In situ observations of nanoparticle precipitation during cooling in Inconel 718
Dunyong Deng (IEI, LiU), Kunpot Mopoung (IFM, LiU), Per Persson (IFM, LiU), Johan Moverare (IEI, LiU)
As a powder bed based additive manufacturing (AM) method, sometimes also referred to as 3D printing, electron beam melting (EBM) builds components in a layer-by-layer fashion. This is done at high vacuum and relatively high temperatures and has been widely applied to e.g. Nickel-based superalloys, such as Inconel 718 (IN718). IN718 has 5% of niobium (Nb) which contributes to strength from precipitation of γ’’- Ni3Nb phase. However, due to its poor diffusivity, Nb is prone to segregate to the interdendritic region during solidification and forms detrimental Laves - (Ni,Fe,Cr)2(Nb,Mo,Ti) phase. Our primary studies on EBM IN718 have confirmed the heterogeneous distribution of different phases and precipitates along the building direction, as shown in the Figure below, which is related to the varied thermal history that different locations experienced during processing. How to correlate this microstructural gradient in EBM material to the thermal history is an important prerequisite in order to understand the EBM process comprehensively. However, this is a topic that has not been addressed to a great extent in published literatures. Thus, the project is motivated to address the following questions:
1. What are the precipitates at different distances from the top surface?
2. Given that during the process, the base plate of the chamber is kept at 1000 °C, how long time does it take to dissolve the detrimental Laves phase and homogenize the microstructure? With the aid of In-situ TEM observation, mapping the evolution of certain elements distribution is possible, and would generate valuable thermodynamic data for development of a homogenization model for the EBM IN718 process.
3. During the in-situ annealing of Laves phase, would the release of Nb to the matrix lead to precipitation of δ phase? The aim is also to study how the γ’’ and γ’ phases precipitate during the cooling down stage after the EBM process? By applying different cooling schemes, the precipitation dynamics of γ’’ and γ’ will be monitored and compared.
In general, the knowledge from this study have a potential to improve EBM process, both in terms of processing speed and material quality and performance.
TEM bright field images showing the heterogeneous precipitates at different locations: (a) 10 µm, (b) 50 µm and (c) 1.5 cm from the top surface of EBM IN718 sample.
High performance light-emitting diodes based on nanometer-sized perovskite crystallites
Heyong Wang, Yong Yu, Mats Fahlman, Feng Gao (IFM, LiU)
Energy saving is one of the most important topics in recent years. The EU has set itself an energy efficiency target of >27% by 2030. Considering that displays and lighting in daily life accounts for a substantial proportion of energy consumption, efficient light-emitting devices (LEDs) will play an important role in reducing energy consumption. Recently, a new type of LEDs based on organometallic halide perovskites (PeLEDs) has been proposed. The figure below shows the crystal structure of 3D perovskites, which can be described by a chemical formula AMX3. The PeLEDs are solution processable and the emission color of perovskites can be tuned and hence constitute a new route towards low-cost and efficient displays and lighting. In this proposal, we aim to develop new ways to form uniform and ultra-flat perovskite films with nanometer-sized grains, allowing us to realize highly efficient PeLEDs. We will use additives in the 3D perovskite precursor solution to impede the growth of 3D perovskite grains and consequently decrease the grain size to < 10 nm. The reduced grain size would spatially confine electrons and holes and thus enhance bimolecular radiative recombination. Uniform perovskite films can also be anticipated based on these nanometer-sized grains, paving the way to realize high performance PeLEDs. We additionally will study the defects in the 2D/3D perovskite films, their nature and how they are influenced by growth conditions in order to optimize the films for use in PeLEDs, while also obtaining basic understanding of the film-forming process that can be used in other perovskite-based applications.
Polyhedral structure of perovskites
Experimental characterization and theoretical modelling of the antioxidant/catalytic properties of cerium oxide nanoparticles
Peter Eriksson, Alexey Tal, Weine Olovsson, Igor Abrikosov, Zhangjun Hu, Kajsa Uvdal (IFM , LiU)
In this project we are combining efforts from experimental characterization and theoretical modelling in order to achieve a better knowledge of the redox capability of cerium oxide nanoparticles (CeNPs). The redox capabilities have found to have high potential use in fuel cells, catalysis and also as antioxidant in biomedicine. However, the redox mechanism has not been fully understood. In last year’s Cenano-project, we successfully characterized the oxidation states of CeNPs by utilizing X-ray absorption near edge structures (XANES)-spectroscopy and verified the achieved XANES-spectra with theoretical ab initio modelling. This year we will experimentally and theoretically investigate the redox-reaction by using UV-VIS absorption spectroscopy, enabling real-time monitoring, and thereby be able to study dynamic oxidation state shifts of CeNPs.
