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Ageing studies of plasma deposited organic films by surface chemical analysis (ESCA, ToF-SIMS, XAS)
(2007)
Plasma-deposited polymer films were prepared from organic molecules and investigated using near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) for aging effects after exposure to air. Results from the investigation of homopolymers are summarized. Primarily the effect of the deposition parameters duty cycle and power are dealt with. The effect of the deposition parameter pressure is briefly discussed. An example to show the effect of feed gas composition on the aging of plasma polymerized ethylene/allyl alcohol and styrene/allyl alcohol copolymer is also given. In general, change in content of unsaturated or aromatic species, change in concentration of monomer functionality, and change in the oxygen content was observed in the plasma polymerized films on aging.
Thin plasma polymer films were deposited using the pulsed plasma mode. These plasma polymers should possess a more regular structure than those produced by the conventional continuous-wave (cw) mode, because of lower monomer fragmentation caused by the plasma pulses and the chemical chain propagation during the plasmaless (free!) periods. The thermoluminescence method was applied to functional groups carrying plasma polymer layers which are used in medical technology. Examples are formation of biocompatible, biosensoric and bioactive coatings or in metal polymer composites such as adhesion-promoting interlayers.
In addition to the use of the conventional X-ray Photoelectron Spectroscopy for thin film characterization, the new method of thermoluminescence was applied to characterize undesired defects and structural specifics produced in the polymer films by pp or cw plasma mode. The main areas of focus were oxygen-containing groups produced by post-plasma oxygen introduction via auto-oxidation, oxidation of implemented unsaturations and trapped radical sites known as typical irregular structures in plasma polymers.
Dünne, mit einem gepulsten Plasma hergestellte Polymerschichten wurden untersucht. Diese Plasmapolymere sollten eine chemisch besser definierte Struktur haben, weil der Anteil an rein chemisch polymerisiertem Produkt während der Plasma-aus-Zeit steigen sollte, während der Anteil an Schichtbildung, der innerhalb der kurzen Plasmapulse durch Monomerfragmentierung und statistische Polyrekombination erzeugt wird, zurückgedrängt wird. Der Monomerfragmentierungsprozeß ist im kontinuierlich brennenden Plasma (cw-Mode) demgegenüber der Hauptprozeß. Neben der Anwendung der klassischen Element- und Bindungsanalysentechnik XPS (X-ray Photoelectron Spectroscopy) wurden hier die Schichten auch mittels Thermolumineszenz untersucht. Defekte und Strukturanomalitäten in Polymeren sollten mit dieser Methode charakterisiert werden können. Untersuchungsobjekte waren funktionalgruppentragende Plasmapolymerschichten, die biosensorische oder biokompatible Funktionen besitzen oder als Haftvermittler in Metall-Polymercompositen eingesetzt werden.
Translated Abstract
Characterization of Plasmapolymers by Thermoluminescence
Thin plasma polymer films were deposited using the pulsed plasma (pp) mode. These plasma polymers should possess a more chemically regular structure because of the lower monomer fragmentation during the short plasma pulses and the chemical chain propagation during the plasma-less periods than those produced by the conventional continuous-wave (cw) mode. In addition to the use of the classic thin film characterization method XPS the method of thermoluminescence was applied to characterize defects and structural specifics in the polymer films produced by pp or cw-plasma mode. The thermoluminescence method was applied to functional groups-carrying plasma polymer layers, which are used in medical technology for forming biocompatible and bioactive coatings or in metal-polymer composites as adhesion-promoting interlayers.
A scanning transmission x-ray microscopy (STXM) based methodology is introduced for determining the dimensions (shell thickness, core and total diameter) of core-shell nanoparticles which exhibit a strong x-ray absorption contrast and a sharp interface between core and shell material. A low radiation dosage during data acquisition and, therefore, less x-ray beam induced damage of the sample is achieved by recording STXM images only at two predetermined energies of maximum absorption contrast instead of recording a stack of images across the whole absorption edge. A model core-shell nanoparticle, polytetrafluoroethylene (PTFE) cores with polystyrene (PS) shell, investigated at the HERMES beamline is presented for demonstration. This STXM based methodology yields particle dimensions in good agreement with the scanning electron microscopy (SEM) results (deviation equal or less than 10%). Extension of this methodology to core-shell nanoparticles with inorganic core and organic shell will also be presented and the challenges encountered will be highlighted.