Synthesis and characterization of chiral organic nanostructures
Lía Fernández del Río, Kenneth Järrendahl (IFM, LiU)
The PhD-project is dedicated to studies of natural systems using Mueller matrix ellipsometry (MMSE). The studies are based on the findings that many beetles in the superfamily Scarabaeoidea has cuticles with a chiral structure reflecting light with a high degree of circular polarization.
The main objectives have been
I) To understand the optical behaviour of the chiral nanostructures using MMSE.
II) To describe the structure behind these phenomena using optical and electron microscopy.
III) To mimic the nanostructures by synthesizing chitin structures and twisted III-nitride structures.
IV) To gain knowledge of the biological aspects of the optical phenomena.
Recent work include comparisons of the green and metallic-like parts of the cuticle for various Chrysina beetles. In the last phase of this PhD-project, emphasis will be on item II and IV. For IV we will develop a budding twinning work where Lía and PhD-student Jesper Fågelholm (supervised by Dominic Wright, IFM) will investigate feathers with similar green appearance as some beetles. Can the MMSE-data support the genetic studies of Red Junglefowl?
Images below are from the recent article: L. Fernández del Río, H. Arwin, K. Järrendahl, Polarizing properties and structure of the cuticle of scarab beetles from the Chrysina genus, Physical Review E 94 (2016) 012409 (DOI:http://dx.doi.org/10.1103/PhysRevE.94.012409)
Supramolecular coiled coil-based hybrid hydrogels for 3D cell culture of primary liver cells
Christopher Aronsson, Jonas Christoffersson, Daniel Aili, Carl-Fredrik Mandenius (IFM, LiU)
One of the major reasons for drug withdrawal during the pharmaceutical development process is hepatotoxicity. Many drug compounds are metabolized in the liver and even if the drug itself is not toxic the metabolite might be. To examine the effects of a new drug cell culture models are used before animal and human experiments to give a hint about the toxicity and efficacy of the compound. However, the complexity of organs is difficult to model in vitro. Standard cell culture models only provide a two dimensional (2D) surface for the cells which does not reflect how the cells are situated in vivo. Instead, the liver is built up by numerous liver lobules in the three dimensional (3D) space. The 3D orientation of liver cells has previously been shown to increase the expression of drug metabolizing enzymes, e.g. proteins belonging to the cytochrome P450 superfamily. This means that a 3D cell culture model could be of better use than 2D models during the pharmaceutical drug development process. Many different materials and methods for 3D cell culture have previously been reported, however, tuning the mechanical properties of the material for a specific cell type needs are often not possible in these systems. In this project, we will use a supramolecular coiled coil peptide-based hybrid hydrogel with tunable mechanical properties to study if primary liver cells shows an improved in vivo-like performance when grown in 3D compared to 2D. Furthermore, after optimization of the material to mimic the mechanical properties of the liver, drug toxicity studies will commence to compare this system with 2D systems.
Experimental characterization and theoretical modelling of the antioxidant/catalytic properties of cerium oxide nanoparticles
Peter Eriksson, Alexey Tal, Zhangjun Hu, Weine Olovsson, Igor Abrikosov, Kajsa Uvdal (IFM, LiU)
We are designing gadolinium-implemented cerium oxide nanoparticles (CeNPs) in order to combine antioxidant capability and contrast enhancement for Magnetic Resonance Imaging. Our aim in this specific project is to investigate the surface catalytic process by studying the electronical structure of CeNPs when swhitching between the 3+ and 4+ oxidative states (Ce3+ and Ce4+), and also consider the influence of oxygen vacancies. The oxidation levels are studied using Near Edge X-ray Absorption Fine Structure (NEXAFS) on the Ce M4,5 level and X-ray Photoelectron spectroscopy (XPS) on Ce 3d electrons. Theoretically modelling (ab initio modeling) will be used as necessary aid for interpretation of measured NEXAFS and XPS spectra. Ab initio modeling for CeO2 (cerium oxide) has been developed for the bulk system, however nanoparticles significantly differ from their bulk configurations. The methodology of ab initio calculations of CeO2 must be revised and its applicability to nano-sized systems must be investigated.
