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Eingeladener Vortrag
- nein (120)
etracyano-p-quinodimethane (TCNQ) molecules encapsulated single-walled carbon nanotubes (SWNTs) were investigated by using core level and valence band x-ray photoemission spectroscopy as well as near-edge x-ray-absorption fine structure spectroscopy. The pi-band and pi*-band structures in these molecular systems were investigated, and it was clearly confirmed that a charge transfer occurred in TCNQ-doped SWNTs. TCNQ molecules were negatively charged as to be expected. A depletion of the pi-band density of states of the SWNTs caused by the charge transfer to the TCNQ molecules was observed.
Es wird gezeigt, dass mit einer Kombination der Oberflächenanalyseverfahren ESCA, ToF- SIMS und XAS eine erfolgreiche chemische Charakterisierung von Plasmapolymerfilmen erreicht werden kann. Es werden Elemente und Bindungstypen identifiziert und (semi-)quantitativ bestimmt. Eine Korrelation zwischen Abscheidebedingungen und chemischen Eigenschaften der Plasmapolymerschichten kann hergestellt werden; eine kontrollierte Abscheidung wird damit möglich. Alterungsprozesse, die als Folge einer Atmosphärenexposition auftreten, können beobachtet werden. Die direkte Verbindung der Analysetechniken mit einem Plasmareaktor ermöglicht es, die Alterungsphänomene der Schichten systematisch mit Bezug auf eine frisch abgeschiedene und keinerlei Atomsphäre ausgesetzte Plasmapolymerschicht zu studieren.
Die Verfahrensweise wird exemplarisch am Beispiel von Ethylen-, Allylamin- und Allylalkohol-Plasmapolymerschichten demonstriert.
The dismutation of CCl2F2 was used to probe the effect of halogenation of chromia by Cl/F exchange reactions to find out the difference between the halogenated inactive and active catalysts. The heterogeneous reactions were performed in a continuous flow Ni reactor and also under simulated reaction conditions in a reactor where after the reaction X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectroscopy (XAES) analyses are possible without air exposure of the catalyst, i.e., under so-called "in situ" conditions. The Cr(III) 2p XP spectra, which revealed multiplet splitting features and satellite emission, were used for chemical analysis by using a simple evaluation procedure which neglects this inherent complexity. Chemical analysis was also applied by using chemical state plots for Cr 3s in order to cross-check Cr 2p related results. Both ex and in situ XPS show that as soon as Cr2O3 is exposed to CCl2F2 at 390°C fluorination as well as chlorination takes place at the catalyst surface. When the XPS surface composition reaches approximately 4 at. % fluorination and 6 at. % chlorination, maximum catalytic activity was obtained. Application of longer reaction times did not change significantly the obtained surface composition of the activated chromia. The fluorination and chlorination of chromia was further investigated by various HF and HCl treatments. The activated chromia samples and the Cr2O3, Cr(OH)3, CrF2OH, CrF3·H2O, α-CrF3, β-CrF3, and CrCl3 reference samples with well-known chemical structures were also characterized by X-ray absorption near edge structure (XANES), time-of-flight secondary ion mass spectroscopy (TOF-SIMS), pyridine-FTIR, wet chemical (F and Cl) analysis, X-ray powder diffraction (XRD), and surface area (BET) analysis. The results suggest that the formation of chromium oxide chloride fluoride species, e.g., chromium oxide halides, at the surface is sufficient to provide catalytic activity. The presence of any CrF3 and/or CrCl3 phases on the activated chromia samples was not found.
Cr3+-doped MgF2 systems are synthesised by a novel non-aqueous soft chemistry route using different Cr precursors and varying Cr loading. These systems have been characterized by X-ray powder diffraction (XRD), BET surface area, TPD of ammonia, FT-IR pyridine adsorption analysis and X-ray photoelectron spectroscopy, and tested for their catalytic activity in dismutation of CCl2F2 and CF3CHClF. Catalysts synthesised starting from CrO3 or (CH3CO2)7Cr3(OH)2 showed better catalytic activity than those prepared with CrCl3. FT-IR pyridine adsorption studies reveal that the catalytic activity is highly correlated with the Lewis acid strength. In TPD of NH3 catalysts prepared from CrO3 and (CH3CO2)7Cr3(OH)2, precursors showed a similar behaviour, different from that of catalysts prepared from CrCl3.
