Microscopy Conference 2017 (MC 2017) - Proceedings

Das Dokument enthält die Kurzfassungen der Beiträge aller Teilnehmer an der Mikroskopiekonferenz "MC 2017", die vom 21. bis 25.08.2017, in Lausanne stattfand

Microscopy Conference 2017 (MC 2017) - Proceedings

Das Dokument enthält die Kurzfassungen der Beiträge aller Teilnehmer an der Mikroskopiekonferenz "MC 2017", die vom 21. bis 25.08.2017, in Lausanne stattfand

Ultra-high-resolution optical imaging for silicon integrated-circuit inspection

This thesis concerns the development of novel resolution-enhancing optical techniques for the purposes of non-destructive sub-surface semiconductor integrated-circuit (IC) inspection. This was achieved by utilising solid immersion lens (SIL) technology, polarisation-dependent imaging, pupil-function engineering and optical coherence tomography (OCT). A SIL-enhanced two-photon optical beam induced current (TOBIC) microscope was constructed for the acquisition of ultra-high-resolution two- and three-dimensional images of a silicon flip-chip using a 1.55μm modelocked Er:fibre laser. This technology provided diffraction-limited lateral and axial resolutions of 166nm and 100nm, respectively - an order of magnitude improvement over previous TOBIC imaging work. The ultra-high numerical aperture (NA) provided by SIL-imaging in silicon (NA=3.5) was used to show, for the first time, the presence of polarisation-dependent vectorialfield effects in an image. These effects were modelled using vector diffraction theory to confirm the increasing ellipticity of the focal-plane energy density distribution as the NA of the system approaches unity. An unprecedented resolution performance ranging from 240nm to ~100nm was obtained, depending of the state of polarisation used. The resolution-enhancing effects of pupil-function engineering were investigated and implemented into a nonlinear polarisation-dependent SIL-enhanced laser microscope to demonstrate a minimum resolution performance of 70nm in a silicon flip-chip. The performance of the annular apertures used in this work was modelled using vectorial diffraction theory to interpret the experimentally-obtained images. The development of an ultra-high-resolution high-dynamic-range OCT system is reported which utilised a broadband supercontinuum source and a balanced-detection scheme in a time-domain Michelson interferometer to achieve an axial resolution of 2.5μm (in air). The examination of silicon ICs demonstrated both a unique substrate profiling and novel inspection technology for circuit navigation and characterisation. In addition, the application of OCT to the investigation of artwork samples and contemporary banknotes is demonstrated for the purposes of art conservation and counterfeit prevention

Advanced Anode and Cathode Materials for Li-ion Batteries: Application to Printing Methodology

Batteries play an important role in energy storage applications spanning from electric vehicles, portable electronic devices to stationary storage grids. Basic structure of a lithium-ion battery (LIB) consists of two electrodes; the anode and the cathode separated by an ion-conductive electrolyte. With the advent of portable electronic products (such as internet of things, IoT), there is a growing need for rechargeable batteries with smaller size, smaller weight and higher energy densities. In recent years, inkjet printing has intrigued with the introduction of solution processed printed electronics (PE). PE and printed batteries have gained interest because they are inexpensive, easy to fabricate, up-scalable for large production and printing is possible on various kinds of substrates. Most research efforts strive for “better” batteries with high reversible capacities or the enhancement of the capacities of the state-of-the-art battery systems. Printing is a fast and inexpensive process and printed batteries with lower thickness values could be developed with the printing technique. The battery ink formulation can be tuned during printing procedure to achieve capacity and potential required for fully printed circuit. The demand for batteries that are thinner, and lighter with higher energy density has motivated the research into the next generation LIB electrodes, some of which will be explored in this work. The first focus of this dissertation is on the development of an alloying type anode material for the LIB, namely silicon (Si) and the assessment of its electrochemical and structural characteristics. The printability of Si/C anode inks and the effect of carbon coating on the improvement of the cycling process are analyzed. Later a full cell comprising of printed Si/C anode and NCM is fabricated. This full cell was used to deliver power to a printed electrolyte gated graphene transistor. In the next part of this work, a new material class was developed, namely the high entropy fluorides (HEFs). To realize the printed full cell battery a printed cathode was needed, so a conversion cathode material composed of fluoride-based materials was formulated. Collectively, high entropy materials (HEMs) consist of the solid solution of various elements, homogenously distributed. HEF based materials were synthesized via a facile direct mechanochemistry route that can be used to incorporate multiple cations in a single-phase rutile structure. Due to high electronegativity of fluorine, transition metal fluorides are interesting candidates for cathode materials because of their high theoretical capacity (>571 mAh/g) in contrast to the conventional intercalation cathodes. The multi-cation substitution may provide a new path for tailorable electrochemical properties of the conversion electrodes via entropy effects. However, the underlying conversion reaction mechanisms in the HEFs are yet to be explored and this forms the second part of this study. The comprehensive examination shows that HEF cathodes follow a conversion reaction mechanism and the capacity loss occurs due to kinetically limiting factors affecting the cathode side. For investigating the performance of the batteries, various electrochemical methods such as galvanostatic cycling, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) are applied. A variety of structural characterization techniques were also employed to confirm the phase purities of electrode materials. Fabrication of batteries via printing was followed in this dissertation. Thickness of printed batteries are in millimeters range due to their reduced size and it can act as a power source for printed electronics. Finally, a full cell with carbon coated Si/C anode and HEF cathode is assembled and the viability of a completely printed full cell is demonstrated

