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A comprehensive characterization of plasma modified polymer surfaces or plasma-polymerized thin films needs access to parameters as
- concentration of saturated/unsaturated carbon species (e.g. aromaticity) or other double bonds as C=N or C=O,
- branching, and
- losses of crystallinty or other degrees of structural order.
Furthermore the complex ageing phenomena of plasma modified polymers/plasma-polymers and the measurement of an in-depth distribution of chemical species are challenges for the analyst. The talk will display selected examples where such challenges have been met by using advanced methods of surface chemical analyses as Photoelectron Spectroscopy with variable excitation energy (“SyncXPS”), X-ray Absorption Spectroscopy (NEXAFS) at C, N and O K-edges and Time-of-Flight Secondary Mass Spectroscopy (ToF-SIMS) combined with Principal Component analysis (PCA).
Polydimethylsiloxane (PDMS)is one of the most appearing
contamination of medical devices.Dedicated analysis of PDMS on surfaces necessary, but the lack of calibration samples provides a bottle neck. There is a demand for metrological tools ensuring traceable and reliable analysis of mass deposition and of the chemical species of
contaminants. Photoelectron spectroscopy (PES) and reference-free GIXRF can be used to qualify bench top instrumentation.
Comparison of PES data and GIXRF data enable the establishment of a traceability chain.
Characterization of bio-molecular surfaces and liquids by means of reference-free X-ray spectrometry
(2016)
An increasing field of application for X-ray spectrometry and related analysis techniques is the investigation of tailor made functional surfaces modified by organic molecules. For a detailed understanding and further development of such functionalized surfaces, a quantitative determination of the surface density of molecular species or even specific functional groups is required. By means of reference-free X-Ray Fluorescence (XRF) spectrometry such customized surfaces can be analyzed quantitatively, when using specific marker elements. A chemical analysis of molecular bonds can be accomplished by X-Ray Absorption Spectroscopy in the Near-Edge region (NEXAFS). Especially in the soft X-ray range an access to relevant light elements like carbon C, nitrogen N and oxygen O is possible. Especially, the characterization of liquids and solid-liquid interfaces aiming at the determination of bio-molecular moieties (functional groups) is of great interest. The characterization of such systems requires the analysis of bio-molecules in their liquid environment. For the understanding of (biomolecular) reactions and binding processes the verification and quantification of biomolecule immobilization is essential. However, the analysis in the soft-X-ray range involves a higher experimental effort. In this contribution various successful applications of the characterizations of organofunctionalized surfaces, solid-liquid interfaces and liquids containing bio-molecular species by means of reference-free X-ray spectrometry will be presented. The experiments were performed at the plane-grating monochromator beamline (PGM-U49) in the soft X-ray range at the synchrotron radiation facility BESSY II. Using calibrated instrumentation and a quantification approach based on atomic fundamental parameters a quantitative access without any calibration sample or reference material is possible. In a complementary analysis by X-Ray Photoelectron Spectroscopy (XPS) and fluorescence measurements based on laserexcitation in the optical light spectrum the functional-group density of silane monolayers were determined. Here, the nitrogen atoms of the head-group of the label molecule employed could be used as specific marker for the reference-free quantitative XRF analysis and is used for traceable calibration of XPS and fluorescence spectroscopy. Furthermore, a novel UHV-compatible liquid-cell developed to investigate liquids and solidliquid interfaces will be presented. Protein attachment at the solid-liquid interface was investigated by detection of the characteristic N1s→π*(O=C-N) amide bond resonance in the N K-edge NEXAFS by using ultra-thin epoxy-functionalized SiC-windows.
Die Bestimmung der chemischen Zusammensetzung einer Oberfläche und deren Quantifizierung mit wichtig für die Qualitätssicherung vieler industrieller Produkte und Materialien. Die chemische Beschaffenheit von Oberflächen bzw. Grenzflächen muss genau kontrolliert werden um die Produktqualität zu garantieren. Diese Prüfung ist oft auch für individuelle Prozessschritte durchzuführen.
Referenzmaterialien sind unverzichtbar, wenn es darum geht, die Richtigkeit und Zuverlässigkeit von Messergebnissen zu gewährleisten. Falsche Messwerte können zu erheblichen Mehrkosten führen. Referenzmaterialien gewährleisten die Rückführung von Messergebnissen auf anerkannte Bezugsgrößen (Standards), dienen der Ermittlung der Messunsicherheit von analytischen Verfahren und wer-den zur Kalibrierung verwendet. Für zertifizierte/akkreditierte (ISO 9000 und ISO 17025) Prüf- und Kalibrierlaboratorien ist der Einsatz von Referenzmaterialien in der Qualitätssicherung obligatorisch.
Ionischen Flüssigkeiten (IL) sind vielversprechende Kandidaten für die Verwendung als Referenzmaterial in oberflächenanalytischen Verfahren wie Energie-dispersive Röntgenspektroskopie (EDX) und Röntgenphotoelektronenspektroskopie (XPS). In zwei Machbarkeitsstudien wurde eine geeignete Klasse von ILs als Referenzmaterial getestet:
Für die Anwendung in EDX wurde die Eignung von ILs als Referenzmaterial zur routinemäßigen Überprüfung der Energieskala, der Energieauflösung und der Spektrometer-Effizienz untersucht. Es kann gezeigt werden, dass mit einer einzigen Messung an einem einzigen Referenzmaterial mehrere Geräteparameter überprüft werden können. Damit ist es im niederenergetischen Bereich möglich, regelmäßige Funktionsprüfungen von Spektrometern durchzuführen, aber auch die Leistungsfähigkeit verschiedener Spektrometer zu vergleichen
Für Die Anwendung in XPS wurde die Eignung von ILs als Referenzmaterial zur Bestimmung der Transmissionsfunktion T(E) von Photoelektronenspektrometern getestet. Dazu wurde die Auswertesoftware UNIFIT entsprechend adaptiert und erlaubt nun T(E) anhand der bekannten Stöchiometrie der IL zu ermitteln. Es wird gezeigt, dass durch die Verwendung ausgewählter ILs als Referenzmaterial die Genauigkeit der Quantifizierung von XPS Daten unter Nutzung einer experi-mentell bestimmten T(E) wesentlich verbessert werden kann.