Exploring 2D topological insulating phase in surface functionalized MXene for spin-sensitive optoelectronic applications
Yuqing Huang, Quanzheng Tao, Johanna Rosén, Weimin Chen (IFM, LiU)
Topological insulator (TI) has been discovered as unique phase of matter where combining effect of spin-orbit interaction and time-reversal symmetry lead to appearing of helical surface/edge state that give rise to exotic physics and promising spintronic applications. Recently, band topology has been theoretically investigated in a series of newly developed two-dimensional (2D) transition metal carbides, named MXene. Along the effort, 2D TI phase has been predicted in the material with great flexibility enabled by tunable surface functionalization and material diversity, which would greatly benefit the TI research.
In this proposed research program, we study the spin dependent process associated with the potential TI phase in various MXene that would lead to novel spin-sensitive optoelectronic applications. The program is developed with cooperation between material synthesis/optimization that lay the material foundation and device characterization that resolves the underlying spin physics. Our aim and program is illustrated with the figure below.
Brief summary of a) material synthesis and functionalization b) spin-sensitive optoelectronic device exploring the potential TI phase in MXene.
Single-phased and nanostructured thin CaMnO3 films for thermoelectric and fuel cell applications
Johan Klarbring, Erik Ekström, Sergei Simak, Per Eklund (IFM, LiU)
Thermoelectric materials generate electricity from a temperature difference across the sample. This can be used to convert waste heat into useful electricity. Thermoelectric devices are thus expected to help providing electricity, for which there is an ever growing demand in the modern society. Good thermoelectric materials are good electric conductors that conduct heat poorly. A promising class of materials in this area is the perovskite-type oxides (see Figure). These materials, in addition to low thermal and high electronic conductivity, have high ionic conductivity and therefore could be promising not only as thermoelectrics but also as cathode materials in solid oxide fuel cells, which produce "green" electricity without polluting the environment.
In this project, we will investigate the prospects of one such material, CaMnO3. We will synthesize thin CaMnO3 films using RF magnetron sputtering. The films will be characterized using a number of techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The thermoelectric properties will be measured and analyzed. The experiments will be complemented by, and compared to, quantum mechanical calculations based on the density functional theory (DFT).
The orthorhombic perovskite-like crystal structure of CaMnO3. Red, purple and light blue spheres represents O, Mn and Ca ions, respectively.
Self-limiting surface chemistry by in situ spectroscopic ellipsometry
Hama Nadhom, Viktor Elofsson, 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. This CeNano project will study the dynamics of the adsorption of precursor molecules on the substrate surface, by in situ spectroscopic ellipsometry (SE). 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.
Thermoplasmonic hydrogels for controlled cell adhesion and cell patterning
Ranjithkumar Ravichandran (IFM, LiU), Mina Shiran Chaharsoughi (ITN, LiU), Magnus Jonsson (ITN, LiU), Jaywant Phopase (IFM, LiU)
Temperature controlled detachment of cells from pNIPAM hydrogels are well known. This is a result of the temperature-mediated structural reorganisation of the pNIPAM polymers caused by the hydrophobic to hydrophilic transition, reducing cell adhesion. Possibilities to precisely modulate hydrogel temperatures locally may facilitate selective patterning of cells and enable fundamental studies of cell-surface interactions, cell mechanobiology, and cell migration. We propose to address this by incorporating plasmonic gold nanorods (AuNRs) in our newly developed bio-polymeric thermoresponsive hydrogel, which acts as local nanoscale heat generators when irradiated at their plasmon frequency. Our objective is to utilize the AuNRs to dynamically tune the properties of the thermoresponsive hydrogels and thus the cellular interactions with the material.
A) Calcein staining (left) showing the temperature dependent detachment of Human Skeletal Muscle Cells from our thermoresponsive collagen hydrogel (red arrows). The right panel shows a bright field (BF) image of the same area. B) Simulation showing the local character of plasmonic heating. The figure shows the temperature distribution around a gold nanorod heated to 50°C from a surrounding of 20°C. (Unpublished data)
Polymorphic self-organized multiple quantum wells in III-N nanorods
Mathias Forsberg, Alexandra Serban, Ching-Lien Hsiao, Galia Pozina (IFM, LiU)
Stacking faults forming periodic quantum wells (QW) have been observed in GaN nanorods grown by DC magnetron sputtering. This QW structures show in photoluminescence (PL) a significantly different polarization response compared to the GaN exciton transition. Using time-resolved μ-PL, we aim to study dynamic and polarization properties of excitons in the bare nanorods and in the hybrid samples covered with polyfluorene. Expecting non-radiative resonant energy transfer (NRET) due to the Förster interaction between QW excitons and polyfluorene film together with polarization properties of emission could be of high importance for nano-photonic applications.
