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The present work shows results on elemental distribution analyses in Cu(In,Ga)Se2 thin films for solar cells performed by use of wavelength-dispersive and energy-dispersive X-ray spectrometry (EDX) in a scanning electron microscope, EDX in a transmission electron microscope, X-ray photoelectron, angle-dependent soft X-ray emission, secondary ion-mass (SIMS), time-of-flight SIMS, sputtered neutral mass, glow-discharge optical emission and glow-discharge mass, Auger electron, and Rutherford backscattering spectrometry, by use of scanning Auger electron microscopy, Raman depth profiling, and Raman mapping, as well as by use of elastic recoil detection analysis, grazing-incidence X-ray and electron backscatter diffraction, and grazing-incidence X-ray fluorescence analysis. The Cu(In,Ga)Se2 thin films used for the present comparison were produced during the same identical deposition run and exhibit thicknesses of about 2 µm. The analysis techniques were compared with respect to their spatial and depth resolutions, measuring speeds, availabilities, and detection limits.
The amount of grafted poly(acrylic acid) on poly(methyl methacrylate) micro- and nanoparticles was quantified by conductometry, 13C solid-state NMR, fluorophore labeling, a supramolecular assay based on high-affinity binding of cucurbit[7]uril, and two colorimetric assays based on toluidine blue and nickel complexation by pyrocatechol violet. The methods were thoroughly validated and compared with respect to reproducibility, sensitivity, and ease of use. The results demonstrate that only a small but constant fraction of the surface functional groups is accessible to covalent surface derivatization independently of the total number of surface functional groups, and different contributing factors are discussed that determine the number of probe molecules which can be bound to the polymer surface. The fluorophore labeling approach was modified to exclude artifacts due to fluorescence quenching, but absolute quantum yield measurements still indicate a major uncertainty in routine fluorescence-based surface group quantifications, which is directly relevant for biochemical assays and medical diagnostics. Comparison with results from protein labeling with streptavidin suggests a porous network of poly(acrylic acid) chains on the particle surface, which allows diffusion of small molecules (cutoff between 1.6 and 6.5 nm) into the network.
Hepcidin-25 was identified as the main iron regulator in the human body, and it by binds to the sole iron-exporter ferroportin. Studies showed that the N-terminus of hepcidin is responsible for this interaction, the same N-terminus that encompasses a small copper(II)-binding site known as the ATCUN (amino-terminal Cu(II)- and Ni(II)-binding) motif. Interestingly, this copper-binding property is largely ignored in most papers dealing with hepcidin-25. In this context, detailed investigations of the complex formed between hepcidin-25 and copper could reveal insight into its biological role. The present work focuses on metal-bound hepcidin-25 that can be considered the biologically active form. The first part is devoted to the reversed-phase chromatographic separation of copper-bound and copper-free hepcidin-25 achieved by applying basic mobile phases containing 0.1% ammonia. Further, mass spectrometry (tandem mass spectrometry (MS/MS), high-resolution mass spectrometry HRMS)) and nuclear magnetic resonance (NMR) spectroscopy were employed to characterize the copper-peptide. Lastly, a three-dimensional (3D)model of hepcidin-25with bound copper(II) is presented. The identification of metal complexes and potential isoforms and isomers, from which the latter usually are left undetected by mass spectrometry, led to the conclusion that complementary analytical methods are needed to characterize a peptide calibrant or reference material comprehensively. Quantitative nuclear magnetic resonance (qNMR), inductively-coupled plasma mass spectrometry (ICP-MS), ion-mobility spectrometry (IMS) and chiral amino acid analysis (AAA) should be considered among others.
A new class of boron-dipyrromethene (BDP or BODIPY) dyes was obtained by phenanthrene fusion to the β-pyrrole positions, absorbing in the wavelength range of important laser sources. Despite a 'propeller-like' distorted structure in the crystalline state, the chromophore absorbs (log ε ≥ 5) and fluoresces (Φf ≥ 0.8) strongly and can be easily turned into a fluorescence light-up probe. Incorporation into latex beads produces bright and photostable single-dye and Förster Resonance Energy Transfer (FRET) particles for microscopy applications.