Graphene-nanoparticle hybrid gas sensor
Marius Rodner, Rickard Gunnarsson, Ulf Helmersson, Jens Eriksson (IFM, LiU)
Two-dimensional materials, such as graphene, offer a unique platform for sensing where extremely high sensitivity is a priority, making them highly useful as gas sensors for detection of chemicals relevant to human health in the scope of air quality control. The Applied Sensor Science Unit at IFM has previously demonstrated that with the right amount of surface decoration with metal/oxide nanoparticles the surface chemistry can be modified to improve sensitivity, selectivity and speed of response toward, e.g., nitrogen dioxide (NO2) and toxic volatile organic compounds such as benzene and formaldehyde. The Plasma & Coatings Physics Division at IFM uses a newly invented technique that provides a new route to decorate materials with an expanded control of the decoration process with different nanomaterials. In this collaboration, we intend to place nanoparticles with different properties (size, composition, etc.) at selected positions on the epitaxial graphene on SiC substrates to investigate the change in sensitivity/selectivity towards different gases to ultimately use different assemblies for a sensor array. We aim to apply these approaches to graphene, the most sensitive transducer material in existence. The technology of epitaxial graphene on SiC, pioneered at LiU, will be leveraged to fabricate highly sensitive and reproducible sensor transducers on uniform monolayer graphene, a prerequisite for optimum sensitivity. Besides the evaluation of the produced chips as promising gas sensors also the surface is examined towards changes in morphology, e.g., using an atomic force microscope or Raman spectroscopy and Raman feature mapping before and after the decoration with nanoparticles.
Utilization of surface directed spinodal decomposition to design nanorod based opto-electronic devices
Elena Alexandra Serban, Fei Wang, Ferenc Tasnadi, Jens Birch, Ching-Lien Hsiao (IFM, LiU)
We will develop novel concepts in controlling the formation of superlattices (SLs) and core shell inside ternary III-nitride nanorods for optoelectronic devices, see Fig. 1. Our approach is to utilize the surface directed spinodal decomposition (SDSD) occurring in metastable InAlN nanostructures, see Fig. 2. A positive effects of the inherent phase instability of InAlN alloys is the facilitation of forming self-organized SLs in thin films and core-shell nanorod structures under specific growth conditions or post-heating treatment. We will understand the role of SDSD in the formation mechanism of InAlN SLs by (i) manipulating growth conditions, (ii) in-situ heating in scanning transmission electron microscope (STEM), and (iii) theoretical simulations.
In situ spectroscopic ellipsometry as a tool to study reductive surface chemistry in plasma CVD
Hama Nadhom, Andreas Jamnig, Kostas Sarakinos, Henrik Pedersen (IFM, LiU)
Metallic thin films play a crucial role as interconnects and barriers in nanoelectronics, where device miniaturization drives increasing demand for conformal film deposition on complex-shaped structures. Conformal film growth is facilitated by self-limiting chemical vapor deposition (CVD) techniques, which constitute a challenge for many of the first row transition metals as they are hard to reduce from ionic to metallic form. Newly started research at IFM seeks to understand the propensity of energetic electrons in pulsed plasmas to reduce metal centers in adsorbed molecules, and explore the viability of an altering adsorbing/reducing surface chemistry to enable self-limiting deposition of metal thin films. (Fig. 1) This CeNano project will study the dynamics of the adsorption of precursor molecules on the substrate surface, by in situ spectroscopic ellipsometry (SE) (Fig. 2). This is a first step towards understanding complex chemical interactions that result in the formation of metallic films using pulsed plasmas. Once the viability of this approach is established, SE can also serve as a tool to monitor the completeness of ligand removal in the plasma-on phase of the deposition cycle, which is crucial to minimize film contamination.
Theoretical characterization of point defects in silicon carbide and other materials
Joel Davidsson, Björn Lundqvist, Viktor Ivady, Rickard Armiento, Igor Abrikosov (IFM, LiU)
Effective engineering of materials defects and defect properties on the atomic (nano-) scale is crucial to create materials for applications in nanotechnology, i.e., ultra miniaturization of sensors, storage, processing, and communication. Silicon carbide (SiC) is a large bandgap semiconductor that have been in focus recently for its potential for applications in quantum information processing. It appears possible to engineer defects in SiC with optical and spin properties that are suitable as single photon sources, and states with long enough lifetime to act as qubit memory. We will generate defect supercells of impurities, interstitials, vacancies, and their complexes and do a systematic large-scale study using ab-initio calculations to enumerate a wide range of point defect properties, in particular, photoluminescence lines and thermodynamical stability. This will generate a dataset useful for identifying defects seen in experiments, explain their physics, and for finding out how to engineer defects with desired properties to target a range of possible nanotechnology applications. Our aim is to develop tools that allows us to extend the study to any material of interest.
