Vakuumbasierte Abscheidung von funktionellen Nanokompositen und deren Modifikation durch Ionenstrahlbehandlung

Nanocomposite thin film coatings with a wide range of metal volume fractions were prepared by co–sputtering of TiO2/Teflon and Ag/Au from two different magnetron sources simultaneously in a home made deposition chamber under high vacuum conditions. Two different types of host materials a polymeric (PTFE) and a ceramic (TiO2) were studied in this work. Morphology, optical and antibacterial properties of these nanocomposites were examined. The formation of metallic nanoparticles upon vapor phase co–deposition of a metal and a dielectric matrix component can be understood in terms of the high cohesive energy of the metal and the low metal-matrix interaction energy which lead to high metal atom mobility on the growing composite surface and metal aggregation whenever metal atoms encounter each other or a metal cluster. Unlike the case of polymers, in the case of Ag nanoparticles on TiO2, segregation of the clusters on the surface also provides a fast pathway for Ostwald ripening without any restrictions by elastic distortions at least for those clusters which are in direct contact with the surface. 3D electron tomography was employed on the TiO2 based nanocomposite thin films to explain the two step model for the particle size distribution. First step involved the formation of small nanoparticles during vacuum phase deposition or on the growing surface. Second step after the deposition process involved the formation of larger particles through particle coarsening by Ostwald ripening and surface segregation. In bimetallic nanocomposites based on sandwich geometry in polymer system, the changes in the particle plasmon spectra of sandwiched Au nanoclusters as a result of the presence of Ag nanoclusters in their vicinity and vice versa was studied. Also, the optimum dielectric barrier thickness for the observation of equal intensity double plasmon resonance was reported. Also efforts towards tuning of the double plasmon resonances by tailoring the dielectric separation were carried out. Special attention was laid on the swift heavy ion irradiation (SHI) of the nanocomposites. The SHI beamlines from both the Hahn–Meitner–Institute in Berlin, Germany and the Inter University Accelerator Center in New–Delhi, India, were employed in this work. The TiO phase formation on SHI irradiation with increasing fluence was understood by the interaction of two different counteracting mechanisms, where at lower fluences, the tendency towards the formation of TiO existed with the larger unaffected areas and at higher fluences, the destruction of the evolved TiO phase into fragments was evident. This served as an evidence for the counter play between "hit" and "no–hit", "single–hit" and "multiple–hit" processes. A comparative study involving the in–situ heating of the TiO2 based nanocomposites in the TEM confirms the absence of the formation of TiO. Changes of the microstructure of the nanocomposite film upon annealing allowed demonstrating the absence of the formation of TiO but rather only the crystallization of the TiO2. SHI irradiation of Ag nanoparticles embedded in PTFE matrix shows a marginal dissolution of Ag nanoparticles along with a slight agglomeration of nanoparticles. At higher fluences, carbon rich areas were observed, which were as a result of the carbonization along the ion tracks. Functionality of the nanocomposites in terms of the antibacterial properties was studied. Cultures of B.megaterium, S.aureus, S.epidermidis and E.coli were used to study the effect on the Ag–TiO2 nanocomposites. Additionally, silver ion release studies were carried out at dfferent MVFs by using X-ray photoelectron and UV-Vis/NIR spectroscopies. Enhancement of the silver ion release after SHI irradiation at a fluence was observed to the fact that the ion trajectories after irradiation provide better silver ion release

Boosting the power performance of multilayer graphene as lithium-ion battery anode via unconventional doping with in-situ formed Fe nanoparticles

Graphene is extensively investigated and promoted as a viable replacement for graphite, the state-of-the-art material for lithium-ion battery (LIB) anodes, although no clear evidence is available about improvements in terms of cycling stability, delithiation voltage and volumetric capacity. Here we report the microwave-assisted synthesis of a novel graphene-based material in ionic liquid (i.e., carved multilayer graphene with nested Fe3O4 nanoparticles), together with its extensive characterization via several physical and chemical techniques. When such a composite material is used as LIB anode, the carved paths traced by the Fe3O4 nanoparticles, and the unconverted metallic iron formed in-situ upon the 1st lithiation, result in enhanced rate capability and, especially at high specific currents (i.e., 5 A g−1), remarkable cycling stability (99% of specific capacity retention after 180 cycles), low average delithiation voltage (0.244 V) and a substantially increased volumetric capacity with respect to commercial graphite (58.8 Ah L−1 vs. 9.6 Ah L−1)

Interaction of Polyoxometalates and Nanoparticles with Collector Surfaces—Focus on the Use of Streaming Current Measurements at Flat Surfaces