The effect of the composite plasma parameter P/F, where P is the plasma power and F is the monomer flow rate, on the chemical character of pulsed plasma deposited allyl alcohol films was investigated by ToF-SSIMS. Information on the unsaturated character, the cross-linked and/or branched character of the plasma polymer films was derived in detail. The problem of the retention of OH groups in plasma deposited allyl alcohol films was elucidated in detail using SSIMS data. The lowest conversion rate from the monomer's hydroxyl groups to other oxygen functionalities in the plasma was concluded for the plasma polymer film produced at a P/F ratio of 0.05 W · sccm-1. It was found that the overall oxygen content of the films decreased vs. increasing P/F ratio. Because the freshly prepared films were investigated without air exposure, ageing on ambient air could be studied in detail. It was found that in the case of plasma deposited allyl alcohol films the ageing on air is probably based on two competing processes which are discussed in detail. Additionally, a review of literature data on the characterization of plasma deposited allyl alcohol films is given.
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.
XPS and NEXAFS spectroscopy were used for the chemical characterization of pulsed plasma-deposited ethylene films before and after exposure to ambient air. The influence of external plasma parameters on the spectroscopic results was investigated. Information on the chemical character of the plasma-polymerized films, such as the regularity of the primary structure, the amount of long-living radicals, and branching or cross-linking or both was derived from this data. Irregularity and radical concentration for post-plasma reactions of the plasma-deposited films increased with the duty cycle or power. A decreased level of monomer fragmentation and, consequently, an increase in regularity is partially concluded from the experimental data when the monomer pressure is increased. The concentration of surface radicals available for post-plasma reactions also increased with monomer pressure. The correlation found between the degree of the post-plasma oxygen incorporation and the variation of the various external parameters agreed with earlier ToF-SSIMS findings.
Scanning transmission X-ray microscopy (STXM) of h-bar preparations of chemically modified DLC films
(2004)
The formation of plasma-deposited materials made from organic molecules is a technologically attractive way to obtain films with unique properties, e.g. adhesion, wettability, conductivity or selected chemical functionalization. A detailed chemical characterization of these films is a great challenge for the analyst because of the co-existence of a large number of chemical species in plasma-deposited films. We investigated these types of organic films using photoelectron spectroscopy for chemical analysis (ESCA, XPS), near edge X-ray absorption fine structure (NEXAFS) spectroscopy at synchrotron radiation source BESSY II and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). A dedicated plasma preparation chamber was designed and added to the main analysis chamber of the respective spectrometers. This approach offers the possibility of studying plasma-deposited films without exposure to air before analysis (often called in-situ analysis) and the influence of post-plasma reactions, i.e. the ageing process. The present investigations are aimed at finding correlations between basic chemical properties of the deposited films and the plasma deposition parameters, e.g. duty cycle in pulsed plasmas and the power of discharge.
Plasma deposited allylamine films were studied by in situ ToF-SSIMS, XPS and NEXAFS Spectroscopy before exposure to ambient air. The influence of external plasma parameters such as duty cycle, plasma power, and monomer flow rate on (i) unsaturation, (ii) branching and cross-linking, (iii) nitrogen surface concentration and (iv) retention of amino groups was investigated. Harder plasma conditions, which can be obtained when high duty cycles, high plasma power, and low monomer flow rates are employed, increase the unsaturated, branched and cross-linked character of the plasma deposited films, while the surface concentration of N as well as the retention of the monomer's amino group decrease. As proven by NEXAFS findings and cross-checked by ToF-SSIMS results, the allylamine monomer's primary amino groups are partially transformed into other nitrogen functionalities during its plasma polymerization. Amongst them imines and nitriles are the conversion products with the highest probabilities of formation. Another conversion channel is the formation of nitrogen species not participating in the film growth. This is the reason for an increased N loss in plasma deposited allylamine films as observed independently by XPS and ToF-SSIMS when the plasma parameters are changed from mild to hard.
Ageing studies of plasma deposited organic films by surface chemical analysis (ESCA, ToF-SIMS, XAS)
(2006)
Static ToF-SIMS analysis of plasma chemically deposited ethylene/allyl alcohol co-polymer films
(2006)
A plasma co-polymerization of ethylene as a chain extending monomer and allyl alcohol as a carrier monomer for hydroxyl groups was studied. The composition of the feed gas was systematically varied and the plasma co-polymers were analyzed in terms of their relative concentrations of OH functional groups by static Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) immediately after their preparation without any air contact, i.e., under so called in situ conditions.
