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[en] Highlights: • Nanolaminate thin films of Al2O3/TiO2 with different bilayer density were prepared by ALD method. • A new multidimensional reconstruction method was implemented to analyze the nanomechanical response of the samples. • Mechanical response of the nanolaminates showed to be improved by layer thickness and follow the behavior of a nanocomposite coating. • The method implemented allows the reconstruction of 4D mechanical data at the nanoscale. A novel method of nanomechanical testing of multilayered Al2O3/TiO2 nanolaminates was implemented by the nanoindentation technique. The indentation data were reconstructed and filtered by a statistical analysis algorithm and presented as a function of the penetration depth of the indenter. Results show the increment of mechanical properties on the laminates as a function of the amorphous interfaces of the individual layers and the effective control of the wear rate of the structures for further applications. The results presented show both important insights on the mechanical behavior of nanolaminates and the further applicability of the reconstruction model for error reduction on mechanical testing of nanolaminate samples.
[en] Highlights: • Porous silicon/TiO_2 nanocomposites have been investigated. • Morphology and chemical composition of PSi/TiO_2 nanocomposites were established. • Valence-band XPS maximums for PSi/TiO_2 nanocomposites were found and analyzed. - Abstract: PSi/TiO_2 nanocomposites fabricated by atomic layer deposition (ALD) and metal-assisted chemical etching (MACE) were investigated. The morphology and phase structure of PSi/TiO_2 nanocomposites were studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) with an energy dispersive X-ray spectroscopy (EDX) and Raman spectroscopy. The mean size of TiO_2 nanocrystals was determined by TEM and Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) was used to analyze the chemical elemental composition by observing the behavior of the Ti 2p, O 1s and Si 2p lines. TEM, Raman spectroscopy and XPS binding energy analysis confirmed the formation of TiO_2 anatase phase inside the PSi matrix. The XPS valence band analysis was performed in order to investigate the modification of PSi/TiO_2 nanocomposites electronic structure. Surface defects states of Ti"3"+ at PSi/TiO_2 nanocomposites were identified by analyzing of XPS valence band spectra
[en] Ultrafast and fast charge separation processes were investigated for complete cells based on several ZnO-based photoanode nanostructures and standard TiO_2 nanoparticle layers sensitized with the indoline dye coded D358. Different ZnO morphologies (nanoparticles, nanowires, mesoporous), synthesis methods (hydrothermal, gas-phase, electrodeposition in aqueous media and ionic liquid media) and coatings (ZnO–ZnO core–shell, ZnO–TiO_2 core–shell) were measured by transient absorption techniques in the time scale from 100 fs to 100 μs and in the visible and near-infrared spectral range. All of ZnO cells show worse electron injection yields with respect to those with standard TiO_2 material. Lower refractive index of ZnO than that of TiO_2 is suggested to be an additional factor, not considered so far, that can decrease the performance of ZnO-based solar cells. Evidence of the participation of the excited charge transfer state of the dye in the charge separation process is provided here. The lifetime of this state in fully working devices extends from several ps to several tens of ps, which is much longer than the typically postulated electron injection times in all-organic dye-sensitized solar cells. The results here provided, comprising a wide variety of morphologies and preparation methods, point to the universality of the poor performance of ZnO as photoanode material with respect to standard TiO_2. - Highlights: • Wide variety of morphologies and preparation methods has been checked for ZnO cells. • All ZnO cells work worse than TiO_2 ones. • Effective refractive index might be an additional factor in solar cell performance. • Excited charge transfer state of indoline dyes participates in the charge separation.
[en] TiO_2 thin films were grown on highly-doped p-Si (100) macro- and mesoporous structures by atomic layer deposition (ALD) using TiCl_4 and deionized water as precursors at 300 °C. The crystalline structure, chemical composition, and morphology of the deposited films and initial silicon nanostructures were investigated by scanning electron microscopy, transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, micro-Raman spectroscopy and X-ray diffraction (XRD). The mean size of TiO_2 crystallites was determined by TEM, XRD and Raman spectroscopy. It was shown that the mean crystallite size and the crystallinity of the TiO_2 are influenced dramatically by the morphology of the porous silicon, with the mesoporous silicon resulting in a much finer grain size and amorphous structure than the macroporous silicon having a partially crystal anatase phase. A simple model of the ALD layer growth inside the pores was presented. - Highlights: • The morphology and chemical composition of TiO_2 and porous Si were established. • The approximate size of TiO_2 nanocrystals was estimated. • The model of the atomic layer deposition coating in the porous Si was presented