Soft X-ray spectro-ptychography on boron nitride nanotubes, carbon nanotubes and permalloy nanorods

Spectro-ptychography offers improved spatial resolution and additional phase spectral information relative to that provided by scanning transmission X-ray microscopes (STXM). However, carrying out ptychography at the lower range of soft X-ray energies (e.g., below 200 eV to 600 eV) on samples with weakly scattering signals can be challenging. We present soft X-ray ptychography results at energies as low as 180 eV and illustrate the capabilities with results from permalloy nanorods (Fe 2p), carbon nanotubes (C 1s), and boron nitride bamboo nanostructures (B 1s, N1s). We describe optimization of low energy X-ray spectro-ptychography and discuss important challenges associated with measurement approaches, reconstruction algorithms, and their effects on the reconstructed images. A method for evaluating the increase in radiation dose when using overlapping sampling is presented.Comment: 32 pages, 7 figure

Lignans in Knotwood of Norway Spruce : Localisation with Soft X-ray Microscopy and Scanning Transmission Electron Microscopy with Energy Dispersive X-ray Spectroscopy

Lignans are bioactive compounds that are especially abundant in the Norway spruce (Picea abiesL. Karst.) knotwood. By combining a variety of chromatographic, spectroscopic and imaging techniques, we were able to quantify, qualify and localise the easily extractable lignans in the xylem tissue. The knotwood samples contained 15 different lignans according to the gas chromatography-mass spectrometry analysis. They comprised 16% of the knotwood dry weight and 82% of the acetone extract. The main lignans were found to be hydroxymatairesinols HMR1 and HMR2. Cryosectioned and resin-embedded ultrathin sections of the knotwood were analysed with scanning transmission X-ray microscopy (STXM). Cryosectioning was found to retain only lignan residues inside the cell lumina. In the resin-embedded samples, lignan was interpreted to be unevenly distributed inside the cell lumina, and partially confined in deposits which were either readily present in the lumina or formed when OsO(4)used in staining reacted with the lignans. Furthermore, the multi-technique characterisation enabled us to obtain information on the chemical composition of the structural components of knotwood. A simple spectral analysis of the STXM data gave consistent results with the gas chromatographic methods about the relative amounts of cell wall components (lignin and polysaccharides). The STXM analysis also indicated that a torus of a bordered pit contained aromatic compounds, possibly lignin.Peer reviewe

Zur chemischen Charakterisierung der Oberfläche von plasma-chemisch abgeschiedenen Polymerfilmen mit der Röntgen-Photoelektronenspektrometrie und der Röntgen-Absorptionsspektrometrie