The Growth and Morphology of Small Ice Crystals in a Diffusion Chamber

Small water ice crystals are the main component of cold tropospheric clouds such as cirrus. Because these clouds cover large areas of our planet, their role in the radiation budget of incoming and outgoing radiation to the planet’s surface is important. At present, the representation of these clouds in climate and weather models is subject to improvements: a large part of the uncertainty error stems from the lack of precise micro-physical and radiation model schemes for ice crystal clouds. To improve the cloud representations, a better understanding of the life time dynamics of the clouds and their composition is necessary, comprising a detailed understanding of the ice particle genesis, and development over their lifetime. It is especially important to understand how the development of ice crystals over time is linked to the changes in observable variables such as water vapour content and temperature and how they change the light scattering properties of the crystals. Recent remote and aircraft based in-situ measurements have shown that many ice particles show a light scattering behaviour typical for crystals having rough surfaces or being of complex geometrical shapes. The aim of this thesis was to develop the experimental setup and experiments to investigate this further by studying the surface morphology of small water ice crystals using scanning electron microscopy (SEM). The experiments I developed study the growth of water ice crystals inside an SEM chamber under controlled environmental conditions. The influence of water vapour supersaturation, pressure and temperature is investigated. I demonstrate how to retrieve the surface topology from observed crystals for use as input to computational light scattering codes to derive light scattering phase functions and asymmetry parameters, which can be used as input into atmospheric models. Difficulties with the method for studying the growth of water ice crystals, such as the effect of the electron beam-gas ionization and charging effects, the problem of facilitating repeated and localized ice growth, and the effect of radiative influences on the crystal growth are discussed. A broad set of nucleation target materials is studied. In a conclusion, I demonstrate that the method is suitable to study the surface morphologies, but is experimentally very challenging and many precautions must be taken, such as imaging only once and preventing radiative heat exchange between the chamber walls and the crystals to avoid unwanted effects on the crystal morphology. It is also left as a question if a laboratory experiment, where crystals will need to be grown in connection to a substrate, can represent the real world well enough. Deriving the required light scattering data in-situ might be an alternative, easier way to collect data for modelling use

Silicon doped boron carbide for armour

Boron carbide is a popular candidate armour ceramic. During high velocity impact, however, amorphous bands form, leading to the collapse of the structure, and reducing the usefulness of boron carbide in such applications. Recent experimental data from the literature suggests that silicon (Si) doping of boron carbide nanowires reduces this amorphisation. This project focuses on creating a process for Si doping of boron carbide that could potentially be up-scaled to commercial quantities. As shown in this thesis, as long as free carbon, or, in fact, carbon-rich boron carbide is present, Si additions react with carbon to form silicon carbide. Therefore, three methods for reducing the carbon content in boron carbide powders were investigated: plasma cleaning, oxidation/reduction, and annealing in the presence of amorphous boron (B). This resulted in a range of boron carbide powders with various carbon contents covering a wide range of the phase diagram. The effect on the structure of the powder will be discussed. Si was mixed with these boron carbides, and evidence for Si-doped boron carbide phase B12(C,Si,B)3 was found in many of the powders produced, as well as with additional phases. An enhancement of the doping correlated with a reduction in initial carbon content for a comparable concentration of Si. A promising result of the reduction of the amorphisation on the doped powder was confirmed for one condition after high pressure diamond anvil testing. Similarly, the reduction of amorphisation was also confirmed by indentation at the interface of a diffusion couple formed from a wafer of Si annealed at 1400 °C between two pieces of boron carbide. The boron carbide at the interface exhibited Raman features similar to the Si-doped powder. These results of powder and interface suggest that a new type of lightweight armour material could be produced that overcomes one of the biggest challenges of this ceramic: the amorphisation.Open Acces

