Bernhard Schnyder

The deposition of anti-adhesive ultra-thin teflon-like films and their interaction with polymers during hot embossing

The chemical and physical interactions of ultra-thin teflon-like films at interfaces are a surface science problem with many technological implications. Such films are the material of choice for protective layers and anti-adhesive coatings. During the replication of microstructures in polymers by hot embossing, interfacial forces between the master and the replica need to be reduced by an anti-adhesive layer, in order to ensure a clean demolding process. In this work, we investigated two different teflon-like films, one obtained by ion sputtering, and the other by plasma polymerization. Using both deposition methods, we deposited thin fluorinated films on nickel substrates and conducted depth-resolved X-ray Photoelectron Spectroscopy (XPS) measurements for a detailed comparison. In a subsequent step, nickel surfaces covered by both anti-adhesive coatings were hot embossed into two different polymers. The chemical composition of both the anti-adhesive film and the polymer replicas was monitored, as a function of the number of embossings made with the same Polytetrafluoroethylene (PTFE)-treated nickel stamp. During the embossing process, a transfer of material was found to occur from the teflon-like film to the embossed polymer, consisting of fluorinated entities or small polymer chains. The influence of the operating parameters on these phenomena was also investigated and resulted in a better understanding of the film/polymer interactions under pressure and at high temperature.

UV-irradiation induced modification of PDMS films investigated by XPS and spectroscopic ellipsometry

UV-irradiation (172 nm) induced changes of PDMS surfaces were investigated with X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). Both methods indicate the modification of the PDMS to a silicalike surface (SiO2). These conclusions could be drawn from the elemental composition determined by XPS and the binding energy shifts in the XPS spectra of the Si 2p and O 1s levels. Similarly the refractive index n determined with ellipsometry reaches a value close to the one of SiO2. Additionally, ellipsometry allows to monitor the decrease of the original film thickness with increasing UV-irradiation time. 2003 Elsevier Science B.V. All rights reserved.

Sulfonated polyaniline films as cation insertion electrodes for battery applications. Part 1.—Structural and electrochemical characterization

Sulfonated polyaniline (SPAN) was synthesized by sulfonation of polyaniline (PANI) base with fuming sulfuric acid. Thin films were cast from polymer solutions in basic media. The polymer films were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible–near-infrared spectroscopy, scanning electron microscopy (SEM) and cyclic voltammetry. XPS in combination with FTIR showed that the preparation procedure led to ca. 47% sulfonation of an otherwise unchanged polyaniline backbone. The NIR spectra of SPAN films showed a polaron band at higher energies than with polyaniline. This is in agreement with the lower conductivity of SPAN as compared with polyaniline. SEM micrographs of the SPAN films showed a compact globular morphology. Electrodes modified with thin SPAN films exhibited two redox steps, both in aqueous and in non-aqueous electrolytes. The specific charge stored in SPAN films was found to be ca. 37 A h kg–1 in aqueous solution (only the first redox step) and ca. 68 A h kg–1 in non-aqueous media (both redox steps). A practical SPAN–Li battery could have 50% more specific energy than a PANI–Li battery. The optical spectra of SPAN films exhibited bands at 310, 450 and 750 nm, the intensities of which changed during the redox process. The absorption coefficients of SPAN (emeraldine base state) solutions had values of a= 410 at 313 nm and a= 239 at 563 nm. The suitability of SPAN for use as a cation-insertion material for battery and electrochromic applications is discussed.

Evolution of BET internal surface area in glassy carbon powder during thermal oxidation

Abstract It is demonstrated that glassy carbon powder can be thermochemically activated. During activation, a film with open pores is created on the glassy carbon particles. This film has a large internal surface area, which is accessible to liquids and gases. A simple model for the evolution of the internal surface area in glassy carbon powder during thermochemical gas-phase oxidation is also presented and compared with experimental data. Experimental results are in qualitative agreement with the model. We found that a sharp particle size distribution is desirable with regard to potential technical applications.

Formation and characterization of protein monolayers on oxygen-exposing surfaces by multiple-step self-chemisorption

Extended protein monolayers were formed by multiple-step self-chemisorption and characterized by scanning force microscopy (SFM), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry, and cyclic voltammetry. These uniform protein monolayers were deposited on oxygen-exposing surfaces (SiO2, mica, glass, etc.) after preexposing these surfaces to 3-aminopropyltriethoxysilane (3-APTS) and reacting the silylated surfaces with glutaric dialdehyde (GD). The samples appear flat and robust under SFM imaging conditions, both at low and molecular resolution. The thickness of the three-layer structure measured by engraving the layer with the SFM tips (4.5 nm) matches fairly well the value expected for the supramolecular architecture. XPSperformed after each of the three different stages of sample preparation confirmed the presence of the elements expected (such as Cu and Sfor the azurin layer) and allowed film growth to be followed. Similar results have been obtained for the thicknesses of the different layers by spectroscopic ellipsometry. Optical absorption spectroscopy has provided data consistent with a 75% surface coverage by a protein (sub)monolayer. Redox proteins immobilized with linkers involving a similar chemistry but providing groups binding to gold (2-mercaptoethylamine and GD) rather than to oxygen-exposing surfaces made it possible to record cyclic voltammograms of single monolayers. These electrochemical experiments have confirmed retention of the protein’s redox activity upon surface immobilization. The chemisorption approach reported in the present paper appears to be applicable to all kinds of proteins. 2002 Published by Elsevier Science B.V.

