Atomic structure and structural stability of Fe90Sc10 nanoglasses

Nanoglasses are non-crystalline solids whose internal structure is characterized by fluctuations of the free volume. Due to the typical dimensions of the structural features in the nanometer-range and the disordered atomic structure of the interfacial regions, the atomic structure and the structural stability of nanoglasses is not yet completely understood. Nanoglasses are typically produced by consolidation of glassy nanoparticles. Consequently, the basis for the understanding of the atomic structure of nanoglasses lies in the atomic structure of the primary glassy nanoparticles. Using electron energy loss spectroscopy, the elemental distribution in the Fe90Sc10 primary glassy nanoparticles and in the corresponding nanoglasses produced by consolidation of these glassy nanoparticles have been studied. Due to surface segregation, Fe has been found to be enriched at the surface of the primary Fe90Sc10 glassy nanoparticles. This behavior was found to be consistent with theoretical results based on a monolayer model for surface segregation behavior of the binary liquid alloys. In addition, the heterogeneous structure of Fe90Sc10 nanoglasses with Fe enriched interfaces was also directly observed, and may be attributed to the segregation of the primary glassy nanoparticles on the surface. Furthermore, the electron density of the isolated and loosely compacted primary glassy nanoparticles was investigated using small- and wide- angle X-ray scattering. The results indicate that the surface shells of glassy nanoparticles have an electron density that is lower than the electron density in the cores of the glassy nanoparticles. The lower electron density seems to result mainly from a lower atomic packing density of the surface shells rather than from compositional variations due to the surface segregation. During the consolidation of the glassy nanoparticles, the inhomogeneous elemental distribution and the short-range order in the shells of Fe90Sc10 glassy nanoparticles can be transferred into the interfaces of the resulting bulk Fe90Sc10 nanoglasses. The free volume within the shells of the Fe90Sc10 glassy nanoparticles may delocalize into the interfaces between the Fe90Sc10 glassy nanoparticles resulting in interfacial regions of lower atomic packing density in the Fe90Sc10 nanoglasses. The structural stability of Fe90Sc10 nanoglasses has been studied by means of low temperature annealing in situ in a transmission electron microscope, and ex situ in an ultra-high-vacuum tube-furnace. The analysis of both experiments showed similar results. The structure of the Fe90Sc10 nanoglasses was stable for up to 2 hours when annealed at 150 °C. Annealing of nanoglasses at higher temperatures resulted in the formation of a metastable nanocrystalline bcc-Fe(Sc) with Sc-enriched interfaces. The crystallization process of Fe90Sc10 nanoglasses was clarified and a plausible mechanism for the structural stability was proposed

Synthesis and Surface Modification of Inorganic Nanoparticles for Application in Physics and Medicine

