RESUMEN
The oxidation behaviour of tungsten disulphide (WS2) nanosheet powder with an average thickness of about 10 nm was studied in the temperature range of 25-700 °C. The samples were subjected to exposure in air in a short continuous mode as well as extended isothermal holding. It was observed that WS2 nanosheets were stable below 350 °C in air for short exposure times. A two-dimensional WS2/WO3 heterostructure evolved at 350 °C on short exposures to the oxidising atmosphere. Complete oxidation of WS2 nanosheets was observed at a temperature of about 450 °C in the continuous heating mode and at 350 °C under isothermal holding for an extended exposure time. During oxidation, WS2 nanosheets were initially transformed to 2D-WO3 nanosheets with an average thickness of about 10 nm. Significant distortion in the monoclinic structure of 2D-WO3 was observed. At higher temperatures, the WO3 nanosheets disintegrated initially to rod-shaped WO3 particles, which were subsequently transformed to thermodynamically stable spherical shaped WO3 nanoparticles.
RESUMEN
Transmission electron microscopy (TEM) has been used intensively in investigating battery materials, e.g. to obtain phase maps of partially (dis)charged (lithium) iron phosphate (LFP/FP), which is one of the most promising cathode material for next generation lithium ion (Li-ion) batteries. Due to the weak interaction between Li atoms and fast electrons, mapping of the Li distribution is not straightforward. In this work, we revisited the issue of TEM measurements of Li distribution maps for LFP/FP. Different TEM techniques, including spectroscopic techniques (energy filtered (EF)TEM in the energy range from low-loss to core-loss) and a STEM diffraction technique (automated crystal orientation mapping (ACOM)), were applied to map the lithiation of the same location in the same sample. This enabled a direct comparison of the results. The maps obtained by all methods showed excellent agreement with each other. Because of the strong difference in the imaging mechanisms, it proves the reliability of both the spectroscopic and STEM diffraction phase mapping. A comprehensive comparison of all methods is given in terms of information content, dose level, acquisition time and signal quality. The latter three are crucial for the design of in-situ experiments with beam sensitive Li-ion battery materials. Furthermore, we demonstrated the power of STEM diffraction (ACOM-STEM) providing additional crystallographic information, which can be analyzed to gain a deeper understanding of the LFP/FP interface properties such as statistical information on phase boundary orientation and misorientation between domains.
RESUMEN
Ag-TiO2 nanocomposite coatings with varying Ag content were prepared by co-sputtering from two separate sputter sources. This technique allows to prepare coatings not only with a large variation of Ag content and different gradient but also allows much better control of nanocomposite thickness and nanostructure compared with mostly used techniques based on wet chemical approaches. Various thicknesses of nanocomposite layers with different deposition parameters were studied to obtain a better understanding on the growth of Ag nanostructures in the TiO2 films. The metal-volume-fraction was varied between 15% and 47%. Structural and microstructural investigations of the nanocomposite films were carried out by transmission electron microscopy. Special attention was paid to surface segregation of Ag and its suppression. The observed segregation on TiO2 contrasts sharply with the well known embedding tendency of Ag clusters on polymers. Functionality of the Ag-TiO2 nanocomposites was demonstrated via UV-Vis spectroscopy and antibacterial tests. It was shown that a thin layer of TiO2 can be used as an effective barrier to tailor the release behaviour of Ag ions.
RESUMEN
We report the synthesis of Ag nanoparticles in polyethylene terephthalate (PET) matrix using atom beam co-sputtering. Metal filling factor was evaluated by Rutherford backscattering spectrometry. Microstructural evolutions of the nanocomposites films were investigated by transmission electron microscopy, which confirmed the formation of irregular shaped Ag nanoparticles. The X-ray photoelectron spectroscopy measurements of the sputter deposited PET film and co-sputtered deposited Ag-PET as well as PET bulk foil (from Goodfellows) were performed to study chemical composition of the nanocomposite films. The optical properties of these nanocomposites were studied by light absorption/transmission, which revealed a narrow transmission of UV light approximately 320 nm and a broad surface plasmon resonance absorption extending up to infrared region (approximately 2400 nm). Swift heavy ion irradiation of Ag-PET nanocomposite resulted in narrowing the full width at half maximum of transmission band.
RESUMEN
We report a strategy to achieve a material showing equal intensity double plasmon resonance (EIDPR) based on sandwich geometry. We studied the interaction between localized plasmon resonances associated with different metal clusters (Au/Ag) on Teflon AF (TAF) in sandwich geometry. Engineering the EIDPR was done by tailoring the amount of Au/Ag and changing the TAF thickness. The samples were investigated by transmission electron microscopy (TEM) and UV-visible spectroscopy. Interestingly, and in agreement with the dipole-surface interaction, the critical barrier thickness for an optimum EIDPR was observed at 3.3 nm. The results clearly show a plasmon sequence effect and visualize the role of plasmon decay.