Electrochemical intercalation of perchlorate ions in HOPG: an SFM/LFM and XPS study

Abstract Highly oriented pyrolitic graphite (HOPG) in perchloric acid was adopted as a model system in order to elucidate the electrochemical anion intercalation process in graphite. The effects of the intercalation process were studied in terms of the changes in surface friction and on the electronic structure of the HOPG. Lateral force microscopy (LFM) combined with cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) indicated that the specific adsorption of perchlorate ions is responsible for changes in friction occurring in proximity of the steps on the HOPG surface. The friction changes reversibly within a narrow potential window preceding intercalation. After an intercalation and deintercalation cycle the change of the friction at a step is irreversible. No change in the friction could be observed on the basal plane. The binding energies in the C 1s, O 1s and Cl 2p XPS spectra of the intercalated compound are shifted relative to those of the non-intercalated host and adsorbed perchlorate ions, which is attributed to a shifted Fermi level.

Structural changes of model Cu/ZnO catalysts during exposure to methanol reforming conditions

Cu/ZnO/Si model catalysts were prepared by resistive evaporation of Cu on ZnO thin films deposited on Si(1 0 0) by DC magnetron sputtering. Exposure of the Cu/ZnO/Si model catalysts to methanol reforming conditions at 550 K causes agglomeration of the supported Cu islands as shown by XPS, AFM and spectroscopic ellipsometry. The Cu remains in the metallic state for O2/CH3OH molar ratios 6 0.25 but is oxidised to Cu(I) for higher oxygen content. When Cu is in the metallic state the degree of agglomeration is larger in the presence of O2 in the gas phase. On the other hand oxidation of the Cu islands is associated with a less pronounced agglomeration upon methanol reforming treatment. The origin of this phenomenon is discussed. 2003 Elsevier Science B.V. All rights reserved.

Tuning molecular orientation in protein films

The rational design of azurin metalloprotein assemblies suitable for biomolecular electronics application has been achieved by exploiting different surface chemical approaches for growing active protein layers on both metal and insulating surfaces. The formed layers, which have been tested extensively by scanning force microscopy (SFM), spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS), and electrochemical measurements (cyclic and linear voltammetry (CV and LV)), consist of redox active molecules endowed with tuneable orientation according to the particular functional group exploited for surface immobilization. The peculiar molecular arrangement has turned out to be responsible for different transport properties in solid state hybrid electronic planar devices.

Anodic oxidation of aluminium in sulphuric acid monitored by ex-situ and in-situ spectroscopic ellipsometry

Abstract The growth of anodic oxide films on bulk aluminium in sulphuric acid (3 M H 2 SO 4 ) was monitored by means of ex-situ and in-situ spectroscopic ellipsometry in the photon energy range 1.5–5.0 eV. The ellipsometric results clearly reveal the growth of a porous film with increasing void fraction. The film thickness is directly proportional to the anodization time. Good agreement between experimental spectra and simulated data is obtained by assuming a two-layer model with an interface layer between the Al substrate and the porous aluminium oxide film. The addition of chloride to the electrolyte drastically reduces the film thickness for Cl − concentrations above 15 mmol. Open-circuit dissolution of the anodic oxide film grown in 3 M H 2 SO 4 proceeds within the pores and is not affected by Cl − in the electrolyte up to concentrations of 80 mmol. The optical properties of the Al substrate and the aluminium oxide are compared with data in the literature. Ex-situ and in-situ spectroscopic ellipsometry results for electrochemical oxide formation on Al are in good agreement, supporting the relevance of ex-situ measurements for this particular system.

Spectroscopic ellipsometry of carbon electrodes during electrochemical activation

Abstract The effect of electrochemical activation on three types of carbon electrode, namely glassy carbon (GC), pyrolytic graphite (PG) and highly oriented pyrolytic graphite (HOPG), was investigated in situ using spectroscopic ellipsometry. The activation procedure consisted of a certain number of potential cycles between −0.5 and 1.86 V with respect to a saturated calomel electrode with a scan rate of 150 mV s -1 in 1 M H 2 SO 4 . For GC and PG electrodes the spectroscopic ellipsometry results can be well described by assuming a porous surface film, consisting of a mixture of GC or PG and electrolyte on top of the bulk substrate. While a film with increasing thickness and a constant void fraction of 80% is obtained for GC during prolonged activation, a decreasing film thickness with increasing void fraction results for PG. For HOPG no film formation is observed. The activation of HOPG leads to irreversible intercalation, indicating delamination at exposed edges.