The relative OH group concentration involved in the CH2OH groups was derived from the normalized yields of the CH3O+ secondary fragment ion. The density of functional groups in the plasma co-polymers was found to vary non-linearly with respect to the mole percentage of the monomers in the feed gas.
Co-polymerization phenomena, i.e. chemical interactions and recombination reactions taking place between monomer molecules in the plasma and/or during the deposition process, become evident in ToF-SIMS spectra.
Chemical properties of plasma-polymerized styrene films can be effectively controlled by the appropriate choice of external plasma parameters, such as duty cycle, power and monomer pressure. Chemical properties here are the regularity of the primary structure, the amount of long living radicals and branching or cross-linking or both in plasma polymerized styrene films, which can be indirectly monitored by X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Principally, XPS and NEXAFS spectra of plasma-polymerized styrene show all the spectroscopic fingerprints characteristic of atactic polystyrene indicating an inherent similarity of the respective primary chemical structures. There is an increase in irregularity and radical concentration for the plasma deposited films with increasing duty cycle or power. With an increase in monomer pressure, a decreased level of monomer fragmentation and, consequently, an increase in regularity must be concluded from the experimental data. The applied power regulates the fragmentation of the monomers as monitored by spectroscopic signals correlated to the aromatic rings. A trend in the extent of the post-plasma oxygen incorporation according to the variation of the various external plasma parameters was deduced, which agrees with earlier ToF-SIMS findings
Pulsed-plasma-deposited ethylene films were studied by time-of-flight static secondary ion mass spectrometry (ToF-SSIMS) before and after exposure to ambient air. The influence of the external plasma parameters on the secondary ion mass spectra of plasma-deposited ethylene films was investigated. From these data, information on the chemical character of the plasma-deposited ethylene films was derived. The investigation of the effect of external plasma parameters on the chemical character of the plasma-deposited ethylene films revealed that there were some drastic changes in the secondary ion mass spectra of the films. It was found that fragmentation and re-arrangement of the monomer molecules in the plasma, which affects the chemical character of the deposited films, vary according to the external plasma parameters. When the plasma polymers are exposed to air, extensive oxygen incorporation occurs. The oxygen uptake is high at the beginning and then it levels of. Some indications for the formation and decay of peroxy radicals (COO) and, subsequently, hydroperoxides (COOH) are found. It was observed that the oxygen uptake of the plasma deposited ethylene films increase when the plasma conditions become harder.
Analysis of carbon materials by X-ray photoelectron spectroscopy and X-ray absorption spectroscopy
(2003)
Since hard coating such as ta:C films are of growing interest for protecting surfaces of industrial machines and high capacity tools against wear and friction or for biomedical applications, more information about the structure-to-property relation is required. Therefore, core level X-ray photoelectron sprectroscopy and X-ray absorption spectroscopy and spectromicroscopy are used to derive chemical information about selected carbon species.
Selected FTIR, XPS and NEXAFS spectroscopy results obtained with films deposited with different plasma polymerization processes and different monomers (styrene, acetylene, ethylene and butadiene) are presented. In detail FTIR spectra, XPS surveys, XPS valence bands and core level signals including shake-up features as well as carbon K-edge absorption spectra are qualitatively and, in some cases, semi-quantitatively considered. Information on the film formation, the chemistry of the films and the film stability against air exposure are derived from spectroscopic features. With styrene chemically rather well defined plasma polymer layers can be formed with rather high deposition rates applying a pulse plasma process. Using ethylene, acetylene or butadiene as a monomer in the plasma deposition process the deposition rates are smaller. Using these monomers plasma polymer films can be obtained with a primary chemical structure which is similar to each other but more or less different from those of the respective conventional polymers. The main difference between these samples is their individual concentration of unsaturated carbon species. Finally, a technologically relevant example, i.e. a plasma deposited polymer barrier layer deposited on the inner wall of a poly(ethylene) vessel is briefly considered.
