J. Rivory

Infrared ellipsometric study of SiO2 films: relationship between LO mode frequency and porosity

Abstract A method for evaluating the pore volume fraction of silica films for different pore connectivities is presented. A series of SiO2 films, evaporated by electron gun with or without ion bombardment, have been studied using visible and infrared ellipsometry. The TO and LO mode frequencies are deduced from the dielectric function calculated from infrared ellipsometric data. The study of both TO and LO mode frequencies is shown to bring independent information on the film microstructure. The TO mode frequency (near 1075 cm−1) varies mainly with the density of the silica matrix. On the other hand, variation in the LO mode frequency (near 1245 cm−1) is mainly due to changes in porosity. In the case of films with pores largely connected, the evaluation of the pore volume fraction from the LO frequency is compared to that obtained from the analysis of the large water absorption band near 3300 cm−1 (H–OH and Si–OH stretching absorption band).

Evolution of the optical properties of Si nanoparticles embedded in SiO2 as function of annealing conditions

The dielectric function of Si nanoparticles embedded in silica has been determined from spectroscopic ellipsometry and photothermal deflexion spectroscopy from 0.7to6eV. The influence of crystalline fraction and diameter of the nanoparticles on their optical properties has been investigated. Above 4nm of diameter, the nanoparticles presented a dielectric function similar to that of fine grained polycrystalline Si (poly-Si) at photon energy higher than 2eV, with the well marked structures associated with the E1 and E2 critical points. In contrast, below 2eV their absorption coefficient was smaller than for poly-Si. Below 2.5nm of diameter, the dielectric function of the nanoparticles drastically changed. The magnitude of the imaginary part of the dielectric function of the nanoparticles near the position of the E1 critical point constantly decreased, whereas it increased at the position of the E2 critical point. These observations can be interpreted as the result of the transfer of the oscillator strength ...

Use of thin films for studying order-disorder transformations☆

Abstract Thin films are used to investigate the transformation by heat treatment of a disordered phase into an ordered phase in two different cases: compositional disorder in the case of metallic (Au-Cu) alloys, and positional disorder in the case of an amorphous semiconductor (Ge). The transformation is followed by simultaneous resistance measurements and controlled by electron diffraction and electron microscopy; its effects on the optical properties are measured. The use of thin films allows one to characterize accurately the phases before and after the transformation, and to check that the transformation has been completed.

Ellipsometric investigation of the Si/SiO2 interface formation for application to highly reflective dielectric mirrors

We present a study of the Si/SiO 2 interface formation during the growth of Si on SiO 2 using in situ ellipsometry measurements performed at one wavelength (X = 0.4 μm). Variable angle X-ray photoelectron spectroscopy (XPS) is also used to confirm the ellipsometric measurements. In situ ellipsometry and XPS provide evidence for the formation of a SiO x (0 <x < 2) interlayer between the SiO 2 and Si layers. The variation of x with depth is analysed from (cos Δ, tan ψ) trajectories and the results obtained allow reproduction of the spectroscopic ellipsometry spectra too. The effects of the substrate temperature on the growth are investigated and show that the higher the substrate temperature the larger the interface. The utilisation of a SiO 2 /Si multilayer stack for elaborating an omnidirectional reflector, angle-insensitive in the near infrared range, is also presented.

Ordered mesoporous organosilica films

Publisher Summary This chapter demonstrates that the optical and mechanical properties of mesoporous silica films provide the possibility to use them as low-index or low dielectric constant coatings. However, the surface of the pores must be carefully controlled to avoid any introduction of contaminations. This implies a chemical modification of the surface of the pores, which must be performed without ignoring the structure of the porosity (proportion and accessibility of micropores and mesopores). A first possibility consists in a post-synthesis gaffing with a reactive silane (chlorosilane, silazane, or alkoxysilane), but some more work is required to optimize this passivation strategy. Other functionalization processes such as the direct co-condensation of organic/inorganic silica precursors are also investigated. In any case, the functional organic group must be chosen to efficiently block the accessibility of the pores, either because of its bulky nature or because of its hydrophobic and oleophobic nature.