[en] An overview is given about microstructure and composition analyses of InGaN quantum wells embedded in Ga(Al)N barriers to study the mechanisms which determine the In distribution in epitaxially grown InGaN layers. The applied technique is transmission electron microscopy (TEM). The main prerequisite for this work was the development of a technique based on high-resolution lattice fringe images that allows quantitative chemical analyses of InGaN on an atomic scale. A large variety of samples was investigated that were produced by molecular beam epitaxy (MBE) and metal-organic vapor phase epitaxy (MOVPE). The effect of the deposition temperature, growth rate, strain and high-temperature annealing treatments on the average In concentration and In distribution was studied to assess the influence of phase separation, In surface segregation and In desorption. Composition fluctuations in InGaN are always observed on two different lateral scales independent of the growth technique and particular set of growth parameters but the strength of the composition fluctuations can be influenced by the details of the growth. (orig.)

[en] We have compared and analysed the morphology of capped and uncapped thin InGaN layers by transmission electron microscopy. The samples were grown under the same conditions by metal-organic chemical vapour deposition. The capped layer appears to be homogenous in thickness whereas the uncapped one is characterized by the presence of large islands. Moreover, the In distribution was determined in both samples by quantitative high-resolution transmission electron microscopy. The average indium concentration was found to be comparable. Fluctuations of the In concentration on a large scale occur in both cases whereas fluctuations on a scale of a few nanometers are more pronounced in the capped layer. (Abstract Copyright [2002], Wiley Periodicals, Inc.)

[en] The morphology and the structure of TiO₂ films, grown on Si (1 0 0) substrates by metal organic chemical vapour deposition (MOCVD) was investigated in 5-500 nm thick films. It was shown that the TiO₂ layer is mainly amorphous at the first stages of deposition. The growth of nanocrystallites begins inside the amorphous TiO₂ layer, and it continues at the expense of the amorphous phase until the crystallized grains occupy the whole layer. Then, the film growth continues with a columnar structure. The coexistence of anatase and rutile phases was evidenced from the beginning of the growth by high resolution transmission electron microscopy and grazing incidence x-ray diffraction. However, the anatase growth overcomes that of rutile, leading to an inhomogeneous phase distribution as a function of the film thickness.

[en] Transmission electron microscopy investigation of the chemical composition of In_x Ga_1-xN/GaN layers by strain state analysis can lead to substantial artefacts. We evaluated simulated images in dependence of specimen thickness, specimen orientation and objective lens defocus. We observed that the measurement is in agreement with the true strain profile for certain conditions only. An analysis of error sources revealed that artefacts are mainly caused by a combination of delocalization and the composition dependence of the phases of the beams contributing to the image formation. The delocalization effect is minimized for interference of the undiffracted beam with one of the 000±2 beams. The least chemical shift of the phases is obtained using the 000+2 beam and a strong excitation of 000+4. Images simulated for these conditions taking into account lattice plane bending and strain using finite-element calculations revealed a good agreement of evaluated and true strain profiles. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] WO₃ nanorods are grown by a simple vapor deposition method on a mica substrate and characterized by Selected Area Electron Diffraction and Energy Dispersive X-rays Spectroscopy. Experimental results show the clear evidence of an unexpected WO₃ hexagonal structure as well as an epitaxial growth on the mica substrate. Besides, potassium is evidenced inside the nanorods. It is thus deduced that a metastable WO₃ hexagonal phase is stabilized by epitaxy through a tungsten bronze interlayer having same hexagonal structure.

[en] Y₂O₃:Er³⁺, Yb³⁺ nanocrystals have been obtained by ball milling and using a combustion synthesis procedure. In both cases the nanocrystals have been successfully coated with SiO₂ following the Stoeber method. The average size of the as-synthesized nanoparticles has been estimated from X-ray diffraction patterns and transmission electron microscopy images. The dependence of the optical properties of these samples on synthesis procedure or dopant concentration has been investigated. Emission, excitation and lifetime measurements have been carried out. Upconversion luminescence has been detected in all samples and an enhancement of the red to green emission ratio has been observed in all samples after infrared compared to visible excitation. The mechanisms responsible for the upconversion phenomena have been discussed.

[en] Nanocomposites consisting of noble metal nanoparticles (NPs) embedded in TiO₂ thin films are of great interest for applications in optoelectronics, photocatalysis and solar-cells for which the plasmonic properties of the metal NPs play a major role. This work investigates the first stages of the formation of gold NPs by thermal annealing of Au-doped TiO₂ thin films grown by magnetron sputtering. A low concentration of gold in the films is considered (5 at.%) in order to study the first stages of the formation of the NPs. Raman spectroscopy is used to follow the crystallization of TiO₂ when increasing the annealing temperature. In addition, low-frequency Raman scattering (LFRS) is used to investigate the formation of gold NPs and to determine their size. Resonant LFRS measurements obtained by using a laser wavelength matching the surface plasmon resonance of the metallic NPs significantly enhances the Raman peak intensity enabling to focus on the first stages of the NPs formation. A double size distribution is observed at T_a = 800 °C calling for additional investigations by transmission electron microscopy (TEM). TEM observations reveal an inhomogeneous in-depth size distribution of gold NPs. The annealed films are structured in two sublayers with bigger NPs at the bottom and smaller NPs at the top. At T_a = 800 °C, a double size distribution is confirmed near the surface. A mechanism is proposed to explain the formation of the sublayers. The modification of the diffusion of gold atoms by stresses in the film near the substrate is assumed to be responsible for the observed two layers structure. - Highlights: • Gold-doped TiO₂ thin films were grown by magnetron sputtering. • The first stages of the formation of Au nanoparticles after annealing are studied. • Au nanoparticles and crystallized TiO₂ are observed above 400 °C. • The size distribution of the gold nanoparticles is complex and depth-dependent

No abstract available

[en] TiO₂ thin films were grown by direct liquid injection atomic layer deposition (DLI-ALD) with infrared rapid thermal heating using titanium tetraisopropoxide and water as precursors. This titanium tetraisopropoxide/water process exhibited a growth rate of 0.018 nm/cycle in a self-limited ALD growth mode at 280 °C. Scanning electron microscopy and atomic force microscopy analyses have shown a smooth surface with a low roughness. XPS results demonstrated that the films were pure and close to the TiO₂ stoichiometric composition in depth. Raman spectroscopy revealed that the films were crystallized to the anatase structure in the as-deposited state at low temperature without necessity of high temperature annealing. Results obtained demonstrate that the liquid injection ALD is an efficient method of elaborating titanium oxide films using titanium tetraisopropoxide as precursor.

[en] Small angle x-ray scattering was used to probe in-situ the formation of nanoparticles in the plasma plume generated by pulsed laser irradiation of a titanium metal surface under atmospheric conditions. The size and morphology of the nanoparticles were characterized as function of laser irradiance. Two families of nanoparticles were identified with sizes on the order of 10 and 70 nm, respectively. These results were confirmed by ex-situ transmission electron microscopy experiments.