First results of an inter-laboratory comparison (27 participants in Europe, Japan and USA) of XPS data obtained with non-conducting samples are presented. Binding energies of Al 2s for alumina, N 1s and imide C 1s for Kapton and Sr 3p3/2 for a strontium titanate film on glass were obtained after static charge referencing with the help of 15 nm gold particles deposited at the surface of the test samples. For the alumina sample C 1s static charge referenced data are also presented. Repeat standard deviations (sr), between standard deviations (sb), reproducibility standard deviations (sR) and total means are evaluated from the experimental data. It can be stated that although the repeat standard deviation is as small as 0.05 eV in the best case, the standard deviation characterizing the reproducibility of the method is obviously not better than 0.15 eV in the best case at the present time. The knowledge of these standard deviations is important for metrology, validations of analytical procedures relying on qualitative photoelectron spectroscopy and XPS databanking.
The dismutation of CHClF2 to CHF3 and CHCl3 was used to probe the effect of γ-Al2O3 fluorination on fluorine-against-chlorine (Cl/F) exchange reactions. X-ray photoelectron spectroscopy (XPS), X-ray excited Auger electron spectroscopy (XAES) and X-ray absorption near edge structure (XANES) spectroscopy were employed to probe the modifications at the surface of γ-Al2O3 accompanying the initial stages of fluorination. The results suggest that fluorine uptake by γ-Al2O3 starts initially at the surface of the oxide particles, with the formation of a fluorine species that is characterised by a single bond and a high effective charge q. Catalytic Cl/F-exchange is only observed after accumulation of higher fluorine concentrations, for which insertion of fluorine into the sub-surface region of the oxide crystallites has commenced. Quantitative XPS shows that the fluorination level must exceed approximately 10 atom% of the anions to achieve catalytic activity. The spectroscopic evidence suggests that the formation of aluminium oxofluorides is sufficient to provide catalytic activity. The presence of an AlF3 phase is not a condition for the observation of catalytic activity, even though defect-rich AlF3 is ultimately the endpoint of the fluorination process and is itself a Cl/F exchange catalyst.
Several possibilities exist to produce a modified polymer surface with a high density of only one sort of functional group such as: (i) the plasma grafting of unfragmented monomer molecules and their polymerization forms OH, NH2, COOH groups, etc. in concentrations of approximately 25 groups per 100 C atoms; (ii) selective plasma bromination provides 1025 CBr groups; (iii) the plasma oxidation of polymer surfaces in an O2 plasma followed by the chemical reduction of all O-containing groups to OH groups by diborane, vitride (Na complex) or LiAlH4 yields 914 OH groups per 100 carbon atoms; and (iv) the grafting of spacers with different endgroups onto OH or CBr groups produces 710 spacer molecules/100 C. This work was focused on the formation of thin plasma deposited polymer layers with a maximum of (homo)functional groups and with a minimum of chemical irregularities using the pulsed plasma technique. The monomers were allylalcohol, allylamine, acrylonitrile and acrylic acid. The further intent was to study the interactions of functional groups (OH, COOH, NH2) and deposited metals (Cr, Al, Ti). It was expected that more basic (NH2), weakly basic or neutral (OH) or more acidic (COOH) groups would show different interactions and chemical reactions with metal atoms.
The retention of chemical structure and functional groups during plasma polymerization was investigated. Usually plasma polymer layers, prepared by a continuous wave radio-frequency plasma, are often chemically irregular in their structure and composition. To minimize these irregularities low wattages and the pulsed plasma technique were applied to avoid fragmentations. The first goal was to produce plasma polymers comprising double or triple bonds as precursors for electrically conducting polymers. Acetylene, ethylene, butadiene and polystyrene were used as monomers and deposited as thin polymer films by pulsed plasmas of low wattages. Styrene polymerization was strongly enhanced in the dark phase (plasma off) of a pulsed r.f. plasma caused by the reactivity of the vinyl-type double bond. This could be confirmed by a verification of a rather high chemical regularity of the film sample. The oxygen content of this film measured by X-ray photoelectron spectrometry (XPS) was in situ 0% and after 24 h exposure to air lower than 1%. Additionally, post-plasma oxidations of trapped radicals with air could be suppressed using NO gas as radical quencher. Such quenched plasma polymer layers were completely stable against oxidation for a number of weeks. During the low-wattage pulse plasma polymerization metal atoms were simultaneously or layer by layer evaporated into the growing layer and in situ measured by XPS. These metal atoms are acting as dopants. Here, Li, K, Mg and Cr were used at different concentrations providing electrical conductivity and magnetic properties for the film.