Plasmapolymerisierte Allylaminschichten (50 nm) wurden auf Polypropylenfolien abgeschieden. Die auf diese Weise generierte NH2-funktionalisierte Polymeroberfläche wurde mit Xanthen-Fluorophoren chemisch umgesetzt. Da die Farbstoff-gekoppelten Folien nur geringe Fluoreszenz aufwiesen, wurden zwei Wege zur möglichen Entkopplung der Farbstoffe von der Oberfläche und damit zur Erhöhung der Fluoreszenzintensität getestet. Als erstes wurde ein Spacer durch die Umsetzung der primären Aminogruppen mit Glutaraldehyd und der nachfolgenden Kettenverlängerung mit Diaminohexan eingeführt. Diese nachfolgende Reaktion ergab eine spacergebundene NH2-Oberfläche, die analog der Allylaminschicht mit den Farbstoffen umgesetzt wurde. Als weiterer Weg wurde der Zusatz einer geeigneten Käfigverbindung, des Cucurbit[6]urils, getestet. Die spacergebundenen und zusätzlich mit Cucurbituril modifizierten aminofunktionellen Oberflächen zeigten nach der Farbstoffankopplung eine verbesserte Fluoreszenzintensität.
Depth profiling of electrically non-conductive layered samples by RF-GDOES and HFM plasma SNMS
(2001)
The work is intended to compare the capabilities of two similar depth profiling techniques to analyse electrically non-conductive samples. In order to get a better evaluation of the depth resolution, various multilayer sandwiches, such as SiO2/TiO2 and Si3N4/SiO2 deposited on glass substrates have been investigated. Optimised depth profiles are presented for both methods, glow discharge optical emission spectrometry (GDOES) and radiofrequency mode (known as HFM in the SNMS literature) of plasma secondary neutral mass spectrometry (SNMS). The optimisation procedure, necessary to get the best set of plasma parameters, which result in the optimal depth resolution, is also described for one selected sample. Additionally, sputtering crater profilometry was carried out in order to check out the flatness of the sputtered crater. The influence of the thickness of the sample substrate on the sputtering rate is discussed. Finally, advantages and disadvantages of the use of these two depth profiling methods, especially for the non-conductive samples, are concluded from this comparative study. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis of a cross-sectioned sample was carried out in order to get supplementary information.
Water-dispersible and (bio)functionalizable nanoclays have a considerable potential as inexpensive carriers for organic molecules like drugs and fluorophores. Aiming at simple design strategies for red-emissive optical probes for the life sciences from commercial precursors with minimum synthetic effort, we systematically studied the dye loading behavior and stability of differently functionalized laponites. Here, we present a comprehensive study of the absorption and emission properties of the red emissive hydrophobic and neutral dye Nile Red, a well-known polarity probe, which is almost insoluble and nonemissive in water. Adsorption of this probe onto disk-shaped nanoclays was studied in aqueous dispersion as function of dye concentration, in the absence and presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB) assisting dye loading, and as a function of pH. This laponite loading strategy yields strongly fluorescent nanoclay suspensions with a fluorescence quantum yield of 0.34 at low dye loading concentration. The dye concentration-, CTAB-, and pH-dependent absorption, fluorescence emission, and fluorescence excitation spectra of the Nile-Red6#8211;nanoclay suspensions suggest the formation of several Nile Red species including emissive Nile Red monomers facing a polar environment, nonemissive H-type dimers, and protonated Nile Red molecules that are also nonfluorescent. Formation of all nonemissive Nile Red species could be suppressed by modification of the laponite with CTAB. This underlines the great potential of properly modified and functionalized laponite nanodisks as platform for optical probes with drug delivery capacities, for example, for tumor and therapy imaging. Moreover, comparison of the Nile Red dimer absorption spectra with absorption spectra of previously studied Nile Red aggregates in dendrimer systems and micelles and other literature systems reveals a considerable dependence of the dimer absorption band on microenvironment polarity which has not yet been reported so far for H-type dye aggregates.
