Stress measurements in aluminium alloy films by the sin2 ψ method

The lattice parameters and the homogeneous elastic stresses in evaporated Al, AlSi and AlCu films 1 μm in thickness with, in part, a high degree of fibre texture have been determined. The stresses measured at room temperature as a function of the substrate temperature can be explained by the difference in the coefficients of thermal expansion between film and substrate in connection with creep processes. The different lattice parameters of the films as compared with bulk aluminium were found to be due to homogeneous elastic stresses and alloying elements.     

Deposition of thick silica-titania sol-gel films on Si substrates

A process for production of thick (>10 μm) titania-doped silica films on Si substrates by repetitive spin-coating of sol-gel material and rapid thermal annealing for 10 s in the range 800–1200°C is described. The dependence of overall thickness and etch rate in buffered HF on annealing temperature is described, and it is shown that films annealed at low (< 1175°C) temperatures have a relatively large thickness and etch rate. However, films having the properties of fully densified material (minimum thickness and etch rate) can be produced by subsequent consolidation. The film stress characteristics are similar to those phosphosilicate glass formed by the same process: films annealed below a critical temperature (< 1075°C) are under tensile stress at the annealing temperature, and crack before a thick film can be built up. Refractive index data are given; these show that only fully consolidated films have the refractive index expected from their SiO₂ and TiO₂ compositions. Finally, discrepancies in results for thickness of unconsolidated single-layer and multilayer films are explained using a simple model that accounts for the effect of cumulative densification.     

Vegetal nanoclusters in hybrid silica films prepared by sol-gel spin coating technique

Hybrid sol-gel films containing Rosemary extract nanoclusters embedded into hybrid silica network have been successfully synthesized using the sol-gel procedure by exploiting the template route, in association with an adequate spin-coating method. Formation of film precursor sols and effect of selected amounts of octyl trimethoxysilane and ethyl oleate succinic anhydride into the starting acid sols on the sol-gel product size have been evaluated by dynamic light scattering technique. The spectral characteristics of hybrid organic-inorganic films have shown that the multiple functional groups from Rosemary extract associated with residual Si-OH groups can cause the increase in the degree of physical interaction. The effect of hybrid sols meaning the silica precursors molar ratio and template concentration on the fluorescence of hybrid films has been also investigated. The fluorescence properties of synthesized films were found to be dependent on template and natural extract concentration. A higher amount of template resulted in doubling the fluorescence intensity in the 400-480 nm domain. The microstructural characteristics of the hybrid films revealed by atomic force microscopy have shown a homogeneous surface morphology with cluster-like structure. Hybrid silica films exhibit a periodic structure with cluster size less than 150 nm.     

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.     

Investigation of inorganic network formation in photopatternable hybrid sol-gel films by Si liquid NMR

Liquid ²⁹Si NMR spectroscopy was used to investigate the sol-gel process of methacryloxypropyltrimethoxysilane. This hybrid precursor was involved in the realization of optical elements in laminated crack-free thick films (up to 100 μm), through spatially controlled photopolymerization. Understanding the formation of the inorganic network was of first importance to insure the creation of crack-free photopatterned thick films in a laminated configuration. Material preparation required evaporation of the volatile solvents released during the sol-gel process and limitation of the condensation degree. Both conditions were achieved by a drying process at room temperature. The structure and the composition of the sols were investigated and compared to non-dried sols. Evolution of inorganic species distribution was also studied under increasing aging time or storage temperature. NMR peak fitting of T1 species gave fruitful information on the sol structure evolution during the sol-gel process. It pointed out the presence of a large variety of oligomers in the sol. The study also allowed the identification of more constraint cyclic species in dried sols stored at room temperature. Their amount significantly decreased when increasing the storage temperature and was attributed to ring opening of cyclic species. Consequently, the structure of the dried sol will depend both of the aging time and of the storage temperature. All these results have to be taken into account when the degree of condensation has to be limited to achieved photopatternable hybrid layers for specific optical applications.     

Ordered structure and preferred orientation of boehmite films prepared by the sol-gel method

Several boehmite films were produced using the sol-gel route. The drying process, the film structure evolution and the final texture of the samples were investigated by means of combined X-ray diffraction and weight variation. A remarkable (0 1 0) preferred orientation (about 97% of the crystallites) was found for xerogel films with thickness ranging from 1.5 to 24 μm. The ordered structure is already present in the sol state and is appeared and enhanced during drying, before gelling. This phenomenon may be attributed to the particular boehmite structure that induces special crystallite organization in the aquagel.     