Illustration of how generated supercells of C and Si vacancies in 4H-SiC are used to predict photoluminescence lines useful for identifying these defects. We will build a dataset for hundreds of defects in SiC and other materials.
Nanostructured single phase CaMnO3 thin films for thermoelectric applications
Erik Ekström, Johan Klarbring, Sergei Simak, Per Eklund (IFM, LiU)
Thermoelectric devices generate electricity from a temperature gradient across the device. In recent years, there has been a growing interest in oxide materials as thermoelectrics. While they are generally less efficient than conventional thermoelectric materials, their high chemical and thermal stability allow for their use in applications where other materials fail, for instance, in high temperature waste heat recovery where heat is converted to useful electricity.
In this project, we will study thin films of CaMnO3 which is one of the most promising n-type oxide thermoelectric materials. We will use a twinned theoretical/experimental approach to study the main factors influencing the thermoelectric efficiency of CaMnO3 thin films, namely phase stability, thermal conductivity and nanostructure formation.
Phase stability in CaMnO3: (Left) Phonon dispersion relation of CaMnO3 in the cubic perovskite phase showing two unstable phonon modes at the M and R points. (Middle) Illustration of the two unstable phonon modes which yields the orthorhombic perovskite-like ground state structure of CaMnO3 (right).
Characterization of Neutrophil Extracellular Traps (NETs) formation on iron oxide and titanium oxide nanoparticle based surfaces
Andreas Skallberg, Rickard Gunnarsson, Sebastian Ekeroth, Ulf Helmersson, Kajsa Uvdal (IFM, LiU)
Neutrophils are white blood cells and a predominant part of the innate immune system. They are short-lived compared to e.g. cells in tissue and they quickly respond to and become activated following a microbial threat. Neutrophils have the capacity to engulf microbes and release anti-microbials to kill invading pathogens. Neutrophils have lately shown to have an additional strategy to attack a possible threat, which is the release of extracellular fibers, primarily composed of granule proteins and chromatin, to form Neutrophil Extracellular Traps (NETs). The underlying mechanism of NET formation is not fully understood. Up until today only a few publications report on neutrophil responses upon nanoparticle treatment. NP parameters affecting the neutrophil behavior are indicated to be composition, size and shape. Neutrophils have several possible pathways leading to activation and it is not known if NPs of various composition triggers activation in the same manner. In the present project we will have the possibility to more precisely control the density of nanoparticles on a surface and correlate this to neutrophil responses such as NET formation. We now have the possibility to in detail study differences in neutrophil activation, signaling and characterizing NET formation on the nanoscale which may e.g. give important information on potential nanotoxicity.
Energy-filtered PEEM images of neutrophils deposited on iron oxide (a) and titanium oxide (b) nanostructured surfaces acquired at E-EF = 4.0 eV, showing NETs formation. Highlighted representation of NETs formation on iron oxide (c) and titanium oxide (d) nanostructured surfaces
Exploring surface functionalized MXene for spin/polarization-sensitive optoelectronic applications
Yuqing Huang, Quanzheng Tao, Johanna Rosen, Weimin Chen (IFM, LiU)
MXenes, a series of newly developed two-dimensional transition metal carbides, have attracted intense attention in many research fields ranging from energy storage to sensor applications. Recently, a 2D topological insulating (TI) phase has been predicted in MXene with the advantage of tunability by surface functionalization. Such “flexible” TI phase, once confirmed, would greatly benefit the TI research and could give rise to potential applications in spin/polarization-sensitive optoelectronics. Additionally, low dimensionality of the material can lead to breaking of local inversion symmetry, which is also critical for the generation of spin/polarization dependent photocurrent.
In this research program, we aim for fabrication and functionalization of monolayer MXene devices for spin/polarization sensitive optoelectronic applications, which will be tested by analyzing the polarization-dependent photocurrent as well as polarization resolved nonlinear optics. The program covers material synthesis/functionalization, micro device fabrication and characterization, as schematically illustrated in Fig. 1.
Fig.1 (a) Summary of our research program, and (b) a schematic illustration of a spin/polarization-sensitive optoelectronic device exploring the potential TI phase in MXene.