I. Title page, table of contents, abstract 1\. Introduction 1 2\. Theoretical Background 4 3\. Experimental 18 4\. Methods of characterization 24 5\. In-situ characterization of plasma deposited polymers 34 6\. In-situ characterization of plasma deposited copolymers 58 7\. Aging of plasma deposited polymer films 75 8\. Conclusions 102 9\. References 105 10\. Publications derived from this work 112 11\. Acknowledgments 115Plasma deposited polymer films using the monomers ethylene, styrene, allyl alcohol and allylamine were investigated using X-ray Photoelectron Spectroscopy (XPS) and Near-Edge X-ray Absorption Fine Structure (NEXAFS) without and after exposure to air. The effects of the various external plasma parameters such as duty cycle, power and pressure on the chemical character of the deposited films were studied in detail. In general it was found that hard plasma conditions (e.g. high duty cycle, high power) lead to deposited films with low retention of the monomer functional group and with high degrees of unsaturation, branching and cross-linking character. The study of plasma deposited copolymer films involved the simultaneous reactions of a chain extending monomer, ethylene or styrene, along with a functional group carrying monomer, allyl alcohol or allylamine. It was possible to control the surface concentration of functional groups and the extent of unsaturation of the copolymer films by the variation in the partial flow rate of the comonomer. The chemical character of the copolymer films was found to depend largely on the reactivity of the individual comonomers. Strong indications of chemical interactions between the comonomers are found. The plasma deposited homopolymer and copolymer films were also investigated after aging in air at different exposure times. All the plasma deposited films, with the exception of films involving allyl alcohol, uptake oxygen on exposure to air. This is attributed to the large concentration of radicals on the surface of these films. Loss of the retained functional groups and loss of unsaturation on aging were also observed. The aging behaviour of the plasma deposited films also show a dependence on the deposition parameter used while preparing the films. In the case of plasma deposited copolymer films the aging behavior was largely dependent on the nature of the comonomers involved. This work highlights again the use of XPS and NEXAFS as efficient and complementary tools in the field of surface analysis of plasma deposited films.Die Oberflächen von plasma-chemisch abgeschiedenen Polymerfilmen wurden mit Hilfe der Analyseverfahren Röntgen-Photoelektronenspektrometrie (ESCA, XPS) und Röntgen-Absorptionsspektrometrie (Feinstruktur an der Absorptionskante, NEXAFS) ohne Atmosphärenkontakt direkt nach ihrer Abscheidung und nach Alterung in Umgebungsatmossphäre untersucht. Als Monomere wurden Ethylen, Styrol, Allylalkohol und Allylamin eingesetzt. Der Einfluss der externen Plasmaparameter Duty Cycle, Plasmaleistung und Druck des gasförmigen Monomers im Reaktor auf den chemischen Charakter der abgeschiedenen Filme wurde im Detail analysiert. Grundsätzlich führt die Anwendung von harten Plasmabedingungen, d.h. bei hoher effektiver Plasmaleistung, zu Filmen mit einer vergleichsweise geringen Retention der Funktionalgruppen der Monomere. Darüber hinaus sind diese Filme stark vernetzt bzw. verzweigt. Eine vergleichsweise hohe Anzahl von ungesättigten Kohlenstoffspezies ist ebenfalls typisch. Die Anwendung milder Plasmabedingungen bewirkt in jedem Fall das Gegeteil. Simultan aus einer Monomermischung plasma-chemisch abgeschiedene Filme wurden ebenfalls hergestellt und analysiert. Zur Einstellung von bestimmten Oberflächenkonzentrationen von OH bzw. NH2 Funktionalgruppen wurden dabei Plasmagasmischungen benutzt, die aus Allylalkohol bzw. Allylamin mit Ethylen oder Styrol bestanden. Es konnte gezeigt werden, dass über die Variation der partialen Gasflüsse der jeweiligen Monomere im Plasmagasstrom die Oberflächenkonzentration von Funktionalgruppen kontrolliert eingestellt werden kann. Der chemische Charakter der resultierenden Plasmapolymerfilme wird wesentlich durch die individuelle Reaktivität der jeweiligen Monomere bestimmt. Die Analysen ergaben starke Hinweise darauf, dass die Monomere im Plasma miteinander reagieren und tatsächlich Ko-Polymerisate als Schichten erhalten werden. Die plasma-chemisch abgeschiedenen Schichten wurden während einer mehrmonatiger Luftexposition zu bestimmten Zeiten mit dem Ziel analysiert, Informationen zum Alterungsprozess zu erhalten. Alle abgeschiedenen Plasmapolymerschichten, mit Ausnahme derer, die mit Allylalkohl hergestellt wurden, zeigten eine ausgeprägte Sauerstoffaufnahme während der Alterung. Dies wird auf Reaktionen, die an den in hoher Zahl in den Filmen existierenden Radikalen starten, zurückgeführt. Verringerungen der Oberflächenkonzentrationen der durch die Monomere eingebrachten Funktionsgruppen und der ungesättigten Kohlenstoffspezies werden ebenfalls als Folge der Alterung beobachtet. In allen Fällen sind die Alterungsphänomene der Plasmapolymerfilme mit den jeweiligen Abscheidebedingungen, d.h. den externen Plasmaparametern, korreliert. Bei den Kopolymerisaten beinflussen die Art der benutzten Monomere und ihre jeweilige Konzentration im Prozessgasstrom zusätzlich die Alterungsphänomene. Die Ergebnisse der vorgelegten Studie verdeutlichen einmal mehr, dass die eingesetzten Analyseverfahren (XPS und NEXAFS) sehr aussagefähige und komplimentäre Ergebnisse auf dem Gebiet der Oberflächencharakterisierung von plasma-chemisch abgeschiedenen Filmen liefern