The certified reference material BAM-L200, a nanoscale stripe pattern for length calibration and specification of lateral resolution, is described. BAM-L200 is prepared from a cross-sectioned epitaxially grown layer stack of AlxGa1-xAs and InxGa1 xAs on a GaAs substrate. The surface of BAM-L200 provides a flat pattern with stripe widths ranging down to 1 nm. Calibration distances, grating periods and stripe widths have been certified by TEM with traceability to the length unit. The combination of gratings, isolated narrow stripes and sharp edges of wide stripes offers a plenty of options for the determination of lateral resolution, sharpness and calibration of length scale at selected settings of imaging surface analytical instruments. The feasibility of the reference material for an analysis of the lateral resolution is demonstrated in detail by evaluation of ToF-SIMS, AES and EDX images. Other applications developed in the community are summarized, too.
BAM-L200 fully supports the implementation of the revised International Standard ISO 18516 (in preparation) which is based on knowledge outlined in the Technical Report ISO/TR 19319:2013.
We aim at preparing, characterising, and applying SURMOFs incorporating electro-active and -switchable mechanically interlocked molecules such as rotaxanes as the basis of functional devices.
Preparation and Positioning
Synthesis, purification and analytical characterization of electro-switchable rotaxanes suitable for SURMOF-formation as well as Layer-by-Layer assembly on surfaces.
Controlled deposition of electro-active SURMOFs and Layer-by-Layer self-assembled multilayers based on these switchable rotaxanes.
Construction of SURMOFs on micro-patterned surfaces.
Structural Characterisation and Physico-Chemical Properties
Electrochemical characterization of these rotaxanes in solution with cyclic voltammetry, chronoamperometry and impedance spectroscopy.
Surface characterization of SURMOFs and multilayers with XPS, NEXAFS, AFM, contact-angle measurements, transmission UV/Vis, ToF-SIMS and – in cooperation with partners from SPP – XRD.
Development of ToF-SIMS (also assisted by Principle Component Analysis of the fragment-ion data) as a method for imaging and depth-profiling.
Development of an appropriate electrochemical cell to perform cyclic voltammetry, chronoamperometry and impedance spectroscopy with SURMOFS and multilayers as working electrodes in a three-electrode cell.
Comparison of the structural and electrochemical properties of the redox-active unit in solution, multilayers and SURMOF focusing on the advantages of SURMOFs.
System Integration and Function Demonstration
Examination of the usability of the electroactive SURMOFS as optoelectronic switch or data storage device with a focus on the robustness of the system.
Usage of the SURMOFs as functional electrodes for electrochemical application.
Selective switching of ordered nanostructures to translate molecular motion to macroscopic property changes.
Covalent modification of surfaces with carbohydrates (glycans) is a prerequisite for a variety of glycomics-based biomedical applications, including functional biomaterials, glycan-arrays, and glycan-based biosensors. The chemistry of glycan immobilization plays an essential role in the bioavailability and function of surface bound carbohydrate moieties. For biomedical applications the stability over time (shelf life) of a glycan-array is a crucial factor. Basic requirements for the production of microarrays are first of all stable signals without any loss of quality. Therefore, the investigation of the shelf life for carbohydrate microarrays is an important part in the development of glycan-arrays.
Motivated by the need of reliable quality control for glycan microarrays, we developed reference arrays using fluorescent model glycans. Since the long term stability of glycan microarrays is a crucial factor for their clinical application the shelf life at different storage conditions of glycan microarrays was studied in detail using the two model glycan compounds.
Herein, we present a shelf life study of model glycan microarrays on epoxy modified glass surfaces over a period of 320 days. This was carried out using different analyzing techniques such as Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), X-ray Photoelectron Spectroscopy (XPS) and Fluorescence Spectroscopy. To analyze and interpret the ToF-SIMS dataset the multivariate technique principal component analysis (PCA) was used. The dependence of the array´s shelf life upon storage conditions was specifically studied.
Characterization of bio-molecular nano-layers by means of reference-free X-ray Spectrometry
An increasing field of application, e.g. in biotechnology is the dedicated adjustment of surface properties by functionalization with organic molecules. For a detailed understanding and further development of such nano-layers, a quantitative determination of the surface density of molecular species is required.
By means of reference-free X-Ray Fluorescence (XRF) spectrometry such surfaces can be analyzed quantitatively by detecting specific marker elements. Using calibrated instrumentation and a quantification approach based on atomic fundamental parameters a SI-traceable quantitative analysis without any calibration sample or reference material is possible. A chemical analysis of molecular bonds can be accomplished by X-Ray Absorption Spectroscopy in the Near-Edge region (NEXAFS). Especially in the soft X-ray range an access to relevant light elements like Carbon C, Nitrogen N and Oxygen is possible.
Here, aminated surfaces with varying densities of amino groups prepared from binary mixtures of silanes were investigated. In a complementary analysis by X-Ray Photoelectron Spectroscopy (XPS) and Fluorescence measurements based on laser-excitation in the optical light spectrum the functional-group density of silane monolayers were determined. The nitrogen atom in the head-group of the silane-molecule could be used as specific marker for the reference-free quantitative XRF analysis and were used for traceable calibration of XPS and Fluorescence Spectroscopy.