Snapshot on cell response on nanoparticles as a function of size, shape and surface density to capture the moment of initial immune response
Andreas Skallberg, Rickard Gunnarsson, Sebastian Ekeroth, Ulf Helmersson, Kajsa Uvdal (IFM, LiU)
Metallic nanoparticles have been widely studied and nanoparticulate-based applications are today available in areas such as medicine, energy and electronics. Nanoparticles in medical applications are very promising when scaling down the material i.e. due to enhanced surface to volume ratio, penetration ability of tissues and cells and capability for targeted drug delivery. Neutrophil granulocytes are inflammatory cells capable of inducing a strong immune response once they encounter a foreign object, e.g. as prepared non-coated nanoparticle. However, the cellular response is shown to be dependent upon several features of the nanoparticle, such as size, shape and surface density. In this project we will investigate cell response on nanoparticles as a function of size, shape and surface density of nanometer scaled structures of titanium oxide and iron oxide and capture the moment of initial immune response, among others. Taken together these experiments will show if and how shape, size and surface density of these nanometer scaled structures of titanium oxide and iron oxide modulate neutrophil cell response. Finally, surface functionalization of the nanoparticles followed by cell exposure will be investigated with NanoESCA. To our knowledge, no previous studies have evaluated cellular responses using NanoESCA.
(Left) Photo emitted electron microscopy image showing neutrophil deposit on a silicon surface. (Upper right) Schematic picture of as prepared titanium oxide nanoparticles prepared by plasma as a function of size. (Lower right) SEM images of increasing size and shape of nanometer scale structures of titanium oxide.
Theoretical study and attempt of synthesis of boron subnitride and boron subcarbonitride
Laurent Souqui, Annop Ektarawong, Björn Alling, Anne Henry (IFM, LiU)
Boron subnitride and boron subcarbonitride belong to the family of icosahedral boron-rich solids, exhibiting several outstanding properties, e.g. high hardness, high melting point, chemical inertness and low density, and thus being promising materials for a wide range of technological applications. Generally, high-temperature high-pressure techniques are used for synthesizing the subnitride [1, 2]. Theses methods, somehow, have a relatively low yield, thus limiting not only its utilization but also accessibility to the material’s properties. Consequently, several issues about the subnitride, e.g. crystal structure, stoichiometry, stability and properties, have not yet been unanimous among the community. The subcarbonitride, on the other hand, has been recently predicted and proposed to be
a new stable phase of icosahedral boron-rich solids [3], where its synthesis has never been reported in any experiment. In this project, the thermodynamic stabilities as a function of pressure and temperature, as well as the properties of these materials will be investigated, using first-principles calculations, which will then be served as a guideline for exploring possible routes for syntheses of the subnitride and subcarbonitride thin films, using chemical vapor deposition. The structures and properties of the as-synthesized films will then be characterized by X-ray diffraction technique, Xray photoelectron spectroscopy, and IR spectroscopy, and compared with the results, obtained from the calculations.
References
[1] H. Hubert, J. Solid State Chem. 133, 356 (1998).
[2] O. O. Kurakevych et al., Acta Cryst. C63, i80 (2007).
[3] H. Zhang et al., Phys. Rev. B. 93, 144107 (2016).
3-dimensional icosahedral network of boron subnitride and boron subcarbonitride on the nano-scale (left figure), built up of B12 icosahedra (white spheres) and inter-icosahedral chains (brown spheres), as a building block (right figure). The inter-icosahedral chains can either be N-B-N or N-V-N (V = vacancy) for boron subnitride, and are N-B-C and C-B-N for boron subcarbonitride, as proposed in Ref. [3].