Streaming current measurements were used to study the interaction of polyoxometalates (POMs) and nanoparticles (NPs) with flat surfaces as an alternative, innovative approach to infer POM and NP properties of potential sparse material in terms of charge and magnitude. With respect to POMs, the approach was able to reveal subtle details of charging properties of +7 vs. +8 charge at very low POM concentrations. For NPs, the sign of charge and even the zeta-potential curve was retrieved. Concerning NPs, mutual interaction between TiO$_{2}$ and SiO$_{2}$ surfaces was studied in some detail via macroscopic measurements. Post-mortem analysis of samples from electrokinetic studies and separate investigations via AFM and HRTEM verified the interactions between TiO$_{2}$ NPs and SiO$_{2}$ collector surfaces. The interactions in the SiO$_{2}$/TiO$_{2}$ system depend to some extent on NP morphology, but in all our systems, irreversible interactions were observed, which would make the studied types of NPs immobile in natural environments. Overall, we conclude that the measurement of streaming currents at flat surfaces is valuable (i) to study NP and POM collector surface interactions and (ii) to simultaneously collect NPs or POM (or other small mobile clusters) for further (structural, morphological or release) investigations

First results from in situ transmission electron microscopy studies of all-solid-state fluoride ion batteries

A focused ion beam (FIB) system is used to fabricate a micron-sized all-solid-state fluoride ion cell from a bulk battery for in situ transmission electron microscopy (TEM) testing. The bulk battery is based on a La0·9Ba0·1F2.9 solid-state electrolyte with a nanocomposite of Cu/C as a cathode and a nanocomposite of MgF2, Mg, La0·9Ba0·1F2.9 and C as an anode. The evolution of the morphology, structure, and composition of the electrodes and their interfaces with the electrolyte is characterized using in-situ TEM during electrochemical cycling. The high-resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy-energy dispersive X-ray (STEM-EDX) analysis of the cathode-electrolyte interface reveal the expected formation of CuF2 phase during charging. During cycling, grain growth of Cu in the cathode ingredients and Cu diffusion from the cathode into the electrolyte are observed in addition to void formation

Interaction of Polyoxometalates and Nanoparticles with Collector Surface — Focus on the Use of Streaming Current Measurements at Flat Surfaces

Streaming current measurements were used to study the interaction of polyoxometalates (POMs) and nanoparticles (NPs) with flat surfaces as an alternative, innovative approach to infer POM and NP properties of potential sparse material in terms of charge and magnitude. With respect to POMs, the approach was able to reveal subtle details of charging properties of +7 vs. +8 charge at very low POM concentrations. For NPs, the sign of charge and even the zeta-potential curve was retrieved. Concerning NPs, mutual interaction between TiO2 and SiO2 surfaces was studied in some detail via macroscopic measurements. Post-mortem analysis of samples from electrokinetic studies and separate investigations via AFM and HRTEM verified the interactions between TiO2 NPs and SiO2 collector surfaces. The interactions in the SiO2/TiO2 system depend to some extent on NP morphology, but in all our systems, irreversible interactions were observed, which would make the studied types of NPs immobile in natural environments. Overall, we conclude that the measurement of streaming currents at flat surfaces is valuable (i) to study NP and POM collector surface interactions and (ii) to simultaneously collect NPs or POM (or other small mobile clusters) for further (structural, morphological or release) investigations

Graphitizability of Polymer Thin Films: An In Situ TEM Study of Thickness Effects on Nanocrystalline Graphene/Glassy Carbon Formation

Polymer pyrolysis has emerged as a versatile method to synthesize graphenoid (graphene like) materials with varying thickness and properties. The morphology of the thin film, especially the thickness, greatly affects the graphitizability and the properties of the graphenoid material. Using in situ current annealing inside a transmission electron microscope (TEM), the thickness-dependent structural evolution of the polymer film with a special focus on thickness effects is followed. At high temperatures, thin samples form large graphene layers oriented parallel to the substrate, whereas in thick samples multi-walled cage-like structures are formed. Moleclar Dynamics (MD) simulations reveal a film thickness of 40 Å below which, the carbonized layers align parallel to the surface. For thicker samples, the orientation of the layers becomes increasingly misoriented starting from the surface to the center. This structural change can be attributed to the formation of bonded multi-layers from the initially unsaturated activated edges. The resulting cage-like structures are stable even during simulated annealing at temperatures as high as 3500 K. An atomistic understanding of the formation of these structures is presented. The results clearly indicate the critical effect of thickness on the graphitizability of polymers and provide a new understanding of the structural evolution during pyrolysis