Preparation and characterization of ZnO-TiO2 films obtained by sol-gel method

The sol-gel route has been applied to obtain ZnO-TiO₂ thin films. For comparison, pure TiO₂ and ZnO films are also prepared from the corresponding solutions. The films are deposited by a spin-coated method on silicon and glass substrates. Their structural and vibrational properties have been studied as a function of the annealing temperatures (400-750 °C). Pure ZnO films crystallize in a wurtzite modification at a relatively low temperature of 400 °C, whereas the mixed oxide films show predominantly amorphous structure at this temperature. XRD analysis shows that by increasing the annealing temperatures, the sol-gel Zn/Ti oxide films reveal a certain degree of crystallization and their structures are found to be mixtures of wurtzite ZnO, Zn₂TiO₄, anatase TiO₂ and amorphous fraction. The XRD analysis presumes that Zn₂TiO₄ becomes a favored phase at the highest annealing temperature of 750 °C. The obtained thin films are uniform with no visual defects. The optical properties of ZnO-TiO₂ films have been compared with those of single component films (ZnO and TiO₂). The mixed oxide films present a high transparency with a slight decrease by increasing the annealing temperature.     

Application of sol-gel derived silica films containing a methyl radical to a slab laser

Films were prepared by dipping slab laser glass into an acid alcoholic solution of tetraethoxysilane and methyltriethoxysilane. Methyltriethoxysilane introduces methyl radicals into the silica film. By introducing methyl radicals and choosing the best mixing ratio, durable, pinhole free films with a low refractive index of 1.38 at 1.054 μm were obtained.

The slab laser, coated with this film had a 1.83 times higher output energy in comparison with an uncoated slab.     

Lateral photovoltage measurements in hydrogenated amorphous silicon and silicon-oxygen thin films

Hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon-oxide alloy films (a-SiO_x:H) were investigated by temperature dependence of lateral photovoltage (LPV) measurements. The suboxide sample with [O] = 27 at.%, was found to exhibit larger LPV compared to the unalloyed sample. It is difficult to simply correlate LPV measurements to related diffusion length measurements, only. On the other hand, the observed magnitude of LPV in a-Si:H and its decrease with temperature, could be explained based on an internal electric field induced by diffusion electron and hole currents, and multiple trapping of the photocarriers.     

Study of the phase transition and the thermal nitridation of nanocrystalline sol-gel titania films

Nanocrystalline titania films were prepared by a complexing agent-assisted sol-gel method and converted to titanium nitride by a thermal nitridation process. The effect of acetylacetone (AcAc), diethanolamine (DEA) and acid catalysts (HCl and HNO₃) on the structure and morphology of the heat-treated titania films and on their nitridation products was examined by FTIR spectroscopy, X-ray diffraction (XRD) and atomic force microscopy (AFM). The carbothermal reduction of titania during the nitridation process with the formation of carboxynitrides has been considered. The results showed that the oxide to nitride transition strongly depends on the complexing agent used to prepare the titania films. The XRD results indicated the dependence of the lattice parameter of the nitridation product on the complexing agent or acid catalyst: AcAc and DEA lead to TiN_x with a lattice parameter α close to the theoretical value, while with HCl the lattice parameter was found sensibly lower showing the presence of an oxynitride. These results are accounted for by the effect of complexing agents and acid catalysts on the size of both TiO₂ and TiN grains and the different reactivity of the anatase and rutile phases. The possibility of tailoring the composition and morphology of TiN films by using complexing agents is envisaged.     

Optical properties of Rh6G molecules ordering in the silica- and titanium dioxide mesoscopic sol-gel films

The sol-gel method has been employed for the fabrication high quality mesostructured hybrid films. The effect of the nature of the matrix on the absorption and fluorescence spectra was found. It was shown that the aggregation of the dye molecules is significantly weaker in the SiO₂-P123/Rh6G based hybrid films. In case of TiO₂-P123/Rh6G films, the loss of isosbestic points in the absorption spectra in a TiO₂ matrix suggests the formation of higher aggregates and spectra concern mostly the red shift of the fluorescence maximum. Optical properties and exited state dynamic of Rh6G make the film a good candidate for producing photonic materials.     