Eine neue Generation von alterungsbeständigen Plasmapolymeren mit definierter chemischer Struktur
(2000)
Polymeroberflächenfunktionalisierungen im gepulsten Plasma mit nachfolgender chemischer Behandlung
(2000)
The chemical and morphological stabilities of polymer segments in the near-surface layer were investigated by spectroscopic methods such as X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. Model studies were undertaken with LangmuirBlodgett films, self-assembled monolayers and oligomer films. For thin polymer layers (30 to 500 nm), the changes in molecular-weight distributions of some polymers were investigated systematically by size exclusion chromatography, matrix-assisted laser desorption/ionizationtime-of-flight mass spectrometry and thermal-field flow fractionation for oxygen- and helium-plasma exposures. The polymer surfaces were found to be relatively stable at exposure to an oxygen low-pressure plasma up to ca. 2 s. This is important information to get maximum adhesion to metals in composites. In correlation to their redox potentials, potassium, aluminium and chromium react with oxygen functional groups at the polymer/metal interface. In a dedicated study, chromium was found to attack aromatic rings and form different reaction products.
Reactions and Intermediates at the Metal-Polymer Interface - Detected by XPS and NEXAFS Spectroscopy
(1998)
Modelling plasma-induced reactions on polymer surfaces using aliphatic self-assembling and LB layers
(1998)
Different types of plasma, irradiative and chemical activation were compared in terms of surface functionalization. Corona and spark jet plasmas are characterized by low gas temperatures and high rates in surface modification. UV irradiation in the presence of ozone does not involve any particle bombardment and acts only by enhanced photooxidative processes. Although ion implantation can be avoided, this method is not free of radiative damage in both the surface-near region and the bulk of polymers. Furthermore, its functionalization rate is low. In relation to low-pressure O2 plasma modification, all treatments mentioned here have a low efficiency in adhesion promotion due to oxidative degradation of macromolecules and formation of molecular debris known as the ''weak boundary layer''.
Plasma-Polymerized C60 Films
(2001)
We studied the polymerization of C60 under different Ar plasma conditions. Films were either deposited in the pressure range between 1.3 and 40 Pa applying input power of 50 W or evaporated C60 films were exposed to Ar plasma of 30 and 50 W. The films were investigated by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and carbon K near-edge X-ray-absorption fine structure spectroscopy (NEXAFS). The films were non-uniform and consisted of unpolymerized C60, dimers, linear chains and polymeric planes. In comparison with evaporated C60 the XPS C 1s peak is broader and asymmetric for the C60 polymer and its shake-up satellites diminished. Furthermore, the features of the valence band as well as the features of the p * antibonding orbitals of the C60 polymer are broader and reduced in intensity.
Auger electron spectroscopy
(2005)
Catalyst characterization
(1998)
Pulsed plasma deposited styrene and ethylene films were studied by Time of Flight Static Secondary Ion Mass Spectrometry (ToF-SSIMS) before and after exposure to ambient air. The influence of the external plasma parameters on the secondary ion mass spectra of plasma deposited films was investigated. Approaches for the interpretation of SSIMS spectra of organic materials were reviewed and applied to the evaluation of SSIMS data of plasma deposited films. From these data, information on the chemical character of the plasma deposited films was derived.
When the plasma polymers are exposed to air oxygen incorporation occurs. The oxygen uptake is high at the beginning and then it levels of.
A relation that higher the regularity of the film lower is the oxygen uptake was found. Harder plasma conditions, which could be obtained by applying higher plasma power or lower monomer flow rate, result in higher oxygen uptake and vice versa.
