Si (100) substrates and heat-treated at 90 °C for 24 h. The chemical bonding in the hybrid films was analyzed by Fourier Transform Infrared Spectroscopy to confirm their hybrid nature. The refractive index of the hybrid films as a function of the TMSPM coupling agent concentration, were determined from a simultaneous analysis of optical reflectance and spectroscopic ellipsometry experimental data. The PMMA–SiO₂ hybrid films were studied as dielectric films using metal-insulator-metal structures. Capacitance–Voltage (C–V) and current–voltage (I–V) electrical methods were used to extract the dielectric properties of the different hybrid layers. The three types of hybrid films were tested as gate dielectric layers in thin film transistors with structure ZnO/PMMA–SiO₂/p-Si with a common bottom gate and patterned Al source/drain contacts, with different channel lengths. We analyzed the output electrical responses of the ZnO-based TFTs to determine their performance parameters as a function of channel length and hybrid gate dielectric layer.     

Sol–gel derived photonic bandgap coatings for solar control

Sol–gel derived photonic bandgap films have been investigated as possible multilayer coatings for solar control glass applications. Multilayer Bragg mirrors, in particular, have been modelled by the Transfer Matrix method, designed to have either near-UV or near-IR reflectivity, but visible transparency, based on alternating aluminosilicate glass/titania quarter-wave stacks. Such composite multilayer structures have been deposited by sol–gel processing on selected glasses and other types of substrates and their optical characteristics have been measured by optical absorption and reflection spectroscopies, as well as spectroscopic ellipsometry to determine the single layer refractive index and thickness. The UV–visible-IR absorption and reflection characteristics of these multilayer coatings revealed solar control properties, due to the presence of peaks near ∼350–400 nm and ∼900–1000 nm, with reflectivities of the order of 70%, which appear promising for solar control application.     

Polyimide/sepiolite nanocomposite films: Preparation, morphology and properties

Polyimide/sepiolite nanocomposite films have been prepared via an in situ polymerization method. The process involves the dispersion of sepioite in N,N-dimethylacetamide, polycondensation of 2,2′-bis [4-(3,4-dicarboxyphenoxy) phenyl] propane dianhydride and 4,4′-oxydianiline in the presence of sepiolite suspension to form poly(amic acid), and the thermal imidization of poly(amic acid)/sepiolite nanocomposite. The morphology, thermal and mechanical performance, and water absorption of nanocomposite films were systematically studied with various sepiolite contents. The results indicated that sepiolite was dispersed homogeneously at a nanometer scale in polyimide matrix. Owing to such nanodispersion of sepiolite, the polyimide/sepiolite nanocomposite films exhibit dramatic improvements on the mechanical properties and the coefficient of thermal expansion while fine thermal stability and low water absorption capacity were also maintained. When the sepiolite content increased to 16% the polyimide/sepiolite nanocomposite film achieved as much as 41% and 94% increase on the tensile strength and modulus respectively, and 50% decreased in coefficient of thermal expansion.     

Impact of various irradiation photon energies and gamma doses on the optical properties of ZnSe nanostructure thin film

ZnSe thin films were prepared by thermal evaporation technique under high vacuum (10⁻⁶ Torr) at 300 K and different film thickness. The structure of thin films was measured using grazing incident in-plane X-ray diffraction (GIIXD) and shows single phase zinc blende structure. The particle sizes of the deposited films were estimated for low film thickness by TEM and high film thickness by GIIXD. The particle size of ZnSe films was decreased from ~8.53 to 3.93 nm as film thickness lowered from 200 to 20 nm which ensures the nanocrystalline structure. The optical transmission (T) and reflection (R) in the wavelength range 190–2,500 nm for irradiated and unirradiated ZnSe thin films under investigation were measured. The effect of irradiation of different energies in range (0.1–1.25 MeV) from X-ray, ¹³⁷Cs and ⁶⁰Co irradiation sources were studied for ZnSe thin films of 100 and 200 nm thicknesses. The dependence of the absorption spectra and refractive index were investigated for different energies irradiation sources. The ZnSe films show direct allowed interband transition. The effect of particle size of nanocrystalline ZnSe thin films for unirradiated and irradiated by gamma (γ) doses from ¹³⁷Cs on the optical properties was studied. Both the optical energy bandwidth and absorption coefficient (α) were found to be (γ) dose dependent.     

Studies of nanocrystalline Pd alloy films coated by electroless deposition

The microstructures of thin coating films of pure palladium and palladium alloys deposited from organic electrolytes onto different metallic substrates by electroless plating method have been investigated. The coatings are dense, pore-free 0.005–1 μm thick films with high adhesive strength to the substrate surface. X-ray spectral analysis, X-ray phase analysis, transmission and scanning electron microscopy were used to determine the composition and structure of alloy coatings of binary systems: Pd–Au, Pd–Ag, Pd–Ni, Pd–Pb, and ternary system Pd–Au–Ni. The coatings of Pd–Au, Pd–Ag, and Pd–Ni have a solid solution structure, whereas Pd–Pb is intermetallic compound. It has been found that the deposited films consist of nanocrystalline grains with sizes in the range of 11–35 nm. Scanning and transmission electron microscopy investigations reveal the existence of clusters formed by nanocrystalline grains. The origin for the formation of nanocrystalline structures of coating films is discussed.     