MC 2019 Berlin Microscopy Conference - Abstracts

Das Dokument enthält die Kurzfassungen der Beiträge aller Teilnehmer an der Mikroskopiekonferenz "MC 2019", die vom 01. bis 05.09.2019, in Berlin stattfand

In situ and Ex situ TEM Studies of Fluoride Ion Batteries

Lithium ion batteries (LIBs) are widely used for portable electronics. However, their application is limited because of energy density, safety issues, and the high cost. This necessitates a search for alternative battery technologies. Many alternative battery systems are currently investigated based on different chemistries, which include sodium, magnesium, chloride, aluminum, and potassium based batteries. Rechargeable batteries based on a fluoride anion shuttle are a promising alternative to Li-ion batteries with theoretical energy densities of more than 5000 WhL-1. However, detailed chemical and structural investigations are necessary to understand the structural changes and the degradation mechanisms to improve the performance of fluoride ion batteries. In the present thesis, TEM has been used to study all-solid-state fluoride ion batteries in situ and ex situ. For in situ TEM studies, two all-solid-state fluoride ion battery systems were used; a half-cell consisting of a Bi composite as electrode and La0.9Ba0.1F2.9 as a solid electrolyte; and a full cell consisting of a Cu composite as cathode, a MgF2 composite as anode, and La0.9Ba0.1F2.9 as a solid electrolyte. Optimization of sample preparation was an essential step to enable reliable in situ TEM studies during electrochemical biasing. Challenges during sample preparation, such as re-deposition/metal contamination, contact resistance, porosity of the battery materials and leakage current were resolved using an optimized FIB based approach. The successful preparation has been demonstrated for two fluoride ion battery systems. The in situ TEM studies of the half-cell revealed the fluorination of Bi and Bi2O3 forming BiF3 and BiO0.1F2.8, and the simultaneous reduction of La0.9Ba0.1F2.9 to La and Ba during charging. During discharging, most of the BiF3 was reduced to Bi metal. Comparing the structural changes with the electrochemical charging curve, the main phase formed was the irreversible phase BiO0.1F2.8, leading to the poor reversibility of the half-cell. On the other hand, the TEM studies of the cathode-electrolyte interface of the full cell revealed fluoride migration into the composite cathode during charging resulting in the formation of CuF2, which was absent in the as-prepared state. Due to the high volumetric changes associated with the CuF2 formation, the cell fractured at the cathode-electrolyte interface during the second charging. However, a detailed electrochemical study during discharging was problematic, as a short circuit between cathode and anode dominated the current. In addition, a fluoride ion battery system consisting of a CuF2 composite as cathode, La0.9Ba0.1F2.9 as a solid electrolyte, and a La sheet as anode was studied ex situ in the as-prepared, discharged, and recharged states. The interfacial studies were performed by lifting-out two lamellae from each pellet at the electrodes-electrolyte interfaces using FIB. The TEM studies of the cathode confirmed the defluorination/fluorination during cycling of CuF2/Cu. However, the TEM studies revealed a high oxygen content in the cathode composite explaining the difference between the theoretical capacity of Cu/CuF2 (528 mAh g-1) and the observed capacity during the first discharge (360 mAh g-1). On the anode side, the presence of La2O3 on the surface led to a side reaction by LaOF formation during recharging, which acts as a significant fluoride trap. Therefore, the capacity faded upon cycling to only 165 mAh g-1 in the second discharge. Moreover, The STEM-EDX maps revealed Cu diffusion from the cathode into the electrolyte due to the high volumetric change in the cathode, partially explain the capacity fading