Analysis of Cr(VI) Bioremediation by <em>Citrobacter freundii</em> Using Synchrotron Soft X-ray Scanning Transmission X-ray Microscopy

Scanning transmission X-ray microscopy (STXM) was utilized for analysing the bioremediation of Cr(VI) by Citrobacter freundii, a species of gram-negative bacteria. The biosorption and bioreduction processes were analysed by the chemical mapping of cells biosorbed at different concentrations of Cr(VI). STXM spectromicroscopy images were recorded at O K-edge and Cr L-edge. A thorough analysis of the X-ray absorption features corresponding to different oxidation states of Cr in the biosorbed cell indicated the coexistence of Cr(III) and Cr(VI) at higher concentrations. This signifies the presence of partially reduced Cr(VI) in addition to biosorbed Cr(VI). In addition, the Cr(III) signal is intense compared with Cr(VI) at different regions of the cell indicating excess of reduced Cr. Speciation of adsorbed Cr was analysed for the spectral features of biosorbed cell and comparison with Cr standards. Analysis of absorption onset, L3/L2 ratio and absorption fine structure concludes that adsorbed Cr is predominantly present as Cr(III) hydroxide or oxyhydroxide. The evolution of absorption features in the duration of biosorption process was also studied. These time lapse studies depict the gradual decrement in Cr(VI) signal as biosorption proceeds. A strong evidence of interaction of Cr with the cell material was also observed. The obtained results provide insights into the biosorption process and chemical speciation of Cr on the cells

X-ray microscopic investigation of molecular orientation in a hole carrier thin film for organic solar cells

International audienceAs dipyranylidenes are excellent hole carriers, applications in organic solar cells or organic light emitting diode are envisaged. In the present study, we investigate the morphology of 2,2′,6,6′-tetraphenyl-4,4′-dipyranylidene (DIPO-Ph$_4$) deposited under vacuum on a silicon nitride (Si$_3$N$_4$) substrate, a paradigmatic system for the study of molecular crystal/inorganic substrate interfaces. Samples with various coating ratios and different thermal treatments were prepared. The films were characterized by atomic force microscopy and scanning transmission X-ray microscopy to gain insight into material growth. The results show a change in orientation at a molecular level depending upon the evaporation conditions. We are now able to tailor an organic layer with a specific molecular orientation and a specific electronic behavior

Spatial distribution of starch, proteins and lipids in maize endosperm probed by scanning transmission X-ray microscopy

he main storage components of the maize endosperm are starch, proteins and lipids. Starch and proteins are heterogeneously deposited, leading to the formation of vitreous and floury regions at the periphery and at the centre of the endosperm. The vitreous/floury mass ratio is a key physical parameter of maize end-uses for the food, feed and non-food sectors, as well as for the resistance of seeds to environmental aggressions. To improve maize breeding for vitreousness, one of the main issues is to finely delineate the molecular and physicochemical mechanisms associated with the formation of endosperm texture. In this context, we use scanning transmission X-ray microscopy at the C K-edge on maize endosperm resin-embedded ultrathin sections. The combination of local near edge X-ray absorption fine structure (NEXAFS) spectroscopy and high-resolution images enable us to achieve a quantitative fine description of the spatial distribution of the main components within the endosperm

Study of degradation mechanism in halide perovskite solar cells using impedance and modulus spectroscopy