The development of dendritic metal ion carrier systems for use in a biological environment is a challenging task as the carrier system must possess multiple features (e.g. a protective shell for metal decomplexation, targeting functions, metal-intradendrimer complexes, etc.) to substitute for the function of metal proteins in processes such as copper metabolism. Thus, Cu(II) complexation by a series of poly(propyleneimine) glycodendrimers ranging up to the fifth generation that have either a dense maltose or maltotriose shell was investigated by UV/Vis spectroscopy and electron paramagnetic resonance (EPR). As a necessary step towards potential biological application, we elucidated the complexation capacity, location of the Cu(II)-dendrimer complexes and the Cu(II) coordination sphere in the dendritic environment. A generation-dependent Cu(II) complexation was found. Furthermore, analysis of the EPR spectra revealed that internal and external Cu(II) coordination and the symmetry (axial and rhombic) of the generated complexes depend on the oligosaccharide shell, dendrimer generation and the relative concentrations of Cu(II) and the dendrimers. Both axial and rhombic symmetries are generation dependent, but also distort with increasing generation number. External coordination of Cu(II) is supported by sugar groups and water molecules. Finally, a third-generation dendrimer with a maltose shell was used to explore the general complexation behaviour of the dendritic poly(propyleneimine) scaffold towards different metal ions [Cu(II), Ag(I), VO(IV), Ni(II), Eu(III) and UO2(VI)].
Metal-based gas diffusion electrodes are utilized in chlor-alkali electrolysis or electrochemical reduction of carbon dioxide, allowing the reaction to proceed at high current densities. In contrast to planar electrodes and predominantly 2D designs, the industrially required high current densities can be achieved by intense contact between the gas and liquid phase with the catalytically active surfaces. An essential asset for the knowledge-based design of tailored electrodes is therefore in-depth information on electrolyte distribution and intrusion into the electrode’s porous structure. Lab-based and synchrotron radiography allow for monitoring this process operando. Herein, we describe the development of a cell design that can be modularly adapted and successfully used to monitor both the oxygen reduction reaction and the electrochemical reduction of CO2 as exemplary and currently very relevant examples of gas-liquid reactions by only minor modifications to the cell set-up. With the reported cell design, we were able to observe the electrolyte distribution within the gas diffusion electrode during cell operation in realistic
conditions.
One of the challenges of high-temperature polymer electrolyte membrane fuel cells is the poisoning of the Pt catalyst with H3PO4. H3PO4 is imbibed into the routinely used polybenzimidazole-based membranes, which facilitate proton conductivity in the temperature range of 120−200 °C. However, when leached out of the membrane by water produced during operation, H3PO4 adsorbs on the Pt catalyst surface, blocking the active sites and hindering the oxygen reduction reaction (ORR).
The reduction of H3PO4 to H3PO3, which occurs at the anode due to a combination of a low potential and the presence of gaseous H2, has been investigated as an additional important contributing factor to the observed poisoning effect. H3PO3 has an affinity toward adsorption on Pt surfaces even greater than that of H2PO4 −. In this work, we investigated the poisoning effect of both H3PO3 and H3PO4 using a half-cell setup with a gas diffusion electrode under ambient conditions. By means of in situ X-ray absorption spectroscopy, it was possible to follow the signature of different species adsorbed on the Pt nanoparticle catalyst (H, O, H2PO4 −, and H3PO3) at different potentials under ORR conditions in various electrolytes (HClO4, H3PO4, and H3PO3). It was found that H3PO3 adsorbs in a pyramidal configuration P(OH)3 through a Pt−P bond. The competition between H3PO4 and H3PO3 adsorption was studied, which should allow for a better understanding of the catalyst poisoning mechanism and thus assist in the development of strategies to mitigate this phenomenon in the future by minimizing H3PO3 generation by, for example, improved catalyst design or adapted operation conditions or changes in the electrolyte composition.