Interfacial coherency and strength in nanostructured nitrides
Fei Wang, Kumar Yalamanchili, Naureen Ghafoor, Ferenc Tasnadi (IFM, LiU)
We tailor explore the interfacial physics of different transition metal nitride superlattices. Beyond the thermodynamic stability we characterize their response (deformation) to external force. Our novel concept is that finding the right interface orientation between the parent materials results in enhanced stability and improved strength, such as matching the LEGO bricks. The combination of different binary nitrides (TiN, TaN, ZrN, HfN, AlN, ScN, etc.) means different interfacial chemistry through the different interfacial orientations what can be tested by micropillar compression.
With ab-initio simulations we explore the interfacial chemistry in different transition nitride multilayers, see Figure. Beyond the perfect interfaces we aim to investigate the effect of vacancies and the presence Oxygen at the interface. The experimental task is that by tuning the growth parameters we alter the interface structure to the theoretically predicted stable interfaces and then we apply external force to test the deformation and the strength of the nanocomposite, see Figure.
Three interfaces between cubic and wurtize phases which are grown in ZrAlN/TiN multilayers and deformation is performed using micropillar compression to compare the fracture resistance.
High resolution graphene based gas/liquid sensor platform
Valdas Jokubavicius, Manuel Bastuck, Mike Andersson, G. Reza Yazdi (IFM, LiU)
This project aims to fabricate a sensor platform for indoor air quality monitoring. The combination of surface engineering of SiC on the micro- and nano-scales through well-defined etching with the procedures for epitaxial processing of graphene on SiC make the fabrication of gas/liquid sensors with tunable properties possible. Graphene, a single layer of carbon atoms arranged in a honeycomb lattice, is highly sensitive to changes in its chemical environment due to its extremely high electron mobility at room temperature, its maximized surface area per unit volume and the electron transport through graphene thus highly sensitive to adsorbed molecular species, as well as its low electrical noise (due to the quality of its crystal lattice and its very high electrical conductivity).
The SiC surface quality is crucial for growth of graphene. Commercial, mechanically polished SiC wafers are often damaged and show a high density of scratches when studied by AFM (Fig. 1a). Here thermal etching will be used prior to the epitaxial growth of graphene to improve the surface quality of the SiC substrates (Fig 1b). Growth of epitaxial graphene with different thickness will be performed after etching (Fig.1c). For device fabrication (Fig. 2a and b), a suspended gate and electrical contacts to the drain, source, and gate terminals will be processed on the SiC/graphene substrate and characterized electrically (Fig. 2c). Then the effect of graphene thickness and bias conditions on the sensitivity to different pollutant gaseous substances will be studied to establish basic principles for the transducer mechanism. The final aim is the optimization of device layout, layer thicknesses, materials and operation in order to develop a sensor platform for indoor air quality monitoring.
Fig. 1 AFM images of SiC surface a) before thermal etching, b) after etching, c) with graphene layers
Fig. 2 displays in (a) the interaction of substances interesting to measure with the graphene layer, which at the same time acts as the channel in a suspended gate (SG) FET device, the electrical characteristics of which depends on the applied suspended gate bias (VGS) and gas adsorption, thereby facilitating tuning of the device for optimum sensitivity
Correlating performance of organic solar cells with nanostructures of active layer via studying the cross-sections of devices with SEM
Deping Qian (IFM, LiU), Pimin Zhang (IEI, LiU), Ru Peng (IEI, LiU), Fengling Zhang (IFM, LiU)
Percolating network of two materials in the active layers determines charge generation and transport in solution processed bulk-heterojunction organic solar cells. Imagining the nanostructure of cross-sections of the active layers with Scanning Electron Microscopy (SEM) will directly provide information on vertical distribution of two materials. However, it is challenge to prepare smooth cross-sections of organic materials on hard/flexible substrates and get clear SEM images with layer thickness only ~100 nm. The high resolution SEM at IEI is capable of imaging very fine microstructural features. With this proposal, we will initiate an interdisciplinary synergetic collaboration between IFM and IEI to better control the device performance and reproducibility (important for industrialization of organic solar cells) as well as lead to a long term collaboration between two departments.
Schematic diagram of a flexible semitransparent OPV. The green layer is an active layer consist of two materials for exciton dissociation. SEM image shows the percolation of two materials.