International audienceOrganic inorganic hybrid halide perovskites have emerged as an innovative material with excellent optoelectronic properties, in bulk or as single crystals with low defect density with specific morphologies [1]–[3]. Perovskite solar cells (PSCs) have become a trending technology in photovoltaic research due to a rapid increase in efficiency in recent years. [4].However, they show a degradation of their performance under operational conditions (light, bias, environmental stress, etc.). To increase their long-term stability is one of the biggest challenges for market applications. The presence of strong internal electric fields, the existence of ferroelectric domains, or the diffusion of ions/defects are suggested as possible causes for the degradation processes. Several authors suggest the existence of native vacancy defects in these materials and attribute to those defects a major role in the control of the optoelectronic properties, such as hysteresis in the photo-induced current-voltage curve, as well as in device degradation and lifetime. [5], [6]Among various degradation mechanism in PSCs, it’s important to understand the mechanism in both bulk perovskite and at the interfaces between perovskite layer and transport layers.Electrochemical impedance spectroscopy (EIS) is a powerful technique to examine the charge carrier dynamics in perovskite solar cells. It gives insight about internal electrical processes in PSCs and distinguishes between bulk and interfacial processes [7]–[9]. Each physical parameter can be extracted in the form of resistance (R), capacitance (C) and Warburg capacitance (W) using an equivalent electrical circuit model. In addition, dielectric modulus is applied for studying the microscopic mechanism of charge transport, contribution of grains (crystals) and grain boundaries and recombination dynamics [10].In this study, we focus on the degradation of inverted planar structure perovskite solar cells through impedance and modulus spectroscopy. Two samples with the same structure are prepared and stored in air and under dark for 30 days. EIS is measured periodically, on the first sample, without J-V measurement to prevent EIS results from being affected by electrical field that occurs during J-V measurements, while J-V characteristic is measured periodically on the second sample. From combined impedance and modulus data, we confirmed that grains and grain boundaries can be distinguished. The results of modulus spectroscopy imply that the grain size decreases and grain boundaries increases which accelerates ionic accumulation and electronic polarization at interfaces. The results of J-V measurement confirms this hypothesis. Furthermore, we prepared two types of PSCs with electron transport layer based on wet- and dry- processes in order to investigate the effect of solvent on degradation mechanism

Study of degradation mechanism in halide perovskite solar cells using impedance and modulus spectroscopy

International audienceOrganic inorganic hybrid halide perovskites have emerged as an innovative material with excellent optoelectronic properties, in bulk or as single crystals with low defect density with specific morphologies [1]–[3]. Perovskite solar cells (PSCs) have become a trending technology in photovoltaic research due to a rapid increase in efficiency in recent years. [4].However, they show a degradation of their performance under operational conditions (light, bias, environmental stress, etc.). To increase their long-term stability is one of the biggest challenges for market applications. The presence of strong internal electric fields, the existence of ferroelectric domains, or the diffusion of ions/defects are suggested as possible causes for the degradation processes. Several authors suggest the existence of native vacancy defects in these materials and attribute to those defects a major role in the control of the optoelectronic properties, such as hysteresis in the photo-induced current-voltage curve, as well as in device degradation and lifetime. [5], [6]Among various degradation mechanism in PSCs, it’s important to understand the mechanism in both bulk perovskite and at the interfaces between perovskite layer and transport layers.Electrochemical impedance spectroscopy (EIS) is a powerful technique to examine the charge carrier dynamics in perovskite solar cells. It gives insight about internal electrical processes in PSCs and distinguishes between bulk and interfacial processes [7]–[9]. Each physical parameter can be extracted in the form of resistance (R), capacitance (C) and Warburg capacitance (W) using an equivalent electrical circuit model. In addition, dielectric modulus is applied for studying the microscopic mechanism of charge transport, contribution of grains (crystals) and grain boundaries and recombination dynamics [10].In this study, we focus on the degradation of inverted planar structure perovskite solar cells through impedance and modulus spectroscopy. Two samples with the same structure are prepared and stored in air and under dark for 30 days. EIS is measured periodically, on the first sample, without J-V measurement to prevent EIS results from being affected by electrical field that occurs during J-V measurements, while J-V characteristic is measured periodically on the second sample. From combined impedance and modulus data, we confirmed that grains and grain boundaries can be distinguished. The results of modulus spectroscopy imply that the grain size decreases and grain boundaries increases which accelerates ionic accumulation and electronic polarization at interfaces. The results of J-V measurement confirms this hypothesis. Furthermore, we prepared two types of PSCs with electron transport layer based on wet- and dry- processes in order to investigate the effect of solvent on degradation mechanism