Plasma polymerised films of acrylic acid, allyl alcohol and allyl amine were prepared and studied by XPS (X-ray photoelectron spectroscopy) and XAS (X-ray absorption spectroscopy). The influence of external plasma parameters on certain chemical aspects of the films was investigated. The use of XPS and NEXAFS (near edge X-ray absorption fine structure) as complimentary tools in the surface characterisation of thin films has been highlighted. Certain chemical aspects of the plasma polymerised films such as presence of ROCdouble bond; length as m-dashO in the case of plasma polymerised acrylic acid films, presence of RCdouble bond; length as m-dashO and RCOR bonds in case of plasma polymerised allyl alcohol films and presence of RCdouble bond; length as m-dashN and C?N in case of plasma polymerised allyl amine films were studied. The concentration of ROCdouble bond; length as m-dashO species was found to decrease with increase in r.f. duty cycle in the case of plasma polymerised acrylic acid films. In case of plasma polymerised allyl alcohol films there is a decrease in the concentration of RCdouble bond; length as m-dashO species and increase in the concentration of RCOR species at higher pressures, while in the case of plasma polymerised allyl amine films the concentration of RCdouble bond; length as m-dashN and C?N increases at higher powers, with an increase in C?N more pronounced at higher powers.
An ethynylterpyridine was 'clicked' to an azide-terminated self-assembled monolayer on gold and characterized by synchrotron radiation based surface analysis as NEXAFS and XPS. The detection of azide and terpyridine signatures confirmed a partial click reaction at room temperature. The absence of the azides after reaction at 50 °C indicates an almost complete conversion. For the latter case successful Pd(II) coordination has been proven. The Au–S interface of the SAMs has been characterized by S 1s and S 2p XPS.
Methods for characterization of epoxy-functionalized substrates used for microarray applications, prepared by silanization with 3-glycidoxypropyltrimethoxysilane, have been developed. Contact angle measurements, X-ray photoelectron spectroscopy, time of flight secondary ion mass spectrometry and fluorescence based methods have been applied to investigate these epoxy-functionalized microarray substrates. The surface density of epoxy-functionalized glass slides was investigated by fluorescence labeling of surface species utilizing Rhodamine 110 as fluorescence probe.
Potential candidates of reference nano-materials are manufactured and systematically characterized in particular with respect to their morphology (shape, size and size distribution) in the frame of the running large European project NanoValid. By exploiting the transmission operation mode in a SEM, known as T-SEM, it is demonstrated by means of three representative examples of nanoparticles how a quick morphological inspection up to a complete, metrological characterization is feasible.
A new high throughput screening method to characterise alloys used as gate metal of Metal/solid Electrolyte/Insulator/Semiconductor (MEIS) gas-sensors was developed. Samples with continuous gradients in alloy concentration for the system Pd1-x-yNiyCoy were analysed regarding H2 sensitivity. First results showed reduced poisoning effects of H2S for Ni concentrations between 4-11 at-% in Pd.
Br bonding on plasma brominated graphite surfaces has been studied by using Near Edge X-ray Absorption Fine Structure (NEXAFS) and X-ray Photoelectron Spectroscopy (XPS). Br2 and bromoform were used as plasma gases in an r.f. cw low pressure plasma process. Kr plasma had been used to study separately the physical and chemical plasma etching effects. At early steps of plasma bromination which lead to only small XPS Br surface concentration values a quick decay of aromaticity has been observed. At low Br surface concentration radical or even electrophilic addition of bromine onto sp2 carbon atoms is discussed as the dominating reaction pathway. At higher Br surface concentrations the inherent formation of sp3 defects in the graphene network by chemical etching processes promotes nucleophilic substitution of bromine at sp3 carbons as a competing reaction pathway. Both reaction pathways lead to CBr species characterized by the same Br 3d XPS binding energy. However more than one Br 3d component in XP spectra has been found at lower Br2 plasma induced Br surface concentrations and complexation of bromine at HOPG is assumed as a third way of interaction with Br2 plasma.
Nitrogen rich plasma polymer films (L-PPE:N) were prepared by low-pressure RF plasma using a 1:1 mixture of ethylene and ammonia and aged for 345 d in four different ambient conditions: (i) at room temperature (RT) in air; (ii) at RT in nitrogen; (iii) at -20?°C in air and; (iv) at –20 °C in nitrogen. The films were analyzed by X-ray photoelectron spectroscopy (XPS) and by time-of-flight secondary ion mass spectrometry (ToF-SIMS) at various intervals over the duration of the experiment. The ageing of primary amines, NH2, was followed by chemical derivatization with 4-trifluoromethyl benzaldehyde. Storage at –20 °C, mostly independently of ambient atmosphere, slowed down ageing to almost undetectable levels as evaluated by the analytical methods used for this study.