M. Gartner

TiO2(Fe3+) nanostructured thin films with antibacterial properties

TiO2-based nanostructured Fe3+-doped coatings have been prepared by the sol–gel method on glass substrates. The coatings were characterized by X-ray diffraction and spectroellipsometry methods. The influence of Fe3+ dopant concentration, number of coatings, and calcination temperature on the films structure was established. The antibacterial activity against E. coli, has been studied applying the so-called antibacterial-drop test. The bactericidal activity for the above bacteria cells was estimated by relative number of bacteria survived calculated from the number of viable cells which form colonies on the nutrient agar plates. The coatings exhibited a high antibacterial activity, which was enhanced with the increase of the temperature of thermal treatment and formation of anatase crystalline structure. The long thermal treatment results in rutile crystalline structure formation followed by the decrease in the antibacterial activity of the coating.

Spectroellipsometric characterization of lanthanide-doped TiO2 films obtained via the sol-gel technique

Abstract TiO 2 (Ln) films deposited by the sol-gel and dip coating technique on Si wafers and soda-lime glass as substrates have been characterized by spectroscopic ellipsometry, X-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. Among the various factors that affect the optical and structural properties of oxide films we focus in this paper on the substrate and the lanthanides (La, Eu, Sm, Gd) as dopants.

Investigation on preparation and physical properties of nanocrystalline Si/SiO2 superlattices for Si-based light-emitting devices

Abstract Structures containing silicon nanocrystals (nc-Si) are very promising for Si-based light-emitting devices. Using a technology compatible with that of silicon, a broader wavelength range of the emitted photoluminescence (PL) was obtained with nc-Si/SiO2 multilayer structures. The main characteristic of these structures is that both layers are light emitters. In this study we report results on a series of nc-Si/SiO2 multilayer periods deposited on 200 nm thermal oxide SiO2/Si substrate. Each period contains around 10 nm silicon thin films obtained by low-pressure chemical vapour deposition at T=625°C and 100 nm SiO 2 obtained by atmospheric pressure chemical vapour deposition T=400°C. Optical and microstructural properties of the multilayer structures have been studied by spectroscopic ellipsometry (using the Bruggemann effective medium approximation model for multilayer and multicomponent films), FTIR and UV–visible reflectance spectroscopy. IR spectroscopy revealed the presence of SiOx structural entities in each nc-Si/SiO2 interface. Investigation of the PL spectra (using continuous wave-CW 325 nm and pulsed 266 nm laser excitation) has shown several peaks at 1.7, 2, 2.3, 2.7, 3.2 and 3.7 eV , associated with the PL centres in SiO2, nc-Si and Si–SiO2 interface. Their contribution to the PL spectra depends on the number of layers in the stack.

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

Abstract 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.

TiO2-Based Porous Materials Obtained from Gels, in Different Experimental Conditions

The gels which are precursors of TiO2 porous materials are prepared by the controlled hydrolysis-condensation of titanium isopropoxide by polymeric method. In the present work, a study of the influence of different experimental conditions (water/alkoxide ratio, solvent/alkoxide ratio and temperature) on the structure and texture of the polymeric gels obtained with the same type of alkoxide has been investigated. The structural and textural modifications for the unsupported materials have been detected using DTA/TGA, XRD, specific surface area and pore size computerized measurements. The optical properties of the supported materials deposited on silicon wafers have been investigated using ellipsometric method. Supported and unsupported porous materials with different structure and texture have been obtained depending on different experimental and thermal treatment conditions.

High-reflectivity II-VI-based distributed Bragg reflectors for the blue-violet spectral range

We report on the realization of a high quality distributed Bragg reflector for the blue-violet spectral range, with both high and low refractive index layers lattice matched to the GaAs substrate. Our structure is grown by molecular beam epitaxy (MBE). The high refractive index layer is made of ZnMgSSe, while the low index material consists of a short period superlattice containing MgS and ZnCdSe. The refractive index step of Δn = 0.43 results in a stop band width of 40 nm and the normalized reflectivity exceeds 99% for 21 Bragg pairs.

Pulsed laser deposition of lithium niobate: a parametric study

We report the deposition of high optical quality LiNbO 3 thin films on Si(111) substrates by pulsed laser ablation using a KrF * excimer laser (λ = 248 nm, τ = 20 ns) source. Experiments have been conducted in oxygen at 5-20 Pa. Si(111) collectors were uniformly heated at 500-700°C. Some of the as-deposited collectors were submitted to an in-situ thermal treatment in oxygen (10 3 -10 4 Pa) at the same temperature. The deposited thin films were characterised by grazing incidence X-ray diffraction (GIXRD), transmission electron microscopy (TEM) and spectroscopic ellipsometry (SE). Our LiNbO 3 thin films, achieved at relatively low temperature (550°C), are the first textured and high optical quality pulsed laser deposited films on Si.

Investigation on optical properties of CVD films used in MOEMS applications

Abstract Low-pressure chemical vapour deposition (LPCVD) amorphous silicon oxynitride (a-SiO x N y ) thin films of various compositions as well as the atmospheric pressure chemical vapour deposition (APCVD) borophosphosilicate glass (BPSG) thin films with varying phosphorus and boron contents were investigated. The dependence of the optical properties of the films on the deposition temperature and the gas flow ratio was studied by spectroellipsometry (SE) and infrared spectroscopy (IR).

Physical-optical properties of LPCVD amorphous silicon rich-nitride and oxynitride

Low pressure chemical vapour deposition (LPCVD) silicon oxynitride and silicon-rich nitride films of various composition (from pure SiO/sub 2/ to pure Si/sub 3/N/sub 4/) were deposited by changing the relative gas flow ratio N/sub 2/O to NH/sub 3/ and SiH/sub 2/Cl/sub 2/ to NH/sub 3/, respectively. The effects of oxygen on the physical properties of the films were studied using spectroellipsometry and Fourier transform infrared spectroscopy. The deconvolution of the IR spectra was made. The characteristic absorption peak for Si/sub 3/N/sub 4/ is at 822 cm/sup -1/ (Si-N bonds), and for SiO/sub x/N/sub y/ is around 973 cm/sup -4/ (Si-O-Si bond). Higher oxygen content decreases the refractive index of SiO/sub x/N/sub y/ films, whereas more silicon in silicon nitride increases the refractive index. The refractive index dispersion is studied by the single-oscillator Wemple Di Domenico model. The optical gap varies monotonically from 5.43 eV for silicon nitride to 9 eV for HTO LPCVD silicon dioxide, and for silicon oxynitride was found to be around 6 eV.

Optical and microstructural properties of TiO2(Ni2+) thin films

Coloured TiO2(Ni2+) thin coatings doped with transitional metals (Ni) were deposited on different substrates (silicon wafers, glass, aluminum) by the sol-gel dip coating process. Complementary techniques (XPS, SE, TEM, XRD, Absorption Spectroscopy) were used to characterize the surface stoichiometry and optical properties, as well as the structure and texture of the thermally treated gels. The presence of fully oxidized film in the outer layers, crystallization in heat treatment to anatase and rutile, formation of porous and coloured films due to the influence of the dopant and the reaction with the substrate, as well as a decrease by three orders of magnitude of the resistivity of Ni-doped films, are reported.