The core focus of this cumulative thesis is the synthesis, the characterization, and the polymer coating or the surface modification of different types of inorganic nanoparticles (NPs), e.g., semiconductor, magnetic, plasmonic, and titanium oxide NPs. These NPs are used in the field of physics, biotechnology, and in nanomedicine or life sciences for both diagnosis and therapy. The applications of these NPs depend on their unique properties, which are correlated to their size, shape, and the material composition. The colloidal stability of these nanocrystals or NPs in different media (e.g. organic, water, cell culture media) was achieved by means of capping agents or by wrapping suitable ligands or surfactants around the core of the NPs. The colloidal NPs that were synthesised during this research work were capped with hydrophobic ligands (e.g. oleic acid, oleylamine, etc.) to keep them stable in the organic media, e.g., toluene, chloroform, etc. The phase transfer from organic to aqueous is a mandatory step prior to their use in the few desired applications, especially when these NPs are exposed to aqueous medium or cell media. This is carried out by wrapping the NPs with an amphiphilic polymer, i.e., poly(isobutylene-alt-maleic anhydride) (Mw= 6000 Da) that is grafted with hydrophobic side chains of dodecylamine. The mentioned four types of produced NPs were: (i) Semiconductor NPs which include the hydrophobic cadmium sulfide (CdS) quantum dots (QDs) that are used: for organic scintillation neutrino detection experiments; for PPO (2, 5-diphenyloxazole) styrene based plastic scintillator detectors; for time resolved spectral measurement, and for fluorescence studies with different surface coatings; additionally, water soluble CdS, manganese doped CdS, and zinc sulphide (ZnS) with and without manganese doping were synthesized and engineered to run several experiments on nanomaterials’ (NMs) behavior in environmental media, e.g., river and lake water; (ii) magnetic NPs (MNPs) that include core only (iron oxide, e.g. magnetite) and core shell composite iron oxide magnetic NPs combined with cobalt and manganese ferrites; (iii) plasmonic NPs such as gold and silver NPs that were used in combination with iron-oxide NPs (4 nm each) for toxicity screening and dose determination assays, and (vi) titanium dioxide iv (TiO2) NPs with different sizes and shapes (i.e. cube, rods, plates, and bipyramids), which were used for in vivo experiments: To evaluate the bio-distribution, organ accumulation, biological barrier passage, and potential organ toxicity after a single intravenous administration of TiO2 NPs, and to assess the influence of the TiO2 NPs shape and geometry on the mentioned effects. Furthermore TiO2 NPs were also used to perform few more in vivo studies to investigate: (i) The effect of biological environment (e.g. lung lining liquid, saliva, gastric/intestinal fluids) on NPs’ behaviour and toxicity, using complex co-culture systems for the intestine and alveoli, (ii) the effect of NPs on the activation of the inflammasome, and (iii) the influence of NPs on the maturation and activation of dendritic cells. In addition to above mentioned experiments for synthesis and surface modification another study was carried out with the aim to transfer three different types of NPs (i.e. plasmonic, fluorescent and magnetic) in aqueous phase to be employed in hydrogels, aerogels, and heterogels applications. In this study bimetallic (gold-copper) plasmonic nanocubes, fluorescent (cadmium selenide/CdS) core shell nanorods and magnetic iron oxide (Fe3O4) nanospheres were successfully transferred to the aqueous phase irrespective of their different sizes ranging from 5-40 nm in at least one dimension. All water soluble NPs were cleaned by means of gel electrophoresis or by ultracentrifugation to get rid of micelles (empty polymer) followed by sterilization for all in vivo studies. The qualitative and quantitative analyses all of these NPs were performed by means of different characterization techniques, e.g., ultraviolet-visible spectroscopy, fluorescence spectroscopy, dynamic light scattering, zeta potential measurements gel electrophoresis, transmission electron microscopy, inductively coupled plasma mass spectrometry, and the X-ray diffraction analysis

Renormalization: an advanced overview

We present several approaches to renormalization in QFT: the multi-scale analysis in perturbative renormalization, the functional methods \`a la Wetterich equation, and the loop-vertex expansion in non-perturbative renormalization. While each of these is quite well-established, they go beyond standard QFT textbook material, and may be little-known to specialists of each other approach. This review is aimed at bridging this gap.Comment: Review, 130 pages, 33 figures; v2: misprints corrected, refs. added, minor improvements; v3: some changes to sect. 5, refs. adde

Formation of Si Nanocrystals for Single Electron Transistors by Ion Beam Mixing and Self-Organization – Modeling and Simulation