Structure of Ni/SiO2 films prepared by sol-gel dip coating

The sol-gel dip coating technique has been used to deposit composite oxide films (NiO)_x(SiO₂)_1−x with x = 0.1 on silicon wafers. Single and multilayer coatings allowed a variation of the film thickness from 70 to 400 nm. Film morphology, atomic structure and atomic composition have been investigated by transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). The local environment of the Ni atoms was characterized by extended X-ray absorption fine structure (EXAFS). The samples were studied in the as-prepared state and after annealing in H₂ at 600 °C for 1 h. The structural and chemical state evolution of clusters present inside the silica matrix is discussed in terms of out-of-equilibrium reaction processes specific to low-dimensional objects and superficial effects.     

Some aspects of property tailoring of sol-gel derived thin SiO2 films

The sol-gel process in the dip-coating variant opens an interesting way for the production of thin metal oxide or transition metal oxide films with useful properties. This paper present result on the desposition and the characterization of thin SiO₂ films. The influence different process parameters, such as the composition and the aging behaviour of the coating solution, the withdrawal speed and the thermal treatment on important properties such as refractive index, film thickness, crystallinity and topography was tested. Viscosity and transmission measurements, Fourier transformation infrared reflection spectroscopy (FTIRS), transmission electron microscopy (TEM) and reflection high energy electron diffraction (RHEED) were used.     

A halogen anion sensor based on the hydrophobic entrapment of a fluorescent probe in silica sol-gel thin films

A halogen anion (Cl⁻, Br⁻, I⁻) sensor has been designed, based on the entrapment of a fluorescent molecule in a sol-gel silica film deposited on a glass substrate. A key factor is the use of the newly synthesized hydrophobic fluorophore, N-dodecyl-6-methoxyquinolinium, so as to avoid the problem of leaching. This probe allows detection and measurement of chloride concentrations in the physiological range (100 mM) coupled with a response time less than 1 s. The fluorescence quenching data are fitted to a model which assumes two quenching sites.     

Distribution of electronic states in amorphous Cd-As thin films on the basis of optical measurements

Transmission and fundamental reflectivity studies, completed on amorphous Cd-As thin films, allowed us to obtain parameters describing the fundamental absorption edge, i.e. the optical pseudogap E_G^opt, Urbach energy E_U and exponential edge parameter E_T. All these data, together with the results of earlier transport measurements, have been utilized in developing simple models of electronic structure (distribution of electronic states) for amorphous Cd-As thin films of various compositions.     

Photochemistry of azobenzene in sol-gel systems

The photophysical and photochemical behavior of azobenzene incorporated into sol-gel systems was studied. Sols doped with azobenzene were prepared by the hydrolysis of tetramethoxysilane. The absorption spectra of azobenzene in sols with and without HCl as a catalyst showed photochromism; UV irradiation changes trans-azobenzene to cis-azobenzene, which returns to trans-azobenzene by successive visible light irradiation. The results indicate that azobenzene is not protonated in the sol prepared by the present conditions. The absorption spectra showed that the azobenzene-doped xerogel prepared without HCl is mostly adsorbed on silica surfaces by the hydrogen bonding between the azo groups and silanol and/or water molecules. The adsorption did not affect photochromic behavior and photo-reversible changes were observed in the xerogels. UV photolysis of the azobenzene-doped xerogel prepared with HCl so produced protonated benzo[c]cinnoline that photochromic behavior was deteriorated. Surface modified xerogels were prepared from the mixture of tetraethoxysilane and methyltriethoxysilane in order to make clear the effect of the surface silanol groups. It was shown that the formation of the protonated benzo[c]cinnoline is suppressed by the introduction of Si-CH₃. These present results confirm that the acidic sites of Si-OH₂⁺ of xerogels play an important role in the photochemical reaction of azobenezene in silica xerogels.     

Carrier mobility and life time measurements in a-InxSe1−x films

The transport properties in a-In_xSe_1?x films have been studied by a time of flight method. The drift parameters sharply decreases with small addition of In (0.5 at.%) and become almost constant with further progressive increase of In, while the transit time dispersion of electron simultaneously increases. The experimental results are explained by an increase in the number of shallow and deep traps generated by the introducing of In.