Preparation of poly(acrylic)/SiO2/EuL3 x 2H2O, hybrid thin films from monodispersed colloidal silica

In this study, poly(acrylic)/SiO2/EuL3 x 2H2O hybrid thin films were prepared from various acrylic monomers (MMA and EDMA/TMPTA), lanthanide metal complexes (EuL3 x 2H2O, L = pyridine carboxylic acid), and monodispersed colloidal silica with a coupling agent, 3-(trimethoxysilyl)propyl methacrylate (MSMA). It is a combination of the sol-gel reaction, thermal polymerization, and spin coating. The silica content in the hybrid thin films is fixed at 20 wt%, and the EuL3 x 2H2O content is varied from 0.01 g to 0.07 g. FTIR and EA analysis confirms the chemical structure of the prepared EuL3 x 2H2O and poly(acrylic)/SiO2/EuL3 x 2H2O hybrid thin films. UV-Vis spectra and n&k analysis shows that the hybrid thin film has good transparency in visible light. The refractive index of hybrid thin films can be effectively controlled through the EuL3 x 2H2O content. The PL spectra shows that the strongest emission peak occurs at 615 nm and the emission intensity increases to the peak maximum at an EuL3 x 2H2O content of 0.05 g. Both TGA and PL analysis show that the prepared hybrid thin films from the crosslinked acrylic polymer moiety have much better film uniformity, thermal stability, and fluorescence properties. The TEM diagram shows that the MSMA/SiO2/EuL3 x 2H2O particles with a size 15-20 nm are well dispersed in the reaction solution. The SEM diagram shows that the particle distribution in the prepared hybrid thin films is uniform and no phase separation is observed. Finally, AFM analysis indicates that the prepared hybrid thin films have an excellent surface planarity.     

Properties of vacuum-deposited polyimide films

Vacuum-deposited polyimide (PI) thin films have been prepared by co-deposition of precursor pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) followed by thermal treatment. The dependency of the optical and electrical properties, chemical resistivity and mechanical stability on the composition (ODA:PMDA) and the degree of imidization of the PI layers have been investigated and discussed. The experimental results have yielded possibilities to microstructure the vacuum-deposited PI films by excimer laser irradiation or reactive ion etching in gas mixture CF₄/O₂.     

Dielectric constant and refractive index of poly (siloxane–imide) block copolymer

Recent technological advances demanded polyimides of improved versatility in terms of electronic, optical and thermal properties. In this work, a series of poly(siloxane–imide) block copolymers were synthesized in order to investigate the effect on their optical and electronic properties. The polyimide unit was derived from 3,3′,4,4′-Biphenyltetracarboxylic dianhydride (BPDA) and 4-(4-{1-[4-(4-aminophenoxy) phenyl]-1-methylethyl} phenoxy) aniline (BAPP) while the siloxane unit was derived from 3-[3-(3-aminopropyl)-1,1,3,3-tetramethyldisiloxanyl] propylamine (DMS) and Poly(dimethylsiloxane), bis(3-aminopropyl)terminated (PDMS). The structure of the polyimide was characterized by fourier transformer infra red (FT-IR), nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, solution viscosity and gas permeation chromatography (GPC). Scanning electron microscope (SEM) analysis suggested a microphase separation between the two components. The refractive index and dielectric properties showed a decreasing trend with increased silicone unit in the polyimide backbone. However ultra violet visible (UV–Vis) and optical transparency was not significantly affected. Electronic and optical properties of this copolymer were discussed in relation to the polysiloxane content.     

Optical properties of organo-soluble polyimide thin films and their applications in liquid crystal displays

Three organo-soluble polyimide powders have been synthesized. Their imidization was verified by Fourier transform infrared (FTIR) and thermal gravimetric analysis (TGA) techniques. The amorphous morphology of their thin films were confirmed by X-ray diffraction. Polyimide thin films were prepared by solution casting or spin coating. UV–visible transmission spectra of thin films revealed that they are almost transparent in the range of visible light. With in-plane orientation, revealed by FTIR spectra, negative birefringence (Δn) of thin films were observed, and refractive indices of the thin films along the film plane (n_TE) and normal to the plane (n_TM) were measured by a prism coupler. Because of negative birefringence of the thin films, they can be substituted for the compensation films for twisted nematic liquid crystal displays (TN-LCDs) to extend their viewing angles. In this paper, a 90°C TN-LCD and 120°C TN-LCD were taken as examples to show the compensation effect of thin films of a qualified polyimide.