The replacement of the conventional field effect transistor (FET) by single electron transistors (SET) would lead to high energy savings and to devices with significantly longer battery life. There are many production approaches, but mostly for specimens in the laboratory. Most of them suffer from the fact that they either only work at cryogenic temperatures, have a low production yield or are not reproducible and each unit works in a unique way. A room temperature (RT) operating SET can be configured by inserting a small (few nm diameters) Si-Nanocrystal (NC) into a thin (<10 nm) SiO2 interlayer in Si. Industrial production has so far been excluded due to a lack of manufacturing processes. Classical technologies such as lithography fail to produce structures in this small scale. Even electron beam lithography or extreme ultraviolet lithography are far from being able to realize these structures in mass production. However, self-organization processes enable structures to be produced in any order of magnitude down to atomic sizes. Earlier studies realized similar systems using a layer of Si-NCs to fabricate a non-volatile memory by using the charge of the NCs for data storage. Based on this, it is very promising to use it for the realization of the SET. The self-organization depends only on the start configuration of the system and the boundary conditions during the process. These macroscopic conditions control the self-formed structures. In this work, ion beam irradiation is used to form the initial configuration, and thermal annealing is used to drive self-organization. A Si/SiO2/Si stack is irradiated and transforms the stack into Si/SiOx/Si by ion beam mixing (IBM) of the two Si/SiO2 interfaces. The oxide becomes metastable and the subsequent thermal treatment induces selforganization, which might leave a single Si-NC in the SiO2 layer for a sufficiently small mixing volume. The transformation of the planar SiOx layer (restriction only in one dimension) into a small SiOx volume (restriction in all three dimensions) is done by etching nanopillars with a diameter of less than 10nm. This forms a small SiOx plate embedded between two Si layers. The challenge is to control the self-organization process. In this work, simulation was used to investigate dependencies and parameter optimization. The ion mixing simulations were performed using binary collision approximation (BCA), followed by kinetic Monte Carlo (KMC) simulations of the decomposition process, which gave good qualitative agreement with the structures observed in related experiments. Quantitatively, however, the BCA simulation seemed to overestimate the mixing effect. This is due to the neglect of the positive entropy of the Si-SiO2 system mixing, i.e. the immiscibility counteracts the collisional mixing. The influence of this mechanism increases with increasing ion fluence. Compared to the combined BCA and KMC simulations, a larger ion mixing fluence has to be applied experimentally to obtain the predicted nanocluster morphology. To model the ion beam mixing of the Si/SiO2 interface, phase field methods have been applied to describe the influence of chemical effects during the irradiation of buried SiO2 layers by 60 keV Si+ ions at RT and thermal annealing at 1050°C. The ballistic collisional mixing was modeled by an approach using Fick’s diffusion equation, and the chemical effects and the annealing were described by the Cahn Hilliard equation. By that, it is now possible to predict composition profiles of Si/SiO2 interfaces during irradiation. The results are in good agreement with the experiment and are used for the predictions of the NCs formation in the nanopillar. For the thermal treatment model extensions were also necessary. The KMC simulations of Si-SiO2 systems in the past were based on normed time and temperature, so that the diffusion velocity of the components was not considered. However, the diffusion of Si in SiO2 and SiO2 in Si differs by several orders of magnitude. This cannot be neglected in the thermal treatment of the Si/SiO2 interface, because the processes that differ in speed in this order of magnitude are only a few nanometers apart. The KMC method was extended to include the different diffusion coefficients of the Si-SiO2 system. This allows to extensively investigate the influence of the diffusion. The phase diagram over temperature and composition was examined regarding decomposition (nucleation as well as spinodal decomposition) and growing of NCs. Using the methods and the knowledge gained about the system, basic simulations for the individual NC formation in the nanopillar were carried out. The influence of temperature, diameter, and radiation fluence was discussed in detail on the basis of simulation results

Interaction of Ion Beam with Si-based Nanostructures

Silicon has been the fundamental material for most semiconductor devices. As Si devices continue to scale down, there is a growing need to gain a better understanding of the characteristics of Si-based nanostructures and to develop novel fabrication methods for devices with extremely small dimensions. Ion beam implantation as a ubiquitous industrial method is a promising candidate for introducing dopants into semiconductor devices. Although the interactions between ion beams and Si nanostructures have been studied for several decades, many questions still remain unanswered, especially when the size of the target structure and the interaction volume of the incident ion beam have similar extents. Recent studies have demonstrated different potential use cases of ion beam interactions with Si nanostructures, such as Si nanocrystals (SiNCs). One of them is to use SiNCs embedded in a SiO2 layer as the Coulomb blockade for a single electron transistor (SET) device. In this work, we demonstrate the ion beam synthesis of SiNCs, as well as other ion beam interactions with Si-based nanostructures. To build the basic structure of a room-temperature SET, both conventional broad-beam implantation and a focused Ne+ beam from a helium ion microscope (HIM) were used for ion beam mixing. Subsequent annealing using rapid thermal processing (RTP) triggered phase separation and Ostwald ripening, where small nucleated Si clusters merge to form larger ones with the lowest surface free energy. Various ion implantation parameters were tested, along with different conditions during the RTP treatment. The SiNC structures were examined with energy-filtered transmission electron microscopy (EFTEM) to determine the optimum fabrication conditions in terms of ion beam fluence and thermal budget for the RTP treatment. Due to their small size and the resulting quantum confinement, SiNCs also exhibited optical activity, which was confirmed by photoluminescence spectroscopy on both broad-beam irradiated blank wafers and vertical hybrid nanopillar structures with embedded SiNCs. By scanning a laser probe over the sample and integrating the signal close to the emission peak, 1 μm-wide micropads with embedded SiNCs could be spatially resolved and imaged, demonstrating a new method of patterning and visualizing the SiNC emission pattern. To integrate SiNCs into vertical nanopillars for the fabrication of the SET, a fundamental study was conducted on the interaction between ions and vertical Si nanopillars. It was discovered that irradiating vertical Si nanopillars with ion fluence up to 2×1016 cm−2 immediately caused amorphization and plastic deformation due to the ion hammering effect and the viscous flow of Si during the irradiation. However, amorphization could be avoided by heating the substrate to above 350 °C, which promotes dynamic annealing. Several factors, including substrate temperature, ion flux, and nanostructure geometry, determine whether ion irradiation causes amorphization. Furthermore, at sufficiently high substrate temperatures, increasing ion fluence gradually reduced the diameter of the nanopillars due to forward sputtering from ions on the sidewalls. With a fluence up to 8×1016 cm−2 from broad-beam Si+, the diameter of Si nanopillars could be reduced by 50% to approximately 11 nm. Similar experiments were conducted on vertical nano-fin structures, which were thinned down to about 16 nm with Ne+ irradiation from the HIM. However, electrical measurements with scanning spreading resistance microscopy (SSRM) showed that the spreading resistance of the fins increased, even at a lower fluence of 2×1016 cm−2, which was too high for subsequent device integration. Nevertheless, these findings contributed to achieving the CMOS-compatible manufacturability of room-temperature SET devices and furthered our understanding of the fundamentals of ion interactions with Si nanostructures

Universal dynamics of rogue waves in a quenched spinor Bose condensate

Universal scaling dynamics of a many-body system far from equilibrium signals the proximity of the time-evolution to a non-thermal fixed point. We find universal dynamics connected with rogue-wave like events in the mutually coupled magnetic components of a spinor gas which propagate in an effectively random potential. The frequency of these caustics is affected by the time varying spatial correlation length of the potential, giving rise to an additional exponent $\delta_\mathrm{c} \simeq 1/3$ for temporal scaling, which is different by a factor $\sim 4/3$ from the exponent $\beta_V \simeq 1/4$ characterizing the scaling of the correlation length $\ell_V \sim t^{\,\beta_V}$ with time. As a result of the caustics, real-time instanton defects appear in the Larmor phase of the spin-1 system as vortices in space and time. The temporal correlations determining the frequency of instanton events to occur scale in time as $t^{\, \delta_\mathrm{I}}$. This suggests that the universality class of a non-thermal fixed point could be characterized by different, mutually related exponents defining the coarsening evolution in time and space, respectively. Our results have a strong relevance for understanding pattern coarsening from first principles and potential implications for dynamics ranging from the early universe to geophysical dynamics and micro physics